JP2001297954A - Device for detecting deterioration of electric double- layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive device that has a simple configuration, and can securely detect deterioration of an electric double capacitor. SOLUTION: This device for detecting deterioration of the electric double- layer capacitor is equipped with a voltage detection means 18 for detecting that the voltage between the terminals of an electric double-layer capacitor has reached a specific value; a voltage comparison means 12 that compares the voltage between the terminals of the electric double-layer capacitor that is supplied via a switch means 16 with a deterioration reference voltage to output a deterioration signal, when the voltage between the terminals reaches the reference voltage; and a control means 28 that controls conduction to the electric double-layer capacitor based on the output of the voltage detection means, turns on the switch means for a specific time when the voltage detection means detects that the voltage between the terminals of the electric double-layer capacitor has reached the specific value, and at the same time judges that the electric double-layer capacitor has deteriorated when the voltage comparison means outputs the deterioration signal within the set time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting deterioration of an electric double-layer capacitor, and more particularly to a hybrid vehicle which is configured to assist driving of an engine output by a driving force of a motor during acceleration or the like. The present invention relates to a device for detecting deterioration of an electric double layer capacitor in an electric double layer capacitor device having a plurality of electric double layer capacitors connected in series, which is suitable for use as a power source for a motor.

[0002]

2. Description of the Related Art An electric double-layer capacitor has the advantage of being semi-permanent in life and capable of being charged with a large current in a very short time because it utilizes a simple physical change not due to a chemical reaction. In view of the above, it has been proposed to use the power supply for an assist motor of a hybrid vehicle. By the way, in a power supply device (electric double layer capacitor device) in which a large number of electric double layer capacitors are connected in series, it is very difficult to determine whether the single cell, that is, a single electric double layer capacitor is functioning normally. .
However, in order to operate the system using the electric double-layer capacitor device as a power supply normally, it is necessary to detect and understand the state in which each cell is functioning without abnormality or the state in which it is abnormal. .

As a conventional method for detecting deterioration of an electric double layer capacitor, there is a technique described in Japanese Patent Application Laid-Open No. Hei 6-342042. This means that, for example, a low-frequency square wave signal is added as a measurement signal from the measurement signal source to the electric double-layer capacitor, a predetermined portion of the response signal is integrated, and the electric double-layer capacitor is integrated based on the integrated value. This is to detect a change in the characteristic.

[0004]

However, the above-described method for detecting deterioration of an electric double layer capacitor requires a circuit section such as a measurement signal source and an A / D converter, and further requires a CP.
Since the signal processing by U is necessary, considering this method to be applied to, for example, an electric double layer capacitor device used as a power supply device of an assist motor mounted on a hybrid vehicle, an electric double layer capacitor device is considered. When the above-mentioned circuit section is provided in each of the electric double layer capacitors in the above, there is a problem that the apparatus becomes very expensive and the method of detecting deterioration is complicated.

The present invention has been made in view of such circumstances, and provides an inexpensive inferiority detecting device for an electric double layer capacitor which can reliably detect deterioration of the electric double layer capacitor with a simple configuration. The purpose is to do.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a voltage detecting means for detecting that a voltage between terminals of an electric double layer capacitor (10) has reached a predetermined value. (18, 180) and switch means (1
6) supplied through the electric double layer capacitor (1).
0) is compared with the degradation reference voltage, and when the inter-terminal voltage reaches the degradation reference voltage, a degradation signal indicating that the electric double layer capacitor (10) is in a degradation state is output. The power supply to the electric double layer capacitor (10) is controlled based on the detection output of the voltage comparison means (12, 120) and the voltage detection means (18, 180), and the voltage detection means (18, 180) When it is detected that the voltage between the terminals of the electric double layer capacitor (10) has reached a predetermined value, the switch means (16) is turned on for a predetermined time and the voltage comparison is performed within the predetermined time. Control means (28) for determining that the electric double layer capacitor (10) is in a deteriorated state when a deterioration signal is output from the means (12, 120).

