JP2013205125A - Device and method for detecting state of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate SOH (State of Health) of a secondary battery even when SOC (State of Charge) and other conditions are changing.SOLUTION: A secondary battery state detection device 1 for detecting the state of a secondary battery 14 includes: computation means (CPU 10a) which computes a ratio of first internal resistance representing internal resistance of the secondary battery when an absolute SOC, computed as a standard initial capacity of the secondary battery, is within a predetermined range, and second internal resistance representing the internal resistance of the secondary battery in a fully charged or nearly fully charged state; and estimation means (CPU 10a) which estimates SOH of the secondary battery on the basis of correlation between the ratio computed by the computation means and SOH.

Description

  The present invention relates to a secondary battery state detection device and a secondary battery state detection method.

  Patent Document 1 discloses a technique for determining deterioration of a secondary battery by comparing a voltage drop amount at the time of starting the engine of a secondary battery with a new article and a voltage drop amount at the time of starting the engine at an arbitrary time point. Has been.

  Patent Document 2 also measures and stores the deterioration characteristics of the internal resistance of the standard secondary battery, collates the change rate of the internal resistance of the target secondary battery with the stored deterioration characteristics, and reaches the lifetime. Technology for determining the number of years and SOH (State of Health) is disclosed.

Japanese Patent Laid-Open No. 2008-087654 JP 2005-37233 A

  By the way, in the technique disclosed in Patent Document 1, even when a secondary battery having the same deterioration degree is measured, the amount of voltage drop varies depending on the charging rate and temperature at the time of engine start, so that it is sufficiently accurate. There is a problem that the degree of deterioration cannot be estimated.

  Further, in the technique disclosed in Patent Document 2, since the secondary battery to be determined is used for emergency power supply, it is assumed that the state of charge (SOC) does not change, and the internal resistance and SOH In a liquid secondary battery having a low correlation, there is a problem that it is impossible to estimate SOH with high accuracy.

  An object of the present invention is to provide a secondary battery state detection device and a secondary battery state detection method capable of accurately estimating SOH even when the charging rate or the like changes.

In order to solve the above-described problems, the present invention provides a secondary battery state detection device for detecting a state of a secondary battery, wherein an absolute SOC calculated based on an initial capacity of the secondary battery is within a predetermined range. A first internal resistance that is an internal resistance of the secondary battery and a second internal resistance that is an internal resistance when the secondary battery is in a fully charged state or a state close to full charge. And calculating means for estimating the SOH of the secondary battery based on a correlation between the value of the ratio calculated by the calculating means and SOH.
According to such a configuration, it is possible to accurately estimate SOH even when the charging rate or the like changes.

In addition to the above-mentioned invention, another invention is characterized in that the calculation means calculates the value of the ratio by dividing the first internal resistance by the second internal resistance.
According to such a configuration, the ratio value can be easily calculated based on the two internal resistances.

According to another aspect of the invention, in addition to the above-described invention, the calculation unit calculates the value of the ratio by dividing a difference between the first internal resistance and the second internal resistance by the first internal resistance. It is characterized by that.
According to such a configuration, the ratio value can be easily calculated based on the two internal resistances.

In addition to the above invention, another invention is characterized in that the estimation means estimates a relative SOC based on a ratio between the remaining capacity of the secondary battery and the SOH.
According to such a configuration, since the relative SOC can be calculated with high accuracy, the state of the secondary battery can be known more accurately.

According to another aspect of the invention, in addition to the above-described invention, the estimating unit may calculate a value calculated by dividing the first internal resistance by the second internal resistance, or the first internal resistance and the second internal resistance. When the value calculated by dividing the difference in resistance by the first internal resistance is smaller than a predetermined threshold value, based on a linear expression indicating the correlation between the ratio value and the SOH. It is characterized by estimating SOH.
According to such a configuration, SOH can be estimated easily and accurately based on the linear expression.

According to another invention, in addition to the above-mentioned invention, the estimating means has a correlation between the ratio value and the SOH for each of a plurality of representative values of the absolute SOC, and the first internal resistance Is corrected so as to correspond to any one of the representative values.
According to such a configuration, it is only necessary to store information indicating the correlation between a plurality of representative values, so that the necessary storage capacity of the memory can be reduced.

