Modified Direct Torque Control of Induction Motor Drives

Abstract

Over past years, direct torque control (DTC) has proven to be a powerful technique for controlling induction motors since, its simple structure, fast performance, and robustness. However, conventional DTC has a major problem in selecting the optimum voltage vector in order to provide fast torque response, due to the nature of the hysteresis controller. This thesis presents a new control topology for DTC, which enables fast torque response and reduced steady state ripple. The proposed scheme utilizes an optimized inverter voltage vector selection process ensuring a higher rate of torque increment during transient periods. Further, two nonlinear adaptation mechanisms are used to replace the hysteresis controllers thus obtain enhanced torque and stator flux regulation. One scheme is based on sliding mode theory and the other method is based on fuzzy logic strategy. A comprehensive simulation study has been performed to evaluate the performances of the proposed sector-advancing algorithm under the two nonlinear control methodologies. The corresponding simulation results and discussion are presented for each section. It is concluded that the proposed DTC algorithms with sliding mode and fuzzy logic strategies demonstrate better characteristics in both transient and steady state operation with regards to the conventional DTC.