Prediction of Radiated Emissions From a Power Converter by Measuring the
Common-Mode Current in the Attached Cable
- Denys Zaikin ,
- Stig Jonasen ,
- Simon L. Mikkelsen
Abstract
Being able to predict radiated emissions before using an accredited
laboratory can be both time-effective and cost-effective. This study
presents a model for predicting radiated emissions from power converters
by measuring the common mode current in the attached cable. When power
converters are tested for radiated emissions, the attached cables tend
to be thick because of the high currents they carry. Ideally, these
cables leave the chamber through connectors in an opening positioned
precisely at the middle of the bottom of the turntable in keeping with
CISPR 32. However, these connectors are typically not intended for
currents higher than 16 A. Consequently, such cables are usually
inserted through the side wall of the chamber and are necessarily laid
horizontally on the chamber floor. When the turntable is to be rotated
with a device on it during a test, the length of the cable attached to
the device can exceed 10 meters. The proposed model in this study is
based on the transmission line model of a cable loaded with reactive
impedance and the assumption that the current distribution along the
cable follows a sinusoidal distribution law, much like in dipole antenna
theory. The analytic equation of the radiation pattern is derived, and a
simplified approximation equation has also been presented. The proposed
model also works with short, attached cables and is thus universal. The
Maxima software code for automated calculation of the radiated field
from measurement data is supplied as supplemental material. The proposed
model was experimentally validated by running the fuel cell converter
module at 5 kW output power.