H∞ loop-shaping controller designs for the single-phase UPS inverters

This paper proposes the H_∞ loop-shaping approach to the design of sinusoidal output voltage tracking controllers for single-phase UPS inverters. By modeling the uncertainty in load as plant output multiplicative perturbation, two H_∞ loop-shaping control schemes that use only a capacitor voltage sensor are presented. The first design adopts a single-loop control scheme which has the advantage of simple control structure and easy implementation. But its transient performance and robustness are not satisfactory. The second controller with a dual-loop structure, additionally employing the output of a capacitor current estimator as feedback, provides improved performance over the single-loop scheme and has the feature of low distortion, good regulating performance and insensitivitye to the variation in load. The results are verified through computer simulation and hardware experiment