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.