Page 193 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

POWER ELECTRONICS, RECTIFIERS, AND PULSE-WIDTH MODULATION INVERTERS

9.20 CHAPTER NINE

FIGURE 9.29 The effect of an inductive load on the current and voltage waveforms of the
circuit shown in Fig. 9.27.

External Commutation Inverters
The two commutation techniques used for inverters are external commutation and self-
commutation. External commutation inverters require energy from an external motor or
power supply to turn off the SCRs (Fig. 9.31). A three-phase synchronous motor is con-
nected to the inverter to provide the countervoltage needed to turn off one SCR when its
companions are fired.

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