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Wu X.,North China Electrical Power University | Liu Z.,North China Electrical Power University | Tian L.,China Electric Power Research Institute | Ding D.,North China Electrical Power University | Chen Z.,Hefei Sungrow Power Supply
Dianwang Jishu/Power System Technology

To enhance power supply reliability of stand-alone photovoltaic (PV) generation system and improve PV utilization, it is necessary to configure the capacity of PV modules and energy storage devices reasonably. Based on the feature of joint-operation of PV generation system with energy storage device and considering dynamic variation of stored energy during the joint operation, taking technical characteristics of energy storage unit as the constraint a joint configuration method of PV capacity and energy storage capacity, in which the loss of power supply probability (LPSP) and energy excess percentage (EXC) are taken as assessment indices, is proposed. Under the conditions of a given case, taking three kinds of batteries, namely the valve regulated lead acid battery (VRLAB), the lithium-ion battery and all-vanadium redox flow battery, into account, the capacity of the three kinds of batteries are respectively configured and taking the minimized initial investment as the objective, the optimized capacity configuration of PV modules and energy storage units is computed. Computation results show that under the same configuration a higher power supply reliability can be achieved by use of all-vanadium redox flow battery, however under the condition of satisfying the requirement of indices, the initial investment can be the minimum while the VRLAB is adopted. Source

Zhang X.,Hefei University of Technology | Yu C.,Hefei University of Technology | Liu F.,Hefei University of Technology | Li F.,Hefei University of Technology | And 3 more authors.
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering

For the resonance problem of multi-paralleled grid-tired inverters in PV systems, Firstly, a small-signal circuit model of single inverter including current control, voltage feed-forward and PWM harmonic characteristics is established, and is expanded into a small-signal model for multi-paralleled inverters. An equivalent method of two inverters and a simplified method of a similar excitation source are proposed. And then, on this basis, the basic resonance characteristics of multi-paralleled inverters are analyzed, and the conclusion of that resonance of multi-paralleled inverters is related to the synchronism of control and carrier wave. Finally, the proposed equivalent model and analysis of resonance characteristics are verified by experiments. © 2014 Chin. Soc. for Elec. Eng. Source

Xie Z.,Hefei University of Technology | Zhang X.,Hefei University of Technology | Song H.,Hefei University of Technology | Yang S.,Hefei University of Technology | Cao R.,Hefei Sungrow Power Supply
Dianli Xitong Zidonghua/Automation of Electric Power Systems

The control strategy of doubly fed induction generator (DFIG) under grid voltage dips has long been a focus of research and development, grid voltage swells will also cause a lot of problems to DFIG based wind turbines. In order to study the characteristic and control strategy of high voltage ride through (HVRT) of DFIG, this paper analyzes the dynamic behavior of DFIG during grid voltage swells. Based on the above analysis, it is found that the active resistance can effectively suppress the rotor current and torque oscillation, avoiding the operation of Crowbar circuit. As to the different speed and grid voltage swell ratios, this paper proposes variable damping based control strategy, enhancing DFIG's HVRT capability compared with grid voltage dips. Simulation and experimental results verify the effectiveness of the variable damping based control strategy. © 2012 State Grid Electric Power Research Institute Press. Source

Zhang X.,Hefei University of Technology | Qu T.,Hefei University of Technology | Xie Z.,Hefei University of Technology | Cao R.,Hefei Sungrow Power Supply
2011 2nd International Conference on Mechanic Automation and Control Engineering, MACE 2011 - Proceedings

With the rapid increase of wind farms especially large offshore wind farms, a new problem associated with the response of doubly fed induction generator to temporary overvoltage has arisen. This paper develops a theoretical analysis of the dynamic behavior during symmetrical three phase voltage swell. Overvoltage may lead to reversal of power in the line side converter. Simulation results are in good agreement with those obtained theoretically. © 2011 IEEE. Source

Xie Z.,Hefei University of Technology | Zhang X.,Hefei University of Technology | Yang S.,Hefei University of Technology | Wang L.,Hefei Sungrow Power Supply
IEEE Transactions on Industrial Electronics

Grid voltage swell causes a transient dc flux component on doubly fed induction generator (DFIG) stator winding even stronger than grid voltage dip, resulting in a much more serious stator, rotor current, and torque oscillation. This paper analyzes the dynamic behavior of DFIG during grid voltage swell. Based on the analysis results, the virtual resistance control strategy manages best to suppress the rotor current and torque oscillation but prolongs the transient duration, resulting in a higher rotor voltage. Thus, this paper proposed a virtual impedance control strategy to enhance the high-voltage ride-through capability of DFIG. In order to improve the dynamic performance, the optimization algorithm of virtual impedance is proposed in the paper. The effectiveness of the proposed control strategy was verified by simulation and experimental results. © 2014 IEEE. Source

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