Torque Ripple Reduction in PMSM Drive based on Instantaneous Voltage Control Technique

This paper illustrates the advantage of using the Instantaneous Voltage Control technique for Direct Torque Control (DTC) of Permanent Magnet Synchronous Machine (PMSM). In this method, time error signals are generated directly from the reference phase voltages and the elegance being it directly generating the switching times of different phases without the need for calculating sector in which the voltage vector lies instantaneously. This reduces the mathematical complexity when compared to the existing method and inclines towards the easy implementation. This method reduces the ripple content in both torque and stator flux at different operating speeds. The problem of variable switching frequency occurring in conventional DTC at different operating speeds is addressed in this method. Especially at lower speeds, the frequency of occurrence of null vector increases which in turn increases the ripple content in the machine dynamics. This issue is solved by maintaining constant switching frequency independent of operating speed achieved by space vector pulse width modulation (SVPWM). A comparison is made between the conventional DTC and proposed DTC. From simulation results, it is observed that ripple content in torque and stator flux have reduced in the proposed algorithm when compared to conventional DTC.