Application Research On PWM Rectifier In Variable Frequency Adjustable Speed System

With the development of new power electronic devices,high-performance digital processing technology and advanced control theory,variable-frequency speed regulating devices have become the key equipment in industrial production.However,diode rectifier bridge is applied to the general inverter,which has problems such as serious input current distortion,low power factor,irreversible power transmission and pump voltage.Therefore,PWM rectifier is used to replace the diode uncontrolled rectifier as an active front end,which has the advantages of low current harmonics,unit power factor control and bidirectional power flow,etc.In this paper,the basic principle of dual-PWM variable-frequency speed regulation system is analyzed in detail.In order to suppress the effect of load disturbance on DC bus voltage,linear active disturbance rejection control(LADRC)method for PWM rectifier is studied,and voltage loop LADRC controller is designed.For traditional three-phase phase-locked loop(PLL),the larger problem is that the angle of grid voltage detected by PLL is seriously distorted under the condition of grid voltage unbalance,which reduces the performance of PWM rectifier,a new decoupled dual synchronous reference phase-locked loop(DDSRF-PLL)is emphatically discussed.The vector control principle of asynchronous motor based on rotor filed orientation is analyzed,and in view of the defects in the high and low speed segments of the conventional rotor flux observer,an improved rotor flux observer is adopted.For traditional dual-PWM rectifier and inverter independent control system,the larger problem is that DC bus voltage greatly fluctuates when inverter side load suddenly changes,the control method of output power feedforward compensation is studied.On the basis of the above theoretical research,simulations of PLL,PWM rectifier and dual PWM variable-frequency speed regulation system are performed in Matlab/Simulink,and an experimental platform based on digital signal processor TMS320F28335 is built,the results of simulations and experiments show the correctness and feasibility of the above control methods.