Bearing currents and shaft voltages of an induction motor under hard and soft switching inverter excitation

Bearing currents and shaft voltages of an induction motor are measured under hard and soft switching inverter excitation. The objective is to investigate whether the soft switching technologies can provide solutions for reducing the bearing currents and shaft voltages. Two of the prevailing soft switching inverters, the resonant DC link (RDCL) inverter and the quasi resonant DC link (QRDCL) inverter, are tested. The results are compared with those obtained using the conventional hard switching inverter. To ensure objective comparisons between the soft and hard switching inverters, all inverters were configured identically and drive the same induction motor under the same operating conditions when the test data is collected. An insightful explanation of the experimental results is also provided to help understand the mechanisms of bearing currents and shaft voltages produced in inverter drives. Consistency between the bearing current theory and the experimental results has been demonstrated. Conclusions are then drawn regarding the effectiveness of the soft switching technologies on the solution to the bearing currents and shaft voltages problems.

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