U.S. patent application number 09/881039 was filed with the patent office on 2002-02-07 for rectifier and transformer thereof.
Invention is credited to Mochikawa, Hiroshi, Tsuda, Junichi.
Application Number | 20020015320 09/881039 |
Document ID | / |
Family ID | 18680802 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015320 |
Kind Code |
A1 |
Mochikawa, Hiroshi ; et
al. |
February 7, 2002 |
Rectifier and transformer thereof
Abstract
There are provided: a main three-phase full-wave rectifier (8)
that converts three-phase AC (R phase, S phase, T phase) into DC; a
transformer (9) that outputs AC of a total of six phases
corresponding to the points that equally divide by three the arcs
drawn in a transformer vector diagram in which an equilateral
triangle is formed whereof the R phase, S phase and T phase are
vertices, centered on each vertex and linking the remaining two
points; and two auxiliary three-phase full-wave rectifiers (12) and
(13) that convert into DC the six-phase AC that is output from the
transformer (9), the output lines of the main three-phase full-wave
rectifier (8) and two auxiliary three-phase full-wave rectifiers
(12) and (13) being connected in parallel. The current flowing in
the DC line through the transformer can therefore be reduced to 1/3
of the whole in the case of an 18-pulse rectifier, so enabling the
capacity of the transformer to be reduced.
Inventors: |
Mochikawa, Hiroshi; (Tokyo,
JP) ; Tsuda, Junichi; (Tokyo, JP) |
Correspondence
Address: |
Richard L. Schwaab
FOLEY & LARDNER
Washington Harbour
3000 K Street, N. W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
18680802 |
Appl. No.: |
09/881039 |
Filed: |
June 15, 2001 |
Current U.S.
Class: |
363/125 |
Current CPC
Class: |
H02M 7/08 20130101 |
Class at
Publication: |
363/125 |
International
Class: |
H02M 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2000 |
JP |
2000-179543 |
Claims
What is claimed is:
1. A rectifier, comprising: a main three-phase full-wave rectifier
that converts three-phase AC (R phase, S phase, T phase) into DC; a
transformer that outputs AC of a total of 3(n'11) phases
corresponding to the points that equally divide by n (n=2, 3) the
arcs drawn in a transformer vector diagram in which an equilateral
triangle is formed whereof said R phase, S phase and T phase are
vertices, centered on each vertex and linking the remaining two
points; and a plurality of (n-1) auxiliary three-phase full-wave
rectifiers that convert into DC the 3(n-1) phase AC that is output
from said transformer, wherein output lines of said main
three-phase full-wave rectifier and said (n-1) auxiliary
three-phase full-wave rectifiers are connected in parallel.
2. The rectifier according to claim 1, wherein said transformer
satisfies a transformer vector diagram obtained by adding to said
equilateral triangle 3(n-1) straight lines extending parallel with
one side of said equilateral triangle which is furthest, on sides
of said equilateral triangle that are closest to respective points
obtained by n equal divisions of said arc, in said transformer
vector diagram.
3. The rectifier according to claim 1, wherein, in said transformer
vector diagram, said transformer satisfies a transformer vector
diagram expressed by a periphery of a 3(n+2)-gon formed by
superimposing a 3(n-1)-gon formed with n points of equal division
of said arc as vertices on said equilateral triangle.
4. The rectifier according to claim 1, wherein, in said transformer
vector diagram, said transformer satisfies a transformer vector
diagram expressed by a hexagon formed by straight lines parallel
with a side opposite said equilateral triangle and passing through
vertices of said equilateral triangle and straight lines parallel
with sides adjacent said equilateral triangle passing through n
points of equal division of said arc.
5. The rectifier according to any of claim 2 to claim 4, further
comprising: a plurality of reactors corresponding to a leakage
inductance of said transformer, that are mounted on each phase of
power lines (R phase, S phase and T phase) between a branch point
to said transformer and said main three-phase full-wave
rectifier.
6. The rectifier according to any of claim 2 to claim 4, further
comprising: a harmonic attenuator that is provided on DC lines
where outputs of said main three-phase full-wave rectifier and said
(n-1) auxiliary three-phase full-wave rectifiers are connected in
parallel.
