ALBERT

Beschreibung: Several strategies have been proposed for operating doubly-fed induction generator (DFIG)-based wind turbine under unbalanced grid voltage conditions. This study focuses on those strategies in which the rotor-side power converter aims at eliminating the oscillations affecting the electromagnetic torque and the stator reactive power. Given the limited size of the DFIG’s power converters, and hence their tolerable current and voltage boundaries, this study analyzes which DFIG power generation capability is under unbalanced grid voltage, and therefrom derives rotor current and stator power controllable ranges. Besides, the feasibility regions of the DFIG are also deduced for different types of imbalance. Furthermore, and based on the outcome of previous analysis, a modified rotor current limiter, as also its equivalent stator power limiter, is proposed. In contrast to the conventional ones, the limiters proposed here take into account that imbalances may arise in the grid voltage. As a consequence, system’s overall performance is considerably enhanced under unbalanced grid voltage conditions. Finally, simulation results establish the validity of the treated issues.

Beschreibung: Wind turbine technology has evolved into a unique technical identity with potential to contribute significantly to the global energy mix powered by renewables. Wind energy, being a fluctuating resource, requires tight control management that addresses stability issues for it to be integrable with the grid system. Difficulty in controller construction for wind energy conversion systems (WECSs) is reinforced by sensitivity to numerical complexity, fast parameter variations due to wind stochasticity, tight performance requirements, as well as the presence of flexible modes that limit the control bandwidth. Proposed herein is a pitch control scheme and a model-based ${cal H}_{infty }$ synthesis controller that yields a multivariable control law governing operation of the power electronic converter for a megawatt-class WECS over the entire nominal operating trajectory. The ${cal H}_{infty }$ control objectives are cast as optimization programs with a unique cost function subject to linear matrix inequality constraints. Simulational analysis confirms the efficacy of the adopted technique: issues regarding uncertainties with respect to system modeling and possible adverse control due to interactions with highly turbulent winds are handled with precision, while significantly improving the quality of voltage and output power.

Beschreibung: A general dynamic hysteresis core loss model has been developed. Experimental data for different lamination thicknesses have been measured and analyzed at various frequencies. Based on the analysis, a dynamic hysteresis finite element core loss model is established and validated by experiments. The developed dynamic hysteresis model is simple and efficient, and has been shown to be very accurate compared with the experiments. Moreover, the model can calculate core losses based on the input parameters obtained from experimental measurements at only one single frequency in a thin lamination. The model, to our best knowledge, is the first one that is capable of calculating core losses for different thicknesses of materials and different operating frequencies, without a massive experimental database. In addition, only the eddy current and hysteresis models are necessary for this calculation but with the important addition of the variation of the flux density within the lamination.

Beschreibung: Conventional active islanding detection methods (IDMs) are designed for the inverter-based distributed generation systems (DGSs) with current control interface. Such strategies can hardly be extended to the DGS with power control interface because the power control loop can affect the IDMs by enlarging the nondetection zones (NDZs). This paper presents an active IDM based on negative-sequence power injections for the DGS with power control interface. Combining with the IDM, the power control of the DGS is achieved with two control loops. One is the positive-sequence power loop that satisfies the conventional power control requirements. The other is the negative-sequence power/current variation loop for the islanding detection. The positive and negative sequences are separated by a simple strategy based on an all digital phase-locked loop. Due to the differences between the grid impedance and the local load impedance, the percentage of the voltage imbalance (VI) at the point of common coupling is utilized to indicate the islanding operation. For the grid-connected DGS, the VI is dominated by the grid voltage, which is a constant. If the DGS is disconnected from the grid, the VI is determined by the injected negative-sequence power/current. The NDZs of the presented scheme with different system configurations, such as grid impedances, load quality factors, etc., are also analyzed in this paper. By injecting the negative-sequence power/current periodically, the NDZs resulting from the imbalance of the grid voltages or the local loads are further mitigated. For multi-DGSs, the IDM is still effective if combined with the conventional under/overfrequency-protection strategy. The simulation and experimental results verify the effectiveness of the IDM.

Beschreibung: This paper presents an analysis of the cost of utilizing battery electric vehicle (BEV) batteries as energy storage in power grids [also known as vehicle-to-grid (V2G)] associated with lessening battery cycle life due to more frequent charging and discharging activities and utilization in elevated ambient temperature. Comparison is made between V2G in the U.K., where annual electricity peak demand is reached in winter, and in China, where peak demand is reached in summer due to the air conditioning load. This paper presents mathematical correlations between charging–discharging, ambient temperature, depth of discharge (DoD), and the degradation of electric vehicle batteries based on manufacturer's data. Simulation studies were carried out for V2G in both the U.K. and China. Numerical results show that ambient temperature and DoD of a BEV battery play a crucial role in the cost of battery wear. Lead-acid and NiMH battery powered BEVs are not cost effective in V2G use due to the present electricity tariff. Under the present electricity tariff structure, no vehicles would be cost effective for the peak power sources in China. However, lithium-ion battery powered BEVs are cost effective in the U.K. due to a much longer cycle life.

Beschreibung: In this paper, an effective new approach for estimating the operating temperature of a photovoltaic (PV) module by using the simple diode model is presented. The developed method is simple and does not need any additional hardware. The proposed approach uses an analytical formula to derive the temperature from the maximum power point voltage and current. Since the temperature estimation (TE) is based on the model of the PV module, at first the model is explained. In the model, effects of the temperature coefficients are considered. Moreover, a new approach to find all parameters of a PV module model is described. Unlike other methods, the parameters’ extraction method that is proposed here only needs manufacturer data from the datasheet and does not need any additional information. Effectiveness of the new TE procedure is investigated through some conducted simulations in MATLAB/Simulink environment and its validity is verified by experiment on a REC-AE220 solar module.

Beschreibung: The most important reference quantities for monitoring and controlling transient stability in real time are the rotor angle and speed of the synchronous generators. If these quantities can be estimated with sufficient accuracy, they can be used in global and local control methods. In the classic state estimation methods, such as the extended Kalman filter (EKF) technique, the linear approximations of the system at a given moment in time may introduce errors in the states. In order to overcome the drawbacks of the EKF, the authors of this paper have applied the unscented Kalman filter (UKF) to estimating and predicting the states of a synchronous machine, including rotor angle and rotor speed, using phasor measurement unit (PMU) quantities. The UKF algorithm propagates the pdf of a random variable in a simple and effective way and is accurate up to the second order in estimating the mean and covariance. The overall impression is that the performance of the UKF is better than the EKF in terms of robustness, speed of convergence, and also different levels of noise. Simulation results including saturation effects and grid faults show the accuracy and efficiency of the UKF method in state estimation of the system, especially at higher noise ratios.

Beschreibung: Using a finite element (FE) model of the electrical machine in a grid solver enables us to take the machine nonlinearities into account with great precision in the simulation of a complete system. Three methods are usually used for linking the grid and FE solver: direct coupling, lumped components, and current or voltage output approach. In this article, the coupling is treated as the resolution of a nonlinear equation system that is solved with the Newton method. The proposed linking scheme has been used to simulate a two phase short circuit on a hydrogenerator. Its results have been validated by running the same simulation with commercially available software.

Beschreibung: The choice of the most suitable control strategy for wave energy converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control, are well known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs implies a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper, the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient tradeoff between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Beschreibung: Coreless dual disks hysteresis motors (CDDHM) have been recently introduced. The CDDHM presents some improvements in power factor and efficiency compared to general hysteresis machines. However, there is not much design or manufacturing experience available and an initial design methodology has not yet been proposed for the new machine. According to this and existing inherent complexity in the model of hysteresis motors, it is difficult to achieve an optimal design solution by applying a conventional optimization method. In this paper, an initial design approach is proposed. Then, a genetic algorithm-based method is developed to find the high-efficiency solution for an optimal CDDHM. The optimized motor has been manufactured and fitted in a test facility with a torque meter. Some experiments are carried out to prove the optimal design. Furthermore, start-up characteristics of the motor are predicted from the model and validated by a routine test.

Beschreibung: This paper presents an investigation of the behavior of a 200-MVA-synchronous hydrogenerator during interturn stator faults, focusing on the affection to the electromagnetic magnitudes, such as the currents and the electromagnetic torque. Two kinds of interturn fault are examined 1) a short circuit between two conductors belonging to the same phase; and 2) a short circuit between two conductors belonging to different phases. These faults have been investigated via simulation using the finite element method. The benefit of this method is that it gives the possibility to calculate, except from the classical electrical magnitudes (e.g., the stator and field currents, the load angle, and the electromagnetic torque), other magnitudes which in general are difficult to compute during transient operation (e.g., the damper currents and the electromagnetic field inside the machine air gap). The main aim of this paper is to highlight quantitative and qualitative the condition in the interior of the machine in the cases of typical faults, which usually can occur during the machine operation. So, it is possible to find out that faults exist in the machine through the measurement of the field and the stator currents.

Beschreibung: A mathematical model of a valve-regulated lead-acid battery under discharge is presented as simplified from a standard electrodynamics model. This nonlinear reaction–diffusion model of a battery cell is solved using an operator splitting method to quickly and accurately simulate sulfuric acid concentration. This splitting method incorporates one-sided approximation schemes to preserve continuity over material interfaces encompassing discontinuous parameters. Numerical results are compared with measured data by calculating battery voltage from modeled acid concentration as derived from the Nernst equation.

