Conducted EMI Propagation in Inverter-Fed AC Motor

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Jarosław Łuszcz, Krzysztof Iwan

Conducted EMI generated by an inverter-fed induction motor drive systems with the pulse with modulation (PWM) are one of the most difficult current technical problem which limits power electronics drive’s evolution. The conducted and radiated emission of PWM drives is essentially related also 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.

Presented identification of the impedance parameters of the evaluated drive system is based on the measurement of impedance characteristics, which allows determining 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 investigated phenomena in the high frequency ranges. Presented analysis and measurement results leads to the conclusion that the impedance characteristic of the converters load can be very helpful for analysing high frequency phenomena in the converter-motor link. The over-voltage and conducted EMI problems in many of ASD application with high power motor and long cable can be clarified by load impedance analysis. The impedance analysis allow to determine the high frequency range where for modelling transmission line based model is evidently necessary, instead of much more simple circuit model.

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