Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-01-29
2001-09-18
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S056090
Reexamination Certificate
active
06292375
ABSTRACT:
The present invention relates to a DC-DC voltage converter of the resonant type, usable in particular for powering travelling wave tubes (TWT), and it relates more particularly to a converter which switches at zero voltage and at zero current.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,959,765 in the name of the Applicant describes a layout corresponding to a resonant converter which switches at zero voltage and at zero current.
In particular, that patent describes a push-pull type device in which the resonant circuit is constituted by a current feed capacitor and by the leakage inductance of the transformer.
That converter is not protected against an accidental short circuit of one of the switches in the push-pull version, or of the sole switch in the other version described.
To obtain a zero voltage switch, the switch of one push-pull branch should be closed only after the switch in the other branch has been opened and the voltage across the terminals of said switch has reached its high value due to the magnetization energy of the transformer, and has reached its low value at the switch which is to be closed under the action of the transformer.
U.S. Pat. 5,140,512 (O'Sullivan) enables such switching at zero voltage to be obtained automatically by detecting the voltage excursion of the transformer. A detection logic circuit is associated with each push-pull switch and alternating push-pull operation is authorized only when the transformer has switched within a time interval during which both push-pull switches are open.
Finally, U.S. Pat. No. 5,249,113 in the name of the Applicant describes a converter having a transformer which enables a rapid transition to be obtained and provides good operation for the layout when the switches are insulated grid field effect transistors (MOSFET) which present high drain-source capacitance tending significantly to slow down the automatic switching of the transformer, or which are responsible for an unfavorable form factor of the current and for poor efficiency. Adjusting the magnetization current of the transformer which does not change the resonance characteristic of the transformer serves to increase the switching speed of the transformer, thereby improving the form factor and the efficiency.
By implementing the three above-cited patents simultaneously, it is possible to make converters having efficiency of 97% or more on a bus regulated at 50 V. Such converters nevertheless require input protection in the event of a short circuit fault, which gives rise to greater complexity.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a converter layout which is usable in practice on buses with voltages of up to about 100 V, and which is capable of being protected against short circuits without significant complication, thereby also making it possible to limit the current passing through the load.
The invention thus provides a DC voltage converter comprising first and second input terminals for receiving an input voltage, a choke component having a first terminal coupled to the first input terminal and a second terminal coupled to a first terminal of a capacitive branch which has a second terminal coupled to the second input terminal, first and second switches controlled in opposition, and an output transformer having a primary and a secondary feeding a load, wherein the capacitive branch presents two capacitive components connected in series with the common terminal thereof being coupled to a first terminal of the primary of said output transformer, wherein the first and second switches are connected in series and present a common terminal coupled to a second terminal of the primary of said output transformer, the other terminals of the first and second switches being coupled respectively to the first and second terminals of the capacitive branch.
In order to obtain mutual protection of the switches against short circuits, the converter has zero voltage switching control on the basis of the voltage at the terminal common to the first and second switches.
In order to obtain automatic protection against an accidental short circuit of a switch, the converter can include a device for measuring the current flowing through said choke component and a comparator comparing said measured current with a reference maximum current, and having its output coupled to a control device which controls opening of the first and second switches whenever the measured current exceeds said reference maximum current.
Said comparator is preferably a comparator with hysteresis.
In a variant enabling an additional voltage adjustment command, the converter has third and fourth switches connected in series and presenting a common terminal coupled to the first terminal of the primary of an auxiliary transformer, the other terminals of the third and fourth switches being coupled respectively to the first and second terminals of the capacitive branch, and the auxiliary transformer presents a secondary connected in series with the primary of the output transformer between the terminal common to the two capacitive elements and the terminal common to the first and second switches. The converter can then include a voltage adjustment device for controlling the third and fourth switches as a function of voltage, either in an additive first mode in which the third and fourth switches are controlled synchronously with the first and second switches respectively, or in a subtractive second mode in which the third and fourth switches are controlled in phase opposition,with the first and second switches respectively.
In a preferred embodiment of this variant, the voltage adjustment device comprises first and second threshold comparators and a control unit for controlling the third and fourth switches so as to cause the third and fourth switches to operate at least in the first and second modes, the first and second threshold comparators having respective first input terminals receiving a signal representative of said input voltage and respective second input terminals receiving signals representative respectively of a high threshold and of a low threshold and presenting respective control outputs applied to inputs of the control unit for causing the control unit to operate in said first mode and in said second mode, respectively.
At least one of said threshold comparators is advantageously a comparator with hysteresis.
In another variant, the phases of the third and fourth switches are offset relative to the phases of the first and second switches, respectively, as a function of said input voltage.
REFERENCES:
patent: 4199807 (1980-04-01), Crowe et al.
patent: 4663699 (1987-05-01), Wilkinson
patent: 4809310 (1989-02-01), Salesses et al.
patent: 5068573 (1991-11-01), Bruning et al.
patent: 5325283 (1994-06-01), Farrington et al.
patent: 5646836 (1997-07-01), Sadarnac et al.
patent: 5771159 (1998-06-01), Sako et al.
patent: 5946200 (1999-08-01), Kim et al.
patent: 5946208 (1999-08-01), Yamamoto et al.
patent: 24 16 985 (1975-10-01), None
patent: 517 226 (1992-12-01), None
patent: 797 289 (1997-09-01), None
“Analysis of a Half-Bridge type Series Resonant DC-DC Converter with Auxiliary Switches” by Asano et al., EPE 1995 6thEuropean Conf. On Power Electronics and Applications, vol. 2,No. CONF. 6.
“Steady State Analysis and Design Optimization of an Inductor-Transformer Resnant DC-DC Conveter” by Kojori et al, vol. 1, No. 87ch2499-2, Oct. 1987.
Agence Spatiale Europeenne
Berhane Adolf Deneke
Sughrue Mion Zinn Macpeak & Seas, PLLC
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