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

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 th at it requires no additional hardware components to achieve a combination o f zero current and voltage turn-off and zero and reduced voltage turn-on. T he 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 w ith the converter. A PSpice (TM) simulation of the new scheme reveals soft- switching waveforms. Practical results are given to support the simulation results and heatsink temperature rise results show a reduction in heatsink temperature rise for the new scheme compared to the old.