Research On The Application Of Direct Torque Control In Multilevel Variable Speed Drives

With the development of multilevel inverter technology, research interest in high performance control method of high voltage and high power drives has grown significantly in the past few years. The characteristics of traditional direct torque control (DTC) and cascaded multilevel inverters are analyzed firstly. Mathematical model of voltage sources inverters; induction motor and three-phase H-bridge inverters are introduced. An improved direct torque control method based on space vector modulation is presented, aiming at the drawbacks and corresponding improvements of traditional DTC method. The system control strategy and digital implement method are designed, comparing with the characteristics of multilevel frequency control system. Simulation results of the proposed control strategy are presented to illustrate the reduction of torque and current ripple. Feasibility of the control algorithm is verified in a multilevel variable-speed drives experimental system. These works provide an idea for the industrial application of DTC in multilevel variable-speed drives.