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Characterization and Design of Three-Phase EMI Noise Separators for Three-Phase Power Electronics Systems

Fig. 1. Three-phase system noise measurement.
EMI filter design usually begins with noise measurement. Finding the best methods to accurately measure the noise voltage spectrum and to separate differential-mode and common-mode noise has become a fundamental challenge for EMI filter design. Previous work on noise separation work well for single-phase DC systems, but the same tool is needed for three-phase systems, as shown in Fig. 1.

In this paper, three-phase noise is first analyzed using a symmetrical component theory. Three-phase noise separators are modeled and characterized using symmetrical component theory and S-parameters. The critical formulas used to evaluate a three-phase noise separator are derived, and a function scheme and circuit structure for three-phase noise separators are proposed based on the theory developed, as shown in Fig. 2 and Fig. 3. The techniques for designing a high-performance, three-phase noise separator are explored, and a three-phase noise separator prototype is built, measured, and evaluated using the theory developed in this paper. The prototype is successfully used to measure electromagnetic interference in a practical three-phase power electronics system.

Fig. 2. DM noise separator circuit.
Fig. 3. CM noise separator circuit.
Fig. 4. Prototype of a three-phase noise separator.