Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-02-24
2001-05-15
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000, C180S065310, C307S010100
Reexamination Certificate
active
06232744
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is based on and claims priority from the following Japanese Patent Applications: Hei 11-47000, filed Feb. 24, 1999; Hei 11-59309, filed Mar. 5, 1999; Hei 11-356921, filed Dec. 16, 1999; and Hei 11-367565, filed Dec. 24, 1999; the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of controlling condition of an assembled battery mounted in a self-generation electric vehicle such as a hybrid vehicle.
2. Description of the Related Art
An assembled battery mounted in an electric vehicle is discharged mostly when the vehicle accelerates and charged when the vehicle runs at a constant speed or decelerates. Therefore, it is necessary to maintain the condition of such a battery at a intermediate level between fully-charged level and fully discharged level.
In order to maintain the battery condition at the intermediate level, it is necessary to frequently detect the remaining capacity. In the past, the remaining capacity was estimated by summing up battery charging currents and battery discharging currents.
JP-A-10-51906 discloses such a method of controlling, as the battery condition, an SOC (State of Charge) ratio which represents the remaining capacity. Data related to terminal voltage and current of an assembled battery at a maximum normal SOC ratio and a minimum normal SOC ratio are stored in a map and are compared with an estimated SOC ratio calculated from currently detected terminal voltage and charge or discharge current of the battery.
If the estimated SOC ratio approaches the maximum normal SOC ratio, the battery is discharged. On the other hand, the battery is charged if the estimated SOC ratio approaches the minimum normal SOC ratio. This control is repeated frequently.
The more errors are accumulated in the estimated SOC ratio as more frequently the above steps are repeated. This may cause improper control of the battery condition.
In the disclosed method, the battery is always controlled so that the SOC ratio stays either at the maximum normal SOC ratio or at the minimum normal SOC ratio. If the battery is controlled at the minimum normal SOC ratio, it is difficult to supply driving energy from the battery to the wheels. On the other hand, if the battery is controlled at the maximum normal SOC ratio, it is difficult to charge the battery with the electric power regenerated from the driving energy of the wheels.
Further, because the assembled battery is comprised of a plurality of battery cells of different remaining capacities (or different SOC ratios) and deterioration speeds, it is always possible that any one of the battery cells is over-discharged or deteriorating.
SUMMARY OF THE INVENTION
A main object of the invention is to provide an improved method of controlling condition of an assembled battery of an electric vehicle which needs not a map.
According to a feature of the invention, a method of controlling condition of a battery of a self-generation electric vehicle comprising the following steps: detecting battery voltage and battery current repeatedly; estimating a constant-power voltage on the basis of the battery voltage and battery current, the constant-power voltage being a function of a remaining capacity of the battery when a preset constant power is charged to or discharged from the battery; setting a target voltage; comparing the constant-power-discharge voltage with the target voltage to provide a difference therebetween; and charging or discharging the battery to reduce the difference.
The following steps can be added to the above steps: setting a maximum-normal voltage and a minimum-normal voltage between a voltage level of the battery that is fully charged and a voltage level of the battery that is completely discharged; and stopping the battery current if the constant-power voltage level becomes out of a range between the maximum-normal voltage and the minimum-normal voltage.
Therefore, this method ensures accurate control of the battery condition.
The target voltage is preferably set at the middle of the maximum-normal voltage and the minimum-normal voltage.
Therefore, battery can be charged or discharged easily. This step also prevents any one of series-connected battery cells of an assembled battery from being over-discharged.
The above step may also have the following steps: estimating the remaining capacity of the battery by summing up the battery current; and correcting the estimated remaining capacity to the target remaining capacity when the constant-power voltage approaches the target voltage.
Therefore, errors are not accumulated in the estimated SOC ratio even if the step of estimating the remaining capacity is repeated, so that improper control of the battery condition can be prevented effectively.
The above step preferably includes a step of resetting battery condition. This step may be comprised of: setting a reference condition range that is defined by a preset voltage range and a preset remaining capacity range; setting an operation condition defined by the constant-power voltage and the estimated remaining capacity; and if the operation condition is found to be out of the reference condition range, controlling the battery current to change the operation condition to be out of a boundary defined by the maximum-normal voltage and the minimum-normal voltage and, subsequently controlling the battery current to return the constant-power voltage to the target voltage while the battery is not operated.
REFERENCES:
patent: 5917305 (1999-06-01), Faulk
patent: 6147473 (2000-11-01), Koo
patent: 908 737 A2 (1999-04-01), None
patent: 10-38985 (1998-02-01), None
patent: 10-51906 (1998-02-01), None
patent: 10-215503 (1998-08-01), None
patent: 11-121048 (1999-04-01), None
Kawai Toshiyuki
Kobayashi Tetsuya
Yamashita Takashi
Denso Corporation
Pillsbury & Winthrop LLP
Toatley, Jr Gregory J.
Wong Peter S.
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