Alternator power converter

Details Alternator power converter Alternator power converter

2000-05-23

2001-04-10

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

Using semiconductor-type converter

C363S039000

Reexamination Certificate

active

06215679

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alternator such as an inverter and the like, and in particular, to the type, positioning, mounting, fixing, connecting method and the like of a smoothing capacitor used in the alternator.
2. Description of the Related Art
FIG. 12
is a block diagram showing the circuit construction of a conventional alternator which converts a DC power source into a three phase alternating current for driving an AC load such as a three-phase AC motor. Taking the case of an electric vehicle as an example, when the vehicle is first started off or accelerated, a switching power module
1
converts the discharge output of a DC power source
8
(battery) from direct current to a three phase current to drive an AC load
9
(three-phase motor). On the other hand, when the vehicle performs regenerative braking, regenerative power from the AC load
9
(three-phase motor) is converted from three phase current to direct current and returned to the DC power source
8
(battery).
Switching elements
2
such as transistors which convert power from direct current to three phase current, i.e, IGBT (Insulated Gate Bipolar Transistor) and MOSFET (Metal Oxide Semiconductor Field Effect Transistor), free-wheel diodes
3
which convert power from three phase current to direct current, snubber capacitors
4
for suppressing a surge voltage occurring in the switching elements
2
section during switching, and a drive circuit section
5
for driving the switching elements
2
are loaded in the switching power module
1
.
Here, the main property demanded of the snubber capacitor
4
is good frequency characteristics. Thus, a film capacitor is generally used as the snubber capacitor
4
. On the other hand, a smoothing capacitor
107
suppresses voltage fluctuation of the DC power source
8
during switching and smoothes a voltage jump and the like, and thus must have a sufficiently large capacitance. Therefore, an aluminum electrolytic capacitor which can easily provide a large capacitance is generally used as the smoothing capacitor
107
.
Furthermore, a control circuit section
6
outputs a control signal to the drive circuit section
5
in the switching power module
1
to control the switching elements
2
. Moreover, since the drive circuit section
5
and control circuit section
6
are generally circuits for driving and controlling the AC load
9
, i.e., three phase motor and the like, detailed drawings thereof are omitted.
Moreover,
FIG. 13
is a partially sectional side elevation view showing the internal construction of a common conventional alternator. In
FIG. 13
, a switching power module
1
, smoothing capacitors
107
, a snubber capacitor board
20
loaded with snubber capacitors
4
(not shown), and a control circuit board
19
loaded with control circuits
6
(not shown) are housed in a case
23
.
Generally, a distributing board
21
such as a copper bus bar or a copper plate and the like is used for connecting the switching power module
1
and the smoothing capacitors
107
which are electrically connected when the distributing board
21
is connected with screws
22
. Also, the snubber capacitor board
20
is generally arranged in the vicinity of a positive electrode (P), negative electrode (N) DC input wiring
10
p
,
10
n
and a U phase, V phase and W phase AC output wiring
11
of the switching power module
1
, and is at the same time fixed and electrically connected with the screws
22
.
The switching power module
1
package is constructed from: a resin switching power module case
13
insert molded with the positive electrode (P), negative electrode (N) DC input wiring
10
p
,
10
n
, the U phase, V phase and W phase AC output wiring
11
and driving circuit board connection wiring
12
; and a switching power module base board
14
. Also, an insulating board
15
, such as a ceramic board and the like, loaded with switching elements
2
and free-wheel diodes
3
, and a driving circuit board
18
(not shown) loaded with the driving circuit section
5
are housed in the switching power module
1
package.
The switching elements
2
and free-wheel diodes
3
are fixed with a bonding member, such as solder and the like, on the switching power module base board
14
via the insulating board
15
which has a conductor pattern. The switching elements
2
and free-wheel diodes
3
are connected with the positive electrode (P), negative electrode (N) DC input wiring
10
p
,
10
n
, the U phase, V phase and W phase AC output wiring
11
and the driving circuit board connection wiring
12
by means of a connecting conductor
16
such as wire bonding and the like. Moreover, the driving circuit board
18
and the driving circuit board connection wiring
12
are electrically connected with solder and the like.
A gel filler
17
is filled between the insulating board
15
and the driving circuit board
18
, and there are also cases where a resin, such as an epoxy and the like, is further filled thereon. Moreover, this gel filler
17
protects the switching elements
2
, free-wheel diodes
3
and connecting conductor
16
so as to prevent the switching elements from being damaged or malfunctioning due to dust and humidity.
The surface of the driving circuit board
18
on the insulating board
15
side is generally beta grounded to obtain an electromagnetic sealed effect so that the driving circuit section
5
does not malfunction due to switching noise generated from the switching elements
2
during power conversion.
Furthermore, a cooling member
24
for cooling the switching elements
2
by means of air-cooling, water-cooling, oil-cooling and the like is attached to the case
23
, and Joule heat generated from the switching elements
2
is dissipated to cooling member
24
via the insulating board
15
and the switching power module base board
14
. Thus, the switching elements are cooled. Moreover, detailed drawings of the mounting position and fixing method of a control circuit board have been omitted.
The smoothing capacitor
107
must have a sufficiently large electrostatic capacity because it smoothes the power of the DC power source to be supplied to the switching elements
2
. Accordingly, it generally has a large size. When an aluminum electrolytic capacitor is used as the smoothing capacitor
107
, since the internal resistance thereof is high, the internally generated heat of the smoothing capacitor
107
is increased by ripple voltage fluctuation of the direct current which occurs during switching.
In order to suppress this generated heat, the structure of the switching power module
1
must be complicated by cooling the smoothing capacitor
107
with the cooling member
24
, or the electrostatic capacity must be increased further. Accordingly, conventional alternators have had a drawback in that the surface area and volume of the smoothing capacitor
107
are large, thus increasing the size of the entire apparatus.
Also, aluminum electrolytic capacitors have drawbacks in that they have a narrow operating temperature range, and a short service life due to electrolyte leakage which accompanies poor sealing.
Furthermore, since the surface area and volume of the smoothing capacitor
107
are large, there is a drawback in that electrical wiring for connecting the switching power module
1
and smoothing capacitor
107
must be long. Hence, the wiring inductance between the switching elements
2
and the smoothing capacitor
107
increases, and because there is a danger that the switching elements
2
will be damaged by a large surge voltage occurring during switching, snubber capacitors
4
must be provided in the vicinity of the positive electrode (P), negative electrode (N) DC input wiring
10
p
,
10
n
and a U phase, V phase and W phase AC output wiring
11
of the switching power module
1
.
Moreover, in the conventional switching power module
1
, the surface of the driving circuit board
18
on the switching elements
2
side is magnetically sealed by means of a beta grounding method and the like so as

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