TITLE
A multiphase transformer rectifier unit.
TECHNICAL FIELD
The present invention relates to a multiphase transformer rectifier unit for
converting a three-phase alternating current supplied from a power
distribution system to direct current supplied to at least one load, and a
method of connecting the same with another multiphase transformer rectifier
unit for reducing current distortion in the power distribution system.
BACKGROUND ART
When supplying electrical power to a DC load from a three-phase AC power
distribution system a conventional six-pulse rectification of the AC will often
result in unacceptable current distortion on the power distribution system and
a low power factor.
Multiphase transformer rectifier unit is a known technology to achieve near
unity power factor and low current distortion when connecting DC loads to
AC networks. Conventional multiphase transformer rectifier units comprises a
magnetic core with a primary winding set and secondary winding set, a
rectifier circuit, and three input terminals for connecting said primary winding
set to a three-phase AC power distribution system. The secondary winding
set is further arranged to generate multiple three-phase systems at its output,
which multiple three-phase systems are phases shifted with respect to each
other to provide an increased number of output phases.
With increasingly smaller phase shift between each output phase, i.e. the
more AC phases that are rectified, the current distortion decreases
correspondingly. Hence, to further reduce current distortion of the power
distribution system, more windings have to be added to the secondary
winding set to provide more output phases. This will however result in higher
conduction losses and increased weight of the unit as the secondary winding
set becomes increasingly complex.
Document US 6,930,578 B2 discloses an arrangement comprising two
multiphase transformers that are configured to reduce harmonic currents in
the power distribution network by a load specific installation of the multiphase
transformers. The document discloses first and second multiphase
transformer connected to a three-phase AC power source, wherein each of
said multiphase transformers feeds an individual AC load. Each transformer
comprises a primary having a plurality of sets of contact points for receiving
power from a three-phase AC power source, and a secondary
electromagnetically coupled to the primary having a single set of contact
points for connection to a plurality of loads. Each set of contact points of the
primary provides a respective primary-to-secondary phase shift, whereby
contacts points of the primary of the first and second transformer are
selected after installation of the transformers, such that a harmonic of a
current from the primary of the first transformer and a harmonic of a current
from the primary of the second transformer substantially cancel. The
disadvantages of the arrangement described in US 6,930,578 B2 are that the
selection of appropriate contact points of the primary of each of the two
transformers is a very complex task that requires suitable measurement
equipment. Moreover, transformer cost increases when additional contacts
points must be provided to the multiphase transformer.
There is thus a need for an improved multiphase transformer rectifier unit
design that provides reduced current distortion on the power distribution
system and an increased power factor.
SUMMARY
The object of the present invention is to provide an inventive multiphase
transformer rectifier unit for converting a three-phase AC to DC, and a
method of connecting the same with another multiphase transformer rectifier
unit for reducing current distortion of the power distribution system, where the
previously mentioned problems can be partly avoided. This object is
achieved by a suitable arrangement of at least two multiphase transformer
rectifier units, each having the features of the characterising portion of claim
1. The multiphase transformer rectifier unit according to the invention
comprises a secondary winding set that is arranged to generate N
substantially equally distributed output phases, wherein N is an odd number
multiple of 3, and N > 3 . The inventive multiphase transformer rectifier unit
further comprises a primary winding set that is arranged to provide said
output phases with a positive or negative phase shift equal substantially to
360 ,
Said object is further achieved by the method steps of the characterising
portion of claim 11. The method according to the invention comprises the
steps of generating N substantially equally distributed output phases by
means of said secondary winding set, wherein N is an odd number multiple
of 3, and N > 3, and providing said output phases with a positive or negative
360
phase shift equal substantially to rdegrees of by means of said primary
(8x N )
winding set. The inventive method further comprises the steps of connecting
a first input terminal of said first and second multiphase transformer to a first
phase of the power distribution system, connecting a second input terminal of
said first multiphase transformer to a second phase of the power distribution
system, connecting a third input terminal of said first multiphase transformer
to a third phase of the power distribution system, connecting a second input
terminal of said second multiphase transformer to the third phase of the
power distribution system, and connecting a third input terminal of said
second multiphase transformer to the second phase of the power distribution
system.
