Unbalanced Loads Control Strategy for Virtual Synchronous Generator in Passive Network

Abstract

The virtual synchronous generator (VSG) control is introduced into voltage source converter based HVDC(VSC- HVDC) which can effectively provide voltage and frequency support for the power grid. And an external control loop that can run in both the networked and passive networks is designed. Considering the unbalanced voltage problem caused by unbalanced loads under passive network, an improved VSG control strategy applied to the receiving converter of VSC-HVDC system is proposed. After the positive and negative sequence separation of the voltage, the VSG positive sequence current loop and the negative sequence voltage loop are respectively established, and the internal voltage-current cascade control is not cancelled. The strategy can effectively suppress the negative sequence voltage and improve the unbalanced carrying capacity of the system under the condition of passive island network. Finally, a simulation model is built in PSCAD/EMTDC. The simulation results verify the correctness and effectiveness of the proposed control strategy.