Research Of Model Predictive Torque Control For Asynchronous Motor Based On Dead-beat Control

Asynchronous motor is a kind of motor which is widely used in production and life and has three kinds of speed regulation methods:variable pole speed regulation,variable slip speed rate regulation and frequency conversion speed regulation.Frequency conversion speed regulation is the most energy-saving way among the three and is advocated and encouraged by the Chinese government.With the development of power electronic technology and integrated circuit,model predictive control which has good dynamic performance has been widely used in frequency conversion speed regulation of AC motor.The model predictive torque control studied in this dissertation is a form of model predictive control in AC motor control,which takes electromagnetic torque and stator flux linkage as the control targets.The mathematical model of asynchronous motor is firstly established in this dissertation based on space vector and coordinate transformation theory,next the iterative expressions of voltage current model and current speed model for stator flux linkage calculation in digital system are derived.Also the switching voltage vector of stator in star-connection and in delta-connection under the two-level voltage source inverter is deduced and compared,and then the realization process of model predictive torque control of asynchronous motor based on modified Euler method is given.Aiming at the problem of one-shot delay of digital system,the realization process of model predictive torque control with delay compensation is deduced.Then aiming at the problem of poor performance in the control of electromagnetic torque and stator flux linkage with model predictive torque control resulting from fixed amplitude and phase of the switching voltage vector,a strategy of model predictive torque control based on dead-beat control is proposed.Firstly,the six effective voltage vectors are expanded into twelve non-zero voltage vectors in order to improve the control effect in phase aspect.Then,according to the principle of dead-beat control on electromagnetic torque,the action time of each voltage vector is calculated.Next the state variables and the electromagnetic torque are predicted using the equivalent voltage vector calculated by the action time which satisfies the change trend of electromagnetic torque.Finally,the the optimal equivalent voltage vector is chosen by the cost function,after that the duty cycle of each phase bridge arm switch is calculated according to SVPWM modulation with the results output to the inverterFinally,the feasibility and effectiveness of the proposed method is verified by MATLAB/Simulink simulation and experiment in the experimental platform based on DSP.