Comparison of discrete control techniques for UPS applications

In this paper a comparison is performed among three discrete control techniques applied to uninterruptible power supplies (UPS), namely: one sample ahead preview (OSAP) with repetitive controller, predictive PID-feedforward control with repetitive controller, and a repetitive controller based on auxiliary states. These discrete control schemes can minimize periodic distortions produced from unknown periodic load disturbances. The implemented PWM inverter system with sinusoidal reference employs a low cost microcontroller. Due to the fact that the most of the low cost microcontrollers available in the market present low processing speed, it is imperious to develop simple algorithms with few instructions, so that its implementation is realizable. Principles and fundamentals of these discrete control techniques are discussed. Simulation and experimental results (110 V_RMS, 1 kVA) are presented to demonstrate the performance of these control techniques under periodic load disturbances