Beschreibung: A significant problem of turbogenerators on complex end structures is overheating of local parts caused by end losses and complex fluid flow in the end region. Therefore, it is important to investigate the 3-D flow and heat transfer process in the end. Using a 200-MW air-cooled turbogenerator as an example, the influences of end cores and the actual shapes and material of the end coils, press finger, press plate, and copper shield are considered for the end field calculation; then, the physical and mathematical models of the coil end with involute portions are created. The 3-D electromagnetic field was calculated and the losses of different parts in the end and its distribution were obtained. Based on this, the losses from magnetic field calculations will be applied to the end as heat sources in the temperature field. For symmetry of the ventilated structure, the fluid and thermal physical models of the generator within the half-axial section were determined. A set of equations of fluid flow and heat transfer were derived from the fluid–solid conjugated heat transfer and the fluid and temperature distributions were obtained after solving the equations. All of the aforementioned will provide a theoretical basis for the generator safe operation.

Beschreibung: The calorimetric method has for a long time been applied for energy conversion efficiency measurement in electrical machines. The number of temperature sensors necessary for its successful application in the field constitutes in one of the major drawbacks of the method. This paper shows how the usage of IR thermal imaging techniques can reduce costs and the necessary time for the calorimetric method application. In addition, contribution to the heat transfer coefficient determination and a new approach to consider conduction losses in the generator shaft are also presented.

Beschreibung: This paper presents a dc-bus voltage control technique for a new power conversion topology feasible for parallel-integrated permanent magnet (PM) wind generation systems. This technique is based on a master–slave hysteresis control scheme in order to solve discrepancy problems that could happen between the controllers. A three-phase semicontrolled rectifier topology is proposed here as an effective interface circuit between each wind generator and the dc-bus. The proposed system provides interconnection extension ability of multiwind converter units sharing the same dc-bus and more economic utilization of the wind generator; by ensuring unity power factor operation. More advantages include voltage disturbance compensation capability, robustness: since a short circuit through a leg is not possible and high efficiency: due to the reduced number of switching elements. The rectifier topology concept, the principle of operation, the control scheme, and test results are presented. The developed technique is also implemented on a 12 kW parallel-connected PM laboratory setup in order to confirm the effectiveness of the proposed system.

Beschreibung: This paper presents the design and analysis of an electromechanical flywheel energy storage system to enhance rural electrification in sub-Saharan Africa. The system consists of a flywheel rotor, an electrical machine, control system, bearings, and a containment structure. With the exception of the power electronics and magnets, local materials were used for the manufacture of the flywheel system. The flywheel rotor is made from glass fiber-epoxy composite, designed using novel shape profiles and utilizes a stress based solution by introducing a central hole for shaft inclusion. The system was accelerated to 6000 r/min storing up to 227 kJ. Numerical stress analyses were performed during the design stage to ensure that the maximum tensile strength is not exceeded. A lumped parameter thermal model is used to estimate the temperature distribution to ensure safe operating conditions of the flywheel system and environment. A life cycle cost analysis performed found that by integrating a flywheel system into a Solar Home System implies a cost savings of 35% per kilowatthour when compared with lead-acid batteries.

Beschreibung: The experimental research, whose most important segments are described in this paper, is one of the first attempts to determine the influence of wind turbine blade rotation on likelihood of getting struck by lightning. The tests were conducted in the high-voltage laboratory, applying the up-and-down method for determination of the 50% flashover standard switching voltage. The impulse voltage waves were applied between the specially designed arching electrode and the blades of a reduced-size wind turbine model, driven by a frequency controlled motor. Two types of lightning protection systems and the case of absent protection system were examined. According to the theory of similarity this paper discusses the characteristics of direct atmospheric discharges for the following typical rotational speeds of the wind turbine: w  =  0 r/min (when the wind turbine is idle), w  =  250 r/min (for the winds of moderate strength), and w   =  400 r/min (rated rotor speed).

Beschreibung: The aim of this paper is to analyze the dynamic behavior of the doubly fed induction generator (DFIG) subject to symmetrical voltage sags caused by three-phase faults. A simple control algorithm is considered and assumed ideal: the rotor current $i_{rf}$ in the synchronous reference frame is kept constant. This hypothesis allows the electrical transient to be solved analytically, providing a comprehensive description of DFIG behavior under symmetrical sags. The fault-clearing physics of symmetrical sags is also analyzed. That is, the fault is cleared in the successive natural fault-current zeros, leading to a voltage recovery in one, two, or three steps. This clearing process, called discrete fault clearing in this paper, results in a more accurate sag modeling than the abrupt or instantaneous fault clearing (the usual modeling in the literature). The fault-clearing process has a strong influence on the rotor voltage required to control the rotor current after fault clearing. To compare the effects of both abrupt and discrete sags, different wind turbine (WT) operating points, which determine different generated powers, are considered. This study helps in the understanding of WT fault ride-through capability.

Beschreibung: A high-fidelity battery model capable of accurately predicting battery performance is required for proper design and operation of battery-powered systems. However, the existing battery models have at least one of the following drawbacks: 1) requiring intensive computation due to high complexity; 2) not applicable for electrical circuit design and simulation; and 3) not capable of accurately capturing the state of charge (SOC) and predicting runtime of the battery due to neglecting the nonlinear capacity effects. This paper proposes a novel hybrid battery model, which takes the advantages of an electrical circuit battery model to accurately predicting the dynamic circuit characteristics of the battery and an analytical battery model to capturing the nonlinear capacity effects for the accurate SOC tracking and runtime prediction of the battery. The proposed battery model is validated by the simulation and experimental studies for the single-cell and multicell polymer lithium-ion batteries, as well as for a lead-acid battery. The proposed model is applicable to other types and sizes of electrochemical battery cells. The proposed battery model is computational effective for simulation, design, and real-time management of battery-powered systems.

Beschreibung: Modern grid codes determine that wind generation plants must not be disconnected from the grid during some levels of voltage sags and contribute to network stabilization. Wind energy conversion systems equipped with the doubly fed induction generator (DFIG) are one of the most frequently used topologies, but they are sensitive to grid disturbances due to the stator direct connection to the grid. Therefore, many efforts have been done in the last few years in order to improve their low-voltage ride-through capability. This paper analyzes the behavior of the DFIG during symmetrical voltage sags using models in the frequency domain. A new strategy, the machine magnetizing current control, is proposed in order to enhance the system response during balanced dips. The method is derived on a theoretical basis and numerically investigated by means of simulation. Experimental results are presented and validate the proposed strategy. Finally, the practical aspects of the use of this strategy are discussed.

Beschreibung: Directly coupled electromagnetic field-electric circuit modeling approach for coupling an electrical machine to its associated external circuit and power electronics has been widely reported in the literature. However, the inclusion of a closed-loop control system, such as conventional vector (field-oriented) control, within a directly coupled electromagnetic field-electric circuit model has not been widely studied. This is partly because it is a rather complex task. This paper introduces a directly coupled electromagnetic field-electric circuit computational model in which a conventional vector control system has been incorporated for detail simulation of vector-controlled electric machinery drive systems. The model has been successfully applied in the design and analysis of a vector-controlled wound field brushless starter-generator system prototype. Comparison between the simulation and test results for both motor and generator modes show excellent correlation that validates the efficacy and computational soundness of the modeling approach.

Beschreibung: In this paper, an oscillating water column-based wave energy conversion plant is modeled and controlled by means of two complementary control strategies in order to improve the conversion of wave energy into electric power. This wave power generation system consists of a capture chamber, a Wells turbine, and an induction generator. The improvement relays on the implementation of a control scheme that combines two different control methods: a rotational speed control and an airflow control implemented by means of a throttle valve in series with the turbine. The use of rotational speed control provides a fast way to react to the abrupt and short changes in the turbine speed, ensuring that the average power of the generator is adequately adjusted according to the incident wave power level. Besides, a throttle-valve is used to control the flow through the turbine so as to increase the amount of energy produced, particularly at the higher incident wave power levels. These two control strategies complement each other, maximizing and improving the quality of supply by controlling and smoothing the generated power for different scenarios of wave oscillations, variations of wave grouping, and changes in the sea state.

Beschreibung: Interests of subsynchronous resonance (SSR) in series compensated electric networks with wind power penetration have arisen recently. To better understand the nature of such systems, modal analysis of a doubly-fed induction generator (DFIG)-based wind energy system interconnected with a series compensated electric network is conducted in this paper. The system model is built in Matlab/Simulink. The major contributions of the paper include: 1) identification of the four system modes (SSR, supersynchronous, electromechanical, and shaft modes) of a DFIG-based wind farm interfaced with a series compensated network, 2) investigation of the impacts of various parameters and operating conditions on those modes, and 3) prediction of the dynamic performance of the system using modal analysis and confirmation of such prediction via time-domain simulation results.

