ELECTRICITY STORAGE DEVICE CONTROL CIRCUIT AND BACKUP POWER SUPPLY SYSTEM INCLUDING SAME

The electricity storage device control circuit includes a voltage detector and a voltage controller. The voltage detector is configured to detect voltages of a plurality of electricity storage devices. The voltage controller is configured to individually control the voltages of the plurality of electricity storage devices by performing, based on a detection result by the voltage detector, at least one of discharging or charging of electrostatic energy stored in the plurality of electricity storage devices.

TECHNICAL FIELD

The present disclosure relates to electricity storage device control circuits and backup power supply systems including the electricity storage device control circuits, and specifically, to an electricity storage device control circuit configured to control a voltage of an electricity storage device and a backup power supply system including the electricity storage device control circuit.

BACKGROUND ART

A power supply circuit is known which is configured to supply electricity from a backup power supply to a load when supply of electricity from a direct-current power supply to the load is stopped (e.g., Patent Literature 1).

CITATION LIST

Patent Literature

Patent Literature 1: JP 2020-5481 A

SUMMARY OF INVENTION

When the backup power supply used for the power supply circuit includes a plurality of electricity storage devices connected in series to each other, a voltage variation which may occur between the plurality of electricity storage devices may vary the deterioration speed of the plurality of electricity storage devices and may thus accelerate the performance deterioration of the backup power supply. Therefore, consideration has to be given to reducing the voltage variation between the plurality of electricity storage devices.

An object of the present disclosure is to provide an electricity storage device control circuit configured to reduce a voltage variation between a plurality of electricity storage devices and a backup power supply system including the electricity storage device control circuit.

An electricity storage device control circuit according to an aspect of the present disclosure includes a voltage detector and a voltage controller. The voltage detector is configured to detect voltages of a plurality of electricity storage devices. The voltage controller is configured to individually control the voltages of the plurality of electricity storage devices by performing, based on a detection result by the voltage detector, at least one of discharging electrostatic energy stored in the plurality of electricity storage devices or charging electrostatic energy into the plurality of electricity storage devices.

A backup power supply system according to an aspect of the present disclosure includes the electricity storage device control circuit and the plurality of electricity storage devices. The plurality of electricity storage devices are configured to be charged by a primary power supply configured to supply electric power to a load. The backup power supply system is configured to supply electric power to the load from the plurality of electricity storage devices when the primary power supply fails.

The present disclosure provides the advantage that a voltage variation between a plurality of electricity storage devices can be reduced.

DESCRIPTION OF EMBODIMENTS

An electricity storage device control circuit1according to an embodiment of the present disclosure and a backup power supply system2including the electricity storage device control circuit1will be described in detail with reference to the drawings. Note that the embodiment and variations described below are mere examples of the present disclosure, and the present disclosure is not limited to the embodiment and the variations. The present disclosure may be modified variously without departing from the scope of the present disclosure, even if not including the embodiment and variations, according to a design or the like.

First of all, an overview of the electricity storage device control circuit1and the backup power supply system2of the present embodiment will be described with reference toFIG.1.

As shown inFIG.1, the electricity storage device control circuit1is a control circuit which controls respective voltages of a plurality of electricity storage devices3. The backup power supply system2including the electricity storage device control circuit1and the plurality of electricity storage devices3may be mounted on, for example, a moving vehicle such as an automobile so as to be used as a backup power supply of a load4such as a brake device. The backup power supply system2is charged by a primary power supply5configured to supply electric power to the load4, and when the primary power supply5fails, the backup power supply system2supplies electric power from the plurality of electricity storage devices3to the load4. Note that between the primary power supply5and the load4, a backflow preventer configured to prevent a current from flowing from the plurality of electricity storage devices3into the primary power supply5is provided. The backflow preventer is, for example, a diode D1. The backup power supply system2may further include a circuit breaker S6disposed between the load4and the plurality of electricity storage devices3and a circuit breaker S7disposed between the primary power supply5and the plurality of electricity storage devices3.

The primary power supply5continues charging the plurality of electricity storage devices3until the total voltage of the plurality of electricity storage devices3equals the voltage of the primary power supply5or reaches a preset voltage. When the charging of the plurality of electricity storage devices3is completed, the amounts of electrostatic energy stored in the plurality of electricity storage devices3are equal. Here, the plurality of electricity storage devices3vary in electrostatic capacitance due to production tolerance, deterioration, or the like. The variation in the electrostatic capacitance causes a voltage variation between the plurality of electricity storage devices3even when the plurality of electricity storage devices3store the equal amounts of electrostatic energy. Charging the plurality of electricity storage devices3having voltages varying from each other may results in that one or more electricity storage devices3of the plurality of electricity storage devices3go into over-voltage. If the one or more electricity storage devices3are left under over-voltage conditions for a long period of time, their deterioration may progress. Therefore, to correct the voltage variation between the plurality of electricity storage devices3, cell balancing has to be performed accordingly. In the present embodiment, the electricity storage device control circuit1performs the cell balancing of the plurality of electricity storage devices3as shown inFIG.1.

