Control device for secondary battery system

Abstract

A control device 5 for a secondary battery system according to the present invention comprises: a current measurement unit 50 that measures a discharge current and a charge current for a secondary battery 2; and an arithmetic unit 51 that holds a first correction value 51a for correcting the values measured for the discharge current and the charge current as measured by the current measurement unit 50, determines a current integrated value obtained by correcting the measurement values using the first correction value 51a from when the secondary battery 2 has finished being charged and is then discharged and charged until again finishing being charged and by integrating the corrected values, obtains a second correction value by dividing the amount of deviation between the current integrated value and 0 by the integration time, and updates the first correction value 51a by adding the second correction value to the first correction value 51a when the temperature difference between the temperature of the secondary battery 2 at the previous end of charging and the temperature of the secondary battery 2 at the current end of charging equals or is less than a predetermined value.

Description

Control device for secondary battery system

[0001] The present invention relates to a control device for a secondary battery system.

[0002] As this type of secondary battery system conventionally used, for example, the configuration disclosed in the following Patent Document 1 can be cited. Patent Document 1 discloses that the discharge capacity of a sodium-sulfur battery as a secondary battery can be obtained by integrating, from an initially set discharge capacity, the current values related to charging and discharging into a control device such as a sequencer and adjusting the values (for example, adding for charging, subtracting for discharging, etc.) before performing integration. Patent Document 1 also discloses that a deviation occurs between the actual discharge capacity and the managed value of discharge capacity managed by the control device.

[0003] Japanese Unexamined Patent Publication No. 2008-84677

[0004] As a method for suppressing the above-mentioned deviation, the following approach can be considered. Specifically, a current measurement unit measures the discharge current and charging current of the secondary battery. From a state where the secondary battery is fully charged, after undergoing discharging and charging until it becomes fully charged again, an integrated current value is obtained by integrating measurement values from the current measurement unit after correcting the values with a predetermined first correction value. Then a second correction value is obtained by dividing the amount of deviation between the integrated current value and zero by the integration time, and the first correction value is updated by adding the second correction value to the first correction value. The integrated current value from when the secondary battery is fully charged, through discharging and charging, until it becomes fully charged again should originally be zero. By adding the second correction value, which takes into account the deviation of the integrated current value from zero, to the first correction value, it is considered that the deviation between the actual discharge capacity and the managed value managed by the control device can be further suppressed.

[0005] However, even when such a deviation suppression method is employed, a deviation may still occur between the actual discharge capacity and the managed value of discharge capacity managed by the control device.

[0006] The present invention has been made to solve the above problems, and one object thereof is to provide a control device for a secondary battery system that can more reliably suppress the deviation between the actual discharge capacity of the secondary battery and the managed value of discharge capacity managed by the control device.

[0007] The inventors investigated the behavior of secondary battery systems and the discharge capacity of secondary batteries, and obtained the following new findings. Specifically, it was found that although secondary battery systems control the temperature of the secondary battery, differences in the discharge capacity of the secondary battery can occur depending on the temperature at which the secondary battery reaches the end of its charge. Furthermore, it was found that even though there are differences in discharge capacity due to temperature, updating the first correction value exacerbates the discrepancy between the actual discharge capacity of the secondary battery and the control value of the discharge capacity managed by the control device, as the difference in discharge capacity due to temperature becomes a factor in the deviation. This invention was made based on these new findings.

[0008] [1] In one embodiment, the present invention relates to a control device for a secondary battery system, comprising: a current measuring unit for measuring the discharge current and charging current of a secondary battery; a calculation unit for holding a first correction value for correcting the measured values ​​of the discharge current and charging current by the current measuring unit; calculating an integrated current value by correcting the measured values ​​by the first correction value and accumulating them from the state where the secondary battery is fully charged until it is fully charged again after undergoing discharge and charging; calculating a second correction value by dividing the amount of deviation between the integrated current value and 0 by the accumulation time; and updating the first correction value by adding the second correction value to the first correction value when the temperature difference between the temperature of the secondary battery at the end of the previous charge and the temperature of the secondary battery at the end of the current charge is less than or equal to a predetermined value.