Beschreibung: This paper proposes a design for a renewable-energy hybrid power plant that is fed by a photovoltaic (PV) source with a supercapacitor (SC) storage device and is suitable for distributed generation applications. The PV array is used as the main generator, and the SC functions as an auxiliary source for supplying the (transient and steady-state) power deficiency of the PV array. For high-power applications, four-phase parallel boost converters and four-phase parallel bidirectional converters are implemented as a PV converter and a storage device, respectively. A reduced-order mathematical model of the PV and SC converters is described for the control of the power plant. Using a nonlinear approach based on the flatness property, we propose a simple solution to the dynamic, stabilization, and robustness problems in the hybrid power system. This is the key innovative contribution of this research paper. We analyze a prototype small-scale power plant composed of a 0.8-kW PV array and a 100-F SC module. The experimental results authenticate the excellent control algorithm during load cycles.

Beschreibung: This paper presents the analyzed results of both dynamic simulations and steady-state performance of a tidal power generation system (TPGS) containing a permanent-magnet synchronous generator (PMSG) driven by a tidal turbine through a gearbox. The stator windings of the tidal PMSG are connected to an onshore distribution system through an ac-to-dc converter, a dc-to-ac inverter, a step-up transformer, and a transmission cable. A d–q axis equivalent-circuit model is employed to establish complete dynamic equations of the studied system under three-phase balanced loading conditions. A frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear-model simulations are both carried out to systematically determine the dynamic stability of the studied system under different operating conditions. It can be concluded from the simulation results that the studied TPGS subject to different disturbance conditions can maintain stable operation.

Beschreibung: A novel photonic beam-space beam-former concept is reviewed and an additional theory addressing precise sampling of desired beam locations for linear arrays is presented. A new, power efficient, method of apodizing an input array's beam pattern via a weighted distribution of the master feed laser to each RF-to-optical up-conversion stage behind the array elements is then presented along with results from several apodization experiments. The experimental results are shown to produce effective, low-sidelobe responses, while also reducing the required prime input power to the system until an artificial side-lobe floor is reached. The root cause of the side-lobe floor is discovered to be due to phase and amplitude errors introduced within the photonic components currently used. Finally, key findings and design considerations are presented with respect to the usage of photonic beam-space sampling on large arrays and several suggestions for performance improvement in future system designs are discussed.

Beschreibung: Due to internal optical absorption loss, which varies with carrier density in the optical confinement region, the operating characteristics can be two valued in semiconductor quantum well lasers. Particularly, there can be two lasing thresholds and two branches in the light–current characteristic. While the internal differential quantum efficiency for the first (conventional) branch of the light–current characteristic is less than 1 and decreases with increasing pump current, that for the second (unconventional) branch is greater than 1 and nonmonotonous.

Beschreibung: Two passive plasmonic demultiplexers with multimode interferometer (MMI) based rectangular and bow-tie designs are demonstrated for 1.31- and 1.55-μm-band wavelength division multiplexing system operation in plasmonic circuits. These demultiplexers are designed using the finite-difference time-domain (FDTD) method and fabricated using complementary metal–oxide–semiconductor compatible processes. SiO 2 films deposited on metal films are etched to form mesa structures by focused ion beam milling, and single-mode waveguides, MMIs, and bow-tie structures are then formed on the metal films. In the plasmonic circuits, 1.31- or 1.55-μm-wavelength surface plasmon polariton (SPP) signals can be distributed to each of the different demultiplexer outputs without any change in signal propagation speed. The SPP intensity distributions that are measured using a scanning near-field optical microscope agree well with the distributions that were calculated using the FDTD method. The insertion loss and crosstalk are then calculated for each demultiplexer. In the rectangular-type demultiplexer, the calculated values were less than 9.5 dB and –2.4 dB, and in the bow-tie-type demultiplexer, the corresponding values were 8.9 dB and less than –2.3 dB, respectively. These results demonstrate the applicability of the developed plasmonic demultiplexers to plasmonic circuits when monolithically integrated on a silicon substrate.

Beschreibung: In this paper, we present a self-referenced broad range optical rotary sensor (ORS) for avionics applications. To achieve the high reliability required for aerospace use, the rotary encoder operates ratiometrically to make it insensitive to source light power variation. This sensor has a higher operating range than rotary variable differential transformers (RVDTs) currently used in fly-by-wire aircraft. The ORS encoder is fabricated on an antireflection coated glass substrate with a reflective aluminum coating. Experimental results prove that the sensor accuracy is 0.8% over the full rotation range from 0° to 356.5°. The proposed ORS has better accuracy and an operating range of at least twice that of RVDTs, which have an accuracy of 1% over a full range of only 80°. We also test the insensitivity of the sensor to source fluctuations, which confirms that the sensor is self-referencing.

Beschreibung: The design and photonic generation of power-efficient impulse radio ultra-wideband (IR-UWB) waveforms is a challenging step in the design and development of IR-UWB over fiber (IR-UWBoF) systems with combined optical and wireless transmission. In this paper, the definition of the spectral power efficiency (SPE) and its associated optimization problem are reformulated. Based on this reformulation, a theoretical upper bound for the SPE is derived and applied to two of the most common types of photonically generated IR-UWB waveforms. Accurate closed-form analytical expressions for the SPE upper bounds of these two waveform types are obtained and optimized. The analytical framework presented in this paper can be extended and applied to other waveform types. Simulation results show excellent agreement with the analytically obtained expressions. Accordingly, these analytical expressions can be used as reliable guidelines for precise and efficient design of practical IR-UWBoF systems that guarantee optimal design, generation, and distribution of IR-UWB waveforms.

Beschreibung: We report two kinds of Q-switched Yb-doped fiber lasers based on a black phosphorus saturable absorber (BP-SA). The BP-SAs are prepared by two different methods, one of which is the mechanical exfoliation method and the other is the liquid-phase exfoliation method. The BP-SAs are inserted into the all-fiber Yb-doped oscillation cavity in different forms. We have experimentally shown that the passively Q-switched pulse trains could be obtained by the two methods. First, we achieve the Q-switched pulse in 1029.63 nm by using a few-layer black phosphorus sheet. The fiber laser was capable of generating pulses with a maximum average output power of 13.12 mW and a repetition rate of 79.46 kHz, corresponding to the maximum single-pulse energy of 165.11 nJ and the shortest single-pulse width of 1.55 μs. In addition, we obtain narrower pulsewidth by dropping the black phosphorus solution onto the tapered fiber. The maximum single pulse energy of 114.72 nJ and the minimum pulsewidth of 1.09 μs were obtained. The repetition rate ranges from 49.13 to 101.3 kHz.

Beschreibung: We propose a wideband linear polarization converter in transmission mode by bilayer metamaterial. The polarization converter operates from 0.55 to 1.37 THz with polarization conversion ratio maintaining nearly 100%. The distribution of surface current and electrical field was numerically simulated to clarify physical mechanism of polarization conversion. Importantly, we introduced the Stokes method to assess the polarization state of transmitted converter. The Fabry–Pérot-like cavity model was established to reveal the enhancement of polarization conversion ratio. The clear expressions including ideal and approximate model were deduced to provide an excellent explanation of Fabry–Pérot cavity in subwavelength bilayer metamaterials structure.

Beschreibung: Non-uniform pulse amplitude modulation (PAM) utilizes unequal distances between its modulation levels. In a multilevel PAM symbol, multiple bits are encoded. Due to the unequal level spacing, some bits can be decoded successfully at a lower received optical power than others. This is well suited for practical passive optical network (PON) deployments wherein the optical powers received by the different optical network units (ONUs) typically vary over a broad range. Thus, more ONUs in the PON can successfully decode non-uniform PAM-4 and PAM-8 than standard PAM-4/8, thereby increasing the aggregated capacity of the network. In systems where signal-dependent noise makes up a significant part of the total received noise level, the non-uniform PAM constellation can be adapted to take this signal-dependent variance into account. In doing so, a lower unequal level spacing can be used, decreasing the received optical power required to successfully decode all the bits in the PAM symbol. The impact of non-uniform PAM on the network throughput is presented by comparison of the experimental results with the actual loss distribution of a commercially deployed PON.

Beschreibung: A combined infrared suspended-core fiber (SCF) is fabricated using a stacked glass extrusion method. As 2 S 3 glass is used as the center core host material, and Ge 20 As 20 Se 15 Te 45 glass is used to form supporting bridges and act as the ring host material. In this paper, a continuous and robust extrusion process was used to fabricate the SCFs on stacked chalcogenide glass substrates. Glass flow disruption and shear band formation at the interfaces between the different glasses were avoided while the suspended core was formed directly from the core glass. The near-field optical energy distribution image of the resulting multimaterial SCF shows that light propagates effectively in the core. The losses of the multimaterial SCF were also measured at wavelengths ranging between 2.5 and 7 μm, and the lowest transmission loss was 1.86 dB/m at 4.8 μm. The spectral behavior of the supercontinuum (SC) in the SCF is investigated by varying the pump wavelength and the pump power. A mid-infrared SC spanning a wavelength range from 2.05 to 6.95 μm is generated in a 19-cm-long combined chalcogenide SCF that is pumped at 4.5 μm using an optical parametric amplifier laser system.