The electricity storage device control circuit1includes a voltage detector11and a voltage controller12. The voltage detector11detects the voltages of the plurality of electricity storage devices3. The voltage controller12individually controls the voltages of the plurality of electricity storage devices3by performing, based on a detection result by the voltage detector11, at least one of discharging electrostatic energy stored in the plurality of electricity storage devices3or charging electrostatic energy into the plurality of electricity storage devices3. That is, the voltage controller12selects, with reference to values of the voltages of the plurality of electricity storage devices3detected by the voltage detector11, one or more electricity storage devices3which require a voltage correction. Then, the voltage controller12adjusts the amount of the electrostatic energy stored in the one or more electricity storage devices3thus selected by performing at least one of the discharge or the charge, thereby controlling the voltage or voltages respectively of the one or more electricity storage devices3thus selected. Thus, the cell balancing of the plurality of electricity storage devices3is performed.

For example, when the backup power supply system2is mounted on a moving vehicle such as an automobile, the primary power supply5is connected to the plurality of electricity storage devices3in response to the start of an engine of the automobile, thereby charging the plurality of electricity storage devices3as show inFIG.2. Here, the electricity storage device control circuit1charges the electricity storage devices3with the electrostatic energy, thereby performing the cell balancing of the electricity storage devices3to equalize the voltages of the electricity storage devices3. Moreover, in response to the stop of the engine of the automobile, the primary power supply5is disconnected from the plurality of electricity storage devices3. Here, the electricity storage device control circuit1discharges the electrostatic energy from the electricity storage device3, thereby performing the cell balancing of the electricity storage device3to keep the voltages of the electricity storage devices3in an equalized state.

The electricity storage device control circuit1and the backup power supply system2according to the present embodiment will be descried in detail below with reference toFIGS.1to5.

(2.1) Electricity Storage Device

The plurality of electricity storage devices3included in the backup power supply system2are connected in series to each other and are used as backup power supplies for the load4. The plurality of electricity storage devices3include an electric double-layer capacitor.

As shown inFIG.1, three electricity storage devices3(31to33) are connected in series to each other, and all the electricity storage devices3are electric double-layer capacitors in the present embodiment. Note that the number of electricity storage devices3and the number of electricity storage devices3, which are electric double-layer capacitors, of the plurality of electricity storage devices3are not limited to the present embodiment and may accordingly be changed.

In the present embodiment, the circuit breaker S6is disposed between the load4and the electricity storage devices31to33, and when the primary power supply5fails, the circuit breaker S6is switched on to supply electric power to the load4from the electricity storage devices31to33. Except for when the primary power supply5fails, the circuit breaker S6is off. The circuit breaker S6is, for example, a semiconductor switch, and as shown inFIGS.1and4, switching on and off of the circuit breaker S6is controlled by a drive controller6. The drive controller6performs control such that the circuit breaker S6is off while the primary power supply5does not fail and the circuit breaker S6is switched on when the drive controller6detects the failure of the primary power supply5.

The electricity storage devices31to33are charged by the primary power supply5, which is a direct-current power supply. In the present embodiment, the circuit breaker S7is disposed between the primary power supply5and the electricity storage device31. The circuit breaker S7is, for example, a semiconductor switch. The drive controller6performs control such that the circuit breaker S7is switched on while the primary power supply5does not fail. When the circuit breaker S7is switched on, the electricity storage devices31to33are connected in series to the primary power supply5, and the electricity storage devices31to33are thus charged.

After the circuit breaker S7is switched on, when the total voltage of the electricity storage devices31to33equals the voltage of the primary power supply5, or when the circuit breaker S7is switched off, charging the electricity storage devices31to33ends.

Note that in the present embodiment, the drive controller6is disposed as a member separate from the backup power supply system2. However, the drive controller6may be included in the backup power supply system2.

The voltage detector11included in the electricity storage device control circuit1includes three voltage sensors111to113respectively connected to the electricity storage devices31to33as shown inFIG.1. The voltage sensors111to113are connected to a positive electrode terminal and a negative electrode terminal of the electricity storage devices31to33, respectively and detects voltages V1to V3of the electricity storage devices31to33, respectively.

Moreover, the voltage sensors111to113transmit signals representing the voltages V1to V3of the electricity storage devices31to33thus detected to the voltage controller12which will be described later.

