Power inverter

Details Power inverter Power inverter

1999-11-08

2001-01-30

Nguyen, Matthew (Department: 2838)

Electric power conversion systems

Current conversion

Using semiconductor-type converter

Reexamination Certificate

active

06181590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the arrangement and structure of smoothing capacitors in a power inverter such as an inverter.
2. Description of the Prior Art
FIG. 8
is a circuit block diagram of a power inverter for inverting DC power into 3-phase AC power to drive an AC load such as a 3-phase AC motor. In
FIG. 8
, reference numeral
1
denotes a DC power source for supplying a DC voltage,
2
a
relatively large-capacity smoothing capacitors for smoothing the voltage of the DC power source
1
,
3
a DC input wire connected to the positive (P) sides of the DC power source
1
and the smoothing capacitors
2
a
,
4
a DC input wire connected to the negative (N) sides of the DC power source
1
and the smoothing capacitors
2
a
,
5
a
to
5
c
switching elements whose collectors are connected to the positive (P) DC input wire
3
, and
5
d
to
5
f
switching elements whose collectors are connected to the respective emitters of the switching elements
5
a
to
5
c
and whose emitters are connected to the negative (N) DC input wire
4
. Denoted by
6
is a drive circuit unit connected to the gates of the switching elements
5
a
to
5
f
to drive the switching elements
5
a
to
5
f
and
7
a control circuit unit for carrying out switching control by outputting a control signal to the drive circuit unit
6
. DC power is inverted into 3-phase AC power by the switching operation of the switching elements
5
a
to
5
f
under the control of the control circuit unit
7
. The switching elements
5
a
to
5
f
are transistors, IGBT's or MOSFET's.
Reference numeral
8
represents free wheel diodes whose cathodes are connected to the collectors of the switching elements
5
a
to
5
f
and whose anodes are connected to the emitters of the switching elements
5
a
to
5
f
to convert 3-phase AC power into DC power. Numeral
9
signifies snubber capacitors which are connected to the collectors of the switching elements
5
a
to
5
f
at one end and to the emitters of the switching elements
5
a
to
5
f
at the other end to suppress a surge generated in the switching elements
5
a
to
5
d
at the time of switching,
10
u
,
10
v
and
10
w
AC output wires connected between the switching elements
5
a
and
5
d
, between the switching elements
5
b
and
5
e
and between the switching elements
5
c
and
5
f
and to which inverted 3-phase (U-phase, V-phase, W-phase) AC power is output, and
11
an AC load, for example, a 3-phase AC motor connected to the AC output wires. The above DC input wires
3
and
4
, the switching elements
5
a
to
5
f
, the drive circuit unit
6
, the free wheel diodes
8
, the snubber capacitors
9
, and the AC output wires
10
u
,
10
v
and
10
w
constitute a switching power module
12
.
The operation of the power inverter will be described hereinunder, taking an electric car as an example. When the car is started or accelerated, the power output of the DC power source
1
which is a battery is changed from DC power to 3-phase AC power to drive the AC load
11
which is a 3-phase AC motor. For the regenerative braking of the car, regenerative power from the AC load
11
is changed from 3-phase AC power to DC power to return it to the DC power source
1
.
Since the main characteristics required for the snubber capacitors
9
are excellent frequency characteristics, a film capacitor is generally used as the snubber capacitor
9
. The smoothing capacitors
2
a
suppress fluctuations in the voltage of the DC power source
1
and smoothens a voltage jump or the like. Since sufficiently large capacitance is required for this purpose, an aluminum electrolytic capacitor which can obtain large capacitance with ease is generally used. The control circuit unit
7
outputs a control signal to the drive circuit unit
6
of the switching power module
12
to control the switching elements
5
a
to
5
f
. The drive circuit unit
6
and the control circuit unit
7
are circuits for driving and controlling the AC load
11
such as an ordinary 3-phase AC motor or the like and hence, their illustrations are omitted.
FIG. 9
is a side view showing the internal configuration of a general power inverter and
FIG. 10
is a plan view showing the internal configuration of the switching power module
12
. In
FIG. 9
, reference numeral
13
denotes a plate-like cooling member, and
14
a case for covering the cooling member
13
. The smoothing capacitors
2
a
, the switching power module
12
, a snubber capacitor substrate
15
for mounting the snubber capacitors
9
and a control circuit board
16
for mounting the control circuit unit
7
are stored in the case
14
.
The number of the smoothing capacitors
2
a
is
3
in this case. These smoothing capacitors
2
a
are aluminum electrolytic capacitors arranged in a row on the cooling member
13
, and one end of a wiring board
17
is fixed and electrically connected to the top portion of each of the smoothing capacitors
2
a
by screws
17
a
. The other end of the wiring board
17
is fixed and electrically connected to the positive (P) and negative (N) DC input wires
3
and
4
of the switching power module
12
by a screw
18
. This wiring board
17
is a copper bus bar, copper plate or the like used to connect the smoothing capacitors
2
a
to the switching power module
12
.
Generally speaking, the snubber capacitor substrate
15
is arranged in the vicinity of the positive (P) and negative (N) DC input wires
3
and
4
and the U-phase, V-phase and W-phase AC output wires
10
u
,
10
v
and
10
w
on the switching power module
12
and fixed and electrically connected to the switching power module
12
by the screws
18
.
The package of the switching power module
12
consists of a resin case
21
molded by inserting the positive (P) DC input wire
3
, the negative (N) DC input wire
4
, the U-phase, V-phase and W-phase AC output wires
10
u
,
10
v
and
10
w
and a drive circuit board connection wire
20
, a cover
26
for covering the resin case
21
from above and a switching power module base plate
22
.
The positive (P) and negative (N) DC input wires
3
and
4
are arranged in parallel as shown in FIG.
10
and connected to the U, V and W phases of AC output in most cases. Thereby, opposite-direction currents run through the positive (P) DC input wire
3
and the negative (N) DC input wire
4
, and the inductance's of the wires offset each other by the mutual induction function of these currents, thereby reducing inductance between the positive (P) DC input wire
3
and the negative (N) DC input wire
4
.
An insulated substrate
23
such as a ceramic substrate for mounting the switching elements
5
a
to
5
f
and the free wheel diodes
8
and a drive circuit board
24
for mounting the drive circuit unit
6
are stored in the package of the switching power module
12
. The switching elements
5
a
to
5
f
and the free wheel diodes
8
are fixed on the switching power module base plate
22
through the insulated substrate
23
having a conductor pattern formed thereon by a bonding material such as solder and connected to the positive (P) DC input wire
3
, the negative (N) DC input wire
4
, the U-phase, V-phase and W-phase AC output wires
10
u
,
10
v
and
10
w
, and the drive circuit board connection wire
20
by a connection conductor
19
such as wire bonding or the like.
The drive circuit board
24
and the drive circuit board connection wire
20
are electrically connected to each other by solder or the like. A gel-like filler
25
is filled in a space between the insulated substrate
23
and the drive circuit board
24
and a resin such as an epoxy resin may be filled over the gel-like filler
25
. The gel-like filler
25
protects the switching elements
5
a
to
5
f
, the free wheel diodes
8
and the connection conductor
19
to prevent the failure or malfunctioning of the switching elements
5
a
to
5
f
caused by moisture or dust. The under surface
24
a
on the insulated substrate side of the drive circuit board
24
is generall

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