0195136047.pdf

766 BASIC CONTROL SYSTEMS

60°, the firing of thyristors occurs in the same sequence as they are numbered. The line

commutation of an even-numbered thyristor takes place with the turning on of the next even-

numbered thyristor, and similarly for odd-numbered thyristors. Thus, each thyristor conducts

for 120° and only two thyristors (one odd-numbered and one even-numbered) conduct at

a time.

Considering the continuous conduction mode for the motoring operation, as shown in Figure

16.1.15, for the converter output voltage cycle fromωt=α+π/3toωt=α+ 2 π/3,

iG 1

T 1

T 4

iA

+

−

(^02) π ωt
0
π
π/3
6-pulse fully controlled rectifier Motor
ia
E = Kmωm
va
La
Ra
T 5
T 2
T 3
T 6
π 2 π ωt
iG 1
(^0) π 2 π ωt
iG 2
(^0) π 2 π ωt
iG 3
(^0) π 2 π ωt
iG 4
(^0) π 2 π ωt
iG 5
(^0) π 2 π ωt
iG 6
vAB
Vm
vBC vCA
vBA
a
vCB vAC
A
B
C
N
Figure 16.1.14Three-phase fully
controlled six-pulse bridge-recti-
fier-fed separately excited dc mo-
tor.