Research on fault phase identification method for double-ended weak-fed systems based on multi-frequency harmonic injection

With the rapid development of renewable energy power generation, flexible DC transmission has been widely applied in the large-scale transmission of new energy. When the fault occurs in the AC system during the transmission of new energy via flexible DC, the traditional sequence component phase selection elements become unsuitable due to the influence of the converter control strategies on both sides of the system. This paper proposes a fault phase identification method based on sequence component analysis under multi-frequency harmonic injection. First, harmonic signals containing negative-sequence and positive-sequence components are injected into the system to construct a sequence network under harmonic injection in the case of fault. Second, the phase relationships between the sequence components in the constructed sequence network are analyzed to summarize the patterns of fault characteristics. Third, based on the phase relationship characteristics derived from the analysis, combined with the requirements for fault phase identification, key criteria elements capable of effectively distinguishing different fault types are extracted. Finally, these key elements are integrated and optimized to construct a phase identification method to identify the fault phase. Simulation results indicate that this solution can accurately identify the faulty phase under conditions of 300 Ω fault resistance and 25 dB noise interference, thereby meeting the protection requirements for fault scenarios at different locations in double-ended weak-fed systems.