[0009] [2] The present invention may also relate to a control device for a secondary battery system as described in paragraph 1, wherein the calculation unit updates the first correction value when the temperature difference is less than or equal to a predetermined value and the temperature of the secondary battery at the end of the current charge falls within a predetermined temperature range.

[0010] [3] The present invention may relate to a control device for a secondary battery system as described in paragraph 1 or 2, wherein the secondary battery is connected to a power converter via a switch, and the calculation unit corrects both the measured values ​​above a predetermined threshold and those below the threshold by the first correction value when the switch is closed, and then integrates them.

[0011] [4] The present invention may relate to a control device for a secondary battery system as described in paragraph 3, wherein the threshold is 30A.

[0012] According to one embodiment of the control device for a secondary battery system of the present invention, when the temperature difference between the temperature of the secondary battery at the end of the previous charge and the temperature of the secondary battery at the end of the current charge is less than or equal to a predetermined value, the calculation unit adds a second correction value to the first correction value to update the first correction value. This makes it possible to more reliably suppress the discrepancy between the actual discharge capacity of the secondary battery and the control value of the discharge capacity managed by the control device.

[0013] This is a schematic block diagram showing a secondary battery system according to an embodiment of the present invention. This is a flowchart showing the correction value update determination operation of the calculation unit in Figure 1.

[0014] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and can be materialized by modifying the components without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

[0015] Figure 1 is a schematic block diagram showing a secondary battery system 1 according to an embodiment of the present invention. As shown in Figure 1, the secondary battery system 1 of this embodiment includes a secondary battery 2, a power converter 3, a switch 4, and a control device 5.

[0016] The secondary battery 2 is electrically connected to the power converter 3, the switch 4, and the control device 5. The secondary battery 2 may be a module battery including a collection of multiple single cells, each consisting of a sodium-sulfur cell, connected in series and / or parallel.

[0017] The power converter 3 is a device that converts the DC power from the secondary battery 2 into AC power and outputs it. The AC power output from the power converter 3 is supplied to the loads of the power system connected to the secondary battery system 1. The power converter 3 converts the AC power from the power system into DC power and supplies it to the secondary battery 2.

[0018] The power conversion device 3 may include a converter 30, a transformer 31, and a conversion control unit 32. The converter 30 is composed of, for example, an inverter and a converter, and is connected to the secondary battery 2. The converter 30 performs DC-AC power conversion. The transformer 31 is placed between the converter 30 and the power system and adjusts the voltage of the AC power from and to the converter 30. The conversion control unit 32 is connected to the converter 30 and the transformer 31 and controls the operation of the converter 30 and the transformer 31. The conversion control unit 32 may be composed of a computing device such as a computer that operates based on a program.

[0019] Switch 4 is interposed between the secondary battery 2 and the power converter 3. When switch 4 is closed, the secondary battery 2 is connected to the power converter 3, and when switch 4 is open, the secondary battery 2 is disconnected from the power converter 3. Charging and discharging of the secondary battery 2 occurs when switch 4 is closed. Switch 4 may also be closed when the secondary battery 2 is in standby mode (when no charging or discharging is occurring).

[0020] The control device 5 is connected to the secondary battery 2, the power converter 3, and the switch 4. The control device 5 manages the discharge capacity of the secondary battery 2. The control device 5 may also control the operation of the power converter 3 (conversion control unit 32). The control device 5 may be housed together with the secondary battery 2 and the power converter 3 in a container or other housing (not shown).

[0021] The control device 5 includes a current measurement unit 50 and a calculation unit 51.

[0022] The current measurement unit 50 measures the discharge current and charge current of the secondary battery 2. The discharge current is the current output from the secondary battery 2. The charge current is the current input to the secondary battery 2. The current measurement unit 50 may be interposed between the secondary battery 2 and the power converter 3, as shown in the illustrated configuration. The current measurement unit 50 may also be interposed between the secondary battery 2 and the switch 4, as shown in the illustrated configuration, or between the switch 4 and the power converter 3.

