Unbalanced Control Strategy of Improved Virtual Synchronous Generator in Power Grid

Virtual synchronous generator (VSG) can provide the power grid with frequency and voltage support. However, under the unbalanced grid voltage, the traditional VSG control can not suppress the unbalanced output of the inverter and reduce the fluctuation components of the active and reactive power of the output. Therefore, an improved virtual synchronizer control strategy is proposed in the case of unbalanced grid voltage. Using the stator electrical equation of the synchronous generator, the current command value at dq coordinates under voltage unbalance is obtained and used as a reference command value. The constraint relationship between the amplitude and phase of positive and negative sequence voltage and current are analyzed to satisfy the balance of active power. The compensation current instruction value is obtained by the positive sequence voltage and the angle relation between the voltage and current on the basis of the reference instruction in the dq coordinate system. The quasi-PR controller is adopted to realize the current tracking control without any difference, and the fluctuation of the active power is significantly suppressed. The results of MATLAB simulation verify the validity and effectiveness of the proposed control strategy.