On the robust control design of multiple resonant controllers for the parallel operation of UPSs

This paper presents a methodology for the synthesis of multiple resonant controllers in the voltage regulation loop of uninterruptible power supplies (UPSs) operating in parallel with droop control. The resonant controller gains are calculated through a convex optimization problem aiming to attenuate the rms value of circulating current between the UPSs. Linear matrix inequalities (LMIs) constraints ensure the robust closed-loop robust stability and performance under the insertion or removal of UPSs and load variations. Experimental results from two 3.5 kVA UPSs illustrate the advantages of the proposed approach.