Decoupled simultaneous complex power sharing and voltage regulation in islanded AC microgrids

Abstract

In islanded AC microgrids, when multiple voltage source inverters (VSIs) operate in parallel, it is challenging to simultaneously obtain both accurate complex (active and reactive) power sharing and voltage regulation (in terms of frequency and amplitude). State-of-the-art strategies that target these two objectives often rely on hierarchical primary droop plus communication-based both secondary controls and adaptive virtual impedance methods. However, control dynamics and/or accuracy are still affected by inverters line impedances mismatches. To overcome these limitations, this paper presents for balanced AC microgrids a distributed control strategy that simultaneously guarantees both voltage regulation and accurate power sharing. The distributed strategy is based on having at each VSI a single controller that merges two control loops that can be designed in isolation, thus decoupling the design of the power sharing control from the design of the voltage control. The cooperative operation of all VSI controllers, that requires exchanging control data over a communication network, ensures meeting both control objectives with independence of the line impedance mismatches or the connection and disconnection of inverters and loads. And these properties are achieved without changing the controller structure and (easy-to-tune) parameters nor increasing the control effort. Experimental results corroborate the control proposal.