Beschreibung: We develop an analytical model to understand the generation of tunable free spectral range frequency comb (FC) and composite FC using two competing phenomena, namely nondegenerate four-wave mixing (FWM) and intensity-dependent modulation instability (MI) in dual-pumped micro-resonator configurations. Our analytical approach is based on the popular four-wave model. The MI rate at the onset, corresponding to the most susceptible frequency component that conditionally accompanies threshold-less comb generation in case of dual pump, is derived. Based on the analytical model, the mutual interplay of nondegenerate FWM and threshold intensity-dependent MI is investigated in detail for the comb generation process, and their regions of operations are clearly demarcated. The proposed analytical model provides a deterministic and quick estimation of micro-resonator parameters for generating a variety of FCs while avoiding the computationally intensive route of solving the Lugiato–Lefever equation. A close agreement between the analytical and numerical simulation is found.

Beschreibung: This work studies how the local current density in a metal–semiconductor–metal photodetector (MSM PD) corresponds to the plasmonic enhancement and therefore affects the overall enhancement of the device. For this type of semiconductor photodetector, the enhancement of incident light due to plasmonic structures is most critical inside the substrate, where the photocurrent is generated. This work develops a relationship between the total device optical enhancement and the current density by considering the average optical enhancement, weighted by the current density in the GaAs layer of a simulated MSM PD. This corresponds to an increased overall current in the device. Effects of the wire and nanoslit widths on the total weighted optical enhancement were studied. The results showed that both widths have a significant impact on the total weighted optical enhancement, improving it by two orders of magnitude when using the smallest possible wire widths and nanoslits.

Beschreibung: Visible light communications is an alternative method of indoor wireless communications that requires sensitive receivers. Ideally, single photon avalanche detectors (SPADs) could be used to create more sensitive receivers. However, the dead time, finite output pulse width, and photon detection efficiency of existing SPAD arrays limit their sensitivity and bandwidth. In this paper, an accurate equation for the impact of dead time on the sensitivity of a SPAD array is presented. In addition, the impact of the width of the output pulses on the on–off keying data rate is investigated. Finally, a comparison between receivers containing an avalanche photo-diode (APD) and a large array of SPADs shows that although the receiver containing the SPAD is more sensitive in the dark, the APD-based receiver is more sensitive in a normal operating condition. However, the models that predict the performance of both receivers suggest that newer SPAD arrays will enable significant improvements in receiver sensitivity.

Beschreibung: In this paper, detection of the fundamental shear horizontal (SH0) guided wave mode in a plate using a surface-bonded Fabry–Perot interferometer formed by a pair of tandem chirped fiber-Bragg-gratings (CFBG-FPI) has been investigated both theoretically and experimentally. Using the developed theory, the underlying mechanism that governs the sensor's response to SH0 mode is explored in detail. Then, the dependence on both the incident angle and frequency (or wavelength) of the SH0 wave is investigated. Owing to the pure shear strain induced by the SH0 mode, the fiber sensor shows a significantly different response in comparison to other ultrasonic waves, such as Lamb-type guided waves. Our results show that 1) the sensor is most sensitive to SH-type waves at an incident angle of around 45° and nonsensitive at the incident angles of 0° and 90° and 2) a minimum sensitivity is reached when the equivalent ultrasonic wavelength impinged on the fiber axis is equal to the effective length of the CFBG-FPI sensor; this effective length is close to the length of each CFBG.

Beschreibung: It has been reported that the full vectorial finite element beam propagation method (FV-FE-BPM) is not always stable. In this paper, we propose a stabilized FV-FE-BPM using a linear filter to suppress unstable modes. Moreover, aiming for improving the computational accuracy of FV-FE-BPM for longitudinally varying optical waveguides, we employ incomplete third order hybrid edge/nodal elements to reduce interpolation error which occurs in finite element mesh update process at each propagation step. The validity and effectiveness of this approach are verified through several numerical examples of uniform waveguides and longitudinally varying waveguides.

Beschreibung: In this paper, Gigabit per second transmission over short-range step-index plastic optical fibre (SI-POF) is implemented with multi-level pulse amplitude modulation (PAM- M ) scheme using a laser diode (LD) as the optical source. In particular, the POF channel distortion and the non-linear distortion from the LD are considered. To mitigate these distortions under various PAM- M levels, the bit error rate (BER) performances of the transversal, Volterra and multi-layer perceptron (MLP) based decision feedback equalizers are evaluated and compared. Furthermore, the inverse polynomial technique for non-linear mitigation is also considered. MLP is shown to offer the best BER performance for PAM scheme using more than eight levels especially for a system with high non-linearities. With the MLP equalizer, we record the highest data rate of 3, 7.8, and 18 Gbps for POF lengths of 60, 30, and 10 m, respectively.

Beschreibung: In this paper, a dual-band photonics-based radar system used for precise displacement measures in a multitarget scenario is described. The radar was designed for monitoring applications to prevent both structural failures of buildings and landslides. The radar system exploits the technique of stepped frequency continuous wave signal modulation and the displacement of the targets is evaluated through differential phase measurements. In this work, encouraged by the results already achieved in the single-target scenario, we present an investigation extended to the case of multiple targets. We aim to evaluate the accuracy of the displacement estimation both from a simulated and experimental point of view, and to understand how multiple targets impact on the final estimate of displacements. Simulation results demonstrate that it is possible to achieve a typical accuracy of less than 0.2 mm for distances up to 400 m. These results are confirmed by preliminary experimental outcomes, which take into account different operative conditions with multiple targets. Finally, concluding remarks and perspectives draw the agenda for our future investigations.

Beschreibung: Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on low-loss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is 8–20 GHz; and the beam scanning range is $pm text{60.2}^circ$ . Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams, and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation.

Beschreibung: This paper presents an energy-efficient visible light communication (VLC) receiver system-on-a-chip (SoC) that employs ambient light rejection (ALR) and post-equalization techniques for emerging light fidelity (Li-Fi) applications using ordinary phosphorescent white light-emitting diodes (LEDs). A current-reuse transimpedance amplifier is proposed for energy-efficient applications. An ALR unit is implemented to eliminate the potential DC interference under strong ambient light. A two-stage continuous-time linear equalizer is utilized to compensate for the limited bandwidth of white LEDs, which is below 3 MHz. Implemented in a 0.18 μm CMOS process, the receiver occupies an area of 0.7 × 0.4 mm 2 and consumes 2.2 mW of power at 24 Mb/s from a 1.8 V power supply. An IEEE 802.15.7 PHY-II compliant Li-Fi link that employs the proposed receiver SoC and a custom transmitter SoC is demonstrated based on 1-W phosphorescent white LEDs without using blue filtering, achieving a bit error rate of 1 × 10 −9 for data rates up to 24 Mb/s over 1.6 m distance, and 22 Mb/s over 2.7 m distance, with on–off keying modulation and 2 11 −1 pseudorandom binary sequence (PRBS-11) optical inputs. The receiver SoC achieves a bit efficiency six times better than that of the prior art using off-the-shelf discrete components, and can tolerate an ambient light level of 3500 lx. A figure of merit accommodating the most important system parameters is also proposed for a comprehensive comparison of different VLC systems.

Beschreibung: A quasi-color-free laser diode (QCFLD)-based 60-Gbit/s long-reach (LR) OFDM-PON with dispersion management is demonstrated. After injection locking, the QCFLD achieves an ultimate back-to-back transmission capacity of 60 Gbit/s. After propagating through 25-, 50-, and 75-km single-mode fiber (SMF)-based LR-OFDM-PON, the RF power fading effect induces signal deterioration to inevitably degrade the transmission capacities of the QCFLD at 45, 27, and 21 Gbit/s, respectively. To avoid the RF fading effect, dispersion management is introduced by using different segments of nonzero dispersion-shifted fiber (NZ-DSF) and dispersion compensating fiber (DCF) with corresponding dispersion constants of +5.6 and −5 ps/nm/km, respectively. Using either 25-km NZ-DSF or 25-km DCF enables the OFDM-PON to operate at up to 57 Gbit/s. Combining the 25-km NZ-DSF with the 25-km DCF establishes the near-zero dispersion to effectively support the 50-km LR OFDM-PON up to 51 Gbit/s, which is nearly twice data rate as compared to the 50-km SMF case. For implementing the 75-km LR OFDM-PON, the scenario of 25-km NZ-DSF in connection with 50-km DCF is employed to achieve 48-Gbit/s transmission capacity. In comparison with the same OFDM-PON constructed with 75-km SMF, the achievable data rate is doubled through the synergy of the LR OFDM-PON technology with dispersion management.

Beschreibung: Phase retrieval has important applications in optical imaging, communications, and sensing. Lifting the dimensionality of the problem allows phase retrieval to be approximated as a convex optimization problem in a higher dimensional space. Convex optimization-based phase retrieval has been shown to yield high accuracy, yet its low-complexity implementation has not been explored. In this paper, we study three fundamental approaches for its low-complexity implementation: the projected gradient method, the Nesterov accelerated gradient method, and the alternating direction method of multipliers (ADMM). We derive the corresponding estimation algorithms and evaluate their complexities. We compare their performance in the application area of direct-detection mode-division multiplexing. We demonstrate that they yield small estimation penalties (less than 0.2 dB for transmitter processing and less than 0.6 dB for receiver equalization) while yielding low computational cost, as their implementation complexities all scale quadratically in the number of unknown parameters. Among the three methods, ADMM achieves convergence after the fewest iterations and the fewest computational operations.

