Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
1999-11-22
2001-07-17
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C323S225000
Reexamination Certificate
active
06262905
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to voltage regulation in distributed power systems and, more particularly, to an AC voltage regulator module suitable for converting AC distribution bus voltage to low DC voltage.
An AC voltage regulator module (VRM) is an on-board power module in an AC distributed power system such as for computers, servers, and other electronic systems. An AC VRM performs two functions: (1) rectification, i.e., conversion of high-frequency AC bus voltage to DC output voltage, and (2) regulation, i.e., tight control of the amount of energy transferred to the load so that the output voltage is regulated regardless of load conditions.
Series resonant type circuits have been proposed as AC VRM's. In particular, regulated resonant rectifiers use a center-tapped transformer followed by a pair of rectifiers, e.g., synchronous rectifiers. Output regulation is achieved by using a variable resonant inductor, or a variable resonant capacitor (e.g., implemented by a switched capacitor), or phase angle controls (e.g., by using a shunt switch across the transformer primary or secondary side). Disadvantages resulting from separation of the rectification and regulation functions include complicated control, too many semiconductor devices, and relatively low efficiency.
Another approach is a primary-side controlled AC VRM wherein an AC switch on the primary side regulates the output voltage by controlling its conduction time. Synchronous rectification is provided by separate FET switches on the secondary side. Shortcomings include relatively high conduction losses due to the voltage drops across both the AC switch on the primary side and the synchronous rectifier on the secondary side, thus resulting in low efficiency.
Design issues for AC VRM's are high-efficiency, high current slew rate, fast control loop and simple topology. In particular, the speed of microprocessors and integrated circuits (IC's) continues to increase, accompanied by a decrease in supply voltage level. For example, DC supply voltage levels of 2.2V, 1.8V, and even voltages below 1V are in demand for next-generation microprocessors and IC's. The reduced output voltage level imposes great challenges on efficiency due in large part to the voltage drop in the rectification stage.
Accordingly, it is desirable to provide a high-efficiency AC VRM, even at low output voltage, high current and high switching frequency. It is also desirable to provide an AC VRM that combines the functions of rectification and regulation into one power conversion stage, thereby reducing conduction losses. It is furthermore desirable to provide an AC VRM that provides soft-switching operation to reduce switching losses.
BRIEF SUMMARY OF THE INVENTION
An exemplary embodiment of an AC voltage regulator module (AC VRM) in accordance with the present invention comprises a secondary-side controlled series resonant AC VRM, comprising a series resonant tank circuit, an isolation transformer, and a pair of AC switches for performing voltage rectification and regulation functions. The AC switches are alternately turned on according to the polarity of the AC bus voltage; and the turn-on instants of the AC switches are controlled by a voltage control loop to achieve the desired regulated output voltage. After the delayed turn-on instant for each respective switch, current through the resonant tank circuit starts to rise from zero, and the resonant tank circuit starts to resonate. When the AC bus voltage changes polarity, the current decreases rapidly to zero. Upon detection of the zero current crossing, the switch is turned off. As a result, conduction and switching losses are minimized, providing high efficiency even at low output voltage, high current and high switching frequency.
In another aspect of the present invention, a dual-device AC switch is provided for use in AC VRM topologies. The dual-device AC switch ensures soft-switching for all power switches and avoids stringent control timing requirements by allowing natural circuit action to turn devices on and off.
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“Component Development for a High-Frequency AC Distributed Power System,” R. Watson, W. Chen, G. Hua, FC Lee; Applied Power Electronics Conference and Exposition, 1996, APEC, 1996, Conference Proceedings, 1996, Eleventh Annual, pp. 657-663.
“Development of a Regulated Resonant Rectifier for AC Distributed Power Systems,” W. Chen, R. Watson, G. Hua, FC Lee; Proceedings of the 12thVPEC Power Electronics Seminar, 1994, pp. 259-265.
Steigerwald Robert Louis
Zhang Richard S.
Breedlove Jill M.
General Electric Company
Laxton Gary L.
Stoner Douglas E.
Wong Peter S.
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