JP2016099251A - Secondary battery state detection device and secondary battery state detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the charging rate of a secondary battery.SOLUTION: There is provided a secondary battery state detection device 1 that applies an open circuit voltage OCV of a secondary battery 14 to a predetermined linear function to obtain a charging rate SOC, the device including: storage means (RAM 10c) for storing information indicating the relationship between the inclination and intercept of the linear function obtained in advance; obtaining means (CPU 10a) for obtaining the inclination of the linear function on the basis of a voltage of the secondary battery and charge-discharge current; specification means (CPU 10a) for specifying an intercept corresponding to the inclination obtained by obtaining means in the storage means; measuring means (voltage sensor 11) for measuring an open circuit voltage of the secondary battery; and calculation means (CPU 10a) for applying the open circuit voltage measured by the measuring means to a linear function having the inclination obtained by the obtaining means and the intercept specified by the specification means to calculate a charging rate SOC.SELECTED DRAWING: Figure 1

Description

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

  In Patent Document 1, an open circuit voltage (OCV) at the time of discharging a secondary battery is measured, and based on a preset relationship between the OCV of the secondary battery and a charge rate SOC (State of Charge). Obtaining the SOC, charging the secondary battery based on the obtained SOC, and measuring the change in the OCV and the change in the SOC during a predetermined time when obtaining the SOC, A technique for correcting the relationship with the SOC is disclosed.

JP 2001-351698 A

  By the way, in the technique disclosed in Patent Document 1, when the SOC in an arbitrary OCV is unknown, the intercept cannot be estimated even if the slope of the linear function indicating the relationship between the OCV and the SOC can be estimated. There is a problem that the SOC of the secondary battery cannot be accurately estimated.

  An object of this invention is to provide the secondary battery detection apparatus and secondary battery state detection method which can detect the charging rate of a secondary battery correctly.

In order to solve the above-mentioned problem, the present invention provides a secondary battery state detecting device for obtaining a charging rate SOC by applying an open circuit voltage OCV of a secondary battery to a predetermined primary function, and a slope of the linear function obtained in advance. A storage means for storing information indicating the relationship between the intercept and the intercept, a seeking means for obtaining the slope of the linear function based on the voltage and charge / discharge current of the secondary battery, and the seeking means. The determining means for specifying the intercept corresponding to the slope from the storage means, the measuring means for measuring the open circuit voltage of the secondary battery, and the open circuit voltage measured by the measuring means And calculating means for calculating the charging rate SOC by applying to the linear function having the intercept determined by the specifying means and the intercept specified by the specifying means.
According to such a configuration, it is possible to accurately detect the charging rate of the secondary battery.

Further, according to the present invention, the obtaining means includes a difference value ΔSOC of the SOC obtained from a ratio of an integrated value of the charge / discharge current and a SOH indicating a dischargeable capacity at full charge within a predetermined period, and the predetermined period. The inclination is obtained from the ratio of the difference value ΔOCV between the OCV at the beginning and the OCV at the end.
According to such a configuration, the inclination can be accurately obtained with a small number of measurements.

In the invention, it is preferable that the predetermined period is a predetermined fixed period.
According to such a configuration, the inclination can be accurately obtained with a simple configuration by using the period as a reference.

Further, the present invention is characterized in that the predetermined period is a period in which the state of the secondary battery changes by a predetermined amount.
According to such a configuration, the inclination can be accurately obtained at an appropriate timing according to the state change of the secondary battery.

Further, the present invention is characterized in that the state of the secondary battery is SOC or OCV.
According to such a configuration, the inclination can be accurately obtained at an appropriate timing with any one of the state quantities of the secondary battery as an index.

Further, the present invention is characterized in that the predetermined period is a period within which ΔSOC is equal to or greater than a predetermined value and within a predetermined fixed period.
According to such a configuration, even if ΔSOC is equal to or greater than a predetermined value, it is possible to avoid affecting the calculation accuracy due to the predetermined period being long and the SOH changing.