According to the first aspect of the present invention, the control means (28) controls the energization of the electric double-layer capacitor (10) and controls the electric double-layer capacitor (10) between terminals. When the voltage between the terminals of the electric double layer capacitor (10) reaches the deterioration reference voltage within a predetermined time after the voltage reaches a predetermined value, it is determined that the electric double layer capacitor (10) is in a deteriorated state. With this configuration, it is possible to reliably detect deterioration of the electric double layer capacitor with a simple configuration and to realize an inexpensive inferiority detecting device for the electric double layer capacitor.

[0008] The invention described in claim 2 is the first invention.
In the deterioration detecting device for an electric double layer capacitor, the control means (28) detects that the voltage between terminals of the electric double layer capacitor (10) has reached a lower limit voltage by the voltage detecting means (18). Then, the discharge of the electric double layer capacitor 10 is stopped based on the detection output of the voltage detecting means (18).

According to the device for detecting deterioration of an electric double layer capacitor according to claim 2, in the device for detecting deterioration of electric double layer capacitor according to claim 1, the control means (28) controls the electric double layer capacitor ( The voltage detecting means (18) that the voltage between terminals of (10) has reached the lower limit voltage.
The electric discharge of the electric double layer capacitor 10 is stopped on the basis of the detection output of the voltage detecting means (18) when it is detected by (1), so that in addition to the effect obtained by the invention according to claim 1, In addition, there is an effect that the deterioration state of the electric double layer capacitor can be determined based on the level of the rebound voltage generated when the discharge is stopped.

[0010] Further, the invention according to claim 3 is based on claim 1.
In the deterioration detecting device for an electric double layer capacitor, the control means (28) detects that the voltage between terminals of the electric double layer capacitor (10) has reached an upper limit voltage by the voltage detecting means (180). The charging of the electric double layer capacitor is stopped based on the detection output of the voltage detecting means (180) when the voltage is detected.

According to the device for detecting deterioration of an electric double layer capacitor according to the third aspect, in the device for detecting deterioration of an electric double layer capacitor according to the first aspect, the control means (28) controls the electric double layer capacitor ( 10) that the voltage between terminals reaches the upper limit voltage.
0), the voltage detecting means (180)
The charging of the electric double layer capacitor is stopped based on the detection output of the electric double layer capacitor. Therefore, in addition to the effect obtained by the invention according to claim 1, the electric double layer capacitor is stopped based on the level of the rebound voltage generated when charging is stopped. There is an effect that the deterioration state of the capacitor can be determined.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the electric double layer capacitor deterioration detecting device according to the first embodiment of the present invention. In the figure, the deterioration detecting device for an electric double layer capacitor according to the first embodiment of the present invention includes a deterioration detecting comparator 12 for detecting a deterioration state of the electric double layer capacitor 10 and an electric double layer capacitor 10. It has a comparator 18 for detecting the state of reaching the lower-limit reference voltage, photocouplers 22, 24 and 26, and a control circuit 28. In the present embodiment, only one electric double layer capacitor is shown for convenience of explanation. However, in practice, a large number of electric double layer capacitors are connected in series, and FIG. (The control circuit 28 is commonly used for each electric double-layer capacitor.)

One input terminal of the comparator 12 is connected to one terminal (charge / discharge side) of the electric double layer capacitor 10 via a PNP transistor 16 as a switching element, and the other input terminal of the comparator 12 is degraded. A degradation reference voltage Vx (for example,
1.65 V) is connected to the other end of the electric double layer capacitor 10 via a deterioration reference power supply 14. Also,
One input terminal of the comparator 18 is connected to the emitter of the PNP transistor 16 and one terminal (charge / discharge side) of the electric double layer capacitor, and the other input terminal of the comparator 18 is connected to the lower limit voltage, that is, the assist of the hybrid vehicle. Lower limit detection reference voltage VLL (for example,
Set to 1.5V. ) Is connected to the other end of the electric double-layer capacitor 10 via a lower-limit detection reference power supply 20 for supplying the same.

