A new soft-switching technique using a modified PWM scheme requiring no extra hardware

Abstract

A new soft-switching PWM scheme for a three-phase, AC-DC, step-down unity power factor converter is described. The main advantage of the scheme is that it requires no additional hardware components to achieve a combination of zero current and voltage turn-off and zero and reduced voltage turn-on. The scheme relies on the repositioning of the PWM pulses within the carrier period to obtain natural commutation from one switching device to the next. The theoretical reduction in the total switching losses is mathematically shown to be 42% compared with the standard center-aligned PWM scheme used with the converter. A PSpice/sup TM/ simulation of the new scheme reveals soft-switching waveforms. Practical results are given to support the simulation results and heat-sink temperature rise results show a reduction in heat-sink temperature rise for the new scheme compared to the old.