Power Coupling Mechanism Analysis and Improved Decoupling Control for Virtual Synchronous Generator

A virtual synchronous generator (VSG) control-based grid-connected converter (GCC) is an attractive solution to improve the stability of a more renewable-energy-integrated power system. Unfortunately, the inherent power coupling (i.e., the interaction between the active power loop and the reactive power loop) defect of VSG control severely restricts the power delivery capacity and the grid support capability of the GCC. The virtual inductor is commonly used to reduce coupling, but its decoupling capability is very limited. In addition, the power coupling mechanism and its limiting factors are not clear. For this issue, the nature of power coupling in the VSG system is investigated first. The decoupling capability of the virtual inductor is studied, and the reason for decoupling effectiveness is revealed. It indicates that the effectiveness of decoupling results from the proper voltage compensation, but this kind of positive effect is limited by the d-axis voltage drop across the virtual inductor. Then, a q-axis voltage-drop-based power decoupling control (QVPDC) is proposed to further reduce the power coupling, which does not consider the d-axis voltage drop when applying the virtual inductor. Compared with the virtual-inductor-based decoupling method, the decoupling performance of QVPDC is better, and the computation burden is reduced by half. Finally, the analysis and the proposed method are validated by simulation and experiment.