By connecting a first and a second identical multiphase transformer rectifier
units according to the invention in parallel to a three-phase power distribution
system, and shifting the order of connection of two of said three input phases
on one multiphase transformer rectifier unit with respect to the other
multiphase transformer rectifier unit, all pulses of the first multiphase
transformer rectifier unit will be phase shifted forward or backward with
respect to the output phases of the second multiphase transformer rectifier
unit, dependent in the connection to the power distribution system, and by
appropriate selection of the number of output phases and primary phase
shift, the pulses of the first multiphase transformer rectifier unit will be
substantially interleaved with the pulses of the second multiphase
transformer rectifier unit.
The number of output phases from an arrangement comprising two
multiphase transformer rectifier unit, each having N output phases, will thus
appear as 2*N to the power distribution system when the pulses from said
two multiphase transformer rectifier units are interleaved. The solution has
thus the performance of a multiphase transformer rectifier unit having 2*N
output phases, but a complexity close to a multiphase transformer rectifier
unit having N pulses. Compared to using a single 2*N output phase
multiphase transformer rectifier unit the inventive solution also provides the
opportunity to supply two separate isolated loads.
Further advantages are achieved by implementing one or several of the
features of the dependent claims
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in detail with reference to the
figures, wherein:
Figure 1 shows a multiphase transformer rectifier unit connected to a
three-phase AC power distribution system and a DC-load;
shows schematically a power converter of the multiphase
transformer rectifier unit of fig. 1;
shows a power distribution arrangement comprising two
multiphase transformer rectifier units according to the invention;
shows a phase diagram of the secondary winding set according
to the invention;
shows a phase shift of the primary winding set according to the
invention;
shows a connection diagram of the primary and secondary
winding sets according to the invention; and
shows a rectifier circuit according to the invention.
DETAILED DESCRIPTION
In the following, the term "winding" refers to a single continuous coil of wire
on a single core leg of a three legged core transformer. The term "primary
winding set" refers to a set of windings that constitute all the windings
connected to a power supply network, whereas a "secondary winding set"
refers to set of windings that constitute all the windings connected to rectifiers
on the load side of the transformer. A "phase set" will refer to two or more
windings that are found on a common core leg of the transformer, wherein a
"primary phase set" refers to two or more windings that are found on a
common core leg and adapted for being connected to the power distribution
system, whereas a "secondary phase set" refers to two or more windings that
are found on a common core leg and adapted for being connected to at least
one load.
Fig. 1 shows a multiphase transformer rectifier unit 1 for converting a threephase
(R, S, T) alternating current (AC) supplied from a power distribution
system 2 to direct current (DC) supplied to a single load 3 .
As shown in fig. 2, the multiphase transformer rectifier unit 1 comprises a
power converter 4 having a magnetic core 5 with a first leg 6, second leg 7
and third leg 8 . A first coil 9, second coil 10, and third coil 1 is wound around
said first, second and third leg 6, 7, 8 respectively. A primary winding set of
the multiphase transformer rectifier unit 1 is connected to the supply phases
R, S, T of a three-phase AC power distribution system 2 by means of a first
input terminal 12, second input terminal 13, and third input terminal 14. The
primary winding set is disposed in inductive relation with said magnetic core
5 for establishing a magnetic flux therein. The secondary winding set is
arranged to provide multiple output three-phase systems by suitable winding
configuration of the secondary winding set, which multiple output threephase
systems are phase shifted with respect to each other to provide evenly
distributed output phases. The secondary winding set is disposed in inductive
relation with said magnetic core 5, and the output phases of the secondary
winding set are provided at a set of output terminals 25.
