POWER STORAGE DEVICE AND TEMPERATURE ESTIMATION METHOD

Abstract

The energy storage device (10) includes an energy storage element (11) and a management unit (2) that measures the voltage of the energy storage element and manages the energy storage element. The management unit measures the voltage of the energy storage element while a direct current flows through the energy storage element, calculates the internal resistance of the energy storage element by a direct current resistance measurement method using the measured voltage, and estimates the amount of heat generated in the energy storage element based on the internal resistance and a current flow profile.

Description

[Technical field]

[0001] The present invention relates to an energy storage device and a temperature estimation method for estimating the temperature of an energy storage element. [Background technology]

[0002] Energy storage devices are widely used in uninterruptible power supplies, DC or AC power supplies included in stabilized power supplies, etc. The use of energy storage devices in large-scale systems that store generated power is also expanding. Typically, a storage system is configured by connecting multiple energy storage devices in series or in series-parallel.

[0003] When a large current flows through an energy storage element or when the energy storage element is exposed to a high-temperature environment, the temperature of the energy storage element increases. In a high-temperature state, the deterioration of the energy storage element is accelerated. For example, the capacity of the energy storage element when fully charged decreases. In order to operate the energy storage element stably, the state of the energy storage element, such as the current, voltage, or temperature, is monitored.

[0004] The current and voltage of the storage element can be detected relatively easily using a current sensor and a voltage sensor. However, it is difficult to detect the internal temperature or heat generation of the storage element. Conventionally, for example, the external temperature of the storage element is measured using a temperature sensor such as a thermistor arranged near the storage element, and the measured temperature is used to control the storage element.

[0005] Patent Document 1 discloses a method for estimating the temperature of an energy storage element. Specifically, the amount of heat generated inside the energy storage element is calculated at predetermined time intervals using an internal resistance map showing the relationship between the internal resistance of the energy storage element obtained using an AC impedance method, the duration since the start of charging / discharging, the SOC (State of Charge) of the energy storage element, and the temperature of the energy storage element. The energy storage element is cooled by a cooling device based on the estimated temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-101884 A Summary of the Invention [Problem to be solved by the invention]

[0007] In practice, electric storage elements are often charged and discharged with direct current. In the AC impedance method described in Patent Document 1, it is difficult to accurately grasp the value of reaction resistance or diffusion resistance, and it is expected to be difficult to obtain the internal resistance of an electric storage element when it is charged and discharged with direct current. When an internal resistance map created in advance by an experiment is used, the estimation error of the heat generation amount increases due to a difference between the conditions during the experiment (for example, the duration from the start of charging and discharging) and the conditions during actual use. In addition, the relationship between the internal resistance of the electric storage element, the duration from the start of charging and discharging, the SOC, and the temperature of the electric storage element changes with the deterioration of the electric storage element. It is difficult to create a precise internal resistance map that takes into account the deterioration of the electric storage element. Therefore, it is difficult to estimate the temperature of an electric storage element during actual use by the method described in Patent Document 1.

[0008] Furthermore, the AC impedance method requires one measuring device for each energy storage element, making it difficult to apply the technology described in Patent Document 1 to an energy storage device or energy storage system including multiple energy storage elements to estimate the temperature of each energy storage element.

[0009] An object of the present invention is to provide an energy storage device and a temperature estimation method that can easily estimate the temperature of an energy storage element. [Means for solving the problem]

[0010] An energy storage device according to one aspect of the present invention includes an energy storage element and a management unit that measures the voltage of the energy storage element and manages the energy storage element, the management unit measuring the voltage of the energy storage element while a direct current flows through the energy storage element, calculating the internal resistance of the energy storage element using a DC resistance measurement method that uses the measured voltage, and estimating the amount of heat generated in the energy storage element based on the internal resistance and a current flow profile.

[0011] A temperature estimation method according to one aspect of the present invention is a method for estimating the temperature of an energy storage element, which includes measuring a voltage of the energy storage element while a direct current flows through the energy storage element, calculating an internal resistance of the energy storage element using a DC resistance measurement method using the measured voltage, estimating the amount of heat generated in the energy storage element based on the internal resistance and a current profile, and performing a thermal conduction simulation based on the amount of heat generated, thereby estimating the temperature of the energy storage element. Effect of the Invention

[0012] With the above configuration, the internal resistance of the electric storage element charged and discharged by DC can be easily calculated, and the amount of heat generated in the electric storage element can be easily estimated. By using the predicted current profile, the temperature of the electric storage element in the future (for example, several seconds or several minutes later) can also be estimated. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an example of the appearance of a storage cell; [Diagram 2] 1 is a schematic diagram showing an example of the appearance of a power storage module; [Diagram 3] 1 is a block diagram showing an example of a functional configuration of a power storage module according to a first embodiment. [Figure 4] 4 is a block diagram showing an example of a functional configuration of a current measuring unit and a voltage measuring unit according to the first embodiment. FIG. [Diagram 5] 3 is a schematic diagram showing an example of the stored contents of a storage unit according to the first embodiment. FIG. [Figure 6] 5 is a flowchart showing a procedure of a process for estimating a temperature of a power storage cell executed by a BMU according to the first embodiment. [Figure 7] FIG. 11 is a block diagram showing an example of a functional configuration of a current measuring unit and a voltage measuring unit according to a second embodiment. [Figure 8] 10 is a flowchart showing the procedure of a process for estimating the temperature of a power storage cell executed by a BMU according to a second embodiment. [Figure 9] FIG. 11 is a block diagram showing an example of a functional configuration of a power storage module and a battery management device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The energy storage device includes an energy storage element and a management unit that measures the voltage of the energy storage element and manages the energy storage element, and the management unit measures the voltage of the energy storage element while a direct current flows through the energy storage element, calculates the internal resistance of the energy storage element using a DC resistance measurement method that uses the measured voltage, and estimates the amount of heat generated in the energy storage element based on the internal resistance and a current flow profile.

