Composite Current-Constrained Control of Stand-Alone Three-Phase Inverters Under Multiple Load Conditions

With the growing penetration of renewable energy sources, distribution network protection and stability are of great importance. This paper aims to propose a current limiting control scheme with anti-disturbance properties to improve the reliability and power quality of stand-alone three-phase inverters under multiple load conditions (including balanced loads, unbalanced loads, and nonlinear loads). A benchmark controller is designed first to achieve voltage regulation and overcurrent protection targets under relatively ideal conditions (e.g., only subject to constant disturbances caused by parameter perturbation or linear balanced load switching). Then, considering the unbalanced and nonlinear load conditions, two composite disturbance observers are constructed to estimate the large-scale, fast-varying harmonic disturbances introduced by the multiple loads. Based on the disturbance estimates and the benchmark controller, a composite current-constrained control scheme with rigorous stability analyses is proposed. The innovative control scheme ensures good output voltage quality and strictly guarantees overcurrent protection, which is validated by the simulations and experiments. Last but not least, extended current limiting control schemes to broaden the application range and enhance the control performance are presented.