Control device

Abstract

To provide a technique capable of accurately estimating a residual amount of a battery.SOLUTION: A battery control device comprises: a circuit constant calculation unit that calculates an estimated value of a circuit constant of an equivalent circuit of the battery on the basis of a time change of a discharge voltage of the battery when a current is discharged from the battery; and a residual amount estimation unit that estimates a residual amount of the battery on the basis of the estimated value of the circuit constant.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present specification relates to a technique for estimating the remaining capacity of a battery. [Background technology]

[0002] Patent Document 1 discloses a technique for estimating the state of a battery using a Kalman filter. In this technique, the remaining capacity of a battery is estimated using a Kalman filter by utilizing the circuit constants of a battery equivalent circuit model. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-096954 A Summary of the Invention [Problem to be solved by the invention]

[0004] This specification provides a technique that can estimate the remaining capacity of a battery with high accuracy. [Means for solving the problem]

[0005] In a first aspect of the present technology, a battery control device includes a circuit constant calculation unit that calculates an estimate of a circuit constant of an equivalent circuit of the battery based on a change over time in a discharge voltage of the battery when a current is discharged from the battery, and a remaining capacity estimation unit that estimates a remaining capacity of the battery based on the estimated value of the circuit constant.

[0006] According to the above configuration, the battery control device calculates an estimate of the circuit constant of the battery's equivalent circuit based on the change over time of the discharge voltage of the battery when a current is discharged from the battery. The change over time of the discharge voltage of the battery varies depending on the state of the battery (e.g., the deterioration state of the battery) when a current is discharged from the battery. Therefore, the circuit constant of the battery can be estimated taking into account the current state of the battery. Then, the remaining capacity of the battery is estimated based on the estimated value of the circuit constant taking into account the current state of the battery, so that the remaining capacity of the battery can be estimated with high accuracy.

[0007] In a second aspect, the first aspect may further include a memory that stores a circuit constant map that stores circuit constants of the equivalent circuit, and a storage control unit that stores a specific value based on the calculated estimated value of the circuit constant in the circuit constant map in the memory.

[0008] For example, in a comparative example in which a circuit constant map is not stored, it is necessary to estimate the circuit constants each time a situation arises in which the circuit constants should be used. On the other hand, according to the above configuration, the control device stores the circuit constant map, so that the circuit constants can be easily grasped.

[0009] In a third aspect, in the second aspect described above, the circuit constant map stores the circuit constants in association with one or more parameters, the control device further includes a temperature acquisition unit that acquires the temperature of the battery, and the one or more parameters include the temperature of the battery, and the memory control unit may further associate the specific value with the temperature of the battery and store them in the circuit constant map.

[0010] According to the above configuration, the circuit constant map stores the circuit constants in association with the battery temperature, so that appropriate circuit constants can be used depending on the battery temperature.

[0011] In a fourth aspect, the third aspect further includes an update amount calculation unit that calculates an update amount based on the estimated value of the circuit constant calculated and the circuit constant stored in the circuit constant map in association with the temperature, and the specific value may be a value obtained by adding the update amount to the circuit constant stored in the circuit constant map in association with the temperature.

[0012] According to the above configuration, the control device stores in the circuit constant map a specific value obtained by adding an update amount to the circuit constant stored in the circuit constant map in association with temperature. The update amount is a value determined based on the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map in association with temperature. In this way, by adding the update amount, it is possible to use a more appropriate circuit constant.

[0013] In a fifth aspect, in any one of the second to fourth aspects, the memory control unit may store the specific value in the circuit constant map when a difference between the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map satisfies a predetermined condition, and may not store the specific value in the circuit constant map when a difference between the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map does not satisfy the predetermined condition.

[0014] According to the above configuration, the storage control unit stores a specific value in the circuit constant map when a difference between the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map satisfies a predetermined condition, and does not store the specific value in the circuit constant map when the difference does not satisfy the predetermined condition. In this way, by separating the situation in which the specific value is stored in the circuit constant map from the situation in which it is not stored, the specific value can be stored in the circuit constant map only in an appropriate situation. As a result, a more appropriate circuit constant can be used.

[0015] In addition, in a sixth aspect of the present technology, a battery control device includes a remaining capacity estimation unit that estimates a remaining capacity of the battery, and the remaining capacity estimation unit includes a switching unit that switches between estimating the remaining capacity of the battery using a Kalman filter method and estimating the remaining capacity of the battery using a current integration method based on a current value of a current flowing through the battery.

[0016] Generally, the remaining battery capacity estimation using the Kalman filter method has a relatively high estimation accuracy, but the calculation load is also relatively high. If the calculation load is high, it may be difficult to estimate the remaining battery capacity in real time. As a result, the accuracy of the real-time estimation of the remaining battery capacity may decrease. The remaining battery capacity estimation using the current integration method has a relatively low calculation load.

