ALBERT

Description: This paper proposes a new simplified model of a doubly fed induction generator (DFIG) that is integrated with a rotor-side converter for studies of large-scale transient stability. This model accurately considers the rotor field dynamics of an induction generator to yield simulation results that are more accurate in terms of voltage stability, as well as angle stability. The purpose of this paper is to provide a simple but effective DFIG model for the study of large-scale transient stability, and to examine the important aspects of rotor voltage and rotor slip power. This new simplified DFIG model with an electric/turbine control system was tested against a six-machine and 23-bus system, and the responses obtained in case studies of transient stability were compared with those of a PSS/E program. Finally, the proposed DFIG model was also validated by comparing the simulation results for a single-machine and infinite-bus system with those of PSCAD/EMTDC.

Description: Power fluctuation caused by wind speed variations may be harmful for the stability of the power system as well as the reliability of the wind power converter, since it may induce thermal excursions in the solder joints of the power modules. Using the wind turbine rotor inertia energy for power leveling has been studied before, but no quantified analysis or generic design method have been found. In this paper, the transfer functions from the wind speed to electrical power, electromagnetic torque, and rotating speed are built based on which the rotating speed controller is designed in the frequency domain for power leveling. Moreover, the impact of other parameters on power leveling, including the time constant of maximum power point tracking (MPPT) and the rotor inertia, are also studied. With the proposed optimal design, the power fluctuations are mitigated as much as possible, while the stability of the rotating speed is still guaranteed. Moreover, the oscillation of the electromagnetic torque is also reduced, and the performance of the MPPT is only weakened slightly.

Description: The precise estimation of efficiency of induction motors is crucial in industries for energy savings, auditing, and management. This paper presents a novel method for in situ induction motors efficiency estimation by applying the genetic algorithm and utilizing IEEE Form F2-Method F1 calculations with pretested motor data. The method requires a dc test, full-load operating point rms voltages, currents, input power, and speed measurements. The proposed algorithm uses a sensorless technique to determine motor speed. The algorithm is not only an in situ tool; it can also be used as an on-site efficiency estimation tool that might replace the expensive dynamometer procedure. The method was validated by testing 30 induction motors.

Description: It has recently been shown that spectrum analysis of instantaneous power can provide sensitive online detection of rotor faults in induction motors compared with current, torque, speed, or vibration spectrum analysis. However, it was reported that monitoring of the twice slip frequency, $2sf_{s}$ , components induced by the fundamental component can produce false rotor fault alarms due to asymmetry in the rotor or low frequency load oscillations. In this paper, the rotor fault components induced in the power spectrum by the stator fifth and seventh space harmonics are derived to evaluate their immunity to false alarms. It is shown that the $(6 - 8s)f_{s}$ component can provide reliable detection of rotor faults under cases where existing methods produce false alarms. An experimental study performed on custom built rotor samples shows that the new components are capable of detecting rotor faults immune to false alarms produced by rotor axial air ducts, rotor anisotropy, and low frequency load oscillations for cases where existing methods fail. The components derived in this paper can also be applied to vibration, speed, torque, or acoustic monitoring for reliable detection of rotor faults.

Description: Analytical models of electric machinery often utilize Carter's coefficient to account for the increased airgap reluctance due to flux entering the sides of the stator teeth. In this letter, a modified coefficient is proposed to account for wide stator slots, wherein a component of flux directly enters the stator backiron. The proposed coefficient is implemented in an analytical model of a wound rotor synchronous machine and is validated using two-dimensional (2-D) finite element analysis.

Description: Design aspects of the trans-rotary magnetic gear (TROMAG) integrated rotary machine are discussed in this paper, with particular focus on optimizing system cost and weight. Analytical models are used for design of the TROMAG. Optimal designs of the rotary machine are found by using a population-based genetic algorithm and two-dimensional finite-element analysis and thermal considerations. Weight, volume, and cost of the resultant system are then compared with the Pareto-optimal set of a permanent magnet linear tubular machine that is designed for the same force and speed specification. It is shown in this paper that, for high-force low-speed reciprocating motion applications, an electromechanical motion system consisting of a TROMAG and a rotary electric machine can far surpass a conventional direct drive linear machine in terms of weight, volume, and initial and operating cost.

Description: This paper presents a decentralized current control approach for a nine-phase wind turbine generator. This type of generator has three different three-phase stators sharing the same machine yoke and connected to the grid by means of three different voltage source back-to-back power converters. Due to the machine configuration, magnetic couplings are present between the three stators, complicating the design and implementation of the machine current controllers. Rather than a centralized control approach, this paper proposes a methodology to design a decentralized machine control to regulate the active and reactive power flowing through each stator independently. A complete dynamic analysis is performed in order to design the controller to reduce the coupling effects within the machine, while ensuring a proper dynamic performance. The control strategy is validated through simulation and experimental results.

Description: The papers in this special section cover the advances in multi-objective design and optimization based on genetic algorithms, surrogate, polynomial regression, and particle swarm optimization techniques. Design of novel trans-rotary magnetic gear, hybrid machines for dc generation, and two degrees of freedom split-stator induction machines highlight new magnetic configurations and their performance evaluations. Multiphysics analysis of magnetothermal and magnetostructural behavior of Switched Reluctance Machine (SRM) and brushless doubly fed machines shed light on analytical and practical aspects of design in electromechanical converters. Finally, control of torque undulation, loss minimization, low speed high torque operation, and advanced digital control of adjustable speed motor drives conclude this unique collection of papers.

Description: There are many kinds of permanent-magnet (PM) motors, which are widely used in modern industry, but the problem of temperature rise is likely to affect the operation performance and even the life of the motor. The semiclosed structure of the PM spherical motor (PMSM) tends to increase the temperature when it works, so the thermal analysis of the PMSM is considered necessary. Based on double Fourier series decomposition, this paper establishes a three-dimensional (3-D) analytical model of PM eddy current loss in the PMSM, which considers the effect of time and space harmonics. Meanwhile, the heat sources such as hysteresis loss and copper loss are discussed. With those heat sources, a 3-D equivalent thermal network model is established. The thermal resistances are calculated. By applying the thermal network model, the influence of different speed and load on temperature rise is analyzed, and a steady-state thermal analysis of the motor is performed by using finite element analysis. The structure of stator is improved and good heat dissipation effect is achieved. This paper provides the theoretical basis for the design of ventilation and cooling system of the PMSM.

