Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2000-11-28
2001-07-24
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S132000
Reexamination Certificate
active
06266256
ABSTRACT:
The present invention relates to a circuit for power-factor correction. Such circuits are also known by the terms “charge pumps” or “pump circuits”. They are used, for example, to satisfy Standard IEC 1000-3-2, in which the electricity supply authorities have defined the acceptable network-current harmonic levels. Accordingly, it is undesirable to draw high-frequency energy from the electricity supply network. The network current which is drawn from the network is, optimally, proportional to the network voltage. Proportionality between the network current and the network voltage allows the maximum amount of power to be transmitted for any given cable size. Reactive currents, which would occur if the network voltage and network current were not proportional, would cause cable losses, additionally loading the cables and thus leading to interference with other loads.
Such circuits for power-factor correction are used, inter alia, for ballasts for the operation of gas-discharge lamps.
The present invention is based on a prior art as is disclosed in the article by W. Chen, F. Lee and T. Yamauchi entitled “An Improved “Charge Pump” Electronic Ballast with Low THD and Low Crest Factor” which appeared in IEEE Transactions on Power Electronics, Vol. 12, No. 5, September 1997 pages 867 to 875. With reference to FIG. 8 there, this article was based on the problem of modifying the circuit from that in FIG. 1 there in such a manner that the voltage at the point A, that is to say V
a
(see the illustration in FIG. 7 there) has a constant high-frequency amplitude. This would result in the power drawn from the network being proportional to the network voltage. The diodes Da
1
and Da
2
were introduced in order to ensure this, as a result of which the point A is clamped to the capacitor C
B
. This precludes any reactions from the load and maintains a V
a
whose high-frequency amplitude is constant, see the illustration in FIG. 9 there.
A disadvantage of the circuit shown in FIG. 8 of this publication is that the lamp voltage is also limited by the diode Da
2
. It is thus impossible to produce the necessary starting voltage unless a transformer is connected between the pump circuit and the lamp to be operated. The additional costs for a transformer are undesirable in mass-produced items such as ballasts for lamps.
The present invention is therefore based on the object of providing a circuit for power-factor correction, that is to say a pump circuit, which needs no transformer.
This object is achieved by a circuit having a rectifier which can be connected on the input side to an AC voltage source and which is connected on the output side to at least one series circuit comprising a capacitor and a diode, with the diode being arranged such that the capacitor cannot be charged through the diode by the output signal from the rectifier. It furthermore comprises a first and a second electronic switch connected in series as part of a half bridge or full bridge, each having a freewheeling diode connected in parallel with the switch and, with the [lacuna] formed by the junction point between the first and second switches [lacuna] an output connection of the half bridge or full bridge is on the one hand connected via an inductance to a point on the connection of the capacitor and diode of each series circuit comprising a capacitor and a diode, and on the other hand forms a connection for a load, with the signal at this connection during operation being at a considerably higher frequency than the output signal from the AC voltage source. It furthermore has an energy-storage capacitor which is connected in parallel with the two switches, as well as at least one further diode which is arranged between the energy-storage capacitor and the rectifier in such a manner that the energy-storage capacitor cannot be discharged through the rectifier.
The invention on the one hand offers the advantage of additional freedom for the design of the elements in the pump and load circuits, by very largely overcoming any reaction between the two circuits. This furthermore makes it simple to adjust the lamp power by appropriate design of the capacitor CS
1
or of the capacitor CS
1
, CS
2
, in such a manner that the voltage on the capacitor or the capacitors reaches the respective present value of the supplying, rectifier AC voltage at least once, in which case it can be assumed that the rectifier AC voltage is constant when a load cycle is considered. Furthermore, the energy which is intended to be pumped into the load depends only on the capacitance of the capacitor CS
1
, or the capacitances of the capacitors CS
1
and CS
2
. The inductance of the inductor L must and can be small, so that it need only be large enough to ensure that the electrical switches are not subjected to excessive currents and that they remain switched on when the voltage is 0 (ZVS).
In an advantageous development, a filter is arranged between the inputs of the rectifier and, when the circuit is connected to an AC voltage source, is arranged in series or parallel with the AC voltage source. Additionally or as an alternative to this, a filter may be arranged in series or parallel with the output of the rectifier.
In a first embodiment, the circuit comprises a series circuit formed by a diode and a capacitor, as well as a further diode. In a further embodiment, which allows pumping when either of the two switches is in the on state, that is to say balancing of the previously mentioned embodiment, the circuit comprises two series circuits formed by a diode and capacitor as well as two further diodes.
As already mentioned, the circuit can be operated in the form of a half bridge or a full bridge. In a full bridge, the circuit comprises two further switches with the junction point between the two further switches forming the second load connection. In the case of a half bridge, the circuit comprises two coupling capacitors, with the junction point between the two coupling capacitors forming the load connection, and with the series circuit formed by the two coupling capacitors being arranged in parallel with the energy-storage capacitor. As an alternative to this, it may also comprise only one coupling capacitor, one of whose connections forms the second load connection, with its second connection being connected to one of the two connections of the energy-storage capacitor.
Further advantageous developments of the invention are defined in the dependent claims.
REFERENCES:
patent: 5408403 (1995-04-01), Nerone et al.
patent: 5561595 (1996-10-01), Smith
patent: 5598326 (1997-01-01), Liu et al.
patent: 5631814 (1997-05-01), Zak
patent: 5959849 (1999-09-01), Batarseh
patent: 6115276 (2000-09-01), Mao
patent: 6198642 (2001-03-01), Kociecki
Wei Chen, et al., “An Improved ‘Charge Pump’ Electronic Ballast with Low THD and Low Crest Factor”, 1996, pp. 622-627, Annual Applied Power Electronics Conference and Exposition (APEC), US, New York, IEEE, vol. CONF. 11, XP000585906.
T.F. Wu, et al., “Analysis and Design of a High Power Factor, Single-Stage Electronic Ballast with Dimming Feature”, 1997, pp.1030-1036, APEC. Annual Applied Power Electronics Conference and Exposition, US, New York, IEEE, vol. CONF. 12, XP000731062.
G. Chae, et al., “High Power Factor Correction Circuit For Low-Cost Electronic Ballasts”, May 1997, pp. 922-922, Electronics Letters, GB, IEE Stevenage, vol. 33, No. 11, XP000727008.
Wei Chen et al. “An Improved ‘Charge Pump’ Electronic Ballast with Low THD and Low Crest Factor”, Sep. 1997, pp. 867-875, IEEE Transactions on Power Electronics, vol. 12, No. 5.
Gueldner Henry
Lehnert Klaus
Raiser Franz
Berhane Adolf Deneke
Bessone Carlo S.
Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MBH
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