(2.3) Voltage Controller

In the present embodiment, the voltage controller12included in the electricity storage device control circuit1performs the cell balancing by performing at least one of discharging electrostatic energy stored in the electricity storage devices31to33or charging electrostatic energy into the electricity storage devices31to33such that the voltages of the electricity storage devices31to33are equalized. Note that the cell balancing as used herein refers to reducing the voltage variation between the plurality of electricity storage devices3.

The voltage controller12includes three control circuits121to123respectively connected in parallel to the electricity storage devices31to33as shown inFIG.1. Each of the three control circuits121to123includes a resistor and a circuit breaker connected in series to each other. In the following description, the resistors included in the control circuits121to123are respectively referred to as resistors R1to R3, and the circuit breakers included in the control circuits121to123are respectively referred to as circuit breakers S1to S3. Here, the circuit breakers S1to S3are, for example, semiconductor switches.

The voltage controller12further includes a processor124and a storage125as shown inFIG.1.

The processor124is connected to the voltage sensors111to113of the voltage detector11and receives signals SigV1to SigV3respectively representing the voltages V1to V3of the electricity storage devices31to33from the voltage sensors111to113. In addition, the processor124is connected to the circuit breakers S1to S3, and based on detection results of the voltages V1to V3, the processor124individually controls switching on and off of the circuit breakers S1to S3respectively by control signals Sig1to Sig3.

The processor124includes, as a main component, a computer system including memory and a processor, for example. That is, the processor executes a program stored in the memory of the computer system, thereby implementing the function of the processor124. The program may be stored in the memory in advance, may be provided over a telecommunications network such as the Internet, or may be provided as a non-transitory storage medium, such as a memory card, storing the program.

The storage125is connected to the processor124and stores, for example, a set voltage to be compared with the voltages V1to V3when the processor124controls, based on the detection results of the voltages V1to V3, switching on and off of the circuit breakers S1to S3. Note that the storage125includes rewritable nonvolatile memory such as Electrically Erasable Programmable Read-Only Memory (EEPROM) or flash memory.

In the backup power supply system2of the present embodiment, the electricity storage device control circuit1performs the cell balancing of the electricity storage devices31to33.

In the present embodiment, the cell balancing is performed by different operation between a discharge mode M1in which the electricity storage devices31to33are not connected to the primary power supply5and a charge mode M2in which the electricity storage devices31to33are connected to the primary power supply5.

The cell balancing operation in the discharge mode M1and the cell balancing operation in the charge mode M2will be described below with reference toFIGS.1to5.

(3.1) Cell Balancing Operation in Discharge Mode

In the discharge mode M1in which the electricity storage devices31to33are not connected to the primary power supply5, the voltage controller12switches on and off the circuit breakers S1to S3respectively included in the control circuits121to123to control the amount of electrostatic energy discharged from the electricity storage devices31to33. Thus, the voltage controller12performs the cell balancing of the electricity storage devices31to33. The cell balancing operation by the voltage controller12when the electricity storage devices31to33are in the discharge mode M1will be described below with reference toFIGS.1to3.

As shown inFIG.1, the discharge mode M1in which the electricity storage devices31to33are not connected to the primary power supply5is a state where the circuit breaker S7is off. In the discharge mode M1, the electricity storage devices31to33are not charged by the primary power supply5. Moreover, in the discharge mode M1, the circuit breakers S1to S3respectively included in the control circuits121to123are off except for when the cell balancing is performed.

First of all, the processor124included in the voltage controller12receives, at a predetermined period, the signals SigV1to SigV3respectively representing the voltages V1to V3of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11. When the processor124receives the signals SigV1to SigV3, the processor124compares the voltages V1to V3with the respective set voltages of the electricity storage devices31to33stored in the storage125(FIG.3ST1).

For example, the respective set voltages of the electricity storage devices31to33are all a set voltage V0in the present embodiment. The set voltage V0is, for example, set to a voltage value which is about ⅓ of the voltage of the primary power supply5. Here, the processor124selects an electricity storage device(s)3having a voltage higher than the set voltage V0as a target(s) to be subjected to the cell balancing by discharging. For example, when the relationship among the voltages V1to V3is expressed as V1>V2>V3=V0, the processor124selects the electricity storage device31and the electricity storage device32as targets to be subjected to voltage control by discharging (FIG.3ST2).

The processor124then switches the circuit breakers S1and S2respectively included in the control circuits121and122respectively corresponding to the electricity storage devices31and32from off to on respectively by the control signals Sig1and Sig2. Thus, the electrostatic energy stored in the electricity storage devices31to32is consumed respectively by the resistors R1and R2respectively included in the control circuits121and122, and the voltages V1and V2respectively of the electricity storage devices31and32decrease (FIG.3ST3).