The number of output three-phase systems can be selected to be appropriate
for the specific application. For example, a secondary winding set can be
arranged to generate three output three-phase systems, adding up to a total
of nine output phases. The output phases of a first output three-phase
system are for example in phase with the supply phases R, S, T of the power
distribution system, the output phases of a second output three-phase
system are leading the supply phases R, S, T with 40°, and the output
phases of a third output three-phase system are lagging the supply phases
with 40°. This will result in nine output phases equally distributed.
Rectification of said nine output phases by means of for example a
polyphase full-wave bridge rectifier circuit, which generates two pulses per
period for each phase, would provide an 18-pulse multiphase transformer
rectifier unit. The primary and secondary winding sets can be configured to
step-up or step-down the input voltage level to achieve higher or lower output
voltage level.
As described in the introduction, the main advantages of generating
additional AC output phases by means of a multiphase transformer rectifier
unit 1 are that less current distortions inflicted by rectification of the output
phases and/or loads are induced in the power distribution system 2, and a
DC output voltage with less voltage ripple is provided. Increased number of
windings in the secondary winding set will however lead to higher conduction
losses, increased weight and higher manufacturing cost of the multiphase
transformer rectifier unit 1 as the secondary winding set becomes
increasingly complex.
This problem is solved by providing the multiphase transformer rectifier unit 1
according to the invention with a phase shift in the primary winding set in
addition to multiple output phases on the secondary winding set, and
connecting two of said multiphase transformer rectifier units 1 to the same
power distribution system 2 but changing the order of connection of one of
the two multiphase transformer rectifier units 1 with respect to the other
multiphase transformer rectifier unit 1. Such an inventive power distribution
arrangement is shown in fig. 3, having a first multiphase transformer rectifier
unit 15 and a second multiphase transformer rectifier unit 16 . By introducing
a phase shift also in the primary winding set, the current distortion of the
power distribution system 2 inflicted by the combined first and a second
identical multiphase transformer rectifier units 15, 16 will be reduced,
provided that the order in which input phases R, S, T of the power distribution
system 2 are connected to a first of said multiphase transformer rectifier units
15, 16 are changed with respect the second of said multiphase transformer
rectifier units 15, 16 . The phase shift generated by the primary winding set is
a primary-to-secondary phase shift that shifts the entire set of output phases
a predetermined degree forward or backward.
The change of order of connection of the input phases R, S, T in combination
with a phase shift generated by the primary winding set of each of said first
and second identical multiphase transformer rectifier units 15, 16 results in a
positive phase shift of the entire set of output phases of one of said first and
second multiphase transformer rectifier units 15, 16, and a negative phase
shift of the entire set of output phases of the other of said first and second
multiphase transformer rectifier units 15, 16 . By appropriate selection of the
phase shift in the primary winding set and the number of output phases of
each of said first and second multiphase transformer rectifier unit 15, 16, the
pulses from said first and second multiphase transformer rectifier units 15, 16
will be interleaved, i.e. the pulses from the first multiphase transformer
rectifier unit 15 will be arranged substantially in the centre between the
pulses from the second multiphase transformer rectifier unit 16 in alternating
and regular manner seen in a phase diagram. Such an arrangement of two
identical multiphase transformer rectifier units 15, 16 results in a degree of
current distortion of the power distribution system 2 similar to a single
multiphase transformer rectifier unit having twice as many output phases as
provided by each of said first and second multiphase transformer rectifier
units 15, 16 separately.
According to one example of how said first and second multiphase
transformer rectifier units 15, 16 can be connected to the power distribution
system 2, the first input terminals 12 of the first and second multiphase
transformer rectifier unit 15, 16 are connected to a first phase R of the 3-
phase power distribution system 2 . The second input terminal 13 of the first
multiphase transformer 15 is connected to a second phase S of the power
distribution system 2, and the third input terminal 14 of the first multiphase
transformer 15 is connected to a third phase T of the power distribution
system. The second input terminal 13 of the second multiphase transformer
16 is connected to the third phase T of the power distribution system, and the
third input terminal 14 of the second multiphase transformer 16 is connected
to the second phase S of the power distribution system, such that a first
plurality of output phases of the first multiphase transformer rectifier unit 15
are phase shifted with respect to a second plurality of output phases of the
second multiphase transformer rectifier unit 16.