Description: This paper presents a comprehensive investigation of various reference frames and their relative speeds in cascaded doubly-fed induction machines (CDFIMs). Then, a compact space-phasor model of CDFIMs in the natural and arbitrary reference frames is presented that is useful for performance analysis of CDFIMs based on rotating phasors. The merits of the proposed model compared with existing models are using a common (single) reference frame for all machines and parts of CDFIMs, and the model formulation is independent of the rotor angle position. The reference frames in the suggested model can be fixed on the common rotor of the CDFIM machines for dynamic analysis or it can be fixed on the stator/rotor flux of each cascaded machines useful for CDFIMs controller design. A two-axes equivalent circuit for a CDFIM is also presented, which enables analysis of CDFIMs in commercially available power circuit simulation software tools. The validity of the model is verified via the investigation of an experimental setup and consists of two mechanically coupled 4-kW DFIMs and a 4-kW dc machine as a load. The setup is investigated under various test scenarios, including free acceleration, load (torque) change, and frequency step change conditions.

Description: Conventional model-predictive torque control (MPTC) requires tedious and time-consuming tuning work for stator flux weighting factor, and presents relatively high torque ripples. To solve these problems, this paper proposes a model-predictive flux control (MPFC) for two-level inverter-fed induction motor (IM) drives. The references of stator flux magnitude and torque in conventional MPTC are converted into an equivalent reference of stator flux vector in the proposed MPFC. As only the tracking error of stator flux vector is required in the cost function, the use of weighting factor is eliminated. The optimal voltage vector is selected based on the principle of stator flux error minimization and its switching instant is optimized rather than being in the beginning of each control period. The proposed MPFC with and without switching instant optimization are both implemented in a 32-bit floating digital signal processor, and they are compared in detail in terms of torque ripple, current harmonics, and average switching frequency. Both digital simulations and experimental tests were carried out on a two-level inverter-fed IM drive, and the obtained results validate the effectiveness of the proposed method.

Description: A generic model of grid-connected doubly-fed induction generator (DFIG)-type wind turbines represented by differential-algebraic equations (DAE) is proposed for short-term transient-stability analysis. From the view of analytical research, vital simplifications are made to the complex physical model of DFIGs, whereas characteristic dynamics are still preserved. When the connection between the wind turbine and grid is weak, transient voltage collapse caused by singularity-induced instability (SII) is observed and analyzed adopting the generic model. In addition, it is shown that collapse might also occur when state variables of the dynamical system get out of control when the connection between the wind turbine and grid is stiff, where fast drop of dc-bus voltage occurs. Critical indices for evaluating transient-stability performances of the DFIG are proposed and parameter sensitivity analysis is carried out. Physical meanings of SII in generators/units with power–electronic interface in vector-oriented control frame are generalized. Novel interaction between the grid and these nonconventional generators/units is highlighted.

Description: Analytical models of electric machinery often utilize a two-axis lumped-circuit approach, wherein the inductance parameters are obtained by applications of Ampere's law in a two-dimensional (2-D) cross section of the machine. A method of incorporating end-effects in the magnetizing inductance calculations of wound rotor synchronous machines is presented, allowing machines with high diameter-to-length ratios to be modeled more accurately. The method is verified using three-dimensional (3-D) finite element analysis.

Description: This paper provides a theoretical analysis on the energy loss of a battery–ultracapacitor hybrid energy storage system based on the equivalent series resistances and a pulsed current load profile. The optimal current distribution that minimizes the overall energy loss is proved to be solely determined by the ratio of internal resistances between battery and ultracapacitor packs. Due to a large difference in the internal resistances, a quasi-optimal current distribution can be considered to let the battery pack provide the average load current and ultracapacitor pack supply the entire dynamic load current. This result clearly demonstrates that the ultracapacitor pack should supply the most of the dynamic load current not only because of battery protection, but also for energy loss minimization. Finally, the theoretical analysis is validated by both simulation and experimental results. Additional discussions, such as sensitivity analysis, the influence of the sizing of ultracapacitors, and a realistic test cycle are also added for reference purposes.

Description: Applications for low-speed high-torque machines include marine propulsion and wind power generation. Since electric machinery size is more directly related to required torque than to required power, high required torque leads to large machines. Mechanical gears increase the speed and lower the required torque of the machine to reduce size. This, however, results in increased noise and maintenance, and decreased reliability. Magnetic gears offer the advantages of mechanical gears without the disadvantages created by physical contact. Integrating magnetic gears into the machine structure offers additional mass savings. This study proposes a novel machine architecture, which integrates magnetic gearing and a permanent magnet synchronous machine to create an inner rotor flux-modulated permanent magnet synchronous machine. Unlike previous arrangements, the proposed machine utilizes a more desirable inner rotor configuration and avoids multiple magnet arrays. This study presents a finite–element-based design model of the proposed machine to be utilized in an optimization-based design environment. A multiobjective design study is presented for a laboratory scale application. The resulting tradeoff between mass and loss is compared with that of a permanent magnet synchronous machine for the same application.

Description: Developing the control algorithms of electric machine drives for less noise and harmonics is proposed here for design improvements. Modern control algorithms for electric machine drives are implemented, and their radiated magnetic fields are measured and imported into a digital signal processing unit. The measurement was implemented using magnetic field antennas which cover low frequencies. A digital signal processing unit was designed for online and real-time measurement and processing of the fields, and categorizing the harmonics. The controller compares the desired and measured signals and modifies the duty cycle of the switches to suppress the existing harmonics. The manual and automatic suppressions of some critical harmonics were implemented in two switching techniques using a defined procedure. Consequently, the modified control algorithm of the drive would radiate the electromagnetic stray field with less noise and harmonics. This leads to lower electromagnetic interference from the machine drive. Since there is no need to locate any sensor inside the machine or the converter, this can be considered as a nondestructive method for industry implementations, where it is impossible to access the parameters of components for online monitoring.

Description: This paper studies the unbalanced magnetic pull in the brushless doubly fed machine (BDFM) caused by both static and dynamic rotor eccentricities. Several parallel winding designs for the two stator windings are proposed, and the practicality of such designs is discussed with respect to direct coupling between the stator windings and with rotor undesirable harmonic fields. Once practical parallel winding designs are established, their effects on reducing deflection as a result of static and dynamic eccentricities are shown and compared with series wound stator. This study has been carried out on a prototype D400 250-kW BDFM.