Beschreibung: We demonstrate an efficient ultra-broadband supercontinuum generation in telecom-grade optical fiber by pumping Q-switched subnanosecond laser pulses (0.77 ns) at 1064 nm in the normal dispersion region of the fiber. The fiber supports several spatial modes at this pump wavelength. Multiple sidebands with six Raman stokes spanning over more than 1100 nm (starting well below 600 nm and extending beyond 1700 nm) are generated using very low input pump power (average 57 mW). Theoretical analysis shows that cascaded Raman and cascaded intermodal four-wave mixing processes can account for the generation of multiple sidebands. We also demonstrate that the modal composition of the input pump profile can provide an extra degree of freedom in tailoring the multiple Raman peaks in the output spectrum.

Beschreibung: We present a systematic study on the spectral characteristics and ultrahigh sensitivity near the dispersion turning point (DTP) of optical microfiber couplers. Numerical simulations reveal that a DTP exists when the group effective refractive index (RI) difference between the even mode and the odd mode equals zero, where both ultrahigh positive RI sensitivities and negative RI sensitivities can be achieved. The position of the DTP is dependent on the coupler width, and it always exists over the surrounding RI (SRI) range of 1.333–1.41, which enables the ultrasensitive RI sensing in this wide RI range. Then, we studied the interference spectra characteristics around the DTP both theoretically and experimentally. We further experimentally demonstrate ultrahigh sensitivities of 59624 nm/refractive index unit (RIU) and −58470 nm/RIU around the SRI of 1.333 and 26999 nm/RIU and −29267 nm/RIU around the SRI of 1.35, respectively. High figure of merits of 4192 and 5280 are also achieved around the SRI of 1.333 and 1.35, respectively. Finally, utilizing the exceptional RI sensitivity, we demonstrate an ultrasensitive temperature sensor with a negative sensitivity of −15.23 nm/°C and a positive sensitivity of +16.78 nm/°C.

Beschreibung: In this paper, a scanning cutback method, developed for the investigation of Bragg fibers waveguide characteristics, is presented. The method relies on fiber excitation by a laser beam focused onto the fiber core and cladding with different radial offsets from the fiber axis and on measuring the delivered power. These variable coupling conditions and the cutback technique allow us to determine a set of attenuation coefficients and coupling efficiencies. The method has been employed for the characterization of silica and air core Bragg fibers with core diameters of 26  $mu$ m and 56  $mu$ m, respectively. Laser radiation delivery was investigated at wavelengths of 1.064 and 1.940  $mu$ m. Curves of the attenuation coefficient and coupling efficiency as a function of the radial offset show the effects of excitation and propagation of different optical modes in the Bragg fibers. Spatial profiles of the delivered output beams are also presented, which enables us to determine the part of the fiber structure in which the laser radiation is guided.

Beschreibung: We propose a variable mode excitation ratio method for measuring the attenuation coefficients of individual transmission modes in few-mode fiber (FMF). The experimental results we obtained with 2LP mode fiber agree well with those measured by the conventional mode-selective launching method and the optical time domain reflectometer (OTDR) method. We also show that the proposed method can be applied to an FMF with more than two mode groups by measuring the transmitted power property under various mode excitation ratios with a multiple mode group combination. Finally, we reveal that our method can provide an accurate modal attenuation coefficient even if we cannot use a mode multiplexer with a sufficient mode extinction ratio.

Beschreibung: This paper aims to address the perception that visible light communication (VLC) systems cannot work under the presence of sunlight. A complete framework is presented to evaluate the performance of VLC systems in the presence of solar irradiance at any given location and time. The effect of solar irradiance is investigated in terms of degradations in signal to noise ratio, data rate, and bit error rate. Direct current (DC) optical orthogonal frequency division multiplexing is used with adaptive bit and energy loading to mitigate DC wander interference and low-frequency ambient light noise. It was found that reliable communication can be achieved under the effect of solar irradiance at high-speed data rates. An optical bandpass blue filter is shown to compensate for half of the reduced data rate in the presence of sunlight. This work demonstrates data rates above 1 Gb/s of a VLC link under strong solar illuminance measured at 50350 lux in clear weather conditions.

Beschreibung: In this article, a novel hybrid plasmonic–photonic–organic electro-optical modulator based on Pockels effect is designed and numerically investigated by employing finite difference time domain and finite element methods at a wavelength of $lambda ,= ,{text{1.55}},mu {text{m}}$ . The presented modulator exhibits unique features such as the half-wave voltage–length product of 0.08 V⋅mm being in the range of modern plasmonic modulators. However, the design presented in this article represents a very low insertion loss of less than 2 dB in the wavelength range of 1.45–1.65 μ m. Moreover, the modulator has an energy consumption of approximately 25 fJ/Bit, modulation depth of approximately 35% and 80% at applied voltages of 5 and 10 V, and electro-optical bandwidth of more than 70 GHz. As the key component of the modulator, a novel hybrid plasmonic slot waveguide is introduced, which combines tight light confinement of plasmonic waveguides with the low loss feature of photonic waveguides. In particular, the presented waveguide enables tight light confinement and guiding in slots as narrow as 40 nm with remarkably low loss of less than 0.2 dB/ μ m, which makes them attractive for other applications in addition to the designed modulator. In this paper, the presented waveguides are thoroughly investigated and compared with plasmonic slot waveguides in terms of loss and modal characteristics.

Beschreibung: We propose two-photon absorption light-induced self-written (LISW) waveguide formation using short-wavelength infrared pulse laser light. It is suitable and efficient for single-mode optical interconnection, and also promising for small-core single-mode optical interconnection. The approach offers the possibility of not only decreasing the insertion loss, but also reducing the interconnection task time. We assessed this approach for single-mode optical interconnection. We obtained an LISW waveguide loss of about 0.06 dB for an LISW waveguide length of 100 μ m and a connection loss per facet of about 0.37 dB. We also presented the results on the interconnection between high-numerical-aperture small-core thermally-diffused expanded-core single-mode fibers having the mode field diameters of about 3 μ m by using the same approach. The results showed the present approach to be a promising alternative route for efficient interconnection of small-core single-mode optical devices, such as silicon nanowires with appropriate configurations.

Beschreibung: We present an improved model for cavity soliton generation by coupling frequency-selective feedback to a vertical-cavity surface emitting laser with a saturable absorber. The frequency-selective feedback is found to lower down the threshold pump power for cavity soliton generation and eventually to broaden the stability regime. A new dynamics of cavity solitons is revealed in form of “all-optical push-broom effect.” Also, stable bound states of cavity solitons that resemble linear diatomic and polyatomic molecules are predicted with their stability regions marked. The findings can be exploited for experimental realization of a soliton force microscope and all-optical memory devices.

Beschreibung: A low-complexity soft-decision concatenated FEC scheme, consisting of an inner LDPC code and an outer staircase code, is proposed. The inner code is tasked with reducing the bit error probability below the outer-code threshold. The concatenated code is obtained by optimizing the degree distribution of the inner-code ensemble to minimize estimated data-flow, for various choices of outer staircase codes. A key feature that emerges from this optimization is that it pays to leave some inner codeword bits completely uncoded, thereby greatly reducing a significant portion of the decoding complexity. The tradeoff between required signal-to-noise ratio and decoding complexity of the designed codes is characterized by a Pareto frontier. Computer simulations of the resulting codes reveals that the net coding-gains of existing designs can be achieved with up to 71% reduction in complexity. A hardware-friendly quasi-cyclic construction is given for the inner codes, which can realize an energy-efficient decoder implementation, and even further complexity reductions via a layered message-passing decoder schedule.

Beschreibung: We present a method for joint optimization of transmitter in-phase, quadrature and interpolarization time skew, amplitude mismatch, and bias voltages. The method is based on a cooperative coevolutionary genetic algorithm with fitness functions extracted from a directly detected reference quadrature amplitude modulation (QAM) signal generated at the transmitter. As a calibration method, it is able to find the values that will statically generate the best possible constellation. To the extent of the simulation investigations conducted, the algorithm is capable to calibrate time skews, bias voltages, IQ phase imbalances, and relative amplitude imbalances with standard deviation of residual error as low as 0.24 ps, 0.019 V, 0.56°, and 0.003, respectively, for a dual-polarization IQ modulator with $V_{pi } = text{4},text{V}$ and a 16-QAM reference signal operating at 16 GBd. An experimental demonstration is also reported.

Beschreibung: An error in the equations in the Appendix of the above-named work [ibid., vol. 35, no. 23, pp. 5237–5249, Nov. 2017] has been identified. The corrected equations fix a contradiction in the printed statement at the end of the Appendix. The numerical results presented, including optimized power allocations and figures, used the incorrect model as printed. For the significantly tilted optimized power allocations considered and at the relatively low total fiber powers considered, using the correct model yields a negligible change to those results, so the interpretation and conclusions remain unaltered. The model as corrected here yields correct results at arbitrary power levels, including levels much higher than those considered in the paper.

Beschreibung: Presents the table of contents for this issue of the publication.

