Research on Time Domain Protection of AC Line in AC/DC Hybrid System

Affected by the access of the DC system, when the AC line fault on the inverter side causes the commutation failure of the DC system, the AC side has the characteristics of frequency offset and high low frequency content. In the traditional protection scheme, the pilot protection is the main protection, and the distance protection is the backup protection. They are all based on the protection of the power frequency, and there are unstable operations. From the perspective of time domain, combined with the method of parameter identification, a time-domain pilot protection scheme suitable for AC/DC hybrid system is proposed, which solves the problems caused by frequency offset in principle and a protection criteria is provided; When a line fault occurs in the AC transmission line of the hybrid system, the proposed time-domain distance protection scheme all adopts the time-domain full amount of fault information, and is also solves the problems caused by frequency offset. The simulation results show that the time-domain pilot protection and time-domain distance in the protection scheme can accurately and quickly identify faults, effectively solving the problem of unstable protection action when commutation failure occurs.