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EMI Behavioral Models of DC-Fed Three-Phase Motor Drive Systems

Fig. 1 : Approximate CM equivalent circuit of the model impedances in motor drive
Behavioral electromagnetic interference (EMI) models based on Thevenin equivalents are pro-posed for a DC-fed three-phase motor drive system. Both common-mode (CM) and differential-mode (DM) noise models are developed to accurately predict the total EMI noise in accordance with the DO-160 standards for aerospace applications. Beyond the switching frequency of the drive, the CM noise model is found to behave like a two-port linear network and is shown to pre-dict changes in the input-side EMI due to any changes in the load-side parameters, or vice ver-sa. Simplified one-port behavioral models for DM noise are then used to predict the total noise at both the input and output sides of the motor drive. Such models can be very useful in system level EMI analysis and also in understanding how EMI filters and harnesses affect the overall EMI in a motor drive system. The models run in the frequency domain and are validated with experiments up to 30 MHz.

Fig. 2. CM impedance of the external network after implementation of RC shunt (shunt condition)
Fig. 3. Output DM impedance of the motor drive and the DM impedance of the network at the output side