JP2013187969A - Voltage equalization circuit and lithium-ion capacitor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurence of overcharge or overdischarge of a lithium ion capacitor.SOLUTION: Voltage-dividing resistors R1 and R2 for voltage setting are connected in parallel to lithium ion capacitor cells C1 and C2, and switches SW1 and SW2 are provided in series between the lithium ion capacitor cells C1 and C2 and the voltage-dividing resistors R1 and R2. A temperature variation detection circuit 2 detects the surface temperature variation of the lithium ion capacitor cells C1 and C2 on the basis of an input signal from thermistors T1 and T2. When detecting a reduction in surface temperature, the temperature variation detection circuit 2 outputs an output signal Idout to an input circuit of a photocoupler CP1. By the output signal Idout, an output circuit of the photocoupler CP1 is conducted, and power is supplied to the switches SW1 and SW2 from an external power supply VDD2. As a result, the switches SW1 and SW2 are conducted, and the equalization of the shared voltages of the lithium ion capacitor cells C1 and C2 is performed by the voltage-dividing resistors R1 and R2.

Description

  The present invention relates to a voltage equalization circuit for a plurality of storage element bodies connected in series. In particular, the present invention relates to a voltage equalization circuit for a lithium ion capacitor module.

  Power storage units such as lithium-ion capacitors and lithium-ion rechargeable batteries are being applied to various applications such as notebook computers and other small machines, industrial machines and devices, automobiles, and power facilities, and high voltage is required. Application to the intended use is also planned. Practically, a high-voltage module is formed by connecting a plurality of cells (storage element bodies) in series, and is used for applications that require a high voltage.

  When a high voltage module is formed using a plurality of lithium ion secondary batteries and electric double layer capacitors, a module having a voltage corresponding to the number of cells can be easily configured by connecting cells in series. However, in general, each cell has slightly different characteristics, and when charging is performed, there is a tendency that a difference occurs in the shared voltage between the cells due to the difference in the characteristics. In addition, since the characteristics of the self-discharge are also different, the voltage difference between the cells varies as the voltage decreases due to the self-discharge. As a result, overdischarge or overcharge occurs in a specific cell, and the performance of the cell is deteriorated accordingly, which eventually leads to failure.

  Therefore, as in Patent Document 1, in an electric double layer capacitor connected in series, a method is used in which voltage dividing circuits are provided in parallel to individual cells and voltage equalization circuits for adjusting the voltage between the cells are used. Yes.

JP 2005-26450 A JP 2009-100580 A

  However, a lithium ion capacitor has a lower limit voltage as well as an upper limit voltage, as in a secondary battery. For this reason, if a voltage dividing resistor is simply provided in parallel with the lithium ion capacitor cell, the lithium ion capacitor is always placed in a discharge state, which may lead to overdischarge early.

  Therefore, the present invention provides a voltage equalization circuit applicable to a lithium ion capacitor, and an object thereof is to provide a technique that contributes to suppressing the occurrence of overcharge or overdischarge of the lithium ion capacitor.

  The shared voltage equalization circuit of the present invention that achieves the above object detects a temporal change in the surface temperature of the storage element body during charging and discharging, and charges the storage element body based on the detected temporal change in the surface temperature. Detect state and discharge state. Then, only when the storage element is in a charged state, the shared voltage of the storage element is equalized by the voltage dividing resistor.

  That is, the shared voltage equalization circuit of the present invention that achieves the above object is connected in parallel to each of a plurality of power storage elements connected in series, and a voltage dividing resistor that equalizes the shared voltage of the power storage elements, Temperature detecting means for detecting a surface temperature of the electricity storage element; temperature change detecting means for detecting a temporal change in the surface temperature of the electricity storage element based on a detection signal of the temperature detecting means; the voltage dividing resistor; A switch unit connected in series between the storage element body and electrically connecting the voltage dividing resistor and the storage element body when the temperature change detection unit detects a decrease in the surface temperature. It is a feature.

  The shared voltage equalization circuit of the present invention that achieves the above object is characterized in that, in the shared voltage equalization circuit, the storage element is a lithium ion capacitor cell.

  Further, the shared voltage equalization circuit of the present invention that achieves the above object is the shared voltage equalization circuit, wherein when the temperature change detection means does not detect a decrease in the surface temperature of the power storage element, the switch means The electrical connection between the storage element body and the voltage dividing resistor is cut off.

