Robust controller design for a single-phase UPS inverter using μ-synthesis

A study on the robust performance of the previously developed H_∞ loop-shaping controller via μ analysis has shown that its tracking performance robustness is not achieved under prescribed perturbations in load. The H_∞ loop-shaping design also neglects the effects due to variation in DC input voltage. A μ-synthesis based approach to reduce these drawbacks is proposed. Under the formulation of linear fractional transformation, both the perturbations in input DC voltage and load are considered and expressed as system static and dynamic uncertainties, respectively. By applying the μ-synthesis principle, feedback controllers that simultaneously achieve robust stability and robust tracking performance are obtained. The robust performance of the resulting controller is theoretically confirmed via μ-analysis. Simulation and experimental results are also given, demonstrating improved performance over the H_∞ loop-shaping design.