Research On Control Strategy Of Dual-PWM Variable Frequency Speed Regulation System

In recent years,with the rapid development of power electronics technology,microcomputer technology and automatic control technology,the advantages of AC variable frequency speed regulation technology have significant energy saving benefits,wide speed regulation range,high speed regulation precision and perfect protection function,gradually getting the attention of the majority of users.The object study in this paper is a dual PWM variable frequency system,which improves the defects of conventional inverters using diode uncontrolled rectification or phase-controlled rectification.The system has the advantages of energy bidirectional flow,four-quadrant operation of the motor,unit power factor operation,small current harmonic distortion rate on the grid side,and small voltage fluctuation on the DC side.Therefore,it has good research value and application prospect.The dual PWM variable frequency speed regulation system includes two parts: PWM rectification side and PWM inverter side.Because the control strategy of inverter was mature,the control strategy of Variable Frequency System rectifier is mainly researched in this paper.Firstly,the topology structure and working principle of the rectification part and the inverter part are analyzed.The mathematical model of the rectifier in three different coordinate systems and the mathematical model of the asynchronous motor are established.Secondly,based on the principle of instantaneous active and reactive power,aiming at the shortcomings of traditional control strategies,an improving virtual flux model predictive direct power control(VF-MPDPC)strategy is proposed.The inner loop of the control algorithm uses a virtual flux model predictive direct power control module,by constructing the minimum objective function of active and reactive errors,minimize the value to get the ideal voltage vector.In addition,the two-step prediction method is used to predict the power reference value,which greatly reduces the error caused by the delay.And use repeated control to correct the steady state active and reactive power errors of the system.The voltage feedback loop acts as an outer loop and output stable DC bus voltage.Secondly,the inverter side adopts the Rotor Flux Orientation Control(FOC)strategy to control the speed and torque of the motor.Finally,the dual PWM variable frequency speed control system is simulated and verified by MATLAB/Simulink environment.The experiment results show that the above control strategy improves the dynamic response speed of the system,improves the anti-interference performance of the system,and has better speed regulation performance.