[0017] According to the above configuration, the control device switches between estimating the remaining battery capacity using the Kalman filter method and estimating the remaining battery capacity using the current integration method based on the current value of the current flowing through the battery. This reduces the computational load of estimating the remaining battery capacity. As a result, it is possible to prevent the accuracy of estimating the remaining battery capacity from decreasing. In other words, it is possible to estimate the remaining battery capacity with high accuracy.

[0018] In a seventh aspect, in the sixth aspect, the battery further includes a circuit constant calculation unit that calculates an estimate of a circuit constant of an equivalent circuit of the battery based on a change over time in a discharge voltage of the battery when a current is discharged to the battery, and the remaining capacity estimation unit may estimate the remaining capacity of the battery based on the estimate of the circuit constant when estimating the remaining capacity of the battery using the Kalman filter method.

[0019] According to the above configuration, the battery control device calculates an estimate of the circuit constant of the battery's equivalent circuit based on the change over time of the discharge voltage of the battery when a current is discharged from the battery. The change over time of the discharge voltage of the battery varies depending on the state of the battery (e.g., the deterioration state of the battery) when a current is discharged from the battery. Therefore, the circuit constant of the battery can be estimated taking into account the current state of the battery. When estimating the remaining capacity of the battery using the Kalman filter method, the remaining capacity of the battery is estimated based on the estimated value of the circuit constant taking into account the current state of the battery, so that the remaining capacity of the battery can be estimated with high accuracy. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic block diagram of a battery and a control device. [Diagram 2] This is an equivalent circuit that models a battery. [Diagram 3] 4 is a flowchart of a process executed by a control device. [Figure 4] 13 is a flowchart of a circuit constant map update process. [Diagram 5] 13 is a flowchart of a remaining amount estimation process. [Figure 6] 4 is a schematic graph showing the discharge current of a battery and the change over time in the discharge voltage of the battery at that time. [Figure 7] 10A and 10B are diagrams for explaining an outline of a circuit constant map and updating of the circuit constant map; [Figure 8] FIG. 1 is a diagram for explaining switching between a Kalman filter method and a current integration method; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] This specification discloses a control device 20 for a battery 10. The battery 10 and the control device 20 of this embodiment are mounted on an electric vehicle 100. The battery 10 is a secondary battery, for example, a lithium ion battery. The electric vehicle 100 further includes a heating unit 12, a cooling unit 14, a charging unit 16, and a load 18. The heating unit 12 is, for example, a heater, and heats the battery 10 when the temperature of the battery 10 is low. The cooling unit 14 is, for example, a liquid-cooling type cooling mechanism, and cools the battery 10 when the temperature of the battery 10 is high. The charging unit 16 includes a power conversion mechanism, for example, a converter, and converts power from the outside to supply a charging current to the battery 10. The load 18 includes, for example, a motor for driving, and is driven by receiving a discharge current from the battery 10.

[0022] The control device 20 controls the operation of the battery 10. In particular, the control device 20 estimates the remaining capacity of the battery 10. The control device 20 includes a rectangular current generating unit 22, a measuring unit 24, a circuit constant calculating unit 26, a memory 28, and a remaining capacity estimating unit 30. The rectangular current generating unit 22 discharges a rectangular current (i.e., a constant current) from the battery 10 in response to an instruction to generate a rectangular current (i.e., a current of a constant magnitude) from the circuit constant calculating unit 26. As will be described in detail later, the rectangular current is used to estimate the circuit constants of an equivalent circuit that models the battery 10. As will be described in detail later, the circuit constants in this embodiment are five parameters, R0 to R2, C1, and C2. The measuring unit 24 includes a current sensor, a voltage sensor, a temperature sensor, etc., and measures the discharge current from the battery 10 (or the charge current to the battery 10), the voltage of the battery 10, the temperature of the battery 10, etc. The circuit constant calculation unit 26 instructs the rectangular current generation unit 22 to generate a rectangular current, and at that time estimates the circuit constant based on the time change in the voltage of the battery 10 measured by the measurement unit 24. A specific method for estimating the circuit constant will be described later. The memory 28 is a storage medium that stores various information, and stores a circuit constant map. The circuit constant map is a map that stores the voltage, temperature, and circuit constants of the battery 10 in association with each other. The control device 20 can easily grasp appropriate circuit constants according to the battery voltage and temperature using the circuit constant map. The circuit constant map is updated based on the circuit constant estimation result by the circuit constant calculation unit 26. The update of the circuit constant map will be described later in detail.

