Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1996-05-13
1997-11-11
Nguyen, Matthew V.
Electric power conversion systems
Current conversion
Using semiconductor-type converter
363 53, H02M 706
Patent
active
056870698
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a rectifier bridge arrangement for starting a DC-driven device with the absence of current surges, wherein the inputs of the rectifier bridge are intended for connection to a three-phase source, and wherein a storage capacitor is connected across the output of the rectifier bridge.
BACKGROUND ART
Electronic apparatus that are powered by alternating current will normally have an energy reservoir in the form of a storage capacitor, which may be supplemented with further circuits elements in order to ensure that energy will be delivered when the level of the AC voltage is low.
The storage capacitor must be relatively large, in order to ensure reliable operation. As a result, an unacceptably high start current, i.e. a current surge, will be delivered to the electronic apparatus when a voltage is applied thereto, unless counteractive measures are taken.
This problem is normally solved with the aid of a resistor connected in series with the storage capacitor in the case of the single-phase connection, or with the aid of resistors connected in series to at least two connecting terminals of the rectifier bridge in the case of the three-phase connection. This resistor, or these resistors, restricts/restrict the level of the charging current to the storage capacitor when starting of the electronic apparatus, whereafter the resistor or resistors is/are short-circuited to enable continued use of the storage capacitor(s) as an energy reservoir.
One serious drawback with this solution is that the resistor or resistors become very hot when the electronic apparatus is started-up repeatedly over a short period of time.
U.S. Pat. No. 4,910,654 teaches a load-connected arrangement which comprises a rectifier bridge which includes four diodes, a series circuit which comprises two storage capacitors and which is connected in parallel between the load and the rectifier bridge, and a third capacitor whose one connecting terminal is connected to an output terminal of the rectifier bridge and whose other connecting terminal is intended for connection to a first connecting terminal on a single-phase source. One connecting terminal of a controllable switch is connected to the other connecting terminal of the third capacitor and the other connecting terminal of the switch is connected to one input terminal on the rectifier bridge. The other input terminal of the rectifier bridge is connected directly to a second connecting terminal on the single-phase source. This arrangement functions by reducing the starting current to a suitable level during a start sequence, by virtue of the third capacitor being connected in series with the two storage capacitors via two of the diodes in the rectifier bridge. The switch is then closed to allow normal operation to take place, wherein the third capacitor functions to control the voltage level across the storage capacitors. This arrangement is very satisfactory in the case of a single-phase source. However, the publication does not mention that the arrangement can be adapted for connection to a three-phase source, nor yet how such adaptation may be effected. However, if the arrangement described in the U.S. publication were to be adapted to a three-phase source, in spite of the lack of a disclosure to this effect, there would be obtained a circuit in which the rectifier bridge also included a fifth and a sixth diode connected in parallel across the storage capacitors, a fourth capacitor whose one connecting terminal is connected to the same output terminal on the rectifier bridge as the third capacitor, and whose other connecting terminal is connected to a first connecting terminal on a second switch whose other connecting terminal is connected to the point of interconnection between the fifth and the sixth diodes. In this case, the point of electrical interconnection between the fourth capacitor and the second switch is intended for connection to a third connecting terminal on the three-phase source. It is also assumed that the two remaining con
REFERENCES:
patent: 4412278 (1983-10-01), Cambier et al.
patent: 4672522 (1987-06-01), Lesea
patent: 4910654 (1990-03-01), Forge
patent: 5200887 (1993-04-01), Ioroi et al.
Irving L. Kosow, Control of Electric Machines, pp. 89-93 (1973).
Groth Eric
Rundkvist Kjell
Nguyen Matthew V.
Telefonaktiebolaget LM Ericsson
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