[0023] The calculation unit 51 calculates the discharge capacity of the secondary battery 2 by integrating the measured values ​​from the current measurement unit 50. As shown in Figure 1, the calculation unit 51 holds a first correction value 51a for correcting the measured values ​​of the discharge current and charge current from the current measurement unit 50. The calculation unit 51 corrects the measured values ​​from the current measurement unit 50 using the first correction value 51a and then integrates them. The first correction value 51a may be a coefficient that is subtracted from the measured values ​​from the current measurement unit 50. The calculation unit 51 acquires the measured values ​​from the current measurement unit 50 at unit time intervals and corrects the measured values ​​by subtracting the first correction value 51a from them. Although not limited to this, the measured value of the discharge current may be a positive value and the measured value of the charge current may be a negative value, and the measured values ​​may be added together to perform the integration of the measured values. The calculation unit 51 may have a timer 51b that measures the time for integrating the measured values. The calculation unit 51 may be composed of a calculation device such as a computer that operates based on a program.

[0024] Next, Figure 2 is a flowchart showing the correction value update determination operation of the calculation unit 51 in Figure 1. The correction value update determination operation shown in Figure 2 is started when it is confirmed that the secondary battery 2 is at the end of its charge. The calculation unit 51 can confirm that the secondary battery 2 is at the end of its charge by detecting that the voltage of the secondary battery 2 has reached the end of its charge voltage.

[0025] The calculation unit 51 calculates an integrated current value by correcting the measured value of the current measurement unit 50 with the first correction value 51a and accumulating it from the state where the secondary battery 2 is fully charged until it is fully charged again after discharge and recharging (steps S1 to S3). The discharge capacity of the secondary battery 2 can be determined from the integrated current value.

[0026] When the calculation unit 51 determines that the secondary battery 2 has reached the end of its charge cycle again (when the answer is Yes in step S3), it calculates a second correction value by dividing the deviation between the integrated current value and 0 by the integration time (step S4). The integrated current value from the state where the secondary battery 2 is at the end of its charge cycle through discharge and charging until it reaches the end of its charge cycle again should ideally be 0. The second correction value, obtained by dividing the deviation of the integrated current value from 0 by the integration time, corresponds to the excess or deficit of the first correction value 51a per unit time. The calculation unit 51 can obtain the integration time based on the signal from the timer 51b.

[0027] After determining the second correction value, the calculation unit 51 determines whether the temperature difference between the temperature of the secondary battery 2 at the end of the previous charge and the temperature of the secondary battery 2 at the end of the current charge is less than or equal to a predetermined value (step S5). If the temperature difference is less than or equal to the predetermined value, the calculation unit 51 adds the second correction value to the first correction value 51a to update the first correction value 51a (step S6), and ends this correction value update determination operation. On the other hand, if the temperature difference exceeds the predetermined value, the calculation unit 51 ends the correction value update determination operation without updating the first correction value 51a. The correction value update determination operation is performed repeatedly.

[0028] The inventors investigated the behavior of the secondary battery system 1 and the discharge capacity of the secondary battery 2, and found that the discharge capacity of the secondary battery 2 can vary depending on the temperature at which the secondary battery 2 reaches the end of its charge. For example, when the temperature at the end of the charge of the secondary battery 2 is 322°C, the discharge capacity of the secondary battery 2 is 52.5 Ah; when the temperature at the end of the charge of the secondary battery 2 is 323°C, the discharge capacity of the secondary battery 2 is 53.0 Ah; and when the temperature at the end of the charge of the secondary battery 2 is 326°C, the discharge capacity of the secondary battery 2 is 54.2 Ah. Furthermore, despite the difference in discharge capacity due to temperature, it was found that when the second correction value is added to the first correction value 51a, the difference in discharge capacity due to temperature becomes a factor in the discrepancy, and the discrepancy between the actual discharge capacity of the secondary battery 2 and the control value of the discharge capacity managed by the control device 5 is exacerbated. As in the control device 5 of this embodiment, when the temperature difference between the temperature of the secondary battery 2 at the end of the previous charge and the temperature of the secondary battery 2 at the end of the current charge is less than or equal to a predetermined value, the calculation unit 51 adds the second correction value to the first correction value 51a to update the first correction value 51a, thereby more reliably suppressing the discrepancy between the actual discharge capacity of the secondary battery 2 and the control value of the discharge capacity managed by the control device 5.

