Research For Speed-Sensorless Direct Torque Control Of Induction Motor

With the development of the technology in power electronics and microprocessor control technology, the technology of the Motor control has achieved great development. It generally experienced the VVVF control, vector control and direct torque control of three stages. Because of the new ideas, simple structure, direct control and excellent dynamic and static characteristics, direct torque control has been widely used. Speed-sensorless direct torque doesn't have to install the speed sensor and has relative small influence by the external environment and can improve the system reliability and so on. All these reasons make it to a research hotspot.The paper firstly introduces the history and the current research situation of direct torque control technology, as well as the direct torque control of the main technical issues involved and the technology of speed sensorless technology. Studying the advantages and disadvantages of several methods, I choose the adaptive flux observer for speed identification. At the same time, in order to improve the poor phenomenon of low-speed, I will use the space vector modulation method instead of the switching table.The paper proposes a simplified steady-state induction motor equivalent circuit (Γmodel). Through the equivalent circuit and motor parameters, I can derive the rotor resistance, stator inductance and rotor inductance value which will be used in the adaptive flux observer. And then studied the Lyapunov stability theory, combined it with the method of adaptive flux observer, derived adaptive speed and stator resistance rate. It can real-time identify speed and stator resistance. According to the derivation of the speed adaptive rates, in MATLAB simulation platform, I will build simulation for the speed sensorless direct torque control system and explain the principle of main modules. Given different conditions through the model, we can observe the experimental results of the acceleration and deceleration, positive and inversion and improved load. Simulation results show that, apart from the without-load to the load moment will be a greater fluctuation, other times through the adaptive flux observer of the estimated speed can be well to follow the motor speed. The fluctuations of the current ad stator flux are very small. It illustrates the speed identification method is feasible.Finally, the hardware and software of direct torque control system based on TMS320F2812 chip have been introduced. The speed identification compiled with C language has been added to the entire software. And then the method has been verified with the hardware platform. Experimental results show that this method is feasible.