Research On Torque Ripple Reduction Of Direct Torque Control Of Induction Motor

Direct Torque Control (DTC) occupies an important position in the AC drive technology for the merits of simple structure, fast torque response and low sensitivity to motor parameters. However, the further development and application of DTC were set back by its disadvantages such as variation of switching frequency, high torque ripple and the excessive starting current. The reason of high torque ripple was investigated in this dissertation and the related methods were proposed to minimize the torque ripple.The electromagnetic torque ripples along with the reference torque generated by PI speed regulator, and the PI speed regulator was optimized in order to output a more smooth reference torque, which provides a better reference for subsequent research to reduce torque ripple. After analyzing mechanism of torque ripple in theory, several main factors that influence torque variation are put forward. According to the relationship of stator flux and the torque variation, a method to reduce torque ripple, which reduces the amplitude of stator flux when motor bears light load under the condition of varying load, is provided. Numerical simulation result shows effectiveness of the method. Additionally, it is the main reason of high torque ripple of conventional DTC that to choose a single voltage vector from a low number of voltage vectors and applies the selected voltage vector in the whole sample time. Accordingly, the scheme of Discrete Space Vector Modulation DTC (DSVM-DTC) is used to solve the problem of high torque ripple. And based on the conclusion which stator flux and torque value generated by plus voltage vector, minus voltage vector and zero voltage vector will be changed as motor's speed varies, the space vector table of DSVM-DTC is improved and numerical simulations have been carried out to validate the improved DSVM-DTC.At last, the primary circuit of AC-DC-AC and the control circuit based on TMSLF2812 DSP were designed to realize DTC scheme and this paves the way for further research.