NEW GENERATION THREE-PHASE RECTIFIER
By
William Phipps
A thesis presented for the degree of Doctor of Philosophy
In Electrical and Electronic Engineering at the
University of Canterbury, Christchurch New Zealand
July 2008
ABSTRACT
This thesis describes the development of a new gener
ation of three-phase rectifier, used to power
telecommunications equipment. The traditional topol
ogy for such power converters is a single-
phase two-stage design, with a boost converter provid
ing power factor correction at the input to the
first stage and an isolated dc-dc converter making up
the second stage. A two-stage design results
in the output power being processed twice and this ca
scade effect results in an overall reduction in
efficiency. A rectifier solution is sought that meet
s with all the requirements of the
telecommunications industry, while not displaying th
e inherent weaknesses associated with a
boost-derived topology, and which can be realised in
a single-stage design. A number of common
three-phase topologies exist that could be realised
as telecommunication power supplies, however,
they do not completely satisfy all the industry requi
rements. A new three-phase rectifier, which is
a single-stage buck-derived topology, is proposed.
As a consequence of incorporating a buck-
derived topology, the three-phase rectifier does not
exhibit any issues resulting from startup inrush
currents, or high currents due to an output short circ
uit condition, as would result in a boost-
derived topology. The new proposed rectifier is modu
lar in nature, which has the added benefit of
redundancy. As a result of the new three-phase rect
ifier having a single-stage topology, it is
expected that the overall efficiency would able to re
ach close to 95%. This is due to the traditional
two-stage designs having efficiencies around the 90%
mark, and therefore by removing a stage, out
of the power conversion process the overall losses w
ould also be halved, resulting in the 5% gain
in efficiency. The rectifier system requires only
one controller as a result of being a single-stage
design, thus also reducing the overall system cost.
ESTA TESIS FUE FINANCIADA POR LA EATON POWER QUALITY LTD.
The initial motivation in developing a new generation of rectifier topology was to see if it would be
possible to have a topology that would yield a significant increase in efficiency over the traditional
two-stage designs. It was identified that in order to achieve a cost reduction in the rectifier system,
an increase the overall efficiency was needed. This would in turn give Eaton Power Quality Ltd.
an advantage in the market place.
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