Modeling And Suppression Of Conducted Electromagnetic Interference In Variable Frequency Drive System

As an improvement solution to the operation efficiency of motors as well as the energy consumption in production,Variable Frequency Drive System(VFDS)has been widely used in kinds of industrial fields.With the advances in control and electronics,SCRs(silicon controlled rectifiers)are replaced by IGBTs(insulated gate bipolar transistors),and PWM(Pulse Width Modulation)becomes the standard approach to operate power modules.High slew rate of voltage dv/dt and high slew rate of current di/dt generated by fast switching operation introduces severe conducted electromagnetic interference(EMI)to components of this system as well as devices around,which hinders the development of VFDS.As a result,it is of great theoretical and practical significance to study and suppress the conducted EMI in VFDS.On the research fundamental of conducted EMI mechanism in VFDS,this paper models the conducted EMI characteristic in the time domain for a VFDS composed by a domestic 7.5kW converter.A novel parameter extraction method for High-Frequency model of induction motor is proposed in this paper.Compared with conventional extraction with expensive impedance analyzer,this method obtains impedance spectrum of motor through online time-domain measurement with the oscilloscope and high frequency probe.A new thought of "modeling-rules of filtering parameters effect-filter design"is utilized in this paper.Based on the conducted EMI model established above,this paper studies the effect of key parameters,especially the filtering parameters,on conducted EMI in the VFDS through simulation in Matlab.Then,two different filter designs are presented according to the rules concluded from model simulation.Experimental results verify that these two filter designs are met with the requirements of EN55011 Class A2 and Class A1 separately.Besides the hardware filter design for VFDS,this paper studies the software suppression methods-Reduced Common-Mode Voltage PWM(RCMV-PWM).The reported RCMV-PWM strategies are reviewed and classified.Suppression principles,problems in implementation and modifications of CMV mitigation techniques based on SVM,CBPWM and other RCMV-PWM strategies are described in detail.The performances of main RCMV-PWM strategies have been simulated and compared in terms of DC voltage utilization,switching loss,output harmonic performance and so on.Features of presented RCMV-PWMs and expected advancements have also been discussed.