[0015] The energy storage device includes an energy storage element and a management unit. The management unit measures the voltage of the energy storage element in a state where a direct current flows through the energy storage element, and calculates the internal resistance of the energy storage element by a direct current resistance measurement method. By using the direct current resistance measurement method instead of the alternating current impedance method, the management unit can easily and accurately calculate the internal resistance of the energy storage element, which is often charged and discharged with direct current. In addition, the management unit estimates the amount of heat generated in the energy storage element based on the internal resistance and the current profile. The internal resistance obtained by the direct current resistance measurement method is a direct current resistance. In many cases, the energy storage element is charged and discharged with direct current, so the heat generation factor of the energy storage element is almost limited to the direct current resistance. Therefore, the amount of heat generated in the energy storage element can be accurately estimated using the internal resistance of the energy storage element calculated by the direct current resistance measurement method.

[0016] The power storage device may use a predicted current supply profile as the current supply profile to estimate a future amount of heat generation in the power storage element. In the past, in situ estimation of the near future heat generation amount of an energy storage element has not been sufficiently considered. In particular, there was room for improvement in sequential estimation of the heat generation amount based on the internal resistance of the energy storage element, without relying on the external temperature of the energy storage element measured by a temperature sensor. By estimating the near future heat generation amount using the internal resistance calculated by a DC resistance measurement method in a management unit provided in the energy storage device, it is possible to suppress deterioration of the energy storage element or to fully utilize the performance of the energy storage element.

[0017] The management unit may measure a current flowing through the energy storage element while a direct current flows through the energy storage element, and calculate an internal resistance of the energy storage element based on an electromotive force of the energy storage element obtained according to the SOC of the energy storage element, the measured current, and the measured voltage. The internal resistance of the energy storage element can be obtained by a simple calculation using the current and voltage measured while a direct current flows through the energy storage element, and the electromotive force of the energy storage element.

[0018] It is preferable to calculate the internal resistance for each of the multiple storage elements (storage cells) connected in series to one current measuring unit based on the electromotive force according to the SOC, the measured current, and the measured voltage of the storage element. Such calculations can be realized by hardware that is normally included in a typical storage device (storage module) (no additional hardware is required for the storage device).

[0019] The management unit may have a current source connected in parallel to the energy storage element, measure a first voltage of the energy storage element when the current source applies a first DC current to the energy storage element while a DC current flows through the energy storage element, measure a second voltage of the energy storage element when the current source applies a second DC current having a value different from the first DC current to the energy storage element while a DC current flows through the energy storage element, and calculate an internal resistance of the energy storage element based on the first voltage and the second voltage. By using a current source, the internal resistance of the energy storage element can be obtained based on the first voltage and the second voltage without using the electromotive force of the energy storage element and the current flowing through the energy storage element.

[0020] The management unit may estimate the temperature of the energy storage element by performing a simulation of heat conduction based on the amount of heat generated. The temperature of the energy storage element can be easily and accurately estimated using the amount of heat generated in the energy storage element that is accurately estimated.

[0021] The management unit may have a memory unit that stores a program and a calculation unit that performs calculations based on the program, and the memory unit may store a program for a real-time OS (Operating System) and a program that operates on the real-time OS to calculate the internal resistance, estimate the amount of heat generated, and estimate the temperature. By using a real-time OS, the management unit can execute processing with high responsiveness. Therefore, the management unit can estimate the future temperature of the energy storage element at high speed. If the responsiveness is sufficient, the management unit does not need to use a real-time OS.

[0022] The management unit may estimate a future heat generation amount of the energy storage element by calculating a heat generation amount using the future current according to the predicted current flow profile and the internal resistance. The future heat generation amount of the energy storage element can be accurately estimated using the internal resistance of the energy storage element calculated by a DC resistance measurement method and the future current according to the current flow profile.

[0023] The management unit may estimate a plurality of heat values ​​based on a plurality of predicted current distribution profiles. The management unit can estimate a plurality of temperatures according to the plurality of heat values. It is possible to estimate the temperature of the energy storage element without narrowing down the current distribution profile to one.

[0024] The electric storage element may be a reused product (recycled product). Even if the electric storage element is a reused product, the internal resistance of the electric storage element can be easily and accurately calculated by the same method, and the temperature of the electric storage element can be easily and accurately estimated. By correctly grasping the internal resistance and temperature of the reused electric storage element, the electric storage element can be appropriately controlled.

[0025] The temperature estimation method is a method for estimating the temperature of an energy storage element, which includes measuring the voltage of the energy storage element while a direct current flows through the energy storage element, calculating the internal resistance of the energy storage element by a direct current resistance measurement method using the measured voltage, estimating the amount of heat generated in the energy storage element based on the internal resistance and a current profile, and simulating heat conduction based on the amount of heat generated, thereby estimating the temperature of the energy storage element. By using the direct current resistance measurement method, the internal resistance of an energy storage element that is charged and discharged by direct current can be easily and accurately calculated. Therefore, the amount of heat generated in the energy storage element can be easily and accurately estimated, and the temperature of the energy storage element can be easily and accurately estimated.

[0026] Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof. (Embodiment 1) FIG. 1 is a schematic diagram showing an example of the appearance of a storage cell 11. The storage cell 11 corresponds to a storage element. The storage cell 11 is a secondary battery such as a lithium ion battery. The storage cell 11 has a prismatic shape. The storage cell 11 includes a case 111 having a rectangular parallelepiped shape, a positive terminal 112, and a negative terminal 113. A positive electrode, a negative electrode, a separator, and an electrolyte (electrolytic solution) are accommodated inside the case 111. The separator is interposed between the positive electrode and the negative electrode. For example, the positive electrode, the negative electrode, and the separator are in the form of sheets, and are accommodated in the case 111 as an electrode body obtained by stacking and rolling them. The electrode body is not limited to a rolled type, and may be a laminated type. The positive electrode is connected to the positive terminal 112, and the negative electrode is connected to the negative terminal 113. The direction in which the length of the storage cell 11 is shortest is defined as the thickness direction. The shape of the storage cell 11 may be a shape other than a rectangular parallelepiped, and may be a pouch shape or a cylindrical shape.

