Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-04-20
2001-03-20
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06205036
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an energy transfer unit which is connected to a plurality of energy storage means to transfer the energy among the energy storage means mutually, and a charge unit and, more particularly, an energy transfer unit which is suitable for uniforming respective inter-terminal voltages of a plurality of energy storage means, and a charge unit and a power supply unit employing the energy transfer unit.
2. Description of the Related Art
As an energy transfer unit of this type, for example, the transfer unit
1061
disclosed in unexamined Japanese Patent Publication (KOKAI) Hei 7-322516 has been known in the conventional art. As shown in
FIG. 30
, a transfer unit
1061
is constructed to uniform storage energy of a plurality of capacitors C
1
to C
4
by transferring the storage energy in any one of the capacitors C
1
to C
4
to other capacitors. More particularly, the transfer unit
1061
comprises a series circuit of a choke coil L
1
and a switch SW
1
connected in parallel with a capacitor C
1
, a switch SW
21
connected to a capacitor C
2
via the choke coil L
1
, a series circuit of a choke coil L
2
and a switch SW
22
connected in parallel with the capacitor C
2
, a series circuit of a choke coil L
3
and a switch SW
31
connected in parallel with a capacitor C
3
, a switch SW
32
connected to the capacitor C
3
via the choke coil L
2
, and a switch SW
4
connected to the capacitor C
4
via the choke coil L
3
.
In the transfer unit
1061
, for example, upon transferring the storage energy of the capacitors C
4
to the capacitor C
1
, first the switch SW
4
is controlled into the ON state. At this time, as shown in
FIG. 30
, the choke coil L
3
is excited by a current I
61
. Then, a current I
62
based on the exciting energy of the choke coil L
3
flows by controlling simultaneously the switch SW
4
and the switch SW
31
into the OFF state and the ON state respectively to charge the capacitor C
3
. Then, the switch SW
31
is controlled into the OFF state and then the switch SW
32
is controlled into the ON state. Thus, a current I
63
flows to excite the choke coil L
2
. In turn, a current I
64
based on the exciting energy of the choke coil L
2
flows by controlling simultaneously the switch SW
32
and the switch SW
22
into the OFF state and the ON state respectively to charge the capacitor C
2
. Then, the switch SW
22
is controlled into the OFF state and then the switch SW
21
is controlled into the ON state. Thus, a current I
65
flows to excite the choke coil L
1
. Finally, a current I
66
based on the exciting energy of the choke coil L
1
flows by controlling simultaneously the switch SW
21
and the switch SW
1
into the OFF state and the ON state respectively to charge the capacitor C
1
. As a result, the storage energy of the capacitor C
4
is transferred to the capacitor C
1
.
The transfer unit
1061
in the conventional art contains the problems described as follows.
In other words, in the transfer unit
1061
, for example, upon transferring the energy from the capacitors C
4
to the capacitors C
3
, the switch SW
4
and the switch SW
31
must be controlled simultaneously into the OFF state and the ON state. In this case, if the switch SW
31
is controlled into the ON state prior to the OFF state of the switch SW
4
, the capacitors C
3
and C
4
are short-circuited via the switches SW
4
and SW
31
, resulting in loss of the storage energy of both capacitors C
3
and C
4
. On the contrary, if the switch SW
4
is controlled into the OFF state prior to the ON state of the switch SW
31
, a very high voltage is generated across the switch SW
4
, resulting in failure of the switch SW
4
. In this manner, in the transfer unit
1061
in the conventional art, there is such a problem that, even if ON/OFF control timings of the switches S
1
to SW
4
are deviated slightly, short-circuit of the circuit and the failure of the circuit parts are brought about and also the energy cannot be transferred.
Also, in transferring the energy from the capacitor C
4
to the capacitor C
1
, ON/OFF of the switches SW
4
to SW
1
must be controlled many times at a precise timing. Hence, in the transfer unit
1061
, there is also such a problem that the control of the switches becomes complicated.
Further, in order to transfer the energy among four capacitors C
1
to C
4
, six switches SW
1
to SW
4
must be used in the transfer unit
1061
. In this case, if the situation that the energy is transferred among a number of capacitors is considered, the number of switches becomes about twice the number of capacitors. For this reason, in the transfer unit
1061
in the conventional art, there is also such a problem that, since the number of switches is increased, the transfer unit becomes expensive and the size of the unit is also increased.
A battery for vehicle and a charge unit for charging the battery have been developed swiftly in recent years. As one of the charge units of this type, a charge unit
1041
shown in
FIG. 31
has already been developed. The charge unit
1041
is constructed to charge a battery BAT, which is constructed by series-connecting a plurality of electric double layer capacitors C
1
to C
4
, for example, with high efficiency in compliance with the simply-constructed chopper system. In this charge unit
1041
, when the control circuit (not shown) controls the switching element
1042
into the ON state, the charge current I
11
, which is generated based on the input voltage VIN such as the pulsating current obtained by rectifying the AC, the stabilized DC voltage, etc., flows through the current path comprising the switch element
1042
, the choke coil
1043
, and the battery BAT to thus charge the battery BAT. In contrast, when the switching element
1042
is controlled into the OFF state, the fly-wheel current IF flows through the current path comprising the choke coil
1043
, the battery BAT, and the commutating diode
44
, based on the energy stored in the choke coil
1043
during the flow of the charge current I
11
, whereby the battery BAT is also charged in this period. In this manner, in the charge unit
1041
, the battery BAT can be continuously charged by the charge current I
11
and the fly-wheel current IF during both periods of the ON period and the OFF period by ON/OFF-controlling the switch element
1042
.
However, the charge unit
1041
in the conventional art contains the problems described as follows. In other words, in the charge unit
1041
, the battery BAT is charged by passing the charge current I
11
and the fly-wheel current IF through the capacitors C
1
to C
4
in series during both periods of the ON period and the OFF period of the switching element
1042
. Therefore, the inter-terminal voltages of the capacitors C
1
to C
4
are not always maintained at the uniform voltage, rather they have a tendency to vary from each other. Meanwhile, the storage energy of the capacitor is in proportion to square of the inter-terminal voltage of the capacitor. Accordingly, even if the inter-terminal voltages are changed slightly, the storage energy of a plurality of capacitors C
1
to C
4
are changed considerably. Thus, such a situation occurs that, although the battery BAT has been charged sufficiently in due course, actually such battery BAT cannot discharge the enough electrical energy. For this reason, if the battery BAT for the electric vehicle is charged by the charge unit
1041
, there is a possibility that the run-down of the battery is brought about after the vehicle travels merely within a short distance. In this manner, in the charge unit
1041
in the conventional art, there is such a problem that it is difficult to charge effectively sufficiently the storage means that is constructed by series-connecting a plurality storage elements. Further, there is another problem that, if the storage means is charged under the condition that the inter-terminal voltages of a plurality of storage elements are fluctuated, the lifetime of the storage elements is shortened.
SUM
Nagano Japan Radio Co. Ltd.
Nguyen Matthew
Rosenthal & Osha L.L.P.
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