7. A transformer, comprising: an input member that inputs
three-phase AC (R phase, S phase and T phase) wherein said
transformer has a transformer vector diagram in which an
equilateral triangle is formed, whose vertices are said R phase, S
phase and T phase; an output member that outputs AC of a total of
3(n-1) phases corresponding to a plurality of points of equal
division by n (n=2, 3) of arcs centered on said each vertex and
drawn connecting remaining two points.
8. The transformer according to claim 7, wherein said transformer
satisfies a transformer vector diagram obtained by adding to said
equilateral triangle 3(n-1) straight lines extending parallel with
said one side of said equilateral triangle which is furthest, on
sides of said equilateral triangle that are closest to respective
points obtained by said n equal divisions of said arc, in said
transformer vector diagram.
9. The transformer according to claim 7, wherein in said
transformer vector diagram, said transformer satisfies a
transformer vector diagram expressed by a periphery of said
3(n+2)-gon formed by superimposing said 3(n-1)-gon formed with n
points of equal division of said arc as vertices on said
equilateral triangle.
10. The transformer according to claim 7, wherein in said
transformer vector diagram, said transformer satisfies a
transformer vector diagram expressed by a hexagon formed by
straight lines parallel with a side opposite said equilateral
triangle and passing through vertices of said equilateral triangle
and straight lines parallel with sides adjacent said equilateral
triangle passing through said n points of equal division of said
arc.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a rectifier and transformer
using this rectifier whereby three-phase AC is converted to DC with
little harmonics.
[0003] 2. Description of the Related Art
[0004] When converting three-phase AC to DC, the most typical
method is to employ a single three-phase full-wave rectifier in
which six rectifying elements are connected in a bridge
configuration. In such a three-phase full-wave rectifier, DC
voltage is output by changing over the rectifying elements so that
they successively conduct at intervals of 60.degree.. However, with
this method, the rectified DC voltage contains a voltage ripple of
large amplitude having a period of six times the power source
frequency; this produces harmonics which cause various
problems.
[0005] As a means of dealing with this, 18-pulse AC/DC converters
have been proposed such as for example in Laid-open Japanese Patent
Publication No. H. 4-229077. As shown in FIG. 1, this is
characterized in that, for the power lines 1r, 1s and 1t, two
transformers 2 and 3 are employed that output six-phase AC of equal
voltage but offset in phase by +40.degree. and -40.degree.,
respectively. An arrangement is adopted wherein three-phase
full-wave rectifiers 4 and 5 are connected to the two transformers
2 and 3 through lines 1r', 1s' and 1t' and 1r", is" and it", while
three-phase full-wave rectifier 6 is directly connected to power
source lines 1r, 1s and 1t. The outputs of the three three-phase
full-wave rectifiers 4, 5 and 6 are connected in parallel to DC
lines 7p and 7n.
[0006] FIG. 2 is a transformer vector diagram corresponding to FIG.
1. R1, S1 and T1 correspond to the phases of the three-phase AC of
the power source, their voltages being input to the three-phase
full-wave rectifier 6. In contrast, voltages corresponding to the
vertices R2', S2', T2' of the equilateral triangle obtained by
rotating by +40' the equilateral triangle formed by the vertices
R1, S1 and T1 are output from transformer 2 and input to
three-phase full-wave rectifier 4. Likewise, voltages corresponding
to the vertices R3', S3' and T3' of the equilateral triangle
obtained by rotating by -40.degree. the equilateral triangle formed
by the vertices R1, S1 and T1 are output from transformer 3 and
input to three-phase full-wave rectifier S.
[0007] Since the three-phase full-wave rectifier 4 or three-phase
full-wave rectifier 5 conduct so as to fill in the valleys of the
DC voltage ripple that is output through three-phase full-wave
rectifier 6 in the 18-pulse transformer constructed in this way,
the voltage ripple becomes small, and harmonics are reduced.