According to another invention, in addition to the above invention, the estimation means obtains a corresponding relative SOC from a relationship between the ratio value and the relative SOC when the absolute SOC is not within the predetermined range. The SOH is obtained based on the charge / discharge amount from the fully charged state to the relative SOC and the relative SOC.
According to such a configuration, the SOH can be estimated even when the absolute SOC is not within the predetermined range.

In addition, the present invention provides a secondary battery state detection method for detecting a state of a secondary battery, wherein the secondary battery when the absolute SOC calculated based on the initial capacity of the secondary battery is within a predetermined range is provided. A calculation step of calculating a ratio value relating to a first internal resistance that is an internal resistance of the second internal resistance and a second internal resistance that is an internal resistance in a state where the secondary battery is fully charged or close to full charge; And an estimation step of estimating the SOH of the secondary battery based on the correlation between the ratio value calculated in the step and SOH.
According to such a method, SOH can be accurately estimated even when the charging rate or the like changes.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the secondary battery state detection apparatus and secondary battery state detection method which can estimate SOH correctly even when a charging rate and temperature change.

It is a figure which shows the structural example of the secondary battery state detection apparatus which concerns on embodiment of this invention. It is a block diagram which shows the detailed structural example of the control part of FIG. It is a figure for demonstrating the state of a secondary battery. It is a figure which shows the relationship between relative SOC and Imp_rate. It is a figure which shows the relationship between relative SOC and Imp_inc_rate. It is a figure which shows the relationship between Imp_rate and SOH in case absolute SOC is 80%. It is a figure which shows the relationship between Imp_inc_rate in case absolute SOC is 80%, and SOH. It is a figure which shows the relationship between Imp_rate and SOH in case absolute SOC is 80% and 60%. It is a figure which shows the relationship between Imp_rate and relative SOC. It is a flowchart for demonstrating operation | movement of this embodiment. It is a figure which shows the range of absolute SOC, and the relationship of representative absolute SOC.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of Embodiment FIG. 1 is a diagram illustrating a power supply system of a vehicle having a secondary battery state detection device according to an embodiment of the present invention. In this figure, the secondary battery state detection device 1 includes a control unit 10, a voltage sensor 11, a current sensor 12, and a temperature sensor 13 as main components, and detects the state of the secondary battery 14. Here, the control unit 10 refers to outputs from the voltage sensor 11, the current sensor 12, and the temperature sensor 13 to detect the state of the secondary battery 14. The voltage sensor 11 detects the terminal voltage of the secondary battery 14 and notifies the control unit 10 of it. The current sensor 12 detects the current flowing through the secondary battery 14 and notifies the control unit 10 of the current. The temperature sensor 13 detects the secondary battery 14 itself or the surrounding environmental temperature, and notifies the control unit 10 of it. The discharge circuit 15 is configured by, for example, a semiconductor switch and a resistance element connected in series, and the secondary battery 14 is intermittently discharged when the control unit 10 performs on / off control of the semiconductor switch.

  The secondary battery 14 is composed of, for example, a lead storage battery, a nickel cadmium battery, a nickel hydrogen battery, or a lithium ion battery, and is charged by the alternator 16 to drive the starter motor 18 to start the engine and load 19 To supply power. The alternator 16 is driven by the engine 17 to generate AC power, convert it into DC power by a rectifier circuit, and charge the secondary battery 14.

  The engine 17 is composed of, for example, a reciprocating engine such as a gasoline engine and a diesel engine, a rotary engine, or the like. The engine 17 is started by a starter motor 18 and drives driving wheels via a transmission to give propulsive force to the vehicle. Drive to generate power. The starter motor 18 is constituted by, for example, a DC motor, generates a rotational force by the electric power supplied from the secondary battery 14, and starts the engine 17. The load 19 is configured by, for example, an electric steering motor, a defogger, an ignition coil, a car audio, a car navigation, and the like, and operates with electric power from the secondary battery 14.

