A novel AC line distance protection scheme for AC/DC hybrid system based on fault component energy equation

Abstract

In view of the mal-operation of AC line distance protection due to DC commutation failure caused by the inverter-side AC system fault, a new AC line distance protection principle for AC/DC hybrid system based on fault component energy equation is proposed. First, by comparing the pre-fault and post-fault conducting states of converter valves, the expressions of fault components of converter bus voltage considering commutation failure are derived. Based on this, the fault supplementary network of DC system with multiple fault supplementary sources is built. Then, combining the fault supplementary network of AC system, the fault component energy equation containing the fault distance and fault resistance is established. And then, distinguish the fault direction according to different characteristics of fault component energy flowing to the converter bus in the case of the DC system fault and the AC line fault. Thus, the linear least squares method is used to solve the equations with data at multi-time sections, so that the fault parameters are calculated and distance protection criterion is constructed. Finally, the simulation results based on the RT-LAB platform verify that, this method can identify different types of internal and external faults on AC line fast and sensitively, unaffected by the commutation failure and fault resistance.