The comparator 18 compares the voltage VC between terminals of the electric double layer capacitor 10 with the lower limit detection reference voltage VLL supplied from the lower limit detection reference power supply 20, and the terminal voltage VC reaches the lower limit detection reference voltage VLL. In this case, a lower limit detection signal indicating that the inter-terminal voltage VC has reached the lower limit detection reference voltage VLL is output. The comparator 12 compares the voltage VC between terminals of the electric double layer capacitor 10 with the deterioration reference voltage Vx supplied from the deterioration reference power supply 14, and when the terminal voltage VC reaches the deterioration reference voltage Vx, A deterioration signal indicating that the capacitor is in a deteriorated state is output. The comparator 12 corresponds to the voltage comparing means of the present invention, and the comparator 18 corresponds to the voltage detecting means of the present invention.
The P-transistor 16 corresponds to the switch means of the present invention.

The control circuit 28 is constituted by, for example, a CPU, controls the energization of the electric double layer capacitor 10, and controls the on / off state of the PNP transistor 16 as a switch. The control circuit 28 outputs a time control signal for turning on the PNP transistor 16 for a predetermined time to the base of the PNP transistor 16 from the comparator 18 when the lower limit detection signal is received, so that the electric double layer is output to the comparator 12 for a predetermined time. Capacitor 10
And the deterioration reference voltage Vx supplied from the deterioration reference power supply 14 is controlled to perform a comparison operation, and at this time, the discharge of the electric double layer capacitor 10 is stopped. The control circuit 28 corresponds to control means of the present invention.

The operation of the electric double layer capacitor deterioration detecting apparatus according to the present embodiment having the above-described configuration will be described with reference to the control flow shown in FIG. 2, the timing chart shown in FIG. 3, and the operation of the electric double layer capacitor 10 shown in FIG. A description will be given with reference to a change characteristic of the voltage over time. In the present embodiment,
During discharging of the electric double layer capacitor 10, that is, during assist in a hybrid vehicle, the electric double layer capacitor 1
When the zero terminal voltage VC reaches the lower limit detection reference voltage VLL, the discharge of the electric double layer capacitor 10 is stopped, and the deterioration state of the electric double layer capacitor 10 is determined based on the level change of the rebound voltage generated at this time. Is what you do.

In FIG. 2, the electric double layer capacitor 10 is in a discharge state by driving assist of the engine output by the assist motor mounted on the hybrid vehicle. First, the comparator 18 compares the terminal voltage VC of the electric double layer capacitor 10 with the lower limit detection reference voltage VLL supplied from the lower limit detection reference power supply 20 (step 100). When VC ≦ VLL, that is, when the terminal voltage VC of the electric double layer capacitor 10 reaches the lower limit detection reference voltage VLL, the comparator 18
A lower limit detection signal (FIG. 3A) that changes from high level to low level at time t1 is output to the control circuit 28 via the photocoupler 22 (step 101).

Next, the control circuit 28, which has received the lower limit detection signal, sets the base of the PNP transistor 16 (TR1) to the base of the PNP transistor 16 (TR1) via the photocoupler 24 for a predetermined time Ti, for example, about 3 seconds to turn on the PNP transistor 16 Output a control signal (FIG. 3B) (Step 10)
2). At the same time, the control circuit 28 outputs a discharge stop signal for stopping discharge in the electric double layer capacitor 10 to an upper controller (not shown), and under the control of the upper controller, the electric double layer capacitor 10
Is stopped. The control for stopping the discharge may be such that the control circuit 28 directly controls the circuit unit that performs the charging / discharging operation of the electric double layer capacitor. As a result, a predetermined time Ti
Only the terminal voltage VC of the electric double layer capacitor 10 can be compared with the deterioration reference voltage Vx supplied from the deterioration reference power supply 14 (step 103).

The terminal voltage VC of the electric double layer capacitor 10 gradually decreases during discharge as shown in FIG.
By stopping the discharge at the time t1, a rebound voltage is generated in a rising direction. This bounce voltage settles to a substantially constant value over time. In FIG. 4, for example, the level ΔV1 of the rebound voltage is 0.1 V,
ΔV2 is 0.2V. In the comparator 12,
As shown in FIG. 4, the voltage VC between the terminals of the electric double layer capacitor 10 increases for a predetermined time T1 from the time t1 when the discharge is stopped.
If the terminal-to-terminal voltage VC does not reach the deterioration detection reference voltage Vx as shown by a solid line in i, the output of the comparator 12 does not change (the electric double layer capacitor 10 is a normal cell) and a predetermined time from time t1. When the voltage VC between terminals reaches the deterioration detection reference voltage Vx at time t2 as indicated by a dashed line in Ti, the comparator 12
A degradation signal that changes from a low level to a high level is output to the control circuit 28 via the photocoupler 26 (FIG. 3).
(C)).