  FIG. 2 is a diagram illustrating a detailed configuration example of the control unit 10 illustrated in FIG. 1. As shown in this figure, the control unit 10 includes a CPU (Central Processing Unit) 10a, a ROM (Read Only Memory) 10b, a RAM (Random Access Memory) 10c, a communication unit 10d, and an I / F (Interface) 10e. ing. Here, the CPU 10a controls each unit based on the program 10ba stored in the ROM 10b. The ROM 10b is configured by a semiconductor memory or the like, and stores a program 10ba or the like. The RAM 10c is configured by a semiconductor memory or the like, and stores data generated when the program ba is executed, and a parameter 10ca such as a table or a mathematical expression described later. The communication unit 10d communicates with an ECU (Engine Control Unit), which is a higher-level device, and notifies the higher-level device of the detected information. The I / F 10e converts the signal supplied from the voltage sensor 11, the current sensor 12, and the temperature sensor 13 into a digital signal and takes it in, and supplies a driving current to the discharge circuit 15 to control it.

(B) Description of Operation Principle of Embodiment Next, the operation principle of the embodiment will be described with reference to the drawings. FIG. 3 is a schematic diagram schematically showing the state of the secondary battery 14 used for a certain period of time. In FIG. 3, the nominal capacity is the nominal capacity (or capacity in the initial state) of the secondary battery 14, and DOD (Depth of Discharge) is the discharge capacity. Further, in FIG. 3, the black-colored portion indicates the capacity that cannot be discharged due to deterioration, the hatched portion indicates the dischargeable capacity, and the white-colored portion indicates the discharged capacity. Show. Thus, when defining the state of the secondary battery 14, absolute SOC is represented by the following formula | equation (1).

  Absolute SOC = ((nominal capacity−DOD) / nominal capacity) × 100 (1)

  Moreover, relative SOC is represented by the following formula | equation (2).

  Relative SOC = ((SOH−DOD) / SOH) × 100 (2)

  The inventor of the present application uses the first internal resistance, which is the internal resistance of the secondary battery 14 in a predetermined absolute SOC, and a state in which the secondary battery 14 is fully charged or nearly fully charged (for example, the absolute SOC is 90%) It has been found that the ratio of the internal resistance to the second internal resistance (first internal resistance / second internal resistance = Imp_rate) has the relationship shown in FIG. 4 regardless of the SOH with respect to the relative SOC. More specifically, FIG. 4 shows the relationship between the relative SOC of the five secondary batteries (Nos. 1 to 5) of the same type and different SOH values and the above-described Imp_rate. As shown in this figure, regardless of the SOH, Imp_rate approaches 1.0 when the relative SOC approaches 100%, and Imp_rate increases when the relative SOC decreases.

FIG. 5 shows a value obtained by subtracting the second internal resistance from the first internal resistance divided by the first internal resistance ((first internal resistance−second internal resistance) / first internal resistance = Imp_inc_rate). It is a figure which shows the relationship between and relative SOC. As shown in FIG. 5, the relative SOC and Imp_inc_rate approach 0 when the relative SOC approaches 100%, and the value of Imp_inc_rate increases as the relative SOC decreases, and the correlation coefficient R ² = 0.9784, indicating that a strong negative correlation exists.

As described above, since there is a negative correlation between the relative SOC and the Imp_rate or Imp_inc_rate in a predetermined absolute SOC regardless of the value of SOH, Imp_rate or Imp_inc_rate has a lower SOH for the same absolute SOC. It increases. FIG. 6 is a diagram showing the relationship between Imp_rate and SOH when the absolute SOC is 80%. The right graph shows a part of the left graph in an enlarged manner. As shown in this figure, an increase in Imp_rate indicates a decrease in SOH. As shown in the graph on the left side of FIG. 6, the relationship between Imp_rate and SOH can be approximated by a quadratic expression (y = 4009.6x ² −9014.8x + 5092.2), and the correlation coefficient R ² = 0. 9793. As shown in the graph on the right side of FIG. 6, when Imp_rate is smaller than 1.1, it can be approximated by a linear expression (y = −392.46x + 457.46), and the correlation coefficient R ² = 0. .975.