Beschreibung: Solid-oxide fuel cell (SOFC) power plant plays a vital role in a hybrid alternative energy based microgrid due to its reliability and flexibility in power supply. However, the control of SOFC is challenging in terms of providing a fast load tracking while maintaining the fuel utilization rate within a safe range. To this end, this paper builds two basic coordinated control strategies (CCS) for power management of SOFC-based microgrid. The first is “Fuel Cell follows Inverter” scheme, where fast tracking is preferred while SOFC may operate on the edge of the safety range. The second is “Inverter follows Fuel Cell” scheme, where high security is guaranteed by sacrificing performance in load tracking. To obtain a robust and simple scheme, energy balance principle is used in CCS such that PI controller is sufficient to fulfill the basic duties. Moreover, a simple supervisory control strategy is proposed for microgrid to provide a reasonable power reference for SOFC. The control system is designed and tuned based on an SOFC plant with inverter's average model. The efficiency of the proposed strategies is validated via a grid-connected SOFC/photovoltaic microgrid.

Beschreibung: In this paper, a wave energy converter (WEC) is designed for a wave climate condition and its interior permanent magnet (IPM) generator is dimensioned for minimum life cycle cost (LCC). The single point absorber movement is simulated and the harnessed annual energy is determined to be 325 MWh. Possible IPM generator sizes are investigated using finite element calculations. Tradeoffs between the generator cost and the annual energy efficiency is performed in order to find the best economical solution. For the economical evaluation, the net present value method is utilized in order to obtain the LCC of the electric generation system of the WEC. Increasing the axial length of the machine 1.6 times results in the lowest LCC, with a $2.5%$ efficiency increase, which means an increment of approximately 1000 €   in the investment cost. Despite the higher investment cost, the LCC of the WEC generator decreases from 8070 €   to 6450 €, due to the lower losses.

Beschreibung: This paper presents an elaborate scheme, which is different from the traditional parameter identification method, to estimate the parameters precisely for high-speed magnetic suspension motor. It is well known that the inductance and resistance of each winding play an important role in ensuring the stability of the controller for motor. There have been sufficient research works on equivalent circuit model, where the input and output data are assumed to be true value, and unknown circuit parameters are obtained by solving the equivalent circuit equations of motor. However, the output data are often interfered with noises, such as measurement error, the high-frequency components from pulse width modulation signals and sampling errors. The system response output data are reconstructed through applying in stochastic theory, which is different from the traditional filter techniques, to eliminate effectively the above-mentioned noises. Thus, the parameters can be estimated precisely. As an experimental verification, parameters estimated by the proposed method are applied in calculation of switching point between pulse width modulation mode and pulse amplitude modulation mode for magnetic suspension motor. The experimental results validate the effectiveness of the proposed method.

Beschreibung: Winding configurations that are applicable to a novel bearingless flux-switching permanent magnet motor with stacked structure are investigated, and one method to evaluate these winding configurations is also proposed in this paper. First, the motor structure and the influence of coil connections on torque and radial force are illustrated, and the fundamental radial force expressions of two diametrically opposite coils are derived. Afterward, two kinds of torque windings and four kinds of radial force windings for the motor are studied and the radial force models are derived accordingly. Following this, the radial force models are verified and the transient radial force and torque characteristics are investigated by finite element analysis. More importantly, an evaluation factor related to the winding copper losses is defined to evaluate the winding configurations. Finally, an optimal winding configuration is determined theoretically and a prototype motor is built to validate the effectiveness of the motor structure and the optimal winding configuration.

Beschreibung: This paper presents a functional observer based technique for estimating gaseous partial pressures in triple phase boundary of a high-order solid oxide fuel cell. Triple phase boundary is a nanoscale region in solid oxide fuel cells where direct measurement of partial pressure of individual gases is not possible. For a reliable and a safe operation those quantities must be monitored. This paper reports a novel functional observer based dynamic state estimation approach that utilizes a system decomposition algorithm to provide a functional observer with minimum order. Therefore, the proposed technique has a simpler structure than conventional state observer based schemes. Case studies of the proposed technique, implemented on a complex nonlinear power system, show accurate and smooth estimations in comparison to full-order state observer based techniques in terms of tracking of nonlinear partial pressures.

Beschreibung: Because excitation winding short-circuit faults that occur in steam-turbine generator will lead to heavy financial losses, accurately detecting excitation winding short-circuits (EWS) can help power generation operations. It can allow them to take timely actions and shorten downtime as well as cut the costs of troubleshooting. This paper introduces a method for detecting EWS faults online using a new detection coil. Here, a large-dimension detection coil is installed inside the generator to span over an iron-core segment in the stator. The even or fractional harmonics induced by the detection coil are used to determine whether an EWS fault has happened, and the short circuit position can also be determined. This method can reveal short-circuit faults that occur in one turn of the excitation winding, and with obviously higher sensitivity.

Beschreibung: The static exciter is dominating among large grid-connected generators due to the weak dynamic performance of conventional brushless exciters. In this contribution, a six-phase double-star outer pole permanent magnet rotating brushless exciter is evaluated with different active rectification topologies. Both thyristor-based and chopper-based topologies are considered. A high speed response brushless excitation system is obtained by replacing the conventional rotating diode bridge rectifier with the proposed active rectification topologies on the shaft. The given two-stage system generates its own excitation power directly from the shaft, contrary to static exciters. The selection of an appropriate rectification topology could minimize the rotor armature phase currents for a given generator field current. The objective is a high-power factor and a high utilization of the exciter machine. An optimal rectification topology makes higher ceiling currents was possible, improving the transient behavior of the synchronous generator. In this paper, we show that six-phase topologies add complexity, but improve exciter redundancy, increase the available ceiling voltage, and reduce the steady-state torque ripple. Experimental results are given for validating the models implemented for the analysis.

Beschreibung: In this paper, a permanent magnet alternator which presently relies on magnetic slot wedges is redesigned to give lower iron loss. The new segmented stator design is used as the basis for a validated loss study—comparing bonded lamination stacks with those held together with a punched notch. Segmentation is shown to improve the production process, reduce losses, and remove the need for wedges, while not significantly altering the acoustic performance. In the first series of prototypes, however, where notching is used to secure lamination packs, the process is shown to have adversely affected material properties of the nickel iron laminations and overall measured losses increased. In the second prototype, with thinner laminations and glued stacks, iron loss predictions and measurement agree and are less than the present slot wedge design.

Beschreibung: This paper has been focused on design, fabrication, and characterization of a new in-line tunable nematic liquid crystal fiber optic device. The application of a biconical optical fiber taper as a core surrounded by liquid crystals’ molecules as cladding gives the possibility to voltage control of spectral characteristics including system losses and its polarization in an optical visible wavelength range from 500 to 700 nm. The device is based on a standard single mode telecommunication fiber and a special, nematic liquid crystalline mixture of a 1550C1 type. The temperature and time course of liquid crystal mixture investigation of the proposed element are also included in the paper.

Beschreibung: Thermo-optical properties of the optical fiber transducers based on a filled Photonic Crystal Fiber used as a temperature threshold sensor were shown in this paper. A simple transducer is a piece of a partially filled PCF spliced with a standard single-mode fibers. As a filling material, a selected group of n-alkanes with the carbon atoms’ number within the range of 12–28 were used. The main advantages of these materials are phase transitions between solid and liquid states for temperatures from −10 up to 60 °C. Each transducer has a bistable switch on/off transmission characteristics depended on a given n -alkane physical state liquid or solid. These properties allow us to propose an optical warning system as a multilevel temperature threshold sensor. This system can be used in industrial applications to control temperature as a point sensor.

Beschreibung: This paper proposes an advanced dynamic modelling approach of the mutually coupled switched reluctance motor (MCSRM) in the $dq$ reference system that can consider saturation, cross-coupling, and spatial harmonics. Different topologies and their operating principles are investigated and an idealized $dq$ -model considering the inductance harmonics is derived. A dynamic model is built based on flux-current lookup tables (LUTs) obtained from finite element analysis (FEA). A simplified method to inverse the two-dimensional LUTs is proposed. A fast computation approach is used to reduce the number of FEA simulations and calculation time to obtain the LUTs. Motor dynamic performances at different speeds are simulated by using the proposed dynamic model and the results are investigated and verified by FEA. The motor dynamic behavior can be accurately obtained in a short simulation time by using the proposed approach. Experiments are carried out on a 12/8 MCSRM, showing good accuracy of the proposed model.

Beschreibung: We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator generated through single sideband modulation from the same laser source, the Brillouin signals carried on a stable intermediate frequency (IF) are extracted by electrical/digital filters and then recovered to baseband by digital signal processing. This increases the signal-to-noise ratio and avoids the need of trace averaging and enables real-time signal acquisition. To eliminate the Brillouin gain fluctuation, two adjacent Brillouin time-domain traces stimulated by two sequential orthogonal pump pulses are recovered after the IF signals are detected in a real-time manner. Based on this configuration, a spatial resolution of 4 m and Brillouin frequency shift uncertainty of 1.473 MHz are realized in distributed temperature sensing over 40.63 km range. With the nonlocal means algorithm and distributed Raman amplification integrated into the system, the BFS uncertainty is enhanced to 0.843 MHz and better spatial resolution of 2 m over the same sensing fiber is achieved.