This will lead to reduced current distortion in the power distribution system 2
inflicted mainly be said first and second multiphase transformer rectifier units
15, 16 and/or loads 3 . In the specific example of changed order of connection
presented above, the order of connection of input phases S and T where
changed. As apparent to the skilled person, the input phases R and S or R
and T could alternatively have been changed with the same result in phase
shift.
The inventive selection of the phase shift in the primary winding set and
number of output phases of each multiphase transformer rectifier unit 15, 16
that provides the effect of doubled output pulses by parallel arrangement of
said first and second multiphase transformer rectifier units 15, 16 can be
defined in general terms. A multiphase transformer rectifier unit 1 having a
secondary winding set provided with N substantially equally distributed output
phases, wherein N is an odd number multiple of 3, and N > 3, should have a
primary winding set that provides a phase shift equal substantially to
360
degrees. For example, a secondary winding set generating nine
output phases (N=9) should according to the invention have a primary
winding set providing a phase shift of 360/(8x9), thus equal to 5°. Nine output
phases results in 360/9=40° between each output phase, and consequently
20° between each pulse. A first multiphase transformer rectifier unit 15
having for example a negative primary phase shift of 5° arranged in parallel
with a second multiphase transformer rectifier unit 16 having a positive
primary phase shift of 5° thus results in 10° between each pulse of the
combined arrangement, wherein said first and second multiphase
transformer rectifier units 15, 16 will supply said pulses to their loads in an
alternating manner. This relation between number of output phases and
phase shift on the primary winding set assures that an arrangement of two of
said multiphase transformer rectifier units 1, connected to the power
distribution system 2 with changed order of the input phases as described
previously, will have substantially interleaved pulses. The number of output
phases of each secondary winding set can according to the invention, for
example, be any of 9, 15, 2 1, 27, 33, or 39, etc.
The phase shift of the primary winding set might not be exactly
360
degrees because the factual primary phase shift depends on the
(8x N )
windings composing the primary winding set. Sometimes, it is not possible to
achieve exactly the desired primary phase shift due to lack of resolution, i.e.
lack of sufficient turns on the legs 5, 6, 7 of the magnetic core 5 .
Correspondingly, in certain circumstances, the output phases of the
secondary winding set might be slightly offset from equally distributed over
the 360° spectrum for the same reason.
The inventive multiphase transformer rectifier unit 1, when arranged in
parallel with an additional identical multiphase transformer rectifier unit 1, and
each multiphase transformer rectifier unit 1 being connected differently to the
three-phase AC power distribution system 2 such that one of the multiphase
transformer rectifier units 1 has negative primary phase shift and the other
multiphase transformer rectifier unit 1 has positive primary phase shift,
results in reduced weight, cost, and conduction losses, compared with a
single multiphase transformer rectifier unit 1 inflicting a similar amount of
current distortion to the power distribution system 2 because only half as
many output phases are required.
Compared with a single multiphase transformer rectifier unit 1 having same
number of output phase but without the primary phase shift, the inventive
multiphase transformer rectifier unit 1, when arranged in parallel with an
additional identical multiphase transformer rectifier unit 1 as described above,
leads to reduction in total harmonic distortion (THD) of the power distribution
system current and a nearly unity power factor.
The phase shift of the primary winding set can be arranged in an extendeddelta
configuration, a zig-zag configuration, or a polygon configuration
dependent on requirements.
In the following one detailed embodiment of the multiphase transformer
rectifier unit 1 according to the invention is shown and described, simply by
way of illustration of one mode of carrying out the invention.