[0023] The remaining capacity estimation unit 30 estimates the remaining capacity of the battery 10. The remaining capacity estimation unit 30 includes a switching unit 32. The switching unit 32 switches between estimating the remaining capacity of the battery 10 using a current integration method and estimating the remaining capacity of the battery 10 using a Kalman filter method based on the magnitude of the current flowing through the battery 10. Details of the current integration method and the Kalman filter method, and details of switching between them will be described later. The above circuit constants are parameters used in estimating the remaining capacity of the battery 10 using the Kalman filter method.

[0024] The battery 10 deteriorates with use. The causes of deterioration of the battery 10 are extremely diverse, including cracks and corrosion of the copper or aluminum collector, loss of the binder between the electrode and the collector, increase and decomposition of the SEI (Solid Electrolyte Interphase) coating, cracking of the electrode, disturbance of the electrode structure, and dendrite formation of lithium, copper, etc. The state of the battery 10 (for example, the degree of deterioration) changes in countless ways due to deterioration of the circuit constants R0 to R2, C1, and C2 depending on the usage method and usage environment, and the circuit constants of the equivalent circuit modeling the battery 10 change. For this reason, it is necessary to individually correct the circuit constants each time in order to estimate the remaining capacity according to the state of the battery 10, so the control device 20 of this embodiment is provided with a circuit constant calculation unit 26 and the like.

[0025] Next, modeling of the battery 10 by an equivalent circuit will be described with reference to Fig. 2. As shown in Fig. 2, in the equivalent circuit of the battery 10, a resistor R0, a parallel connection of a resistor R1 and a capacitor C1, and a parallel connection of a resistor R2 and a capacitor C2 are connected in series. In the following, the magnitudes of the resistances of the resistors R0 to R2 are also represented by the symbols R0 to R2, respectively. Similarly, the electrostatic capacitances of the capacitors C1 and C2 are also represented by the symbols C1 and C2, respectively.

[0026] Resistor R0 in the equivalent circuit represents the resistance to charge transfer in the electrolyte. Resistor R1 and capacitor C1 connected in parallel represent the effect of the SEI coating and are relatively fast reactions. Resistor R2 and capacitor C2 connected in parallel represent the intercalation of lithium ions in the electrode, the double layer of charge near the electrode, and are relatively slow reactions. Note that the equivalent circuit of battery 10 in this embodiment is an example, and the parallel connection of resistors and capacitors may be one or three or more.

[0027] Next, the processing executed by the control device 20 will be described with reference to Figures 3 to 5. The processing in Figure 3 is started with the start of the battery 10 (for example, the main switch of the electric vehicle 100 being turned on) as a trigger. Note that each of the following processing is executed by the CPU (not shown) of the control device 20, but for ease of understanding, each processing will be described as the subject of the control device 20 or each of the units 22 to 32, instead of describing the CPU as the subject of each processing.

[0028] In S10, the control device 20 acquires the voltage and temperature of the battery 10 by the measurement unit 24, and stores them in the memory .

[0029] In S12, the control device 20 judges whether the voltage and temperature stored in S10 are within a predetermined range. More specifically, the control device 20 judges whether the voltage and temperature of the battery 10 are in a state suitable for using the battery 10. The control device 20 proceeds to S14 if the voltage and temperature of the battery 10 are within the predetermined range (YES in S12), and proceeds to S40 if at least one of the voltage and temperature of the battery 10 is not within the predetermined range (NO in S12).

[0030] In S14, the control device 20 discharges a rectangular current into the battery 10 for a fixed time and measures the voltage of the battery 10 at that time. Specifically, first, in S14, the circuit constant calculation unit 26 of the control device 20 instructs the rectangular current generation unit 22 to generate a rectangular current. Then, the measurement unit 24 measures the voltage of the battery 10 while the rectangular current is being discharged from the battery 10.

[0031] A specific example of the process of S14 in Fig. 3 will be described with reference to Fig. 6. Fig. 6(a) is a graph of current versus time, and Fig. 6(b) is a graph of voltage versus time.

[0032] As shown in FIG. 6(a), at time T1, the battery 10 starts discharging a rectangular current. In this case, as shown in FIG. 6(b), at time T1, the voltage increases steeply. This steep change in voltage is caused by the resistor R0 in the equivalent circuit (see FIG. 2). Thereafter, between time T1 and time T2, the voltage gradually increases. This change in voltage is caused by a relatively fast reaction represented by the parallel connection of the resistor R1 and the capacitor C1 in the equivalent circuit. After time T2, the voltage changes more slowly than the change in voltage between time T1 and time T2. This change in voltage is caused by a relatively slow reaction represented by the parallel connection of the resistor R2 and the capacitor C2 in the equivalent circuit. In this way, by discharging a rectangular current to the battery 10, a graph showing the time change in the output voltage of the battery 10 as shown in FIG. 6(b) is obtained.