FIG. 7 is a diagram showing the relationship between Imp_inc_rate and SOH when the absolute SOC is 80%. The right graph shows a part of the left graph in an enlarged manner. As shown in this figure, an increase in Imp_inc_rate indicates a decrease in SOH. Further, as shown in the graph on the left side of FIG. 7, the relationship between Imp_inc_rate and SOH can be approximated by a quadratic expression (y = 5371.9x ² -1201x + 92.479), and the correlation coefficient R ² = 0. 9777. Further, as shown in the graph on the right side of FIG. 7, when Imp_inc_rate is smaller than 0.09, it can be approximated by a linear expression (y = −454.51x + 67.211), and the correlation coefficient R ² = 0. 9752.

  FIG. 8 is a diagram illustrating the relationship between Imp_rate and SOH when the absolute SOC is 80% and 60%. In this figure, the graph on the right side shows an enlarged part of the graph on the left side. As shown in this figure, there is a positive correlation between Imp_rate and SOH in both cases where the absolute SOC is 80% and 60%. As shown on the left side of the figure, when approximated by a quadratic equation, the correlation coefficient between Imp_rate and SOH is 0.9793 at 80% and 0.9203 at 60%. Also, as shown on the right side of the figure, when approximated by a linear expression, the correlation coefficient between Imp_rate and SOH is 0.975 at 80% and 0.8936 at 60%. From the comparison of FIG. 8, the correlation coefficient between Imp_rate and SOH increases as the absolute SOC increases. According to the experiment by the present inventor, it has been found that if the absolute SOC is 60% or more, these correlation coefficients are sufficiently large and the SOH can be estimated with high accuracy. Although not shown in the figure, a similar relationship exists between Imp_inc_rate and SOH. Therefore, in the present embodiment, the absolute SOC is obtained, and when the absolute SOC is 60% or more, for example, the SOH is estimated based on Imp_rate or Imp_inc_rate and the relationship between SOH (the relationship shown in FIGS. 6 and 7). .

  As described above, when the absolute SOC is the same, a certain relationship is established between SOH and Imp_rate or Imp_inc_rate. Therefore, in the present embodiment, information indicating this relationship is stored for each representative absolute SOC, and first, the absolute SOC of the secondary battery 14 is measured, and the above-described relationship corresponding to the measured absolute SOC is shown. Information is acquired, and SOH is estimated based on this information. More specifically, the relationship between SOH and Imp_rate or Imp_inc_rate is shown, for example, a linear expression is stored, the absolute SOC is in a predetermined range (for example, 60% or more), and Imp_rate or Imp_inc_rate is a range in which the primary expression is applicable. If this is the case, SOH is estimated using this linear equation. On the other hand, when the absolute SOC does not fall within the predetermined range, or when Imp_rate or Imp_inc_rate does not fall within the range where the primary expression can be applied, an expression (or illustration) showing the relationship between the relative SOC and Imp_rate shown in FIG. The relative SOC is calculated based on the relationship between the relative SOC and Imp_inc_rate that is not performed), and the SOH is estimated by the following equation (3).

  SOH = DOD / ((100−relative SOC) × 0.01) (3)

  According to such processing, when the absolute SOC belongs to a predetermined range, SOH can be accurately obtained from the relationship between Imp_rate or Imp_inc_rate and SOH.

  Next, the detailed operation of the embodiment of the present invention will be described with reference to the flowchart shown in FIG. The process of this flowchart is executed when the secondary battery 14 is in a fully charged state or close to that state (for example, a state in which the absolute SOC is 90%). Or depending on the use condition of a vehicle, it is performed for every fixed period (for example, once a month). When the processing of the flowchart shown in FIG. 10 is started, the following steps are executed.

  In step S10, the CPU 10a determines whether or not the battery is fully charged. If the battery is fully charged (step S10: Yes), the process proceeds to step S11. Otherwise (step S10: No), the process ends. . Specifically, the CPU 10a estimates an OCV (Open Circuit Voltage) at a reference temperature (for example, 25 ° C.), determines that the OCV is greater than a predetermined threshold, determines that the battery is fully charged, and proceeds to step S11. In addition, you may make it progress to step S11 not only in the case of a full charge but also in the state (for example, absolute SOC is 90% or more) near a full charge.

