Improved transient and steady state voltage regulation for single and three phase uninterruptible power supplies

Most of the many reported control algorithms for uninterruptible power supplies use either filter inductor or filter capacitor currents as feedback variables to regulate the output voltage. This paper explores the fundamental performance issues associated with the use of these quantities as feedback variables, with a view to determining their contribution to the transient system response in any particular situation. Then a proportional plus resonant (P+resonant) compensator is added into the outer voltage regulation loop to achieve zero steady error, to develop a high performance UPS control algorithm which is applicable to both single and three phase systems. Theory, simulation and experimental results are presented in the paper.