EMI characterization with parasitic modeling for a permanent magnet motor drive

In this paper, a permanent magnet AC motor drive is tested extensively, and the prominent frequencies in EMI spectrum are identified for their relationship with the noise sources and their propagation paths. Switching characteristics of the power MOSFETs are evaluated by simulation and experiment for the noise source modeling. Major parasitic components and noise propagating mode paths are measured with a time-domain reflectometry method and verified with a 3-dimensional finite element analysis tool. The inverter circuit model is then constructed using pertinent parasitic inductance and capacitance values for the active device modules, the passive components, the leads, and the interconnects. To verify the validity of the inverter model, a comparative study is performed with computer simulations and hardware experiments. The fundamental mechanisms by which the EMI noises are excited and propagated are analyzed, and the significant roles of parasitic elements coupling with device switching dynamics in EMI generation are examined. The results indicate that the identification of parasitic inductance helps verify the noise peaking frequencies. The noise mitigation effects of added DC choke and RC snubbers are also characterized and proven with both simulation and measurement.