Direct Torque Predictive Control Of Induction Motor Based On Voltage Flux Observer

Asynchronous motor has the advantages of simple structure, low noise, low cost, good stability and so on. It has been a research focus in the field of transmission control. In the field of AC speed control, the control of frequency ratio and slip frequency control is developed to vector control and direct torque control, and the control effect is more and more excellent. Direct torque control is a kind of high performance control technology in the field of AC drive, which has the advantages of simple structure, little dependence on the parameters of the motor, fast dynamic response and so on. However, its low speed, high torque ripple, and low accuracy of the stator flux has been hindering the direct torque control of asynchronous motor in the industrial field of wide application.The direct torque control of induction motor is the direct torque control of flux and electromagnetic torque as the control variables, so the accurate observation of the stator flux is related to the control performance. The main problem of stator flux observation is that the low speed dynamic and static performance is poor, for the further analysis of the problem, the traditional stator flux observer is deeply studied. The effects of DC drift, cutoff frequency, stator angle and frequency on the flux observer based on the traditional low pass filter are analyzed. Theory, the paper deduced the low-pass filter is improved for the pure integrator algorithm, based on low pass filter for the amplitude and phase compensation, considering the cut-off frequencies in the vicinity of the dynamic problem, proposed programming the cutoff frequency of low pass filtering algorithm, stator angular frequency error of flux observation performance impact analysis, according to the error of stator angular frequency compensation and put forward a kind of improvement can be programmable low pass filter algorithm. The model of direct torque control of induction motor is established on MATLAB/Simulink, and the theoretical deduction of the optimized low pass filter is analyzed and demonstrated by simulation.The torque ripple is another difficult problem in the direct torque control. The traditional direct torque control has the flux linkage and torque hysteresis width, which makes the system have the torque ripple. However, by reducing the hysteresis band width to suppress the torque pulsation method, the corresponding increase in switching frequency, resulting in increased switching loss, the control system to increase the load. Aiming at problem of high pulse, the prediction algorithm is introduced into the direct torque control system. Analysis original predictive current control strategy and based on this, proposed based on the rotor flux approximation to select the optimal voltage space vector, analysis the method can maintain constant switching frequency of the premise, to reduce the effect of torque ripple. The correctness and feasibility of the method are verified by the Simulink simulation platform.Finally, by building a driving system experimental platform based on DSP chip, detailing the hardware circuit design, expounds the using C language, modular software development, and each interrupt and function flow chart. The advantages of the proposed control algorithm are verified by experimental data and experimental waveforms.