Here, when the voltages V1and V2reach the set voltage V0(FIG.3ST4: YES), the processor124individually controls the circuit breakers S1and S2respectively by the control signals Sig1and Sig2such that the circuit breakers S1and S2are switched off to stop controlling the voltages V1and V2. That is, the electricity storage devices31and32are respectively disconnected from the resistors R1and R2, which stops discharging the electricity storage devices31and32, and the voltages V1and V2are thus kept at the set voltage V0. Here, the circuit breaker S3corresponding to the electricity storage device33remains off, the voltage V3of the electricity storage device33is kept unchanged from that before the cell balancing, and the relationship that V3=V0is kept as it is. In this way, the voltages V1to V3are in the relationship that V1=V2=V3=V0, and the processor124stops controlling the electricity storage devices31to33, thereby completing the cell balancing (FIG.3ST5). Note that respective set voltages different from each other may be set for the electricity storage devices3. Moreover, the present embodiment is not limited to that the control is stopped when the voltages V1to V3are adjusted to a voltage exactly equal to the set voltage V0, but the control may be stopped when the difference from the set voltage V0is less than or equal to a prescribed error voltage.

For example, when the backup power supply system2is mounted on a moving vehicle such as an automobile, the circuit breaker S7is switched off in response to the stop of the engine as described above. That is, the primary power supply5is disconnected from the electricity storage devices31to33in response to the stop of the engine, and the electricity storage devices31to33enter the discharge mode M1as shown inFIG.2, thereby performing the cell balancing by discharging the electricity storage devices31to33.

In the present embodiment, the circuit breakers S1to S3are all off after the cell balancing is performed in the discharge mode M1, and therefore, the electrostatic energy stored in the electricity storage devices31to33is less likely to be lost by discharging. This provides the advantage that when the electricity storage devices31to33are charged by connecting to the primary power supply5, a time required to fully charge the electricity storage devices31to33is reduced.

(3.2) Cell Balancing Operation in Charge Mode

In the charge mode M2in which the electricity storage devices31to33are connected to the primary power supply5, the voltage controller12switches on and off the circuit breakers S1to S3respectively included in the control circuits121to123to control the amount of electrostatic energy to be charged into the electricity storage devices31to33. Thus, the voltage controller12performs the cell balancing of the electricity storage devices31to33. The cell balancing operation by the voltage controller12when the electricity storage devices31to33are in the charge mode M2will be described below with reference toFIGS.4and5.

As shown inFIG.4, the charge mode M2in which the electricity storage devices31to33are connected in series to the primary power supply5is a state where the circuit breaker S7is on. Here, the electricity storage devices31to33are charged by the primary power supply5. Moreover, also in the charge mode M2, the circuit breakers S1to S3respectively included in the control circuits121to123are off except for when the cell balancing is performed.

When the total voltage of the electricity storage devices31to33substantially equals the voltage of the primary power supply5immediately before charge completion of the electricity storage devices31to33, a current flowing through the electricity storage devices31to33becomes very small. This state is referred to as a float charge mode. Here, switching on and off the circuit breakers S1to S3applies a voltage from the primary power supply5to the resistors R1to R3respectively included in the control circuits121to123to cause a current to flow.

First of all, the processor124included in the voltage controller12receives, at a predetermined period, the signals SigV1to SigV3representing the voltages V1to V3respectively of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11. In the float charge mode after a definite time period has elapsed since the electricity storage devices31to33entered the charge mode M2(FIG.5ST10: YES), when the processor124receives the signals SigV1to SigV3, the processor124compares the voltages V1to V3with the respective set voltages of the electricity storage devices31to33stored in the storage125(FIG.5ST11).

For example, the respective set voltages of the electricity storage devices31to33are all a set voltage V0in the present embodiment. Here, the processor124selects an electricity storage device(s)3having a voltage lower than the set voltage V0as a target(s) to be subjected to the cell balancing by charging. For example, when the relationship among the voltages V1to V3is expressed as V1=V2=V0>V3, the processor124selects the electricity storage device33as a target to be subjected to voltage control by charging (FIG.5ST12).

The processor124then switches on the circuit breakers S1and S2except for the circuit breaker S3included in the control circuit123corresponding to the electricity storage device33by the control signals Sig1and Sig2. Here, the circuit breaker S3remains off. Thus, a current flowing through the resistors R1to R3flows from the resistors R1and R2into the electricity storage device33. The electricity storage device33is charged by the current flowing thereinto from the resistors R1and R2, and the voltage V3of the electricity storage device33increases relative to the voltages V1and V2(FIG.5ST13).

When the voltage V3reaches the set voltage V0(FIG.5ST14: YES), the processor124switches off the circuit breakers S1and S2by the control signals Sig1and Sig2to stop controlling the voltage V3. Thus, the voltage V3is kept at the set voltage V0. Here, the voltages V1and V2of the electricity storage devices31and32are kept unchanged from that before the cell balancing, and the relationship that V1=V2=V0is kept as it is. In this way, the voltages V1to V3are in the relationship that V1=V2=V3=V0, and the processor124stops controlling the electricity storage devices31to33, thereby completing the cell balancing (FIG.5ST15). Note that respective set voltages different from each other may be set for the electricity storage devices3.

