Optimization Based on Fuzzy Logic Control of Discharge Lamp-Electronic Ballast System for Water Purification

Abstract

The low-pressure electric discharge established in mercury rare gas mixtures is the basis of many applications both in the field of lighting as for industrial applications. This present work presents the design of a high-frequency current supply based on a pulse width modulation inverter powering a low-pressure ultraviolet lamp dedicated for a germicidal effect in water purification. The basic open-loop system delivers voltage and current at a frequency of 50 kHz modulated in an envelop oscillating at 1 kHz, thus decreasing the operating efficiency of the system for an optimal germicide effect. A proportional-integral controller introduced in the ballast suppresses the modulation of the RMS intensity envelop but cannot assume robustness to external disturbances such as variation of the temperature of the water to disinfect. Thus, to increase the reliability of the whole system, the classic controller is originally replaced by a fuzzy controller, which significantly improves the quality of the waveforms of the lamp arc current and arc voltage. This new control strategy is more robust since it supports very large perturbations of the temperature of the water basin.