  Further, the voltage equalization circuit of the present invention that achieves the above-described object is provided with a plurality of power storage units in which a plurality of power storage elements are connected in series, and connected in parallel to each of the power storage units. Based on the voltage dividing resistor to be equalized, the temperature detection means for detecting the surface temperature of at least one power storage element of the power storage unit, and the time change of the surface temperature of the power storage element based on the detection signal of the temperature detection means A temperature change detecting means for detecting, and the voltage dividing resistor and the power storage unit are connected in series between the voltage dividing resistor and the power storage unit, and the temperature change detecting means detects a decrease in the surface temperature. And switch means for conducting the power supply.

  The lithium ion capacitor module of the present invention that achieves the above object is connected to a plurality of lithium ion capacitor cells connected in series and in parallel with the lithium ion capacitor cell, and equalizes the shared voltage of the lithium ion capacitor cell. A voltage dividing resistor, temperature detecting means for detecting a surface temperature of the lithium ion capacitor cell, and temperature change detection for detecting a time change of the surface temperature of the lithium ion capacitor cell based on a detection signal of the temperature detecting means Means, and the voltage dividing resistor and the lithium ion capacitor cell are connected in series, and when the temperature change detecting means detects a decrease in the surface temperature, the voltage dividing resistor and the lithium ion capacitor cell And switch means for conducting the current.

  In addition, the method for detecting a charge / discharge state of a lithium ion capacitor cell according to the present invention that achieves the above object detects a change in the surface temperature of the lithium ion capacitor cell, and based on the change in the surface temperature of the lithium ion capacitor cell, It is characterized by detecting a charged state and a discharged state of the ion capacitor cell.

  According to the above invention, it can contribute to suppressing the occurrence of overcharge or overdischarge of the lithium ion capacitor.

It is a circuit diagram which shows the structure of a lithium ion capacitor module provided with the voltage equalization circuit which concerns on embodiment of this invention. It is a figure which shows the time change of the cell voltage when the lithium ion capacitor is discharged with the discharge current of 48 A, and the surface temperature of the lithium ion capacitor. It is a figure which shows the time change of the cell voltage when charging a lithium ion capacitor with the charging current of 24A, and the surface temperature of a lithium ion capacitor. It is a figure which shows the time change of the cell voltage when a lithium ion capacitor is discharged with the discharge current of 12A, and the surface temperature of a lithium ion capacitor.

  With reference to the drawings, a voltage equalization circuit, a lithium ion capacitor module, and a charge / discharge state detection method for a lithium ion capacitor cell according to an embodiment of the present invention will be described in detail.

(Embodiment)
FIG. 1 is a circuit diagram showing a configuration of a lithium ion capacitor module 1 including a voltage equalization circuit according to an embodiment of the present invention.

  The lithium ion capacitor cells C1 and C2 have a structure in which a positive electrode made of activated carbon or the like and a negative electrode mainly made of graphite or graphite are opposed to each other through a separator, and the positive electrode is an electric double layer capacitor, a negative electrode Has the same configuration as the lithium ion secondary battery. The space between the electrodes is filled with an organic solvent containing an electrolyte salt.

  By connecting the lithium ion capacitor cells C1 and C2 in series, a lithium ion capacitor unit is formed. The terminals P and N at both ends of the lithium ion capacitor unit are not shown, but the charging circuit is used when charging the lithium ion capacitor cells C1 and C2, and the lithium ion capacitor cell is used when discharging the lithium ion capacitor cells C1 and C2. A drive circuit driven by the energy accumulated in C1 and C2 is connected. The number of lithium ion capacitor cells C1 and C2 is not limited to two, but the number of lithium ion capacitor cells C1 and C2 connected in series according to the voltage required for the lithium ion capacitor module 1 Is determined.

  The voltage setting voltage dividing resistors R1 and R2 are connected in parallel to the lithium ion capacitor cells C1 and C2, respectively, and between the lithium ion capacitors C1 and C2 and the voltage dividing resistors R1 and R2, respectively. Switches SW1 and SW2 are provided in series.

  An output circuit of the photocoupler CP1 is connected to the switches SW1 and SW2, and the switch is turned on / off according to the output signal of the photocoupler CP1. That is, when the switches SW1 and SW2 are in the on state, the voltage dividing resistors R1 and R2 are connected in parallel to the respective lithium ion capacitor cells C1 and C2. On the other hand, when the switches SW1 and SW2 are in the off state, the voltage dividing resistors R1 and R2 are electrically disconnected from the lithium ion capacitor cells C1 and C2.