  In step S11, the CPU 10a measures the internal resistance of the secondary battery 14. More specifically, the CPU 10a controls the discharge circuit 15 to pulse discharge the secondary battery 14, reads changes in voltage and current at that time with the voltage sensor 11 and the current sensor 12, and calculates the internal resistance.

  In step S12, the CPU 10a corrects the internal resistance obtained in step S11 to a resistance value at the reference temperature. Specifically, the CPU 10a detects the temperature of the secondary battery 14 with the temperature sensor 13, and refers to a table showing the relationship between the temperature and the internal resistance stored in the parameter 10ca of the RAM 10c, and obtained in step S11. The value of the internal resistance is corrected to the value of the internal resistance at a reference temperature (for example, 25 ° C.).

  In step S13, the CPU 10a stores the internal resistance corrected in step S12 in the parameter 10ca of the RAM 10c as a second internal resistance (internally charged or close to it).

  In step S14, the CPU 10a measures the internal resistance at a predetermined timing. Specifically, the CPU 10a controls the discharge circuit 15 to cause the secondary battery 14 to perform pulse discharge when a predetermined period (for example, one month) has elapsed since it was determined to be fully charged. The voltage and current are detected by the voltage sensor 11 and the current sensor 12, and the internal resistance is calculated.

  In step S15, the CPU 10a corrects the value of the internal resistance measured in step S14 to the value of the internal resistance at the same reference temperature (for example, 25 ° C.) as in step S12 by the same process as in step S12.

  In step S16, the CPU 10a determines whether or not the absolute SOC is equal to or greater than a predetermined value. If the absolute SOC is equal to or greater than the predetermined value (step S16: Yes), the process proceeds to step S17. Otherwise (step S16: No). Proceed to step S22. Specifically, for example, when the absolute SOC is 60% or more, as will be described later, the SOH can be accurately estimated by linear approximation. In that case, the process proceeds to step S17, and otherwise In step S22 described later, the relative SOC is calculated from Imp_rate, and the SOH is calculated from the relative SOC and DOD. As a method for obtaining the absolute SOC, for example, the voltage of the secondary battery 14 when the vehicle is stopped, for example, the voltage relaxation behavior after charging / discharging as an exponential function as disclosed in JP-A-2005-43339, for example. As a result, it is estimated as the OCV in a state where the polarization is eliminated, and then the stable OCV is estimated by correcting the OCV with the stratified voltage estimated by the method disclosed in Japanese Patent Application Laid-Open No. 2009-300209. To do. The absolute SOC can be obtained from the obtained stable OCV based on the relationship between the OCV and the absolute SOC.

  In step S17, the CPU 10a determines whether or not the absolute SOC is within a predetermined range. If the absolute SOC is within the predetermined range (step S17: Yes), the process proceeds to step S19, and otherwise (step S17: No). Proceed to step S18. Specifically, information (information indicating the relationship between Imp_rate and SOH) corresponding to a plurality of representative values of the absolute SOC is stored as the parameter 10ca in the RAM 10c. As a plurality of representative values, for example, as shown in FIG. 11, information indicating the straight lines of FIGS. 7 and 8 when the absolute SOC is 60%, 70%, 80%, and 90% is stored as the parameter 10ca. . Then, the absolute SOC of the target secondary battery 14 is within a predetermined range centered on these representative absolute SOCs (SOCs indicated by bold lines in FIG. 11) (for example, a range of each representative absolute SOC plus or minus 3 in FIG. 11). (In the hatched area), the process proceeds to step S19, and otherwise, the process proceeds to step S17. For example, when the absolute SOC is 72%, it falls within the range of the representative absolute SOC 70% plus or minus 3, so the process proceeds to step S19, and when it is 74%, it does not fall within the range, the process proceeds to step S18.

