Calculation of Shaft Voltage and Bearing Current of Brushless DC Motor Driven by PWM Inverter

This paper describes the calculated and measured waveforms of shaft voltage and bearing currents of the brushless DC motor driven by PWM inverter. At first, we discussed the current path of the bearing current when unloaded side bearing is conducting and load side bearing is not conducting. Next, we derive a common mode equivalent circuit, and calculate the shaft voltage and bearing current. Finally, to confirm the validity of the derived circuit, calculated waveforms are compared with measured waveforms