Control strategy ensuring multi-mode seamless transition for a single-phase LCL inverter

摘要

A unified control structure of a capacitor voltage - inductor current double closed-loop is modified to fulfill the function of the single-phase inverter to not only be capable of operating in both grid-connected mode and stand-alone mode but also can support the DC bus when the front-end DG units fails to supply enough energy. The system configuration, including the main circuits and the control block diagrams under different operation modes, together with the mode transition procedure, is presented in detail. Experiments on a laboratory prototype help to verify that the proposed control strategy can realize successful transition between different modes without causing severe distortion in the load voltage and inverter output current waveforms while reducing the system dependence on the performance of islanding detection techniques.