[0033] Here, the theoretical output voltage of the battery 10 is V calc First, as shown in Figure 2, the voltage of resistor R0, the voltage of resistor R1 and capacitor C1 connected in parallel, and the voltage of resistor R2 and capacitor C2 connected in parallel are respectively set to V0, V1, and V2. Then, the following relational expression 1 is satisfied.

[0034]

number

[0035] I in Equation 1 represents the current flowing through the equivalent circuit. By solving the second and third differential equations in Equation 1, V1 and V2 can be calculated using Equation 2 below.

[0036]

number

[0037] Here, I0 is the magnitude of the rectangular current discharged from the battery 10. Therefore, the theoretical value V of the output voltage of the battery 10 when a rectangular current of magnitude I0 is discharged is calcThe equation expressing the change over time is expressed by the following equation 3, using the circuit constants R0 to R2, C1, and C2 as parameters.

[0038]

number

[0039] As described above, each of the circuit constants R0 to R2, C1, and C2 of the equivalent circuit of the battery 10 is a value that depends on the state (e.g., the degree of deterioration) of the battery 10. Therefore, the theoretical value V calc is also a value that depends on the state of the battery 10.

[0040] Returning to the explanation of Fig. 3, the control device 20 executes a circuit constant map update process in S20. The circuit constant map update process will be described in detail later with reference to Fig. 4.

[0041] Thereafter, in S22, the control device 20 starts using the battery 10. That is, the control device 20 determines the output current to be supplied to the load 18 based on, for example, an accelerator operation by the user, and starts discharging the battery 10 with the determined current.

[0042] In S30, the control device 20 executes a remaining capacity estimation process while the battery 10 is in use. Details of the remaining capacity estimation process will be described later with reference to Fig. 5. When the process of S30 ends, the process of Fig. 3 ends.

[0043] Furthermore, the control device 20 executes processing according to the voltage and / or temperature determined not to be within the predetermined range in S40. For example, if the voltage of the battery 10 is determined to be relatively low and the answer is NO in S12, the control device 20 outputs a charge request in S40 to charge the battery 10. For example, if the temperature of the battery 10 is determined to be relatively low (or high) and the answer is NO in S12, the control device 20 executes processing for heating (or cooling) the battery 10 in S40. When the processing of S40 ends, the processing of S10 is executed again.

[0044] Next, the circuit constant map update process of S20 in Fig. 3 will be described with reference to Fig. 4. As described above, the circuit constants are values ​​that can change depending on the state of the battery 10. The circuit constant map update process is executed to more appropriately model the current state of the battery 10.

[0045] In S100, the control device 20 acquires from the memory 28 the voltage and temperature of the battery 10 that have been stored in S10 of Fig. 3. In a modified example, the control device 20 may acquire the voltage and temperature of the battery 10 by newly measuring the voltage and temperature of the battery 10 by the measurement unit 24 in S100.

[0046] Next, the circuit constant calculation unit 26 of the control device 20 executes a process of calculating an estimated value of the circuit constant from the voltage change due to the rectangular current (S102 to S110). In this embodiment, the estimated value of the circuit constant is calculated by the gradient descent method. Specifically, first, in S102, the circuit constant calculation unit 26 fixes a set of circuit constants R0[1] to R2[1], C1[1], and C2[1], and sets a vector having the circuit constants as elements as an initial value a[1]. The initial value a[1] set here may be a value determined randomly, may be a value determined in advance, or may be a value read out from a circuit constant map.

[0047] In S104, the circuit constant calculation unit 26 calculates the loss value Loss[i]. For a natural number i, the loss value Loss[i] is defined by the following Equation 4.

[0048]

number

[0049] In the formula 4, V calc [i](t n ) are R0 to R2, C1, C2, and t in the formula 3, respectively R0[i] to R2[i], C1[i], C2[i], and t n Here is the formula with t n is the measured value V meas In this embodiment, for example, 100 different times t1 to t 100 In this case, 100 actual measurements V meas (t1)~V(t 100 ) is measured. Therefore, the loss value Loss[i] is an index showing the degree of deviation between the theoretical value of the output voltage of the battery 10 and the actually measured value.

[0050] In S106, the circuit constant calculation unit 26 judges whether the loss value Loss[i] calculated in S104 is less than a predetermined value (e.g., 0.01). When the loss value Loss[i] is less than the predetermined value, it means that the deviation between the theoretical value and the actual measured value of the output voltage of the battery 10 is sufficiently small. On the other hand, when the loss value Loss[i] is equal to or greater than the predetermined value, it means that the theoretical value and the actual measured value of the output voltage of the battery 10 deviate to a certain extent. When the loss value Loss[i] is less than the predetermined value (YES in S106), the circuit constant calculation unit 26 proceeds to S110, and when the loss value Loss[i] is equal to or greater than the predetermined value (NO in S106), it proceeds to S108.

