A High-Frequency Small-AC-Signal Injection Based Decentralized Secondary Frequency Control Method for Islanded Low-Voltage AC Microgrids with Background Harmonics

Small-AC-signal (SACS) injection-based secondary frequency control method demonstrates superior performance in restoring frequency and maintaining power sharing without communication in islanded AC microgrids. However, a major issue with the existing method is that the frequency of injected SACS often overlaps with that of pre-existing background harmonic, leading to oscillations in both fundamental frequency and output power. To solve the problem, this article proposes a high-frequency SACS (HF-SACS) injection based method. Unlike the existing method that limits SACS to a low frequency range, a HF-SACS lying beyond the pre-existing background harmonics can be selected by using the proposed injection-and-detection circuit. Moreover, to maintain reactive power sharing, a novel HF-SACS synchronization mechanism is also constructed by extending the range of SACS power angle. Finally, experimental results verify the effectiveness of proposed method.