A Modified Discrete Control Law for UPS Applications

This paper presents a model reference controller with a repetitive control action for uninterruptible power supply (UPS) applications. The model reference controller modifies the structure of the plant so that the closed-loop transfer function is equal to a chosen reference model transfer function, whereas the repetitive control action minimizes periodic distortions caused by unknown periodic disturbances. Design procedure and stability analysis of the control scheme are discussed. Simulation and experimental results for a single-phase PWM inverter (110 VRMS, 1 kVA) controlled by a low cost microcontroller are presented to verify the performance of the proposed control approach under different load conditions.