DC side line-to-line fault analysis of VSC-HVDC and DC-fault-clearing methods

As the fault voltage and current change raptly in case of DC side line-to-line fault of voltage source converter, it´s a serious threat to the whole system. Aiming at this problem, the mechanism of DC side line-to-line fault in three kinds of converters including two-level converter, three-level diode-clamped converter and Modular Multilevel Converter, was analyzed firstly. Without converter blocked, the calculation of fault over-current and voltage collapse expressions was proposed as well. Finally, theoretical analysis of the short-circuit fault process was validated through the RT-LAB simulation. The derivation and simulation waveform provide a reference for disconnecting the faulty branch. The results indicate that quick removal of the fault is better to be done by DC circuit breaker or converter with self-clearing. A low-voltage low-current laboratory prototype of hybrid DC circuit breaker has been built in the laboratory, which verify DC circuit breaker can disconnect the fault current absolutely.