Arm Overcurrent Protection and Coordination in MMC-HVDC

This paper discusses the coordination of arm overcurrent protective functions, which are configured both in valve controls and DC protections of modular multilevel converter based HVDC (MMC-HVDC). Since the parameter mismatching in valve control and DC protection may lead to unexpected block, the ac protection coordination diagram is used to analyze the setting and time delay of arm overcurrent protections. A temporary blocking function in valve control is introduced and is configured properly with other protection stages in DC protection device. Simulation results based on a detailed PSCAD model prove the proposed protection coordination method can avoid the protection malfunction during ac fault low voltage ride through (LVRT). Meanwhile the protection logic guarantees the safety of power electronic devices during dc fault by fast triggering the shunted thyristor.