  Here, the temperature change detection circuit 2 that outputs the output signal Idout to the input circuit of the photocoupler CP1 will be described.

  The temperature change detection circuit 2 detects a change in the surface temperature of the lithium ion capacitors C1 and C2, and outputs an output signal Idout to the photocoupler CP1 when the rate at which the surface temperature decreases is equal to or greater than a predetermined threshold value. Output. The temperature change detection circuit 2 is driven by an external power supply VDD1 and includes a timer. This timer calculates the temperature decrease rate per unit time. Signals from thermistors T1 and T2 provided on the surfaces of lithium ion capacitor cells C1 and C2 (surfaces near the negative electrode) are input to the temperature change detection circuit 2 via the AD converter 3. And the change per unit time of the surface temperature of each lithium ion capacitor cell C1, C2 is calculated. The temperature change detection circuit 2 outputs to the input circuit of the photocoupler CP1 when the rate at which the surface temperature decreases is equal to or greater than a predetermined threshold (for example, the surface temperature decrease is 0.01 ° C./s). The signal Idout is output.

When the output signal Idout of the temperature change detection circuit 2 is input to the input circuit of the photocoupler CP1, in the output circuit of the photocoupler CP1, power is supplied from the external power supply VDD2, and the switches SW1 and SW2 are turned on.
(Example)
The operation of the voltage equalization circuit and the lithium ion capacitor module 1 according to the embodiment of the present invention will be described in detail with specific examples.

  The lithium ion capacitor module 1 (capacitance: 2200F) provided with the voltage equalization circuit shown in FIG. 1 was charged to the rated voltage upper limit of 3.8 V, and then discharged to a rated voltage lower limit of 2.2 V with a discharge current of 48 A. . FIG. 2 shows temporal changes in the surface temperature and cell voltage of the lithium ion capacitor cells C1 and C2 at this time. The thermistors T1 and T2 are provided on the surface of the aluminum laminate film that covers the lithium ion capacitor module 1 and in contact with the electrodes of the lithium ion capacitor cells C1 and C2.

  As shown in FIG. 2, the cell surface temperature increased by about 5 ° C. over the course of the discharge time. Therefore, since the temperature change detection circuit 2 detects an increase in the surface temperature, the output signal Idout is not output from the temperature change detection circuit 2. As a result, the output circuit of the photocoupler CP1 remains nonconductive, and the switches SW1 and SW2 are kept off (the voltage dividing resistors R1 and R2 and the lithium ion capacitor cells C1 and C2 are insulated). . That is, when the lithium ion capacitor cells C1 and C2 are discharged, the voltage dividing resistors R1 and R2 are electrically disconnected from the lithium ion capacitor cells C1 and C2.

  Next, the lithium ion capacitor module 1 after being discharged to the rated voltage lower limit of 2.2 V was charged with a charging current of 24 A to the rated voltage upper limit of 3.8 V. FIG. 3 shows temporal changes in the surface temperature and cell voltage of the lithium ion capacitor cells C1 and C2 at this time.

  As shown in FIG. 3, the cell surface temperature decreased by about 3 ° C. over the course of the charging time. Therefore, the temperature change detection circuit 2 detects a decrease in the surface temperature. When the detected rate of decrease in the surface temperature is equal to or higher than a predetermined threshold value, the output signal Idout is output from the temperature change detection circuit 2 to the input circuit of the photocoupler CP1. When the output signal Idout is input to the input circuit of the photocoupler CP1, the output circuit of the photocoupler CP1 becomes conductive. As a result, power is supplied to the switches SW1 and SW2 from the external power supply VDD2, and the switches SW1 and SW2 are turned on (a state where the voltage dividing resistors R1 and R2 and the lithium ion capacitor cells C1 and C2 are conducted). As a result, a circuit including voltage dividing resistors R1 and R2 provided in parallel with the lithium ion capacitor cells C1 and C2 conducts, and the voltage dividing resistors R1 and R2 are used as the lithium ion capacitor cells C1 and C2 are charged. Thus, voltage equalization between the lithium ion capacitor cells C1 and C2 is achieved. After that, when the rated voltage is reached and a constant voltage charging or charging standby state is reached, the rate at which the surface temperature decreases (time change of the surface temperature) becomes smaller than that during charging before reaching the rated voltage. Therefore, the temperature change detection circuit 2 stops outputting the output signal Idout when the time change of the surface temperature becomes less than 0.01 ° C. per unit time. When the output of the output signal Idout is stopped, the output circuit of the photocoupler CP1 becomes non-conductive, and as a result, the switches SW1 and SW2 are turned off. Then, the voltage dividing resistors R1 and R2 are again electrically disconnected from the lithium ion capacitor cells C1 and C2.