Description: The nonlinear induction motor model is appropriately integrated by incorporating the dynamics of the power electronic converter in a manner that permits the design of stable field-oriented control (FOC) operating with minimum losses. As already proven, the challenging issue of operating the induction machine with minimum copper losses requires a varying rotor flux opposed to the standard FOC technique, which keeps the rotor field magnitude constant and tracks the electric torque to the desired level. To this end, exploiting the Hamiltonian structure of the developed motor/converter model, an innovated nonlinear controller is proposed that guarantees the technical limits of the converter (linear modulation) and simultaneously operates under FOC at steady state to achieve accurate speed regulation with varying rotor flux according to the minimal losses requirements. Under these circumstances, the conventional FOC stability analysis does not hold anymore, and therefore for the first time, a new rigorous analysis is provided that proves stability and convergence to the desired equilibrium for the complete closed-loop motor converter system. Finally, the theoretical contribution is examined in comparison to the traditional FOC operation by simulations obtained for an industrial size induction motor, while it is further evaluated by real-time results of a motor with similar parameters.

Description: A new type of electric machine with two free rotating rotors [dual mechanical port (DMP)] is investigated in this paper. Since this DMP machine has a squirrel-cage outer rotor, it is named as SCDMP machine. First, the electromagnetic characteristic of the SCDMP machine is analyzed. Then, the transient model and steady-state model of the SCDMP machine are derived. The proposed machine models are verified by finite element method and simulation. The results show that the proposed models accurately represent the unique electromagnetic characteristics of the SCDMP machine.

Description: This paper focuses the analysis around a grid-connected converter that operates under unbalanced voltage and current conditions. Two different scenarios have been selected to validate the proposed algorithms. In the first scenario, the converter operates as a reactive power compensator, exchanging reactive power with the grid, and minimizing the dc bus voltage oscillations. The second scenario is more challenging, since it operates as a load balancer. In this application, the unbalanced current consumption of the load is compensated by the converter, exchanging positive and negative sequence currents with the grid. Another objective in this second scenario is to compensate the reactive power of the unbalanced load. It is important to highlight that in both scenarios, any maximum limit of the converter can be exceeded due to the specific unbalanced voltage and current conditions. Three variables are considered critical for the converter: 1) output ac current limit; 2) output ac voltage limit; and 3) dc bus voltage oscillation limit. Thus, this paper proposes a control method, which limits online the reactive power reference in the first scenario and the exchanged current references in the second scenario in order not to exceed any of the mentioned critical variables. The corresponding experimental results are shown in Part II of this paper so as to validate the limitation algorithm obtained by means of the mathematical analysis carried out in Part I.

Description: The fault current contribution of the doubly fed induction generator-based wind turbines (DFIG-WTs) is dictated by a combination of factors, including the electrical parameters of the machine and the controller configuration of the converters. This paper presents an analytical derivation of short-circuit current quantities considering the controller influences. Mathematical models of the short-circuit current were first developed based on the closed-loop transfer functions, and approximate expressions for time constants and frequencies were derived. The mathematical models and the expressions for time constants and frequencies were later validated using a manufacturer-based simulation model and a nonlinear optimization for parameter extraction.

Description: A mesh-based magnetic equivalent circuit has been derived to model the dynamics of wound rotor synchronous machines (WRSMs). A particular focus has been placed on the derivation of flux tubes to model machines with an arbitrary number of damper bars placed at an arbitrary depth in the rotor pole tip. Faraday's Law is applied to establish a state model in which winding and damper bar flux linkages are selected as state variables. The resulting coupled magnetic equivalent circuit/state model is solved to predict machine dynamics. An important attribute of the model is that saturation is represented without the need for a relaxation factor, which enables its use as a practical tool in machine design. Data obtained from hardware experiment and a finite-element model are used to validate the proposed methods.

Description: The maximum capacity, the amount of maximal electric charge that a battery can store, not only indicates the state of health, but also is required in numerous methods for state-of-charge estimation. This paper proposes an alternative approach to perform online estimation of the maximum capacity by solving the recursive total-least-squares (RTLS) problem. Different from prior art, the proposed approach poses and solves the RTLS as a Rayleigh quotient optimization problem. The Rayleigh quotient-based approach can be readily generalized to other parameter estimation problems including impedance estimation. Compared with other capacity estimation methods, the proposed algorithm enjoys the advantages of existing RTLS-based algorithms for instance, low computation, simple implementation, and high accuracy, and thus is suitable for use in real-time embedded battery management systems. The proposed method is compared with existing methods via simulations and experiments.

Description: The high power pulsed charging power supply is usually necessary for the pulsed power devices with high power repetitive discharge. This paper first introduces a new topology structure of a charge and discharge system for high voltage capacitor and its operating principle, then comes up with technical requirements for the pulsed alternator. Afterward, design features of the inductor pulsed alternator, including the structure, main dimensions, and sizes of rotor teeth and slots are studied, and the main parameters of homopolar inductor pulsed alternator (HIPA) prototype are provided. The choice of rotor material and bearing failure phenomenon are also investigated to find a responsible solution. Finally, the experimental waveforms of HIPA prototype without and rated load when charging capacitor are given. The research shows that the pulsed power supply based on the inductor pulsed alternator is competitive for its high energy storage density, moderate power density, and high reliability, which is suited to the charging power supply of pulsed capacitor.

Description: This paper presents an unexpected fluctuation of voltage for a 30-kW wound rotor brushless doubly-fed machine (BDFM) in a standalone power generation system. To address this issue, an improved method of harmonic injection is introduced. A voltage and current double closed-loop control strategy, based on control winding (CW) current decoupling, is applied through the entire experiment. Consequently, the experimental outcomes are fairly aligned with the dynamic simulations in most conditions. However, the voltage fluctuation in the power winding (PW) can be observed for a certain speed range. Harmonic analysis is then carried out on experimental data of PW voltage and CW current. A pair of interharmonic waves, which are symmetric with respect to the fundamental wave, is demonstrated to exist in PW voltage and CW current. Due to the analysis, these harmonic conjugate waves are caused by the high-order magnetomotive force tooth harmonics and current harmonics within a specific speed range. Accordingly, the control strategy of harmonic injection is employed to effectively eliminate these harmonic conjugate waves. The experimental results further highlight that the voltage amplitude can be maintained with less harmonic contents by our tailored control scheme. In addition, the formation and presence of harmonic conjugate waves may lead to the voltage amplitude fluctuation of BDFM in the standalone power generation system.

Description: Application of electric machines in the traction and transmission systems of hybrid/electric vehicles has been studied for many years. The hybrid vehicle based on dual mechanical port (DMP) electric machine has gained more and more attention, because it eliminates the need for planetary gear and combines the motor and the generator into a compact electric machine. The DMP machine with a squirrel-cage outer rotor (SCDMP) is investigated in this paper. Due to its unique electromagnetic characteristics, control algorithms for conventional machines cannot be applied to the SCDMP machine. The methods to calculate the correct current commands and estimate the outer rotor flux position are proposed. Based on these two methods, a control algorithm for the SCDMP machine is proposed and estimated by simulation. The results show that the proposed control algorithm is able to independently control the torque productions and the flux levels of the two rotors of the SCDMP machine.

