The Development Of PWM Rectifier Applied In Variable-frequency Drive

Variable-Frequency Drive(VFD)is a power electronic converter used in industrial production which usually adopts the AC-DC-AC structure.For most of the low and medium power VFD,the diode front-end(DFE)is usually employed.It may lead to not only serious harmonic pollution and lower power quality,but also negative effects on the lifetime service performance of the device and the reliability of the system.By utilizing the PWM rectifiers,the problems of severe harmonic pollution and low power factor can be improved and the energy can be fed back to grid when motor brakes.This work focuses on the PWM rectifier applied in VFD which takes place of the DFE.Firstly,the structure,principle and mathematical model established under the synchronization reference frame are analyzed.Secondly,to acquire the accurate phase and frequency of the grid,a single synchronous reference frame software phase locked loop method is adopted.The key to the control of PWM rectifier is the control of DC-side voltage and the grid currents.Thus,the double closed loop control and SVPWM current control that is used.Thirdly,a model is built in Simulink for simulation verification,during which the problems of inrush current,overshoot of dc bus voltage and dynamic response are optimized.The adjustable dc bus voltage,sinusoidal current of grid side,unity power factor and THDi lower than 5% are realized in simulation.Lastly,a control system using TMS320F2808 is designed and programmed for the PWM rectifier.A 5.5kW experimental platform of PWM rectifier is established as well.Experiments validates the adjustable DC bus voltage,sinusoidal current of grid side,unity power factor,the efficiency higher than 90% and THDi is within 8% when fully loaded.