A novel power distribution strategy for parallel inverters in islanded mode microgrid

This paper presents a novel wireless load-sharing control strategy, active droop positioning, for islanding parallel inverters in an ac-distributed system. Normally, the microgrid is intended to operate in islanded mode when the disconnection from the upstream MV network occurs. In this condition, the inverter-interfaced microsources acts as a voltage source, with the magnitude and frequency of the output voltage controlled through droops. However, under overload or underload circumstance, this droop characteristic may lead to large frequency deviation. The mild droop characteristic can avoid this large deviation, but it´s hard to realize a good power sharing among inverters. Compared with the conventional droop control method, by automatically changing the droop position of some large capacity microsources, the proposed control strategy can bind system frequency deviations in an endurable range while ensure good current sharing performance among most microsources. Under this control strategy, almost all the micro sources in the microgrid can work around rated power, and when the load reduces dramatically, the distributed energy resources (like wind power and solar power) can also be taken full advantage. The analysis of the proposed method and design procedure are provided. Simulation and experimental results validate the proposed control strategy.