9.3 Voltage and Current Common Mode Component

As mentioned at the beginning of this chapter, unwanted bearing currents appear in the drives with voltage inverters. This occurs because the voltage inverter with classical pulse width modulation (PWM) is a source of CM voltage, which forces the bearing current to flow.

To clarify the CM voltage effect, the voltage inverter structure presented in Figure 9.3 is analyzed.

In voltage inverters, only one of eight transistor switching combinations is possible. Due to the voltage notation presented in Figure 9.3, the inverter output voltages for each of the eight states are presented in Table 9.1.

It is noted that the zero-component voltage changes according to changes in the transistors switching combination. The peak value of the u_{0} voltage is very high and equal to the inverter DC link voltage U_{d}. The u_{0} frequency is equal to the inverter PWM switching frequency. A typical u_{0} voltage waveform is presented in Figure 9.4.

9.3.1 MATLAB/Simulink ...

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