Decentralised adaptive control design for single-phase parallel-inverter systems

Single-phase inverters are widely installed to integrate distributed generations into microgrids. To further improve the reliability and flexibility, several inverter modules connected in parallel are usually preferred. Besides achieving bus voltage regulation, another control objective of parallel-inverter systems is to guarantee load current sharing performance among multiple inverter modules. To attain these objectives in the presence of physical differences and uncertain system parameters, advanced control schemes are needed. In this study, a state-feedback decentralised adaptive control algorithm is firstly presented for single-phase parallel-inverter systems with unknown system parameters. Adaptive laws are designed to compensate for the uncertainties. In addition, the proposed control algorithm is decentralised in the sense that only local information is required for each inverter's controller. To overcome the practical problem that not all system states are available due to the presence of the unknown system parameters and load current, an output-feedback version of the decentralised adaptive controller is introduced through observers. The closed-loop system stability is proved via Lyapunov analysis. Finally, extensive simulation studies on parallel-inverter systems of different levels of detail are conducted to illustrate that the proposed control algorithm can provide satisfactory voltage regulation and current sharing performance under various loading conditions.