[0008] However, with this system, it is necessary that voltage of
magnitude equal to the three-phase AC voltage of the power source
should be output from the transformer, and the current flowing must
also be uniform in order for the three three-phase full-wave
rectifiers to conduct equally. Consequently, the current that is
rectified through the transformers is large at 2/3 of the total,
and transformers are required which can withstand this current
capacity. Effective miniaturization of the 18-pulse rectifier is
therefore impeded by the fact that practically all of its capacity
is accounted for by the transformers.
SUMMARY OF THE INVENTION
[0009] Accordingly, one object of present invention is to provide a
novel 12- or 18-pulse rectifier and transformer using such a
rectifier whereby performance equivalent to the above can be
achieved using a transformer of even smaller size.
[0010] In order to achieve the above object, a rectifier according
to the present invention comprises: a main three-phase full-wave
rectifier that converts three-phase AC (R phase, S phase, T phase)
into DC; a transformer that outputs AC of a total of 3(n-1) phases
corresponding to the points that equally divide by n (n=2, 3) the
arcs drawn in a transformer vector diagram in which an equilateral
triangle is formed whereof the R phase, S phase and T phase are
vertices, centered on each vertex and linking the remaining two
points; and (n-1) auxiliary three-phase full-wave rectifier(s) that
convert into DC the 3(n-1) phase AC that is output from the
transformer, the output lines of the main three-phase full-wave
rectifier and the (n-1) auxiliary three-phase full-wave
rectifier(s) being connected in parallel.
[0011] With a rectifier constructed in this way, the output voltage
from the transformer becomes lower than the power source voltage.
Furthermore, the current flowing through the transformer in the DC
line can be reduced to 1/4 of the whole in the case of a 12-pulse
rectifier and to 1/3 of the whole in the case of an 18-pulse
rectifier, so transformer capacity can be reduced.
[0012] In a rectifier according to the present invention the
transformer satisfies a transformer vector diagram obtained by
adding to the equilateral triangle 3(n-1) straight lines extending
parallel with the one side of the equilateral triangle which is
furthest, on the sides of the equilateral triangle that are closest
to the respective points obtained by the n equal divisions of the
arc, in the transformer vector diagram.
[0013] With a rectifier constructed in this way, a transformer can
be realized with a straightforward winding construction.
[0014] In a rectifier according to the present invention, in the
transformer vector diagram, the transformer satisfies a transformer
vector diagram expressed by the periphery of the 3(n+2)-gon formed
by superimposing the 3(n-1)-gon formed with the n points of equal
division of the arc as vertices on the equilateral triangle.
[0015] With a rectifier constructed in this way, the total number
of turns of the winding becomes fewer than in the case of the
transformer described above and the capacity becomes smaller, so
further miniaturization of the transformer can be achieved.
[0016] In a rectifier according to the present invention, in the
transformer vector diagram, the transformer satisfies a transformer
vector diagram expressed by the hexagon formed by straight lines
parallel with the side opposite the equilateral triangle and
passing through the vertices of the equilateral triangle and
straight lines parallel with the sides adjacent the equilateral
triangle passing through the n points of equal division of the
arc.
[0017] With a rectifier constructed in this way, a transformer of
small capacity can be achieved with a simpler winding
construction.
[0018] In a rectifier according to the present invention, reactors
corresponding to the leakage inductance of the transformer are
mounted on each phase of the power lines (R phase, S phase and T
phase) between the branch point to the transformer and the main
three-phase full-wave rectifier.
[0019] With a rectifier constructed in this way, the drop in output
voltage into the auxiliary three-phase full-wave rectifiers
resulting from the leakage inductance of the transformer is
balanced by a lowering of input voltage to the main three-phase
full-wave rectifier produced by the provision of the reactors, so
the conduction angle of the main three-phase full-wave rectifier
and auxiliary three-phase full-wave rectifiers can easily be
adjusted.
[0020] In a rectifier according to the present invention, harmonic
attenuators such as DC reactors are provided on the DC lines where
the outputs of the main three-phase full-wave rectifier and the
(n-1) auxiliary three-phase full-wave rectifiers are connected in
parallel.
[0021] With a rectifier constructed in this way, the slight
remaining voltage ripple in the DC that is output through the main
three-phase full-wave rectifier and auxiliary three-phase full-wave
rectifiers can be further reduced.
