Multiphase transformer having main and auxiliary transformers

Details Multiphase transformer having main and auxiliary transformers Multiphase transformer having main and auxiliary transformers

2001-01-16

2002-07-23

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Phase conversion without intermediate conversion to d.c.

By induction-type converter

C363S064000

Reexamination Certificate

active

06424552

ABSTRACT:

This invention relates generally to multi-phase transformer systems and more particularly to multi-phase power transformer systems having improved phasor balance and reduced total harmonic distortion (THD).
As is known in the art, many electrical systems require direct current power. Such direct current (DC) is typically produced by rectifying three-phase alternating current (AC) voltage. The rectifiers, however, induce harmonic distortion in the input line. Such effect is described in U.S. Pat. No. 4,779,181 entitled “Multiphase Low Harmonic Distortion Transformer”, inventors Traver et al., issued Oct. 18, 1988. The total harmonic distortion (THD) generated by rectification can be improved by increasing the number of AC phases fed to the rectifiers. Some of these multi-phase transformer systems are described in the U.S. Pat. Nos.: 4,779,181, 4,255,784, 5,148,357, 4,532,581, and 4,488,211. The line harmonics for these systems are inversely proportional to the number of phases according to the following equation:
K
H
=2*m*(n+/−1),
where K
H
is the harmonic order
m is the number of phases
n =0, 1,2, . . .
For example, the harmonics of a 12-phase system are:
23
,
25
,
47
,
49
,
71
,
73
.
A schematic diagram for a conventional 18-phase, single transformer is shown in
FIGS. 1A and 1B
. Thus, the transformer
10
has a three-phase primary winding
12
magnetically coupled to a secondary winding section
16
through a core
14
. The secondary winding section
16
has a set of six main Y-configured, three-phase secondary windings
16
a
-
16
f
. The voltage produced in the three secondary windings of set
16
a
are {overscore (A)}, {overscore (B)} and {overscore (C)} where {overscore (A)}, {overscore (B)} and {overscore (C)} have equal magnitudes and 120 degrees of relative phase shift with respect to each other. The voltages produced in the three secondary windings of set
16
b
are K
1
{overscore (A)}, K
1
{overscore (B)} and K
1
{overscore (C)} where K
1
is a less than one. Thus, the number of turns in each of the three windings in set
16
a
are equal to each other and the number of turns set
16
b
are equal to each other the number of turns in the three sets of windings in set
16
b
are a fraction of the number of turns in the three windings in set
16
a
. Thus, the voltages K
1
{overscore (A)}, K
1
{overscore (B)} and K
1
{overscore (C)} have equal magnitudes, here 1/K
1
th the voltage in each of the windings set
16
, and 120 degrees of relative phase shift with respect to each other. That is, the voltages K
1
{overscore (A)}, K
1
{overscore (B)} and K
1
{overscore (C)} are in-phase with the voltages {overscore (A)}, {overscore (B)}, and {overscore (C)} in set
16
a
. In like manner, the voltages in sets
16
c
through
16
f
are: K
2
{overscore (A)}, K
2
{overscore (B)} and K
2
{overscore (C)}; K
3
{overscore (A)}, K
3
{overscore (B)} and K
3
{overscore (C)}; K
4
{overscore (A)}, K
4
{overscore (B)} and K
4
{overscore (C)}; and K
5
{overscore (A)}, K
5
{overscore (B)} and K
5
{overscore (C)}, respectively, where K
3
=1, K
1
=K
4
, K
2
=K
5
, K
2
<K
1
and such relationship is determined by the relative number of turns in the windings.
The secondary section
16
also includes six sets
16
g
-
16
l
of auxiliary windings magnetically coupled to the primary
12
though core
14
. Each set has three windings. Each one of the windings in the set produces a voltage in-phase with a corresponding one of the three voltage {overscore (A)}, {overscore (B)}, and {overscore (C)}. The magnitudes of the voltages in sets
16
g
-
16
l
are scaled relatively to the magnitudes of the voltages {overscore (A)}, {overscore (B)}, and {overscore (C)} by factors of: 1/K
6
through 1/K
11
, respectively. It is noted that the windings in sets
16
a
through
16
f
are connected to the windings in sets
16
g
through
16
l
selectively as shown to thereby produce voltages V
O1
through V
O18
which may be represented as: {overscore (C)}+K
6
{overscore (A)};
