Secondary battery control device, power storage device, and impedance measurement method

Abstract

To accurately measure the impedance of a secondary battery even when an unstable charging current is supplied during charging of the secondary battery.SOLUTION: A secondary battery control device includes: a measuring unit that repeatedly measures the battery voltage and charging current of a secondary battery, which is a nickel-metal hydride battery; and a control unit that acquires a battery voltage value and a charging current value at a first timing during charging of the secondary battery and a battery voltage value and a charging current value at a second timing during charging of the secondary battery, and acquires an impedance of the secondary battery by calculating a value obtained by dividing a battery voltage difference between the first timing and the second timing by a charging current difference between the first timing and the second timing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a secondary battery control device, a power storage device, and an impedance measurement method.

Background Art

[0002] Conventionally, rechargeable secondary batteries such as nickel-metal hydride batteries have become widespread as power sources for operating various devices and the like. As a charging method for secondary batteries, for example, in the case of nickel-metal hydride batteries, a constant current charging method in which the secondary battery is charged with a constant charging current (constant current) is generally used. In the constant current charging method, internal resistance (impedance) measurement based on a constant current is performed. This impedance measurement is performed, for example, for battery life determination. For example, in the prior art described in Patent Document 1, the impedance of a secondary battery is measured by dividing the difference between the voltage when current is flowing through the battery and the voltage when no current is flowing through the battery by the value of the flowing current (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in recent years, technologies for storing electric power generated by a power generation method using renewable energy such as solar power generation or wind power generation have been put into practical use. However, since such a power generation method is affected by environmental conditions such as the weather, the charging current may become unstable during charging of the secondary battery. Therefore, even in a secondary battery adopting a constant current charging method, there has been a problem that it is difficult to ensure the measurement accuracy in impedance measurement based on a constant current.

[0005] An object of the present invention is to provide a secondary battery control device, a power storage device, and an impedance measurement method capable of accurately measuring the impedance of a secondary battery even when an unstable charging current is supplied during charging of the secondary battery.

Means for Solving the Problems

[0006] One aspect of the secondary battery control device according to the present invention is a measurement unit that repeatedly measures the battery voltage and charging current of a secondary battery that is a nickel-metal hydride battery, respectively; obtain the battery voltage value and charging current value at a first timing during charging of the secondary battery and the battery voltage value and charging current value at a second timing during charging of the secondary battery, and calculate a value obtained by dividing the battery voltage difference between the first timing and the second timing by the charging current difference between the first timing and the second timing to obtain the impedance of the secondary battery, a control unit; and has

[0007] One aspect of the power storage device according to the present invention is a secondary battery that is a nickel-metal hydride battery; the above secondary battery control device; and has

[0008] The impedance measurement method according to the present invention is an impedance measurement method executed in a secondary battery control device that repeatedly measures the battery voltage and charging current of a secondary battery that is a nickel-metal hydride battery, respectively, obtain the battery voltage value and charging current value at a first timing during charging of the secondary battery and the battery voltage value and charging current value at a second timing during charging of the secondary battery, and calculate a value obtained by dividing the battery voltage difference between the first timing and the second timing by the charging current difference between the first timing and the second timing to obtain the impedance of the secondary battery.

Effects of the Invention

[0009] According to the present invention, even when an unstable charging current is supplied during charging of a secondary battery, the impedance of the secondary battery can be accurately measured.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

[0012] (Configuration) FIG. 1 is a circuit diagram schematically showing the configuration of the power storage device 1 according to the present embodiment. The power storage device 1 is connected to a power line 4 that connects an external power source 2 and a load device 3. The power storage device 1 charges a secondary battery BA built in the power storage device 1 itself with the power supplied from the external power source 2. Further, when the power supply from the external power source 2 to the load device 3 stops due to a factor such as a power outage, the power storage device 1 discharges the power stored in the secondary battery BA and supplies it to the load device 3. Note that the power storage device 1 according to the present embodiment can charge the secondary battery BA while supplying power to the load device 3.

[0013] The external power source 2 is, for example, a solar cell panel that generates electricity from sunlight or a windmill that generates electricity from wind power, etc., and is a power supply device that generates electricity using renewable energy. That is, since the power storage device 1 is connected to the external power source 2 that generates electricity using renewable energy to obtain the charging current of the secondary battery BA, the charging current may become unstable due to reasons such as weather.

