Torque ripple minimization in DTC induction motor drive using constant frequency torque controller

Direct Torque Control of induction machines is known to offer fast instantaneous torque and flux control with a simple control structure. However, this scheme has two major disadvantageous namely variable inverter switching frequency and high torque ripple. These problems occur due to the use of hysteresis comparators in the conventional DTC scheme, particularly in controlling the output torque. This paper reviews on the utilization of constant frequency torque controller (CFTC) in DTC to solve these problems and at the same retain the simple control structure of DTC. Some extensions of study utilizing the CFTC will be carried out in this paper which can further reduce the torque ripple; this is particularly useful for a system which has limited/low sampling frequency. The feasibility of the CFTC with extended carrier frequency in minimizing the torque ripple is verified through some experimental results.