Coordinated Control Strategy for Fault-Blocking of Modular Multilevel Converter in Hybrid Cascaded Ultra High Voltage Direct Current Transmission Systems Based on Protection Signal

Abstract

For the abnormal phenomenon of non-faulty MMC after fault MMC blocking in Hybrid Cascaded Ultra High Voltage Direct Current (HC-UHVDC) transmission system, a coordinated control strategy based on control signals is proposed. The mechanism of overcurrent and overvoltage in non-fault MMC was analyzed. Additional current was added in the LCC rectifier control to suppress overcurrent and overvoltage. DC voltage is out of control when the MMC master station is fault-blocked. To solve this problem, an optimal control strategy is adopted to convert the slaver station to the new master station. The scheme is based on the protection signal to identify the fault converter station. After the converter station is blocked, the system can be safely and effectively restored to the stable state.