Fig. 4 shows a phase diagram of the secondary winding set of an isolated
multiphase transformer rectifier unit 1 according the invention having three
input phases R, S, T and 15 output phases R 1, S 1, T 1, R2, S2, T2, R3, S3,
T3, R4, S4, T4, R5, S5, T5. Fig. 5 shows the phase shift of the primary
winding set of said multiphase transformer rectifier unit 1 according the
invention, and fig. 6 shows the corresponding connection diagram of the
primary and secondary winding sets.
In Fig. 6, each row of windings in the connection diagram corresponds to the
individual windings of each separate leg 6, 7, 8 of the three-legged magnetic
core 5 . The upper part corresponds to the primary winding set 17, and the
lower part corresponds to the secondary winding set 18 . Each phase set 19
of the primary winding set 17 comprises a main winding 20 consisting of 100
turns (n=1 00) and an auxiliary winding 2 1 consisting of 6 turns (n=6), wherein
the phases R, S, T of the power distribution system are connected such that
current flowing from one phase to another phase of said phases R, S, T,
flows through one main winding 20 and one auxiliary winding 2 1 . The phase
shift angle in the primary winding set 17 is determined by the ratio of the
main winding 20 to the auxiliary winding 2 1, which in the present
configuration results in a 3° phase shift in the primary winding set 17 . The
main winding 20 can be wound as a single winding, or alternatively as
multiple electrically connected windings on the same core leg accumulating
to the desired number of turns. Fig. 5, which shows the phase shift and
winding of the primary winding set 17, corresponds to the upper part of fig. 6 .
The lower part of fig. 6 shows the connection diagram of the secondary
winding set 18 comprising 15 output phases R 1-R5, S 1-S5, T 1-T5
corresponding the five phase-shifted three-phase systems. Fig. 4, which
corresponds to lower part of fig. 6, shows said 15 output phases distributed
substantially equally over the 360° circle, such that an internal phase shift a
of substantially 360/1 5 = 24 0 between neighbouring phases is achieved. The
crossings where the dotted lines meet the illustrated circle indicate the
optimal position of the output phases for equal distribution. The factual
position of these output phases is however dependent on an integer number
of turns on appropriate core legs 6, 7, 8, such that the factual position in
certain situations is arranged slightly offset from the optimal position, which
can be seen for example at point R 1 in fig. 4 . Each direction A, B, C of the
cornered line connecting said output phases in the phase diagram indicates
windings on a specific leg 6, 7, 8 of the magnetic core 5 . The complete
connection diagram of the primary and secondary winding set 17, 18 is
disclosed in fig. 6, in which the number next to each winding represents the
number of turns of said winding. The individual windings of the primary and
secondary winding sets 17, 18 are separated with isolation foil to provide
galvanic isolation between primary and secondary winding sets 17, 18 .
The 15 output phases will after full-wave rectification give rise to 30 current
pulses 12° apart, because two pulses are provided by each output phase per
period. Moreover, in combination with a first and second identical multiphase
transformer rectifier unit 15, 16, each having a 3° phase of the primary
winding set, and the change of order in which the input phases R, S, T are
connected to said first and second multiphase transformer rectifier units 15,
16, one multiphase transformer rectifier unit 15, 16 will have a positive 3°
phase shift, whereas the other multiphase transformer rectifier unit 15, 16 will
have a negative 3° phase shift, such that the pulses of the first and second
multiphase transformer rectifier units 15, 16 will be 6° out of phase. This
configuration leads to interleaving of the 30 output pulses of the first
multiphase transformer rectifier unit 15 with the 30 output pulses of the
second multiphase transformer rectifier unit 16, such that the current
distortion corresponding to a single multiphase transformer rectifier unit 1
having 60 output pulses will be provided.