  In step S18, the CPU 10a corrects the internal resistance to a resistance value corresponding to the representative absolute SOC. Specifically, when the absolute SOC described above is 74%, the internal resistance value is corrected to 80%, which is the upper representative absolute SOC. The reason why the value is corrected to a value corresponding to the representative absolute SOC that is one level higher is that the estimation accuracy increases as the absolute SOC increases. As a correction method, a graph or a relational expression indicating the relationship between the absolute SOC and the internal resistance when the secondary battery 14 is new is stored, and the value of the internal resistance is corrected based on the graph or the relational expression. Can do. Therefore, according to the processes in steps S16 to S18 described above, when the absolute SOC belongs to the hatched region shown in FIG. 11, the internal resistance is not corrected, and the representative curve indicated by the solid line is shown. Processing is performed based on information in the absolute SOC value. On the other hand, in the case of belonging to the white region in FIG. 11, the internal resistance at the representative value indicated by the wavy line is corrected, and the process is executed based on the information on the value of the representative absolute SOC indicated by the wavy line.

  In step S19, the CPU 10a calculates Imp_rate. Specifically, the temperature is corrected in step S15, and if necessary, the value of the first internal resistance corrected in step S18 is divided by the value of the second internal resistance stored in step S13, so that Imp_rate ( = First internal resistance / second internal resistance).

  In step S20, the CPU 10a determines whether Imp_rate is equal to or less than a predetermined threshold value Th1, and if it is equal to or less than the threshold value Th1 (step S20: Yes), the process proceeds to step S21, and otherwise (step S20: In No), it progresses to step S22. For example, when the absolute SOC is 80%, when Imp_rate is 1.1 or less, it can be approximated by a linear expression, so the process proceeds to step S21. Otherwise, the process proceeds to step S22. Since this threshold Th1 differs for each representative absolute SOC, a threshold Th1 can be prepared in advance for each representative absolute SOC, and determination can be made based on the prepared threshold Th1.

  In step S21, the CPU 10a calculates SOH by linear approximation of the corresponding absolute SOC. More specifically, the CPU 10a acquires information regarding the corresponding representative absolute SOC from the RAM 10c, and calculates SOH based on this information. For example, when the representative absolute SOC is 80%, the SOH can be calculated from the relationship between Imp_rate and SOH using the graph or the relational expression shown on the right side of FIG.

  In step S22, the CPU 10a calculates a relative SOC from Imp_rate, and calculates an SOH from the relative SOC and DOD. Specifically, the relative SOC is calculated from Imp_rate based on the graph shown in FIG. 9 or the formula shown in FIG. And SOH is calculated based on the following formula | equation (4).

SOH = DOD / (relative SOC / 100) (4)

  In step S23, the CPU 10a calculates a relative SOC. Specifically, the CPU 10a calculates the relative SOC based on the relationship shown in FIG. 4 or FIG. 9, for example.

  According to the above processing, when the correlation between Imp_rate and SOH is high, that is, when the absolute SOC is equal to or higher than a predetermined value and Imp_rate is equal to or lower than the predetermined value, SOH is calculated by linear approximation. It becomes possible to obtain SOH with high accuracy. Further, since SOH is obtained from the relationship shown in FIG. 9 in a range where linear approximation cannot be used, SOH can be calculated in a wide range. In addition, since the SOH can be accurately estimated in the high absolute SOC, it is not necessary to perform a deep discharge that deteriorates the secondary battery 14, and the discharge time is short, so that the convenience for the user is not impaired.

  Further, in the above processing, the case where the absolute SOC is 60% or more is set as a processing target for obtaining SOH. However, since the absolute SOC is in a range of 60% to 100% in a normal vehicle, the range is limited to such a range. This makes it possible to perform estimation within a range that matches the actual vehicle usage situation and to improve estimation accuracy. Further, by estimating the relative SOC in such a range, the relative SOC can be estimated with high accuracy.

  Further, in the above processing, as shown in FIG. 11, the predetermined range (the hatched range in the figure) closest to the representative absolute SOC is executed without correcting the internal resistance, and the range deviated therefrom Since the internal resistance is corrected (in the white range in the figure), SOH can be calculated efficiently with minimal processing.

(D) Description of Modified Embodiment The above embodiment is an example, and it is needless to say that the present invention is not limited to the case described above. For example, in the above embodiment, calculation and determination are performed using Imp_rate in the flowchart shown in FIG. 11, but Imp_inc_rate may be used instead of Imp_rate. Also by such a method, SOH can be calculated with high accuracy.

