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|Title: ||Mathematical modelling of balanced and unbalanced HVDC power transmission links|
|Authors: ||Fitton, Colin Robert|
|Keywords: ||Applied mathematics|
Electric power transmission
|Issue Date: ||1988|
|Publisher: ||© Colin Robert Fitton|
|Abstract: ||In high voltage direct current power transmission, the need to filter
the non-sinusoidal current wave forms drawn by the converters from the
ac supply has long been acknowledged.
Assessment of the harmonic content of these waveforms to the best
accuracy possible is a desirable objective to aid filter design. The
conventional analytical technique necessitates making simplifying
assumptions and produces only approximate results. Such practical
considerations as system unbalance cannot be taken into account.
The objective of the research was to perform in-depth analyses of hvdc
transmission links, by developing a mathematical model which, in
addition to perfectly balanced conditions, allows for the following
practical operational abnormalities:
(i) Unbalanced 3-phase ac supply voltages
(ii) Unbalanced converter transformer impedances
(iii) Asymmetrical thyristor valve triggering,
whilst not making the usual assumptions of infinite dc side inductance
and zero ac system impedance. In other words to develop a completely
comprehensive mathematical model.
The initial approach was to develop the tensor analysis of a six-pulse
Graetz bridge supplied first by a star-star, and then by a star-delta
connected transformer. A twelve-pulse converter system was then
investigated by modelling the series connection of these two
The technique of diakoptlcs was introduced and combined with the
previous tensor analysis to model a complete dc link with a twelve
pulse converter at each end of a transmission line. The diakoptic
approach enables the full circuit to be torn, for the purpose of the
analysis, into the two twelve pulse converters and the dc line.
The final stage of the development of the model involved the inclusion
of a more sophisticated representation of the ac system impedance and
the addition of tuned or damped filters at the ac busbars.
To verify the program, computed results from the mathematical model
are compared with corresponding experimental results obtained from a
laboratory-scale model of a typical hvdc link configuration.
Comparisons are also made with conventionally based calculations
involving the assumptions included in the computer-based results, in
order to investigate the relative accuracy of the computed solution.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment 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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