Investigation of EMI noise transfer characteristic of variable speed drive system

Electromagnetic compatibility is becoming an essential consideration for variable speed drive systems. Many methods are proposed to predict the conducted electromagnetic interference level. They ask to model all components of the drive system including cable and motor. In this paper, it is supposed that the measured noise level is determined in two phases. The first is the main noise source level and the second is the conversion efficiency from main noise source level to measured noise level. The noise transfer characteristic is investigated to understand the conversion mechanism. A transfer ratio is defined afterwards which is independent of the cable and motor. It can be used to evaluate the EMC design of a converter. A simplified model is used to explain this characteristic. Laboratory tests on a 12 kW PWM drive system are carried out to verify this hypothesis. Thorough test results are included in this paper