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|Title: ||The forced commutation of thyristors connected in series|
|Authors: ||Hall, John K.|
|Issue Date: ||1972|
|Publisher: ||© John Keith Hall|
|Abstract: ||Widespread high voltage application of forced commutation was then, and still is, some years ahead. The thesis puts foward methods which have been devised for ensuring satisfactory thyristor turn-off in this
context and suggests Some possible future trends in application.
Individual tbyristor turn-off characteristics are first studied
together with the equivalent diode characteristics. The difficulties
of using thyristors in series for high voltage working are described
and the limitations of the conventional resistive-capacitive voltage
sharing network discussed in relation to forced commutation. Three forms of improved voltage sharing network are presented
together with developments which use these in suitable combination.
All have been tested with series-connected thyristors operating in
a high voltage force-commutated chopper circuit. The advantages and disadvantages, and a design procedure, are given for each form of
network. The two most appropriate voltage sharing arrangements are
applied to the series thyristors and diodes in a high voltage,
variable frequency d.c. chopper, and their overall influence on
chopper performance is considered in detail.
Owing to the possibility of cascade failure when many semiconductor
devices are connected in series, extensive component
damage can result from circuit malfunction or incorrect component
connection. Great care has therefore. been necessary in the design,
construction and checking of the high voltage experimental equipment.
It is concluded that the voltage sharing methods devised make
possible forced commutation of thyristors at high voltages and do
not, in themselves, provide the practical constraints on system
performance. The methods are compared on a technical and economic basis. Possible future applications are reviewed, with particular emphasis placed on the transformation of d.c. at high voltages using chopping techniques. Other problems which must be solved before such applications become realisable outside the laboratory are outlined and suggestions made for future work.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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