[0022] A transformer according to the present invention inputs
three-phase AC (R phase, S phase and T phase) and, in a transformer
vector diagram in which an equilateral triangle is formed whose
vertices are the R phase, S phase and T phase, outputs AC of a
total of 3(n-1) phases corresponding to the points of equal
division by n (n=2, 3) of the arcs centered on each vertex and
drawn connecting the remaining two points.
[0023] With a transformer constructed in this way, the output
voltage is lowered compared with a transformer in which the
position vectors of the output voltage are distributed on a circle
passing through the vertices R1, S1, T1 of an equilateral triangle,
as shown in the prior art example.
[0024] A transformer according to the present invention satisfies a
transformer vector diagram obtained by adding to the equilateral
triangle 3(n-1) straight lines extending parallel with the one side
of the equilateral triangle which is furthest, on the sides of the
equilateral triangle that are closest to the respective points
obtained by the n equal divisions of the arc, in the transformer
vector diagram.
[0025] With a transformer constructed in this way, the transformer
can be realized by a straightforward winding construction.
[0026] A transformer according to the present invention, in the
transformer vector diagram, satisfies a transformer vector diagram
expressed by the periphery of the 3(n+2)-gon formed by
superimposing the 3(n-1)-gon formed with the n points of equal
division of the arc as vertices on the equilateral triangle.
[0027] With a transformer constructed in this way, the total number
of turns of the windings is smaller, and the capacity is also
smaller, so even further miniaturization of the transformer can be
achieved.
[0028] A transformer according to the present invention, in the
transformer vector diagram, satisfies a transformer vector diagram
expressed by the hexagon formed by straight lines parallel with the
side opposite the equilateral triangle and passing through the
vertices of the equilateral triangle and straight lines parallel
with the sides adjacent the equilateral triangle passing through
the n points of equal division of the arc.
[0029] With a transformer constructed in this way, a transformer of
small capacity can be realized with a simpler winding
construction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily obtained
as the same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0031] FIG. 1 is a layout diagram of a prior art 12-pulse
rectifier;
[0032] FIG. 2 is a prior art transformer vector diagram;
[0033] FIG. 3 is a layout diagram of an 18-pulse rectifier
according to a first embodiment of the present invention;
[0034] FIG. 4 is a transformer vector diagram of the first
embodiment of the present invention;
[0035] FIG. 5 is a diagram illustrating the conduction condition of
a main three-phase full-wave rectifier and two auxiliary
three-phase full-wave rectifiers of an 18-pulse rectifier according
to a first embodiment of the present invention;
[0036] FIG. 6 is a transformer vector diagram of a second
embodiment of the present invention;
[0037] FIG. 7 is a diagram of the winding structure of a
transformer according to a second embodiment of the present
invention;
[0038] FIG. 8 is a transformer vector diagram of a third embodiment
of the present invention;
[0039] FIG. 9 is a diagram of the winding structure of a
transformer according to a third embodiment of the present
invention;
[0040] FIG. 10 is a transformer vector diagram of a fourth
embodiment of the present invention;
[0041] FIG. 11 is a diagram of the winding structure of a
transformer according to a fourth embodiment of the present
invention;
[0042] FIG. 12 is a layout diagram of a 12-pulse rectifier
according to a fifth embodiment of the present invention;
[0043] FIG. 13 is a transformer vector diagram of a fifth
embodiment of the present invention;
[0044] FIG. 14 is a diagram illustrating the conduction condition
of a main three-phase full-wave rectifier and auxiliary three-phase
full-wave rectifiers of a 12-pulse rectifier according to a fifth
embodiment of the present invention;
[0045] FIG. 15 is a transformer vector diagram of a sixth
embodiment of the present invention;
[0046] FIG. 16 is a diagram of the winding structure of a
transformer according to a sixth embodiment of the present
invention;
[0047] FIG. 17 is a transformer vector diagram of a seventh
embodiment of the present invention;
[0048] FIG. 18 is a diagram of the winding structure of a
transformer according to a seventh embodiment of the present
invention;
[0049] FIG. 19 is a transformer vector diagram of an eighth
embodiment of the present invention;
[0050] FIG. 20 is a diagram of the winding structure of a
transformer according to an eighth embodiment of the present
invention;
[0051] FIG. 21 is a layout diagram of an 18-pulse rectifier
according to a ninth embodiment of the present invention; and
[0052] FIG. 22 is a layout diagram of an 18-pulse rectifier
according to a tenth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and more particularly to FIG. 3, FIG. 4 and FIG. 5
thereof, one embodiment of the present invention will be
described.