The control circuit 28 receives the output signal of the comparator 12 via the photocoupler 26 and determines whether or not the output of the comparator 12 has changed within the time Ti (steps 104 and 105). Time T from time t1
When the deterioration signal is input from the comparator 12 to the control circuit 28 via the photocoupler 26 in the control signal i, the control circuit 28 recognizes that the output of the comparator 12 has changed and the electric double layer capacitor 10 is in a deteriorated state. I do.
At this time, the control circuit 28 outputs a warning signal indicating that the electric double layer capacitor 10 is in a deteriorated state to another circuit unit, for example, a display unit, and confirms that a deteriorated cell (electric double layer capacitor) exists. Is displayed. The warning signal may be a sound warning.

As described above, according to the electric double layer capacitor deterioration detecting apparatus according to the first embodiment of the present invention, the control circuit 28
When the comparator 18 detects that the terminal voltage of 0 has reached the lower limit voltage (lower limit detection reference voltage VLL), the discharge of the electric double layer capacitor 10 is stopped at the detection output of the comparator 18, so that It is possible to reliably detect the deterioration of the electric double layer capacitor with a simple configuration and realize an inexpensive inferiority detection device for the electric double layer capacitor, and based on the level of the rebound voltage generated when the discharge stops, the electric double layer capacitor There is an effect that the deterioration state of the can be determined.

Next, FIG. 5 shows the configuration of an apparatus for detecting deterioration of an electric double layer capacitor according to a second embodiment of the present invention. The electric double layer capacitor deterioration detecting device according to the present embodiment is different in configuration from the electric double layer capacitor deterioration detecting device according to the first embodiment in the structure of the electric double layer capacitor deterioration detecting comparator 12. , A comparator 120 having a different reference voltage for deterioration detection is used, and a comparator 180 for detecting the upper limit of the electric double layer capacitor 10 during charging is used instead of the comparator 18 for detecting the lower limit. 14. Deterioration reference power source 14 having a different degradation detection reference voltage from degradation reference power source 14 instead of lower limit detection reference power source 20
0 is that the upper limit detection reference power supply 200 is used, and the other configuration is the same as that of the deterioration detection device according to the first embodiment.

The operation of the electric double layer capacitor deterioration detecting apparatus according to the present embodiment having the above-described configuration will be described with reference to the control flow shown in FIG. 6, the timing chart shown in FIG. 7, and the operation between the terminals of the electric double layer capacitor 10 shown in FIG. A description will be given with reference to a change characteristic of the voltage over time. In the present embodiment,
While the electric double layer capacitor 10 is being charged, that is, during deceleration running in a hybrid vehicle, the electric double layer capacitor 1
When the zero terminal voltage VC reaches the upper limit detection reference voltage VUL, the charging of the electric double layer capacitor 10 is stopped, and the deterioration state of the electric double layer capacitor 10 is determined based on the level change of the rebound voltage generated at this time. Is what you do.

In FIG. 6, the electric double layer capacitor 10 in the electric double layer capacitor device used as a power supply device for the assist motor mounted on the hybrid vehicle is running because the hybrid vehicle is decelerating. The battery is being charged to function as a generator. First, the comparator 180 compares the voltage VC between terminals of the electric double layer capacitor 10 with the upper limit detection reference voltage VUL (for example, set to 2.7 V) supplied from the upper limit detection reference power supply 200 (step). 300). V
If C ≧ VUL, that is, electric double layer capacitor 1
When the terminal-to-terminal voltage VC of 0 has reached the upper limit detection reference voltage VUL, the upper limit detection signal (FIG. 7A) that changes from low level to high level at time t1 from the comparator 180 via the photocoupler 22 is output. It is output to the control circuit 28 (step 301).

