Research Of Three-Phase PWM Rectifier In Electric Servo Loading System

In the development of motor control systems,the servo loading system is an important semi-physical simulation device.Due to its advantagements as small-size,flexible and stable control mode,strong signal tracking capability,high loading resolution,clean working environment and no pollution,the Electric Servo Loading System has gradually replaced the traditional hydraulic loading system and mechanical loading system.Because of its energy bidirectional flow and strong anti-interference ability,the Three-phase PWM Rectifier has been widely used in electric servo loading systems.This paper studied the dynamic response speed and anti-interference ability of the Three-phase PWM Rectifier.According to vector control theory,the time domain mathematical models of three-phase voltage source PWM rectifier are established in three-phase static coordinate system and two-phase synchronous rotating coordinate system respectively.According to the two different working modes of three-phase PWM rectifier in electric servo loading system,the rectification model and energy feed model of the rectifier are further discussed.The current decoupling control algorithm of rectifier DQ axis in synchronous DQ coordinates is studied.In the cases of load increased suddenly and decrease suddenly,this paper stu,died the response speed and anti-interference ability of Three-phase Voltage Source PWM Rectifier,controled in double closed-loop PI control.Combined with the existing fast response control strategy and coordinated control method,this paper proposed a kind of control stragy,named variable iq load power feedforward control.When the load changes abruptly,the capacitor voltage change rate is feed-forward to the given value of q-axis current,and the load power is feed-forward to the current loop.By compensating the active current,the power balance between the rectifier and the inverter is coordinated,thus avoiding the problem of th,e rectifier res’ponse lag caused by the output saturation of the PI controller in the voltage loop.Aiming at the problem that the traditional software phase-locked loop technology is insufficiently locked under the unbalanced power grid,combined/with the DSC delay fi,ltering algorithm,the traditional software phase-locked loop is improved Through two delay filtering,the normal operation of the phase-locked loop is realized under the unbalanced power grid.For the inrush current phenomenon accompanying the rectifier start-up process,the inrush current segmentation suppression method is studied:the current limiting resistor is used to suppress the current in the uncfontrolled rectification phase;in the PWM boost rectification phase,the variable iq control algorithm and the voltage command ramp given algorithm are used to slow down the step voltage impulse response of the system ·The Three-phasc PWM Rectifier is simulated in the Simulink environment.The TMS320F28335 is used as the digital controller,and the SiC MOSFET of the type SCT20N120 is used as the switching device.The experimental platform of the three-phase PWM rectifi,er is designed.Combined with hardware and theoretical researches,the system software is planed.The fast response characteristics and strong anti-interference ability of the three-phase voltage-type PWM rectifier are verified by experiments,which can meet the application requirements in the electric servo loading system.