Hysteresis current controlled single-phase ac to dc converter with unity power factor and low losses

H-bridge PWM converter is often used for unity power factor (UPF) rectification. Hysteresis current control is one of the popular schemes for generating PWM pulses for the converter. The hysteresis current control has drawbacks like variable switching frequency and reduced performance under supply voltage distortion. To improve the current quality the hysteresis band is made small but at the expense of increased switching losses. In H-bridge converter the common practice is to turn on the diagonal switches of the bridge together, giving rise to bipolar PWM output voltage. This paper examines the advantages of a unipolar PWM output under hysteresis current control for single phase ac to dc conversion. The average switching frequency of the converter reduces significantly. The hysteresis current control scheme needs to be modified for distorted grid voltage. A frequency-tuned resonant filter is suggested to extract fundamental component from grid voltage, which then is used to generate reference current for the controller. The unipolar PWM based controller's effectiveness is analysed mathematically and validated through detailed MATLAB/Simulink simulations for a single-phase grid-connected system. The experimental study, conducted on a 500W non-linear load in a laboratory setting, demonstrates a Total Harmonic Distortion (THD) of 5.8% in the grid-side current, with a power factor near unity, in line with IEEE standards.