[0054] FIG. 3 is a layout diagram illustrating the layout of an
18-pulse rectifier, wherein a main three-phase full-wave rectifier
8 is connected by power lines 1r, 1s and 1t to a three-phase AC
power source (not shown). Furthermore, transformer 9 is connected
to power lines 1r, 1s and 1t and the total of six phases that are
output on the secondary side of this transformer 9 are respectively
input to two auxiliary three-phase full-wave rectifiers 12 and 13
through three power lines 10r, 10s and 10t, and 11r, 11s and 11t.
The outputs of the main three-phase full-wave rectifier 8 and the
two auxiliary three-phase full-wave rectifiers 12 and 13 are
connected in parallel to DC lines 7p and 7n.
[0055] FIG. 4 is a transformer vector diagram representing the six
phase voltage vectors that are output from transformer 9. The three
arcs X1Y1 (X, Y =R, S, T (X.noteq.Y)) in the Figure have at their
centers the vertices of the equilateral triangles formed by the
three-phase AC: R1, S1 and T1 of the power source.
[0056] Also, the points X3 and Y2 on the arcs represent positions
that trisect arcs X1Y1 at intervals of 20.degree.; the voltages
represented by these six position vectors are output from
transformer 9 to the two auxiliary three-phase full-wave rectifiers
11 and 12.
[0057] If such a transformer is employed, the output voltages are
lower than for a transformer such as would give output voltage
position vectors on the circle passing through vertices R1, S1 and
T1 of the equilateral triangle as shown in the prior art
example.
[0058] Furthermore, FIG. 5 shows the conduction condition of the
main three-phase full-wave rectifier 8 and two auxiliary
three-phase full-wave rectifiers 12 and 13 for the respective
phases of the first embodiment.
[0059] Whereas the conductive condition of the phases R1, S1 and T1
of the main three-phase full-wave rectifier 8, including the plus
side and the minus side occurs for 160.degree. out of 360.degree.
of a single cycle, in the case of the six phases of the auxiliary
three-phase full-wave rectifiers 12 and 13, including the plus side
and the minus side, the conductive condition occurs for 40.degree.,
which is only 1/4 of that of the main three-phase full-wave
rectifier 8.
[0060] Consequently, of the current flowing from the AC power
source lines 1r, 1s and 1t to the DC lines 7p and 7n, the current
flowing through transformer 9 and the two auxiliary three-phase
full-wave rectifiers 12 and 13 is 1/3 of the total. This means
that, compared with the situation in the prior art example in which
the current flows equally in the three three-phase full-wave
rectifiers and 2/3 of the total current flows through the
transformers, the current is halved, so the transformer capacity
can be halved.
[0061] Next, a second embodiment of the present invention will be
described.
[0062] FIG. 6 shows a second embodiment of the present invention
and is a transformer vector diagram illustrating a specific winding
construction of the transformer illustrated in the first
embodiment. Points X4 and X5 in the Figure are positioned on the
sides of the equilateral triangle whose vertices are R1, S1 and T1,
and straight lines X2X4 and X3X5 are positioned so as to be
parallel with sides Y1Z1 (Z=R S, T (Z.noteq.X, Y)).
[0063] FIG. 7 represents diagrammatically the actual winding
construction of the transformer represented in FIG. 6. In this
construction, the primary windings of transformer 9 connected to
power lines 1r, 1s, and 1t constitute a delta connection and two
sets of secondary windings are provided corresponding to each
primary winding. The total of six connection points X4, X5 provided
between primary windings X1Y1 corresponding to the transformer
vector diagram of FIG. 6 are respectively connected to the
corresponding secondary windings. X2 and X3 of the secondary
windings are output terminals and are connected to the two
auxiliary three-phase full-wave rectifiers 12 and 13.