[0027] FIG. 2 is a schematic diagram showing an example of the appearance of the energy storage module 10. The energy storage module 10 corresponds to an energy storage device. The energy storage module 10 includes a plurality of energy storage cells 11 connected in series and / or parallel. The energy storage module 10 includes a rectangular parallelepiped housing 12, which is an example of a holding member. The plurality of energy storage cells 11 are arranged in the thickness direction and held (stored) in the housing 12. Alternatively, the holding member may be formed of a pair of end plates and a plurality of fastening bars connecting the end plates. The plurality of energy storage cells 11 are connected in series and / or parallel by a bus bar (not shown).

[0028] Furthermore, the power storage module 10 includes a BMU (Battery Management Unit) 2. The BMU 2 corresponds to a management section. In FIG. 2, the BMU 2 is indicated by a dashed line. The BMU 2 has a configuration in which various components are arranged on a board. The BMU 2 manages the power storage cells 11 included in the power storage module 10. Specifically, the BMU 2 calculates the SOC of the power storage cells 11 by a current integration method. The SOC is expressed as a ratio of the amount of electricity charged in the power storage cells 11 to the full charge capacity of the power storage cells 11. The BMU 2 also performs a process of estimating the temperature of the power storage cells 11.

[0029] 3 is a block diagram showing an example of a functional configuration of the power storage module 10 according to the first embodiment. In the power storage module 10, for example, a plurality of power storage cells 11 are connected in series. The BMU 2 includes a calculation unit 21, a memory 22, a storage unit 23, a current measurement unit 24, a voltage measurement unit 25, and a temperature measurement unit 26. The calculation unit 21 is, for example, a CPU (Central Processing Unit). The memory 22 stores information required for calculation in the calculation unit 21. The storage unit 23 is non-volatile and stores programs and data. The calculation unit 21 executes processing according to the program stored in the storage unit 23. For example, the storage unit 23 is a non-volatile semiconductor memory. The temperature measurement unit 26 measures the temperature outside the power storage module 10 using a temperature sensor.

[0030] 4 is a block diagram showing an example of a functional configuration of the current measurement unit 24 and the voltage measurement unit 25 according to the embodiment 1. The current measurement unit 24 includes a shunt resistor 241 connected in series to the multiple storage cells 11 connected in series, and a voltmeter 242 that measures the voltage across the shunt resistor 241. The voltmeter 242 is connected to the calculation unit 21.

[0031] When a direct current flows through the multiple storage cells 11 connected in series, the same current I flows through the shunt resistor 241 as through the multiple storage cells 11. The voltmeter 242 measures the voltage V across the shunt resistor 241. S Measure the measured voltage V S The value of R is input to the calculation unit 21. s The value of is stored in advance in the storage unit 23. The calculation unit 21 calculates the resistance R s is read from the storage unit 23, and the voltage V S Using this, I=V S / R s The current I is calculated by performing the above calculation. In this way, when a direct current flows through a plurality of storage cells 11 connected in series, the BMU 2 uses the current measurement unit 24 to measure the current I flowing through the plurality of storage cells 11. When a plurality of sets of storage cells 11 are connected in parallel to each other in the storage module 10, one shunt resistor 241 is connected in series to the storage cells 11 of each set.

[0032] The voltage measurement unit 25 includes a voltmeter 251 connected to both ends of each storage cell 11. Each voltmeter 251 is connected to the calculation unit 21. The voltmeter 251 measures the voltage across each storage cell 11, and inputs the measured voltage value to the calculation unit 21. In this manner, the BMU 2 measures the voltage of each storage cell 11 using the voltage measurement unit 25.

[0033] 4 shows an equivalent circuit of the storage cell 11. The storage cell 11 is represented by an equivalent circuit in which an electromotive force 114 and an internal resistance 115 are connected in series. The value of the internal resistance 115 is R0, the value of the electromotive force 114 is E0, the voltage measured by the voltmeter 251 is V, and the current flowing through the storage cell 11 is I. The value R0 of the internal resistance 115 is calculated by R0=(V-E0) / I. The calculated value R0 of the internal resistance 115 is the DC resistance of the storage cell 11.

[0034] 5 is a schematic diagram showing an example of the contents stored in the storage unit 23 according to the first embodiment. The storage unit 23 stores an OS program 231, which is a program for a real-time OS (Operating System), and a calculation program 232, which is a program for performing various calculations. The calculation unit 21 realizes the real-time OS by executing processing in accordance with the OS program 231. The calculation program 232 runs on the real-time OS. In accordance with the calculation program 232, the calculation unit 21 performs calculations of the SOC of the power storage cell 11 by a current integration method, calculations of the internal resistance of the power storage cell 11, calculations for estimating the amount of heat generated in the power storage cell 11, and calculations for estimating the temperature of the power storage cell 11.

[0035] The storage unit 23 stores characteristic data 233 including information indicating various characteristics of the power storage module 10, which is necessary for performing various calculations. For example, the characteristic data 233 includes the resistance R s and includes the thermal conductivity, specific heat, density, and heat transfer coefficient to the outside of each portion of the power storage module 10. The characteristic data 233 also includes an SOC-OCV curve that indicates the correlation between the SOC and OCV (Open Circuit Voltage) of the power storage cell 11. Information included in the characteristic data 233 is specified in advance and stored in the storage unit 23. The storage unit 23 stores history data 234 that includes a history of measured values ​​and calculated values. The history data 234 includes, for example, a history of measured current and voltage, and a history of calculated SOC. The values ​​included in the history data 234 are obtained by processing of the BMU2, and are stored in the storage unit 23 in sequence.

[0036] Next, the process executed by the BMU 2 will be described. The BMU 2 calculates the SOC of each storage cell 11 by a current integration method. More specifically, the calculation unit 21 calculates the current flowing through each storage cell 11 based on the measurement result of the current measurement unit 24, and calculates the SOC by successively integrating the calculated current according to the calculation program 232. The calculation unit 21 repeats the SOC calculation, and stores the calculated SOC in the memory unit 23.

