Systematic Methods to Eliminate the Transient Circulating Powers in the Multi-VSGs System

When multiple virtual synchronous generators (VSG)s operate in parallel in an islanded microgrid, the sudden load power change could lead to significant transient circulating (and oscillating) power. In this paper, the transient circulating power is first analyzed with the two-VSGs small signal model. On this basis, the paper defines parameter design principles that theoretically eliminate all transient circulating power. Due to the line impedances uncertainty in practice, the ideal parameter design is not always available. Then, to suppress the remaining transient circulating power, an enhanced VSG (EVSG) control strategy is further proposed, by deriving and revising a two-VSGs transfer function from load disturbance to power angles difference. The proposed parameter design principles and the EVSG can be applied sequentially, so that the transient circulating power can be systematically suppressed without the side-effects as in existing methods. An experimental platform with 3 VSGs is established. The parameter design principles and the EVSG are thoroughly validated by experimental results. This is also the first time the 3-VSGs experimental results are reported, while all the existing literature has 2-VSGs data. It confirms that the two-VSGs analytical results can be extended to systems with more VSGs.