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A Universal High-Frequency Three-Phase Electric-Motor Model Suitable for the Delta- and Star-Winding Connections

A universal high-frequency three-phase electric-motor model to be used in the design process of the electric-motor drive systems is proposed. The model can be combined with the models of the filter, cable, and inverter to form a complete drive system. It allows for a common and differential-mode high-frequency analysis in studying the bearing currents, electromagnetic interference, and overvoltages in the motor windings caused by the high-frequency reflections. The model phase is symmetrical meaning that the beginning and end of each phase are equal and the central part is inserted between them. This enables modeling of both the delta and star-winding connections of the three phases. The equations used to calculate the model parameters are presented. They are based on the common and differential-mode impedance measurements. The model can be simplified when considering only electric-discharge machining bearing currents, as they are affected only by the common-mode states. A simplified model to be used in the delta-winding connection is also presented. The model-calculated common and differential-mode impedances are compared with the impedances measured on a 6.5-kW outer-rotor brushless direct-current motor. This paper ends by providing the obtained simulation and measurement results for the common and differential-mode currents and bearing voltages of the studied three-phase delta-winding-connected electric motor.