The Research On Direct Torque Control System Of Induction Motor Driven By Multi-level Inverter

Direct Torque Control (DTC) is a new developing AC motor speed control strategy with simple structure and easy implementation but high performance. In this paper the basic theory of DTC is introduced briefly, and three kind of flux-models of induction motor are constructed in MATLAB. The simulation results show that the u-n model with PI regulator to compensate voltage drop caused by the resistance of stator is much better in performance than other models. A kind of simulation model of direct torque control system is established use this u-n model, the results show that the conventional DTC has some drawbacks such as large ripple in low speed region and switch frequency variation according to the change of motor parameters and motor speed. Because the tight relations among the voltage vector, stator flux linkage and torque, we proposed a new kind of control strategy based on three-level inverter. Take the advantage of more voltage vector is available, we tried to used the inter-mediate voltage to replace the traditional selector and found that the demagnetization problem is resolved when the motor running in low speed region. Further study about the multi-level inverter is proposed in the following chapters. The voltage vector selecting rules are listed out in the form of tables, also a kind of application scheme of DTC based on the Flying Capacitor Five-level inverter is presented.In the last part, the hardware design of real-time DTC system driven by three-level inverter is proposed based on DSP (TMS320F240), the central control circuit and PWM signal generation circuit are described in detail, and also parts of the main program flow charts of the control system are given out.