Efficiency improvement of converter for switched reluctance motor drives by mixed parallel operation of IGBT and MOSFET

This paper presents a method to improve the efficiency of a standard asymmetric half-bridge converter for 3-phase, 12/8 switched reluctance motor (SRM) drives at low speed operation. At that speed range, the converter operates mainly in current chopping modes. The proposed method employs mixed parallel operation of IGBT/MOSFET pairs. The technique is aiming for minimizing the turn-off switching losses of IGBT which are the main chopping switches. MOSFET are placed in parallel with each IGBT in order to momentarily conduct the phase current during IGBT´s turn-off intervals. While the MOSFET is on, the voltage across the IGBT is close to zero resulting in substantially decreased turn-off loss. Those fast switching MOSFET later instantaneously turn-off the current with almost lossless. The algorithm is verified by computer simulation and experimental results. The results have satisfactorily shown validity of the proposed concept. Furthermore, performance of the proposed strategy is superior to those of the typical hard switching technique and the conventional soft switching scheme using optimum sized snubber capacitors.