In response to global warming, the deployment of distributed energy resources based on renewable energy has been expanding. However, since these resources are connected to the power grid via inverters, they have lower inertia than conventional synchronous generators, leading to a reduction in overall power system inertia. As a result, deterioration of frequency stability is a concern, and a decrease in short-circuit capacity has also become an issue. To address these challenges, grid-forming inverters (GFMs) have attracted increasing attention.

GFM inverters provide virtual inertia by emulating the characteristics of synchronous generators, thereby contributing to improved frequency stability during power system disturbances. However, since they operate as voltage sources, they tend to produce overcurrent during disturbances such as ground faults.

The authors have previously proposed an overcurrent suppression method for GFM inverters using a current limiter applied to the instantaneous values of three-phase AC currents. Although the method effectively suppresses overcurrent during faults, it causes waveform distortion in the output current during the suppression period.

This paper investigates an overcurrent suppression method combining virtual resistance and active power reference control. The proposed method is evaluated using time-domain simulations, with particular attention to the transient response associated with circuit breaker (CB) reclosing.

Simulations were carried out using the simulation model shown in Fig. 1. A three-phase-to-ground fault was applied at the midpoint of one of the two transmission circuits at t = 3.00 s. The CB on the faulted circuit was opened at t = 3.05 s and reclosed at t = 3.20 s. The initial active and reactive power references were set to 0.8 pu and 0.0 pu, respectively, and the current limiter threshold was set to 1.0 pu. The proposed method was validated by comparing the GFM inverter output current waveforms and transient responses during CB reclosing with those obtained using the conventional method based solely on a current limiter.

Simulation results showed that the proposed method effectively suppressed the GFM inverter current within 1.0 pu during the ground fault. Furthermore, the waveform distortion observed with the conventional method was reduced. The proposed method also suppressed the overcurrent caused by phase deviation immediately after CB reclosing.

The full paper will further investigate the effects of parameter variations on the overcurrent suppression performance of the proposed method.