A Decentralized Secondary Voltage Control Method With Unbalance Voltage Compensation Capability for Parallel Inverters in Islanded Microgrids

To stabilize voltage and improve power quality at the point of common coupling (PCC), this article extends the previous work by proposing secondary voltage control with unbalanced voltage compensation capability in islanded microgrids, which is fully independent of communication links. By injecting an extra small-ac-signal (SACS) into the output of each inverter, a droop relation is built between the SACS frequency and the voltage compensation components. The SACS active power is then calculated and coupled with the measured feeder impedance to adjust the voltage compensation components generated by the estimated positive and negative sequence voltage at the PCC, which in turn affects the SACS active power distribution. Compared with the existing method, the proposed method fully utilizes only one single injected SACS to achieve both secondary voltage control and unbalanced voltage compensation simultaneously, which reduces the control complexity and total harmonic distortion at the PCC. Meanwhile, the proposed method remains effective for both inaccurate PCC voltage estimation and activation delays. Moreover, the control parameters are designed in detail based on a small-signal differential mode model with complex feeder impedance. Finally, the simulation and experimental results demonstrate the effectiveness of the proposed method.