Output‐Feedback Nonlinear Adaptive Control of Single‐Phase Half‐Bridge Ups Systems

We consider the problem of controlling single-phase half-bridge power converters in UPS systems operating in the presence of changing load. The control objective is twofold: i ensuring a satisfactory power factor correction PFC at the grid-UPS connection; ii guaranteeing a tight regulation of the DC bus voltage and the half-bridge inverter output voltage despite changes in load. The considered control problem entails several difficulties including: i the high dimension and strong nonlinearity of the system; ii the numerous state variables that are inaccessible to measurements; iii the uncertainty that prevails on some system parameters. The problem is dealt with using a multi-loop nonlinear adaptive control system that makes use of the backstepping design technique. The inner loop ensures the PFC objective and involves an adaptive observer estimating the grid voltage and impedance parameters. The intermediary loop regulates the inverter output voltage to its reference, which is a sinusoidal wave, and it also contains an observer estimating the current in the inverter coil. The outer loop regulates the DC bus voltage up to small size ripples. The controller performances are formally analyzed using system averaging theory.