Description: This article presents results from the integration of a noncontact physiological radar monitoring system (PRMS) with a type I polysomnography (PSG) system to perform sleep monitoring. The PRMS system consists of two continuous-wave Doppler radars operating at the industrial, scientific, and medical (ISM) band of 2.45 GHz. The system can acquire data, perform digital processing, and output appropriate conventional analog outputs with a latency of approximately 130 ms, which can be recorded and displayed by a gold standard sleep monitoring system along with other standard sensor measurements. Radar data was also used to successfully detect paradoxical motion that was simulated using linear movers and to categorize normal breathing, apnea, and hypopnea in sleeping subjects with obstructive sleep apnea (OSA).

Description: A quantitative and explicit validation of the performance and safety of microwave systems and devices that have electromagnetic interaction with the human body is critical in the technological development process. Although a numerical model of the system environment can be ideally simulated, it cannot reflect the realistic environment that is vulnerable to various electrical, mechanical, and environmental interferences. Hence, the presence of the human body is the best measurement environment for these systems. However, newly designed devices/ systems that rely on the human body electromagnetic field interactions require multiple tests/measurements under a controlled environment. This environment is needed to validate the performance in all the possible scenarios of operation and make sure of the safety of those devices and systems. For example, a breast imaging system needs to be evaluated by detecting tumors in multiple locations, and it is unthinkable to do that on a real patient; hence, breast phantoms are needed to obtain an optimum system design and algorithms before moving to human clinical trials. Moreover, some experiments, such as the specific absorption rate (SAR) and hyperthermia, cannot be done on human beings due to the need to monitor the variation of the power intensity and temperature inside tissues. Employing live human participants for testing devices exposes the entire test procedure to several inherent uncertainties, such as respiratory movement, cardiovascular vibration, and variable skin humidity in addition, of course, to the safety concern of the new devices. Also, the application of the devices and systems on human subjects or human-related materials is a serious ethical issue where the researchers must receive an ethical clearance from the proper authorities, and it can be difficult to reasonably estimate and investigate the level of risks from various scientific, physical, and psychological aspects beforehand. Thus, the utilization of ar- ificial tissue-emulating (ATE) phantoms is highly beneficial for testing a device or system.

Description: Fault diagnosis of rotor asymmetries in induction machines working at a very low slip, through Fourier-based methods, usually requires a long acquisition time to achieve a high spectral resolution and a high sampling frequency to reduce aliasing effects. However, this approach generates a huge amount of data, which makes its implementation difficult using embedded devices with small internal memory, such as digital signal processors and field programmable gate arrays or devices with low computing power. In this paper, a new simplified diagnostic signal designated as the reduced envelope of the stator current is introduced to address this problem. The reduced envelope signal is built using only one sample of the current per cycle without any further processing, and it is demonstrated that it carries the same spectral information about the fault as the full-length current signal. Based on this approach, an embedded device has only to store and process a minimal set of samples compared with the raw current signal for a desired resolution. In this paper, the theoretical basis of the proposed method is presented, as well as its experimental validation using two different motors with broken bars: 1) a high-power induction motor working in a factory; and 2) a low-power induction motor mounted in a laboratory test bed.

Description: This paper investigates the spectral effects that stator supply harmonics can induce in wound rotor and doubly-fed induction generators. The purpose of this study is to clarify the nature and the origin of the reported significant inter harmonic effects in these machines. To this end, the authors derive analytical expressions that define the spectral signature frequencies of individual supply harmonics in the current and torque signals. The expressions are first validated through comparison with the spectra calculated using a harmonic time-stepped machine model and then by spectral measurements on a laboratory test rig comprising a 30 kW machine excited by a programmable power supply unit. It is shown that the presence of supply harmonics can result in multiple and variable wide-band interharmonic effects in the current and torque signals. Finally, the interharmonic current emissions for the wound rotor and the doubly-fed mode of operation are experimentally quantified using the relevant IEC standard indices.

Description: Three-phase nonoverlapping stator wound-field synchronous (NSWFS) machines having salient pole rotors are investigated systematically in this paper. The influence of the rotor pole number on the NSWFS machines is investigated via optimized designs. Using two-dimensional (2-D) finite-element analysis (FEA), the NSWFS machines are found to exhibit higher torque than the nonoverlapping segmented rotor NSWFS (SNSWFS) machines. The FEA-predicted back-electromotive force (EMF), cogging torque, and static torque of the NSWFS machines are validated by experiments on prototype machines.

Description: This paper proposes an advanced vector control method for rotor side converter of doubly-fed induction machine (DFIM)-based storage hydropower in order to enhance the fault ride-through capability in both generating and motor modes. In this method, the active power and stator voltage control loops are on the d -axis and q -axis, respectively. Since the active power and the stator voltage control loops are inherently slow and nonlinear, an effective input signal (EIS) based on Lyapunov theory is designed and added to the d -axis of the rotor voltage. It is shown that the EIS can compensate the induced voltage in the rotor windings, rotor back electromotive force during the large disturbances, when it is added to the conventional vector controller. The sizing of the converters, considering the active and reactive power priority, are also investigated in order for the EIS to comply to the existing actual limitations. The effectiveness of the proposed rotor side controller is examined in a 381 MVA adjustable speed-pumped storage hydropower, operating in both generating and motor modes. Finally, simulation results performed in Matlab/SimPowerSys is presented in order to validate the proposed control system.

Description: In this study, we address the topic of monitoring the drive speed of synchronous generators by time-frequency analysis of electromagnetic quantities available at the machine's outputs. In this regard, after recalling the commonly used techniques to deal with signals of scalable spectral content, we present and discuss the detection of an abrupt variation of the drive speed by suitable processing of load currents. Afterward, we propose an alternative technique based on the instantaneous frequency estimation of the stray flux. Through experimental trials conducted on a laboratory test-rig, the effectiveness of the suggested approach has been assessed under various load conditions, and its performance has been judged against those stemming from load currents processing. Promising results have been concluded in terms of generator speed monitoring by the use of a low-cost noninvasive sensor.

