Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-07-06
2001-03-20
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S024000
Reexamination Certificate
active
06205035
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a DC/DC converter with bi-directional energy flow.
Such converters can be used for example in motor vehicle technology for the purpose of transferring energy between a starter battery and a fuel cell system.
In the case of an electric vehicle drive fed by fuel cells, the starting operation may necessitate the provision of auxiliary energy with a DC voltage of more than 200 V and a power of approximately 2 kW. Using a step-up converter, the required auxiliary energy can be drawn e.g. from a 12 V starter battery during the starting operation. The starter battery can be subsequently recharged using a step-down converter by the electrical energy that can be supplied by the fuel cell battery with a DC voltage of 250 V, for example.
The use of both a step-up converter and, in addition, of a step-down converter in such an application signifies a considerable outlay.
A DC/DC converter that operates as a step-up converter in a first direction of energy flow and alternately as a step-down converter in the opposite direction is therefore desirable. At the same time, it is necessary to provide DC decoupling of the electric circuits to be connected by the DC/DC converter.
In many applications, particularly in motor vehicle technology, DC/DC converters that operate only as step-down converters but likewise have potential isolation are also required. Such unidirectional DC/DC step-down converters as well as the above-mentioned bi-directional DC/DC converter should be able to be realized particularly compactly in a manner that saves both materials and costs.
One approach to realizing particularly compact converters is provided by Published, Non-Prosecuted German Patent Application DE 195 42 357 A1. A magnetic compound unit and a number of converter circuits can be found therein. The magnetic compound unit can be used to realize converter circuits in which the function of an energy storage inductor with a center tap can be combined together with the function of a potential-isolating transformer in a single inductive component. Various embodiments of the magnetic compound unit are specified in
FIGS. 7
,
8
and
8
a
of the Published, Non-Prosecuted German Patent Application DE 195 42 357 A1.
An AC/DC converter circuit which operates as a step-up converter is specified in
FIG. 6
of the Published, Non-Prosecuted German Patent Application DE 195 42 357 A1. Although this circuit can be changed into a DC/DC step-up converter in a straightforward manner by omitting the rectifier bridge on the input side, it operates only in one direction of energy flow.
FIG. 11
of the Published, Non-Prosecuted German Patent Application DE 195 42 357 A1 shows a further AC/DC converter circuit, which, depending on the driving, can operate as a step-up or step-down converter, although only ever in one direction of energy flow. This circuit could be embodied as a DC/DC step-down converter in a straightforward manner by omitting the rectifier bridge on the input side. However, the converter has a non-continuous HF output current in the stepping down mode on the output side downstream of the rectification, the AC component of which output current stresses the output capacitor. Therefore, although this configuration is suitable for large output powers, it is not suitable for large output currents.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a DC/DC converter which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which a potential-isolated, bi-directionally operable DC/DC converter and also a potential-isolated DC/DC step-down converter are in each case disclosed and intended to be realized with a particularly low cost and outlay.
With the foregoing and other objects in view there is provided, in accordance with the invention, a DC/DC converter acting alternately as a step-up converter in a first direction of energy flow and as a step-down converter in a second direction of the energy flow, including:
a magnetic compound unit having an iron core with an air gap-free limb, an air gap-containing magnetic circuit for realizing an energy store function, and an air gap-free magnetic circuit for realizing a transformer function disposed parallel to the air gap-containing magnetic circuit, the magnetic compound unit further having two series-connected low-voltage windings with a junction point there-between routed out as a center tap and two series-connected high-voltage windings, a respective low-voltage winding of the two series-connected low-voltage windings disposed together with one of the series-connected high-voltage windings on the air gap-free limb of the iron core;
a first switch circuit connected to the two series-connected low-voltage windings;
a first rectifier circuit connected to the two series-connected high-voltage windings;
a first smoothing circuit connected to the first rectifier circuit;
a controller connected to the first rectifier circuit and the two series-connected low-voltage windings;
the controller, the first switching circuit, the first rectifier circuit and the first smoothing circuit defining step-up converter components for performing step-up converter operations;
a second switching circuit connected to the first rectifier circuit;
a second rectifier circuit connected to the two series-connected low-voltage windings;
a second smoothing circuit connected to the two series-connected low-voltage windings;
the second switching circuit, the second rectifier circuit, the second smoothing circuit and the controller defining step-down converter components for performing step-down converter operations; and
an energy flow circuit for controlling a direction of energy flow.
The circuit according to the invention in conjunction with the magnetic compound unit, which can also be embodied in a flat configuration, makes it possible to produce particularly compact converters.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a DC/DC converter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
REFERENCES:
patent: 3986097 (1976-10-01), Woods
patent: 4953068 (1990-08-01), Henze
patent: 5140509 (1992-08-01), Murugan
patent: 5181169 (1993-01-01), Murugan
patent: 5255174 (1993-10-01), Murugan
patent: 5381327 (1995-01-01), Yan
patent: 5903448 (1999-05-01), Davila
patent: 5930134 (1999-07-01), Glennon
patent: 6021052 (2000-02-01), Unger et al.
patent: 195 42 357 A1 (1999-04-01), None
Lorenz Helmut
Schell Andreas
Vollmer Ludwig
Ascom Energy Systems AG
Greenberg Laurence A.
Lerner Herbert L.
Stemer Werner H.
Sterrett Jeffrey
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