[0051] In S108, the circuit constant calculation unit 26 updates the vector a having the circuit constants as elements based on the gradient ∇Loss[i] (see Equation 5) of the loss value Loss[i]. Specifically, the circuit constant calculation unit 26 defines the vector a[i+1] using the vector a[i], the learning rate α, and the gradient ∇Loss[i] according to the following Equation 5. Then, the updated vector a[i+1] is used to execute the processes of S104 and S106.

[0052]

number

[0053] In S110, the circuit constant calculation unit 26 determines the estimated values ​​of the circuit constants, and stores the circuit constants in the memory 28 in association with the voltage and temperature of the battery 10 acquired in S100. Specifically, when it is determined that the loss value Loss[m] (m is a natural number) is less than a predetermined value, the circuit constant calculation unit 26 determines and stores each of the components R0[m] to R2[m], C1[m], and C2[m] of the vector a[m] as the estimated values ​​of the circuit constants. In this manner, the estimated values ​​of the circuit constants are calculated. In a modified example, instead of calculating the estimated values ​​of the circuit constants by the gradient descent method, the estimated values ​​of the circuit constants may be calculated by another method such as Bayesian optimization or the Monte Carlo method.

[0054] Thereafter, the circuit constant calculation unit 26 executes a process for updating the circuit constant map (S112 to S118). Specifically, first, in S112, the circuit constant calculation unit 26 acquires from the memory 28 the most recent three estimated values ​​of the battery voltage, temperature, and circuit constants that were associated and stored in the above-mentioned S110. As shown in FIG. 3, the circuit constant map update process (S20) is executed when the battery 10 is started. Therefore, when the battery 10 is started, the estimated values ​​of the circuit constants are calculated. Therefore, "the most recent three estimated values ​​of the battery voltage, temperature, and circuit constants" means the estimated values ​​of the battery voltage, temperature, and circuit constants that were stored in S110 of FIG. 4 at the current start-up, the previous start-up, and the time before the previous start-up of the battery 10 (see FIG. 7(a)). In a modified example, the most recent one or two estimated values ​​of the battery voltage, temperature, and circuit constants may be obtained, or the most recent four or more estimated values ​​of the battery voltage, temperature, and circuit constants may be obtained.

[0055] In S114, the circuit constant calculation unit 26 judges whether or not the difference between the map value of the circuit constant and the estimated value of the circuit constant for each of the most recent three estimated values ​​of the battery voltage, temperature, and circuit constant that have already been acquired is less than a predetermined value. Specifically, the circuit constant calculation unit 26 first identifies the value of the circuit constant associated with the current battery voltage and temperature from the circuit constant map. Then, the circuit constant calculation unit 26 calculates the difference between the value of the circuit constant identified from the circuit constant map and the estimated value of the circuit constant associated with the current battery voltage and temperature that have already been acquired in S112. The same process is performed for the previous and previous-previous estimated values ​​of the battery voltage, temperature, and circuit constant to calculate the difference between the value of the circuit constant identified from the circuit constant map and the estimated value of the circuit constant. Then, the circuit constant calculation unit 26 judges whether or not each of these three differences is less than a predetermined value. If all of the three differences are less than the predetermined value, the circuit constant calculation unit 26 judges YES in S114, skips the processes from S116 onwards, and ends the process in Fig. 4. On the other hand, if any of the three differences is equal to or greater than the predetermined value, the circuit constant calculation unit 26 judges NO in S114 and proceeds to S116.

[0056] In S116, the circuit constant calculation unit 26 calculates the update amount of the circuit constant map. Specifically, the circuit constant calculation unit 26 defines the update amount Δz at an arbitrary battery voltage x and an arbitrary temperature y by the following formula 6.

[0057]

number

[0058] In the above formula 6, x1, x2, and x3 respectively indicate the current battery voltage, the previous battery voltage, and the battery voltage before the previous one. y1, y2, and y3 respectively indicate the current temperature, the previous temperature, and the temperature before the previous one. δz1, δz2, and δz3 respectively indicate the current difference, the previous difference, and the difference before the previous one. The above formula 6 indicates the equation of a plane passing through three points (x1, y1, δz1), (x2, y2, δz2), and (x3, y3, δz3) in a three-dimensional space (see FIG. 7(b)). In a modified example, instead of a plane passing through the above three points, the above three points may be approximated by a curved surface or the like, and the update amount δz may be defined using the curved surface.

