Research on Control Strategy of Improved Virtual Synchronous Generator for Improving the Operating Capability of Passive Isolated Islands

In the case of flexible HVDC transmission system supplying power to passive island power grid, the inertia of receiving end system is small, and it is difficult for inverters to provide frequency support for it. Therefore, it is necessary to study and improve its control mode. According to the concept of virtual synchronous generator, a control method which can simulate the operation characteristics of synchronous generator is proposed. It can provide virtual moment of inertia for the system. In this paper, an improved virtual synchronous machine controller is designed by simulating the inverting side of flexible HVDC system as synchronous generator operation and traditional virtual synchronous machine control. A detailed model of flexible HVDC transmission system is built in PSCAD/EMTDC, and digital simulation is carried out for normal working condition and abrupt change of load power. Under different operating conditions, the system is simulated with inner and outer loop control, VSG and improved virtual synchronous machine control. The simulation results show that the control strategy of virtual synchronous machine can provide strong frequency support for the system.