Analysis and Mitigation of Background Harmonics Effect on Small-AC-Signal Injection Based Decentralized Secondary Voltage Control for Parallel Inverters in Islanded Microgrids

In order to ensure the voltage stability and reliability at the point of common coupling (PCC), the small-ac-signal (SACS) injection based secondary voltage control methods was proposed, which can achieve precise PCC voltage compensation even with inaccurate feeder impedance and maintain reactive power sharing performance under different activation times of secondary voltage control. However, to guarantee that the injected signal is well controlled and can be easily extracted, the frequency of the SACS must be carefully chosen to avoid the pre-existing background harmonic in the system, which limits its application. Therefore, in this paper, the effect of background harmonics in the SACS injection based secondary voltage control is analyzed and solved in the proposed method. Meanwhile, the solution of background harmonics can also be used in other SACS injection based methods, which greatly extend its applications. Simulation and experimental results are provided to validate the effectiveness of the proposed method.