The present invention also shows the relationship between the slope and intercept of the primary function obtained in advance in a secondary battery state detection method for obtaining the charging rate SOC by applying the open circuit voltage OCV of the secondary battery to a predetermined primary function. A storage step for storing information in a storage means, a obtaining step for obtaining an inclination of the linear function based on the voltage and charge / discharge current of the secondary battery, and the inclination obtained in the obtaining step. The identifying step for identifying the corresponding intercept from the storage means, the measuring step for measuring the open circuit voltage of the secondary battery, and the open circuit voltage measured by the measuring means are obtained in the obtaining step. And a calculation step of calculating the charging rate SOC by applying to the linear function having the output slope and the intercept specified by the specifying means.
According to such a method, it becomes possible to accurately detect the charging rate of the secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the secondary battery detection apparatus and secondary battery state detection method which can detect the charging rate of a secondary battery correctly.

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 which shows the relationship between E and F of the relational expression of SOC and OCV. It is a figure which shows the time change of the relationship between OCV and SOC. It is a figure which shows an example of the process performed in embodiment shown in FIG.

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

(A) Description of Configuration of Embodiment of the Present Invention FIG. 1 is a diagram showing 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, a temperature sensor 13, and a discharge circuit 15 as main components, and detects the state of the secondary battery 14. To do. 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, and is started by a starter motor 18 to drive driving wheels through a transmission to provide 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 10ba is executed and parameters 10ca such as a table or a mathematical expression described later. The communication unit 10d communicates with an ECU (Electronic Control Unit) that is a host device and notifies the host 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 of Embodiment Next, the operation of the embodiment of the present invention will be described with reference to the drawings. It is known that the following linear function is established between the open circuit voltage OCV and the charging rate SOC.

  SOC = E × OCV + F (1)

  Here, E is the slope and F is the intercept. The inventor of the present application measured a large number of secondary batteries of different types and states, and found that there is a relationship as shown in FIG. 3 between the slope E and the intercept F in the above-described equation (1). The horizontal axis in FIG. 3 indicates the inclination E, and the vertical axis indicates the intercept F. The inventor of the present application measured 270 secondary batteries having different manufacturers, initial capacities, deterioration states, etc., and plotted them as diamonds on the coordinate axes in FIG. It was found that there is a relationship indicated by a solid line and the contribution rate is 0.99989. That is, it became clear that the relationship shown in FIG. 3 is established between the slope E and the intercept F regardless of the type of the secondary battery 14.

  In the present embodiment, the slope E is obtained by actually measuring the secondary battery 14, and the intercept F corresponding to the slope E is obtained using the relationship shown in FIG. Then, by substituting the obtained slope E and intercept F into equation (1) and substituting the measured OCV into equation (1), the charging rate SOC of the secondary battery 14 can be accurately obtained. .

  Next, details of the operation of the present embodiment will be described. In the present embodiment, the CPU 10a refers to the output of the voltage sensor 11 when the secondary battery 14 is attached to the vehicle in the manufacturing process of the vehicle or when the secondary battery 14 is replaced at a maintenance shop or the like. Then, OCV1 which is the open circuit voltage of the secondary battery 14 is measured. In addition, the CPU 10a causes the discharge circuit 15 to pulse discharge the secondary battery 14 at a predetermined cycle, measures the voltage and current at that time with the voltage sensor 11 and the current sensor 12, and measures the internal impedance. When the measurement of the internal impedance is completed, the CPU 10a obtains SOH (State of Health) indicating the dischargeable capacity at the time of full charge of the secondary battery 14 based on the measured internal impedance. Note that other methods may be used for obtaining SOH.

  Next, the CPU 10 a obtains a time integration value ΔDOD of the current value flowing through the secondary battery 14. More specifically, the CPU 10a refers to the output of the current sensor 12, and obtains ΔDOD by integrating the output value over time. Next, the CPU 10 a refers to the output of the voltage sensor 11 and measures OCV <b> 2 that is the open circuit voltage of the secondary battery 14.