[0029] "The temperature of the secondary battery 2 at the end of the previous charge" refers to the temperature of the secondary battery 2 when the correction value update determination operation is started, and "the temperature of the secondary battery 2 at the end of the current charge" refers to the temperature of the secondary battery 2 when Yes is determined in step S3. The calculation unit 51 can detect the temperature of the secondary battery 2 based on the signal from the thermometer provided on the secondary battery 2. The "predetermined value" (temperature difference threshold) used to determine whether or not to update the first correction value 51a can be determined based on the difference in discharge capacity at the end of the charge of the secondary battery 2. For example, if the temperature difference is 3°C or more, the first correction value 51a is not updated.

[0030] Furthermore, the calculation unit 51 may take into account the temperature of the secondary battery 2 at the end of the current charge cycle when determining whether to update the first correction value 51a. That is, the calculation unit 51 may update the first correction value 51a when the above-mentioned temperature difference is less than or equal to a predetermined value and the temperature of the secondary battery 2 at the end of the current charge cycle falls within a predetermined temperature range. For example, the first correction value 51a is not updated when the temperature of the secondary battery 2 is 310°C or less or 325°C or more.

[0031] Returning to Figure 1, the calculation unit 51 corrects both the measured values ​​above and below a predetermined threshold by the first correction value 51a when the switch 4 is closed, and then integrates them. The calculation unit 51 can detect that the switch 4 is closed based on the signal from the switch 4. The threshold may be 30A.

[0032] Compared to measured values ​​above a threshold, measured values ​​below a threshold contain a larger proportion of measurement error. Therefore, conventionally, attempts have been made to improve the accuracy of managing the discharge capacity of the secondary battery 2 by ignoring measured values ​​below a threshold (i.e., by integrating only measured values ​​above a predetermined threshold). However, ignoring measured values ​​below a threshold also means ignoring the standby power of the secondary battery 2 when the switch 4 is closed, and this ignoring also has considerable consequences. The inventors investigated the behavior of the secondary battery system 1 and the discharge capacity of the secondary battery 2 and concluded that the benefits of integrating measured values ​​below a threshold in addition to those above a threshold outweigh the benefits of ignoring measured values ​​below a threshold. In other words, it was found that the accuracy of managing the discharge capacity of the secondary battery 2 can be improved by integrating measured values ​​below a threshold in addition to those above a threshold. As in this embodiment, when the switch 4 is closed, both measured values ​​above and below a predetermined threshold are corrected by the first correction value 51a and then integrated, thereby improving the accuracy of managing the discharge capacity of the secondary battery 2.

[0033] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0034] 1: Secondary battery system 2: Secondary battery 3: Power conversion device 4: Switch 5: Control device 50: Current measurement unit 51: Calculation unit 51a: First correction value

Claims

1. A control device for a secondary battery system, comprising: a current measuring unit for measuring the discharge current and charging current of a secondary battery; a calculation unit for holding a first correction value for correcting the measured values ​​of the discharge current and charging current by the current measuring unit; calculating an integrated current value by correcting the measured values ​​with the first correction value and accumulating them from the state where the secondary battery is at the end of charging until it is at the end of charging again after undergoing discharge and charging; calculating a second correction value by dividing the amount of deviation between the integrated current value and 0 by the accumulation time; and updating the first correction value by adding the second correction value to the first correction value when the temperature difference between the temperature of the secondary battery at the end of the previous charging and the temperature of the secondary battery at the end of the current charging is less than or equal to a predetermined value.

2. The control device for a secondary battery system according to claim 1, wherein the calculation unit updates the first correction value when the temperature difference is less than or equal to a predetermined value and the temperature of the secondary battery at the end of the current charge falls within a predetermined temperature range.

3. The control device for a secondary battery system according to claim 1 or 2, wherein the secondary battery is connected to a power converter via a switch, and the calculation unit corrects both the measured values ​​above a predetermined threshold and those below the threshold by the first correction value when the switch is closed, and then integrates them.

4. The control device for a secondary battery system according to claim 3, wherein the threshold is 30A.

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