Page 64 - Rashid, Power Electronics Handbook

3 Thyristors 49

GATE

Islands
(Cathode)

Anode

A1 A2 A3 A8
Cell Cell Cell Cell
Model Model Model Model
RGC1 1 RGC2 2 RGC3 3 RGC8 8
G1 K1 G2 K2 G3 K3 G8 K8
RKC1 RKC2 RKC3 ...................................... RKC8

M 12 M 23

Delay
Delay
Delay
Gate Circuit Circuit Circuit

Cathode
FIGURE 3.30 Thyristor multicell circuit model containing eight cells.

This model does not accurately represent spatial effects such conducting area of the thyristor and by the magnetic ®eld
as current crowding at turn-on (the di=dt limit), when only generated by the changing conduction current. Gate-contact
part of the device is conducting, and, in the case of a GTO, and cathode-contact resistance can be included for each cell as
current crowding at turn-off , when current is extracted from well. To model these effects, Tsay et al. [13] propose a multicell
the gate to turn off the device. Current crowding is caused by circuit model, in which the device is discretized in a number of
the location of the gate connection with respect to the conducting cells, each having the structure of Fig. 3.30. This
model, shown in Fig. 3.31, takes into account the mutual
inductive coupling, the delay in the gate turn-off signal due to
i d positions of the cells relative to the gate connection, and
nonuniform gate- and cathode-contact resistance. In particu-
+ L d lar, the RC delay circuits (series R with a shunt C tied to the
cathode node) model the time delays between the gate
triggering signals due to the position of the cell with respect
to the gate connection; coupled inductors, M's, model
L s magnetic coupling between cells; resistors, R 's, model non-
KC
uniform contact resistance; resistors, R 's, model gate con-
GC
+ tact resistances. The various circuit elements in the model
can be estimated from device geometry and measured
v s v d Load electrical characteristics. The choice of the number of cells is
-
TABLE 3.6 Element values for each cell of a multicell GTO model
Model Component Symbol Vaue
Delay resistor R 1 mO
Delay capacitor C 1 nF
Mutual coupling inductance M 10 nH
- Gate contact resistance R GC 1 mO
Cathode contact resistance R KC 1 mO
FIGURE 3.31 Single-phase controlled recti®er circuit.