In fig. 5, said relation between the number of turns of the main and auxiliary
winding and the resulting phase shift is schematically illustrated, as well as
the 30 output pulses R 1-R1 0, S 1-S1 0, T 1-T1 0 of each multiphase
transformer rectifier unit 15, 16 . The essentially triangular vector-winding
diagram in fig.5, which is composed of the three main- and three auxiliary
windings 20, 2 1, will have a right-rotation or a left-rotation dependent in the
order of connection of the input phases R, S, T to the first, second and third
input terminals 12, 13, 14. Hence, said vector-winding diagram will have a
left-rotation in one of the first and second multiphase transformer rectifier
units 15, 16 and right-rotation in the other of said first and second multiphase
transformer rectifier units 15, 16 .
It is evident that the inventive multiphase transformer rectifier unit 1 can be
used either in combination with another multiphase transformer rectifier unit 1
as described above to obtain reduced current distortion on the power
distribution system 2 and an increased power factor, or as a single
multiphase transformer rectifier unit 1.
One of the benefits of the implementations described above is that two
identical multiphase transformer rectifier units 1 are used, and merely the
connection of said multiphase transformer rectifier units 1 to the power
distribution system changes. This results in increased flexibility in terms of
use and installation, as well as reduced manufacturing costs due to simplified
production and logistics.
Fig.7 shows a preferred embodiment of a rectifier circuit of each multiphase
transformer rectifier unit 1, formed as a polyphase full-wave bridge rectifier
circuit 22. A full-wave rectifier unit comprising two diodes 23 for each output
phase converts the whole of the input waveform to one of constant polarity at
its output. Each generated three-phase system of the secondary winding set
18 requires a three-phase full-wave bridge rectifier circuit, such that the
complete multiphase transformer rectifier unit 1 according to the disclosed
embodiment, which is composed of five such three-phase system adding up
to 15 output phases, requires five three-phase full-wave bridge rectifier
circuits connected in parallel. The outputs of these circuits are joined to form
a polyphase rectifier circuit 22 suitable for the multiphase transformer rectifier
unit 1 according to the invention. The design of the rectifier circuit 22 is
however not limited to the embodiment shown in fig. 7 and other designs of
the rectifier circuit 22 are possible.
The three-phase R, S, T AC power distribution system 2 can be of almost
any voltage and frequency, but the multiphase transformer rectifier unit 1 is
particularly suitable for use in an aircraft, in which the power distribution
system typically comprises three-phase 115 volt AC at 400 Hz supplied from
an aircraft generator 24. AC/DC conversion of variable frequency AC is also
possible without further adaption. The inventive multiphase transformer
rectifier unit 1 may however advantageously be used also in land-, or seabased
vehicles, as well as in fixed constructions.
The inventive multiphase transformer rectifier unit 1 is particularly suitable for
supplying DC-power to all types of high power DC-loads 3, in particular high
power DC-loads 3 arranged in aircrafts. One example of such a high power
DC-loads 3 is a radar system. The multiphase transformer rectifier unit 1
steps down or up the supplied voltage level according to specific demands of
the load 3 or loads. Multiple loads of equal of varying power size can be
connected to the transformer in series, parallel or a combination thereof. The
loads can take various forms, such as pure resistive loads, or combination of
resistive, inductive and capacitive loads. The current distortion inflicted on the
power supply system 2 by two multiphase transformer rectifier units 1
connected with different primary phase shifts will be further reduced if the
loads 4 of each multiphase transformer rectifier unit 1 are of the same
magnitude.
An output filter may be arranged between the multiphase transformer rectifier
unit 1 and load 3 to provide improved voltage level and ripple smoothening,
and in input filter may be arranged between the multiphase transformer
rectifier unit 1 and power distribution system 2 to suppress common mode
voltages and to protect generator and other electronic equipment connected
to the power distribution system 2 from high frequency harmonics.