Description: The accurate determination of stator leakage inductances is presently an open issue in the analysis and testing of multiphase electric machines. Calculation methods are available, which involve complicated and often poorly precise three-dimensional (3-D) analyses. Experimental determination techniques, using measurements on the wound stator with the rotor removed, are also possible, but quite impractical, as they need to be performed during machine manufacturing or require rotor withdrawal. In this paper, a new approach is proposed to determine all the stator self- and mutual leakage inductances of a nine-phase synchronous machine based on a minimal set (a couple) of magnetostatic finite-element (FE) simulations, and on the measurements taken during no-load and short-circuit routine tests. The procedure is applied to a wound-field salient pole nine-phase synchronous generator for validation, showing good accordance with the results obtained from measurements on the machine with the rotor removed. A discussion is also proposed on the possibility to extend the presented procedure to other multiphase topologies.

Description: Backstepping controllers are obtained for distributed hybrid photovoltaic (PV) power supplies of telecommunication equipment. Grid-connected PV-based power supply units may contain dc–dc buck–boost converters linked to single-phase inverters. This distributed energy resource operated within the self-consumption concept can aid in the peak-shaving strategy of ac smart grids. New backstepping control laws are obtained for the single-phase inverter and for the buck–boost converter feeding a telecom equipment/battery while sourcing the PV excess power to the smart grid or to grid supply the telecom system. The backstepping approach is robust and able to cope with the grid nonlinearity and uncertainties providing dc input current and voltage controllers for the buck–boost converter to track the PV panel maximum power point, regulating the PV output dc voltage to extract maximum power; unity power factor sinusoidal ac smart grid inverter currents and constant dc-link voltages suited for telecom equipment; and inverter bidirectional power transfer. Experimental results are obtained from a lab setup controlled by one inexpensive dsPIC running the sampling, the backstepping and modulator algorithms. Results show the controllers guarantee maximum power transfer to the telecom equipment/ac grid, ensuring steady dc-link voltage while absorbing/injecting low harmonic distortion current into the smart grid.

Description: Bearings are divided into two main categories: rolling bearings and sleeve bearings. The sleeve bearings are normally used in electrical machines above 200-hp rating. In this paper, dynamic modeling and simulation of a squirrel cage induction motor with sleeve bearings under oil-whirl fault is performed. The required air gap function under the fault is defined using earlier experimental results. Then, a winding function approach is used for modeling and simulation of the motor with faulty sleeve bearings. Accuracy of the simulation is approved by comparison to the corresponding experimental results. The stator line current harmonics produced by the bearing oil-whirl fault are identified, and the best harmonics as the fault index are chosen considering sensitivity of the harmonics to the fault severity, as well as the load level change and supply voltage unbalance. Selected index is used to determine the severity of oil-whirl fault in sleeve bearing of an induction motor working in a real production line.

Description: The local magnetic saturation in tooth-tips of surface-mounted permanent magnet (SPM) machines generates on-load terminal voltage distortion, especially when small or closed slot openings are adopted. This paper focuses on investigating the influence of slot and pole number ( N s /2 p ) combinations on this phenomenon in both fractional slot and integer slot SPM machines. The mechanism of this phenomenon and how it is influenced by current advance angle and tooth-tip geometric parameters are introduced first. Then, voltage distortion pattern is proposed to analyze the occurring time or rotor positions of voltage ripples and their relative amplitudes according to the winding arrangements of different N s /2 p combinations, with the influence of PM leakage flux considered. By 2-D finite-element analysis, the voltage distortion of various machines is calculated and compared, such as $N_{s} pm 1 = 2p$ , $N_{s} pm 2 = 2p$ , N s /2 p = 3/2 (3/4), and integer slot machines with slot number per pole per phase $q = 1$ or 2. The analysis results reveal that under the same comparison conditions, the integer slot machines have less voltage distortion than the fractional slot machines, especially when $q geq 2$ . Meanwhile, for the same slot number, the fractional slot machines with $N_{s} > 2p$ suffer from on-load voltage distortion less than their counterparts with $N_{s} 〈 2p$ . Finally, three prototype machines with 12/10, 12/14, and 12/8 slot/pole numb- rs are manufactured and tested to validate the analyses.

Description: This paper proposes a new four-phase flux-reversal dc-field (FRDC) machine for the wind power generation applications. The key distinction of the proposed generator is to artfully design its stator pole and winding arrangement in a way imitating the permanent-magnet (PM) configurations, which the profound FRPM machine has. Hence, the proposed FRDC generator can provide the bipolar flux-linkage patterns and achieve performances similar to that of the high-quality FRPM generators. The proposed generator can regulate its controllable dc-field winding to vary its flux density effectively. Thus, it can achieve the constant-output-voltage characteristics at different situations in order to extend the battery life and to protect the power grid system. Without installation of any high-cost PM materials, the proposed magnetless FRDC generator can achieve better cost-effectiveness than its PM counterparts. The key performances of the proposed wind power generator are thoughtfully analyzed by the finite-element method, while the experimental prototype is also setup for verifications.

Description: Lists the Best Papers for this publication as well as the reviewers who contributed to this publication in 2015.

Description: This paper presents an optimized design method for the magnetic circuit of brushless doubly fed machines (BDFMs). The BDFM is an attractive electrical machine, particularly for wind power applications, as a replacement for doubly fed slip-ring generators. This study shows that the conventional design methods for the BDFM stator and rotor back iron can be modified, leading to a lighter and smaller machine. The proposed design concepts are supported by analytical methods, and their practicality is verified using two-dimensional finite-element modeling and analysis. Two BDFMs with frame sizes D180 and D400 are considered in this study.

Description: Presents a discussion on the following paper, ???Electrical machine PWM loss evaluation basics (Ruderman, A. and Welch,R.) in Proc. Int. Conf. Energy Efficiency Motor Driven Syst.,Sep. 2005, vol. 1, pp. 58???68.

Description: Core losses in an electrical machine vary depending on the type of material, frequency of operation, and flux density magnitude and waveform. Loss prediction using pulsating models is insufficient for estimating core losses in a machine, since it does not take into account rotational core losses. Moreover, superposition of pulsating losses in the radial and tangential direction overestimates losses especially at higher flux densities. The objective of this paper is to study rotational flux distribution in the stator of the generator under different operating conditions. Distribution of rotational flux in a large hydrogenerator stator is studied by plotting the aspect ratio. It was found that increasing the yoke length and reducing the air gap increases the area of the stator with rotational flux. Varying the output power showed slight changes in the rotational flux distribution. Different optimized machine designs are investigated for rotational flux distribution; moreover, rotational core losses are measured and used for a comparative study radially across the stator.

Description: In this study, we developed a dynamic equivalent model for large-scale wind power plants based on an aggregation technique. The model is obtained in steps that include wind turbine clustering, development of slow dynamic models for the clusters, and aggregating of the models with the rest of wind power plant network. To confirm the effectiveness of the proposed method, the developed model is tested against the original large-scale wind power plant connected to the power system through computer simulations.

