Study On Induction Motor Direct Torque Control System

Direct Torque Control (DTC) scheme has been widely studied and used during recent years due to its novel strategy, simple control structure and excellent dynamic and static performances. In this thesis, a direct torque control system of induction motor is studied. The thesis includes four parts.In the first part, the paper presents the developments of AC speed regulation technology and electric traction. It also analyzes the principle of induction motor direct torque control. The two stator flux observing models of u-i and i-n are derived , and the proper area and features of these two models are analyzed, then a u-n model which is suitable in the range of all speed is derived. The u-n model features: using i-n model in the low speed and u-i model in the high speed range. The transition between low speed and high speed can be smooth, as the current regulator can compensate the observed current, the precision of the observation is raised greatly.The second part mainly introduce the application of direct torque control in AC electric locomotive system. Based on traction characteristics of electric locomotive, the different torque control strategies are applied in the different ranges of speed:(1) Indirect torque control with circular stator flux in the low-speed range.(2) Direct torque control with hexagon stator flux in the high-speed range.(3) The torque is adjusted by setting different references of the stator flux in weaken flux area. The system power is invariable.The elementary principles and features of these torque control methods are introduced respectively. The simulation model of DTC is set up by using MATLAB/SIMULINK. And the simulation results are given which proves the feasibility of these control strategies.In the third part, the experimental system is introduced. The system mainlyincludes control circuit based on the digital signal processor (DSP) TMS320C32 and inverter circuit based IPM. The debugging and experimental research of open-loopSVPWM system have been done.Finally, the speed sensorless direct torque control is presented. The thesis deduces the identification method of rotor speed based on model reference adaptive system (MARS). The simulation model is set up and the results are also given.