Abstract
Using virtual impedance technology to optimize the double closed-loop control structure can improve the equivalent output impedance of the inverter to be inductive, improve the power distribution accuracy of traditional sensibility droop control strategy in low-voltage microgrid, and effectively restrain the circulation. But rarely consider the impact of virtual impedance on system stability. Therefore, Derive the transfer function of the three loop control structure including virtual impedance, line impedance and common point voltage, establish a parallel models of inverters with different voltage levels considering virtual complex impedance and simplify the model using Thevenin's equivalent. According to the Nyquist stability criterion Analyze the effect of virtual impedance on system stability under various operating conditions. The analysis results show that the multi-inverter parallel system can maintain stable operation after adding the virtual impedance.
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