Set battery charging condition detecting apparatus

Details Set battery charging condition detecting apparatus Set battery charging condition detecting apparatus

2002-07-01

2003-05-13

Luk, Lawrence (Department: 2838)

Electricity: battery or capacitor charging or discharging

Serially connected batteries or cells

C320S119000

Reexamination Certificate

active

06563291

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-212486 filed on Jul. 12, 2001.
FIELD OF THE INVENTION
The present invention relates to a charging condition detecting apparatus for detecting the charging condition of a large number of unit cells which are connected in series to form a set battery.
BACKGROUND OF THE INVENTION
Various electric vehicles (EV) and hybrid electric vehicles (HEV) are proposed, because these vehicles generate no or less exhaust gas. As a secondary battery used as the power source of these HEV and EV, a lead-acid battery, nickel-cadmium battery, nickel-hydrogen battery or the like are known. Moreover, in recent years, attention is paid to a lithium battery because this battery has a higher weight energy density, about four times the lead-acid battery of the same capacity and about two times the nickel-hydrogen battery. These battery can therefore be expected to provide reduction in size and weight.
The Japanese Unexamined Utility Model Publication H2-136445 discloses a method in which a cell voltage of each unit cell is detected by using voltage detectors which are connected in parallel to each unit cell. In this method, the charging/discharging current is controlled so that the cell voltage of any unit cell does not exceed, at the time of charging operation, the preset upper limit voltage and does not become lower than the preset lower limit voltage at the time of discharging operation.
Here,
FIG. 8A
is a circuit diagram showing an example of a charging condition detecting apparatus P-CMUi which divides a set battery into cell groups CGi (i=1 to m), each of which is constructed by n unit cells, and detects whether there is a unit cell in the over-charge or over-discharge condition among those Ci
1
to Cin forming the cell group CGi.
The charging condition detecting apparatus P-CMUi has an over-charge determining circuit Puij which determines, for every unit cell Ci
1
to Cin forming the cell group CGi, whether the unit cell Cij (j=1 to n) is in the over-charge condition or not and generates a cell over-charge detection signal CUij indicating the result of determination. It also has an over-discharge determining circuit PLij which determines whether the unit cell Cij is in the over-discharge condition or not and generates a cell over-discharge detection signal CLij indicating the result of determination.
As shown in
FIG. 8B
, each over-charge determining circuit PUij is constructed by a voltage dividing circuit
120
comprising resistors RUa and RUb to divide a cell voltage VCij across the unit cell Cij, a constant voltage circuit
122
comprising a resistor RUc and a voltage generation source DU to generate a constant upper limit reference voltage VRU and a comparator
123
. To the comparator
123
, a voltage depending on the cell voltage VCij is impressed to its non-inverting input via the voltage dividing circuit
120
and the upper limit reference voltage VRU generated by the constant voltage circuit
122
is impressed to its inverting input.
Moreover, each over-discharge determining circuit PLij is constructed by a voltage dividing circuit
124
comprising resistors RLa, RLb to divide the cell voltage VCij, a constant voltage circuit
126
comprising a resistor RLc and a voltage generation source DL to generate a constant lower limit reference voltage VRL and a comparator
127
. To the comparator
127
, a voltage depending on the cell voltage VCij is impressed to its non-inverting input via the voltage dividing circuit
124
and the lower limit reference voltage VRL generated by a constant voltage circuit
126
is impressed to its inverting input.
However, the voltage generation sources DU, DL generate the reference voltages VRU, VRL by utilizing, for example, a forward voltage of a diode and a breakdown voltage of a Zener diode. The upper limit reference voltage VRU generated by the voltage generation source DU of the over-charge determining circuit PUij is set to a value, VU·Rub/(RUa+RUb), obtained by dividing the upper limit value VU of the allowable voltage range of the cell voltage VCij in a voltage dividing ratio of the voltage dividing circuit
120
. The lower limit reference voltage VRL generated by the voltage generation source DL of the over-discharge determining circuit PLij is set to a value, VL·RLb/(RLa+RLb), obtained by dividing the lower limit value VL of the allowable voltage range of the cell voltage VCij in a voltage dividing ratio of the voltage dividing circuit
124
comprised of resistors RLa, RLb.
The over-charge detection signal CUij generated by the over-charge determining circuit PUij becomes high level indicating that the unit cell Cij is in the cell over-charge condition when the cell voltage VCij is larger than the upper limit value VU of the allowable voltage range. It becomes low level when the cell voltage is smaller than the upper limit value VU. Moreover, the cell over-discharge detection signal CLij generated by the over-discharge determining circuit PLij becomes low level indicating that the unit cell Cij is in the over-discharge condition when the cell voltage VCij is smaller than the lower limit value VL of the allowable voltage range.
In addition, as shown in
FIG. 8A
, the charging condition detecting apparatus P-CMUi is provided with a logical sum (OR) circuit
132
which provides a high level output when any one of the cell over-charge detection signals CUi
1
to CUin from each over-charge determining circuit PUi
1
to PUin is in the high level. The detecting apparatus P-CMUi is further provided with a logical product (AND) circuit
133
which provides a low level output when any one of the cell over-discharge detection signals CLi
1
to CLin from each over-discharge determining circuit PLi
1
to PLin is in the low level. Thereby, an output of the OR circuit
132
is used as a groop over-charge detection signal OUi, while an output of the AND circuit
133
as a group over-discharge detection signal OLi.
That is, when all unit cells Ci
1
to Cin forming a cell group CGi are in the normal charging condition (VL≦VCij≦VU), the group over-charge detection signal OUij becomes low level, while the group over-discharge detection signal OLij becomes high level. On the other hand, when any one of the unit cells Ci
1
to Cin is in the over-charge condition (VCij>VU), the group over-charge detection signal OUi becomes high level. When any one of the unit cells is in the over-discharge condition (VCij<VL), the group over-discharge detection signal OLi becomes low level.
However, the charging condition detecting apparatus P-CMUi still has a problem that the unit cell Cij is continuously used under the over-charge or over-discharge condition. Thus the unit cell Cij, more specifically a set battery as a whole, can no longer be used because this apparatus cannot detect the over-charge condition or over-discharge condition of the unit cell Cij when the cell overcharge detection signal CUij, cell over-discharge detection signal CLij, group over-charge detection signal OUi or group over-discharge detection signal OLi is fixed to the signal level indicating the normal condition for some reason.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to detect faults or irregular conditions of a charging condition detecting apparatus for detecting, in the simplified structure, the charging condition of unit cells in every group.
According to the first aspect of the present invention, a charging condition detecting apparatus is respectively provided with a first voltage comparator and a second voltage comparator for each unit cell forming a chargeable/dischargeable set battery. In the first voltage comparator, when a cell voltage which is a voltage across the unit cell is higher than a first threshold value voltage which is set to the upper limit value of the allowable voltage range of the cell voltage, an output of this first comparator becomes an active level, while in the seco

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