  Next, the CPU 10a obtains ΔSOC from ΔDOD and SOH by the following equation (2). Then, the CPU 10a continues to measure ΔDOD until ΔSOC becomes a predetermined value (for example, 20%) or more. When ΔSOC is equal to or greater than a predetermined value, the CPU 10a calculates the values of OCV2, F, and F by a process to be described later within a predetermined period (for example, several days to several months) since the previous estimation of SOH. If the predetermined period is exceeded, the above-described processing for calculating OCV1, SOH, ΔDOD, etc. is executed again. In addition, when a predetermined period has elapsed since the previous estimation of SOH, the values of OCV1, SOH, ΔDOD, etc. are calculated again because the SOH changes with the passage of time and the calculation result has an error. This is to prevent it from occurring.

  ΔSOC = ΔDOD / SOH (2)

  Next, CPU10a calculates | requires (DELTA) OCV from the OCV1 and OCV2 by the following formula | equation (3).

  ΔOCV = OCV1-OCV2 (3)

  Next, the CPU 10a substitutes ΔSOC obtained by the equation (2) and ΔOCV obtained by the equation (3) into the following equation (4) to obtain the slope E.

  E = ΔSOC / ΔOCV (4)

  When the inclination E is obtained, the CPU 10a refers to the graph shown in FIG. 3 and obtains an intercept F corresponding to the inclination E. When the slope E and the intercept F are obtained as described above, the slope E and the intercept F are substituted into the equation (1). By applying the measured OCV to the formula (1) thus obtained, the SOC at that time can be accurately obtained. In the present embodiment, since SOH is used as a constant value for calculation, it is preferable to set the above-described predetermined period to a period in which SOH does not change significantly.

  By the way, the values of the slope E and the intercept F in the equation (1) change as the secondary battery 14 deteriorates. For this reason, for example, when a predetermined time has elapsed or when the state of the secondary battery 14 has changed, the above-described processing is executed again, and the values of the slope E and the intercept F are newly obtained. As shown in FIG. 4, the solid line indicating the relationship between the OCV and the SOC at a certain time changes as a one-dot chain line as time elapses. At this time, when ΔOCV is the same, ΔSOC is ΔSOC1 in the solid line and ΔSOC2 in the one-dot chain line. Therefore, the equation (1) obtained from these results is SOC = E × OCV + F in the solid line, and SOC = E ′ × OCV + F ′ in the one-dot chain line. Here, E ≠ E ′ and F ≠ F ′. Thus, by obtaining again the inclination E and the intercept F according to the change in the state of the secondary battery 14, the equation (1) according to the state change of the secondary battery 14 is obtained, and the SOC is always obtained accurately. Can do.

  As described above, the slope E shown in Expression (1) is obtained by actual measurement, and the intercept F is obtained by applying the obtained slope E to the relationship shown in FIG. In addition, the SOC can be accurately obtained from the OCV by using the equation (1). Further, since the relationship shown in FIG. 3 is established regardless of the type of secondary battery 14 and changes over time, the SOC can be accurately obtained regardless of the secondary battery 14 used. . Further, when the state of the secondary battery 14 changes, the SOC can always be accurately obtained from the OCV by obtaining the slope E and the intercept F again.

  Next, an example of processing executed in the embodiment shown in FIGS. 1 and 2 will be described with reference to FIG. The processing shown in FIG. 5 is realized by the CPU 10a reading and executing the program 10ba stored in the ROM 10b shown in FIG. 5 is executed when the secondary battery 14 is mounted in the vehicle assembly process, or when the secondary battery 14 is replaced in a maintenance factory or the like. After that, for example, the process shown in FIG. 5 is executed at a predetermined cycle. When the process shown in FIG. 5 is started, the following steps are executed.

  In step S10, the CPU 10a refers to the output of the voltage sensor 11, obtains the open circuit voltage of the secondary battery 14, and sets the obtained open circuit voltage as OCV1. In addition, when not much time has passed since the charging / discharging of the secondary battery 14 is executed, the open circuit voltage cannot be accurately measured due to stratification, polarization, etc., so the engine 17 is stopped. It is desirable to measure the open circuit voltage after a predetermined time (for example, several hours) has passed.