For example, when the backup power supply system2is mounted on a moving vehicle such as an automobile, the circuit breaker S7is switched on in response to the start of the engine as described above. That is, the primary power supply5is connected to the electricity storage devices31to33in response to the start of the engine, and the electricity storage devices31to33enter the charge mode M2as shown inFIG.2, thereby allowing the cell balancing by charging in the float charge mode immediately before charge completion.

Variations of an electricity storage device control circuit1of the embodiment described above will be described below. Note that component common with those in the electricity storage device control circuit1of the embodiment described above are denoted by the same reference signs, and the description thereof will be accordingly omitted. Moreover, each of configurations of the variations described below may be applicable in combination with the configuration of the embodiment described above.

(4.1) First Variation

An electricity storage device control circuit1according to a first variation will be described below.

In the electricity storage device control circuit1of the embodiment described above, the voltage controller12stops controlling the voltages of the electricity storage devices31to33when the voltages of the electricity storage devices31to33reach their respective set voltages.

The first variation is different from the embodiment described above in that the voltage controller12stops controlling the voltages of the electricity storage devices31to33when the absolute value of a voltage difference among the electricity storage devices31to33is within a set voltage difference. The cell balancing operation of the voltage controller12in the discharge mode M1and the charge mode M2of the first variation will be described below with reference toFIGS.1andFIGS.4to12.

(4.1 1) Cell Balancing Operation in Discharge Mode of First Variation

In the first variation, the processor124included in the voltage controller12first receives, at a predetermined period, the signals SigV1to SigV3representing the voltages V1to V3respectively of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11in the discharge mode M1as shown inFIG.1. When the processor124receives the signals SigV1to SigV3, the processor124obtains absolute values of the voltage difference among the voltages V1to V3, that is, dV12=|V1−V2|, dV13=|V1−V3|, and dV23=|V2−V3| (FIG.6ST20).

Here, when all of the absolute values dV12, dV13, and dV23are not within a set voltage difference dV0stored in the storage125, the processor124selects two electricity storage devices3between which the absolute value of the voltage difference is largest as a target to be subjected to voltage difference control by discharging. For example, as shown inFIG.7, when V1=4 (V), V2=5 (V), and V3=2 (V), dV12=1 (V), dV13=2 (V), and dV23=3 (V). Here, for example, when dV0=1 (V), each of dV13and dV23is not within dV0=1 (V) (FIG.6ST21: NO). Thus, the processor124selects the electricity storage devices32and33between which the voltage difference is largest as the target to be subjected to the voltage difference control by discharging (FIG.6ST23).

The processor124then switches the circuit breaker S2from off to on by the control signal Sig2. The circuit breaker S2is included in the control circuit122corresponding to the electricity storage device32, which has a larger voltage, of the electricity storage devices32and33thus selected. Thus, electrostatic energy stored in the electricity storage device32is consumed by the resistor R2included in the control circuit122, and thereby, the voltage V2of the electricity storage device32decreases as shown inFIGS.7and8(FIG.6ST24).

Here, when the voltage V2decreases to V2=3 (V), dV23=1 (V) holds true, and dV23is thus within dV0=1 (V) (FIG.6ST25: YES), the processor124switches off the circuit breaker S2to stop controlling the electricity storage device32. That is, the voltage difference control by discharging the electricity storage devices32and33is stopped (FIG.6ST26).

Here, as shown inFIG.8, V1=4 (V), V2=3 (V), and V3=2 (V), and therefore, dV12=1 (V), dV13=2 (V), and dV23=1 (V). Thus, dV13is not within dV0=1 (V) (FIG.6ST21: NO). Thus, the processor124selects the electricity storage devices31and33between which the absolute value of the voltage difference is largest as the target to be subjected to the voltage difference control by discharging (FIG.6ST23).

Moreover, the processor124switches the circuit breaker S1from off to on by the control signal Sig1. The circuit breaker S1is included in the control circuit121corresponding to the electricity storage device31, which has a larger voltage, of the electricity storage devices31and33thus selected. Thus, electrostatic energy stored in the electricity storage device31is consumed by the resistor R1included in the control circuit121, and thereby, the voltage V1of the electricity storage device31decreases as shown inFIGS.8and9(FIG.6ST24).

Here, when the voltage V1decreases to V1=3 (V), dV13=1 (V) holds true, and dV13is thus within dV0=1 (V)(FIG.6ST25: YES), the processor124switches off the circuit breaker S1to stop controlling the electricity storage device31. That is, the voltage difference control by discharging the electricity storage devices31and33is stopped (FIG.6ST26).