[0064] The voltage ratio between the terminals i.e. the turns ratio
of the windings is designed to be proportional to the length of the
leads in FIG. 6. If it is difficult to match the turns ratio
precisely, a suitably approximated ratio is selected. By adopting
such a winding construction, the transformer winding construction
is simplified, so the proposed 18-pulse rectifier can be realized
at low cost.
[0065] Next, a third embodiment of the present invention will be
described.
[0066] FIG. 8 illustrates a third embodiment of the present
invention and is a transformer vector diagram illustrating the
specific transformer winding construction illustrated in the first
embodiment. Comparing this with the transformer vector diagram of
FIG. 6 that illustrates the second embodiment, this is represented
by a vector diagram in which straight line X5Y4 is deleted and
instead X3 and Y2 are connected by a straight line.
[0067] FIG. 9 shows the actual winding construction of the
transformer illustrated in FIG. 8 represented diagrammatically. In
this embodiment, all the primary windings and secondary windings
are connected to a single one and X2 and X3, which are intermediate
terminals, constitute the output terminals to the two auxiliary
three-phase full-wave rectifiers 12 and 13. In this case, just as
in the second embodiment, the voltage ratios between the terminals
i.e. the turns ratio of the windings are designed so as to be
proportional to the length of the respective leads in FIG. 8.
[0068] In FIG. 8, the length of straight line X3Y2 is shorter than
that of straight line X5Y4. This means that, compared with the
second embodiment, the apportionment ratio produced by the turns
ratio is smaller, so the voltage share of the winding is decreased,
decreasing the transformer capacity and, in addition, decreasing
the number of turns, thus making it possible to realize an even
smaller transformer.
[0069] Next, a fourth embodiment of the present invention will be
described.
[0070] FIG. 10 illustrates a fourth embodiment of the present
invention and is a transformer vector diagram illustrating a
specific winding construction of the transformer illustrated in the
first embodiment. It is represented by a hexagon, in which the
sides X6X7 passing through X1 are parallel with the sides Y1Z1 of
the equilateral triangle and sides X7Y6 pass through points X3, Y2
which equally divide the arcs.
[0071] FIG. 11 represents diagrammatically the actual winding
construction of the transformer illustrated in FIG. 10. In this
embodiment, transformer 9 is of a single winding construction, and
AC power lines 1r, 1s and 1t are connected at an intermediate point
of the secondary winding. The output terminals to the two auxiliary
three-phase full-wave rectifiers 12, 13 are X2 and X3, which are
midway along the primary winding. In this case, just as in the case
of the second embodiment and third embodiment, the turns ratio of
the respective windings is determined so as to practically coincide
with the length ratio of the corresponding leads in FIG. 10.
[0072] With this winding construction, compared with the third
embodiment, the voltage apportionment ratio of the windings is the
same, but the number of terminals is reduced, so a transformer
construction which is restricted to small capacity can be realized
with an even simpler winding construction, thereby making it
possible to achieve further cost reduction.
[0073] A 12-pulse rectifier constituting a fifth embodiment of the
present invention is described with reference to FIG. 12, FIG. 13
and FIG. 14.
[0074] FIG. 12 is a layout diagram illustrating the construction of
a 12-pulse rectifier, in which main three-phase full-wave rectifier
8 is connected to a three-phase AC power source (not shown) by
power lines 1r, 1s and 1t. In addition, transformer 9 is connected
to power lines 1r, 1s and 1t and the three-phase that is output on
the secondary side of this transformer 9 is input to auxiliary
three-phase full-wave rectifier 12 through the three power lines
10r, 10s and 10t. The outputs of the main three-phase full-wave
rectifier 8 and auxiliary three-phase full-wave rectifier 12 are
connected in parallel to DC lines 7p and 7n.
