Main System and Microgrid Support using a Distributed Generator through Back-to-back Inverters

This paper discusses the interconnection of a distributed generator (DG) to an ac distribution system and a microgrid using power electronics based back-to-back voltage source converters (VSCs). The DG is assumed to produce a constant dc output voltage. The DG is connected to the microgrid through a VSC that ensures that the voltage of the microgrid is regulated to be balanced sinusoids having a fixed peak despite the loads of the microgrid being unbalanced and non-linear. The DG is also connected to the main ac system through another VSC. The VSC interfacing the DG to the main ac distribution system controls the real power to be injected into the distribution system. The main system VSC also additionally performs as an active filter by compensating for non-linear and unbalanced loads that may be connected to the main distribution system load bus. Control of both the VSCs have been described. The DG is seen to perform effectively even when the main distribution bus voltages are unbalanced and distorted. Simulations performed using PSCAD/EMTDC support the theory presented in the paper.