  In the above embodiment, the absolute SOC is 60% or more, but the range other than this may be the processing target. Specifically, it is possible to use a lower value or a higher value.

  Further, in the above embodiment, as shown in FIG. 11, as the representative absolute SOC, a value of 10 (step value) is used, but a representative absolute SOC of a step smaller than this is used, It is also possible to use a large step representative SOC.

  In the above embodiment, the relationship between SOH and Imp_rate or Imp_inc_rate is held as an expression or a graph, but may be held as information such as a table.

  In the above embodiment, only the relative SOC or SOH is obtained. For example, based on the obtained relative SOC or SOH, for example, the idling stop execution for stopping the idling of the engine 17 is controlled. You may make it do. Specifically, when it is determined that the relative SOC is higher than a predetermined threshold value, idling stop is executed, and when it is determined that the relative SOC is lower than the predetermined threshold value, idling stop is not executed. Also good. Further, when the relative SOC is approaching the above-described threshold value, for example, the operation of the load 19 may be stopped to prevent further consumption of the secondary battery 14. Furthermore, when SOH is smaller than a predetermined value, a message instructing to replace the secondary battery 14 may be displayed.

DESCRIPTION OF SYMBOLS 1 Secondary battery state detection apparatus 10 Control part 10a CPU (calculation means, estimation means)
10b ROM
10c RAM
10d Display unit 10e I / F
DESCRIPTION OF SYMBOLS 11 Voltage sensor 12 Current sensor 13 Temperature sensor 14 Secondary battery 15 Discharge circuit 16 Alternator 17 Engine 18 Starter motor 19 Load

Claims (8)

In the secondary battery state detection device for detecting the state of the secondary battery,
A first internal resistance that is an internal resistance of the secondary battery when an absolute SOC calculated based on an initial capacity of the secondary battery is within a predetermined range; and a state in which the secondary battery is fully charged or full A calculating means for calculating a ratio value related to the second internal resistance which is an internal resistance in a state close to charging;
Estimating means for estimating the SOH of the secondary battery based on the correlation between the value of the ratio calculated by the calculating means and SOH;
A secondary battery state detection device comprising:   The secondary battery state detection device according to claim 1, wherein the calculation unit calculates the value of the ratio by dividing the first internal resistance by the second internal resistance.   2. The secondary according to claim 1, wherein the calculation unit calculates the value of the ratio by dividing a difference between the first internal resistance and the second internal resistance by the first internal resistance. Battery state detection device.   4. The secondary battery state detection device according to claim 1, wherein the estimation unit estimates a relative SOC based on a ratio between a remaining capacity of the secondary battery and the SOH. 5.   The estimation means divides the value calculated by dividing the first internal resistance by the second internal resistance or the difference between the first internal resistance and the second internal resistance by the first internal resistance. The SOH is estimated based on a linear expression indicating a correlation between the ratio value and the SOH when each of the calculated values is smaller than a predetermined threshold value. 5. The secondary battery state detection device according to claim 4.   The estimation means has a correlation between the ratio value and the SOH for each of a plurality of representative values of the absolute SOC, and the value of the first internal resistance corresponds to any one of the representative values. The secondary battery state detection device according to any one of claims 1 to 5, wherein the correction is performed as follows.   When the absolute SOC is not within the predetermined range, the estimation means obtains a corresponding relative SOC from the relationship between the ratio value and the relative SOC, and a charge / discharge amount from the fully charged state to the relative SOC. 6. The secondary battery state detection device according to claim 1, wherein the SOH is obtained based on the relative SOC. 7. In the secondary battery state detection method for detecting the state of the secondary battery,
A first internal resistance that is an internal resistance of the secondary battery when an absolute SOC calculated based on an initial capacity of the secondary battery is within a predetermined range; and a state in which the secondary battery is fully charged or full A calculation step for calculating a value of a ratio related to a second internal resistance that is an internal resistance in a state close to charging;
An estimation step of estimating the SOH of the secondary battery based on the correlation between the value of the ratio calculated in the calculation step and SOH;
A secondary battery state detection method comprising:

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