Next, the control circuit 28, which has received the upper limit detection signal, sets the base of the PNP transistor 16 (TR1) via the photocoupler 24 to the base of the PNP transistor 16 (TR1) for a predetermined time Ti, for example, a time for turning on the PNP transistor 16 for about 3 seconds. Output a control signal (FIG. 7B) (Step 30)
2). At the same time, the control circuit 28 outputs a charge stop signal for stopping the charging of the electric double layer capacitor 10 to a higher-level controller (not shown), and controls the charging of the electric double layer capacitor 10 under the control of the higher-level controller. Is stopped. The control for stopping the charging may be performed by the control circuit 28 directly controlling the circuit unit that performs the charging / discharging operation of the electric double layer capacitor. As a result, a predetermined time T
i, the voltage VC between terminals of the electric double layer capacitor 10;
Deterioration reference voltage Vx supplied from deterioration reference power supply 140
(This deterioration reference voltage Vx is set to, for example, 2.55 V.) (step 303).

The terminal voltage VC of the electric double layer capacitor 10 gradually increases during charging as shown in FIG.
When charging is stopped at time t11, a rebound voltage is generated in the reverse direction. This bounce voltage settles to a substantially constant value over time. In FIG. 8, for example, the level ΔV1 of the rebound voltage is 0.1 V,
ΔV2 is 0.2V. In the comparator 120, as shown in FIG. 8, the voltage VC between the terminals of the electric double layer capacitor 10 is changed within the predetermined time Ti from the time t11 when the charging is stopped, as shown by the solid line.
Does not reach the deterioration detection reference voltage Vx, the output of the comparator 120 remains at the high level and does not change (the electric double layer capacitor 10 is a normal cell), and within a predetermined time Ti from the time t11, as indicated by a dashed line. At time t
When the inter-terminal voltage VC reaches the deterioration detection reference voltage Vx at step 12, the comparator 12 outputs a deterioration signal that changes from high level to low level to the control circuit 28 via the photocoupler 26 (FIG. 7C). ).

The control circuit 28 takes in the output signal of the comparator 120 via the photocoupler 26 and
Then, it is determined whether or not the output of the comparator 12 has changed (steps 304 and 305). When a deterioration signal is input from the comparator 120 to the control circuit 28 via the photocoupler 26 within the time Ti from the time t11, the control circuit 28 changes the output of the comparator 120, and the electric double layer capacitor 10 is in a deteriorated state. Recognize that there is. At this time, the control circuit 28 outputs a warning signal indicating that the electric double layer capacitor 10 is in a deteriorated state to another circuit unit, for example, a display unit, and confirms that a deteriorated cell (electric double layer capacitor) exists. Is displayed. The warning signal may be sounded as in the first embodiment.

The circuit configuration of the deterioration detecting device shown in the first and second embodiments except for the control circuit 28 is different from that of the electric double-layer capacitor of the electric double-layer capacitor device in which a plurality of electric double-layer capacitors are connected in series. Although it has been described on the premise that the circuit is provided for each of the electric double-layer capacitors, the provision of the circuit section of the deterioration detection device for each electric double-layer capacitor leads to an increase in cost. A circuit section may be provided. In this case, assuming that a plurality of electric double layer capacitors are used as one module, if a module including a deteriorated cell is detected, the module may be replaced so as to be replaced.

As described above, according to the electric double layer capacitor deterioration detecting apparatus according to the second embodiment of the present invention, the control circuit 28 controls the electric double layer capacitor 1
When the comparator 180 detects that the terminal-to-terminal voltage has reached the upper limit voltage (upper limit detection reference voltage VUL), the charging of the electric double layer capacitor 10 is stopped based on the detection output of the comparator 180. As a result, it is possible to reliably detect deterioration of the electric double layer capacitor with a simple configuration, to realize an inexpensive inferiority detecting device for the electric double layer capacitor, and to perform the detection based on the level of the rebound voltage generated when charging is stopped. There is an effect that the deterioration state of the electric double layer capacitor can be determined.

[0030]

According to the apparatus for detecting deterioration of an electric double layer capacitor according to the first aspect of the present invention, the control means (28) controls the energization of the electric double layer capacitor (10) and controls the electric double layer capacitor (10). The electric double layer capacitor (10) within a predetermined time from the time when the voltage between terminals reaches a predetermined value.
When the voltage between the terminals reaches the deterioration reference voltage, it is determined that the electric double layer capacitor (10) is in a deteriorated state. Therefore, it is possible to reliably detect the deterioration of the electric double layer capacitor with a simple configuration. And an inexpensive electric double layer capacitor inferiority detection device can be realized.

