Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells
Reexamination Certificate
1998-09-28
2002-06-11
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
C320S124000, C307S010700
Reexamination Certificate
active
06404165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electricity accumulator formed as a storage battery comprising a large number of battery cells connected in series, and more particularly to an electricity accumulator suitable for use in electric automobiles.
2. Description of Background Art
Techniques have recently been developed for an enhancement in the practical use of electric automobiles, and as the present power supply for electric automobiles, a storage battery comprising a large number of battery cells connected in series has been used.
In the case of such a storage battery comprising a large number of battery cells connected in series, the output of the storage battery depends upon the battery cell whose voltage is lowest, so the storage battery cannot use all the battery cells equally and exhibit the capability of each battery cell maximally.
Incidentally, as in a lithium-ion battery cell, in a battery cell in which its output voltage is determined in dependence on its discharge amount (see FIG.
4
), the discharge amounts of all battery cells (conversely speaking, charge amounts or residual capacities) can be equalized with one another by equalizing the voltages of all battery cells. Therefore, if charging or discharging is performed so that the voltages of all battery cells become equal to one another, the storage battery can exhibit the capability of each battery cell maximally.
Hence, a voltage equalizing circuit for a storage battery has been provided, and it is constructed as shown in FIG.
5
.
The circuit shown in
FIG. 5
is a voltage equalizing circuit corresponding to one battery cell (or one module) of a storage battery, and therefore, the same circuit is provided in each battery cell.
In such a circuit, a charging operation is first performed and then a discharging operation is performed at the end of the charging operation.
That is, the terminal voltage of a battery cell
101
is raised by the charging operation. This raised state is monitored by a voltage monitoring circuit (voltage detection circuit)
104
, and if the voltage VB across both terminals of the battery cell
101
exceeds a set voltage, a discharging switch
102
will be caused to be in an ON state (closed state).
With the above operation, current conduction to a discharging resistor
103
is performed, whereby electric energy is converted to heat and dissipated. With this dissipation, if the cell voltage VB becomes equal to or less than the set voltage, the discharging switch
102
will be caused to be in an OFF state (open state).
By reiterating such on-off control of the discharging switch
102
, the voltage VB of the battery cell is adjusted to the set voltage.
Note that in the actual circuit of the voltage equalizing circuit, instead of the discharging switch
102
a power device such as a power transistor is generally used to adjust voltage by linear control rather than by on-off control.
The aforementioned conventional electricity accumulator, however, have the following disadvantages.
That is, in the above-mentioned circuit, the energy exceeding a set voltage is dissipated in the form of heat by the discharging resistor
103
. For this reason, there are significant problems that power loss becomes great and that a countermeasure to radiate heat has to be considered.
In addition, the voltage equalization is possible only when the cell voltage VB at the end of the charging operation rises, and therefore, there is a problem that the voltage equalization can not be performed during discharge or for a vacant time during which a vehicle is not in use.
The aforementioned conventional electricity accumulator, therefore, cannot be utilized in electric automobiles that are not charged to its full charge during travel while generating electrical energy, as in hybrid electric automobiles.
Furthermore, since large-capacity components, such as a discharge resistor, a heat radiating plate, and a switching element, must be used, the overall device size is increased and a cooling unit for heat radiation is required, so that there is also a problem that the entire device becomes structurally complicated.
Hence, an equalizing circuit which is not required of a discharging method is necessary, and as the example, a technique disclosed in Japanese Laid-Open Patent Application No. HEI 6-319287 has been proposed.
In the aforementioned technique, both ends of a storage battery comprising a large number of battery cells connected in series are connected to a capacitor so that all battery cells are uniformly charged. However, a capacitor with a large capacitance is required and the control of detecting the terminal voltage of each battery cell and selecting a battery cell to be charged is logically complicated.
Hence, it is conceivable that a plurality of capacitors corresponding in number to battery cells connected in series are provided. And a first connection mode in which all capacitors are respectively connected in parallel with the corresponding battery cells and a second connection mode in which the capacitors are respectively connected in parallel with the battery cells adjacent to the corresponding battery cells are alternately switched, whereby the voltages of all battery cells are equalized with one another.
In the above case, the voltage equalization between battery cells is performed by moving electric charge between battery cells through capacitors.
However, in the aforementioned constitution, since electric charge is moved only between adjacent battery cells, there is a problem that the time required for voltage equalization is increased as the number of battery cells is increased. Also, as each battery cell requires a capacitor, the voltage equalizing circuit is increased in size, so that there is also a problem that the production cost is increased.
For the storage battery constituted by a plurality of battery cells connected in series, the aforementioned Japanese Laid-Open Patent Publication No. HEI 6-319287 discloses a technique in which a battery cell to be charged is selected, while the terminal voltage of each battery cell and the voltage of a capacitor are being monitored in performing a charging operation by the capacitor charged by regenerative current.
In the above technique, some of a plurality of battery cells are selected and charged so that the sum total of the terminal voltages of the selected battery cells becomes lower than the capacitor voltage. With this, even if the capacitor voltage were reduced, charging can be performed, and by charging a battery cell whose terminal voltage is low, a plurality of battery cells are uniformly charged.
Although the aforementioned technique can equalize the voltages of all battery cells in charging the storage battery, it cannot perform the voltage equalization except during charge.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problems. Accordingly, it is an object of the invention to provide an electricity accumulator which is capable of equalizing the voltages of a plurality of electricity accumulating means with inexpensive and simple constitution and quickly even in a state which is not a fully charged state, while preventing dissipation of electrical energy.
To achieve this end and in accordance with one aspect of the present invention, there is provided an electricity accumulator comprising: a plurality of electricity accumulating means connected in series; a capacitor connectable in parallel with at least two of the plurality of electricity accumulating means; and connection switching means to switch selectively a first connection mode in which the capacitor is connected to first electricity accumulating means of the plurality of electricity accumulating means so that the capacitor is charged or discharged through the first electricity accumulating means and a second connection mode in which the capacitor is connected to second electricity accumulating means differing from the first electricity accumulating means so that the capacitor i
Shinpo Toshiya
Suzuki Hiroyasu
Mitsubishi Jidosha Kogyo
Toatley Jr. Gregory J
Wong Peter S.
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