Symmetrical and Asymmetrical H-Bridge Multilevel Inverter for DTC Induction Motor Drive Automotive Applications

Several works have been reported in the literature on multilevel inverters topologies, control techniques and applications. However, there are few works that actually discuss or evaluate the performance of induction motor drives associated to three-phase multilevel inverter. This paper presents then a comparison study for a cascaded H-bridge multilevel DTC induction motor drive. In this case, symmetrical and asymmetrical arrangements of five and seven level H-bridge inverters are compared in order to find an optimum arrangement with lower switching losses and optimized output voltage quality. The carried out experiments shows that an asymmetrical configuration provides nearly sinusoidal voltages with very low distortion, using less switching devices. Due to the small dv/dt’s, torque ripple is greatly reduced. In addition, it generates a high switching frequency output voltage with less switching losses, since only the small power cells of the inverter operate at high switching rate. Therefore a high performance and also efficient torque and flux controller is obtained, enabling a DTC solution for multilevel inverter powered induction motor drives.