Over-voltage Suppression Methods for the MMC-VSC-HVDC Wind Farm Integration System

In this paper, we study the cascading failure mitigation methods in the system where the remote large-scale wind farm is integrated to the bulk AC power system through high voltage direct current (HVDC) transmission based on voltage source converter (VSC) in modular multilevel converter (MMC) topology. We first analyze the over-voltage formation mechanism in the MMC-VSC-HVDC wind farm integration system after the short-circuit fault of an AC feed line, and find that the saturation of the integers in the PI controller are the main causes. Based on the analytical conclusions derived, we propose two improvement control strategies implemented in the MMC controller to suppress the over-voltage. We do simulations on a test case with PSCAD. Simulation results verify the efficacy of the proposed methods in the suppression of over-voltage as well as the prevention of cascading failure in power systems.