Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2001-06-12
2002-03-05
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S056030, C323S908000
Reexamination Certificate
active
06353545
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an inverter apparatus provided with a converter and, in particular, to an inverter apparatus provided with an inrush current limiting device for limiting an inrush current into a smoothing capacitor of a converter at the instant of connection to a commercial AC power line.
BACKGROUND ART
FIG. 4
shows a configuration of an inverter apparatus provided with an inrush current limiting device as a prior art described in Japanese Unexamined Patent Publication No. Hei-9-19154.
In
FIG. 4
,
101
denotes a three phase power supply,
102
denotes a power failure detection circuit,
103
denotes a converter,
104
denotes an inverter,
105
denotes a motor,
106
denotes a control circuit,
107
and
108
denote bypass contacts, r and R denote current limiting resistors, C
1
and C
2
denote smoothing capacitors, P denotes a positive bus, and N denotes a negative bus.
Now, operations according to the configuration of FIG.
4
will be described. As shown in
FIG. 4
, a series circuit comprising the current limiting resistor r and the smoothing capacitor C
1
is connected between the positive bus P and the negative bus N on the output end of the converter
103
and the bypass contact
107
is connected in parallel with the current limiting resistor r. A resistance value of the current limiting resistor r is determined by setting a charging constant of the smoothing capacitor C
1
and a wattage (instantaneous withstanding capacity) is determined by a electrostatic capacity of the smoothing capacitor C
1
. The opening and closing timing of the bypass contact
107
is controlled by an opening/closing control signal to be supplied from the power failure detection circuit
102
. Similar to the above, a series circuit comprising the current limiting resistor R and the smoothing capacitor C
2
is also connected between the positive bus P and the negative bus N on the output end, the bypass contact
108
is connected in parallel with the current limiting resistor R, and similar to the bypass contact
107
, the opening and closing timing of the bypass contact
108
is also controlled by an opening/closing control signal to be supplied from the power failure detection circuit
102
.
In the above configuration, both bypass contacts
107
and
108
are opened at the instant of connection to the power line and as an output current from the converter
103
, a charging current flows through a route from the output terminal of the converter
103
, the positive bus P, the current limiting resistors r and R, the smoothing capacitors C
1
and C
2
, the negative bus N to the negative output of the converter
103
. After completion of the charging of the smoothing capacitors C
1
and C
2
, the bypass contacts
107
and
108
are closed and the current limiting resistors r and R are bypassed, and hereafter the charging and discharging of the smoothing capacitors C
1
and C
2
are carried out via the bypass contacts
107
and
108
, respectively.
In this configuration, a charge/discharge current of the smoothing capacitor Cl connected to the bypass contact
107
is the only current which flows through the bypass contact
107
and similarly, a charge/discharge current of the smoothing capacitor C
2
connected to the bypass contact
108
is the only current which flows through the bypass contact
108
.
Incidentally, in the above configuration shown in
FIG. 4
, a rectified DC high voltage is to be impressed between positive and negative terminals of the transistor of the inverter
104
in an instant by the converter
103
. At this time, due to the stray capacitance existing between terminals of each transistor (herein, IGBTs are tentatively used) as shown in
FIG. 5
, a voltage generates between gate and emitter of both upper and lower IGBTs. And, as a result, both upper and lower IGBTs are turned on and a short circuit current generates and there is a problem in that the IGBTs brake.
Furthermore, at the time of regenerative operation of the inverter apparatus, in this case, the energy returns from the motor
105
to the side of the inverter apparatus, however if the bypass contact malfunctions and is turned off during the regeneration, a regenerative current then flows into the smoothing capacitor via the current limiting resistor, therefore a high voltage generates between the positive and negative terminals of the inverter
104
in an instant and exceeds the voltage tolerance of the IGBTs of the inverter
104
and diodes of the converter
103
and there is a problem in that these elements brake.
DISCLOSURE OF THE INVENTION
In order to solve the above described problems, according to the present invention, as described in Claim 1, an inverter apparatus comprises: a converter
3
for converting AC power to DC power; an inverter
4
for inverting the converted DC power to AC power having a predetermined frequency; a first smoothing capacitor
12
between positive and negative buses that connect the output terminal of the converter and the input terminal of the inverter; a first resistor
14
connected in either the positive or negative bus between the converter
3
and the first smoothing capacitor
12
; and a first switch means
16
connected in parallel with the first resistor, wherein
a second smoothing capacitor
11
connected in series with a parallel circuit comprising a second resistor
13
and a second switch means
15
connected in parallel with each other is connected between the positive and negative buses between the converter
3
and the first switch means
16
.
In the inverter apparatus having the construction as set forth in Claim 1, since both the first switch device and the second switch device are open when the AC power line is connected, a charging current for the first smoothing capacitor which flows from the positive output terminal of the converter via the first resistor and the first smoothing capacitor to the negative output terminal of the converter and a charging current for the second smoothing capacitor which flows from the positive output terminal of the converter via the second resistor and the second smoothing capacitor to the negative output terminal of the converter generate. Then, when the charging for both first and second smoothing capacitors is completed, both first and second switch devices are closed and power outputting operation of the inverter is started. During this power outputting operation of the inverter, power corresponding to the power output is supplied from the commercial AC power line
1
, and currents supplied from this commercial AC power line to the converter of the inverter apparatus respectively flow via the converter through the following three routes inside the inverter apparatus and then return via the converter to the commercial AC power line without change.
First, through the first route, the current flows to the positive terminal of the converter, the first switch device, the first smoothing capacitor, and the positive terminal of the converter (hereinafter, referred to as “route 1”), then through the second route, the current flows to the positive terminal of the converter, the second switch device, the second smoothing capacitor, and the negative terminal of the converter (hereinafter, referred to as “route 2”), and through the third route, the current flows to the positive terminal of the converter, the first switch device, semiconductor switching elements on the lower arm side of the inverter, a load, semiconductor switching elements on the lower arm side of the inverter apparatus, and the negative output terminal of the converter (hereinafter, referred to as “route 3”). Also, as a matter of course, the currents supplied from the commercial AC power line
1
are not consecutive currents, therefore, the energy charged in the first and second smoothing capacitors is discharged in a time zone where no current is supplied, so that the power outputting operation of the inverter is carried out. The reduced amount of the charged energy of the smoothing capacitors is recharged by a current supplied from t
Kabushiki Kaisha Yaskawa Denki
Vu Bao Q.
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