The characteristics of synchronous generator can be emulated by power electronic devices to provide moment of inertia and damping for the power grid. It is considered an effective way to connect sustainable energy generation to the power grid. If the voltage of grid-connection point drops because of power grid failure, it may lead to overcurrent, unbalance and instability for virtual synchronous generator (VSG). Therefore, a low-voltage ride-through (LVRT) control strategy for VSG is proposed in the paper. The power loop of VSG is analyzed based on the small-signal model. When an asymmetric fault occurs in the power grid, the positive and negative sequence current control is performed to achieve output current balance. The transient and steady current can be restrained by extra virtual reactance. At the same time, the reactive power is increased to support power grid voltage and the active power is decreased to restrain the steady current and improve the stability. The simulation and experimental results show that the control strategy is effective.
Keywords Virtual Synchronous Generator, Small Signal Model, Low-voltage Ride-through, Power Loop