Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-08-24
2002-10-15
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021040, C363S056100, C363S097000
Reexamination Certificate
active
06466460
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention generally relates to voltage converters and more particularly to an apparatus and method of utilizing a Class E converter for improved efficiency.
Voltage converters are typically used to convert voltage at one level to a second desired voltage level. Typically, in order to develop a high output voltage (i.e., several thousand volts) from a low input voltage (i.e., 28 volts), a double conversion process is used. The input voltage is first converted to an intermediate voltage (i.e., several hundred volts), then stepped-up to the final output voltage. A pre-regulator may be used which may provide the advantages of improved regulation and simplified high voltage transformer design, yet a high component count and low efficiency results.
One application for class E resonant power converters is to convert an input voltage level to a desired output voltage level. Such converters typically use a switch for controlling the flow of current to a resonant circuit. A transformer is connected in parallel to the resonant circuit and provides the necessary switching of the power supply in order to increase the voltage. High switching frequencies provide improved efficiency for the Class E resonant power converter by eliminating the cause of switching power dissipation which exists.
However, efficiency decreases if the switch is not correctly operated. Specifically, if the switch is operated during a high current and high voltage situation, power dissipated through the switch is high thereby resulting in decreased efficiency. Therefore, if ideal switching conditions are not met, the efficiency of the Class E power converter is decreased thereby negating any benefits thereof.
The present invention addresses the above-mentioned deficiencies in current Class E power converters by providing a converter which provides ideal switching conditions. Specifically, the switch for the power converter of the present invention will be operated only at an ideal condition by sensing the current flowing through the resonant circuit. The power converter of the present invention provides a Class E power converter with an increase in efficiency because switching losses are minimized.
BRIEF SUMMARY OF THE INVENTION
A high efficiency power converter for generating a high voltage supply from a low voltage supply. The power converter comprises a source inductor in electrical communication with the input low voltage power source. A switch is in electrical communication with the source inductor and a control circuit. The control circuit is operative to open and close the switch thereby generating a conduction period of the switch. The power converter further includes a resonant capacitor in electrical communication with the switch, the power supply inductor, and shunt capacitor as well as a resonant inductor in electrical communication with the resonant capacitor. Accordingly, the resonant capacitor and the resonant inductor from a resonant circuit of the power converter. In electrical communication with the resonant inductor is a transformer operative to generate the high voltage supply from the voltage of the resonant inductor. In order to control the conduction period of the switch, the power converter further includes a current sense circuit in electrical communication with the resonant inductor and the control circuit. The current sense circuit is operative to determine the amount of current flowing through the resonant inductor and control the conduction period of the switch based thereon. In this respect, the switch will be opened and closed under ideal situations based upon the amount of current flowing through the resonant inductor.
In order to provide a DC voltage, the power converter of the present invention may further include a rectification and filtering circuit. The rectification and filtering circuit will be in electrical communication with the output of the transformer such that the power converter will supply a regulated DC voltage. Typically, the input voltage is about 28 volts and the output of the transformer is thousands of volts. In this respect, the transformer may be operative to provide an output voltage to a Traveling Wave Tube (TWT).
In order to provide the output voltage, the power converter may include a shunt capacitor in electrical communication with the switch. Specifically, the shunt capacitor may be connected in parallel across the switch. Furthermore, the transformer is connected in parallel with the resonant inductor. The resonant capacitor will be connected in series with the resonant inductor.
In accordance with the present invention, there is provided a method of generating an output voltage with a power converter constructed in accordance with the preferred embodiment. The method comprises supplying an input voltage to the resonant inductor and the transformer of the power converter. Next, the current through the inductor is sensed. The switch of the power converter is closed in response to the current sensed and the switch is opened in response to the output voltage of the transformer. The output voltage may be compared to a reference voltage in order to open the switch. In this respect, the switch will be opened after switch conduction periods determined by the variation between the output voltage and the reference voltage. Accordingly, a voltage higher than the input voltage is generated at the output of the transformer. It will be recognized that the output of the transformer can be rectified and filtered in order to produce a DC voltage.
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Perkins Jeffrey C.
Rein John M.
Northrop Grumman Corporation
Stetina Brunda Garred & Brucker
Vu Bao Q.
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