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

This paper proposes the H-infinity loop-shaping approach to the designs of sinusoidal output voltage tracking controllers for single-phase UPS inverte rs. Selection of weighting functions is introduced, which is quite differen t from the case of step tracking, By modeling the uncertainty in load as pl ant output multiplicative perturbation, two H-infinity loop-shaping control schemes that use only capacitor voltage sensor are presented. The first de sign adopts single-loop control scheme which has the advantage of simple co ntrol structure and easy implementation. But its transient performance and robustness are not satisfactory. The second controller with a dual-loop str ucture, additionally employing output of a capacitor current estimator as f eedback, provides improved performance over the single-loop scheme and has the feature of low distortion, good regulating performance and insensitivit y to the variation in load. Simulation and hardware experimental results, w ith comparison to the PI-based multiple feedback loop design, are given to validate the robustness property and regulating performance of the proposed controllers.