Here, as shown inFIG.9, V1=3 (V), V2=3 (V), and V3=2 (V), and thus, dV12=0 (V), dV13=1 (V), and dV23=1 (V). All of dV12, dV13, and dV23are thus within dV0=1(V) (FIG.6ST21: YES). In this case, the processor124stops controlling the electricity storage devices31to33, and the cell balancing is completed (FIG.6ST22).

(4.1.2) Cell Balancing Operation in Charge Mode of First Variation

In the first variation, the processor124included in the voltage controller12first receives, at a predetermined period, the signals SigV1to SigV3representing the voltages V1to V3respectively of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11in the charge mode M2as shown inFIG.4. In the electricity storage devices31to33being in the float charge mode immediately before charge completion (FIG.10ST30), when the processor124receives the signals SigV1to SigV3, the processor124calculates absolute values of the voltage difference among the voltages V1to V3, that is, dV12=|V1−V2|, dV13=|V1−V3|, and dV23=|V2−V3|, (FIG.10ST31).

Here, when all of the absolute values dV12, dV13, and dV23are not within a set voltage difference dV0stored in the storage125, the processor124selects two electricity storage devices3between which the absolute value of the voltage difference is largest as a target to be subjected to voltage difference control by charging. For example, as shown inFIG.11, when V1=4 (V), V2=5 (V), and V3=2 (V), dV12=1 (V), dV13=2 (V), and dV23=3 (V). Here, for example, when dV0=1 (V), each of dV13and dV23is not within dV0=1 (V) (FIG.10ST32: NO). Thus, the processor124selects the electricity storage devices32and33between which the voltage difference is largest as the target to be subjected to the voltage difference control by charging (FIG.10ST34).

Next, the processor124switches the circuit breakers S1and S2from off to on by the control signals Sig1and Sig2except for the circuit breaker S3included in the control circuit123corresponding to the electricity storage device33having a smaller voltage of the electricity storage devices32and33thus selected. Here, the circuit breaker S3remains off. Thus, a current flows to the electricity storage device33, and as shown inFIGS.11and12, the electricity storage device33is charged, and the voltage V3increases (FIG.10ST35).

Here, when the voltage V3increases to V3=4 (V), dV23=1 (V) holds true, and dV23is thus within dV0=1 (FIG.10ST36: YES), the processor124switches off the circuit breakers S1and S2to stop controlling the electricity storage device33. That is, the voltage difference control by charging the electricity storage devices32to33is stopped (FIG.10ST37).

Here, as shown inFIG.12, V1=4 (V), V2=5 (V), and V3=4 (V), and thus, dV12=1(V), dV13=0 (V), and dV23=1(V). Thus, all of dV12, dV13, and dV23are within dV0=1(V) (FIG.10ST32: YES). In this case, the processor124stops controlling the electricity storage devices31to33, and the cell balancing is completed (FIG.10ST33).

(4.2) Second Variation

In a second variation, the voltage controller12uses one of the electricity storage devices31to33as a reference electricity storage device30. The voltage controller12is different from that in the embodiment and the first variation described above in that when the absolute value of a voltage difference between the reference electricity storage device30and each of control target electricity storage devices34being the electricity storage devices31to33except for the reference electricity storage device30is within the set voltage difference, the voltage controller12stops controlling the voltages of the control target electricity storage devices34. The cell balancing operation of the voltage controller12in the discharge mode M1and the charge mode M2of the second variation will be described below with reference toFIGS.1,4,13, and14.

(4.2.1) Cell Balancing Operation in Discharge Mode of Second Variation

In the second variation, the processor124included in the voltage controller12first receives, at a predetermined period, the signals SigV1to SigV3representing the voltages V1to V3respectively of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11in the discharge mode M1as shown inFIG.1. When the processor124receives the signals SigV1to SigV3, the processor124obtains the absolute values of the voltage difference of the voltages V1to V3from the voltage Vs of the reference electricity storage device30, that is, dV1=|V1−Vs|, dV2=|V2−Vs|, and dV3=|V3−Vs| (FIG.13ST40). Here, in the discharge mode M1in the second variation, the reference electricity storage device30is, for example, an electricity storage device3having the lowest voltage of the electricity storage devices31to33.

Here, when all of the absolute values dV1to dV3are not within the set voltage difference dV0stored in the storage125, the processor124controls the voltages V1to V3such that all of dV1to dV3are within the set voltage difference dV0by discharging. For example, when V1=4 (V), V2=5 (V), and V3=2 (V), the reference electricity storage device30is the electricity storage device33, and Vs=V3=2 (V). Moreover, dV1=2 (V), dV2=3 (V), and dV3=0 (V). Here, for example, when dV0=1 (V), each of dV1and dV2is not within dV0=1 (V) (FIG.13ST41: NO). Thus, the processor124selects the electricity storage devices31and32as the control target electricity storage devices34to be subjected to voltage control by discharging (FIG.13ST43).

