Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2002-07-15
2004-05-11
Patel, Rajnikant B (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C323S299000, C323S908000, C361S058000, C361S111000
Reexamination Certificate
active
06735098
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an inrush current limiting circuit, a power source device and a power conversion device; in particular, relates to an improvement thereof to limit an inrush current with high reliability and durability while reducing the overall weight and volume of the device even under a high rated power.
BACKGROUND ART
FIG. 16
is a circuit diagram showing a structure of a conventional power conversion device (which will be hereinafter referred to as “first prior art”) having an inrush current limiting circuit. This power conversion device
451
comprises a main power source
10
, an inrush current limiting circuit
301
and an inverter
13
. The main power source
10
is connected to input terminals PP and NN of the inrush current limiting circuit
301
, and the inverter
13
is connected to the output terminals P and N. The power conversion device
451
is utilized by connecting a three-phase load
100
, such as a motor, to output terminals U, V and W of the inverter
13
.
The inrush current limiting circuit
301
comprises switches
11
and
11
a
, a resistor
11
b
, and a capacitor
12
. The main power source
10
supplies the input terminals PP and NN with a DC (i.e. direct current) source voltage V
DC1
. The capacitor
12
so functions as to hold the source voltage V
DC1
at a constant level by means of its capacitance C
DC
. The switch
11
, structured as a relay, functions as a main switch that turns ON when starting the inverter
13
and turns OFF when stopping it.
The switch
11
a
and the resistor
11
b
are interposed between the main power source
10
and the capacitor
12
so as to limit an inrush current which flows to charge the capacitor
12
immediately after the switch
11
turns on. After the switch
11
turns ON to start the inverter
13
, the switch
11
a
remains OFF until charging of the capacitor
12
is almost completed. Accordingly, the inrush current is limited by the resistor
11
b.
When the charged voltage across the capacitor
12
almost reaches the source voltage V
DC1
, the switch
11
a
turns on. Thereafter, the inverter
13
starts its normal operation. Thus, a DC current is supplied to the inverter
13
by the main power source
10
with little loss, during the normal operation of the inverter
13
.
However, since a large current supplied by the main power source
10
flows through the switch
11
a
and the resistor
11
b
, the switch
11
a
and the resistor
11
b
are required to have a high rated power, as well as the switch
11
as the main switch. In the power conversion device
451
, therefore, it has been a problem that overall weight and volume of the device are large and a manufacturing cost thereof is high.
Further, since the switch
11
and the switch
11
a
(in particular, the switch
11
) have to operate mechanically while a high voltage being applied, the reliability and durability thereof have been problematic. In particular, arcing is influential to the reliability and durability. Moreover, conduction losses of both the switch
11
and the switch
11
a
during the normal operation of the inverter
13
have also been not negligible concerns.
FIG. 17
is a circuit diagram showing a structure of another conventional power conversion device (which will be hereinafter referred to as “second prior art”) having an inrush current limiting circuit. This power conversion device
452
is disclosed in Japanese Patent Application Laid-Open No. 8-289546 (1996), and is characteristically different from the power conversion devices
451
in that a transistor
30
a
and a base drive circuit lid are used for an inrush current limiting circuit
302
in place of the switch
11
a.
Even though the power conversion device
452
eliminates the problem arising from the switch
11
a
, it still needs the resistor
11
b
which must have a high rated power. Therefore, the power conversion device
452
has also been disadvantageous in that the weight and volume of the device are large and the manufacturing cost thereof is high. Further, the switch
11
has to operate mechanically while a high voltage being applied similarly to that of the power conversion device
451
, and therefore, the reliability and durability of the switch
11
has been problematic.
FIG. 18
is a circuit diagram showing a structure of still another conventional power conversion device (which will be hereinafter referred to as “third prior art”) having an inrush current limiting circuit. This power conversion device
453
is characteristically different from the power conversion device
451
according to the first prior art in that an NTC (negative coefficient thermistor)
11
c
is used for an inrush current limiting circuit
303
in place of the switch
11
a
and the resistor
11
b.
Usually when starting the inverter
13
, since the NTC
11
c
is low in temperature, it has high resistance. The inrush current flowing after the switch
11
turns ON, therefore, is limited by a high resistance of the NTC
11
c
. The temperature of the NTC
11
c
rapidly rises up due to loss heat generated in the NTC
11
c
. Accordingly, the resistance of the NTC
1
c
rapidly decreases, which decreases loss in the NTC
11
c.
The loss generated in the NTC
11
c
during the operation of the inverter
13
, however, is not negligible, and therefore, the power conversion device
453
has been disadvantageously applicable only to devices having a low rated power (e.g. few kW or less). Further, if the inverter
13
starts operation before the NTC
11
c
has sufficiently been cooled down, e.g. the inverter
5
restarts immediately after it has stopped, the NTC
11
c
does not sufficiently function as an inrush current limiter, which has also degraded the reliability of the device.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to obtain an inrush current limiting circuit which eliminates the above mentioned problems and limits an inrush current with high reliability and durability while reducing overall weight and volume of the device even under a high rated power, and to provide a power source device and a power conversion device having the inrush current limiting circuit.
In order to achieve the object, a first aspect of the present invention is directed to an inrush current limiting circuit. The inrush current limiting circuit comprises: a first capacitor; a first switching element of a charge driven type, one main electrode thereof being connected to one end of the capacitor; and a second capacitor, one end thereof being connected to the one main electrode of the first switching element, and other end thereof being connected to a control electrode of the switching element.
According to a second aspect of the present invention, in the initial current limiting circuit of the first aspect, the inrush current limiting circuit further comprises: a first resistor interposed between the one main electrode and the control electrode of the first switching element and connected in series to the second capacitor.
According to a third aspect of the present invention, in the initial current limiting circuit of the first aspect, the inrush current limiting circuit further comprises: a first diode connected in inverse-parallel to the first switching element.
According to a fourth aspect of the present invention, in the initial current limiting circuit of the first aspect, the inrush current limiting circuit further comprises: a drive circuit connected to the control electrode of the first switching element, and driving the first switching elements in response to a control signal.
According to a fifth aspect of the present invention, in the initial current limiting circuit of the fourth aspect, the drive circuit comprises a first output resistor interposed into a path of a drive current which drives the first switching element to turn ON.
According to a sixth aspect of the present invention, in the initial current limiting circuit of the fourth aspect, the drive circuit comprises: a second switching element, one main electrode thereof being connected to a
Hiyama Kazuaki
Hussein Khalid Hassan
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Rajnikant B
LandOfFree
Inrush current limiting circuit, power source device and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inrush current limiting circuit, power source device and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inrush current limiting circuit, power source device and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3252196