The term "N is an odd number multiple of 3, and N > 3" provides three
constraints on the number N:
1) N must be an odd number
2) N must be a multiple of 3 . This is herein defined as any number
resulting from multiplying 3 with a positive integer, such as 3x1 , 3x2,
3x3 etc.
3) N must be larger than 3 .
Examples of N fulfilling all these constraints are 9, 15, 2 1, 27, 33, 39, 45, etc.
As will be realised, the invention is capable of modification in various obvious
respects, all without departing from the scope of the appended claims.
Accordingly, the drawings and the description thereto are to be regarded as
illustrative in nature, and not restrictive.
Reference correspondence table
1 Multiphase transformer rectifier unit
2 Power distribution system
3 Load
4 Power converter
5 Magnetic core
6 First leg
7 Second leg
8 Third leg
9 First coil
10 Second coil
11 Third coil
12 First input terminal
13 Second input terminal
14 Third input terminal
15 First multiphase transformer rectifier unit
16 Second multiphase transformer rectifier unit
17 Primary winding set
18 Secondary winding set
19 Phase set of primary winding set
20 Main winding
2 1 Auxiliary winding
22 Rectifier circuit
23 Diode
24 Generator
25 Output terminals

CLAIMS
A multiphase transformer rectifier unit ( 1 ) for converting a three-phase
(R, S, T) alternating current (AC) supplied from a power distribution
system (2) to direct current (DC) supplied to at least one load (3),
wherein said multiphase transformer rectifier unit ( 1 ) comprises a
magnetic core (5) having a primary winding set ( 17) and secondary
winding set ( 18), and a rectifier circuit (22),
characterised in that
- said secondary winding set ( 18) is arranged to generate N
substantially equally distributed output phases, wherein N is an
odd number multiple of 3, and N > 3;
- said primary winding set ( 17) is arranged to provide said output
phases with a positive or negative phase shift equal
360
substantially to degrees.
2 . The multiphase transformer rectifier unit ( 1) according to claim 1,
characterised in that said primary winding set ( 17) is disposed in
inductive relation with said magnetic core (5) for establishing a
magnetic flux therein, and each phase set ( 19) of the primary winding
set ( 17) comprises a main winding (20) and an auxiliary winding (21 ) ,
wherein said resulting phase shift is determined by the ratio of the
main winding (20) to the auxiliary winding (21 ) .
The multiphase transformer rectifier unit ( 1) according to claim 2,
characterised in that said main winding (20) is composed of at least
two electrically connected separate windings wound on the same core
leg.
4 . The multiphase transformer rectifier unit ( 1) according to any of claims
1 to 3, characterised in that said secondary winding set ( 18) is
disposed in inductive relation with said magnetic core (5), and said
secondary winding set has a N output terminals (25), each
corresponding to an output phase.
The multiphase transformer rectifier unit ( 1) according to any of claims
1 to 4, characterised in that the primary winding set ( 17) is arranged in
an extended-delta configuration, a zig-zag configuration, or a polygon
configuration.
The multiphase transformer rectifier unit ( 1) according to any of clai
1 to 5, characterised in that said rectifier circuit (22) for AC/DC
conversion is a polyphase full-wave bridge rectifier.
7 . The multiphase transformer rectifier unit ( 1) according to any of claims
1 to 6, characterised in that said multiphase transformer rectifier unit
( 1 ) is suitable for supplying DC to a high-power load (3), which
preferably is arranged on an aircraft.
