Analysis of EMI in a variable frequency drive through modelling and experimental validation

Abstract

The fast voltage and current transitions in the variable frequency drives contribute to various high frequency disturbances in power systems and equipment connected to it. Developing high frequency model for the devices and their analysis are essential for predicting the electromagnetic interferences (EMI) issues and designing suitable mitigation methodologies. In this paper it is shown that a high frequency model of an induction motor can be developed by the impedance measurement at the terminals of the standstill machine. The model is verified through actual measurements by assembling a Line Impedance Stabilization Network (LISN) for conducted emission measurement. In addition to the Electromagnetic Compatibility (EMC) issues at the utility supply side, the conducted emission also causes unwanted Electromagnetic Interference effects at the motor side. Hence an EMI filter is to be incorporated at both sides of the drive. It is seen that by suitably selecting the switching frequency and the inverter configuration, the EMI filter at the motor side can be dispensed with.