Virtual Synchronous Generators (VSGs) can reduce the frequency and power oscillation in the grid. For parallel multi-VSGs in island microgrid, the differences of equivalent output impedance and line impedance affect the orderly sharing of reactive power and restraining of circulating current greatly. The power sharing and circulating current characteristics of VSGs are analyzed in this paper. To solve this problem, an optimization control method for parallel VSGs is proposed, which included the inner voltage and current loop and the outer reactive power loop. In the inner voltage and current loop, a virtual complex impedance including a resistive component and an inductive component is introduced. It reduces the coupling between active power and reactive power, and it reduces the disorderly distribution of power due to impedance differences. In the reactive power loop, the output voltage feedback and integrator links are adopted, which reduce the deviation of output voltage and restrain circulating current. The effects on the equivalent output impedance in the different control parameters and virtual complex impedance are analyzed, the effects on system stability in the different resistive components of virtual complex impedance are analyzed, and the proper parameters are selected. Simulation and experimental results show the correctness and validity of the proposed control method.

中文翻译：

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孤岛并联虚拟同步发电机的优化控制策略

虚拟同步发电机（VSG）可以减少电网中的频率和功率振荡。对于岛型微电网中的并联多VSG，等效输出阻抗和线路阻抗的差异会极大地影响无功功率的有序分配和循环电流的抑制。本文分析了VSG的功率共享和循环电流特性。为了解决这个问题，提出了一种并联VSG的优化控制方法，包括内部电压电流回路和外部无功功率回路。在内部电压和电流环路中，引入了包括电阻分量和电感分量的虚拟复阻抗。它减少了有功功率和无功功率之间的耦合，并且减少了由于阻抗差异而导致的无序功率分布。在无功功率回路中，采用了输出电压反馈和积分器环节，减少了输出电压的偏差并限制了循环电流。分析了不同控制参数和虚拟复阻抗对等效输出阻抗的影响，分析了虚拟复阻抗的不同电阻分量对系统稳定性的影响，并选择了适当的参数。仿真和实验结果表明了该控制方法的正确性和有效性。分析了虚拟复阻抗的不同电阻分量对系统稳定性的影响，并选择了适当的参数。仿真和实验结果表明了该控制方法的正确性和有效性。分析了虚拟复阻抗的不同电阻分量对系统稳定性的影响，并选择了适当的参数。仿真和实验结果表明了该控制方法的正确性和有效性。