[0059] In S118, the circuit constant calculation unit 26 updates the circuit constant map. Specifically, the circuit constant calculation unit 26 updates the circuit constant map by adding the update amount corresponding to each combination of battery voltage and temperature calculated in S116 to the value of the circuit constant associated with that combination in the circuit constant map. When the difference between the value of the circuit constant map and the estimated value of the circuit constant is relatively large (NO in S114), the value of each circuit constant in the circuit constant map may not be consistent with the current state of the battery 10. In this embodiment, by updating the circuit constant map in such a case, the value of each circuit constant in the circuit constant map can be made consistent with the state of the battery 10.

[0060] Next, the remaining capacity estimation process in S30 in Fig. 3 will be described with reference to Fig. 5. In S200, the remaining capacity estimation unit 30 of the control device 20 measures the current value I of the discharge current of the battery 10 (or the current value of the charge current to the battery 10) via the measurement unit 24. meas Obtain the current value I meas is used to estimate the remaining battery capacity, and is also used to determine whether to switch the method of estimating the remaining battery capacity.

[0061] In S202, the switching unit 32 of the remaining capacity estimation unit 30 switches the current value I meas Id switch Whether or not it is less than Ic switch The switching unit 32 determines whether the current value is greater than Id switch Less than or equal to Ic switch If the current value is greater than Id switch More than Ic switch If it is equal to or lower (NO in S202), the process proceeds to S230. That is, the switching unit 32 switches between estimating the remaining battery capacity by the processes of S210 to S216 and estimating the remaining battery capacity by the process of S230, depending on the current value of the current discharged from the battery 10. In this embodiment, the processes of S210 to S216 are for estimating the remaining battery capacity by the Kalman filter method. Also, the process of S230 is for estimating the remaining battery capacity by the current integration method.

[0062] Here, with reference to FIG. 8, the reason for switching the estimation method of the remaining battery capacity in this embodiment will be described. FIG. 8(a) is a graph that shows a schematic relationship between the error of the current sensor and the error in the estimation of the remaining battery capacity. As shown in FIG. 8(a), in both the Kalman filter method and the current integration method, the larger the error of the current sensor, the larger the error in the estimation of the remaining battery capacity. However, if the error of the current sensor is the same, the error in the estimation by the Kalman filter method is smaller than the error in the estimation by the current integration method. However, the estimation of the remaining battery capacity by the Kalman filter method requires a higher computation load than the estimation of the remaining battery capacity by the current integration method.

[0063] Moreover, Fig. 8(b) is a graph showing a schematic relationship between the magnitude of the discharge current or charge current of the battery 10 and the error of the current sensor. As shown in Fig. 8(b), the error of the current sensor increases as the magnitude of the discharge current or charge current increases.

[0064] That is, the larger the discharge current or charge current of the battery 10, the larger the error in estimating the remaining battery capacity. In particular, if only the current integration method is used as a method for estimating the remaining battery capacity, the error in estimating the remaining battery capacity is likely to be large. Furthermore, if only the Kalman filter method is used as a method for estimating the remaining battery capacity, the error in estimating the remaining battery capacity is smaller than when only the current integration method is used, but the computation load is high. If the computation load is high, it takes a long time to estimate the remaining battery capacity. If it takes a long time to estimate the remaining battery capacity, it becomes impossible to estimate the remaining battery capacity in real time. This can result in a situation where the accuracy of the calculation estimation is high but the accuracy of the real-time estimation of the remaining battery capacity is low.

[0065] Therefore, the remaining capacity estimation unit 30 of this embodiment estimates the remaining battery capacity using the current integration method, which has a low calculation load, in a range in which the error in estimating the remaining battery capacity is relatively small even when the current integration method is used.On the other hand, the remaining capacity estimation unit 30 estimates the remaining battery capacity using the Kalman filter method in a range in which the error in estimating the remaining battery capacity is relatively large when the current integration method is used.

[0066] Specifically, as shown in FIG. 8(a), when the accuracy required for estimating the remaining battery capacity is given, the error range of the current sensor that can estimate the remaining battery capacity within the required accuracy is determined by estimating the remaining battery capacity using the current integration method. Here, the threshold value is σ switch That is, if the error of the current sensor is σ switch If the current value of the discharge current (or charge current) of the battery 10 is Idswitch More than Ic switch If the error of the current sensor is σ switch The process of S202 is therefore a process for determining whether or not it is possible to estimate the remaining battery capacity with the necessary accuracy by estimating the remaining battery capacity using the current integration method. This reduces the computational load for estimating the remaining capacity of the battery 10. As a result, it is possible to prevent a decrease in the accuracy of estimating the remaining capacity of the battery 10. In other words, it is possible to estimate the remaining capacity of the battery 10 with high accuracy.

