0195136047.pdf

16.1 POWER SEMICONDUCTOR-CONTROLLED DRIVES 761

Vao

Va

(a) (b) (c)

α

Va

Ia

0

+

−

Vao

Imax

Ia

Va

90 ° 180 °^0

Fully controlled

rectifier

1- or 3-phase

ac source

Motor

I

Quadrant I:

forward

motoring

(rectifying)

Quadrant IV:

forward

regeneration

(inverting)

IV

Figure 16.1.11Fully controlled rectifier-fed separately excited dc motor drive and its characteristics.(a)
Line diagram.(b)Output voltage versus firing angle curve.(c)Quadrants of operation.

converters.Imaxis the rated rectifier current. In quadrant 4, the rectifier works like a line-
commutated inverter with a negative output voltage, and the power flows from the load to the ac
source.
Let us now consider the single-phase, fully controlled, rectifier-fed separately excited dc
motor shown in Figure 16.1.12(a). Note that the armature has been replaced by its equivalent
circuit, in whichRaandLa, respectively, represent the armature-circuit resistance and inductance
(including the effect of a filter, if connected), andEis the back emf.
Figure 16.1.12(b) shows the source voltage and thyristor firing pulses. The pairT 1 andT 3
receives firing pulses fromαtoπ, and the pairT 2 andT 4 receives firing pulses from (π+α)to
2 π.

iG 1

T 1

iG 4

T 4

vs

(a) (b)

is

+

−

+

−

ωt

vs −vs

2 π

0

0

π

π

2-pulse fully

controlled rectifier

Seperately

excited motor

ia

iG 2

vs = Vm sin ωt

E = Kmωm

va

La

Ra

T 2

iG 3

T 3 ωt

α 2 π

(^0) α ππ + α 2 π ωt
iG 1 , iG 3
iG 2 , iG 4
Figure 16.1.12Single-phase two-pulse fully controlled rectifier-fed separately excited dc motor.