A Small-AC-Signal Injection Based Decentralized Secondary Voltage Control for Parallel Inverters with Accurate Reactive Power Sharing in Islanded Microgrids

To compensate for the voltage deviation at the point of common coupling (PCC) without communication links among distributed generations (DGs) in an islanded microgrid, proportional-integral regulator based secondary voltage control (PI-SVC) has been proposed in the literature. However, PI-SVC will degrade reactive power sharing performances, resulting from the activation time differences of secondary control. Moreover, PI-SVC may even cause reactive power divergence because of inaccurate estimated PCC voltages among DGs. To achieve precise PCC voltage restoration and maintain excellent reactive power sharing performance, this article proposes a small-ac-signal injection based secondary voltage control (SACS-SVC) in which an additional small-ac-signal (SACS) is injected into the output voltage of each DG. An additional positive droop relation is built between the injected SACS frequency and the voltage compensation value, which can be trimmed to be equal in each DG. As a result, PCC voltage deviations can be eliminated and reactive power sharing performances can be maintained. Meanwhile, the parameters of the proposed SACS-SVC are comprehensively designed through a small-signal differential mode model of the system. The effectiveness of the proposed method is demonstrated by the simulation and experimental results.