Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-08-25
2002-08-27
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S132000
Reexamination Certificate
active
06442047
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power conversion apparatus and methods, and more particularly, to switching converters and methods of operation thereof.
DC-to-DC power conversion is commonly achieved using switching regulator circuits. These switching regulator circuits often include one or more switching elements that selectively couple a DC power source to a primary winding of a transformer such that an AC voltage is produced on a secondary winding of the transformer. This AC voltage may then be rectified and filtered to produce a DC output voltage. The DC output voltage may be regulated by controlling the switching frequency and/or duty cycle of the switching elements.
It is generally desirable that the switching element(s) of a switching regulator operate at high frequencies to allow for the use of small and lightweight magnetic components (e.g., lightweight transformers and inductors). An unfortunate result of such high frequency switching operations may be increased power dissipation due to resistance and capacitance associated with the switching element(s). Accordingly, it is generally desirable for the switching element(s) of a switching regulator to switch under minimized current and/or voltage conditions to reduce power dissipation.
Examples of power converters that may provide reduced or “zero current” switching (ZCS) are described in U.S. Pat. No. 4,415,959 to Vinciarelli; and in U.S. Pat. No. 4,823,249 to Garcia, II. Examples of power converters that may provide for reduced or “zero voltage” switching (ZVS) are described in “Design Review: 500 W, 40 W/in
3
Phase Shifted ZVT Power Converter,” Topic 4, SEM-900
Power Supply Design Seminar Manual
, Unitrode Integrated Circuit Corporation; “Optimum ZVS Full-Bridge DC/DC Converter with PWM Phase Shift Control: Analysis, Design Considerations, and Experimental Results,” by Balogh et al.,
APEC
'94
Proceedings
, pp. 159-165 (1994); “A Novel Soft-Switching Full Bridge DC/DC Converter: Analysis, Design Considerations, and Experimental Results At 1.5 kW, 100 kHz,” by Redl et al.,
PESC
'90
Proceedings
, pp. 162-172 (1990); “Designing a Phase Shifted Zero Voltage Transition (ZVT) Power Converter,” Topic 3
, SEM
-900
Power Supply Design Seminar Manual
, Unitrode Integrated Circuit Corporation; “A Fixed Frequency ZVS High Power SMR Converter with Zero to Rated Load Variation Capability,” by Moshopolous et al.,
INT
-
ELEC
'92
Proceedings
, pp. 351-358 (1992); “UC3879 Phase-Shift Resonant Controller” Data Sheet, Unitrode Integrated Circuit Corporation; “The New UC3879 Phase Shifted PWM Controller Simplifies the Design of Zero Voltage Transition Full Bridge Converters,”
Application Note
U154, Unitrode Integrated Circuit Corporation.
SUMMARY OF THE INVENTION
According to embodiments of the invention, a power conversion apparatus, e.g., a DC-to-DC converter, includes a transformer having primary and secondary windings. A first switching circuit has an input port configured to be coupled across a DC power source and an output port coupled to the primary winding of the transformer. A switch control circuit is operatively associated with the first switching circuit and causes the first switching circuit to alternately apply first and second polarity voltages to the primary winding. A second switching circuit is operative to transfer energy to a load from the secondary winding via a first capacitor responsive to application of the first polarity voltage to the primary winding and to transfer energy to the load from the secondary winding via a second capacitor responsive to application of the second polarity voltage to the primary winding.
According to embodiments of the invention, the first switching circuit comprises at least one switch, and the switch control circuit constrains the at least one switch to operate when current in the at least one switch falls to a predetermined level, e.g., substantially near zero. The switch control circuit may operate the at least one switch responsive to a current through the transformer. Alternatively, the switch control circuit may estimate a time when current in the at least one switch will reach the predetermined level and may operate the at least one switch based on the estimated time.
According to other embodiments of the invention, the first switching circuit comprises first and second half bridges, and the switch control circuit controls a time delay between operations of the first and second half-bridges. The switch control circuit may control the time delay such that the first and second half-bridges operate under substantially zero current switching conditions. In some embodiments of the invention, the switch control circuit maintains a fixed time delay between operations of the first and second half-bridges. In other embodiments, the switch control circuit controls the time delay responsive to a sensed current through the transformer and/or responsive to an input voltage applied to the switching circuit.
According to other aspects of the invention, the first switching circuit comprises at least one switch, and the switch control circuit constrains the at least one switch to operate when voltage across the at least one switch falls to a predetermined level, for example, substantially near zero. The first switching circuit may comprise a first half-bridge including first and second switches and a second half-bridge including third and fourth switches. The switch control circuit, in transitioning the first switching circuit from a first state in which the second and third switches are closed and the first and fourth switches are open and a second state in which the first and third switches are closed and the second and fourth switches are open, may open the second switch before closing the first switch such that a voltage across the first switch is reduced, for example, to a voltage substantially near zero, before the first switch closes. The switch control circuit, in transitioning the first switching circuit from the second state to a third state in which the first and fourth switches are closed and the first and third switches are open, may also open the third switch before closing the fourth switch such that a voltage across the fourth switch is reduced, for example, to a voltage substantially near zero, before the fourth switch closes.
In other embodiments of the invention, a power conversion apparatus includes a transformer having primary and secondary windings. First and second half-bridges are configured to be coupled across a DC power source and coupled to respective first and second terminals of the primary winding of the transformer. An output circuit is coupled to the secondary winding of the transformer and includes first and second capacitors and at least one inductor configured to be coupled to a load. The output circuit is operative to transfer energy to the load from the secondary winding via the first capacitor responsive to application of a first polarity voltage to the primary winding of the transfer and to transfer energy to the load from the secondary winding via the second capacitor responsive to application of a second polarity voltage to the primary winding of the transformer. A switch control circuit, operatively associated with the first and second half-bridges, varies a frequency at which the first and second half-bridges operate responsive to an output voltage produced by the output circuit.
In some embodiments of the invention, the switch control circuit is operative to control a time delay between operations of the first and second half-bridges. For example, the switch control circuit may control the time delay such that the first and second half-bridges operate under substantially zero current switching conditions.
For example, the switch control circuit maintains a fixed time delay between operations of the first and second half-bridges, or the switch control circuit may vary the time delay responsive to a sensed current and/or to an input voltage applied to the first and second half-bridges.
In still o
Lambda Electronics Inc.
Patel Rajnikant B.
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