Multiple-Loop H-Infinity Control Design for Uninterruptible Power Supplies

This paper presents an innovative tuning strategy for the design of multiple-loop lag-lead compensators for uninterruptible power supplies (UPSs) based on the H-infinity robust control theory. Taking into account an average model of a UPS, the parameters of a double-loop controller are synthesized such that the upper bound on the two-norm of the input-to-output operator is minimized while guaranteeing local stability of the closed-loop system for all admissible load variations. The stabilization conditions are cast in terms of linear matrix inequalities that are solved via standard software packages. To improve regulation dynamics, a newer technique to compute the root-mean-square value of the output voltage is also proposed. Practical results considering a commercial UPS system demonstrate the effectiveness of the proposed approach as a tool for tuning multiloop controllers