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

A simple yet effective scheme for improving the power factor and waveshape of input current drawn by a single phase bridge rectifier is presented. A rectifier with filter capacitor draws current from the supply discontinuously, in short pulses. This introduces several problems including reduction of available power and increased loss. The scheme presented here uses a single MOSFET switch on the AC side to provide alternative path for the input current to flow and hence makes it continuous. The rectifier is connected to AC mains through a series combination of inductor and capacitor, which keeps the input current smooth and in-phase with the supply voltage. The simulated results reveal that the Total Harmonic Distortion (THD) of the scheme presented is below 2% with overall efficiency around 90%.

I. Introduction

All electronic circuits in modern power appliances require a stable and regulated dc power supply. AC to DC conversion is therefore found as one of the most common operations in power electronics. The output voltage of a bridge rectifier used for converting AC to DC is a pulsating DC which is smoothed by connecting a filter capacitor across the load. The effect of the filter capacitor is that instead of drawing smooth sinusoidal currents, the rectifier draws currents in short pulses which leads to low input power factor and injection of harmonics into the lines. This introduces several problems including voltage distortion, increased loss in distribution conductors and transformers, reduction of available power and heating of the ac lines, lower rectifier efficiency due to large rms values of the input current, etc [1]–[3]. For these reasons AC to DC converters connected to AC mains are forced to accomplish certain standards that limit the injection of low frequency harmonics in the utility system. Development of AC to DC converters/rectifiers with improved input current waveform has gained importance to meet stringent power quality regulations and strict limits on the total harmonic distortion (THD) of input current placed by IEC 1000–3-2 and IEEE 519–1992 standards [3], [4]. Understandably considerable research efforts are being made in order to devise various techniques for power quality improvement and input current wave shaping by modifying classical diode bridge rectfier followed shaping a bulk capacitor.