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In the last fourteen years the power quality concept and its related issues have gained a lot of attention. Mainly in industrial sites where critical loads are supplied with poor electric power quality, more attention is dedicated to this area. This paper presents a feedforward control technique used in a three-phase PWM inverter In order to compensate any variation on the AC output waveforms (voltage & current), under typical electric power disturbances, such as sags or swells. Voltage sag is a momentary decrease in the rms voltage values and swell is a momentary increase in the rms voltage values. The IGBT PWM inverter system detects those disturbances and a feedforward control compensates to maintain the output quantities under nominal output values. Analysis and simulation results are presented based on a 220 V, 5 kVA, three-phase PWM inverter. Furthermore, experimental results are carried out to illustrate the variation on the output waveforms due to two-phase voltage sags and/or swells. It is also proposed the use of a DSP (digital signal processor) to implement the approach of a feedforward control technique on ASD or UPS systems.