Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells
Reexamination Certificate
2002-09-26
2004-12-07
Luk, Lawrence (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
C320S117000
Reexamination Certificate
active
06828757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for adjusting the charging rate of cell modules constituting cells in combination which have a high voltage, for example, for use as a power source for drive motors for electric motor vehicles such as hybrid cars. The term “charging rate” as used herein means the percentage to which the cells in combination are charged relative to the full capacity thereof.
2. Description of the Related Art
Power sources conventionally mounted in electric motor vehicles, such as hybrid cars, for drive motors comprise secondary cells connected in series for use in combination. Because combinations of such cells must produce a high voltage usually of 200 to 300 V, for example, 60 to 80 lithium secondary cells each having an output of about 3.6 V are connected in series, or about 200 NiMH secondary cells each having an output of about 1.2 V are connected in series for use in combination.
It is desired that all the secondary cells in combination be equivalent in charged state. Suppose one secondary cell is 70% in charging rate, and another secondary cell is 50% in charging rate. In this case, the amount of electricity chargeable into these cells in combination is 30% which corresponds to the amount of charge for the cell with the charging rate of 70% when it is to be charged to the full. If the two cells are charged to an amount in excess of 30%, the secondary cell with the charging rate of 70% will be charged more than 100% to become greatly shortened in life. Consequently the combination of cells is also shortened in life.
Variations in the amount of electricity remaining in the secondary cells in combination are dependent on the efficiency (charge-discharge efficiency) of the individual cells. For example, suppose the secondary cells in combination are all 100% in charge efficiency and 99.0 to 99.5% in discharge efficiency. If the cells are charged at 10 Ah, charge of 10 Ah is stored in each cell. When the cells are subsequently discharged at 10 Ah, charge of 10.1 Ah (=10 Ah/0.990) is delivered from the cell with a discharge efficiency of 99.0%, and charge of 10.05 Ah (=10 Ah/0.995) is delivered from the cell with a discharge efficiency of 99.5%. Charge which is 0.05 Ah greater will then remain in the cell with the higher discharge efficiency of 99.5%. Accordingly, the amount of remaining electricity varies from cell to cell as a result of repetition of charge and discharge. Especially in the case of lithium ion secondary cells which are exceedingly high in charge-discharge efficiency, slight variations in charge-discharge efficiency result in a pronounced tendency for the cells to vary in the amount of remaining electricity.
Accordingly, a charging rate adjusting circuit
6
shown in
FIG. 9
is used for discharging secondary cells having a greater amount of charge and thereby giving them the same amount of remaining electricity as those of smaller amount of charge. In the case of the circuit, one or a plurality of secondary cells constitute a cell module
70
, and four cell modules are connected in series to provide a cell block
71
. Two cell blocks
71
are further connected in series to provide cells in combination.
Voltage detecting lines
61
extend from the opposite terminals of each cell block
71
and from the points of connection between two of the cell modules
70
and are connected to a voltage measuring circuit
62
. Opposite terminals of each cell module
70
are connected to a discharge circuit
63
which will be described below. The voltage measuring circuits
62
,
62
and the discharge circuits
1
to
8
are connected to an unillustrated control circuit. The control circuit controls the discharge operation of the discharge circuits
1
to
8
based on voltage across each cell module
70
measured by the voltage measuring circuits
62
,
62
.
FIG. 10
shows an example of construction of the discharge circuit
63
. When a photocoupler
64
is turned on, an on-off switch
65
comprising a MOSFET is closed, causing a current to flow from the cell module
70
to a discharge resistor
66
, whereby the charging rate of the cell module
11
can be lowered.
With the charging rate adjusting circuit
6
shown in
FIG. 9
, the control circuit specifies the cell module(s)
70
of high charging rate based on the voltage measuring result obtained from the voltage measuring circuit
62
62
, turning on the photocoupler of the discharge circuit
63
connected to each module
70
of high rate. This reduces the cell module
70
of high rate in charging rate, making all the cell modules equivalent in charging rate.
However, the conventional charging rate adjusting circuit
6
must be provided with a discharge circuit
63
for every cell module
70
constituting the cells in combination, thereby making the circuit large in size, hence the problem of impairing reliability of circuit operation and of a higher cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a charging rate adjusting circuit for a cell combination which is adapted to reduce the number of components.
The present invention provides a first charging rate adjusting circuit for a cell combination comprising a plurality of cell blocks each having a plurality of cell modules connected to one another in series, the circuit being adapted to provide one of a uniform charging rate and a uniform voltage to the cell modules. The circuit comprises:
first connecting/disconnecting means for connecting or disconnecting the cell blocks one another in series,
second connecting/disconnecting means for connecting or disconnecting one another in parallel the cell modules corresponding to one another in the cell blocks,
a plurality of discharge circuits each being connected to opposite electrodes of each of the cell modules constituting at least one cell block and performing discharge operation in response to a discharge command,
a voltage detection circuit for detecting voltage across each of the cell modules constituting at least one cell block, and
a control circuit for setting the first connecting/disconnecting means into connecting state and setting the second connecting/disconnecting means into disconnecting state in usual operation when the cell combination is operated as a power supply source, while for setting the first connecting/disconnecting means into disconnecting state and setting the second connecting/disconnecting means into connecting state when the charging rate of the cell modules are adjusted, and giving the discharge command to one or a plurality of discharge circuits based on detection result obtained by the voltage detection circuit.
With the first charging rate adjusting circuit of the present invention, in the usual operation, the first connecting/disconnecting means is set into connecting state and the second connecting/disconnecting means is set into disconnecting state. Accordingly, the plurality of cell blocks are connected to one another in series, whereby the overall cell combination is operable as a power supply source.
On the other hand, when the charging rate is adjusted, the first connecting/disconnecting means is set into disconnecting state and the second connecting/disconnecting means is set into connecting state. Accordingly, the plurality of cell modules corresponding to each other in the plurality of cell blocks are interconnected in parallel, and thereby charge moves from a cell module of high charging rate to a cell module of low charging rate. In this way, charge and discharge is conducted between the cell modules, with the result that the plurality of cell modules interconnected in parallel are uniformized in charging rate in the plurality of cell blocks. Variations in charging rate among the cell modules constituting each cell block still remains.
The charging rate of the cell module reflects a voltage value across the cell module with high correlation, and particularly lithium ion secondary cells have this pronounced tendency. Suppose one cell module constituting one
Luk Lawrence
Sanyo Electric Co,. Ltd.
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