Transformer/rectifier for aircraft ground power unit

Details Transformer/rectifier for aircraft ground power unit Transformer/rectifier for aircraft ground power unit

2000-11-17

2001-11-20

Han, Jessica (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S087000, C323S361000

Reexamination Certificate

active

06320773

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to aircraft ground power units and transformer/rectifier systems used in such units for converting 3-phase ac input into a substantially stable dc output and, more particularly, to a transformer/rectifier arrangement which provides reduced voltage drops across diodes in high output current systems.
BACKGROUND OF THE INVENTION
Aircraft ground power units are utilized to power aircraft when on the ground. Larger aircraft tend to utilize ground power units which output ac power while smaller aircraft tend to utilize ground power units which output dc power, typically at about 28 volts and in the range of several hundred amps. In ground power units that output dc power, the de power may be developed from a 3-phase ac source such as a static converter or a generator. In either case a transformer/rectifier arrangement may be used to convert the 3-phase ac power to the desired dc output.
Transformer/rectifier configurations for converting 3-phase power to a de output are known, with each configuration including its own set of advantages and disadvantages. One such configuration
10
is illustrated in
FIG. 1
which shows a full wave center tap connection
12
with
6
pulse rectification of a 3-phase (A, B, C) input. Notably, the 3 input phases A, B, and C are connected in a STAR (Y) configuration
14
and share a common neutral connection
16
, and a single 3-phase transformer
18
defined by one magnetic member can be used for coupling the primary windings
20
A,
20
B,
20
C to the secondary windings
22
A,
22
B,
22
C. Each side of each secondary winding connects to the anode side of a respective diode
24
(d
1
-d
6
) to provide the 6 pulse rectification. Notable characteristics of this arrangement are (1) that only one diode
24
conducts at any one time such that each diode conducts for 60 electrical degrees with its peak current equal to the dc load current and (2) the current rating of each transformer secondary winding is 0.408 times the dc load current. Characteristic (1) is undesired when high current systems are implemented because the voltage drop across the diodes can be significant. Characteristic (2) influences the size of the transformer because the higher the current through the secondary windings, the greater the cross-section of the wire needed to form the secondary winding of the transformer.
Accordingly, it would be desirable to provide a transformer/rectifier arrangement with lower diode drops in systems having high dc current output such as in aircraft ground power units.
SUMMARY OF THE INVENTION
In one aspect of the present invention, an aircraft ground power unit includes a transformer/rectifier arrangement for converting 3-phase ac power to dc power. The transformer/rectifier arrangement includes an A-phase transformer formed by an A-phase magnetic member, an A-phase primary winding having first and second sides, and an A-phase secondary winding; a B-phase transformer formed by a B-phase magnetic member, a B-phase primary winding having first and second sides, and a B-phase secondary winding; and a C-phase transformer formed by a C-phase magnetic member, a C-phase primary winding having first and second sides, and a C-phase secondary winding. The A-phase primary winding first side is connected to receive A-phase power, the B-phase primary winding first side is connected to receive B-phase power, and the C-phase primary winding first side is connected to receive C-phase power. The A-phase primary winding second side, B-phase primary winding second side and C-phase primary winding second side are connected together for delivering current traveling out of one of the second sides into at least one of the other second sides.
In such arrangement the A-phase, B-phase, and C-phase secondary windings are arranged in a full wave center-tap transformer output connection which includes an output for delivering current to a load when connected thereto. In operation, where the center-tap configuration includes six diodes, two diodes conduct at any one time, the peak dc current through each diode is limited to ½ the dc current delivered to the load, and the current rating of each secondary winding is 0.286 times the dc current delivered to the load.


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