Model-based assessment of electromagnetic interference impact on electric motor drive systems

Abstract

Insulated Gate Bipolar Transistors (IGBTs) are extensively used in variable frequency drives due to their exceptional efficiency. However, their high switching frequencies also result in significant common-mode (CM) noise. Common-mode current has long been a major factor contributing to losses in motor drive systems, with bearing currents directly causing electric discharge machining (EDM)-induced pitting on bearings. This thesis presents a comprehensive analysis based on practical measurements, analyses, and calculations of an inverter-motor system driving a 22kW three-phase induction motor. A precise motor model incorporating high-frequency parasitic parameters was developed, then the frequency-impedance characteristics at the inverter side was derived by introducing various impedances into the system. Based on above preliminary experimental result, an LC common-mode filter was selected and designed to provide maximum attenuation. Furthermore, a correlation analysis between the CM current and bearing current obtained during the experiments revealed a linear relationship, confirming the feasibility of effectively attenuating internal bearing currents in the motor by applying a common-mode filter within the inverter-motor system.