Method and device for limiting the current surge in a...

Electric power conversion systems – Current conversion – Using semiconductor-type converter

Reexamination Certificate

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C363S150000

Reexamination Certificate

active

06222749

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to power converters for providing d.c. rectified power supplies, and, more particularly, to a circuit for limiting the current surge in a storage capacitor at the powering-on of a rectifier.
2. Discussion of the Related Art
FIG. 1
is a schematic block diagram of an exemplary correctional circuit for limiting the current surge in a storage capacity Cf associated with a rectifier
2
. The rectifier
2
is connected, through terminals E
1
and E
2
, to an a.c. power supply and provides, on terminals P and M, a d.c. rectified power supply. Typically, terminal M is a ground terminal. Terminals P and M supply a load
1
generally associated with a power converter such as a switched mode power supply. A device for correcting the power factor may be provided, in which case the storage capacitor Cf may be included as part of the device.
The powering-on of the conventional circuit shown in
FIG. 1
is generally performed by means of a manually- or automatically-controlled switch
4
, located between the a.c. power supply and the rectifier
2
. The powering-on of the circuit causes a current surge ranging from several tens to several hundreds of amperes due to the initial charge of capacitor Cf. To avoid this, a device
5
for limiting the current surge is commonly placed between terminal P and capacitor Cf.
Device
5
generally includes a series resistance Rs. In order to avoid the resistor Rs from continuously dissipating power, a switch
6
is generally provided to short-circuit the resistor Rs once the power converter has reached a steady state. The control line
7
of switch
6
is typically provided by the power converter and may be based on, for example, a measurement of the charge current of capacitor Cf.
A disadvantage of a conventional device such as shown in
FIG. 1
is that the presence of a series resistance on the rectified power line results in significant power consumption by the resistor Rs during the initial transient charge phase of capacitor Cf.
Another disadvantage of such a conventional device for limiting the current surge upon power-on is that it requires auxiliary circuits that continuously dissipate power. These auxiliary circuits are required to cause and maintain the short-circuiting of resistance Rs in a steady state. For example, if the power converter includes a transformer, the control
7
of switch
6
generally requires an additional secondary winding Further the very presence of switch
6
on the positive rectified power supply line results in steady-state power consumption due to the resistance of switch
6
when it is closed.
Another disadvantage of the device of
FIG. 1
is that, should a mains failure occur for a duration such that the voltage across capacitor Cf dissipates below the range associated with steady state, the switch
6
opens, causing the power consumption by resistance Rs.
Another disadvantage is that the operation of the device for limiting the current surge can be altered in case of a temporary drop of the mains voltage. This may occur, for example, after a strong current consumption of another load connected to the electric network. Particularly, when switch
6
is controlled by a relay, and assuming that the voltage drop remains within the devised operating range (that is, switch
6
mans in the “on” state), a very large current peak appears as the mains voltage rises back to the initial level.
SUMMARY OF THE INVENTION
The present invention aims at overcoming the disadvantages of conventional devices for limiting the current surge in a capacitor associated with a rectifier by providing a device with reduced steady-state power consumption.
The invention also aims at providing a device with a steady-state power consumption that is independent of the mains voltage and frequency.
The invention also aims at providing a device which operates regardless of the type of load (resistive, capacitive, etc.), and has a power consumption that is independent of the type of load.
The invention also aims at providing a device which does not require an auxiliary power supply for its control.
To achieve these objectives, the present invention provides a method for limiting the current surge in a capacitor connected to the output of a rectifying bridge having its input connected to an a.c. power supply, consisting in:
using a composite bridge; and
authorizing the bridge to conduct only after a zero crossing of the a.c. voltage.
The present invention also provides a device for limiting a current surge in a capacitor connected to the output of a rectifying bridge having its input connected to an a.c. power supply, including means for synchronizing the turning-on of the bridge from the zero crossings of the a.c. power supply voltage, the bridge being preferably a composite bridge.
According to an embodiment of the present invention, the device includes a detector for detecting the zero crossing of the voltage at the input of the composite bridge and a controller for controlling switches of the composite bridge.
According to another embodiment of the present invention, the detector includes at least two differential inputs receiving the a.c. power supply. The controller includes at least two outputs for respectively controlling the composite bridge switches.
According to another embodiment of the present invention, the bridge includes at least two diodes and at least two thyristors.
According to another embodiment of the present invention, each input of the detector is connected to an input of the composite bridge via a rectifying diode. The anodes of the rectifying diodes are connected to an output terminal of the composite bridge via a first resistive voltage dividing bridge. The midpoint of the first dividing bridge is connected, at least via a first zener diode, to the gate of an auxiliary thyristor, the anode of which constitutes an output of the detector.
According to another embodiment of the present invention, the controller includes a second resistive voltage dividing bridge having its midpoint connected to the output of the detection block. The midpoint of the second dividing bridge is also connected, via a second Zener diode, to the anodes of at least two diodes, the respective cathodes of which constitute the outputs of the controller. The outputs are connected, respectively, to the gates of the thyristors of the composite bridge. In addition, a damping capacitor is mounted in parallel to the auxiliary thyristor.
According to another embodiment of the present invention, the resistive dividing bridges include resistors having resistance values such that the voltage across the damping capacitor is, at low frequencies, always substantially higher than the voltage between the midpoint of the first resistive dividing bridge and the cathode of the auxiliary transistor.
According to another embodiment of the present invention, the cathode of the auxiliary thyristor is connected to the cathodes of the rectifying diodes of the detector, the thyristors of the composite bridge being cathode-gate thyristors.
According to an embodiment of the present invention, the cathode of the auxiliary thyristor is connected to the output terminal of the composite bridge, the thyristors of the composite bridge being anode-gate thyristors.


REFERENCES:
patent: 3852654 (1974-12-01), Gyugyi et al.
patent: 4019100 (1977-04-01), Barrus
patent: 4161022 (1979-07-01), Kanazawa et al.
patent: 4580205 (1986-04-01), Matsuse
patent: 4689548 (1987-08-01), Mechlenburg
patent: 4811189 (1989-03-01), Harvest et al.
patent: 5202819 (1993-04-01), Min
patent: 5420780 (1995-05-01), Bernstein et al.
patent: 5621631 (1997-04-01), Vinciarelli et al.

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