Fuzzy logic and digital PI control of single phase power factor preregulator for an online UPS-a comparative study

A fuzzy logic control (FLC) and a digital PI control are proposed for the application in feedback control of a power factor corrected (PFC) pre-regulator used in a high performance online uninterruptible power supply (UPS). Performance of these two controllers are compared through the digital simulation. Fuzzy logic controllers have an advantage in coping with the time varying nonlinearity of switches in PFC pre-regulator, and it does not require an accurate mathematical model of the PFC pre-regulator when the controller is being designed. On the other hand, digital PI controller design requires a accurate mathematical model of the plant and it failed to perform satisfactorily under parameter variation, nonlinearity, load disturbance, etc. The simulation results show that the fuzzy logic inference based controller can achieve better dynamic response than its digital PI counterpart under large load disturbance and plant uncertainties. The practical implementations of the two controllers for an online UPS are discussed.