Control strategy of virtual synchronous generator under three-phase grid unbalance

The utilization of Virtual Synchronous Generator (VSG) control in grid-connected inverters has the potential to enhance grid inertia and damping. However, when the grid voltage is unbalanced, the grid-connected current of the inverter is unbalanced and the output power experiences double-frequency fluctuations, which leads to the decline of the output power quality. In response to the above issues, this paper proposes a VSG strategy based on coordinated control of unbalanced current and power, enhancing positive and negative sequence separation using the Second Order Generalized Integrator (SOGI). Introducing mode selection parameter λ for different control requirements (grid-connected current balance, constant active power, and constant reactive power) in the rotating coordinate system of dq enables obtaining unified negative sequence current reference value under all three operating conditions. Coordinated current-power control is implemented through negative sequence current loop control, allowing for separate achievement of grid-connected current balance and constant output of grid-connected power. Finally, this strategy is verified. on experimental platform; results from experiments demonstrate feasibility and effectiveness of the improved control.