Page 220 - Rashid, Power Electronics Handbook

12 Three-Phase Controlled Recti®ers 209

Variable-speed constant-frequency generation also can be
used in either hydraulic or thermal plants. This allows for
optimal adjustment of the ef®ciency-speed characteristics of
the machines. In Japan, wound rotor induction generators
working as variable speed synchronous machines are being
used as constant frequency generators. They operate in
hydraulic plants that are able to store water during low
demand periods. A power converter is connected at the slip
rings of the generator. The rotor is then fed with variable

FIGURE 12.65 Amplitude modulation of the ‘‘H'' bridges of Fig. 12.62.

+

FIGURE 12.66 Frequency converter with force-commutated converters.

TRACTION
MOTOR DRIVING - CHARGING
ELECTRONIC SWITCH
SELECTOR

FIGURE 12.67 Electric bus system with regenerative braking and battery charger.

a

V

FIGURE 12.68 Variable-speed constant-frequency wind generator.