Integrated Multiport Flexible Voltage Clamp Circuit Breaker with DC Chopper Applied to MMC-HVDC System

Given the wide application of DC grids, the protection equipment of power grids must be improved during the fault period. This study proposes an integrated multiport flexible voltage clamp circuit breaker with a DC chopper acting on the receiving end converter to solve the DC short circuit fault and surplus power because of AC low-voltage fault; it has a modular design. As a DC circuit breaker, the device utilizes the voltage-clamping principle and thyristor semi-control to remove faults. As the fault current increases, the branch circuit outputs different voltage levels by selecting different gears, thereby controlling the voltage-clamping effect. This device can distinguish between different fault types to prevent secondary shocks in the system. As a DC chopper, the voltage at both ends of the energy dissipation resistor is varied by switching submodules, consuming surplus power to complete AC low-voltage faults and minimizing the impact of low-voltage faults on the system’s transmission capacity. Finally, the effectiveness and applicability of the equipment are verified using wind turbines connected to a flexible DC transmission three-terminal power grid model in PSCAD/EMTDC, and two fault simulation types are analyzed. A comparison of the electrical quantities (fault current, system voltage and branch voltage) of the proposed circuit breaker with other similar equipment shows that due to the efficiency of the proposed equipment, the peak fault current is reduced by at least 35.8%. The required voltage stress of key power electronic equipment is reduced by at least 71.5%. Therefore, the equipment ensures that the per-unit voltage of the DC system does not exceed 1.05 during AC fault crossing.