Torque Ripple Reduction in Six-phase Induction Motor Drive using DTC Technique

This work presents a Direct Torque Control (DTC) technique for a six-phase asymmetrical induction motor fed with a two-level six-phase inverter for torque ripple minimization. By increasing the levels in conventional torque hysteresis controller, high torque ripples (which is a major problem in basic DTC) can be minimized and dynamic torque response can be improved. But in practice, the inevitable delay existing in the implementation of hysteresis controllers will cause undesirable overshoot and undershoot in the torque response resulting in high ripples. Also, the torque decreasing rate is comparatively higher than that of torque increase which further boosts the torque ripples and degrades the steady-state performance. A five-level torque controller with modified output status is presented here by taking into account the above two limitations. The auxiliary subspace which is inherently present in a six-phase machine causing stator current distortion is also controlled by generating virtual voltage vectors. The resulting DTC drive is validated using MATLAB/Simulink software.