[0037] The BMU 2 performs a process of estimating the temperature of each storage cell 11 as needed. FIG. 6 is a flowchart showing the procedure of the process for estimating the temperature of the storage cell 11 performed by the BMU 2 according to the first embodiment. The calculation unit 21 performs the following process according to the calculation program 232. Hereinafter, steps are abbreviated as S. When the energy storage module 10 performs charging / discharging, a direct current flows through the energy storage cell 11. The calculation unit 21 measures the current flowing through the energy storage cell 11 and the voltage of the energy storage cell 11 in a state in which a direct current flows through each storage cell 11 (S11). In S11, as described above, when a direct current flows through the energy storage cell 11 due to charging / discharging of the energy storage module 10, the calculation unit 21 calculates the current I flowing through the energy storage cell 11 using the measurement result of the current measurement unit 24. Furthermore, when a direct current flows through the energy storage cell 11, the calculation unit 21 acquires the voltage V of the energy storage cell 11 by receiving the value of the voltage measured by the voltage measurement unit 25.

[0038] The calculation unit 21 then calculates the value of the electromotive force 114 of each storage cell 11 (S12). The SOC-OCV curve represents a one-to-one correlation between the SOC and the OCV. When the SOC of the storage cell 11 is known, the OCV of the storage cell 11 is obtained according to the SOC-OCV curve. The OCV of the storage cell 11 is approximately equal to the value of the electromotive force 114 of the storage cell 11. The SOC-OCV curve specified in advance for each storage cell 11 may be stored in the storage unit 23, or an average SOC-OCV curve may be stored in the storage unit 23. In S12, the calculation unit 21 reads out the latest SOC and SOC-OCV curve of each storage cell 11 from the storage unit 23, and specifies the OCV corresponding to the SOC according to the SOC-OCV curve. The calculation unit 21 sets the identified OCV for each storage cell 11 as the value E0 of the electromotive force 114.

[0039] The calculation unit 21 then calculates the value of the internal resistance 115 of each of the storage cells 11 (S13). In S13, the BMU 2 calculates the internal resistance by a DC resistance method. Using the current I and voltage V measured in S11 with a DC current flowing through the storage cell 11, and the value E0 of the electromotive force 114 calculated in S12, the calculation unit 21 calculates R0 = (V - E0) / I to calculate the value R0 of the internal resistance 115 of each of the storage cells 11.

[0040] Thereafter, the calculation unit 21 performs a process of estimating the future temperature of the power storage cell 11 by calculating the future heat generation amount in the power storage cell 11 using the value R0 of the internal resistance 115 and simulating the heat conduction in the power storage module 10. The value R0 of the internal resistance 115 calculated in S13 is the value of the internal resistance 115 at time t0. The calculation unit 21 performs a process of estimating the temperature of the power storage cell 11 t1 hours after time t0. The value of the time t1 is determined in advance and stored in the storage unit 23. The value of the time t1 may be changeable.

[0041] The calculation unit 21 calculates the amount of heat generated in each of the storage cells 11 (S14). The storage cells 11 generate heat due to activation overvoltage and ohmic overvoltage. The amount of heat generated due to activation overvoltage is denoted as Q react(unit: W), the current flowing through the storage cell 11 is I (unit: A), the activation overvoltage (unit: V) is η, and the reaction resistance is R react (The unit is ohms.) The heat generated by the activation overvoltage is Q react =Iη, and the activation overpotential is η=IR react The heat generated by ohmic overvoltage is expressed as Q ohm (unit: W), ohmic overvoltage (unit: V) ohm , ohmic resistance R ohm (The unit is ohms.) Heat generation due to ohmic overvoltage is Q ohm =IV ohm and ohmic overvoltage is V ohm =IR ohm It is expressed as:

[0042] From the equations for heat generation due to activation overvoltage and ohmic overvoltage, the activation overvoltage η and ohmic overvoltage V ohm Eliminating and, the total heat generation amount Q total (unit: W) is expressed by the following formula: Q total =Q react +Q ohm =I 2 (R react +R ohm )=I 2 R total R total is the total resistance, and is the same value as the value R0 of the internal resistance 115 obtained in S13. In other words, the amount of heat generated by the storage cell 11 can be calculated using only the current I flowing through the storage cell 11 and the value R0 of the internal resistance 115 of the storage cell 11.

[0043] In S14, the calculation unit 21 estimates the current I based on the predicted energization profile, and calculates Q=I using the estimated current I and the value R0 of the internal resistance 115 calculated in S13. 2By calculating R0, the heat generation amount Q of each storage cell 11 is calculated. When calculating the heat generation amount Q at time t0 in S14, the calculation unit 21 uses the current I measured in S11. When calculating the heat generation amount Q after time t0, the calculation unit 21 estimates the future current I according to the current flow profile, and calculates the heat generation amount Q using the estimated current I. As the predicted current flow profile, a predicted (assumed) specific current flow profile is used. For example, as the predicted current flow profile, the calculation unit 21 may continue to use the current I measured in S11, assuming a current flow profile in which the current is constant. Alternatively, the calculation unit 21 may calculate an average current within a predetermined time in the past based on the history of the current stored in the storage unit 23, and use the calculated average current as the current I. Alternatively, the calculation unit 21 may identify a maximum current within a predetermined time in the past, assume a current flow profile in which the maximum current flows, and use the maximum current as the current I. Alternatively, the calculation unit 21 may predict an energization profile by statistical calculation or machine learning based on the history of the current, and use the current I according to the predicted energization profile.

[0044] The calculation unit 21 then performs a simulation of heat conduction (S15). In S15, the calculation unit 21 performs a calculation to solve a heat conduction equation by numerical calculation using a predetermined method such as the finite element method, the finite volume method, or the finite difference method, thereby calculating the temperature at each part of the power storage module 10 after a predetermined time Δt. The heat conduction equation is expressed by the following formula (1).

