JP4440406B2 - Power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply device that uses a large-capacity electric double layer capacitor, and more particularly to a power supply device that can display the remaining charge / discharge time and extend the operation time using the charge / discharge characteristics of the capacitor.
[0002]
[Prior art]
The electric double layer capacitor is a capacitor having an extremely large capacitance, and a capacitor having a capacitance of about 50 to 500 F is already being put into practical use and attracting attention. This capacitor can be rapidly charged and discharged, and the number of repeated discharges can be, for example, 1000 times or more, so that it can be used as a power supply device that replaces a battery rather than a simple capacitor. . An electric double layer capacitor as a power supply that replaces a battery is smaller and lighter than, for example, a lead-acid battery, and does not use heavy metals such as lead, and therefore has good environmental compatibility.
[0003]
On the other hand, a solar cell is a conversion element that converts light into electrical energy by a pn junction of a semiconductor such as silicon. This solar cell can also be manufactured by forming amorphous silicon on a substrate such as glass by vapor deposition or the like, and forming a transparent electrode film on the surface thereof, and is becoming widespread as a clean power source.
[0004]
Therefore, a combination of a solar cell, a generator, a commercial power source and the like and the electric double layer capacitor makes it possible to configure a power supply facility that can be replaced with a small, light and clean battery. In particular, battery-driven electric vehicles and the like need to be equipped with a large-capacity storage battery, which is suitable for such applications.
[0005]
However, in a power storage device such as a battery, it is essential to be able to check the remaining usable time at the time of discharge. Usually, a voltmeter is provided and the charge / discharge status can be confirmed by monitoring the voltage. it can. However, in a power supply device using an electric double layer capacitor, since the capacitor is charged and stored, the terminal voltage drops rapidly as the capacitor discharge proceeds, making it difficult to check the remaining charge / discharge time. It was.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the circumstances described above, and can accurately display and extend the remaining charge / discharge time of an electric double layer capacitor whose voltage fluctuates greatly, and can also be operated. An object of the present invention is to provide a power supply device using an electric double layer capacitor that can be operated with a further extension.
[0007]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the chargeable / dischargeable power supply device using the electric double layer capacitor, the means for measuring the voltages E ₁ and E ₂ at the _first time t ₁ and the second time t ₂ are used. And a means for calculating the time constant RC by using the relationship of charge / discharge characteristics of the capacitor, E = Eo (1-e− ^{(t / RC)} ), or E = Eoe− ^{(t / RC)} And means for calculating the remaining charge / discharge time of the capacitor from the charge / discharge characteristics of the capacitor by using the calculated time constant RC, and a display device for displaying the calculated remaining charge / discharge time. This is a power supply device.
[0008]
This makes it possible to calculate and display the charge / discharge characteristics of an electric double layer capacitor with a large capacitance and the remaining charge or discharge time, so the internal resistance of the power supply during charging or the load resistance during discharging is unknown. However, it is possible to accurately know the remaining charge / discharge time of the electric double layer capacitor. That is, there is generally a load resistance of a load device at the time of discharge or an internal resistance of, for example, a solar battery that is a charging power source at the time of charging. Alternatively, the remaining discharge time can be detected. Therefore, since the correct remaining time is always displayed regardless of the magnitude of the internal resistance on the power supply side during charging, and regardless of the magnitude of the load resistance during discharging, a charging / discharging device using an electric double layer capacitor is required. It can be used practically.
[0009]
In addition, it is preferable to use a solar cell for charging the electric double layer capacitor. As a result, it is possible to configure a power supply device having a clean and sufficient power capacity using an electric double layer capacitor and a solar battery.
[0010]
Also includes a plurality of the electric double layer capacitor, a switching circuit for switching connection several capacitors plurality in series and in parallel, and a means for determining the switching time period from the measurement result of the voltage E ₁ and E ₂ further It is preferable to provide. As a result, when the discharge of the electric double layer capacitor proceeds and falls below the required minimum voltage on the load side, the terminal voltage of the electric double layer capacitor is increased by connecting the electric double layer capacitors connected in parallel in series. The remaining dischargeable time can be extended and used. Even in such a case, since the time constant changes, the remaining charge / discharge time after connection switching can be continuously calculated.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0012]
FIG. 1 shows a power supply device using an electric double layer capacitor according to an embodiment of the present invention. In this embodiment, a solar battery 11 is used as a charging power supply device, and thereby the electric double layer capacitor 12 is charged. A switch 14 is connected between the charging power supply device 11 and the electric double layer capacitor 12. When this switch is closed, current is supplied to the electric double layer capacitor 12 from the solar cell 11 side which is a power supply source. The capacitor 12 is charged. Here, the power supply device 11 normally outputs a voltage of about 0.6 to 0.7 V per stage of the pn junction, but a plurality of stages are connected in series to obtain a voltage output sufficient for driving the load device. It is preferable to be able to do so.