[0067] Returning to the description of the process in Fig. 5, in S210, the remaining capacity estimation unit 30 acquires the voltage and temperature of the battery 10 by the measurement unit 24. The battery voltage acquired here is a non-circuit voltage, and V meas is equivalent to.

[0068] In S212, the remaining capacity estimating unit 30 identifies the circuit constants associated with the battery voltage and temperature acquired in S210 from the circuit constant map.

[0069] In S214, the remaining capacity estimation unit 30 calculates the current value I meas , and the circuit constants specified in S212, a pre-estimation process is executed according to the Kalman filter method. The pre-estimation process is a process for theoretically estimating the remaining battery capacity from a model of the battery 10 using an equivalent circuit (see FIG. 2), and is specifically the following process.

[0070] First, V1(k), V2(k), and RC(k) are respectively the voltage at the parallel connection of resistor R1 and capacitor C1, the voltage at the parallel connection of resistor R2 and capacitor C2, and the remaining battery charge at a certain point in time k. Also, Δt is the calculation period of the process in Fig. 5 (i.e., the time from when the process of S200 is executed until the next time the process of S200 is executed when the battery 10 is activated). Then, x(k), A, and U are defined as the following equation 7.

[0071]

number

[0072] At this time, in the equivalent circuit of the battery 10, the equation expressing the change in voltage and remaining battery capacity over discrete time periods is expressed by the following equation 8.

[0073]

number

[0074] In the formula (8), i is the standard deviation of the error of the current sensor, and w is a random number following the standard normal distribution. That is, the formula (8) represents the change in the voltage and the remaining battery capacity taking into account the error of the current sensor.

[0075] And the process equation for the pre-estimation process is given by Equation 9 below.

[0076]

number

[0077] Here, in the equation of FIG. 9, Q is a variance-covariance matrix representing noise due to error in the current sensor, and is given by the following equation 10.

[0078]

number

[0079] In this way, a pre-estimated value of the remaining battery capacity is calculated by the pre-estimate process in S214. After that, in S216, the remaining capacity estimation unit 30 executes a post-estimate process using the result of the pre-estimate process. The post-estimate process is a process for correcting a value theoretically calculated by the pre-estimate process using an actually observed value. Specifically, the process is as follows.

[0080] First, the observation equation for the posterior estimation process is given by the following Equation 11.

[0081]

number

[0082] In the formula (11), v is the standard deviation of the error of the voltage sensor, and w1 and w2 are random numbers that follow the standard normal distribution. Here, functions z and h are defined as in the following formula (12).

[0083]

number

[0084] Then, the relationship between the functions z and h satisfies the following formula 13.

[0085]

number

[0086] Then, the equation for the posterior estimation process is given by the following Equation 14.

[0087]

number

[0088] Here, in equation 14, the Kalman gain g(k) and σ w , c(k) is given by the following equation 15.

[0089]

number

[0090] In this manner, an estimate of the remaining battery capacity is calculated using the Kalman filter method by the post-estimation process in S216.

[0091] Thereafter, in S220, the remaining capacity estimation unit 30 determines whether or not the battery 10 has been terminated. For example, when the main switch of the electric vehicle 100 is turned off, the remaining capacity estimation unit 30 determines that the battery 10 has been terminated. When the battery 10 has been terminated (YES in S220), the remaining capacity estimation unit 30 ends the process in FIG. 5. On the other hand, when the battery 10 has not been terminated (i.e., when the use of the battery 10 continues, NO in S220), the remaining capacity estimation unit 30 executes the processes from S200 onwards again.

[0092] Furthermore, the remaining capacity estimating unit 30 executes a current value integration process in S230. Specifically, the remaining capacity estimating unit 30 estimates the remaining capacity of the battery 10 by the following Equation 16.

[0093]

number

[0094] In this manner, the remaining capacity estimating unit 30 can estimate the remaining capacity of the battery 10. The process of S232 executed thereafter is similar to the process of S220.

[0095] According to the above configuration, the control device 20 calculates an estimate of the circuit constant of the equivalent circuit of the battery 10 based on the time change of the discharge voltage of the battery 10 when the battery 10 is discharged with a rectangular current. As described above, the time change of the discharge voltage of the battery 10 changes depending on the state of the battery 10 (e.g., the deterioration state of the battery 10) when the battery 10 is discharged with a rectangular current. Therefore, the circuit constant of the battery 10 can be estimated taking into account the current state of the battery 10. Since the remaining capacity of the battery 10 is estimated based on the estimated value of the circuit constant taking into account the current state of the battery 10, the remaining capacity of the battery 10 can be accurately estimated. The value obtained by adding the update amount Δz to the circuit constant of the circuit constant map is an example of the "specific value". The measurement unit 24 is an example of the "temperature acquisition unit". The determination of NO in S114 of FIG. 4 is an example of "the predetermined condition being satisfied".