Description: This paper details the analysis and design of an air-core permanent-magnet-based energy-harvest system for use within an in-pipe mobile water-quality sensor. The sensor is a free-moving/free-rotating device of which the energy-harvest system occupies an appreciable volume. Therefore, the electrical and mechanical dynamics of the device are strongly coupled, which poses a modeling challenge. To address this challenge, a rigorous electrical/mechanical model is established to determine expected energy harvest, given the geometric/material parameters and electrical/mechanical inputs. The model was utilized within a single-objective optimization—maximizing energy harvested from impacts—to design a prototype, which was constructed and used for model validation. Subsequently, multiobjective optimizations were performed to establish the tradeoff between energy harvest versus device volume and impact-based versus rolling-based energy-harvest efficacy.

Description: The fully rated converter of type 4 wind turbines is capable of providing dynamic voltage control during grid faults by injecting controlled reactive currents. This paper describes three different dynamic voltage control options during unbalanced grid faults: 1) the positive sequence voltage control with only a positive sequence reactive current injection and suppression of the negative sequence current; 2) the positive sequence voltage control with limitation of the positive sequence reactive current injection and suppression of the negative sequence current; and 3) the positive and negative sequence voltage control with both a positive and a negative sequence reactive current injection. These different control options are compared in simulations of a wind power plant connected to a meshed power system, including synchronous generators. It is shown that both the positive sequence voltage control with limitation and the positive and negative sequence voltage control can overcome the voltage rise and voltage distortion that can occur with pure positive sequence voltage control without limitation. Both of these options have a distinct fault response, where the positive and negative sequence voltage control results in a fault response that resembles the fault response of a synchronous generator with higher fault current contributions in the faulted phases.

Description: This paper develops a magnetic equivalent circuit model suitable to the design and optimization of the synchronous ac homopolar machine. The ac homopolar machine is of particular interest in the application of grid-based flywheel energy storage, where it has the potential to significantly reduce self-discharge associated with magnetic losses. The ac homopolar machine features both axial and radial magnetizing flux paths, which requires finite element analysis to be conducted in 3-D. The computation time associated with 3-D finite element modeling is highly prohibitive in the design process. The magnetic equivalent circuit model developed in this paper is shown to be a viable alternative for calculating several design performance parameters and has a computation time which is orders of magnitude less than that of 3-D finite element analysis. Results obtained from the developed model are shown to be in good agreement with finite element and experimental results for varying levels of saturation.

Description: This paper proposes a novel transient reconfiguration solution and coordinating control strategy for power converters to enhance the fault ride through and transient voltage support capabilities of a doubly-fed induction generator with an energy storage device (DFIG-ESD). During a grid fault, the connection of the grid-side converter is reconfigured such that it is connected to the rotor circuit in parallel with the rotor-side converter to provide an additional route for the rotor current, while the ESD is responsible for dc-link voltage regulation. A coordinated demagnetizing and reactive current control strategy is designed for the reconfigured DFIG during transient conditions. Specifically, the demagnetizing current is used to counteract the dc and negative-sequence stator flux components so that the transient electromotive force will be reduced. Simultaneously, the reactive current is added to meet the reactive power support requirement. The enhanced low-voltage ride through (LVRT) and transient voltage support capabilities obtained from the proposed design are demonstrated on the DFIG-ESD wind conversion system under different severe fault scenarios (asymmetrical and symmetrical fault). Additionally, The enhanced transient voltage support capability of the proposed design is further demonstrated by comparing with different control strategies.

Description: These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal.

Description: A fuzzy-logic sliding-mode control strategy is proposed to capture the maximum wind energy and reduce the generator-side current harmonics for a direct-driven wind power system. The control strategy mainly consists of a fuzzy logic controller for generating the optimum dc-side current and a double integral sliding-mode current controller capable of accurately tracking the optimum dc-side current. A resonant filter is also incorporated into the fuzzy logic controller to eliminate the generator-side current harmonics. Detailed design procedure, existence, and stability conditions of the proposed control strategy have been thoroughly investigated and presented. The capability and effectiveness of the proposed control strategy have been validated by comparative experimental results.

Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.

Description: This paper presents a new transfer function approach for calculating both the average temperature and hot spot temperature of an induction machine with the consideration of temperature-dependent material properties and speed-dependent heat transfer coefficient. Green's functions are introduced and taken as the new transfer functions. Online thermal monitoring models for induction machines are obtained based on Green's function method. Using the presented method, the hot spot temperature and average temperature can be calculated accurately and rapidly. The proposed method is validated via finite-element method and experimental measurement.

Description: In this paper, a model is developed to incorporate the magnetic hysteresis effects into a brushless exciter model. The developed model reconstructs the magnetization flux linkage current loops using the Energetic hysteresis model. The model requires measurements from the armature and field terminals of the brushless exciter at standstill, and the model can be applied for detailed analysis of brushless excited synchronous generators. The developed model is also verified experimentally through measurements on a brushless excited synchronous generator.

Description: Optimization-based design of electric machinery over a large design space requires the use of computationally efficient models to predict machine behavior. In this research, an analytical design model is developed for wound rotor synchronous machines, a key technology for power generation. The model is designed to be used in a rigorous multi-objective optimization algorithm, providing the trade-off between competing mass and loss objectives. A formalized approach is presented to calculate the field distribution, as well as qd -axis model parameters, terminal quantities, loss, and developed torque from design data containing material properties, stator and rotor geometries, and winding layout. The calculated parameters include resistances, inductances, and the back-EMF of the machine. The model is verified using finite element analysis and hardware experiment.

Description: The main objective of this study is to assess the potential for energy savings in the cooling water circuit of a vessel through the use of variable speed drives (VSDs). A small-scale cooling system was set up in the laboratory and relevant tests were carried out by simulating field conditions. Moreover, the payback period from VSDs installation on an existing 8000 TEU container ship based on the operational scenario of a representative journey was calculated. The result of the analysis revealed significant savings with a payback period of only a few months for VSD-controlled sea water pumps of a container vessel.

Description: The complexity and strong nonlinearity of the model of a self-excited induction generator hinder the systematic design of a voltage regulation system. Using a special reference frame aligned with the stator voltage vector, the paper succeeds in developing a control-oriented linearized model that relates small deviations of the capacitance, load admittance, and angular velocity, to corresponding deviations of the voltage amplitude. Transfer functions are also computed based on the linear model. A stability analysis predicts rapidly decaying oscillatory transients combined with a primary component with slower exponential decay. Simulated transient responses of the full and linearized models demonstrate the validity of the approximation and are in good agreement with experiments.

