The balanced, unbalanced and harmonic current sharing inaccuracy caused by the mismatched wire impedances of distributed generation (DG) units influences the normal operation of islanded microgrids. To deal with this issue, an iterative virtual impedance regulation (IVIR) strategy is proposed in this paper, both the resistive and reactive parts in the output impedances of DG units are regulated. The whole process is decomposed into several successive iterations. In each iteration, the fixed virtual impedance and adaptive virtual impedance regulation are combined to generate a virtual resistance increment and uniform virtual reactance increment according to the uniform output current magnitude and phase angle respectively. Based on these increments, the virtual impedance at fundamental-negative and harmonic frequencies also are modified. With the proposed strategy, all the balanced, unbalanced and harmonic current sharing is accurate with a relatively small virtual impedance. Only the local current information is required for the IVIR process, and the communication is merely used to exchange the VIR mode status flags at the beginning and the end of the IVIR process, the dependency on communication is minimized. The feasibility of the proposed strategy is verified with the simulation and experimental results.

中文翻译：

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孤岛微电网中增强平衡、不平衡和谐波均流的迭代虚拟阻抗调节策略


分布式发电（DG）机组导线阻抗不匹配导致的平衡、不平衡和谐波均流不准确，影响孤岛微电网的正常运行。针对这一问题，本文提出了一种迭代虚拟阻抗调节（IVIR）策略，对DG单元输出阻抗中的阻性和电抗部分进行调节。整个过程被分解为几个连续的迭代。在每次迭代中，固定虚拟阻抗和自适应虚拟阻抗调节相结合，分别根据均匀的输出电流幅度和相位角生成虚拟电阻增量和均匀虚拟电抗增量。基于这些增量，基波负频率和谐波频率处的虚拟阻抗也被修改。采用所提出的策略，所有平衡、不平衡和谐波均流都是准确的，且虚拟阻抗相对较小。 IVIR过程只需要本地电流信息，并且通信仅用于在IVIR过程的开始和结束时交换VIR模式状态标志，对通信的依赖性被最小化。仿真和实验结果验证了所提策略的可行性。