[0075] FIG. 13 is a transformer vector diagram representing the
three-phase voltage vectors that are output from transformer 9. In
the Figure, the three arcs X1Y1 (X, Y=R, S, T (S.noteq.Y)) have at
their centers the respective vertices of the equilateral triangles
formed by the three-phase AC R1, S1 and T1 of the power source.
[0076] Also, the points Y2 on the arcs represent the positions in
which arcs X1Y1 are bisected at an interval of 30.degree. in each
case; the voltages represented by these three position vectors are
output from transformer 9 to auxiliary three-phase full-wave
rectifier 12.
[0077] When such a transformer is employed, the output voltage is
lowered compared with a transformer in which the position vectors
of the output voltage are distributed on a circle passing through
the vertices R1, S1 and T1 of an equilateral triangle, as shown in
the prior art example.
[0078] Further, FIG. 14 shows the conduction conditions of the main
three-phase full-wave rectifier 8 and auxiliary three-phase
full-wave rectifier 12 for each phase of the fifth embodiment.
Whereas the conductive condition of the phases R1, S1 and T1 of the
main three-phase full-wave rectifier 8, including the plus side and
the minus side occurs for 180.degree. out of 360.degree. of a
single cycle, in the case of the three phases of the auxiliary
three-phase full-wave rectifier 12, including the plus side and the
minus side, the conductive condition occurs for 60.degree., which
is only 1/3 of that of the main three-phase full-wave rectifier
8.
[0079] Consequently, of the current flowing from the AC power
source lines 1r, 1s and 1t to the DC lines 7p and 7n, the current
flowing through transformer 9 and the auxiliary three-phase
full-wave rectifier 12 is 1/4 of the total so the transformer
capacity can be greatly reduced.
[0080] Next, a sixth embodiment of the present invention will be
described.
[0081] FIG. 15 illustrates a sixth embodiment of the present
invention and is a transformer vector diagram illustrating the
specific winding construction of the transformer illustrated in the
fifth embodiment. Points X4 in the Figure is positioned on the
sides of the equilateral triangle whose vertices are R1, S1 and T1,
and straight lines X2X4 are positioned so as to be parallel with
sides Y1Z1 (Z=R, S, T (Z.noteq.X, Y) ).
[0082] FIG. 16 represents diagrammatically the actual winding
construction of the transformer represented in FIG. 15. In this
construction, the primary windings of transformer 9 connected to
power lines 1r, 1s, and 1t constitute a delta connection and one
set of secondary windings is provided corresponding to each primary
winding. The total of three connection point X4 provided between
primary windings X1Y1 corresponding to the transformer vector
diagram of FIG. 6 are respectively connected to the corresponding
secondary windings. X2 of the secondary windings are output
terminals and are connected to the auxiliary three-phase full-wave
rectifier 12.
[0083] The voltage ratio between the terminals i.e. the turns ratio
of the windings is designed to be proportional to the length of the
leads in FIG. 15. If it is difficult to match the turns ratio
precisely, a suitably approximated ratio is selected. By adopting
such a winding construction, the proposed 12-pulse rectifier can be
realized at low cost, using a transformer of simple
construction.
[0084] Next, a seventh embodiment of the present invention will be
described.
[0085] FIG. 17 shows a seventh embodiment of the present invention
and is a transformer vector diagram illustrating a specific winding
construction of the transformer illustrated in the fifth
embodiment. Points X4 and X5 in the Figure are positioned on the
sides of the equilateral triangle whose vertices are R1, S1 and T1,
and straight lines X2X4 are positioned so as to be parallel with
sides Y1Z1 (Z=R, S, T (Z.noteq.X, Y)), while straight lines X2Y5
are positioned so as to be parallel with sides X1Z1 (Z=R, S, T
(Z.noteq.X, Y)).
[0086] FIG. 18 represents diagrammatically the actual winding
construction of the transformer represented in FIG. 17. In this
embodiment, all the primary windings and secondary windings are
connected to a single one and X2, which are intermediate terminals,
constitute the output terminals to the auxiliary three-phase
full-wave rectifier 12. In this case, just as in the sixth
embodiment, the voltage ratios between the terminals i.e. the turns
ratio of the windings are designed so as to be proportional to the
length of the respective leads in FIG. 17.
