Introduction to Electrical Power and Power Electronics

385AC–DC–AC Converters

the past but was generally out of favor for many years due to complex controls and

many more switching devices, which makes it more expensive, less reliable, and less

efcient. The new power electronics devices and new cycloconverter designs, how-

ever, are gradually bringing this old technology into a new light.

Example 14.10

A 3-ph, 5000-hp, 12-pole, 60-Hz synchronous motor uses a cycloconverter to

vary speed. Determine the maximum speed at which it can be operated to limit

the harmonics to the generally acceptable level.

Solution:

The maximum output frequency of the cycloconverter must be limited to one-third

of the input frequency, that is, 60/3 = 20 Hz in 60-Hz drives. At this frequency, the

12-pole motor can run at a ...