BEARING CURRENTS AND SHAFT VOLTAGES OF AN INDUCTION-MOTOR UNDER HARD-SWITCHING 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 sol utions for reducing the bearing currents and shaft voltages. Two of th e prevailing soft-switching inverters, the resonant de-link inverter a nd the quasi-resonant dc-link inverter, are tested. The results are co mpared with those obtained using the conventional hard-switching inver ter. To ensure objective comparisons between the soft- and hard-switch ing inverters, all inverters were configured identically and drove the same induction motor under the same operating conditions when the tes t data were collected. An insightful explanation of the experimental r esults is also provided to help understand the mechanisms of bearing c urrents and shaft voltages produced in the inverter drives. Consistenc y between the bearing current theory and the experimental results has been demonstrated, Conclusions are then drawn regarding the effectiven ess of the soft-switching technologies as a solution to the bearing cu rrent and shaft voltage problems.