[0014] The power storage device 1 includes a secondary battery BA and a charge / discharge switch SW1 that includes a first switching element Q1 and a second switching element Q2. The secondary battery BA is composed of one or a plurality of secondary battery cells. When the secondary battery BA is composed of a plurality of secondary battery cells, the plurality of secondary battery cells are connected in series, for example. In the present embodiment, the secondary battery BA is a nickel-metal hydride battery. Since a conventionally known technique can be adopted for the internal configuration of the nickel-metal hydride battery, detailed description thereof is omitted here. Generally, the nickel-metal hydride battery is safe because the electrolyte is inorganic and non-flammable. Also, in the present embodiment, the power storage device 1 includes one secondary battery BA, but may include a plurality of secondary batteries BA. In this case, the plurality of secondary batteries BA are connected in parallel with each other.

[0015] The charge / discharge switch SW1 includes a first switching element Q1 and a second switching element Q2. The power storage device 1 further includes a regulator 10, an input voltage measurement unit 12, a battery voltage measurement unit 14, a charge / discharge current measurement unit 16, a battery temperature measurement unit 18, a drive switch SW2, and a control unit 101. The drive switch SW2 includes a third switching element Q3 and a fourth switching element Q4. Also, the power storage device 1 has a diode D for preventing reverse current of the current at an appropriate position.

[0016] As shown in FIG. 2, the control unit 101 includes a storage unit 101a, a processing unit 101b, and a communication unit 101c, and is realized by, for example, a microcomputer or the like. The processing unit 101b is realized by, for example, a CPU (Central Processing Unit) or the like. The storage unit 101a includes a storage device realized by, for example, a ROM (Read Only Memory) or the like and a memory device realized by, for example, a RAM (Random Access Memory) or the like. The storage unit 101a stores various control programs for realizing each function of the power storage device 1, and various data such as a table T described later used in the various control programs. The communication unit 101c is realized by a communication device capable of communicating with a terminal device (not shown) of a remotely located user via a wired or wireless communication network.

[0017] The processing unit 101b reads out various control programs for realizing each function of the power storage device 1 from the storage device and stores them in the memory device. The processing unit 101b executes the various control programs.

[0018] The storage device may be a removable storage medium such as a flash memory. In this case, the control unit 101 is configured to be able to attach and detach the storage medium, and reads a program or the like from the storage medium. Note that in the control unit 101, the communication unit 101c may download a program from the outside to the storage device via the communication network.

[0019] The above-described storage device, memory device, and removable storage medium are examples of non-transitory computer-readable storage media.

[0020] The control unit 101 constitutes the secondary battery control device 100 together with the regulator 10, the input voltage measurement unit 12, the battery voltage measurement unit 14, the charge and discharge current measurement unit 16, the battery temperature measurement unit 18, the charge and discharge switch SW1, and the drive switch SW2. Note that the combination of the input voltage measurement unit 12, the battery voltage measurement unit 14, the charge and discharge current measurement unit 16, and the battery temperature measurement unit 18 constitutes a measurement unit that repeatedly measures the input voltage (charging voltage), battery voltage, charge and discharge current, and battery temperature of the secondary battery BA.

[0021] The charge and discharge switch SW1 executes charging or discharging of the secondary battery BA under the control of the control unit 101. The first switching element Q1, which is a charging switch, and the second switching element Q2, which is a discharging switch, are provided in parallel in the electrical path between the power supply line 4 and the secondary battery BA. The gate of the first switching element Q1 is connected to the control unit 101. The drain of the first switching element Q1 is connected to the power supply line 4. The source of the first switching element Q1 is connected to the secondary battery BA. The gate of the second switching element Q2 is connected to the control unit 101. The drain of the second switching element Q2 is connected to the secondary battery BA. The source of the second switching element Q1 is connected to the power supply line 4.

[0022] During the operation of the power storage device 1, the charge and discharge switch SW1 executes charging or discharging of the secondary battery BA by performing the on / off operation of the first switching element Q1 or the second switching element Q2 under the control of the control unit 101. When the charge and discharge switch SW1 executes charging of the secondary battery BA, it turns on the first switching element Q1 and turns off the second switching element Q2. Thereby, power is supplied from the external power supply 2 to the secondary battery BA via the first switching element Q1, and power is stored in the secondary battery BA. Also, when the charge and discharge switch SW1 executes discharging of the secondary battery BA, it turns on the second switching element Q2 and turns off the first switching element Q1. Thereby, power is supplied from the secondary battery BA to the load device 3 via the second switching element Q2. Note that during the shutdown of the power storage device 1, both the first switching element Q1 and the second switching element Q2 of the charge and discharge switch SW1 are off.

