DSVM and duty ratio control combined direct torque control for bearingless induction motor

In low-speed, direct torque control has such problems, like inevitable serious ripples in flux, disorder of the switching frequency, and else. Combined discrete space vector modulation (DSVM) with direct torque control (DTC) for bearingless induction motor torque control. Through the multi-torque hysteresis comparator to increase the number of target vectors, and reduce the torque ripple. Because fix the duty ratio, it can not obtain the expectant torque. This paper introduces the duty ratio control in DSVM, improves the process of vector modulation, so we get a system which has advantages of simple structure, fast response, and wide speed range. In the end check this system, certified the system can restrain torque ripple, reduce current harmonics significantly in low-speed.