Zero-Sequence Current and Voltage Control Strategy of Multiple MMCs for Single-Phase Ground Fault Protection in AC–DC Hybrid Distribution Networks

The ac/dc hybrid distribution network (HDN) is facing great challenges under single-phase ground (SPG) fault. To ensure the continuous and stable operation of ac/dc HDNs, it is essential that the converters have fault control and relay protection capabilities. The previous studies focused only on a single converter, this article first proposes a zero-sequence current and voltage control strategy for multiple modular multilevel converters (MMCs). The zero-sequence current control strategy includes active arc suppression and zero-sequence current suppression. The active arc suppression can achieve relay protection functions such as arc suppression, fault type determination, fault localization, and fault removal perception. The zero-sequence current suppression can achieve SPG fault isolation to ensure that the power quality of the nonfaulty grid is not affected. The zero-sequence voltage control strategy includes zero-sequence voltage cooperative control and zero-sequence voltage feedforward control, which can optimize the voltage capacity of each MMC and reduce the fault control requirements of the ac/dc HDN. The whole proposed strategy can realize the self-healing of SPG faults, which can improve the reliability of distribution network power supply. The effectiveness of the strategy is fully verified by simulation and experiment.