[0023] When the power storage device 1 is started up, the control unit 101 turns on the third switching element Q3 and the fourth switching element Q4 of the drive switch SW2. When the power storage device 1 shuts down, the control unit 101 turns off the third switching element Q3 and the fourth switching element Q4 of the drive switch SW2.

[0024] The gate of the third switching element Q3 is connected to the drain of the fourth switching element Q4. The drain of the third switching element Q3 is connected to the connection point where the source of the first switching element Q1 and the drain of the second switching element Q2 are connected, and to the power supply line 1. The source of the third switching element Q3 is connected to the regulator 10. The gate of the fourth switching element Q4 is connected to the control unit 101. The drain of the fourth switching element Q4 is connected to the gate of the third switching element Q3. The source of the fourth switching element Q4 is grounded. When a predetermined gate voltage is applied to the gate of the fourth switching element Q4 by the control unit 101, the fourth switching element Q4 turns on. Further, when the fourth switching element Q4 turns on, a gate voltage is applied to the gate of the third switching element Q3. Thereby, the third switching element Q3 turns on, the regulator 10 is driven, and the control unit 101 obtains the power for driving the charge / discharge switch SW1.

[0025] The input voltage measurement unit 12 measures the voltage (input voltage) of the power supplied from the external power supply 2, obtains an input voltage value, and notifies the control unit 101. The measurement of the input voltage is repeatedly executed at a predetermined time interval. In the present embodiment, for convenience of explanation, it is assumed that the input voltage measurement unit 12 measures the input voltage every second. However, the input voltage measurement unit 12 may measure the input voltage at a short time interval such as in units of several milliseconds. The input voltage measurement unit 12 includes circuit elements such as resistors.

[0026] The battery voltage measurement unit 14 measures the battery voltage of the secondary battery BA, obtains a battery voltage value, and notifies the control unit 101. The measurement of the battery voltage is repeatedly executed at a predetermined time interval. In the present embodiment, for convenience of explanation, it is assumed that the battery voltage measurement unit 14 measures the battery voltage every second. However, the battery voltage measurement unit 14 may measure the battery voltage at a short time interval such as in units of several milliseconds. The battery voltage measurement unit 14 is configured to include circuit elements such as resistors.

[0027] The charge / discharge current measurement unit 16 measures the charge current or discharge current of the secondary battery BA (hereinafter, also generically referred to as "charge / discharge current"), obtains a charge current value or a discharge current value (hereinafter, also generically referred to as "charge / discharge current value"), and notifies the control unit 101. The measurement of the charge / discharge current is repeatedly executed at a predetermined time interval. In the present embodiment, for convenience of explanation, it is assumed that the charge / discharge current measurement unit 16 measures the charge / discharge current every second. However, the charge / discharge current measurement unit 16 may measure the charge / discharge current at a short time interval such as in units of several milliseconds. The measurement of the charge / discharge current is preferably executed simultaneously in synchronization with the measurement of the input voltage. The charge / discharge current measurement unit 16 is configured to include circuit elements such as resistors.

[0028] The battery temperature measurement unit 18 measures the battery temperature of the secondary battery BA, obtains a battery temperature value, and notifies the control unit 101. The measurement of the battery temperature is repeatedly executed at a predetermined time interval. In the present embodiment, for convenience of explanation, it is assumed that the battery temperature measurement unit 18 measures the battery temperature every second. However, the battery temperature measurement unit 18 may measure the battery temperature at a short time interval such as in units of several milliseconds. The battery temperature measurement unit 18 is configured to include circuit elements such as thermistors.

[0029] Next, the operation of the secondary battery control device 100 will be described. FIG. 3 is a flowchart for explaining a method for measuring the impedance of the secondary battery BA executed in the secondary battery control device 100.

[0030] In step S1, the processing unit 101b controls the charge and discharge switch SW1 to start charging the secondary battery BA. The trigger for starting the charging is, for example, that the SOC (State of Charge) based on the battery voltage value or the like falls below a predetermined threshold value.

[0031] In step S2, the processing unit 101b acquires the battery voltage value and the charging current value from the battery voltage measurement unit 14 and the charge and discharge current measurement unit 16. In step S3, the processing unit 101b stores the acquired battery voltage value and charging current value in the table T in the storage unit 101a. The acquisition and storage of the battery voltage value and the charging current value in steps S2 and S3 are repeatedly performed each time the battery voltage and the charging current are measured, and are performed until the charging of the secondary battery BA is completed (step S4). The trigger for ending the charging is, for example, that the SOC based on the battery voltage value or the like reaches the full charge level (for example, 100%).

