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  • Institute of Electrical and Electronics Engineers (IEEE)  (13,913)
  • 2015-2019  (13,913)
  • 2017  (13,913)
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  • 2015-2019  (13,913)
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  • 1
    Publication Date: 2017-03-21
    Description: This paper presents an adaptive droop-based power-sharing control strategy. The primary objective is to control the sharing of the active power transmitted by a multiterminal voltage-source converter based high voltage direct current network among a number of onshore ac grids or offshore loads based on the desired percentage shares. The shared power is generated by remote generation plants (e.g., offshore wind farms) or is provided as surplus from ac grids. The desired percentage shares of active power are optimized by the system operator in order to fulfil the active power requirements of the connected grids with respect to meeting goals such as supporting energy adequacy, increasing renewable energy penetration, and minimizing losses. The control strategy is based on two hierarchal levels: voltage-droop control as the primary controller and an optimal-power flow based secondary (supervisory) controller for selecting the optimal droop reference voltages. Based on the dc voltage transient and steady-state dynamics, a methodology for choosing the droop gains for droop controlled converters has been developed. The proposed control strategy has been validated through simulation on the CIGRE B4 dc grid test system. The results confirmed the flexibility and effectiveness of the power-sharing control provided by the new control strategy.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 2
    Publication Date: 2017-03-21
    Description: This paper presents a new nonlinear current control strategy based on backstepping control and high-order sliding mode differentiator in order to employ distributed generation (DG) unit interfacing converters to actively compensate harmonics/interharmonics of local loads. The converter-based DG unit is connected to a weak grid (with uncertain impedance) and local load (that can be parametrically uncertain and topologically unknown) through an LCL filter. The proposed strategy robustly regulates the inverter output currents and delivers pure sinusoidal, three-phase balanced currents to the grid. The new controller demonstrates the robust performance and robust stability of the DG unit system with respect to the filter parameters uncertainties, grid impedance, grid frequency, and grid voltage as well as the unknown load dynamics that include unbalanced loads and nonlinear loads with harmonic and interharmonic currents. We should remark that the local compensation of the loads with interharmonic current using a DG unit system is first proposed in this paper. When compared with the popular parallel proportional resonant control technique, the proposed controller offers smoother transient responses and a lower level of current distortion. The performance of the proposed control strategy is verified in MATLAB/SimPowerSystems toolbox.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 3
    Publication Date: 2017-03-21
    Description: Optimally dispatching photovoltaic (PV) inverters is an efficient way to avoid overvoltage in active distribution networks, which may occur in the case of the PV generation surplus load demand. Typically, the dispatching optimization objective is to identify critical PV inverters that have the most significant impact on the network voltage level. Following, it ensures the optimal set-points of both active power and reactive power for the selected inverters, guaranteeing the entire system operating constraints (e.g., the network voltage magnitude) within reasonable ranges. However, the intermittent nature of solar PV energy may affect the selection of the critical PV inverters and also the final optimal objective value. In order to address this issue, a two-stage robust centralized-optimal dispatch model is proposed in this paper to achieve a robust PV inverter dispatch solution considering the PV output uncertainties. In addition, the conic relaxation-based branch flow formulation and the column-and-constraint generation algorithm are employed to deal with the proposed robust optimization model. Case studies on a 33-bus distribution network and comparisons with the deterministic optimization approach have demonstrated the effectiveness of the proposed method.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 4
    Publication Date: 2017-03-21
    Description: The dynamic economic dispatching of power system connected with multiple wind farms is a typical stochastic programming problem. How to model the randomness of wind power and how to solve this complex stochastic optimization problem are the key points. In this paper, copula theory is used to formulate the correlation of multiwind farms generation. Then, the dynamic economic dispatching model is founded with the fuel consumption, gas pollution emission fees, and electricity purchase costs as the optimized objective. The two-stage compensation algorithm is then introduced to solve the dispatching problem. In this algorithm, the conventional (nonstochastic) decision variables and stochastic variables are decoupled, which separate the dynamic dispatching model into two stage modes. The optimal dispatching result is worked out by iteration between the two stage models. Case studies on IEEE118-bus system and an actual provincial power grid show that the proposed algorithm can drastically reduce computational burden, and satisfy the actual requirements of engineering practice.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 5
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-03-21
