Considering the low power allocation accuracy of paralleled inverters system using traditional double-loop control and the voltage and frequency deviations caused by droop control in micro-grid
the power allocation mechanism and output voltage characteristics of a parallel system are discussed
and a balanced control strategy of power and voltage for inverters parallel operation is proposed based on virtual impedance and instantaneous output voltage/frequency regulation. Virtual impedance is added to existing control loops to improve the characteristics of output impedance
and the power allocation accuracy is enhanced with P-ω
Q-V droop control. A scheme for regulating output voltage magnitude and frequency also participates in the loops to exert secondary regulation on the voltage and frequency deviations from droop control
and the higher output voltage quality remains. The simulation and experiment demonstrate that the proposed balanced control strategy for power and voltage makes the paralleled inverters share the load power better and preserves the rated output voltage and frequency in islanded micro-grid.
CHEN Hongzhi, WANG Xu, LIU Jianchang. Current sharing method for parallel inverters based impedance matching mode[J]. Proceedings of the CSEE, 2012, 32(6): 24-32.
SHI Hongtao, ZHUO Fang, HOU Lixiang, et al. Small-signal stability analysis of a microgrid operating in droop control mode[C]∥2013 IEEE Energy Conversion Congress and Exposition Asia. Piscataway, NJ, USA: IEEE, 2013: 882-887.
GUERRERO J M, VICUNA L G, MATAS J, et al. Output impedance design of parallel-connected UPS inverters with wireless load-sharing control[J]. IEEE Transactions on Industrial Electronics, 2005, 52(4): 1126-1135.
SHI Hongtao, YANG Zhen, YUE Xiaolong, et al. Calculation and measurement of harmonic impedance for a microgrid operating in islanding mode[C]∥2012 7th International Power Electronics and Motion Control Conference. Piscataway, NJ, USA: IEEE, 2012: 356-361.
MOHAMED Y A R I, EL-SAADANY E F. Adaptive decentralized droop controller to preserve power sharing stability of paralleled inverters in distributed generation microgrids[J]. IEEE Transactions on Power Electronics, 2008, 23(6): 2806-2816.
YAO Wei, CHEN Min, MATAS J, et al. Design and analysis of the droop control method for parallel inverters considering the impact of the complex impedance on the power sharing[J]. IEEE Transactions on Industrial Electronics, 2011, 58(2): 576-587.
YAO Wei, CHEN Min, CHEN Jingjing, et al. An improved wireless control strategy for parallel operation of distributed generation inverters[J]. Transactions of China Electrotechnical Society, 2008, 23(1): 84-89.
HE Jinwei, LI Yunwei. Analysis, design, and implementation of virtual impedance for power electronics interfaced distributed generation[J]. IEEE Transactions on Industrial Applications, 2011, 47(6): 2525-2538.
GUERRERO J M, DE VICUNA L G, MATAS J, et al. A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems[J]. IEEE Trans on Power Electronics, 2004, 19(5): 1205-1213.
YAO Wei, CHEN Min, MOU Shanke, et al. Paralleling control technique of microgrid inverters based on improved droop method[J]. Automation of Electric Power Systems, 2009, 33(6): 77-80.
ZHANG Qinghai, PENG Chuwu, CHEN Yandong, et al. A control strategy for parallel operation of multi-inverters in microgrid[J]. Proceedings of the CSEE, 2012, 32(25): 126-132.
WANG Chengshan, XIAO Zhaoxia, WANG Shouxiang. Synthetical control and analysis of microgrid[J]. Automation of Electric Power Systems, 2008, 32(7): 98-103.
ZHOU Niancheng, JIN Ming, WANG Qianggang, et al. Hierarchical coordination control strategy for multi-microgrid system with series and parallel structure[J]. Automation of Electric Power Systems, 2013, 37(12): 13-18.
ZANG Dong, ZHUO Fang, SHI Hongtao, et al. Design of the software phase locked loop for the three phase converter in distributed power generation system[J]. Power Electronics, 2013, 47(10): 43-45.