Novel soft-switching inverter using resonant inductor freewheeling

A novel topology of the voltage-source soft-switching inverter for induction motor drives is presented. The key of this topology is to employ two fractional-duty auxiliary switches and one resonant inductor per phase to provide a favorable zero-voltage turn-on condition for those main switches. By fully utilizing the inherent natural freewheeling of the inverter, the auxiliary switches need to operate in the resonant inductor freewheeling only in a fractional duty. Apart from providing the soft-switching environment with minimum voltage and current stresses, the distinct advantage of this topology is the capability to control the operation of each phase individually. Therefore, this inverter can readily adopt the well-established PWM techniques while possessing the advantages of soft switching - namely PWM-oriented soft switching. Moreover, a new concept of zero-voltage soft-switching vector is introduced to determine whether the auxiliary circuit needs to operate for achieving soft switching. The theoretical analysis has been conducted and then verified by using both computer simulation and experimental results.