According to the device for detecting deterioration of an electric double layer capacitor according to the second aspect, in the device for detecting deterioration of an electric double layer capacitor according to the first aspect, the control means (28) controls the electric double layer capacitor ( The voltage detecting means (18) that the voltage between terminals of (10) has reached the lower limit voltage.
The electric discharge of the electric double layer capacitor 10 is stopped on the basis of the detection output of the voltage detecting means (18) when it is detected by (1), so that in addition to the effect obtained by the invention according to claim 1, In addition, there is an effect that the deterioration state of the electric double layer capacitor can be determined based on the level of the rebound voltage generated when the discharge is stopped.

According to the deterioration detecting device for an electric double layer capacitor described in claim 3, in the deterioration detecting device for an electric double layer capacitor according to claim 1, the control means (28) controls the electric double layer capacitor ( 10) that the voltage between terminals reaches the upper limit voltage.
0), the voltage detecting means (180)
The charging of the electric double-layer capacitor is stopped based on the detection output of the electric double layer capacitor. Therefore, in addition to the effect obtained by the invention according to the first aspect, the electric double layer capacitor is stopped based on the level of the rebound voltage generated when the charging is stopped. There is an effect that the deterioration state of the multilayer capacitor can be determined.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a deterioration detecting device for an electric double layer capacitor according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control operation of the electric double layer capacitor deterioration detecting device shown in FIG.

FIG. 3 is a timing chart showing an operation state of each unit of the electric double layer capacitor deterioration detecting device shown in FIG. 1;

FIG. 4 is a voltage characteristic diagram showing a change state of the inter-terminal voltage with time during a deterioration test of the electric double layer capacitor by the deterioration detection device shown in FIG. 1;

FIG. 5 is a block diagram showing a configuration of an electric double layer capacitor deterioration detecting device according to a second embodiment of the present invention.

FIG. 6 is a flowchart showing a control operation of the electric double layer capacitor deterioration detecting device shown in FIG. 5;

FIG. 7 is a timing chart showing an operation state of each part of the electric double layer capacitor deterioration detecting device shown in FIG. 5;

FIG. 8 is a voltage characteristic diagram showing a change state of the inter-terminal voltage with time during a deterioration test of the electric double layer capacitor by the deterioration detection device shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electric double layer capacitor 12 Comparator (voltage comparison means) 14 Deterioration reference power supply 16 PNP transistor TR1 (switching means) 18 Comparator (voltage detection means) 20 Lower limit detection reference power supply 22, 24, 26 Photocoupler 28 Control circuit (control means)

Claims (3)

[Claims] A voltage detecting means for detecting that a voltage between terminals of the electric double layer capacitor has reached a predetermined value; a voltage between terminals of the electric double layer capacitor supplied via a switch means; A voltage comparison unit that outputs a deterioration signal indicating that the electric double layer capacitor is in a deteriorated state when the inter-terminal voltage reaches a deterioration reference voltage, based on a detection output of the voltage detection unit. Controlling the energization of the electric double layer capacitor, and when the voltage detecting means detects that the voltage between the terminals of the electric double layer capacitor has reached a predetermined value, the switch means is turned on for a predetermined time. And control means for determining that the electric double layer capacitor is in a deteriorated state when the deterioration signal is output from the voltage comparison means within the predetermined time. A deterioration detecting device for an electric double layer capacitor, characterized in that: 2. The control means according to claim 1, wherein when the voltage detection means detects that a voltage between terminals of the electric double layer capacitor has reached a lower limit voltage, the control means controls the electric power based on a detection output of the voltage detection means. The electric double layer capacitor deterioration detecting device according to claim 1, wherein the discharge of the double layer capacitor is stopped. 3. The control means, when the voltage detection means detects that a voltage between terminals of the electric double layer capacitor has reached an upper limit voltage, based on a detection output of the voltage detection means. The device for detecting deterioration of an electric double layer capacitor according to claim 1, wherein charging of the double layer capacitor is stopped.