Beschreibung: Recent studies demonstrated the potential of increasing the Lamb wave detection sensitivity of fiber Bragg grating (FBG) sensors by bonding the optical fiber away from the grating location, instead of the conventional method of bonding the FBG directly. The FBG located at a remote location further along the optical fiber collects the guided traveling wave in the optical fiber generated from the Lamb wave signal. This remote bonding method could potentially be extended to a series of multiplexed FBGs. However, previous experiments also detected coupling to guided traveling waves in both directions in the optical fiber, which could have significant effects on multiplexed signals. In this paper, we measure the coupled signal amplitudes in both forward and backward directions, when ultrasonic waves couple from a thin plate to an optical fiber and from an optical fiber to a thin plate. The forward- and backward-induced modes are measured in both the optical fiber and the plate. The same experiment is then performed for the case when ultrasonic signal is coupled from the optical fiber to the plate. In addition, two different types of bonding, cyanoacrylate adhesive and frictional bond, are explored to investigate how the signal conversion depends on the bonding method. The results demonstrate that the coupling of ultrasonic waves from a thin structure to an optical fiber and from an optical fiber to the structure is complex. The coupling does not only occur in the direction of the wave propagation, but can be coupled into both forward and backward modes, depending on the bonding configuration used.

Beschreibung: Fast synchronization of generators and microgrids will be a critical technology in future power systems with high penetration of nondispatchable power resources. Existing synchronization methods rely on generator controls and their performance is limited by the generator characteristics. Speed of microgrid synchronization is further limited by the communication link among generation units. These factors lead to a slow and sometimes faulty synchronization, predominantly because of the phase mismatch during interconnection. This paper frames the generator synchronization problem as a phase-locked loop (PLL) design problem and introduces a voltage-source converter (VSC) based synchronizer for implementing the PLL-based active synchronization method. The VSC-based synchronizer is connected at the point of common coupling and it relies only on local measurements for control. It ensures zero phase error during interconnection by taking the advantage of the fact that the phase is not regulated in the generator controls. Relation between the synchronizer rating, control design, and synchronization speed is developed using describing function analysis of frequency and phase control loop gains. The operation and performance of the VSC-based synchronizer is demonstrated using simulations of a 555 MVA, 24 kV synchronous generator.

Beschreibung: In this paper, an extended Kalman filter (EKF) is employed to estimate stator currents, rotor speed, rotor position, and mechanical torque of a direct-driven surface-mounted permanent-magnet synchronous generator (PMSG) based variable-speed wind turbine systems controlled by a robust predictive deadbeat (DB) algorithm. Therefore, the flux-oriented control of the PMSG is realized without mechanical sensors (i.e., no position encoders or speed transducers). The estimated stator currents are fed back to the prediction model in order to compensate the one-step delay caused by the digital controller and to reduce the total harmonic distortion of the stator currents. Thus, the torque ripples are also reduced. Furthermore, a simple disturbance observer is presented, which estimates the perturbations caused by parameter variations of the PMSG or by any unmodeled dynamics in order to enhance the robustness of the proposed DB algorithm. The proposed scheme is experimentally validated using a 14.5-kW PMSG and a dSPACE DS1007 real-time platform. Its performance is compared with that of the conventional DB control strategy for all operation conditions and under parameter variations of the PMSG.

Beschreibung: As interturn short fault (ISF) in a permanent-magnet synchronous machine (PMSM) degrades its energy efficiency and may cause other problems, accurate fault diagnosis for the PMSMs is necessary. In this paper, we present a method that uses voltage and current residual components to diagnose the phase and the severity of the ISF in PMSMs. A faulty-winding model (FWM) is introduced to analyze the fault; the model describes a relationship between the voltage decrease of the faulty winding to the characteristics of the fault such as a fault resistance and a fault turn ratio. Based on the model, we suggest a fault index (FI) that shows the severity of the ISF. As the ISF induces residual components to both voltage and current, the proposed method utilized those components with the FWM. A least squares (LS) method is used to estimate the FI and to diagnose the ISF of PMSMs. Experimental results demonstrate that the proposed method diagnose the ISF effectively.

Beschreibung: An interior permanent magnet (IPM) machine with ∇ + U shape rotor topology is proposed and its electromagnetic performance with typical V shape and ∇ shape for electric vehicle (EV) applications are compared. The pole-arc to pole-pitch ratios are optimized to maximize the fundamental air-gap flux density and minimize its total harmonic distortion (THD) of all the three IPM machines by the finite element (FE) method. It can be obtained that ∇ + U shape rotor topology has the lowest THD of the air-gap flux density. The back electromotive force and its THD orders, cogging torque, torque density, torque ripple, d - and q -axis inductances, saliency ratio, and iron loss of three machines are analyzed and compared. It is demonstrated that the ∇ shape IPM machines have the highest average torque, and the torque ripples of the V shape and ∇ shape machines are almost the same. The ∇ + U shape IPM machine has the lowest torque ripple and iron loss with only a little reduction of average torque. Finally, the ∇ + U shape IPM machine is prototyped to verify the results of the FE analysis.

Beschreibung: The rising use of renewable power generation plants is highlighting the need for an integrated research combining multiple disciplines in order to achieve a commercially competitive technology stage. The demonstrative NEREIDA wave power plant installed in the northern coast of Spain constitutes a good example of this effort. This paper deals with the design, modeling, and control of the oscillating-water-column-based wave energy converter in order to maximize the power output of the NEREIDA power plant. The power optimization relies on two control strategies proposed to avoid the stalling behavior, a characteristic drawback of the Wells turbine, which limits the system's power. The first control strategy is an airflow control using a PID controller tuned by the particle swarm optimization algorithm and its recent memetic variant called fractional particle swarm optimization memetic algorithm. This controller will control a throttle valve to regulate the airflow in the turbine duct. The second one consist of adequately controlling the rotational speed of the generator by means of the rotor-side converter of the back-to-back converter connected to the doubly fed induction generator to provide a swift way to respond to the rapid variations in the turbine speed. The results show that both controls provide a higher power generation compared to the uncontrolled case.

Beschreibung: For the purpose of avoiding the drawbacks of large volume, heavy weight, complex wiring, and low reliability caused by the mechanical position sensors in aeronautic power drives, the self-sensing control of permanent magnet synchronous machines (PMSMs) has been getting increasing attention. High-frequency (HF) pulsating current injection is an efficient method to obtain the rotor position at low speeds. However, in this method, the rotor position is extracted from the command voltage instead of the actual measurement due to the lack of voltage sensors, and the control performance of the HF current is nonideal because of the proportional-integral controller (PI) current regulators. Both these shortcomings give rise to position estimation error. To avoid the aforementioned problems, a novel current regulator consisting of the PI and second-order generalized integrator (SOGI) is presented. The different combinations of the PI and SOGI in the d–q axes current regulators are studied. The system stabilities of the proposed and existing HF pulsating current injection-based self-sensing control strategies are comparatively analyzed considering the current control error and some other aspects. The experimental results demonstrate the feasibility of the proposed strategy by a surface-mounted PMSM vector controlled system.

Beschreibung: This paper proposes an optimum design for the dc-based DFIG generation system in a dc grid to make its cost optimal. As the stator is connected to a dc bus by the stator side converter, its voltage and frequency are not enslaved to an ac grid, which makes it possible to decrease the synchronous speed, rotor speed, and gearbox ratio. Three aspects are improved. First, control targets are optimized to minimize the increased generator current with decreasing gearbox ratio. Second, optimum design of a generation system is made by regulating gearbox ratio at the cost of increase in the generator current. Significant decreases in cost and losses are analytically obtained from the elaborated cost and losses models, whose parameters are taken directly from the practical and commercial wind generation system. Third, the coordinated model predictive control is adopted in the stator flux-oriented frame with a stator flux and rotor current predictive method. Finally, as the synchronous speed and rotor speed decrease to low levels, simulation and experiment studies are carried out to verify the operational feasibility of DFIG and analyze its steady and transient performance.

Beschreibung: Magnetic-geared machines are based on the flux-modulation principle and typically constructed with a flux-modulated double rotor (FMDR). The modulator experiences high torsional stresses when designed for high torque transmission. As a result, the FMDR has high probability of failure if not designed appropriately. In this paper, the FMDR design options are investigated with mechanical and electromagnetic finite element (FE) modeling. The addition of filler material in between the poles of the modulator pole-pieces is found to reduce the shear stresses by $61.7%$ to $87.2%$ at the cost of $2.6%$ to $3.2%$ lower pull-out torque. Possible shear stress reduction with the design of bridged modulators is investigated. Increase in pole number is shown to increase localized stress levels in bridged modulators. Electromagnetic simulations show that for a given FMDR specification, the highest pull-out torque is at an optimal pole number. The tradeoff between FMDR weight, losses, and shear stress are discussed. A scaled-size prototype FMDR with a bridged modulator is constructed. The FMDR is tested and is shown to achieve comparable results with the FE simulations. At field intensity levels above 600 kA/m in the periphery, the FMDR achieves reduced pull-out torque $28.7%$ lower in comparison with three-dimensional simulations. The losses at different load levels of the FMDR are also compared with experimental and FE simulation result and are shown to confirm the FE simulation results.

Beschreibung: This paper investigates the effect of the stator winding connection on the performance of a six-phase switched reluctance machine (SRM). Five winding connection types are proposed for the machine. Finite element analyses (FEAs) of flux distribution, output torque, and core losses are presented under single-phase and multiphase excitation for each connection and the results are used to compare the average torque and torque ripple ratio characteristics and to develop understanding of the respective contributions of mutual inductance in the torque development. Experimental tests on a six-phase conventional SRM verify the torque performance and mutual inductance effects of the different winding connections. An optimum winding configuration for a six-phase SRM is proposed.