{overscore (A)}+K
6
{overscore (B)};
{overscore (B)}+K
6
{overscore (C)};
K
1
{overscore (C)}+K
7
{overscore (A)};
K
1
{overscore (A)}+K
7
{overscore (B)};
K
1
{overscore (B)}+K
7
{overscore (C)};
K
2
{overscore (C)}+K
8
{overscore (A)};
K
2
{overscore (A)}+K
8
{overscore (B)};
K
2
{overscore (B)}+K
8
{overscore (C)};
K
3
{overscore (C)}+K
9
{overscore (A)};
K
3
{overscore (A)}+K
9
{overscore (B)};
K
3
{overscore (B)}+K
9
{overscore (C)};
K
4
{overscore (C)}+K
10
{overscore (A)};
K
4
{overscore (A)}+K
10
{overscore (B)};
K
4
{overscore (B)}+K
10
{overscore (C)};
K
5
{overscore (C)}+K
11
{overscore (A)};
K
5
{overscore (A)}+K
11
{overscore (B)};
K
5
{overscore (B)}+K
11
{overscore (C)}, respectively.
These voltages VO
1
through VO
11
are fed to a rectification system, as shown. The rectified voltages are combined in combiner
20
to produce the here 18-phase combined output voltage, VOUT.
SUMMARY
In accordance with the present invention, a multi-phase transformer system is provided having a main transformer fed by an N-phase voltage and a separate auxiliary transformer fed by the N-phase voltage. Windings in the main transformer are connected to secondary windings in the auxiliary transformer to provide pairs of connected windings. Each pair of connected windings has one of the windings of the main transformer and one of the secondary windings of the auxiliary transformer. The windings in such connected pair are arranged to produce voltages having different phases with each pair of windings producing an output voltage equal to the vector sum of the voltages produced by the such connected pair of windings.
With such an arrangement, by having two separate transformers, i.e., the main transformer and the auxiliary transformer, fabrication of a multi-phase transformer system is simplified. Further, leakage inductance in the auxiliary transformer may be readily adjusted and increased to thereby suppress higher harmonic distortion without the need for an additional filter. The increased leakage inductance of the auxiliary transformer does not cause higher harmonic distortion in the low frequency part of the spectrum that occurs if the leakage inductance of the main transformer is increased.
In one embodiment, secondary windings of the main transformer are connected to the secondary windings of the auxiliary transformer. In such embodiment, each pair of connected windings includes one of the secondary windings of the main transformer and one of the secondary windings of the auxiliary transformer.
In a second embodiment, the N-phase voltage is connected directly to the primary winding of the auxiliary transformer and indirectly to the primary windings of the main transformer through the secondary windings of the auxiliary transformer. In such embodiment, each pair of windings includes one of the secondary windings of the auxiliary transformer and one of the primary windings of the main transformer.
In accordance with still another aspect of the invention, a multi-phase transformer system is provided having a main transformer and a separate auxiliary transformer. The main transformer includes a main secondary winding section magnetically coupled to a main primary winding section. One of the winding sections of the main transformer includes a plurality of M sets of main windings, where M is an integer greater than one. Each one of the M sets has a plurality of N main windings for producing N voltages having the same amplitudes and a predetermined phase relationship. The amplitudes of the voltages produced by one of the sets are different from the amplitude of the voltages produced by another one of the sets. The auxiliary transformer includes an auxiliary primary winding section having inputs connected to the main transformer. The auxiliary transformer includes a plurality of M auxiliary secondary winding sets magnetically coupled to an auxiliary primary winding section. Each one of the M sets of auxiliary seco

Affiliated with

Also associated with

Rating

Multiphase transformer having main and auxiliary transformers does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multiphase transformer having main and auxiliary transformers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiphase transformer having main and auxiliary transformers will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2879642