A Hybrid Transient Virtual Resistor Method for Restraining Transient Overcurrent of Grid-Forming Inverter During Grid Fault and Postfault Recovery

With the growing capacity of renewable energy, grid-forming (GFM) inverters are considered as promising solutions for low-inertia power grids. However, the overcurrent problem of GFM inverters during large grid disturbances is still a significant challenge. Generally, the GFM inverter has two types of overcurrent problems: 1) the steady-state overcurrent; and 2) the transient overcurrent. To address the steady-state overcurrent problem, a virtual power angle limiter method has been proposed in existing literature, which can limit steady-state overcurrent and maintain transient stability simultaneously during grid faults. Nevertheless, the transient overcurrent problem has not been fully addressed, which is still a remaining issue. To address the transient overcurrent problem, a hybrid transient virtual resistor (HTVR) method is proposed in this article, which can increase the generating speed of the transient virtual resistor as fast as possible. Thus, the transient overcurrent of the GFM inverter can be restrained below 1.2 or 1.1 p.u. in the grid fault and recovery scenarios by using the HTVR method. Simulation and experiments verify the effectiveness of the proposed method.