Fault Control Strategy of Grid‐Forming Converter Considering the Voltage Support of Faulty Phase

Abstract

The grid-forming converter (GFC) is used to regulate the voltage and frequency of a local grid. However, due to the limited current capacity, the GFC must actively modify its control strategy when a serious external fault occurs, thus to avoid the possible damage caused by overcurrent. This paper proposes a novel voltage reference generation method for GFC based on the external equivalent impedance magnitude (EEIM), which has the following merits: (i) the faulty phase currents and the non-faulty phase voltage can be controlled within their operational limits. (ii) The voltage reference unbalance factor (VRUF) of the GFC can be adjusted flexibly if necessary. Then, in order to achieve the optimal support effect for the faulty phase voltages, a two-stage GFC fault control strategy is proposed in this paper. In the first stage, the fault type is judged by computing and comparing the EEIM of each phase. In the second stage, the voltage reference mode is determined according to the fault type, and the VRUF is adjusted to its optimum value through a search algorithm. Simulation results based on Matlab/Simulink verify the effectiveness of the proposed GFC fault control strategy in terms of current limiting and faulty phase voltage support.