Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – Having variable number of cells or batteries in series
Reexamination Certificate
1999-11-16
2001-05-01
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
Having variable number of cells or batteries in series
C320S166000
Reexamination Certificate
active
06225781
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates an electrical storage capacitor system consisting of capacitors connected in series.
DESCRIPTION OF THE PRIOR ART
Where large-capacity capacitors are combined to constitute an electrical storage unit, if the capacitors are connected in series, uniform voltage must be assigned to the capacitors. We have already proposed an electrical storage system, referred to as an energy capacitor system (ECS), using electric double-layer capacitors. In this energy capacitor system, parallel monitors for monitoring and controlling voltages are connected in series with the capacitors. This permits maximum charging within the range of breakdown voltages of the capacitors.
FIG. 8
shows an example of the circuit configuration of such a parallel monitor.
FIG. 9
is a graph illustrating the charging/discharging characteristics of the prior art circuit shown in
FIG. 8
when and after the capacitor C is initialized.
In a parallel monitor, as shown in
FIG. 8
, a comparator CMP compares the voltage developed across a capacitor C with a reference voltage Vr. If this compared voltage reaches a set value determined by the reference voltage Vr, a transistor Tr is turned on, thus bypassing a charging current. As the charging operation progresses, the voltage developed across the capacitor C rises but is then kept at the set value as indicated by (1) in FIG.
9
. With respect to other series connected capacitors having larger capacitances, the voltages rise with delays and reach full charge at point (2). After reaching full charge, relaxation charging is performed with a constant voltage until a next discharging (3) is commenced.
In this way, the prior art energy capacitor system (ECS) is initialized set such that the voltages developed across the capacitors become equal to the upper limit of voltage (full charge voltage) at point (1). Then, each capacitor is started to be charged and discharged from this initial condition.
The above-described structure is simple and economical to realize. Also, the operation is reliable. Therefore, this structure has played a great role in putting the energy capacitor system into practical use. However, during the period (1) to (2), the parallel monitor is turned on, and the charging current is bypassed. During this period, the charging energy is wasted as heat, thus constituting a problem. In particular, in the parallel monitor shown in
FIG. 8
, the transistor Tr is driven into conduction when the set voltage at (1) is reached. This forms a bypass circuit. The voltage is clamped to prevent the voltage from rising further. Therefore, the bypass circuit generates loss, or heat, corresponding to the “charging current×full charge voltage”.
The heat generated during the period (1) to (2) is produced every charging/discharging cycle if the device is a secondary battery. On the other hand, a capacitor produces heat only once at the initializing. After the initializing, the terminal voltage of each capacitor varies downwardly from the set, full charge voltage, by discharging as indicated by (4). If charging is done after discharging, all the capacitors are almost simultaneously fully charged again with the original voltage (5) and so little bypass current flows. Strictly, the capacitors reach full charge with slight time differences because of slight characteristic variations and leakage currents during use. During the slight time differences, a bypass current flows. Consequently, some loss takes place after the initializing operation.
SUMMARY OF THE INVENTION
The present invention is intended to solve the problem of charging energy loss that would have been inevitably caused during initializing charging and during subsequent storage charging in the prior art technique.
It is an object of the present invention to provide an electrical storage capacitor system which is simple in structure and capable of reducing charging energy loss during initializing charging and during subsequent storage charging.
This object is achieved by an electrical storage capacitor system for charging capacitors connected in series, the capacitor system comprising voltage detection means, voltage-limiting means, initializing charging means, and storage charging means. The voltage detection means sense that the voltage developed across each capacitor has reached a first reference voltage. The voltage-limiting means limit the voltage developed across each capacitor to a second reference voltage. During initializing charging, the initializing charging means initially charges the capacitors connected in series while operating the voltage-limiting means. The storage charging means charge the capacitors connected in series to store energy. During the charging by the storage charging means, the full charging means perform charging until the outputs from the voltage detection means indicate that the voltage developed across any one capacitor reaches the first reference value.
In one feature of the invention, the first reference value can be the full charge voltage and the second reference value is set to be lower than the full charge voltage. The second reference value may be selected to be opposite in polarity to the full charge voltage.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
REFERENCES:
patent: 5528121 (1996-06-01), Okamura
patent: 5578914 (1996-11-01), Morita
patent: 5677613 (1997-10-01), Perelle
patent: 5969505 (1999-10-01), Okamura
“A Basic Study on Power Storage Capacitor Systems”, Michio Okamura,Electrical Engineering in Japan, vol. 116, No. 3, 1996, pp. 40-51.
Okamura Michio
Shinozuka Masahiko
Jeol Ltd.
Tso Edward H.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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