[0096] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Modifications of the above embodiments are listed below.

[0097] (Variation 1) The control device 20 does not need to store a circuit constant map. In this case, for example, the control device 20 may execute the processes of S100 to S110 in Fig. 4 each time a circuit constant should be used (for example, S210 to S216 in Fig. 5) to calculate an estimated value of the circuit constant.

[0098] (Modification 2) In the above embodiment, the circuit constant map stores the battery voltage, temperature, and circuit constants in association with each other. Alternatively, the circuit constant map may be, for example, a map that stores the battery voltage and circuit constants in association with each other, or a map that stores the temperature and circuit constants in association with each other. Also, the circuit constant map may be a map that stores parameters other than the battery voltage and temperature in association with each other.

[0099] (Modification 3) The control device 20 may omit the processes of S112 to S116. In this case, in S118, the control device 20 may store in the circuit constant map the battery voltage and temperature acquired in S100 and the estimated values ​​of the circuit constants determined in S110 in association with each other. In this modification, the "update amount calculation unit" can be omitted.

[0100] (Modification 4) The control device 20 may omit the process of S114 in Fig. 4 and execute the processes of S116 and S118. That is, generally speaking, the "storage control unit" may store a specific value in the circuit constant map regardless of whether or not the "difference satisfies the predetermined condition."

[0101] (Variation 5) In S114 of FIG. 4, the control device 20 may determine NO in S114 if, for example, the average value of the three differences is equal to or greater than a predetermined value, or if all of the three differences are equal to or greater than a predetermined value (an example of "the differences satisfy a predetermined condition"), etc.

[0102] (Variation 6) The battery voltage on the axis of the circuit constant map may be the open circuit voltage. Until the open circuit voltage is obtained from the map based on the estimated remaining battery capacity and the actual measured battery temperature, the current open circuit voltage value may be calculated from the open circuit voltage map using the estimated remaining battery capacity and the actual measured battery temperature, and the circuit constant map may be further specified from the open circuit voltage value and the battery temperature.

[0103] (Modification 7) The open circuit voltage map may be corrected according to the deterioration state. For example, a neural network may be used in which the latest circuit constant map is input, and the output may be in the form of a deterioration correction coefficient.

[0104] The technical elements described in this specification or drawings have technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0105] 10: battery, 12: heating section, 14: cooling section, 16: charging section, 18: load, 20: control device, 22: rectangular current generating section, 24: measuring section, 26: circuit constant calculating section, 28: memory, 30: remaining capacity measuring section, 32: switching section

Claims

1. A battery control device, a circuit constant calculation unit that calculates an estimate of a circuit constant of an equivalent circuit of the battery based on a time change in a discharge voltage of the battery when a current is discharged from the battery; a remaining capacity estimation unit that estimates a remaining capacity of the battery based on the estimated value of the circuit constant; A control device comprising:

2. The control device according to claim 1 , a memory for storing a circuit constant map for storing circuit constants of the equivalent circuit; a storage control unit that stores a specific value based on the calculated estimated value of the circuit constant in the circuit constant map in the memory; The control device further comprises:

3. The control device according to claim 2, the circuit constant map stores the circuit constants in association with one or more parameters; The control device further includes a temperature acquisition unit that acquires a temperature of the battery, the one or more parameters include a temperature of the battery; The storage control unit further stores the specific value and the temperature of the battery in association with each other in the circuit constant map.

4. The control device according to claim 3, an update amount calculation unit that calculates an update amount based on the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map in association with the temperature, The specific value is a value obtained by adding the update amount to the circuit constant stored in the circuit constant map in association with the temperature.

5. The control device according to claim 2, The storage control unit, storing the specific value in the circuit constant map when a difference between the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map satisfies a predetermined condition; when a difference between the calculated estimated value of the circuit constant and the circuit constant stored in the circuit constant map does not satisfy the predetermined condition, the specific value is not stored in the circuit constant map. Control device.

6. A battery control device, a remaining capacity estimation unit that estimates a remaining capacity of the battery, The control device, wherein the remaining capacity estimation unit is provided with a switching unit that switches between estimating the remaining capacity of the battery using a Kalman filter method and estimating the remaining capacity of the battery using a current integration method based on the current value of the current flowing through the battery.

7. The control device according to claim 6, a circuit constant calculation unit that calculates an estimated value of a circuit constant of an equivalent circuit of the battery based on a time change in a discharge voltage of the battery when a current is discharged from the battery; The control device, wherein the remaining capacity estimating unit estimates the remaining capacity of the battery based on the estimated value of the circuit constant when estimating the remaining capacity of the battery using the Kalman filter method.

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