Description: With the increasing capacity of grid connected wind farms, the influence of wind power to stable operation of an electric power system is becoming more and more important. In order to analyze the active power output characteristics of wind farm, a multimachine representation dynamic equivalent method based on the fuzzy clustering algorithm is proposed. First, indicators which can characterize the active power output performance of a doubly fed induction wind generator (DFIG) are researched. Second, a fuzzy C-means (FCM) clustering algorithm is first applied to the modeling of wind farm. DFIGs are divided into groups by analyzing the indicator data with FCM. Finally, DFIGs of the same group are equivalent as one DFIG to realize the dynamic equivalent modeling of wind farm with DFIG. Simulation results demonstrated that the established dynamic equivalent model can reflect the active power dynamic response characteristics of wind farm with DFIG effectively; meanwhile, the model of wind farm is simplified and computation complexity is reduced.

Description: In this paper, a novel induction motor (IM) stator current controller is proposed based on the stationary frame feed forward controlling structure. The proposed regulator represents an improved variant of the existing stationary and rotational frame IM stator current regulators based on the back EMF compensation. The paper novelty consists of the stationary frame controlling structure based on two feed forward actions that enable asymptotic reference tracking. Namely, the novel stationary frame regulator includes a proportional integral (PI) regulation term combined with a stator resistance voltage drop and back EMF feed forward compensations, with the back EMF compensation based on the stator flux value estimated by means of a programmable low-pass filter. The feedback term is based on a PI controller, with the corresponding parameter tuning procedure outlined in the paper. The simulation runs are included in the paper in order to examine the regulator performance in relation to the factors critical to the IM stator current regulation: variable IM model parameter values, transport delay introduced in the control loop, variable stator frequency, and rotor speed values. Also, the experimental tests are presented and carried out on an experimental setup for different operating conditions typical for an IM drive.

Description: A standalone photovoltaic (PV) system with energy storage requires a complex control architecture to take into account the various operating modes. In many cases, a supervisory controller is necessary to manage the change of the control architecture according to the applied mode. This paper presents a flexible architecture of a PV power conditioning system with energy storage. The proposed conditioning unit contains a boost converter (BC), a single-phase inverter, and a bidirectional dc/dc converter connected to the PV side of the BC. The BC regulates the dc-link bus-voltage. The bidirectional dc/dc converter endures battery bank charge/discharge control and PV maximum power point tracking (MPPT). Such architecture guarantees nonchange in controller configuration when the storage disconnects. Therefore, the previously needed supervisory controller is eliminated. A system control strategy based on sliding-mode control (SMC) ensures a reliable output voltage regulation such as fast dynamic response, small steady-state error, and low total harmonic distortion (THD) under step changes and nonlinear loads. The controller structure, the dynamic behavior, and the design procedures are introduced. Finally, the validity of the proposed module with control strategy is verified through hardware experiments on a 500-W prototype test bed with a single TMS320F28335 DSP module.

Description: Multiple-voltage-region control, in which the bus-voltage range is divided into several regions, is usually implemented for dc microgrid operation in distributed manner. Voltage/power droop relationships are imposed for active power sharing among slack terminals. Conventionally, threshold voltages for voltage region partition are determined with fixed percentage of variation around the nominal value, which may result in unevenness of droop coefficients in different regions. If system droop coefficient is too high, significant bus-voltage step change due to load variation will occur. On the other hand, significant power sharing error among slack terminals will be induced if the droop coefficient is too low. In this paper, a compromised solution with power-capacity-based bus-voltage region partition is proposed to equalize the droop coefficients in different regions. However, the droop coefficients are determined based on the rated power capacity of system units. Bus-voltage discontinuity appears when the power capacity reduces in actual implementation. To eliminate the voltage discontinuity, online droop coefficient tuning according to the real-time power capacity is implemented. Algorithms for local power capacity estimation of solar photovoltaic (PV) and battery energy storage have been proposed. A lab-scale dc microgrid has been developed for verification of the proposed methods.

Description: The power generator is typically maintained with a time- or usage-based strategy, which could result in a substantial waste of remaining useful life, high maintenance cost, and low plant availability. Recently, the field of prognostics and health management offers diagnostic and prognostic techniques to precisely assess the health condition and robustly predict the remaining useful life (RUL) of an engineered system, with an aim to address the aforementioned deficiencies. This paper explores a smart health reasoning system to assess the health condition of power generator stator bars against moisture absorption based on the statistical analysis of the capacitance measurements on bar insulators. In particular, a relative health measure, namely the directional Mahalanobis distance, is proposed to quantify the health condition of a stator bar. The smart health reasoning system is validated using five years’ field data from seven generators, each of which contains 42 turns.

Description: This paper presents and compares two permanent magnet vernier (PMV) motors with fractional slot concentrated windings (FSCWs) and integral slot distributed windings (ISDWs). The ISDW PMV motor is newly proposed and optimized for a fair comparison with the existing FSCW one. The equations of back electromotive force of both motors are investigated and derived showing that the ISDW PMV motor has the potential to obtain higher torque capability. Also, their electromagnetic performances, such as torque capability, fault tolerance, loss, and efficiency, are calculated and compared by using the finite-element analysis. Then, the maximum power strategy for PMV motors operating at high speed is presented. The simulated results show that both motors possess excellent flux weakening capability. Finally, the effectiveness of the theoretical analysis is verified by the finite-element analysis results and experiments on a prototype FSCW PMV motor.

Description: This paper proposes a novel neural network (NN)-based vector control method for a three-phase induction motor. The proposed NN vector control utilizes the rotor flux-oriented reference frame, and the role of the NN controller is to substitute the two decoupled current-loop proportional-integral (PI) controllers in conventional vector control techniques. The objective of NN training is to approximate optimal control and the NN controller was trained by Levenberg–Marquardt (LM) algorithm. Forward Accumulation Through Time algorithm for induction motor was developed to calculate Jacobian matrix needed by the LM algorithm. The simulations showed that the NN vector control can provide better current tracking ability than the conventional vector control, such as less oscillations and low harmonics. Especially, the NN vector control can better overcome the problem of detuning effects than the conventional vector control. The hardware experiments further demonstrated the great advantage of the NN vector control. The NN vector control can succeed in driving the induction motor without audible noise using relatively lower switching frequency or lower sampling rate compared with the conventional vector control, and thus has the potential to improve efficiency and reduce size and cost of an induction motor drive system.

