Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Reexamination Certificate
2000-12-20
2002-10-01
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
Reexamination Certificate
active
06459236
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cell balance adjusting circuit, an abnormal cell voltage detecting circuit, a method of adjusting a cell balance and a method of detecting an abnormal cell voltage, and more particularly to a cell balance adjusting circuit for adjusting a balance between cells connected in series in an application circuit having combined secondary batteries with a simple control circuit configuration.
A conventional technique for charging combined secondary batteries such as lithium batteries will be described.
FIG. 1
is a circuit diagram illustrative of a conventional circuit for charging combined secondary batteries such as lithium batteries. A series connection of first to sixth battery cells CE
1
, CE
2
, CE
3
, CE
4
, CES and CE
6
is connected between a charging circuit
100
and a ground line. A voltage monitoring control circuit
200
is also provided. A first side of the first battery cell CE
1
is connected to the charging circuit
100
. The first side of the first battery cell CE
1
is further connected through a first series connection of a first switch S
1
and a first resistance R
1
and also through a first by-pass to the voltage monitoring control circuit
200
. A second side of the first battery cell CE
1
is connected to a first side of the second battery cell CE
2
. The second side of the first battery cell CE
1
and the first side of the second battery cell CE
2
are further connected through a second series connection of a second switch S
2
and a second resistance R
2
and also through a second by-pass to the voltage monitoring control circuit
200
. A second side of the second battery cell CE
2
is connected to a first side of the third battery cell CE
3
. The second side of the second battery cell CE
2
and the first side of the third battery cell CE
3
are further connected through a third series connection of a third switch S
3
and a third resistance R
3
and also through a third by-pass to the voltage monitoring control circuit
200
. A second side of the third battery cell CE
3
is connected to a first side of the fourth battery cell CE
4
. The second side of the third battery cell CE
3
and the first side of the fourth battery cell CE
4
are further connected through a fourth series connection of a fourth switch S
4
and a fourth resistance R
4
and also through a fourth by-pass to the voltage monitoring control circuit
200
. A second side of the fourth battery cell CE
4
is connected to a first side of the fifth battery cell CE
5
. The second side of the fourth battery cell CE
4
and the first side of the fifth battery cell CE
5
are further connected through a fifth series connection of a fifth switch S
5
and a fifth resistance R
5
and also through a fifth by-pass to the voltage monitoring control circuit
200
. A second side of the fifth battery cell CE
5
is connected to a first side of the sixth battery cell CE
6
. The second side of the fifth battery cell CE
5
and the first side of the sixth battery cell CE
6
are further connected through a sixth series connection of a sixth switch S
6
and a sixth resistance R
6
and also through a sixth by-pass to the voltage monitoring control circuit
200
. A second side of the sixth battery cell CE
6
is connected to the ground line. The first series connection of the first switch S
1
and the first resistance R
1
is connected between the first and second side of the first battery cell CE
1
. The second series connection of the second switch S
9
and the second resistance R
2
is connected between the first and second side of the second battery cell CE
2
. The third series connection of the third switch S
3
and the third resistance R
3
is connected between the first and second side of the third battery cell CE
3
. The fourth series connection of the fourth switch S
4
and the fourth resistance R
4
is connected between the first and second side of the fourth battery cell CE
4
. The fifth series connection of the fifth switch S
5
and the fifth resistance R
5
is connected between the first and second side of the fifth battery cell CE
5
. The sixth series connection of the sixth switch S
6
and the sixth resistance R
6
is connected between the first and second side of the sixth battery cell CE
6
.
The voltage monitoring control circuit
200
monitors individual voltages of the first to sixth battery cells in the charge process. If one of the battery cells is completely charged up, then a charge current is by-passed to the corresponding resistance, whilst the remaining battery cells are continued to be charged.
In this case, the cell balance adjustment is made only in the charging process. If the capacitance balance of the cells is imperfect or lost, a dischargeable power in the discharge process is limited by a minimum cell capacity in the battery cells. This means that the large capacity cells show imperfect discharge. Namely, an unnecessary power is consumed in the charging process, and further the perfect discharge of the charged up power is difficult.
In order to have solved the above problem, the following conventional technique has been proposed, which is disclosed in Japanese laid-open patent publications Nos. 11-146570 and 11-098698. In the charging and discharging processes, a voltage across terminals of each cell is measured, so that two cells are selected on the basis of the measured voltage values. A charge accumulation device such as the capacitor is connected in parallel to first one of the selected two cells before this connected is switched into that the charge accumulation device is connected in parallel to second one of the selected two cells. This processes will be repeated to reduce the difference in voltage between the selected two cells.
Subsequently, the cell voltage is measured and then the above switching processes will further be repeated to take a balance among the individual cells. The use of the voltage judging circuit enables that the selected two cells have almost the same voltage. The voltage measuring operations will be repeated to adjust the voltage balances among the plural cells.
The conventional balance adjusting circuit using the charge accumulation device is thus capable of adjustment to the cell balance in the charge and discharge processes. The conventional balance adjusting circuit using the charge accumulation device, however, has the following problems.
The first problem is as follows. To select the two cells to be connected in parallel, it is necessary to measure the cell terminal voltages every times for judgement. The judgement and control circuit is made complicated. Particularly, in case of the large number of the battery cells connected in series, a large withstand voltage of the voltage measuring circuit is necessary.
A battery to be used for a hybrid car shows a high output voltage of 240V. In order to measure the cell voltage for judgement, the circuit is required to have an extremely high withstand voltage. This makes increased a cost or a price of the circuit.
To obtain a driving energy for the hybrid car, a high voltage is necessary. A responsible IC with a high withstand voltage for measuring and judgement to the voltage is expensive.
The second problem is as follows. Under the high voltage conditions, an averaged voltage difference between the comparing cells is about 1.2V if the cells are nickel hydrogen battery. The averaged voltage difference between the comparing cells is only 3.62V if the cells are lithium secondary battery. An accuracy in a few milli-voltage order is necessary to detect the voltage difference. Higher voltages in the range of 240V to 280V are used for the hybrid cars, electric cars and fuel battery cells. In such high voltage level, the accuracy in a few milli-voltage order is necessary for the circuit to detect the voltage difference. The circuit having such the high accuracy is expensive.
A large number of the small voltage cells is connected in series, for example, several tends to a few hundreds, so that a potential voltage from the ground level is 240V. This means
NEC Corporation
Tibbits Pia
Tso Edward H.
Young & Thompson
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