Research On Speed-Sensorless Direct Torque Control System Of Induction Motor

Direct Torque Control (DTC) of induction motors, which has been developed in the recent decade, is a powerful control method for motor drives. Following the vector control technique, the quick development of DTC makes itself a new high performance AC driving technique paralleling to the vector control. In recent years speed-sensorless DTC control of induction motor has gained much attention on the application and research of AC speed-adjustable system.In order to weaken the torque ripple and improve the accuracy of the observation, the author changes the method of regulating stator flux, the machine parameters are adapted on-line and the method of speed estimate was improved. The works in this paper are listed as follows:In this thesis, according to the faults of traditional direct torque control and the requirement of an induction motor's control strategy, the author changes the method of regulating stator flux to make its path approximate to a circle as possible as could and put forward a new way to use a three-value torque regulator. Traditional direct torque control uses two-value torque regulator which makes zero voltage vector work long and makes flux shape bad seriously and makes response time long when the speed of induction motor is very low or drops down quickly.To deal with the defect of traditional six-section control of voltage select table, twelve section control method of voltage select table and the implementation are presented. At the same time, the classic switching table is replaced with a two-level hysteresis band for the flux, and a five-level hysteresis band for the torque, which widens the speed range of drive system.The speed estimation without speed sensor is an important trend of modem AC drive. This thesis has probed several primary methods of speed estimation and analyzed emphatically the method of speed estimate based on model reference adaptive system. The accuracy of the rotor speed estimation in speed sensorless direct torque control system of induction motor is sensitive to parameter errors of the internal machine model. To eliminate the speed estimation error, the machine parameters are adapted on-line, based on a mutual model reference adaptive system (MRAS). An improved mutual MRAS model is built with variable parameters.Simulink is an applying tool box of MATLAB and can be used for constituting model, simulation and analyzing. This thesis constitutes DTC simulations with twelve section control and speed sensorless technology. The simulation results prove that above methods are feasible.At last the thesis introduces the design method of control system with TMS320F2407A. This control method has simple counting and strong function and great developing value.