[0032] In step S5, the processing unit 101b searches for two current stable intervals. The current stable interval is a time period during which the charging current is stable. Since the external power supply 2 is a power supply device that uses natural energy, the charging current is unstable as a whole during the charging period of the secondary battery BA. Nevertheless, since there is a time period during which the charging current is temporarily stable during the charging period, the processing unit 101b identifies that time period as the current stable interval. In the present embodiment, since two current stable intervals are required for impedance measurement, at least two current stable intervals are searched for. Note that the interval searched for as the second current stable interval does not overlap with the first current stable interval.

[0033] Specifically, the processing unit 101b reads a table T (see FIG. 4) showing the battery voltage values and charging current values acquired at each time during the charging period in time series. Then, while sequentially shifting the start position of a search section having a predetermined time length (5 seconds as an example in this embodiment) from time t1, the processing unit 101b identifies a search section in which the charging current value is the same value over the predetermined time length. A search section in which the charging current value is the same value over the predetermined time length (that is, the charging current is stable) is a current stable section. The processing unit 101b sequentially searches for the first current stable section and the second current stable section. The time period of the first current stable section is determined as the first timing, and the time period of the second current stable section is determined as the second timing.

[0034] In this way, in impedance measurement, various measurement values at the timing when the charging current temporarily stabilizes can be utilized.

[0035] Note that the search for the current stable section (step S5) described above is preferably executed when the SOC of the secondary battery BA is within a predetermined range. The predetermined range is, for example, 20% to 80%. By restricting the execution condition of the current stable section search based on the SOC of the secondary battery BA, the impedance measurement accuracy can be more reliably improved.

[0036] In step S6, the processing unit 101b acquires the first battery voltage value and the first charging current value, and the second battery voltage value and the second charging current value. The first battery voltage value and the first charging current value are the battery voltage value and the charging current value at the first timing. The second battery voltage value and the second charging current value are the battery voltage value and the charging current value at the second timing.

[0037] At the first timing, since the charging current value is the same throughout the first current stable section, the charging current value at the first timing is uniquely determined. In the following description, the first charging current value is referred to as "I1". The battery voltage value can vary from moment to moment in the first current stable section. Therefore, the processing unit 101b obtains the first battery voltage value by averaging a plurality of battery voltage values at the first timing. In the following description, the first battery voltage value is denoted as "V1".

[0038] At the second timing, since the charging current value is the same throughout the second current stable section, the charging current value at the second timing is uniquely determined. In the following description, the second charging current value is referred to as "I2". The battery voltage value can vary from moment to moment in the second current stable section. Therefore, the processing unit 101b obtains the second battery voltage value by averaging a plurality of battery voltage values at the second timing. In the following description, the second battery voltage value is denoted as "V2".

[0039] In this way, the input voltage value used for impedance measurement can be easily determined.

[0040] In step S7, the processing unit 101b calculates the impedance using the first battery voltage value V1, the first charging current value I1, the second battery voltage value V2, and the second charging current value I2. The processing unit 101b obtains the impedance by calculating the value obtained by dividing the battery voltage difference between the first battery voltage value V1 and the second battery voltage value V2 by the charging current difference between the first charging current value I1 and the second charging current value I2.

[0041] More specifically, first, the processing unit 101b determines the magnitude relationship between the first charging current value I1 and the second charging current value I2.

[0042] When I2 > I1, the processing unit 101b calculates the impedance by performing the operation of (V2 - V1) / (I2 - I1). When I1 > I2, the processing unit 101b calculates the impedance by performing the operation of (V1 - V2) / (I1 - I2). Thereby, the value obtained by dividing the battery voltage difference by the charging current value can be accurately calculated.

[0043] In addition, in order to calculate the impedance more accurately, the value obtained by dividing the battery voltage difference by the charging current value, for example, may be corrected based on the battery temperature value.

[0044] The calculated impedance can be used, for example, to determine the life of the secondary battery BA. For example, when the calculated impedance becomes larger than a predetermined threshold value, it can be determined that the secondary battery BA has deteriorated. Note that since a conventionally known technique can be adopted for the life determination of the secondary battery BA based on the impedance, a detailed description thereof is omitted here.

