2. MUHAMMAD ILYAS GHUMMAN
ROLL No.12063122-088
SERIES OPERATION OF THYRISTORS.
AND
PARALLEL OPERATION OF THYRISTORS.

3. REVIEW SOME BASICS
Vacuum tubes

4. SOLID STATE PHYSIC
DIODES, BJTS ,FETS,THYRISTORS, ICS

5. UNDERSTAND JUNCTIONS OF THYRISTOR

6. VARIOUS TRIGGERING METHODS OF
THYRISTOR
There are some methods for practically triggering of
thyristors.
1 : Forward voltage triggering method.
2 : Thermal or temperature method.
3 : Radiation or light triggering method.
4 : dvdt triggering method.
5 : Gate triggering method.

7. THYRISTOR EQUIVALENT CCT , WORKING
AND 5 WAYS TO ON THE THYRISTORS.

8. INTRODUCTION OF (SCR) THYRISTOR ITS
LATCHING AND CHECKING METHOD

9. INTRODUCTION OF (GTO) THYRISTORS ,
OPERATION AND CHECKING METHOD

10. WORKING OF THYRISTOR

11. THYRISTOR IN ON CONDITION
THROUGH GATE

12. THYRISTOR IN OFF CONDITION

13. CONTROL OF THYRISTR BY
+Ve AND –Ve PULSE

14. SERIES OPERATION OF THYRISTORS :
 For high voltage application two or more then two
thyristors can be connected in series to provide
specific voltage rating .
How ever due to the production spread,
characteristics of thyristors of the same type are
not identical.

15. SERIES OPERATION OF THYRISTORS :
 In the case of diodes , only the reverse blocking
voltages have to be shared .
 where as for thyristors , the voltage sharing
networks are required for both reverse and off state
condition .
 The voltage sharing is normally accomplished by
connecting resistors across each thyristor .

16. SERIES OPERATION OF THYRISTORS
For equal voltage sharing ,the off- state current
differ . Let here be ns, thyristors in the string .
The off-state current of thyristor T1 is ID1 and that
of other thyristors are equal such that ID2=ID3=IDn,
andID1<ID2.
Because thyristor T1 has the least off state
current,T1 shares higher voltage.

17. SERIES OPERATION OF
THYRISTORS :

18. SERIES OPERATION OF THYRISTORS :
If I1 is the current through the resistor R
acrossT1 and current through other resistors are
equal so that I2=I3=In, the off-state current
spread is shown on the next page.

19. SERIES OPERATION OF THYRISTORS :

20. SERIES POERATION OF
THYRISTORS :

21. SERIES POERATION OF
THYRISTORS :

22. PARALLEL OPERATION OF THYRISTOR
When thyristors are connected in parallel ,the load
current is not shared equally due to differences in
their characteristics .
 If a thyristor carries more current than that of the
others ,its power dissipation increases , their by
increasing junction temperature.

23. Parallel operation of thyristors :
The junction temperature and decreasing
internal resistance . This in turn increases
its current sharing and may damage the
thyristor .
This thermal runaway may avoided
By having common heat ,so that all units
operate at the temperature.

24. PARALLEL OPERATION OF THYRISTOR
A small resistance ,as shown in figure may be
connected in series with each the thyristor to force
equal current sharing ,but they may be considerable
power loss in the series resistances .
A common approach for current sharing is to be
use magnetically coupled inductors .

25. PARALLEL OPERATION OF
THYRISTOR
 If the current through thyristor T1 increases, a
voltage of opposite polarity can be induced in the
winding of the thyristor T2 and impedance through
the path of T2 can be reduced , their by increasing the
current flow through T2.

26. PARALLEL OPERATION OF
THYRISTOR
Due to unequal current division, current through
SCR increases, its temp also increases by this ,
decreases the resistance.
Hence further increase in current takes place & this
is a cumulative process, known as thermal , run away ,
which can damage the device.
 To overcome this problem SCRs would be
maintained at same temp. This is possible by
mounting them on same heat sink.

27. PARALLEL OPERATION OF
THYRISTOR

28. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT

29. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT WITH OSC.

30. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT

31. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT WITH OSC.

32. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT

33. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT WITH OSC.

34. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT

35. PARALLEL OPERATION AS CURRENT
AND PHASE CONTROL CCT WITH OSC.

36. VIEW OF OSCILLOSCOPE OUTPUTS
OF PHASE CONTROL CCT

37. PARALLEL OPERATION OF
THYRISTORS
Once the GTO thyristor is turned on, forward
gate current must be continued for hole of the
conduction to ensure the device remains in
conduction .
 Other wise the device cannot remain in
conduction during the on state period ,it will be in
the off state (GTO will be not in saturation state) .

38. PARALLEL OPERATION OF THYRISTORS
AS A CURRENT CONTROLLER IN UPS

39. PARALLEL OPERATION OF GTO THYRISTORS
AS WORKING IN H. BRIDGE (UPS)

40. PARALLEL OPERATION OF
THYRISTORS.
When we give the output of oscillator to the parallel
fitted of thyristors to gate as shown in H . Bridge .
Positive voltages are given via C.T Transformer to
anode and Negative battery voltages are given via
fuse at the Cathode of GTO at two sides of the H .
Bridge.
 When positive voltages or pulse will appear On the
Gate thyristor will conduct ,otherwise it will not
conduct as off state.

41. GTO THYRISTORS IN UPS WORLD
CHALLING ENERGY SOURCE

42. Any Question.