High-Frequency Modeling of Delta- and Star-Connected Induction Motors

In this article, a high-frequency (HF) six-port delta- and star-connected three-phase induction motor model is proposed. The model consists of multistage RLC circuits, which include the mutual inductances between the phases. The three-phase HF motor model is derived from common-mode (CM) and differential-mode (DM) equivalent circuits, which are extracted from CM and DM measurements on the motor. A methodology is developed to consider the nonlinear DM inductance effect in the low-frequency (LF) range. The per-phase circuit is symmetric concerning the begin and end points. This symmetry allows us to connect a star configuration into a delta configuration by simply changing the phase connections of the proposed three-phase circuit without recalculating the parameters and vice versa. The three-phase motor model is eventually combined with external circuitry and simulated by a standard circuit solver. The proposed model allows impedance predictions with good accuracy up to 100 MHz. The method is verified with two induction machines, which have 3- and 11-kW rated powers. The proposed HF six-port three-phase motor model can be used for decoupled CM and DM noise predictions as well as for six-port mixed-mode noise prediction.