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 <i>dq</i> 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.