  In step S11, the CPU 10a refers to the internal impedance obtained in step S14 and obtains the deterioration state SOH of the secondary battery 14. More specifically, for example, SOH can be obtained by referring to R_ohm, which is a conductive resistance and a liquid resistance. Of course, SOH may be obtained by other methods.

  In step S12, the CPU 10a obtains a time integration value ΔDOD of the charge / discharge current flowing through the secondary battery 14 within a predetermined period. In the present example, the current flowing through the secondary battery 14 within a predetermined period is detected by the current sensor 11 and time integration is performed.

  In step S13, the CPU 10a measures the elapsed time since the SOH estimation time. More specifically, the CPU 10a measures the time that has elapsed since the SOH was estimated in step S11.

  In step S14, the CPU 10a refers to the output of the voltage sensor 11, obtains the open circuit voltage of the secondary battery 14, and sets the obtained open circuit voltage as OCV2. Note that it is desirable to measure the voltage after a predetermined time (for example, several hours) has passed since the engine 17 was stopped, as described in step S10.

  In step S15, the CPU 10a substitutes ΔDOD obtained in step S12 and SOH obtained in step S11 into the equation (2), and sets the obtained value as ΔSOC.

  In step S16, the CPU 10a determines whether or not ΔSOC is equal to or greater than a predetermined threshold value. If it is determined that ΔSOC is equal to or greater than the predetermined threshold value (step S16: Yes), the process proceeds to step S17. In the case (step S16: No), the process returns to step S12 and the same process as described above is repeated. For example, when ΔSOC is 20% or more, it is determined as Yes and the process proceeds to step S17. Note that 20% is an example, and other values may be used.

  In step S17, the CPU 10a determines whether or not it is within a predetermined period from the previous estimation of SOH. If it is determined that it is within the predetermined period (step S17: Yes), the process proceeds to step S18. In other cases (step S17: No), the process returns to step S10 and the same processing as described above is repeated. More specifically, for example, when several days to several months have passed since the previous SOH was estimated, the determination is Yes and the process returns to step S10 to recalculate the values such as SOH. The reason for executing such processing is that when the predetermined period is exceeded, the value of SOH may be changed, and in this case, an error is caused in the calculation result. That is, in this embodiment, since SOH is used as a constant value for calculation, SOH may change and cause an error in the calculation result when a predetermined period is exceeded. Calculate the value of again.

  In step S18, the CPU 10a substitutes the OCV1 obtained in step S10 and the OCV2 obtained in step S14 into the equation (3), and sets the obtained value as ΔOCV.

  In step S19, the CPU 10a substitutes ΔSOC obtained in step S15 and ΔOCV obtained in step S18 into the equation (4), and sets the obtained value as the slope E.

  In step S20, the CPU 10a obtains an intercept F corresponding to the inclination E obtained in step S19 from the relationship shown in FIG. More specifically, a table storing a numerical value corresponding to the relationship shown in FIG. 3 or a relational expression indicating the relationship is stored as the parameter 10ca of the RAM 10c, and the CPU 10a stores the intercept corresponding to the slope E obtained in step S19. F is obtained from a table or a relational expression.

  In step S21, the CPU 10a can obtain an equation indicating the relationship between OCV and SOC by substituting the slope E obtained in step S19 and the intercept F obtained in step S20 into equation (1). By substituting the OCV obtained by the measurement into the equation (1) thus obtained, the SOC at that time can be accurately estimated.

  As described above, in the embodiment of the present invention, the slope E of the equation (1) indicating the relationship between the OCV and the SOC is obtained by actual measurement, and the intercept F based on the relation between the slope E and the intercept F shown in FIG. I asked for. For this reason, SOC can be calculated | required correctly.

  In the embodiment of the present invention, the relationship shown in FIG. 3 is unchanged regardless of the type and state of the secondary battery 14, and therefore, the formula (1) The inclination E and the intercept F can be accurately obtained.