  Further, the lithium ion capacitor module 1 charged to the upper limit of the rated voltage of 3.8 V was discharged with a discharge current of 12 A to the lower limit of the rated voltage of 2.2 V. FIG. 4 shows temporal changes in the surface temperature and cell voltage of the lithium ion capacitor cells C1 and C2 at this time.

  As shown in FIG. 4, the cell surface temperature increased by about 4 ° C. over the course of the discharge time. Therefore, since the temperature change detection circuit 2 detects an increase in the surface temperature, the output signal Idout is not output from the temperature change detection circuit 2. As a result, the output circuit of the photocoupler CP1 remains nonconductive, and the switches SW1 and SW2 are kept off. That is, at the time of discharging, the voltage dividing resistors R1 and R2 are electrically disconnected from the lithium ion capacitor cells C1 and C2.

  As described above, according to the lithium ion capacitor module including the voltage equalization circuit according to the embodiment of the present invention, the charge state and the discharge state of the lithium ion capacitor module are detected based on the change in the surface temperature of the lithium ion capacitor. can do. When the battery is in a charged state, voltage equalization of each lithium ion capacitor cell can be performed using a voltage dividing resistor.

  Therefore, according to the voltage equalization circuit and the lithium ion capacitor module according to the embodiment of the present invention, when the lithium ion capacitor module is charged, it is possible to reduce variation in the shared voltage between the cells and effectively overcharge. Can be prevented. Since the cell voltage is uniform at the start of discharge of the lithium ion capacitor module, the energy stored in each lithium ion capacitor cell can be substantially uniform, and a specific cell may overdischarge. Can be reduced.

  In addition, since the voltage dividing resistor is electrically disconnected from the lithium ion capacitor cell during the discharge of the lithium ion capacitor module, the energy accumulated in the lithium ion capacitor cell during the discharge is consumed by the voltage dividing resistor. There is no. Therefore, the energy stored in the lithium ion capacitor cell can be efficiently used during discharge.

  Furthermore, since the voltage dividing resistor is electrically disconnected from the lithium ion capacitor cell during standby for charging or during storage, the lithium ion capacitor can be stored for a long period of time. That is, it is possible to realize a voltage equalizing circuit for a storage element body with little energy loss.

  The lithium ion capacitor module has an operating voltage range of 2.2 V to 3.8 V higher than that of the electric double layer capacitor by preliminarily storing lithium ions in the negative electrode and applying a potential. With this high operating voltage, it is possible to store 3 to 4 times as much energy as the electric double layer capacitor. For this reason, the energy density of the electric double layer capacitor is insufficient, and it can be applied to a use requiring high energy or a use requiring a long discharge time. Furthermore, superiority can be obtained over electric double layer capacitors and secondary batteries in applications such as power backup. However, since the lithium ion capacitor module has a potential applied to the electrodes in advance, if a voltage dividing resistor is provided in parallel, the lithium ion capacitor module is always in a discharged state, resulting in early overdischarge.

  Therefore, the lithium ion capacitor module of the present invention and the voltage equalization circuit of the present invention perform voltage equalization between lithium ion capacitor cells using voltage dividing resistors when the lithium ion capacitor is in a charged state. The voltage dividing resistor is electrically disconnected from the circuit. As a result, charging can be performed using a voltage equalization circuit that equalizes the voltage of the lithium ion capacitor cell during charging, and energy stored in the lithium ion capacitor is efficiently supplied to the drive circuit during discharging. be able to.

  Moreover, according to the charging / discharging state detection method of the lithium ion capacitor cell of this invention, the charging / discharging state of a lithium ion capacitor cell can be detected based on the difference in the surface temperature change at the time of charge and discharge. A general electric double layer capacitor generates heat depending on the internal resistance in both cases of charging and discharging. As a result, in the electric double layer capacitor, the surface temperature increases in both cases of charging and discharging. On the other hand, the surface temperature of a lithium ion capacitor is reduced during charging. This tendency is considered to be unique to lithium ion capacitors. 2 to 4, it is considered that the temperature change during charging / discharging depends on the magnitude of the charging (discharging) current. Therefore, the threshold value for determining charge / discharge (rate of change in temperature per unit time) is not limited to the embodiment, and may be set as appropriate based on the magnitude of the charge (discharge) current. In addition, since this temperature change is minute, when the temperature outside the lithium ion capacitor is measured and compared with the rate of change in the temperature of the outside air temperature, there is a marked difference in the surface temperature change of the lithium ion capacitor. Only determine the state of charge (discharge). Further, the change in the surface temperature of the lithium ion capacitor cell after reaching the rated voltage (both upper limit and lower limit) of the lithium ion capacitor is less gradual than before the rated voltage is reached. Therefore, it is possible to detect that the lithium ion capacitor has been charged (or discharged) to the rated voltage by detecting the change in the surface temperature of the lithium ion capacitor cell.

