Modelling conducted EMI in inverter-fed AC motor

This paper investigates conducted EMI gener- ated by a inverter-fed induction motor drive systems with the pulse with modulation (PWM). The conducted and radiated emission of PWM drives is essentially related to the electric behaviour of the frequency converter's load which is AC motor and motor cable. Detailed analysis of the impedance characteristics of the converters load (motor and cable) is fundamental to interpret the common and differential mode of emission spectra of the converter. Identification of the imped- ance parameters of the evaluated drive system is based on the measurement of impedance characteristics, which allows to determine the adequate circuit model for different frequency ranges. Obtained results illustrate the different behaviour of the investigated motors for different frequency ranges and explain the influence of the motor power cable on the investi- gated phenomena in the high frequency range. lem to resolve, related to this phenomena, is generation of high frequency currents flowing in all parts of the drive system due to the existence of high levels of the dU/dt of output voltage pulses of the inverter. In the ASDs we can distinguish two components of this currents: differential mode which flows between power lines and common mode flowing between power lines and ground. Each of this current sources can cause serious application problems such as: conducted and radiated electromagnetic emission (EMI), over voltages in the motor winding, bearing currents and many others. To reduce this unacceptable effects a number of com- plex analysis should be carried out. To make this analy- sis possible adequate and reasonable complex models are needed. Lumped elements circuit models are mostly recommended and useful for analysing power electron- ics converters feeding AC motor by using Spice type simulators. This research aims to develop a simple method which allow to determine the approximate frequency ranges in which the lumped element circuit models are relatively effective. Lumped circuit model of the AC motor that allows to analyse the high frequency effects in the motor windings with the good balance between the its complexity and adequacy in the range of fre- quency of conducted EMI.