[0087] Next, an eighth embodiment of the present invention will be
described.
[0088] FIG. 19 illustrates an eighth embodiment of the present
invention and is a transformer vector diagram illustrating a
specific winding construction of the transformer illustrated in the
fifth embodiment. It is represented by a hexagon, in which the
sides X6X7 passing through X1 are parallel with the sides Y1Z1 of
the equilateral triangle and sides X7Y6 pass through points X2
which equally divide the arcs.
[0089] FIG. 20 represents diagrammatically the actual winding
construction of the transformer illustrated in FIG. 19. In this
embodiment, transformer 9 is of a single winding construction, and
AC power lines 1r, 1s and 1t are connected at an intermediate point
of the secondary winding. The output terminals to the auxiliary
three-phase full-wave rectifier 12 are X2, which are midway along
the primary winding. In this case, just as in the case of the sixth
embodiment and seventh embodiment, the turns ratio of the
respective windings is determined so as to practically coincide
with the length ratio of the corresponding leads in FIG. 19.
[0090] With this winding construction, compared with the seventh
embodiment, the voltage apportionment ratio of the windings is the
same, but the number of terminals is reduced, so the transformer
can be further simplified.
[0091] FIG. 21 is a layout diagram illustrating a ninth embodiment
of the present invention. In contrast to FIG. 3, which illustrates
the first embodiment, reactors 14 are respectively mounted on the
power lines 1r, 1s and 1t between the branch points to transformer
9 and the main three-phase full-wave rectifier 8. The inductance of
the reactors 14 is selected to be equal to the leakage inductance
of transformer 9.
[0092] Since, unlike an ideal transformer, a real transformer
possesses leakage inductance, the voltage that is output on the
secondary side is somewhat lowered. As a result, there is a
possibility of the balance between the output voltage from the main
three-phase full-wave rectifier 8 and the output voltages from the
two auxiliary three-phase full-wave rectifiers 12 and 13 being
lost, with the result that sufficient reduction of harmonics cannot
be achieved. Reactors 14 have the action of lowering the input
voltage to main three-phase full-wave rectifier 8 by the amount
that the output voltage of transformer 9 is lowered; balance of the
output voltages from the main three-phase full-wave rectifier 8 and
the two auxiliary three-phase full-wave rectifiers 12 and 13 is
thereby maintained, making it possible to achieve even better
reduction of harmonics.
[0093] Although hereinabove the example of an 18-pulse rectifier
was described, this could of course be applied to a 12-pulse
rectifier also.
[0094] FIG. 22 is a layout diagram illustrating a tenth embodiment
of the present invention. In contrast to the layout of FIG. 3 which
illustrates the first embodiment, DC reactors 15 are added to the
DC lines 7p and 7n to which are connected in parallel the outputs
of the main three-phase full-wave rectifier 8 and the two auxiliary
three-phase full-wave rectifiers 12 and 13. DC reactors 15 have the
action of further suppressing the harmonics that have already been
reduced in some degree by passage through main three-phase
full-wave rectifier 8 and transformer 9 and the two auxiliary
three-phase full-wave rectifiers 12 and 13. They are therefore
extremely useful in cases where even better measures against
harmonics are required.
[0095] Although hereinabove the example of an 18-pulse rectifier
was described, this could of course be applied to a 12-pulse
rectifier also.
[0096] As described in detail above, with a rectifier according to
the present invention, the current passing through the transformer
and auxiliary three-phase full-wave rectifiers can be reduced to
1/4 of the whole in the case of a 12-pulse rectifier and to 1/3 of
the whole in the case of an 18-pulse rectifier. Transformer
capacity can therefore be greatly reduced compared with
conventionally, making it possible to achieve miniaturization of
the pulse rectifier as whole. Also, miniaturization of the
transformer can be achieved with a straightforward winding
construction.
[0097] Obviously, numerous additional modifications and variations
of the present invention are possible in light of the above
teachings. It is therefore to be understood that within the scope
of the appended claims, the present invention may be practiced
otherwise than as specially described herein.
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