Differential protection for active distribution networks based on the similarity of injected harmonic currents

Abstract In response to the complex fault characteristics of inverter-interfaced distributed generation (IIDG) and the impact of their fault ride-through currents on the system, the adaptability of traditional current differential protection is insufficient. This paper constructs an equivalent model for IIDG, analyzes the characteristics of IIDG output fault currents and their specific impacts on traditional current differential protection, and quantitatively describes the similarity of harmonic current waveforms at both ends of the protection by injecting harmonic currents from IIDG into the system. Consequently, an active distribution network differential protection based on the similarity of injected harmonic currents is proposed. Addressing the limitations of the original waveform similarity algorithm, which solely measures waveform characteristics and is affected by unmeasurable branch loads within the feeder, a corresponding comprehensive waveform measurement method is proposed. Both theoretical analysis and simulation results verify the effectiveness of the proposed protection scheme, which is unaffected by fault types, transition resistance, unmeasurable branch loads, and distribution network topology.