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This paper proposes a method of eliminating common-mode voltage (CMV) and shaft voltage in dual three-phase motors using the carrier phase shift of space vector pulse width modulation (SVPWM). SVPWM for the dual three-phase motor is simply implemented using two traditional three-phase SVPWM structures. The representative work of the study is to eliminate the shaft voltage by applying the carrier phase shift method due to the cancellation of CMV. It was verified that the proposed method could reduce the shaft voltage with a simple technique, rather than applying a complex algorithm to reduce it. Also, the motor current and torque behaviors are analyzed to confirm that the proposed method does not affect the motor characteristics. The proposed method has been analyzed based on an equivalent circuit model and it has been verified through the experiment that the shaft voltage is simply eliminated by applying the proposed method.INDEX TERMS Bearing fault, common-mode voltage, dual three-phase motor, pulse width modulation inverter, shaft voltage.

Common-Mode Voltage (CMV) induces shaft voltage and bearing current due to the electrical interaction with the parasitic capacitance of the motor. CMV, shaft voltage, and bearing current are considered the major causes of bearing fault. Motor fault in a traction system poses a risk of accidents. Therefore, it is necessary to reduce the CMV and the shaft voltage to ensure the reliability of the bearing. However, some existing CMV reduction methods are based on asynchronized space vector pulse width modulation (SVPWM), which will cause unacceptable harmonic distortion at a low switching frequency. Alternatively, some CMV reduction methods based on synchronized SVPWM burden the processor because they require a lot of calculation. In this paper, the method to reduce CMV and shaft voltage is proposed using carrier wave phase shift in SVPWM. CMV is explained in traditional SVPWM, and CMV is reduced by shifting the carrier wave phase of one phase. The simulation model is constructed through MATLAB/SIMULINK and Maxwell 2D/Twin Builder. Considering the proposed method, CMV, shaft voltage, and bearing current are analyzed by an equivalent circuit model. Moreover, the output torque behaviors with different input currents are analyzed through the simulation.

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