Conducted electromagnetic emissions in induction motor drive systems part I: Time domain analysis and identification of dominant modes

Stray components distributed in a pulsewidth modulation (PWM) drive system form parts of resonant circuits which can be excited to produce radio frequency (RF) noise driven by the pulsed switching action of the power devices. The dynamic response of such circuits is complex. It is essential to identify the dominant oscillation modes in the system so that electromagnetic interference (EMI) reduction techniques can be effectively implemented. This paper (Part I) investigates the mechanisms of conducted EMI emissions associated with a typical PWM inverter induction motor drive system. A numerical model, which includes the high-frequency effects within the machine, is established to evaluate the emissions in the time domain. The dominant high-frequency current paths are identified, and this allows the oscillation frequencies to be predicted from knowledge of the component values. The analysis is confirmed using laboratory measurements. Simplified frequency domain methods for direct calculation of the emission spectra based on the dominant high-frequency current paths are discussed in Part II.