[0045]

number

[0046] In equation (1), ρ is density (unit: kg / m 3 ), C p is the specific heat at constant pressure (unit: J / kg / K), T is the temperature (unit: K), t is the time (unit: s), k is the thermal conductivity (unit: W / m / K), and ∇ is the nabla. The calculation unit 21 calculates the thermal conductivity k and the specific heat at constant pressure C pThe calculation unit 21 uses values ​​stored in advance in the storage unit 23 as the heat transfer coefficient, density ρ, and heat transfer coefficient to the outside. The calculation unit 21 may use a different value for the thermal conductivity k depending on the direction of heat transfer. The calculation unit 21 also uses the outside temperature measured by the temperature measurement unit 26 as the outside air temperature required for the simulation. The calculation unit 21 calculates Q in formula (1) total The total heat generation amount calculated in S14 is Q total The calculation unit 21 uses the internal temperature of the power storage module 10 measured by the temperature measurement unit 26 as the temperature at each part of the power storage module 10 at time t0. The calculation unit 21 may perform a process of generating a model of the power storage module 10 required for numerical calculation, or may read and use a model of the power storage module 10 stored in advance in the storage unit 23. The same method can also be applied when the outside of the power storage module 10 is liquid-cooled by water cooling or the like. Also, Q total An entropy heat term (reversible reaction heat in which heat generation and absorption are reversed depending on the direction of charging and discharging) may be further added.

[0047] The calculation unit 21 then determines whether or not the temperature of each of the power storage cells 11 from time t0 to time t1 has been calculated by the process of S15 (S16). If the temperature from time t0 to time t1 has not yet been calculated (S16: NO), the calculation unit 21 returns the process to S14. By the processes of S14 and S15 which are executed next, the calculation unit 21 calculates the temperature at each part of the power storage module 10 from time Δt later. The calculation unit 21 repeats the processes of S14 to S16 until the temperature from time t0 to time t1 is obtained.

[0048] When the temperature of each storage cell 11 from time t0 to t1 has been calculated (S16: YES), the calculation unit 21 ends the process of estimating the temperature of the storage cell 11. By executing the processes of S11 to S16, the BMU 2 estimates the temperature of each storage cell 11 from time t0 to t1. The calculation unit 21 executes the processes of S11 to S16 so that the calculation process time required to calculate the temperature from time t0 to t1 is less than time t1.

[0049] The calculation unit 21 may perform a process of calculating a plurality of heat values ​​based on a plurality of current-flow profiles in S14, and calculating a plurality of temperatures based on the plurality of heat values ​​in S15. In this case, a plurality of estimated temperatures according to the plurality of current-flow profiles are obtained. The temperature of the power storage cell 11 can be estimated and calculated simultaneously without narrowing down the current-flow profile to one. The BMU 2 can appropriately adjust the temperature of the power storage cell 11 by comparing the plurality of estimated temperatures, selecting a current-flow profile that provides an appropriate temperature, and controlling the current according to the selected current-flow profile. The BMU 2 can also compare the plurality of estimated temperatures with the actual temperature measured by the temperature measurement unit 26, and select a current-flow profile that brings the estimated temperature closer to the actual temperature.

[0050] The BMU2 executes the processes of S11 to S16 as necessary, and controls the operation of the power storage module 10 based on the estimated temperature. For example, the BMU2 adjusts the temperature of the power storage cell 11 by adjusting the current flowing through the power storage cell 11 based on the estimated temperature. For example, the BMU2 adjusts the current flowing through the power storage cell 11 so that the temperature of the power storage cell 11 does not exceed a predetermined upper limit temperature. It is also possible to simulate the deterioration of the power storage cell 11 according to the temperature of the power storage cell 11 estimated by the BMU2.

[0051] As described above in detail, in this embodiment, the BMU 2 calculates the value of the internal resistance 115 of the power storage cell 11 by the DC resistance measurement method, estimates the amount of heat generated in the power storage cell 11 based on the value of the internal resistance 115, and estimates the future temperature of the power storage cell 11 based on the amount of heat generated. In the DC resistance measurement method, the value of the internal resistance 115 obtained is the value of DC resistance. In many cases, the power storage cell 11 is charged and discharged by DC, so that the heat generation factor of the power storage cell 11 is almost limited to DC resistance. For this reason, it is possible to accurately estimate the amount of heat generated in the power storage cell 11 by using the value of the internal resistance 115 of the power storage cell 11 calculated by the DC resistance measurement method. This estimation can be realized by hardware that is normally included in a typical power storage module 10 (no additional hardware is required for the power storage module 10).

[0052] The BMU2 uses the DC resistance measurement method instead of the AC impedance method, and can more accurately calculate the value of the internal resistance 115 of the storage cell 11 that is charged and discharged with DC. The BMU2 estimates the heat generation amount of the storage cell 11 without using an internal resistance map that causes an error, and can estimate the heat generation amount with a small error. The BMU2 estimates the value of the internal resistance 115 in situ based on the SOC, current, and voltage when the storage cell 11 is actually charged and discharged, and can easily estimate the value of the internal resistance 115 of the storage cell 11 that is actually in use. In addition, since the AC impedance method is not used, one measuring device is not required for each storage cell 11. Therefore, a large number of measuring devices are not required to calculate the values ​​of the internal resistances 115 of multiple storage cells 11. Therefore, in this embodiment, the BMU2 can easily and accurately calculate the value of the internal resistance 115 of the storage cell 11 that is in use, and can easily and accurately estimate the heat generation amount in the storage cell 11 and the future temperature of the storage cell 11.

[0053] By using the value of the internal resistance 115 of the power storage cell 11 measured by the DC resistance measurement method, the calculation formula required to estimate the temperature of the power storage cell 11 becomes a simple formula. Therefore, the BMU 2 can quickly perform calculations to estimate the temperature of the power storage cell 11. By using a real-time OS, the BMU 2 can perform processing with high responsiveness, such as reducing the calculation processing time required for processing to estimate the temperature of the power storage cell 11 after t1 time to less than t1. Therefore, the BMU 2 can quickly estimate the future temperature of the power storage cell 11 in advance. If the responsiveness is sufficient, the BMU 2 does not need to use a real-time OS.

[0054] Since the BMU 2 can accurately estimate the temperature of the power storage cells 11, it can appropriately control the operation of the power storage module 10 in accordance with the estimated temperature. The BMU 2 can also accurately predict the deterioration of the power storage cells 11 in accordance with the temperature. For example, it can accurately predict the time to replace the power storage cells 11 that have deteriorated to a certain extent.