    Description: A single-stage flyback PV inverter with maximum power point tracking (MPPT) high-speed capability is presented in this paper. The proposed stand-alone photovoltaic energy system (SAPES) incorporates the use of hybrid MPPT to ensure peak energy harvesting under all weather conditions. The proposed hybrid MPPT method combines the conventional short current pulse (SCP) MPPT method and the perturb and observe (P&O) methods. Measurement of the offline parameter [short-circuit current of PV module ( ${I}_{rm sc}$ )] for SCP is made on the basis of the difference between the offline parameter and the instantaneous current of PV module ( ${I}_{rm pv}$ ). Use of a single power conversion stage is achieved by employing a modified flyback inverter operating in a discontinuous-conduction mode. The control structure of the conventional flyback inverter is also modified to incorporate the hybrid MPPT algorithm. The proposed SAPES method is tested using computer-aided simulations and real-time hardware in the loop experimentation using the dSPACE DS1104 board. The results obtained using the proposed systems are better than those for the conventional algorithms under the environmental conditions tested.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 6
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-03-21
    Description: The large-scale integration of a grid-scale energy storage and the increasing penetration of renewable resources motivate the development of techniques for determining the optimal ratings and locations of storage devices. This paper proposes a method for identifying the sites where energy storage systems should be located to perform spatio-temporal energy arbitrage most effectively and the optimal size of these systems. This method takes a centralized perspective where the objective is to minimize the sum of the expected operating cost and the investment cost of energy storage. It has been tested on a realistic 240-bus 448-line model of the Western Electricity Coordinating Council (WECC) interconnection. The influence on the results of the following parameters is analyzed: Maximum number of storage locations, maximum size of storage systems, capital cost of deploying storage, value assigned to spillage of renewable energy, marginal cost of conventional generation, and renewable generation capacity. These numerical results are used to characterize the benefits that energy storage can provide in prospective large-scale power systems with renewable generation.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 7
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-03-21
    Description: In this study, we propose a novel distributed secondary control scheme for both voltage and frequency in autonomous microgrids. By incorporating predictive mechanisms into distributed generations, the secondary voltage control is converted to a tracker consensus problem of distributed model predictive control, with the synchronous convergence procedure for voltage magnitudes to the reference value drastically accelerated at a low communication cost. A sufficient local stability condition with the parameter analysis is established. Thus, a distributed proportional integral method combined with a finite-time observer to estimate the global reference information is presented in the frequency restoration while maintaining accurate active power sharing. Our approach accommodates model uncertainty, plug-and-play capability, and especially robustness against information update intervals, which is essential when the conventional method probably yields toward a poor performance. Meanwhile, the distributed architecture implemented on the local and neighboring information allows for a sparse communication network and eliminates the requirement for a centralized controller. Simulation results are provided to verify the effectiveness of the proposed control methodology.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 8
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-03-21
    Description: This paper proposes an $mathrm{H}_{infty}$ robust current controller for doubly-fed induction-generator (DFIG)-based wind turbines subject to grid voltage distortions. The controller is to mitigate the impact of the grid voltage distortions on rotor currents with DFIG parameter perturbation. The grid voltage distortions considered include asymmetric voltage dips and grid background harmonics. An uncertain DFIG model is developed with uncertain factors originating from distorted stator voltage, and changed generator parameters due to the flux saturation effect, the skin effect, etc. Weighting functions are designed to efficiently track the unbalanced current components and the fifth and seventh background harmonics. The robust stability and robust performance of the proposed controller are verified by the structured singular value μ. The performance of the $mathrm{H}_{infty}$ robust current controller was demonstrated with a 1.5-MW DFIG model, showing its harmonics suppression ability with DFIG parameter perturbation and improved robustness.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 9
    Publication Date: 2017-03-21
    Description: This paper presents a comprehensive sensitivity analysis to identify the uncertain parameters which significantly influence the decision-making process in distributed generation (DG) investments and quantify their degree of influence. To perform the analysis, a DG investment planning model is formulated as a novel multistage and multiscenario optimization problem. Moreover, to ensure tractability and make use of exact solution methods, the entire problem is kept as a mixed-integer linear programming optimization. A real-world distribution network system is used to carry out the analysis. The results of the analysis generally show that uncertainty as well as operational variability of the considered parameters have meaningful impacts on investment decisions of DG. The degree of influence varies from one parameter to another. But, in general, ignoring or inadequately considering uncertainty and variability in model parameters has a quantifiable cost. Hence, the analysis made in this paper can be very useful to identify the most relevant model parameters that need special attention in planning practices.
    Print ISSN: 1949-3029
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 10
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2017-03-21
    Print ISSN: 2168-6831
    Topics: Architecture, Civil Engineering, Surveying , Electrical Engineering, Measurement and Control Technology , Geosciences , Computer Science
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