Improvement of Direct Torque Control Low-speed Performance by Using Fuzzy Logic Technique

To increase traditional direct torque control (DTC) of induction motor control precision and decrease large torque ripple in low speed, a fuzzy DTC control system was proposed. On the basis of conventional PI regulator, a fuzzy speed PI regulator was designed according to speed error and its rate of change, which could adjust the proportional coefficient k_p and integral coefficient k_I dynamically to adapt the speed variations. A voltage vector fuzzy controller was designed to decrease the torque ripple, which the stator flux angle, the stator flux error, and the torque error were reasonably fuzzified into several fuzzy subsets to optimize selection of the voltage vector. The experimental results show that the proposed fuzzy control system can ensure swift speed response, small overshooting, and high steady speed precision, and can effectively decrease torque ripple in low speed, and enhances the robustness of the whole system