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Comparison of Fault Isolation Methods Used in Hybrid High-Voltage Direct-Current Transmission System Consisting of LCC and VSC

Directing at the hybrid high-voltage direct-current (HVDC) system with line commutated converter (LCC) and voltage source converter (VSC), it is of significance to investigate a feasible approach to isolate the DC-line fault rapidly and validly. In this study, the performance comparison of employing AC and DC circuit breakers for removing the DC-line fault is conducted. Firstly, the theoretical model and control strategy of the hybrid HVDC system are depicted. Then, the transient characteristics of the fault currents contributed by the LCC and VSC are analyzed. Based on the MATLAB platform, the isolation behaviors of the AC and DC breakers are compared, and herein the peak value of the DC fault currents and the breaking time are selected as the performance indexes. In addition, different action delays of the circuit breakers are taken into consideration. From the simulation results, it is found that using the DC circuit breakers is better than employing the AC breaker to address the DC-line fault, and the isolation time can be controlled within several milliseconds. Finally, some beneficial technical discussions for the fault isolation methods are performed, and it is descried to provide possible improvement directions.