[0045] As described above, according to the present embodiment, the secondary battery control device 100 includes a measurement unit (battery voltage measurement unit 14 and charge / discharge current measurement unit 16) that repeatedly measures the battery voltage and the charging current of the secondary battery BA, which is a nickel-hydrogen battery, respectively. Further, the secondary battery control device 100 includes a control unit 101. The control unit 101 acquires the battery voltage value (first battery voltage value V1) and the charging current value (second charging current value I1) at the first timing during the charging of the secondary battery BA, and the battery voltage value (second battery voltage value V2) and the charging current value (second charging current value I2) at the second timing during the charging of the secondary battery BA. The control unit 101 calculates a value obtained by dividing the battery voltage difference between the first timing and the second timing by the charging current difference between the first timing and the second timing, and acquires the impedance of the secondary battery BA.

[0046] Thereby, even when an unstable charging current is supplied during the charging of the secondary battery BA, the impedance of the secondary battery BA can be accurately measured.

[0047] In addition, it becomes possible to reduce the constant current circuit for impedance measurement, which was necessary in the past. Therefore, it becomes possible to charge the secondary battery BA, which is a nickel-hydrogen battery, even by a method different from the constant current charging method that has been common for nickel-hydrogen batteries. Thus, the configuration of the power storage device 1 can be simplified by reducing the constant current circuit.

[0048] Also, according to the present embodiment, the power storage device 1 includes a secondary battery BA that is a nickel-metal hydride battery and the above-described secondary battery control device 100. Further, according to the present embodiment, the power storage device 1 is connected to an external power source 2 that generates power using renewable energy, and obtains a charging current for the secondary battery BA from the external power source 2.

[0049] Therefore, it is possible to provide a very advantageous power supply system that combines a secondary battery (secondary battery BA) based on a non-flammable and safe nickel-metal hydride battery and an environmentally friendly power supply device (external power source 2) that generates power using renewable energy such as sunlight or wind power.

[0050] As described above, the present embodiment has been described. However, the present invention is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the gist of the present invention.

Explanation of Reference Numerals

[0051] 1 Power storage device 2 External power source 3 Load device 4 Power line 10 Regulator 12 Input voltage measurement unit 14 Battery voltage measurement unit 16 Charge / discharge current measurement unit 18 Battery temperature measurement unit 100 Secondary battery control device 101 Control unit BA Secondary battery D Diode Q1 First switching element Q2 Second switching element Q3 Third switching element Q4 Fourth switching element SW1 Charge / discharge switch SW2 Drive switch

Claims

1. A measurement unit that repeatedly measures the battery voltage and charging current of a secondary battery that is a nickel-metal hydride battery, respectively; A control unit that acquires the battery voltage value and charging current value at a first timing during charging of the secondary battery and the battery voltage value and charging current value at a second timing during charging of the secondary battery, and calculates a value obtained by dividing the battery voltage difference between the first timing and the second timing by the charging current difference between the first timing and the second timing to obtain the impedance of the secondary battery; A secondary battery control device having the above.

2. The control unit: Let the battery voltage values at the first timing and the second timing be V1 and V2, respectively, Let the charging current values at the first timing and the second timing be I1 and I2, respectively, And when I2 > I1, By calculating (V2 - V1) / (I2 - I1), calculate the value obtained by dividing the battery voltage difference by the charging current difference. The secondary battery control device according to Claim 1.

3. The control unit: Let the battery voltage values at the first timing and the second timing be V1 and V2, respectively, Let the charging current values at the first timing and the second timing be I1 and I2, respectively, And when I1 > I2, By calculating (V1 - V2) / (I1 - I2), calculate the value obtained by dividing the battery voltage difference by the charging current difference. The secondary battery control device according to Claim 1.

4. The control unit determines a first section where the charging current value is the same over a predetermined time period as the first timing, and determines a second section that does not overlap with the first section and where the charging current value is the same over the predetermined time period as the second timing. The secondary battery control device according to Claim 1.

5. The control unit obtains the battery voltage value at the first timing by averaging a plurality of battery voltage values in the first section, and obtains the battery voltage value at the second timing by averaging a plurality of battery voltage values in the second section. The secondary battery control device according to Claim 4.

6. A secondary battery that is a nickel-metal hydride battery, The secondary battery control device according to Claim 1, A power storage device having the above.

7. Connected to a power supply device that generates electricity using renewable energy, and obtaining the charging current from the power supply device. The power storage device according to Claim 6.

8. An impedance measurement method executed in a secondary battery control device that repeatedly measures the battery voltage and charging current of a secondary battery that is a nickel-metal hydride battery, obtaining the battery voltage value and charging current value at a first timing during charging of the secondary battery and the battery voltage value and charging current value at a second timing during charging of the secondary battery, and calculating a value obtained by dividing the battery voltage difference between the first timing and the second timing by the charging current difference between the first timing and the second timing to obtain the impedance of the secondary battery, Impedance measurement method.

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