Multiple-Objective Control Scheme for Input-Series–Output-Series LCL-Filtered Grid-Connected Inverter System

An input-series–output-series inverter system is suitable for the large-capacity high-voltage ac power applications. If such a combined system comprising a number of small-capacity inverters is utilized in the high-power grid-connected power generation to replace a single high-capacity inverter, the voltage stress of the module would be greatly reduced. Additionally, the reliability of the whole grid-connected system could be effectively heightened owning to its flexible assembled-connection architecture. The principal issues for this grid-connected combined system touch upon multiple control objectives, including power balance, high power factor of the grid current, suppression of LCL resonance spike, and redundant operation of the system. Above all, the control variables are attentively screened to obtain a concise scheme to achieve the first three fundamental demands. Furthermore, the control units are dispersed into each module and a hot-swap technique is proposed to actualize the last objective, acquiring the superior reliability of the system. Finally, a three-module prototype is fabricated and the experimental results verify the effectiveness of the proposed strategy.