The processor124then controls the voltages V1and V2of the electricity storage devices31and32such that dV1and dV2are within dV0=1 (V). The processor124switches the circuit breakers S1and S2included in the control circuits121and122corresponding to the electricity storage devices31and32from off to on by the control signals Sig1and Sig2. Thus, electrostatic energy stored in the electricity storage devices31and32is consumed by the resistors R1and R2respectively included in the control circuits121and122, and thereby, the voltages V1and V2of the electricity storage devices31and32decreases (FIG.13ST44).

(4.2.2) Cell Balancing Operation in Charge Mode of Second Variation

In the second variation, the processor124included in the voltage controller12first receives, at a predetermined period, the signals SigV1to SigV3representing the voltages V1to V3respectively of the electricity storage devices31to33from the voltage sensors111to113of the voltage detector11in the charge mode M2. In the electricity storage devices31to33being in the float charge mode immediately before charge completion (FIG.14ST50), when the processor124receives the signals SigV1to SigV3, the processor124obtains the absolute values of the voltage difference of the voltages V1to V3from the voltage Vs of the reference electricity storage device30, that is, dV1=|V1−Vs|, dV2=|V2−Vs|, and dV3=|V3−Vs| (FIG.14ST51). Here, in the charge mode M2in the second variation, the reference electricity storage device30is, for example, an electricity storage device3having the highest voltage of the electricity storage devices31to33.

Here, when all of the absolute values dV1to dV3are not within the set voltage difference dV0stored in the storage125, the processor124controls the voltages V1to V3such that all of dV1to dV3are within the set voltage difference dV0by charging. For example, when V1=4 (V), V2=5 (V), and V3=2 (V), the reference electricity storage device30is the electricity storage device32, and Vs=V2=5 (V). Moreover, dV1=1 (V), dV2=0 (V), and dV3=3 (V). Here, for example, when dV0=1 (V), dV3is not within dV0=1 (V) (FIG.14ST52: NO). Thus, the processor124selects the electricity storage device33as the control target electricity storage device34to be subjected to voltage control by charging (FIG.14ST54).

The processor124then controls the voltage V3of the electricity storage device33such that dV3is within dV0=1(V). The processor124switches the circuit breakers S1to S2from off to on by the control signals Sig1and Sig2except for the circuit breaker S3included in the control circuit123corresponding to the electricity storage device33. Here, the circuit breaker S3remains off. Thus, a current flows to the electricity storage device33, the electricity storage device33is charged, and the voltage V3increases (FIG.14ST55).

Here, when the voltage V3increases to V3=4 (V), dV3=1 (V) holds true, and dV3is thus within dV0=1 (V) (FIG.14ST56: YES), the processor124switches off the circuit breakers S1and S2to stop controlling the electricity storage device33(FIG.14ST57).

(4.3) Other Variations

Other variations of the embodiment will be described below. The variations described below may be accordingly combined with each other.

The electricity storage device control circuit1in the present disclosure includes a computer system. The computer system includes a processor and memory as principal hardware components. The functions of the electricity storage device control circuit1according to the present disclosure may be implemented by making the processor execute a program stored in the memory of the computer system. The program may be stored in advance in the memory of the computer system. Alternatively, the program may also be downloaded through a telecommunications line or be distributed after having been recorded in some non-transitory storage medium such as a memory card, an optical disc, or a hard disk drive, any of which is readable for the computer system. The processor of the computer system may be made up of a single or a plurality of electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). As used herein, the “integrated circuit” such as an IC or an LSI is called by a different name depending on the degree of integration thereof. Examples of the integrated circuits include a system LSI, a very-large-scale integrated circuit (VLSI), and an ultra-large-scale integrated circuit (ULSI). Optionally, a field-programmable gate array (FPGA) to be programmed after an LSI has been fabricated or a reconfigurable logic device allowing the connections or circuit sections inside of an LSI to be reconfigured may also be adopted as the processor. Those electronic circuits may be either integrated together on a single chip or distributed on multiple chips, whichever is appropriate. Those multiple chips may be aggregated together in a single device or distributed in multiple devices without limitation. As used herein, the “computer system” includes a microcontroller including one or more processors and one or more memories. Thus, the microcontroller may also be implemented as a single or a plurality of electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit. Thus, the microcontroller may also be implemented as a single or a plurality of electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

Also, the plurality of functions of the electricity storage device control circuit1are aggregated together in a single housing. However, this is not an essential configuration for the electricity storage device control circuit1. Alternatively, these constituent elements of the electricity storage device control circuit1may be distributed in multiple different housings. Still alternatively, at least some functions of the electricity storage device control circuit1(e.g., some functions of the processor124) may be implemented as a cloud computing system as well.