Description: This paper presents a dual motor drive system based on a multifunctional energy conversion system with energy storage. The proposed structure and control are directly applicable for a tandem compressor drive in heating, ventilation, and air conditioning (HVAC) systems adding an energy storage functionality. Based on the new structure, a multifunctional control scheme has been introduced to manage the charging/discharging of the energy storage and to regulate two capacitor voltages, which are inverter input voltages, simultaneously. Two independent sensorless adjustable speed motor drives, which are connected to the two capacitors, are controlled in real time for HVAC applications. Simulation and experimental results verify that the proposed structure and multifunctional control scheme are able to control both the two inverter input voltages and the charging/discharging current of energy storage for a dual motor drive system.

Description: Presents a closure to the discussion from the following paper, ???Electrical machine PWM loss evaluation basics (Ruderman, A. and Welch,R.) in Proc. Int. Conf. Energy Efficiency Motor Driven Syst.,Sep. 2005, vol. 1, pp. 58???68.

Description: This page or pages intentionally left blank.

Description: The multilevel method has been presented for design optimization of electrical machines and drive systems for optimal system performances and efficiency in our previous work. For framework design of the multilevel optimization method, four techniques are presented in this paper, including the sizing equation, local sensitivity analysis, global sensitivity analysis, and design of experiments techniques. For each technique, a general and theoretical analysis procedure is presented before the application study. To demonstrate the effectiveness, a permanent magnet claw-pole motor with soft magnetic composite core and 3-D finite-element analysis model is investigated to minimize the material cost and maximize the output power while keeping the volume constant. The calculated motor performance based on this 3-D finite-element model has been verified by the experimental results. As shown, these techniques are simple to implement, and the resultant multilevel optimization framework can significantly improve the motor performance and reduce the required sample number of finite-element analysis.

Description: In this paper, design and optimization of a ladder-type single-sided linear induction motor (Ladder SLIM) for machine tool applications is investigated. High-speed linear induction machines suffer from the end-effect phenomenon, which can reduce the thrust and result in declined output characteristics. Although it is common to consider this phenomenon in high-speed applications, it is essential to take it into account in the design and analysis of low-speed low-air-gap linear machines. In addition, Ladder SLIMs have significant flux density ripples, and using skewed bars for secondary of the machine is a common solution for it. Therefore, providing required equations, an algorithm for designing a Ladder SLIM considering the end-effect phenomenon based on Duncan model is proposed, and effect of several design parameters on the output characteristics are analyzed. In order to find the optimum design parameters, a multiobjective optimization problem considering efficiency, power factor, and braking force due to the end effect is defined. This problem is optimized with two algorithms, interior point and genetic algorithms, and results are compared. Finally, the validity of the obtained solution is verified using a 2-D and 3-D time-stepping finite-element method.

Description: The brushless doubly fed machine (BDFM) is an alternative to the doubly fed induction generator, widely used in wind turbines without use of brush gear and slip ring. Rotor design is important for achieving an optimal multi-MW BDFM. To date, nested-loop rotors have been exclusively used in various BDFMs, although they may not be ideal for larger machines. This paper studies, both analytically and experimentally, different rotors for the D160 and D400 frame size BDFMs. An optimization on the rotor equivalent circuit parameters is carried out and verified with different parameter extraction methods. A comparison of the performance of the suggested rotors is also presented.

Description: Hydropower has long been recognized as a renewable power source. Due to economic reasons, high and medium head potentials have been primarily developed. Later, low-head potentials became a feasible solution with the application of modern Bulb generators. Although Bulb generators have been developed and applied since the 1930s, new techniques and materials have been used to overcome technical and design challenges, which are described herein.

Description: The main objective of this special issue is to collect and disseminate publications that highlight recent advances and breakthroughs in the area of renewable energy resources. The use of these resources for production of electricity is increasing rapidly worldwide. As of 2015, a majority of countries have set renewable electricity targets in the 10%???40% range to be achieved by 2020???2030, with a few notable exceptions aiming for 100% generation by renewables. We are experiencing a truly unprecedented transition away from fossil fuels, driven by environmental, energy security, and socio-economic factors.Electric machines can be found in a wide range of renewable energy applications, such as wind turbines, hydropower and hydrokinetic systems, flywheel energy storage devices, and low-power energy harvesting systems. Hence, the design of reliable, efficient, cost-effective, and controllable electric machines is crucial in enabling even higher penetrations of renewable energy systems in the smart grid of the future. In addition, power electronic converter design and control is critical, as they provide essential controllability, flexibility, grid interface, and integration functions.

Description: This paper is to investigate the inertial dynamics of virtual-synchronous-controlled (VSynC) doubly fed induction generator (DFIG)-based wind turbines (WTs). VSynC, different from the conventional synchronization method based on phase-locked-loop (PLL) synchronizing technique, makes DFIG-based WT synchronize with power grid via the active power control (APC), and thus provide the desired inertial support to power grid. Further, an effective approach for describing the inertial dynamics of DFIG-based WT with VSynC is proposed by establishing the WT's electromechanical motion equation. The approach synthetically considers the impacts of the WT's different controller parameters, operating points, and, in particular, the variations of mechanical power caused by the rotational speed or pitch angle changes during the inertial response period. It also makes the essential of DFIG-based WT's inertia clearer, which, as a matter of fact, is controllable and manifests frequency-dependent characteristics, and noticeably differs from the fixed inertia time constant featured in synchronous generator (SG). The impacts of different controller parameters and operating points on single WT's frequency response characteristics are studied. Simulated results also validate the superiority of VSynC on inertial support capability and operation stability to the typical PLL-based vector control (VC), especially for weak grid conditions. Finally, the frequency response on wind power plant (WPP) level is initially explored and further research to improve VSynC is discussed.

Description: Advertisement, IEEE.

Description: This paper proposes and implements a new single-phase magnetless flux switching machine (FSM) for rooftop wind power generation. The key is to integrate an outer-rotor FSM and an inner-rotor FSM with shared stator yoke and stator drum windings. In such a way, this proposed machine can not only realize flux switching function to regulate magnetic flux effectively, but also incorporate the field and armature windings within one stator to reduce the copper losses and improve the overall machine efficiency. Meanwhile, the structure is compact and rotors can be directly driven by blades to capture the wind power. The machine design guidelines from both magnetic and electric aspects are illustrated, the machine characteristics are analyzed by using time-stepping finite-element method, and the system performances are evaluated based on mathematical modeling. Both simulation and prototyping test are conducted to verify the validity of the proposed machine and system.

Description: Presents the 2015 author/subject index for this publication.

Description: Most advanced wireless communication systems use spectrally efficient complex modulation to pack more users into the crowded frequency spectrum. Complex modulation simultaneous modulates a signal's amplitude and phase (polar coordinates) or, equivalently, the I and Q components (rectangular coordinates).