(C) Description of Modified Embodiment It goes without saying that the above embodiment is merely an example, and the present invention is not limited to the case described above. For example, in the above embodiment, in the process of step S16, the process proceeds to step S18 when ΔSOC is equal to or greater than a predetermined value. However, for example, when ΔOCV exceeds a predetermined threshold, the process proceeds to step S18. You may make it go. According to such a method, two different points of data can be reliably acquired.

  In step S11, SOH is obtained from the internal impedance of secondary battery 14. However, SOH may be obtained by other methods.

  In step S19, the slope E is directly obtained. However, for example, a new value of the slope E may be estimated from a temporal change of the slope E obtained in the past.

  In step S20, the intercept F is obtained based on the mathematical formula. However, the relationship between the slope E and the intercept F may be stored as a table, and the intercept F may be obtained based on this table.

  In addition, as a frequency of executing the processing shown in FIG. 5, for example, when the SOH changes by a predetermined threshold or more, when the liquid reduction amount becomes a predetermined threshold or more, or the integrated temperature becomes a predetermined threshold or more. In such a case, the process may be executed to update the slope E and the intercept F. According to such a configuration, the SOC can be constantly and correctly obtained by updating the slope E and the intercept F at the timing when the state of the secondary battery 14 changes.

  Moreover, in the above embodiment, although the temperature of the secondary battery 14 is not mentioned, the temperature of the secondary battery 14 is estimated from the output of the temperature sensor 13, and the secondary battery 14 of the secondary battery 14 is estimated based on the estimated temperature. The parameter may be corrected. According to such a configuration, the SOC can be obtained correctly regardless of the environmental temperature.

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

Claims (7)

In the secondary battery state detection device for obtaining the charging rate SOC by applying the open circuit voltage OCV of the secondary battery to a predetermined linear function,
Storage means for storing information indicating the relationship between the slope and intercept of the linear function obtained in advance;
Obtaining means for obtaining the slope of the linear function based on the voltage and charge / discharge current of the secondary battery;
Identifying means for identifying the intercept corresponding to the inclination obtained by the obtaining means from the storage means;
Measuring means for measuring an open circuit voltage of the secondary battery;
A calculating means for calculating the charging rate SOC by applying the open circuit voltage measured by the measuring means to the linear function having the slope obtained by the obtaining means and the intercept specified by the specifying means. When,
A secondary battery state detection device comprising:   The obtaining means includes an SOC difference value ΔSOC obtained from a ratio of an integrated value of the charge / discharge current within a predetermined period and SOH indicating a dischargeable capacity at full charge, an OCV at the start of the predetermined period, and an end of the predetermined period The secondary battery state detection device according to claim 1, wherein the inclination is obtained from a ratio with a difference value ΔOCV of the OCV.   The secondary battery state detection apparatus according to claim 2, wherein the predetermined period is a predetermined fixed period.   The secondary battery state detection device according to claim 2, wherein the predetermined period is a period in which the state of the secondary battery changes by a predetermined amount.   The secondary battery state detection device according to claim 4, wherein the state of the secondary battery is SOC or OCV.   6. The secondary battery state detection apparatus according to claim 5, wherein the predetermined period is a period within which ΔSOC is equal to or greater than a predetermined value and is within a predetermined fixed period. In the secondary battery state detection method for obtaining the charging rate SOC by applying the open circuit voltage OCV of the secondary battery to a predetermined linear function,
A storage step of storing in a storage means information indicating a relationship between the slope of the linear function obtained in advance and an intercept;
Obtaining a slope of the linear function based on the voltage and charge / discharge current of the secondary battery;
A specifying step of specifying, from the storage means, the intercept corresponding to the inclination obtained in the obtaining step;
A measuring step of measuring an open circuit voltage of the secondary battery;
A calculating step of calculating a charging rate SOC by applying the open circuit voltage measured by the measuring means to the linear function having the slope obtained in the obtaining step and the intercept specified by the specifying means; ,
A secondary battery state detection method comprising:

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