  The shared voltage equalization circuit, the lithium ion capacitor module, and the charge / discharge state detection method for the lithium ion capacitor cell of the present invention are not limited to the above-described embodiment, and may be appropriately modified within a range that does not impair the effect. Is possible. For example, the position where the thermistor is provided is not limited to the embodiment as long as the temperature change of the electrode can be detected, and may be a form in which the electrode temperature is directly measured. Moreover, since the thermistor should just be what can detect electrode temperature, temperature measuring apparatuses, such as a thermocouple, can be used, for example.

  Further, when a plurality of lithium ion capacitor cells are connected in series and connected as a lithium ion unit in series, by using the voltage equalization circuit of the present invention, each lithium ion unit The shared voltage can be equalized.

  In addition, the shared voltage equalization circuit of the present invention is not limited to a circuit configured from a lithium ion capacitor cell, but is a circuit configured from a storage element body in which temperature changes of electrodes at the time of charging and discharging are different. By applying, a voltage equalization circuit with little energy loss can be realized.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion capacitor module 2 ... Temperature change detection circuit (temperature change detection means)
3. AD converters C1, C2 ... Lithium ion capacitor cell (storage element)
CP1 ... photocoupler R1, R2 ... voltage dividing resistor SW1, SW2 ... switch (switch means)
T1, T2 ... thermistor (temperature detection means)

Claims (6)

A voltage dividing resistor connected in parallel to each of a plurality of power storage elements connected in series and equalizing a shared voltage of the power storage elements;
Temperature detecting means for detecting the surface temperature of the electricity storage element;
Based on a detection signal of the temperature detection means, temperature change detection means for detecting a temporal change in the surface temperature of the electricity storage element body;
Switch means connected in series between the voltage dividing resistor and the electricity storage element, and when the temperature change detecting means detects a decrease in the surface temperature, the switch means for conducting the voltage dividing resistor and the electricity storage element. And a shared voltage equalizing circuit. The shared voltage equalization circuit according to claim 1, wherein the power storage element is a lithium ion capacitor cell. The switch means cuts off an electrical connection between the power storage element and the voltage dividing resistor when the temperature change detection means does not detect a decrease in the surface temperature of the power storage element. The shared voltage equalization circuit according to claim 1 or 2. A plurality of power storage units in which a plurality of power storage elements are connected in series;
A voltage dividing resistor connected in parallel to each of the power storage units and equalizing the shared voltage of the power storage units;
Temperature detecting means for detecting a surface temperature of at least one power storage element of the power storage unit;
Based on a detection signal of the temperature detection means, temperature change detection means for detecting a temporal change in the surface temperature of the electricity storage element body;
Switch means connected in series between the voltage dividing resistor and the power storage unit, and electrically connecting the voltage dividing resistor and the power storage unit when the temperature change detecting means detects a decrease in the surface temperature; A shared voltage equalizing circuit comprising: A plurality of lithium ion capacitor cells connected in series;
A voltage dividing resistor connected in parallel with the lithium ion capacitor cell and equalizing a shared voltage of the lithium ion capacitor cell;
Temperature detecting means for detecting a surface temperature of the lithium ion capacitor cell;
Based on a detection signal of the temperature detection means, a temperature change detection means for detecting a time change of the surface temperature of the lithium ion capacitor cell;
The voltage dividing resistor and the lithium ion capacitor cell are connected in series, and when the temperature change detecting means detects a decrease in the surface temperature, the voltage dividing resistor and the lithium ion capacitor cell are made conductive. A lithium ion capacitor module. A lithium ion capacitor cell characterized by detecting a change in surface temperature of the lithium ion capacitor cell and detecting a charge state and a discharge state of the lithium ion capacitor cell based on a change in the surface temperature of the lithium ion capacitor cell. Charge / discharge state detection method.

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