Independent predictive control with current limiting capability of three-phase four-leg inverter-interfaced isolated microgrids

Over-current restriction in converter-interfaced distributed energy resources within a microgrid is a crucial challenging issue, arising from the limited thermal capacity of power electronic switching devices. Available current limiting studies are only concerned with linear balanced loads, exerting poor voltage quality under unbalanced and/or non-linear loads. Moreover, they exhibit sluggish dynamic response, especially under heavy load conditions as well as at load dropouts. This paper proposes a novel control structure in conjunction with a peak detection-based current limiting function for droop-controlled converters with independently controlled neutral leg topology. Furthermore, a finite control set-model predictive control is designed and employed, allowing direct generation of the voltage switching signals, enabling aggregated voltage and current control. An auxiliary sliding mode control-based voltage controller is also utilized to provide reference current for the proposed current limiting strategy. Simulation results are examined on the isolated CIGRE benchmark low voltage microgrid. Comparison results demonstrate the excellent performance of the proposed control structure under various load conditions. Faster and robuster dynamic response and higher voltage quality delivery at output terminals are clearly observed. Lastly, the results are verified by real-time simulations.