Analyzing and Characterizing Common Mode Chokes for Three Phase Systems

Common mode chokes (CMCs) are widely employed to reduce common mode emissions of three phase systems. This work presents an advanced technique for analyzing and characterizing CMCs with three or four windings. The central idea of the method is a modal analysis of the choke, where the modes are based on the modes of the noise signal transmitted by the three-phase line. These modes are defined following the criterion of its suitability from the perspective of electromagnetic interference control. This modal analysis is used to propose a circuit model of the choke that accounts for the impact of high-frequency parasitic effects and, at the same time, allows for a straightforward parameter identification. This parameter identification is achieved by using a characterization technique that makes use of measurements of the response of the CMC in simple connections, whose suitability is justified thanks to the ability of the modal analysis to provide analytical and easy-to-interpret expressions of these connections. This makes also possible to predict and quantify mode conversions caused by the device in the three-phases line. The accuracy of the obtained circuit model within a wide frequency range has been demonstrated by comparing measurements with calculated responses for several three- and four-wires CMCs.