The impact of conventional and wide bandgap semiconductor PWM inverter EDM bearing currents on motor bearings.


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The pulse width modulated (PWM) ac motor drive has revolutionized the industrial sector by drastically reducing energy consumption and improving the efficiency of industrial processes. To continue the transition towards an electrified society, power density in electric motor drives must continue to increase. To this end, motor drives of the future will contain wide bandgap (WBG) semiconductor devices such as silicon carbide (SiC) and gallium nitride (GaN). The introduction of these WBG devices into motor drives comes with exacerbated application issues due to faster dv/dt device turn on/off times and relatively higher switching frequencies for the same device cooling requirements as conventional silicon (Si) devices. A key issue produced by these PWM motor drives is premature bearing failure due to an increase in vibration from the damage caused by electric discharge machining (EDM) bearing currents. This dissertation presents detailed discharge circuit modeling of motor bearing currents, investigates the impact of discharge energy on the damage produced on the bearing race and ball surfaces through the use of a finite element (FE) model, presents a novel technique to statistically characterize EDM amplitudes over various motor operating conditions, and uses this statistical approach along with experimental evidence to predict a bearing’s lifetime. The work presented here is a key contribution to developing intricate predictive maintenance models for motor bearings, which are of great value to industrial operators because of the enormous costs associated with motor down time.



EDM bearing currents. PWM motor drive. SiC. Lifetime prediction. Common mode voltage. Common mode current.