The work detailed in the thesis compares the performance of
single-phase thyristor bridge converters under different
control strategies; considering in particular the efficiency,
ac side power factor and harmonic content of the current and
Extensive practical investigations were performed, in which,
analogue and digital control circuits were developed to
provide the drive signals necessary for a converter to operate
in the different control modes for:
a) A series -connected fully-controlled double thyristor
bridge (used mainly in traction applications) operating
under sequence control and;
b) A fully controlled single-bridge operating under
sequence and conventional control.
A novel pulse-width modulation control strategy was developed
for the single-bridge converter, using gate turn-off
thyristors as the switching elements, whereby output voltage
control is obtained by variation of the modulation index.
Turn-on and turn-off signals for the power devices were
obtained using an analogue control circuit. The advantages
and disadvantages of this switching strategy compared with
conventional and sequence control were studied, and results
clearly showed that an improved input power factor and lower
supply current and load voltage harmonics were all
Mathematical models for single and double bridge converters
operating under sequence and conventional control were
developed using tensor techniques. Using these models,
computer programmes were written in Fortran 77 on the University mainframe computer, to assemble automatically and
solve the network equations as the converter topology
changes. In addition, analytical models were also developed
on the assumption that the load current is completely smooth.
However, such an assumption is not justifiable with ac-to-dc
converters and consequently a novel technique was developed to
include the load current ripple in calculating the supply
current harmonics. The results obtained are compared with
both the computed and experimental ones.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.