8 . Power distribution arrangement comprising of a first multiphase
transformer rectifier unit ( 15) and a second multiphase transformer
rectifier unit (16), each according to any of claims 1-7, characterised in
that said first and second multiphase transformer rectifier units ( 15,
16) are connected to a three-phase (R, S, T) alternating current (AC)
power distribution system (2) by means of a first input terminal ( 12), a
second input terminal ( 13), and a third input terminal (14), said first
input terminal ( 12) of said first and second multiphase transformer
rectifier unit (15, 16) is connected to a first phase (R) of the power
distribution system (2), said second input terminal ( 13) of said first
multiphase transformer rectifier unit ( 15) is connected to a second
phase (S) of the power distribution system (2), said third input terminal
(14) of said first multiphase transformer rectifier unit ( 15) is connected
to a third phase (T) of the power distribution system (2), said second
input terminal ( 13) of said second multiphase transformer rectifier unit
( 16) is connected to said third phase (T), and said third input terminal
(14) of said second multiphase transformer rectifier unit ( 16) is
connected to said second phase (S), such that a first plurality of output
phases of the first multiphase transformer rectifier unit ( 15) are phase
shifted with respect to a second plurality of output phases of the
second multiphase transformer rectifier unit (16) in order to reduce
current distortion in said power distribution system (2) inflicted by said
rectifier circuit (22) and/or load (3).
9 . The arrangement according to claim 8, characterised in that said first
and second multiphase transformer rectifier units ( 15, 16) are
connected to individual loads (3) of substantially the same magnitude.
10 .The arrangement according to any of claims 8 or 9, characterised in
that said first and second multiphase transformer rectifier units (15,
16) have identical design.
11.Method for reducing current distortion in a power distribution system
by means of an arrangement of a first and a second multiphase
transformer rectifier unit ( 15, 16) connected to a three-phase (R, S, T)
alternating current (AC) power distribution system (2) and at least one
DC-load (3), wherein each of said multiphase transformer rectifier
units ( 15, 16) comprises a rectifier circuit (22) for polyphase AC/DC
conversion, and a magnetic core (5) having a primary winding set (17)
and secondary winding set ( 18), and wherein each primary winding set
( 17) is connected to said phases (R, S, T) of said power distribution
system (2) by means a first input terminal ( 12), a second input terminal
( 13) and a third input terminal (14),
characterized by the steps of
- generating N substantially equally distributed output phases by
means of said secondary winding set ( 18), wherein N is an odd
number multiple of 3, and N > 3;
- providing a positive or negative phase shift of said output
360
phases equal substantially to degrees by means of said
(8x N )
primary winding set ( 17);
- connecting said first input terminal (12) of said first and second
multiphase transformer rectifier unit ( 15, 16) to a first phase (R)
of the power distribution system (2);
- connecting said second input terminal ( 13) of said first
multiphase transformer rectifier unit ( 15) to a second phase
(S) of the power distribution system (2);
- connecting said third input terminal (14) of said first multiphase
transformer rectifier unit ( 15) to a third phase (T) of the power
distribution system (2);
- connecting said second input terminal (13) of said second
multiphase transformer rectifier unit ( 16) to said third phase
(T);
- connecting said third input terminal (14) of said second
multiphase transformer rectifier unit ( 16) to said second phase
(S), such that a first plurality of output phases of the first
multiphase transformer rectifier unit ( 15) are phase shifted with
respect to a second plurality of output phases of the second
multiphase transformer rectifier unit ( 16).
12 .The method according to claim 11, characterised by the step of
disposing said primary winding set ( 17) in inductive relation with said
magnetic core (5) for establishing a magnetic flux therein, and
providing each phase set ( 19) of the primary winding set ( 17) with a
main winding (20) and an auxiliary winding (21 ) , wherein said resulting
phase shift is determined by the ratio of the main winding (20) to the
auxiliary winding (21 ) .
3 .The method according to any of claims 11 or 12, characterised by the
step of arranging the primary winding set ( 17) in an extended-delta
configuration, a zig-zag configuration, or a polygon configuration.
4 .The method according to any of claims 11 to 13, characterised by the
step of designing said rectifier circuit (22) for AC/DC conversion as a
polyphase full-wave bridge rectifier.
5 .The method according to any of claims 11 to 14, characterised by the
step of supplying DC to a high-power load (3) by means of the
multiphase transformer rectifier unit ( 1) , which high-power load (3)
preferably is arranged on an aircraft.