Grid-Forming Converter Current Limiting Design to Enhance Transient Stability for Grid Phase Jump Events

Grid-forming converters (GFs) are seen as a replacement for synchronous machines in future power systems. Compared with synchronous machines, GFs provide much reduced overcurrent capability and hence they experience current saturation more frequently for the same capacity. Moreover, once in current saturation, GFs have limited regulation capability, and can become unstable if the current limiting control is improperly designed. Hence, in order to enhance GF stability when subject to phase jump down disturbances and current saturation, a combination of virtual impedance (VI) current limiting and scaling current reference saturation control is proposed. A relatively large virtual reactance-resistance ratio is also recommended. To speed up GF recovery, an (increased) transient P/f droop gain is proposed for downward phase jumps, but not fault conditions. Simulation studies on a simple system under large phase-jump events, i.e. ±60°, confirm the effectiveness of the proposed approach.