Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1998-05-04
2000-12-26
Wong, Peter S.
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363124, 363 21, 323222, H02M 3335, G05T 1613
Patent
active
061669245
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to the field of voltage converters and more particularly to the field of converting alternating voltage to a continuous voltage or direct current voltage. More specifically, the invention relates to an arrangement and to a method for measuring minimum input voltage, the transformer TR1 is supplied with current mainly by the capacitors in the two valley-fill circuits 12, 14.
DESCRIPTION OF THE PRIOR ART
IEC 1000-3-2 is a standard which discloses what appearance the voltage input and current input to an arrangement from an alternating voltage source shall have in order to be classed as a class A-type apparatus. One such arrangement is described in DE-A-4 243 943, among other things. The arrangement described in this publication includes a capacitor which is charged during that time period in which the absolute value of the source voltage exceeds the voltage across the capacitor, and is discharged when the absolute value of the source voltage is below this voltage. Another arrangement which fulfils the requirement of the aforesaid standard is described in the article "A New Family of Single-Stage Isolated Power-Factor Correctors with Fast Regulation of the Output Voltage", by R. Redl, L. Balogh and N.O. Sokal in PESC 94, Record, pages 1137-1144. This document is concerned mainly with how two switches can be combined to form one switch. The document discloses a plurality of different converter circuits. One of these circuits is a voltage converter that includes a rectifier bridge whose one output -terminal is connected to a coil which, in turn, is connected to a valley-fill circuit. The valley-fill circuit is connected to a fly-back converter which includes three windings. A controllable switch is connected between the other output terminal of the rectifier bridge and the interconnection junction between the coil and the valley-fill circuit. This circuit functions to charge the source voltage up to the two capacitors when the switch is switched-off. When the switch is made, one end of the coil is earthed and the entire voltage content of the source at that moment in time is applied across the coil. The two capacitors are discharged simultaneously in parallel through their respective windings, so as to generate a voltage across the third winding, which is used to generate a d.c. voltage. The coil is driven in this circuit in a discontinuous conducting mode (DCM), in other words it delivers all of its stored energy to the two capacitors. If the coil works in a continuous conducting mode (CCM) and the converter is connected to a load which draws only a small amount of current, the capacitors would not be discharged at the same rate as they are charged through the coil. This results in an elevated voltage across the capacitors, which in turn influences the pulsewidth that controls the switch. The voltage across the capacitors can then become so great as to require unnecessarily large and powerful capacitors, or the provision of several capacitors. Alternatively, a high voltage protector may be required to limit this voltage. These measures render the circuit relatively expensive. The problem can also be rectified by using a further control loop, although this solution requires a further controlled switch which, in turn, requires a different control than the first switch. This also adds to the cost of the arrangement.
SUMMARY OF THE INVENTION
The present invention solves the problem by virtue of the fact that in a converter which includes a transformer at least one inductor means and at least one valley-fill circuit obtain a high power factor and good functioning in a continuous conducting mode at low load while, at the same time, fulfilling the requirement concerning the appearance of the input voltage and input current from an a.c. voltage source to an arrangement in accordance with the standard IEC 1000-3-2.
The problem is solved by connecting a controlled switch means in the same current loop as the primary winding of the transformer, so that energy delive
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"A New Family of Single-Stage Isolated Power-Factor Correctors with Fast Regulation of the Output Voltage," by R. Redl, et al., PESC 94, Record, 1994, pp. 1137-1144.
Patel Rajnikant B.
Telefonaktiebolaget LM Ericsson
Wong Peter S.
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