CONDUCTED ELECTROMAGNETIC EMISSIONS IN INDUCTION-MOTOR DRIVE SYSTEMS PART II - FREQUENCY-DOMAIN MODELS

Predicting conducted emissions in pulsewidth modulation (PWM) inverter induction motor drive systems requires various frequency-dependent ef fects to be considered, A frequency domain method has advantages in su ch cases compared to a time domain approach. Based on the modal analys is presented in Part I, this paper develops frequency domain models to evaluate the spectra of the conducted emissions directly. The common and differential mode excitation sources are modeled in the frequency domain and related to the switching functions of the PWM inverter. Net work models are established where the induction motor is represented u sing its frequency-dependent impedance characteristics, which can be o btained from measurements. The influences of system unbalances and of transmission-line effects due to long cables are investigated. Predict ed emission spectra are compared with laboratory measurements and thos e derived from the time domain simulation. Pt is found that the agreem ent is good. The proposed method allows emission spectra to be predict ed without recourse to specialist circuit simulators.