Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1999-02-10
2000-04-25
Tso, Edward H.
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
H01M 1046
Patent
active
060548401
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power supply apparatus, particularly to a power supply apparatus comprising a plurality of secondary batteries connected serially, and more concretely to a control of charging and discharging in such power supply apparatus, to eliminate a variance in capacity among the batteries and to prevent an accelerative deterioration of the batteries.
BACKGROUND ART
Various power supply apparatuses in which many secondary batteries such as alkaline secondary batteries and nickel-metal hydride secondary batteries are connected serially have been proposed. Such power supply apparatuses are now attracting a great deal of attention especially as driving power sources of electric vehicles. Since a high voltage of 200-300 V is required as a driving power source of an electric vehicle, each of such power supply apparatuses is provided with a battery unit including about 200 secondary batteries connected serially. In such a power supply apparatus, the battery unit is charged by an external power source and discharged to an external load such as a motor. Usually, the electrical power unit is provided with monitor and control means for monitoring a state of each battery to prevent both overcharging and overdischarging. The monitor and control means stops the charging when the battery unit voltage reaches a predetermined upper limit thereby to prevent overcharging in charging, and the monitor and control means stops the discharging when the battery unit voltage drops to a predetermined lower limit thereby to prevent overdischarging in discharging.
Regardless of the battery type, a deterioration of a secondary battery including a decrease in battery capacity and an increase in internal resistance thereof progresses acceleratively as charge/discharge cycles are repeated. Further, if many secondary batteries are used, the deterioration of battery badly affects other batteries. According to the control as described above, for example, a secondary battery whose capacity is reduced due to the deterioration is further deteriorated since it is apt to be overdischarged. In addition, heat due to the increase in internal resistance of the secondary battery causes a drop in output or deterioration of other secondary batteries. Also a normal secondary battery deteriorates and generates heat thereby increasing the surrounding temperature and even when charged fully, may be overcharged, if the charging efficiency of the secondary battery around it drops.
If many batteries are to be used, a temperature difference among batteries, for example, causes the deterioration of batteries. In addition to the facilitation of the deterioration due to high temperature, a difference in charging efficiency or self-discharge characteristics among the batteries caused by a temperature difference also causes the overcharging or the overdischarging of the batteries. Further, even when every secondary battery is used under the same condition, a difference in original characteristics among respective batteries such as capacity, charging efficiency and self-discharging characteristics also becomes a factor is the deterioration.
Therefore, various means to suppress such accelerative deterioration in battery characteristics have been proposed. For example, the Official Gazette of Unexamined Japanese Patent Publication No. Hei 6-231805 has proposed a method in which a voltage of a battery unit composed of a plurality of batteries connected serially is monitored and a voltage of each battery is also monitored, then a charge upper limit voltage is corrected to be lower and a discharge lower limit voltage is corrected to be higher when a variance in battery voltage becomes large.
As shown in FIG. 4, a power supply apparatus 30 comprises a battery unit 32 for supplying an electric power to a load 33 such as a motor, and control and monitor means 34 for controlling and monitoring the battery unit 32.
A charging operation of the power supply apparatus proposed in the above-mentioned gazette will be explained with refer
Nakanishi Toshiaki
Torii Yuji
Matsushita Electric - Industrial Co., Ltd.
Tso Edward H.
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