[0055] (Embodiment 2) In the second embodiment, another example of a method for calculating the internal resistance of the energy storage cell 11 is shown. FIG. 7 is a block diagram showing an example of a functional configuration of the current measurement unit 24 and the voltage measurement unit 25 according to the second embodiment. The configuration of the current measurement unit 24 is the same as that of the first embodiment. The voltage measurement unit 25 includes a current source 252 connected to both ends of each energy storage cell 11. The current source 252 is connected to the energy storage cell 11 in parallel with the voltmeter 251. The current source 252 can generate a direct current and can change the direction in which the direct current flows. The configuration of the BMU2 other than the voltage measurement unit 25 is the same as that of the first embodiment. The configuration of the energy storage module 10 other than the BMU2 is the same as that of the first embodiment.

[0056] When a DC current flows through the power storage cell 11, a current that current source 252 flows through the power storage cell 11 in the same direction as current I flowing through the power storage cell 11 is defined as a first DC current. When a DC current flows through the power storage cell 11, a current that current source 252 flows through the power storage cell 11 in the opposite direction to current I flowing through the power storage cell 11 is defined as a second DC current. The second DC current is in the opposite direction to the first DC current. The absolute value of the first DC current and the absolute value of the second DC current are the same value, and this value is defined as i.

[0057] When a direct current I flows through the storage cell 11 and the current source 252 also passes a first direct current through the storage cell 11, the voltage (first voltage) V1 measured by the voltmeter 251 is expressed as V1=E0+R0(I+i). As in the first embodiment, the value of the internal resistance 115 is R0 and the value of the electromotive force 114 is E0. When a direct current I flows through the storage cell 11 and the current source 252 also passes a second direct current through the storage cell 11, the voltage (second voltage) V2 measured by the voltmeter 251 is expressed as V2=E0+R0(Ii). By eliminating the value E0 of the electromotive force 114 from the two equations, the value R0 of the internal resistance 115 is expressed as R0=(V1-V2) / 2i.

[0058] As in the first embodiment, the BMU 2 repeatedly calculates the SOC of each storage cell 11 by the current integration method, and stores the calculated SOC in the storage unit 23. As in the first embodiment, the BMU 2 performs a process of estimating the temperature of each storage cell 11 from time to time. FIG. 8 is a flowchart showing a process procedure for estimating the temperature of the storage cell 11 performed by the BMU 2 according to the second embodiment. The BMU 2 measures the voltage of each storage cell 11 in a state where a direct current flows through each storage cell 11 (S21). In S21, in a state where a direct current flows through the storage cell 11, the current source 252 passes a first direct current through the storage cell 11, and the voltmeter 251 measures a first voltage V1. Furthermore, in a state where a direct current flows through the storage cell 11, the current source 252 passes a second direct current through the storage cell 11, and the voltmeter 251 measures a second voltage V2. The voltmeter 251 inputs the measured first voltage V1 and second voltage V2 to the calculation unit 21.

[0059] The calculation unit 21 then calculates the value of the internal resistance 115 of each of the storage cells 11 (S22). In S22, the BMU 2 calculates the internal resistance by a DC resistance method. Using the first voltage V1 and the second voltage V2 measured in a state in which a DC current flows through the storage cell 11 in S21 and the absolute values ​​i of the first DC current and the second DC current, the calculation unit 21 calculates the value R0 of the internal resistance 115 of each of the storage cells 11 by calculating R0=(V1-V2) / 2i. The absolute values ​​i of the first DC current and the second DC current are stored in advance in the storage unit 23. The calculation unit 21 reads out the absolute values ​​i of the first DC current and the second DC current from the storage unit 23 and executes the process of S22.

[0060] Alternatively, the absolute value i1 of the first direct current and the absolute value i2 of the second direct current may be different values. In this case, the value R0 of the internal resistance 115 is expressed as R0=(V1-V2) / (i1+i2). The calculation unit 21 calculates the value R0 of the internal resistance 115 of each storage cell 11 by calculating R0=(V1-V2) / (i1+i2). As is clear from this formula, even if the first direct current and the second direct current are generated in the same direction, it is theoretically possible to obtain the value R0 of the internal resistance 115. However, in consideration of the measurement accuracy and resolution of the voltmeter, it is preferable that the difference between the values ​​V1 and V2 is large. Therefore, as described above, it is preferable to perform measurement using currents in the opposite directions.

[0061] The calculation unit 21 thereafter uses the value R0 of the internal resistance 115 to calculate the future heat generation amount in the power storage cell 11, and performs processing for estimating the future temperature of the power storage cell 11 by simulating heat conduction in the power storage module 10. The calculation unit 21 calculates the heat generation amount Q in each power storage cell 11 based on the predicted current distribution profile, similar to the processing in S14 (S23). The calculation unit 21 performs a simulation of heat conduction, similar to the processing in S15 (S24). The calculation unit 21 determines whether or not the temperature of each power storage cell 11 after t1 hours from time t0 has been calculated by the processing in S24 (S25). If the temperature after t1 hours from time t0 has not yet been calculated (S25: NO), the calculation unit 21 returns the processing to S23. If the temperature of each power storage cell 11 after t1 hours from time t0 has been calculated (S25: YES), the calculation unit 21 ends the processing for estimating the temperature of the power storage cell 11.

[0062] By executing the processes of S21 to S25, the BMU 2 estimates the temperature of each of the power storage cells 11 from time t0 to t1. The BMU 2 executes the processes of S21 to S25 as needed, and controls the operation of the power storage module 10 based on the estimated temperatures.

[0063] In this embodiment, the BMU 2 uses the current source 252 to calculate the value of the internal resistance 115 of the power storage cell 11 based on the first voltage V1 and the second voltage V2. The value of the internal resistance 115 can be obtained without using the value E0 of the electromotive force 114 of the power storage cell 11 or the value of the current flowing through the power storage cell 11. Therefore, the BMU 2 can more accurately calculate the value of the internal resistance 115 of the power storage cell 11, and can more accurately estimate the amount of heat generated in the power storage cell 11 and the future temperature of the power storage cell 11.

