Design of a single phase rectifier with switching on the AC side for high power factor and low total harmonic distortion

Abstract

A scheme for improving the input current waveshape of a single phase bridge rectifier has been proposed and analyzed. A bridge rectifier with filter capacitor connected to reduce ripples of output voltage draws discontinuous and nonsinusoidal current from the supply. In this work a switching scheme has been developed which exploits a single MOSFET switch driven by rectangular gate pulses whose duty cycle is continuously varied over the period of supply voltage. The switch provides an alternative path for the input current during the periods when due to the reverse biasing of rectifier diodes input current ceases to flow otherwise. The variation of duty cycle of the switching pulses has been intuitively varied like a rectified cosine wave. The switching scheme combined with an input LC (inductor-capacitor) filter that has a resonating frequency almost equal to that of supply voltage, has been found very effective in improving the input current waveshape. Analytical expression for the input current drawn by the rectifier with proposed switching is derived and detail simulation results are presented which shows that the rectifier with the proposed scheme draws sinusoidal current at unity power factor and has high overall efficiency. The Total Harmonic Distortion (THD) in input current is reduced below 2%. Different combinations of LC filter elements and switching frequency have been considered to obtain optimum results in terms ofTHD and overall circuit efficiency.