计及负序电流注入策略的双端弱馈交流系统纵联保护研究

Aiming at the problem that traditional negative-sequence pilot directional protection may fail to operate or maloperate due to the influence of converter control strategies，this paper proposes a pilot protection scheme for double-ended weak AC systems based on negative-sequence impedance difference characteristics under negative-sequence current injection by Modular Multilevel Converters （MMC）. Firstly，the impact of negative-sequence current suppression strategies on both sides of the system under asymmetrical faults on traditional negative-sequence pilot directional protection is investigated. Secondly，considering multiple factors，a negative-sequence current injection strategy that suppresses active power fluctuations is introduced. On this basis，the differences in negative-sequence impedance characteristics under internal and external faults are analyzed. Finally，a detrended fluctuation analysis method is introduced to calculate the fluctuation functions at both ends and transmit logic quantities，thereby constructing a pilot protection scheme for double-ended weak AC systems. Simulation results show that the proposed pilot protection scheme can operate reliably under a transition resistance of 300 Ω and with 20 dB noise interference.