Reactive Power Matching Through Virtual Variable Impedance for Parallel Virtual Synchronous Generator Control Scheme

Virtual synchronous generator (VSG) control has received much attention for interfacing renewable energy sources, thus creating a low-inertia microgrid. However, proportional reactive power-sharing and voltage accuracy is still a serious concern due to unequal feeder impedances between VSG controlled DGs and the point of power coupling. This article proposes a virtual variable impedance (VVI) based VSG control technique to mitigate the reactive power sharing error by improving the line-impedance ratio among multiple DGs. The proposed VVI control is designed to estimate the value of variable virtual impedance by establishing an exponential relationship with the inverter's output reactive power. The reactive power communication method is also introduced to identify the proportion of reactive power share being injected by the DG. The effectiveness of the proposed VVI control is further analyzed through the small-signal stability analysis and Lyapunov stability analysis of a multi-VSG system. Finally, the proposed controller is tested in MATLAB/Simulink software and on an experimental setup that includes inverter hardware and dSPACE simulator. Results have shown that the proposed method allow only 0.026% of reactive power sharing error as compared to the conventional droop control and state-of-the-art virtual capacitor-based droop control that experiences 2.86% and 2.8% error, respectively.