Active Power and Voltage Cooperative Control for Improving Fault Ride-Through Capability of Grid-Forming Converters

The grid-forming (GFM) converter has excellent active support capabilities, but it will face problems of transient instability and transient overcurrent during grid faults, which brings challenges to its large-scale application. Aiming at this problem, in this article, we analyze the transient instability mechanism and the transient overcurrent causes of the GFM converter. The analysis results show that active power imbalance is the essential reason that drives the power angle to increase and even causes transient instability, and the increase in power angle and the approximately constant internal potential cause the converter to generate transient overcurrent. Based on the above analysis, an active power and voltage cooperative control strategy is proposed to improve the fault ride-through capability of the GFM converter. This strategy consists of transient active power control and transient voltage control, which can eliminate the active power imbalance and flexibly regulate the internal potential according to the fault current, thus ensuring the transient stable operation of the converter while suppressing transient overcurrent. More importantly, the proposed control strategy is not affected by the fault degree and fault duration. Simulation and experimental results verify the effectiveness of the proposed strategy.