Reduction of shaft voltages and bearing currents in five-phase induction motors

Induction motors are commonly used in numerous industrial applications. To maintain a reliable operation of the motor, it is important to identify the potential faults that may cause the motor to fail. Bearing failures are one of the main causes of motor breakdown. In some cases, bearings fail due to the electric current passing through them. In this paper, bearing currents in inverter driven five-phase induction motors are studied and a novel solution is proposed. First, theories of shaft voltage and bearing current are presented. Then, new switching patterns are proposed for the five-phase induction motor. The system is simulated and the results of the new switching patterns are compared with the conventional switching pattern. Finally, the new schemes are experimentally tested using a digital signal processor (DSP) to control the power converter. The experiments verified that the new switching pattern could reduce shaft voltages and bearing current without affecting motor performance.