Comparison of fuzzy logic and digital PI control of single phase power factor pre-regulator for an on-line UPS

A fuzzy logic control (FLC) and a digital proportional and integral (PI) control are proposed for the application in feedback control of a power factor corrected (PFC) pre-regulator used in a high performance on-line uninterruptible power supply (UPS). Performance of these two controllers are compared through the digital simulation. Since the performance of a fuzzy logic controller depends only on the selection of membership functions and the inference of fuzzy rules, so also fuzzy set theory, in nature, is capable of working with nonlinear systems. Thus, fuzzy logic controllers have an advantage in coping with the time varying nonlinearity of switches in a PFC pre-regulator, and it does not require an accurate mathematical model of the PFC pre-regulator when the controller is designed. On the other hand, digital PI controller design requires an 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 implement consideration of both controllers for an on-line UPS are also discussed.