[0064] In this embodiment as well, the BMU 2 can easily and accurately calculate the value of the internal resistance 115 of the power storage cell 11 that is charged and discharged with DC by using the DC resistance measurement method. Therefore, the BMU 2 can easily and accurately estimate the amount of heat generated in the power storage cell 11, and can also easily and accurately estimate the future temperature of the power storage cell 11.

[0065] (Embodiment 3) In the third embodiment, a battery management device external to the energy storage module 10 estimates the temperature of the energy storage cells 11. FIG. 9 is a block diagram showing an example of the functional configuration of the energy storage module 10 and the battery management device 3 according to the third embodiment. The CMU (Cell Monitoring Unit) 20 includes a communication unit 27. The communication unit 27 has a function of transmitting and receiving information to and from the outside of the energy storage module 10. The configuration of the CMU 20 other than the communication unit 27 is the same as the BMU 2 in the first or second embodiment. The configuration of the energy storage module 10 other than the CMU 20 may be the same as the first or second embodiment.

[0066] The communication unit 27 is connected to a battery management device 3 that is external to the power storage module 10. The battery management device 3 includes a control unit 31, a communication unit 32, and a storage unit 33. The battery management device 3 is configured with a computer. The battery management device 3 may be configured with multiple computers. The battery management device 3 may be connected to the CMU 20 via a communication network such as the Internet.

[0067] The control unit 31 is configured, for example, using a CPU and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The control unit 31 controls the entire battery management device 3. The control unit 31 may be configured using a CPU and a GPU (Graphics Processing Unit), a multi-core CPU, or a TPU (Tensor Processing Unit). The storage unit 33 is non-volatile and is configured, for example, using a hard disk or a non-volatile memory. The storage unit 33 stores a computer program 331. The computer program 331 includes, for example, a program corresponding to the OS program 231 and the calculation program 232. The control unit 31 executes information processing based on the computer program 331.

[0068] The CMU 20 transmits information indicating the current measured using the current measuring unit 24 and information indicating the voltage measured using the voltage measuring unit 25 from the communication unit 27 to the battery management device 3. The battery management device 3 receives the information transmitted from the CMU 20 at the communication unit 32 and stores the received information in the storage unit 33. The characteristic data 233 may be stored in the storage unit 33 in advance, or may be read out from the storage unit 23 as necessary and transmitted from the communication unit 27 to the battery management device 3. The history data 234 may be stored in the storage unit 33, or information included in the history data 234 may be read out from the storage unit 23 as necessary and transmitted from the communication unit 27 to the battery management device 3.

[0069] The CMU 20 measures the current flowing through each storage cell 11, and transmits information indicating the measured current from the communication unit 27 to the battery management unit 3. The battery management unit 3 receives the information indicating the current via the communication unit 32, and the control unit 31 calculates the SOC of each storage cell 11 by a current integration method based on the current indicated by the received information. The control unit 31 repeatedly calculates the SOC of each storage cell 11, and stores the calculated SOC in the memory unit 33. The SOC may be calculated by the calculation unit 21.

[0070] The CMU 20 and the battery management unit 3 perform a process to estimate the temperature of each of the storage cells 11. The CMU 20 performs a process similar to the process of S11 in the first embodiment, and transmits information indicating the current flowing through the storage cell 11 and the voltage of the storage cell 11 from the communication unit 27 to the battery management unit 3. Alternatively, the CMU 20 performs a process similar to the process of S21 in the second embodiment, and transmits information indicating the measured first voltage V1 and second voltage V2 from the communication unit 27 to the battery management unit 3.

[0071] The battery management device 3 receives the information transmitted from the CMU 20 at the communication unit 32. The control unit 31 estimates the temperature of each of the power storage cells 11 from time t0 to t1 by executing the same processes as those of S12 to S16 in the first embodiment. Alternatively, the control unit 31 estimates the temperature of each of the power storage cells 11 from time t0 to t1 by executing the same processes as those of S22 to S25 in the second embodiment. The calculation unit 21 may perform a process of generating a model of the power storage module 10 required for the numerical calculation. Alternatively, the model of the power storage module 10 may be stored in advance in the storage unit 33, or may be transmitted from the CMU 20 to the battery management device 3 as necessary.

[0072] The battery management unit 3 transmits information indicating the estimated temperature of each storage cell 11 from the communication unit 32 to the CMU 20. The CMU 20 receives the information indicating the temperature of each storage cell 11 via the communication unit 27. The CMU 20 and the battery management unit 3 execute a process of estimating the temperature of each storage cell 11 as needed. The CMU 20 controls the operation of the storage module 10 based on the estimated temperature.

[0073] In the present embodiment as well, the battery management device 3 can easily and accurately calculate the value of the internal resistance 115 of the power storage cell 11 that is charged and discharged with DC by using the DC resistance measurement method. Therefore, the battery management device 3 can easily and accurately estimate the amount of heat generated in the power storage cell 11, and can also easily and accurately estimate the future temperature of the power storage cell 11.

[0074] 9 shows an example in which the CMU 20 included in a single power storage module 10 is connected to the battery management unit 3. Alternatively, a plurality of CMUs 20 included in a plurality of power storage modules 10 may be connected to the battery management unit 3. The battery management unit 3 transmits and receives information to and from each CMU 20, and performs a process of estimating the temperature of the power storage cells 11 for each power storage module 10.

[0075] The storage cells 11 in the first to third embodiments may be reused products (recycled products). For example, all the storage cells 11 included in the storage module 10 may be reused products, and reused storage cells 11 and new storage cells 11 may be mixed in the storage module 10. While demand for secondary batteries such as lithium ion batteries is expected to increase, it is predicted that there will be a shortage of production of certain elements such as cobalt, which is used as a material for secondary batteries. For this reason, it is expected that storage cells will be reused.

[0076] The reused storage cells are deteriorating and have an increased internal resistance. The degree of deterioration is affected by many factors, such as the amount of current flowing through them, their usage history, and the number of years they have been in use. Because of the increased internal resistance, reused storage cells are more likely to increase in temperature and further deteriorate than new storage cells.