Beschreibung: A comprehensive modular state-space model of a microgrid is developed that handles basic components and loads, as well as inverter-based generation, such as PQ inverter and voltage-source inverter (VSI). Specifically, the developed model is suitable for control design utilizing the nominal set-point values of frequency and voltage of the VSI inverters, and active and reactive power set points of the PQ inverters. The model is also useful for small-signal stability assessment and enhancement. It is shown that when a PQ inverter is added to the system, the low-frequency modes of the power-sharing dynamics drift to new locations and the relative stability is improved. Meanwhile, to preserve the power-sharing stability, a decentralized droop controller of paralleled VSI inverters is designed. Finally, the dynamic model is used to design and implement distributed secondary frequency controllers taking into consideration the characteristics of storage devices. The proposed modeling and control methodologies are demonstrated using an 11 bus microgrid with and without PQ inverters.

Beschreibung: For permanent magnet synchronous generators (PMSGs) based dc microgrids working autonomously, load sharing among multiple PMSGs is necessary when the available wind power is more than the load demand. During the load-sharing process, PMSG may prone to instability due to possible over deceleration. To address this issue, this paper presents a new distributed control scheme, which can achieve stable and optimal load sharing among multiple PMSGs in a dc microgrid. This scheme has a two-layer structure. Based on the distributed model predictive control approach, the upper layer controllers coordinate the operation of parallel-connected grid-side converters, thus providing power references for each PMSG. The computed power references are sent to the lower layer PMSG controllers for execution. The salient feature of this scheme is that by incorporating the rotor kinetic energy and the generation margin into the controller design, it not only achieves the optimal load sharing, but also ensures stable operation of all PMSGs. Simulation results verify the effectiveness of the proposed scheme.

Beschreibung: In this paper, a multiparameter, multisensor system for comprehensive electrical machine condition monitoring has been developed and the results of an evaluation reported. The fiber Bragg grating-based system developed allows for the simultaneous monitoring of key parameters including machine vibration, rotor speed, torque, spin direction, temperature distribution along the stator windings and on the rotor surface as well as the stator wave frequency. This all-optical sensing solution has been designed to be compatible with being fitted in the tight confines of an electric motor and uses the optical nature of the measurement and the insulating nature of the sensor material to avoid problems of electrical interference. The system reduces the component count over conventional sensor systems, i.e., all sensing elements are contained within the machine and operated by a single sensing interrogation unit, thereby reducing cost and allowing for a convenient interface for the user. The design of the system is presented, as are results on the testing and evaluation of the device the sensing system has been successfully integrated into and tested on a permanent magnet motor prototype.

Beschreibung: A highly compact biocompatible microprobe type fiber optic temperature sensor was experimentally demonstrated utilizing an inherently high thermo-optic coefficient of DNA biopolymer. The sensor was based on an all-fiber multimode interferometer (MMI) along a coreless silica fiber (CSF) spliced to an end of a single mode fiber. Au film was deposited the CSF end facet to provide a double path for MMI and it also worked as a probe terminal. The circumferential area of CSF was coated with DNA-cetyltrimethylammonium chloride (CTMA) thin solid film, which served as a temperature sensing head. We experimentally investigated thermo-optical properties of DNA-CTMA thin solid films to find its large negative thermo-optical coefficient −4.15 × 10 −4 /°C in the temperature range from 20 to 70 °C. DNA-CTMA coated fiber optic probe was immersed in a water bath to simulate the bio compatible environment whose temperature was varied in the range from 30 to 70 °C. The proposed sensor showed a high-temperature sensitivity of −0.22 nm/°C in the spectral shifts, and 0.085 dB/°C in the reflected optical power changes. The proposed probe can be readily applied in various types of in vivo point of care temperature monitoring.

Beschreibung: In many applications in the industry, securely attaching fiber optic sensors to metallic structures is important for optimum monitoring, overcoming the limitations of glues and adhesives which are known to degrade under certain circumstances. To avoid that problem, creating a metallic bond to attach the sensors securely to the metal surface is important. Commercial fiber optics with metal coatings can be used but it is important not to damage the sensor itself which is written in the thin optical fiber. In this work, an alternative laser cladding technology has been studied for embedding metal-coated fiber optics into which fiber Bragg grating (FBG) sensors have been written. A three-step strategy was selected for embedding the metal coating fibers to create the best conditions to allow high-quality measurements. This has been seen to allow good control of the embedding process to be achieved and to minimize the thermal and mechanical stress generated. The research undetaken has shown that it is possible to embed Cu- and Ni-coated fiber optics containing sensors to over 300 μ m with low losses, of between 0–1.5 dB (or 0–30%) and yet still enable satisfactory strain and temperature measurement results to be obtained. The research has shown that both Ni- and Cu-coated FBG-based fiber optic sensors could be embedded successfully and shown to give good mechanical and thermal response to similar nonembedded sensors and excellent cross-comparison with the conventional gauge used for calibration. The results are, therefore, particularly encouraging for the use of sensors of this type when incorporated to create metallic “smart structures” achieving durability of the sensors through the use of this innovative technique.

Beschreibung: Fast and high-resolution simultaneous measurement of temperature and strain is experimentally demonstrated. A Fabry–Perot interferometer fabricated in a polarization-maintaining fiber has sharp transmission peaks, which are divided into two sets corresponding to the polarization of the transmitted light. The sharp transmission peaks shift in response to changes in temperature and strain, and because the dependence coefficients are different for each set, temperature and strain can be simultaneously measured with high resolution. To read the position of a sharp transmission peak, wavelength sweeping with narrowband light is necessary. By using injection current modulation in a laser diode, high-speed wavelength sweeping and short measuring time are realized. We performed simultaneous measurements with a measurement time of 20  $mu$ s; measurement resolution of 0.1  $^circ$ C and 0.8  $mu epsilon$ for temperature and strain, respectively; and noise spectral density of 30 n $epsilon /sqrt{rm Hz}$ . We further experimentally demonstrated that vibration with an amplitude of 20  $mu epsilon$ and a frequency of 1 Hz and heating at a rate of 0.7  $^circ$ C $/$ s can be simultaneously measured.

Beschreibung: We demonstrate a quasi-distributed sensor for cantilever health inspection measurements using a fiber Bragg grating (FBG) array inscribed in a polymer optical fiber. The FBGs were characterized and calibrated for axial strain, temperature, and relative humidity prior to their mounting on a carbon cantilever beam, the tail rotor of a helicopter. By using the zero-crossing demodulation algorithm, we recovered the time-dependent, wavelength response from each Bragg grating sensor and the vibration response of the beam was extracted. We used the response of the beam to study how the addition of masses at different positions on the beam influences the vibrational behavior and mimics the location of “damage” through the time-dependent results. We show that health inspection measurements are feasible with polymer-based fiber Bragg gratings, offering accurate and rapid detection of damage points on a structural beam.

Beschreibung: This paper presents an online augmented surveillance system that aims at real-time monitoring of activities along a pipeline. The system is deployed in a fully realistic scenario and exposed to real activities carried out in unknown places at unknown times within a given test time interval (the so-called blind field tests). We describe the system architecture that includes specific modules to deal with the fact that continuous online monitoring needs to be carried out, while addressing the need of limiting the false alarms at reasonable rates. To the best of our knowledge, this is the first published work in which a pipeline integrity threat detection system is deployed in a realistic scenario (using a fiber optic along an active gas pipeline) and is thoroughly and objectively evaluated under realistic blind conditions. The system integrates two operation modes: the machine+activity identification mode identifies the machine that carries out a certain activity along the pipeline, and the threat detection mode directly identifies if the activity along the pipeline is a threat or not. The blind field tests are carried out in two different pipeline sections: the first section corresponds to the case in which the sensor is close to the sensed area, while the second one places the sensed area about $text{35}$ km far from the sensor. Results of the machine+activity identification mode showed an average machine+activity classification rate of $text{46.6}%$ . For the threat detection mode, $text{eight}$ out of $text{ten}$ threats were correctly detected, with only $text{one}$ fals- alarm appearing in a $text{55.5}$ -h sensed period.

Beschreibung: An external magnetic field (EMF) fiber sensor by combining nanomagnetic fluid and Hi-Bi nonadiabatic tapered optical fiber in fiber loop mirror (THB-FLM) is demonstrated experimentally and theoretically. The polarization controllers (PCs) in FLM are adjusted to excite different cladding modes in the sensor. By variation of the PCs’ settings, the sensitivity of the sensor to EMF in the range from 0 to 21 mT could be tuned from 255 to 402 pm/mT. As compared to the reported magnetic fluid (MF) based sensors, the achieved sensitivity of the proposed sensor, with only 0.1% of the volume concentration of MF nanoparticles, enhanced by 5.6 orders of magnitude relative to in-line nonadiabatic tapered optical fiber sensor. The detection limit of the THB-FLM to EMF in the range of 0 to 21 mT and 22 to 50 mT was 5 and 18.9 μ T, respectively. Experimental results show that the sensitivity to the EMF increased with the order of the cladding mode. In addition to the EMF sensing capability, the proposed structure can simultaneously provide temperature information.