Measurement of conducted electromagnetic emissions in PWM motor drive systems without the need for an LISN

This paper presents a technique for measuring the conducted electromagnetic emissions produced by pulse-width modulated (PWM) inverter induction motor drive systems. The method does not require an artificial Line-impedance st abilizing network (LISN) but does, however, allow the emission le, els to b e calculated as if an LISN were present. Testing can be performed when an L ISN is either unavailable, prohibitively expensive, or impractical to inclu de in the supply. This is often the case for large drive systems or for sys tems already installed in the field. A normal RF voltage probe and a spectr um analyzer are used to measure the spectra of the common-mode and differen tial-mode excitation sources due to the inverter switching. Line inductors for high-frequency (HF) isolation are required for some of the tests, but t he cost and complexity of these compared to an LISN is low. Common-mode and differential-mode Thevenin equivalent circuits are then derived from measu red impedances. The emissions for any defined supply; impedance (including an LISN) can then he determined. A laboratory test on a 15 kW PWM drive sys tem is carried out to verify the accuracy and effectiveness of the proposed method.