[0077] In the first to third embodiments, even if one or more storage cells 11 included in the energy storage module 10 are reused products, the value of the internal resistance 115 of the energy storage cell 11 can be easily and accurately calculated by the same method, and the future temperature of the energy storage cell 11 can be easily and accurately estimated. By correctly grasping the value and temperature of the internal resistance 115 of the reused energy storage cell 11, the operation of the energy storage module 10 can be appropriately controlled. For example, the operation of the energy storage module 10 can be controlled while suppressing further deterioration of the energy storage cell 11.

[0078] In the first to third embodiments, the power storage module 10 includes a plurality of power storage cells 11. Alternatively, the power storage module 10 may include a single power storage cell 11. In the first to third embodiments, the power storage device is the power storage module 10. Alternatively, the power storage device may be a bank configured by connecting a plurality of power storage modules 10 in series, or a domain configured by connecting a plurality of banks in parallel. The same processing as in the first to third embodiments is performed by a battery management device provided in the bank or domain, or a battery management device connected to the bank or domain. In the first to third embodiments, the energy storage element is the energy storage cell 11. Alternatively, the energy storage element may be an energy storage module 10 or a bank.

[0079] The simulation model used for simulating heat conduction may be a model in which the electrode body inside the energy storage element is divided into detailed elements. It is also possible to use one energy storage element as one calculation element, or in the case of a large-scale energy storage device, to use multiple energy storage elements as one calculation element. The present invention can be implemented more effectively by determining the model by comprehensively taking into account the performance of the calculation unit, the size of the energy storage device, the communication speed, etc.

[0080] The CMU 20 and the battery management unit 3 in the third embodiment may be built in the same storage box (battery panel) or may be arranged in close proximity to each other so as to be connected by wireless communication. From the viewpoint of real-time responsiveness or communication load, it is preferable to perform the estimation by the BMU 2 provided in the power storage module as in the first embodiment.

[0081] The techniques of the first to third embodiments may be applied when new or reused energy storage cells are converted into power supply systems for industrial use. Many energy storage modules are used in power supply systems for power adjustment and AGVs (Automated Guided Vehicles). The techniques of the first to third embodiments may be applied to improve the maintenance efficiency of these energy storage modules and further stabilize the system operation. When using reused energy storage cells, it is expected that the effects of applying the techniques of the first to third embodiments are particularly high.

[0082] In the first to third embodiments, the future heat generation amount of the energy storage element is estimated using the predicted energization profile. Alternatively, the current heat generation amount of the energy storage element may be estimated using a past energization profile (history data).

[0083] The present invention is not limited to the contents of the above-described embodiment, and various modifications are possible within the scope of the claims. In other words, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention. [Explanation of symbols]

[0084] 10 Energy storage module (energy storage device) 11 Energy storage cell (energy storage element) 114 Electromotive force 115 Internal Resistance 2 BMU (Management Department) 20 CMU 21 Arithmetic section 23 Memory section 231 OS Program 232 Calculation Program 24 Current measurement section 241 Shunt Resistor 242 Voltmeter 25 Voltage measurement section 251 Voltmeter 252 Current Source 3 Battery management device

Claims

1. A storage element; a management unit that measures a voltage of the storage element and manages the storage element, The management department: Measure the voltage of the storage element while a direct current flows through the storage element; Calculating the internal resistance of the energy storage element by a DC resistance measurement method using the measured voltage; estimating a heat generation amount in the energy storage element based on the internal resistance and the current flow profile, using an equation including an entropy heat generation term and expressing a heat generation amount in the energy storage element; The management unit A predicted current profile is identified based on a history of a current flowing through the storage element, and a future heat generation amount in the storage element is estimated using the predicted current profile as the current profile. Energy storage device.

2. The management unit Measure the current flowing through the storage element while a direct current is flowing through the storage element; Calculating the internal resistance of the storage element based on the electromotive force of the storage element obtained according to the SOC of the storage element, the measured current, and the measured voltage. The power storage device according to claim 1 .

3. The management unit A current source connected in parallel to the storage element, measuring a first voltage of the storage element when the current source applies a first direct current to the storage element in a state in which a direct current flows through the storage element; measuring a second voltage of the storage element when the current source applies a second direct current, the second direct current being different from the first direct current, to the storage element in a state in which a direct current flows through the storage element; Calculating an internal resistance of the energy storage element based on the first voltage and the second voltage. The power storage device according to claim 1 .

4. The management unit A simulation of heat conduction is performed based on the amount of heat generated, thereby estimating the temperature of the electric storage element. The power storage device according to claim 1 .

5. The management unit A storage unit that stores a program; A calculation unit that performs calculations based on the program, The storage unit is A real-time OS (Operating System) program, A program that runs on the real-time OS and that calculates the internal resistance, estimates the amount of heat generated, and estimates the temperature is stored. The power storage device according to claim 4.

6. The management unit A future heat generation amount in the electric storage element is estimated by calculating a heat generation amount using a future current according to the predicted current flow profile and the internal resistance. The power storage device according to claim 1 .

7. The management unit estimates a plurality of heat generation amounts based on a plurality of predicted current distribution profiles. The power storage device according to claim 1 .

8. The storage element is a reused item. The power storage device according to claim 1 .

9. A method for estimating a temperature of a storage element, comprising: Measure the voltage of the storage element while a direct current flows through the storage element; Calculating the internal resistance of the energy storage element by a DC resistance measurement method using the measured voltage; estimating a heat generation amount in the energy storage element based on the internal resistance and the current flow profile, using an equation including an entropy heat generation term and expressing a heat generation amount in the energy storage element; estimating a temperature of the energy storage element by performing a simulation of heat conduction based on the amount of heat generated; When estimating the temperature of the storage element, a predicted current profile is specified based on a history of a current flowing through the storage element, and the predicted current profile is used as the current profile to estimate a future heat generation amount in the storage element. Temperature estimation method.

10. A predicted current profile is used as the current profile to estimate a future heat generation amount in the power storage element. The temperature estimation method according to claim 9.

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