An Improved Control Strategy of Virtual Synchronous Generator under Unbalanced Conditions

Virtual synchronous generators (VSG) have the potential to solve the stability problems caused by large-scale grid-connected of distributed generation (DG). However, traditional VSG control will lead to current unbalance and power oscillations under unbalanced conditions. Aiming at these problems, an improved comprehensive control strategy of VSG is proposed based on the traditional VSG control method with voltage and current inner loops. By analyzing the relationship among unbalanced current, power oscillation and negative sequence current, the reference currents under different control targets are obtained. On this basis, the comprehensive control of power fluctuation and current quality is realized by the idea of weighted control. Moreover, the proposed control strategy does not change the voltage source properties of VSG, providing voltage and frequency support for the system, and improving the ability of VSG with unbalanced load under islanded conditions. Simulation results verify the effectiveness of the proposed control strategy.