Charging device and charging method thereof

Electricity: battery or capacitor charging or discharging – Capacitor charging or discharging

Reexamination Certificate

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C320S121000

Reexamination Certificate

active

06323623

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-235260, filed Aug. 23, 1999; and No. 11-235392, filed Aug. 23, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a charging device for accumulating electric energy in a capacitor bank having a plurality of capacitors as power elements, and a charging method thereof.
Recently, a study has been conducted to accumulate electric energy in an electrical double layer capacitor and use the accumulated electric energy as a driving power source of an electric vehicle or the like. Meanwhile, a charging device for storing electric energy in a plurality of electrical double layer capacitors has been developed.
FIG. 19A
is a block diagram showing a major portion of a conventional arrangement of such a charging device, and
FIG. 19B
is a view explaining an operation of the charging device.
As shown in
FIG. 19A
, the charging device comprises a power source circuit
110
for supplying a charging current, a capacitor bank
120
composed of a plurality of electrical double layer capacitors C
11
-C
14
connected in series, and parallel monitor circuits
130
A-
130
D respectively connected to the electrical double layer capacitors C
11
-C
14
, and the device is arranged in such a manner that, by supplying the capacitor bank
120
with a predetermined charging current IC from the power source circuit
110
, charges corresponding to the charging current IC are accumulated in each of the electrical double layer capacitors C
11
-C
14
.
Generally, a voltage (charged voltage) V across a capacitor including the electrical double layer capacitor is expressed by the following equation:
V=Q/C  (1)
where Q is a charge quantity and C is a capacity of the capacitor.
The charge quantity Q is expressed by the following equation:
Q=I·t  (2)
where I is a current flowing through the capacitor, that is, a charging current, and t is a charging time.
Hence, the charged voltage V is expressed by the following equation:
V=(1/C)·I·t  (3).
That is, if the charging current I is constant, the charged voltage V increases as the charging time t extends. It should be noted that the voltage (charged voltage) V across the capacitor has a tolerance limit value (withstand proof voltage), and if the charged voltage V exceeds the withstand proof voltage of the capacitor, the capacitor is damaged or deteriorated, or the charging device breaks. Therefore, when charging the capacitor, the charging operation should be controlled so that the charged voltage will not exceed the withstand proof voltage of the capacitor.
For this reason, as shown in
FIG. 19A
, the conventional charging device is arranged in such a manner that the parallel monitor circuits
130
A-
130
D are provided to the respective electrical double layer capacitors C
11
-C
14
, so that the parallel monitor circuits
130
A-
130
D detect and monitor the terminal voltages of their respective capacitors C
11
-C
14
as the charged voltages. In other words, as shown in
FIG. 19B
, the conventional charging device is arranged in such a manner that, let VL be the withstand proof voltage of the capacitors, then when the charged voltage in each capacitor exceeds the withstand proof voltage VL, the charging device bypasses the charging current IC to the parallel monitor circuits
130
A-
130
D side, thereby stopping the charging operation for the electrical double layer capacitors.
In the foregoing conventional charging device, however, in order to charge a plurality of electrical double layer capacitors connected in series, a voltage monitor circuit for detecting and monitoring the charged voltage has to be connected to each electrical double layer capacitor in parallel. For this reason, the conventional charging device has a problem that its size undesirably increases as the number of the electrical double layer capacitors used therein increases, and so does the cost of production.
In addition, the conventional charging device is arranged in such a manner that, when the value of the charged voltage exceeds the predetermined withstand proof voltage, the charging current is bypassed to the parallel monitor circuits. Thus, a heat quantity is generated in response to the power consumption of the parallel monitor circuits. In other words, as shown in
FIG. 19B
, the heat quantity W generated in the charging device by bypassing the charging current is expressed by the following equation:
W=IC·VL·n  (4)
where IC is the charging current, VL is the withstand proof voltage of the electrical double layer capacitors, and n is the number of the parallel monitor circuits. Hence, the heat quantity W generated by the voltage monitor circuits provided in the charging device increases in proportion to the number n of the voltage monitor circuits provided in the charging device. Also, the number of the voltage monitor circuits corresponds to the number of the electrical double layer capacitors used in the charging device. Therefore, the conventional charging device has a problem that a larger heat quantity is generated as the number of the electrical double layer capacitors used therein increases, and downsizing the charging device becomes more difficult as the number of the electrical double layer capacitors used therein increases.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a markedly downsized, inexpensive charging device capable of accumulating electric energy in a capacitor bank composed of a plurality of capacitors including electrical double layer capacitors, and a charging method thereof.
In order to achieve the above object, a charging device of the present invention includes a power source circuit for supplying a charging current, a capacitor bank having a plurality of capacitors and changeover switches for switching an interconnection state of the plurality of capacitors, a connection control circuit for switching the plurality of capacitors from a serial connection state to a parallel connection state and vice versa by controlling the changeover switches, and a voltage monitor circuit for controlling a charging state of the plurality of capacitors by monitoring a charged voltage therein, and the charging device is arranged such that the connection control circuit connects the plurality of capacitors in series and to the power source circuit when charging the plurality of capacitors, and when monitoring the charged voltage, connects the plurality of capacitors in parallel and disconnects the plurality of capacitors from the power source circuit, and monitors the charged voltage by using the voltage monitor circuit.
In addition, a charging method of the present invention is characterized by repetitively carrying out a step of performing a charging operation, in which the plurality of capacitors are switched to the serial connection state and connected to the power source circuit by controlling the changeover switches in the capacitor bank, and a step of disconnecting the plurality of capacitors from the power source circuit, switching the plurality of capacitors to the parallel connection state, and reconnecting the plurality of capacitors to the voltage monitor circuit to monitor a charged voltage in the capacitors by controlling the changeover switches.
Also, the charging method is characterized in that, in the charged voltage monitoring step, the charged voltage in the capacitors is compared with a preset reference voltage based on the withstand voltage of the capacitors, and when the former reaches or exceeds the latter, the charging operation is ended by cutting the supply of the charging current from the power source circuit.
As has been discussed, according to the charging device and the charging method thereof of the present invention, by connecting the plurality of capacitors in series when charging the same, the power sour

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