[0013]
The electric double layer capacitor 12 is connected to a load device 13 such as an automobile motor or an electronic device when used as a power source. Similarly, a switch 15 is disposed between the load device 13 and the electric double layer capacitor 12. When this switch is closed, a current is supplied to the load device 13 from the electric double layer capacitor 12 side. Operate. The electric double layer capacitor 12 may be a single capacitor or a plurality of capacitors connected in parallel. Furthermore, it is preferable that a plurality of electric double layer capacitors can be switched between parallel connection and series connection as will be described later.
[0014]
A voltage detection circuit 16 is connected to both ends of the electric double layer capacitor 12 to detect a voltage appearing at both ends of the electric double layer capacitor 12. Then, the detected voltage is subjected to arithmetic processing by the arithmetic device 17, and the remaining charge / discharge time is calculated. The calculation result is displayed on the display device 18. The display device 18 may be an analog display meter, or may be a digital display device that displays the remaining charge / discharge time in minutes, for example. Further, the power of the voltage detection circuit 16, the arithmetic unit 17 and the display device 18 may be supplied from the terminal of the electric double layer capacitor 12, or a separate power circuit may be used.
[0015]
The charging characteristics of the capacitor are expressed as shown in FIG. That is, when the charging power supply voltage Eo, the internal resistance R, and the capacitor C are connected in series, the charging voltage E across the capacitor C is expressed by the following equation (1).
E = Eo (1-e- ^{(t / RC)} ) (1)
That is, when the voltage E across the capacitor is charged from zero with a constant DC charging power supply voltage Eo, the voltage E across the capacitor increases according to a logarithmic function and gradually approaches a constant value Eo. Here, the product CR of the capacitor capacitance C and the internal resistance R has a time dimension, which is called a time constant τ (= CR), and when t = τ,
E = Eo (1-e ⁻¹ )
It becomes. In other words, the time constant τ is an index indicating the gradual rise or fall of the logarithmic function curve. For example, when C = 100 (F) and R = 10 (Ω), τ = 100 (F) × 10 (Ω) = 1000 seconds, and when t = τ (1000 seconds), E = 0.632 Eo And approximately approaches the charging power supply voltage Eo in 5τ (5000 seconds).
[0016]
Since the charging characteristics of the capacitor as the voltage rises in accordance with a logarithmic curve as shown in FIG. 2, by detecting the voltage E ₂ of the voltage E ₁ and the time t ₂ at time t _1, a time thereby The constant τ = CR is calculated, and from this, for example, the remaining time until charging is completed (for example, 5τ = 0.993 Eo) can be calculated.
[0017]
FIG. 3 shows a characteristic curve during discharge. That is, the characteristic at the time of discharge is expressed by the following equation (2):
E = Eoe− ^{(t / RC)} (2)
Here, the resistance R is the load resistance of the load device 13, and the capacitance C is the capacitance of the electric double layer capacitor 12. In this case as well, when the initial voltage is Eo, the voltage E across the capacitor 12 falls according to a logarithmic function with the passage of time t and gradually approaches a constant value of zero. At time τ (= CR), which is a time constant, the voltage decreases to 0.368 Eo, and further decreases to 0.007 Eo which is substantially zero at time 5τ.
[0018]
Thus in the same way as described above, the voltage _{E 1} was measured at time _{t 1} by the voltage detection circuit 16 measures the voltage _{E 2} at time _{t 2.} Then, a time constant τ = CR is obtained by the arithmetic unit 17. The time constant τ (= CR) is obtained by the following calculation.
E ₁ = Eoe ^{− (t1 / CR)}
E ₂ = Eoe ^{− (t2 / CR)}
Here, if the charging power supply voltage Eo is erased,
^{_{E 1 e - (t2 / CR}} ) = E 2 e - (t1 / CR)
Taking the logarithm of the base e on both sides,
logE ₁ − (t ₂ / CR) = logE ₂ − (t ₁ / CR)
This
CR = (t ₂ -t ₁ ) / (logE ₁ -logE ₂ )
Is obtained.
[0019]
With further substantially discharge at the end of time, for example, 3 [tau] from the time t _2, the can be calculated discharge time remaining until the time according to a logarithmic function 3 [tau] (voltage at the E = 0.05Eo).
[0020]
By displaying the remaining time detected by the voltage detection circuit 16 and the arithmetic unit 17 on the display device 18 in this manner, the electric double layer capacitor 12 is taken into consideration without considering the internal resistance of the power source or the load resistance R of the load device. The remaining charging time or remaining discharging time can be displayed. Even when the load resistance during discharging or the internal resistance during charging changes, the remaining time corresponding to the change can be displayed immediately. In this embodiment, the time when the discharge is completed is based on the time 3τ when the remaining voltage is about 5%, but the load device is considered in consideration of the minimum operable voltage of the load device and the magnitude of the initial voltage Eo. It is necessary to determine appropriately according to the characteristics.
