Page 192 - HVAC Pump Handbook

Rishel_07.qxd 20/4/06 6:29 PM Page 189

Pump Drivers and Variable-Speed Drives

Pump Drivers and Variable-Speed Drives 189

Figure 7.4 Current-source and voltage source drives. (From Keith H.
Sneker, private communication, Halmar Robicon Group, Pittsburgh,
Pa., 1994.)

675-V constant-potential bus. This is an actual requirement for a
PWM drive on a 480-V, 60-Hz motor. The switching frequency is about
1 kHz in this example.
At the beginning and end of the 40-Hz sine wave, the switching is
mostly “off,” but the duty cycle rises to two-thirds at the peak to generate

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