As described above, an electricity storage device control circuit (1) of a first aspect includes a voltage detector (11) and a voltage controller (12). The voltage detector (11) is configured to detect voltages of a plurality of electricity storage devices (3). The voltage controller (12) is configured to individually control the voltages of the plurality of electricity storage devices (3) by performing, based on a detection result by the voltage detector (11), at least one of discharging electrostatic energy stored in the plurality of electricity storage devices (3) or charging electrostatic energy into the plurality of electricity storage devices (3).

This aspect enables the voltages of the plurality of electricity storage devices (3) to be changed to respective desired values.

In an electricity storage device control circuit (1) of a second aspect referring to the first aspect, the voltage controller (12) is configured to perform at least one of the discharging or the charging of the electrostatic energy such that the voltages of the plurality of electricity storage devices (3) are equalized.

This aspect enables a voltage variation between the plurality of electricity storage devices (3) to be reduced.

In an electricity storage device control circuit (1) of a third aspect referring to the first or second aspect, the voltage controller (12) is configured to, when the voltages of the plurality of electricity storage devices (3) reach respective set voltages, stop controlling the voltages of the plurality of electricity storage devices (3).

This aspect enables the voltages of the plurality of electricity storage devices (3) to be maintained at the set voltages.

In an electricity storage device control circuit (1) of a fourth aspect referring to the first or second aspect, the voltage controller (12) is configured to, when an absolute value of a voltage difference between the plurality of electricity storage devices (3) is within a set voltage difference, stop controlling the voltages of the plurality of electricity storage devices (3).

This aspect enables the voltage difference between the plurality of electricity storage devices (3) to be maintained at the set voltage difference.

In an electricity storage device control circuit (1) of a fifth aspect referring to the first or second aspect, the voltage controller (12) is configured to use one of the plurality of electricity storage devices (3) as a reference electricity storage device (30), and the voltage controller (12) is configured to, when an absolute value of a voltage difference between the reference electricity storage device (30) and each of one or more control target electricity storage devices (34) being the plurality of electricity storage devices (3) except for the reference electricity storage device (30) is within a set voltage difference, stop controlling a voltage or voltages respectively of the one or more control target electricity storage devices (34).

This aspect enables the voltage difference between the reference electricity storage device (30) and each of the one or more control target electricity storage devices (34) to be maintained at the set voltage difference.

In an electricity storage device control circuit (1) of a sixth aspect referring to any one of the first to fifth aspects, the voltage controller (12) includes a plurality of control circuits each connected in parallel to a corresponding one of the plurality of electricity storage devices (3). Each of the plurality of control circuits includes a resistor and a circuit breaker which are connected in series to each other. The voltage controller (12) is configured to, in a discharge mode (M1) in which the plurality of electricity storage devices (3) are not connected to the primary power supply (5), switch the circuit breaker on and off to control an amount of the electrostatic energy discharged from the plurality of electricity storage devices (3).

In this aspect, discharging the plurality of electricity storage devices (3) enables the voltage variation between the plurality of electricity storage devices (3) to be reduced.

In an electricity storage device control circuit (1) of a seventh aspect referring to the sixth aspect, the voltage controller (12) is configured to, in a charge mode (M2) in which the plurality of electricity storage devices (3) are connected to the primary power supply (5), control an amount of the electrostatic energy to be charged into the plurality of electricity storage devices (3) by switching the circuit breaker on and off.

With this aspect, charging the plurality of electricity storage devices (3) enables the voltage variation between the plurality of electricity storage devices (3) to be reduced.

A backup power supply system (2) of an eighth aspect includes the electricity storage device control circuit (1) of any one of the first to seventh aspects and the plurality of electricity storage devices (3). In the backup power supply system (2), the plurality of electricity storage devices (3) is configured to be charged by a primary power supply (5) configured to supply electric power to a load (4), and the backup power supply system (2) is configured to supply electric power to the load (4) from the plurality of electricity storage devices when the primary power supply (5) fails.

This aspect provides the backup power supply system (2) having a reduced voltage variation between the plurality of electricity storage devices (3).

In a backup power supply system (2) of a ninth aspect referring to the eighth aspect, the plurality of electricity storage devices (3) include an electric double-layer capacitor.

This aspect provides the backup power supply system (2) configured to supply required electric power to the load (4) when the primary power supply (5) fails.

Note that the second to seventh aspects are not essential configurations of the electricity storage device control circuit (1) and may accordingly be omitted. Moreover, the ninth aspect is not an essential configuration of the backup power supply system (2) and may accordingly be omitted.

REFERENCE SIGNS LIST