Resonant Based Overvoltage Restraining Strategy for MMC-HVDC Wind Power Transmission System under Sending End Grid Fault

An overvoltage restraining strategy for offshore modular multilevel converter based high-voltage direct current (MMC-HVDC) wind power transmission system under sending end grid fault is proposed in this paper. The mathematical models of the grid-side and MMC-side voltages are deduced under different sending end grid faults, and the overvoltage mechanism is analyzed. On this basis, a resonant based overvoltage restraining strategy is proposed by improving the configuration method of the reference voltage. The PI controllers and coordinate transformation process for the negative sequence currents and circulating currents are simplified by using resonant controllers. Simulation results show that the proposed strategy can restrain overvoltage under different grid faults effectively. In addition, no negative sequence current is injected into the grid current, and the grid voltage can recover smoothly after the faulty line is cut off.