Page 267 - Rashid, Power Electronics Handbook
P. 267
256 J. Espinoza
As expected, the actual and reference values are identical. reduces the speed of an electrical machine this can be consid-
Finally, the relationship Eq. (14.83) is a matrix that is not ered a transient condition. Downhill belt conveyors in mining
diagonal. This means that both actual and reference load- applications can be considered a normal operating condition.
phase voltages are coupled. In order to obtain a decoupled In order to simplify the notation, it could be said that an
control, the decoupling block in Fig. 14.44 should be properly inverter operates in the motoring mode when the power ¯ows
chosen. from the dc to the ac side, and in the regenerative mode when
the power ¯ows from the ac to the dc side.
14.6 Regeneration in Inverters
14.6.1 Motoring Operating Mode in Three-Phase
Industrial applications are usually characterized by a power VSIs
¯ow that goes from the ac distribution system to the load. This
is, for example, the case of an ASD operating in the motoring This is the case where the power ¯ows from the dc side to the
mode. In this instance, the active power ¯ows from the dc side ac side of the inverter. Figure 14.45 shows a simpli®ed scheme
to the ac side of the inverter. However, there are an important of an ASD where the motor has been modeled by three RLe
number of applications in which the load may supply power to branches, where the sources e are the back-emf. Because
abc
the system. Moreover, this could be an occasional condition as the ac line voltages applied by the inverter are imposed by the
well a normal operating condition. This is known as the pulsewidth-modulation technique being used, they can be
regenerative operating mode. For example, when an ASD adjusted according to speci®c requirements. In particular,
FIGURE 14.45 Three-phase VSI topology with a diode-based front-end recti®er.
FIGURE 14.46 The ASD based on a VSI. Motoring mode: (a) dc bus voltage; (b) dc bus current; (c) ac line-load voltage; (d) ac phase-load voltage;
(e) motor line current and back-emf; (f) shaft power.