[0021]
As described above, in a power supply device using an electric double layer capacitor, the discharge characteristics do not decrease almost linearly as in a lead battery, but the voltage decreases exponentially after the start of discharge. For this reason, when the voltage drops to some extent, the required minimum operating voltage of the load device 13 is interrupted even though charges are accumulated in the capacitor 12, and current cannot be supplied to the load device. In order to improve this point, a plurality of capacitors Ca and Cb may be provided as the capacitor 12, and a switching circuit for connecting them in series and in parallel may be provided (see, for example, JP-A-11-332112). .
[0022]
FIG. 4A shows an equivalent circuit when a plurality of capacitors Ca and Cb are connected in parallel and power is supplied to the load device 13. On the other hand, FIG. 4B shows an equivalent circuit when a plurality of capacitors Ca and Cb are connected in series and power is supplied to the load device (resistor R) 13. Here, as an example, when Ca = Cb = Co, the time constant τ in parallel connection is
τ = 2CoR, and the time constant τ when connected in series is τ = CoR / 2.
[0023]
FIG. 5 shows an example of operating characteristics during discharging of the power supply device when this switching circuit is used. Also in this device, the overall circuit configuration as the charge / discharge device is the same as that shown in FIG. That is, first, as shown in FIG. 4A, the capacitors Ca and Cb are operated in parallel as the electric double layer capacitor 12, and the voltage across the electric double layer capacitor 12 is monitored using the voltage detection circuit 16. In this embodiment, when the voltage drops to 1/2 of the initial voltage Eo, the parallel connection of the capacitors Ca and Cb is switched to the serial connection as shown in FIG. As a result, the voltage rises again to the initial voltage Eo and then decreases again along the logarithmic curve. Therefore, the dischargeable time of the capacitor can be extended by the operation time t _{B in the} series operation with respect to the operation time t _A in the parallel operation.
[0024]
At this time, the time constant during the parallel operation is τ = 2CoR, whereas the time constant during the series operation is τ = CoR / 2, so that t _B = t _A / 4. Only the operating time can be extended. Also in this embodiment, the time constant τ (= 2 CoR) is calculated from the relationship between the first time t ₁ and the voltage E ₁ at that time, and the second time t ₂ and the voltage E ₂ at that time, and the above-mentioned Thus, since the time constant during the series operation can also be calculated, the remaining dischargeable time including the time t _B during the series operation can be calculated and displayed.
[0025]
In addition, although the above description demonstrated the example which calculates remaining charging / discharging time from the measurement of the terminal voltage of the both ends of an electric double layer capacitor, it was made to calculate remaining charging / discharging time from the electric current which flows into an electric double layer capacitor. Also good.
[0026]
【The invention's effect】
As described above, according to the present invention, the remaining charge / discharge time can be displayed in the power supply device using the electric double layer capacitor. Thereby, the practical usability of the power supply device using the electric double layer capacitor can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a charge / discharge circuit of a power supply device according to an embodiment of the present invention.
FIG. 2 is a diagram showing charging characteristics of the power supply device shown in FIG.
FIG. 3 is a diagram showing discharge characteristics of the power supply device shown in FIG. 1;
4A is an equivalent circuit diagram of a parallel connection, and FIG. 4B is an equivalent circuit diagram of a series connection in a power supply device including a plurality of capacitors.
5 is a diagram showing discharge characteristics when the switching circuit of the parallel connection and the series connection shown in FIG. 4 is used. FIG.
[Explanation of symbols]
11 Charging power supply (solar cell)
12 Electric Double Layer Capacitor 13 Load Device 14, 15 Switch 16 Voltage Detection Circuit 17 Arithmetic Device 18 Display Device

Claims (3)

In a chargeable / dischargeable power supply using an electric double layer capacitor,
Means for measuring the voltages E ₁ and E ₂ at the first time t ₁ and the second time t ₂ ;
Capacitor charge / discharge characteristics,
E = Eo (1−e− ^{(t / RC)} ), or E = Eo− ^{(t / RC)} ,
Means for calculating the time constant RC using the relationship
Means for calculating the remaining charge / discharge time of the capacitor from the charge / discharge characteristics of the capacitor using the calculated time constant RC;
A display device for displaying the calculated remaining charge / discharge time;
A power supply device comprising: The power supply device according to claim 1, wherein a solar cell is used for charging the electric double layer capacitor. Comprising a plurality of the electric double layer capacitor, a switching circuit for switching connection several capacitors plurality in series and in parallel, further comprising a means for determining the switching time period from the measurement result of the voltage E ₁ and E ₂ The power supply device according to claim 1.

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