Method for generating an energy storage element model, apparatus for generating an energy storage element model, and program

Abstract

To provide a power storage element model generator, a power storage element model generation method and a program with which it is possible to appropriately simulate the behavior of a power storage element.SOLUTION: In order to simulate a transient real voltage behavior when a real current is caused to flow in a real power storage element for a prescribed period, a power storage element model generation method adjusts parameters so that a transient model voltage behavior when a model current equivalent to the real current is caused to flow for a prescribed period in a power storage element model that includes the parameters becomes closer to the real voltage behavior. The power storage element model generation method changes the parameters in the above adjustment so as to simulate the state transition of the power storage element model in association with the flow of the model current.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for generating a power storage element model, a device for generating a power storage element model, and a program.

Background Art

[0002] As one of the methods for estimating the behavior of a secondary battery, there is a method of applying a Kalman filter to an equivalent circuit model representing the secondary battery by an electric circuit to estimate the behavior of the secondary battery such as SOC (State of Charge) (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding an equivalent circuit model (ECM: Equivalent Circuit Model) that simulates the current-voltage characteristics of a power storage element such as a secondary battery, sufficient consideration has not yet been given to the state transition of the power storage element, such as changes in SOC, temperature changes, and deterioration of the power storage element, associated with the operation of the power storage element.

[0005] An object of the present disclosure is to provide a method for generating a power storage element model, a device for generating a power storage element model, and a program that can appropriately simulate the behavior of a power storage element.

Means for Solving the Problems

[0006] A method for generating an energy storage element model according to one aspect of this disclosure adjusts the parameters such that the transient model voltage behavior when a model current equivalent to the actual current is passed through an energy storage element model, which includes parameters, for a predetermined period of time, approaches the actual voltage behavior, in order to simulate the transient actual voltage behavior when an actual current is passed through an actual energy storage element for a predetermined period of time. In the adjustment, the method for generating an energy storage element model changes the parameters so as to simulate the state transition of the energy storage element model in accordance with the flow of the model current. [Effects of the Invention]

[0007] According to this disclosure, it is possible to generate an energy storage device model that accurately simulates the transient voltage behavior with respect to current in real energy storage devices. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of an ECM (Electronic Control Module) for an energy storage element. [Figure 2] This is a conceptual diagram showing an example of table data for circuit parameters. [Figure 3] This is an explanatory diagram illustrating the method of obtaining circuit parameters in conventional ECM (Electronic Circuit Measurement). [Figure 4] This graph shows the relationship between DC resistance and SOC (State of Current). [Figure 5] This is a conceptual diagram illustrating the overall process of calculating the lifespan of energy storage elements. [Figure 6] This is a block diagram of the generating apparatus according to this embodiment. [Figure 7] This is an explanatory diagram illustrating the method for obtaining circuit parameters in the energy storage element model of this embodiment. [Figure 8] This is a flowchart showing an example of the process for generating an energy storage element model. [Figure 9] This graph shows the verification results of the ECM generated by the method of this embodiment. [Figure 10] This graph shows the relationship between the DC internal resistance of a lithium-ion battery and its capacity retention rate. [Figure 11]This figure shows an example of an ECM of a storage element in the second embodiment. [Figure 12] This is an explanatory diagram illustrating the method for obtaining circuit parameters in the energy storage element model of the second embodiment. [Figure 13] This is a flowchart showing an example of the energy storage element model generation process in the second embodiment. [Figure 14] This figure shows an example of an ECM of a storage element in the third embodiment. [Figure 15] This is a flowchart showing an example of the energy storage element model generation process in the third embodiment. [Figure 16] This is an explanatory diagram illustrating a method for obtaining circuit parameters in the energy storage element model of the fourth embodiment. [Figure 17] This flowchart shows an example of the procedure for generating a storage element model in the fourth embodiment. [Figure 18] This graph shows the verification results of the ECM generated by the method of the fourth embodiment. [Modes for carrying out the invention]

[0009] The method for generating an energy storage element model involves adjusting the parameters such that the transient model voltage behavior when a model current equivalent to the actual current is passed through an energy storage element model for a predetermined period of time, in order to simulate the transient actual voltage behavior when an actual current is passed through an actual energy storage element for a predetermined period of time, approaches the actual voltage behavior. In the adjustment, the method for generating an energy storage element model involves changing the parameters so as to simulate the state transition of the energy storage element model in accordance with the flow of the model current.

[0010] Here, "real energy storage element" refers to a physically existing energy storage element. "Real current" refers to the current flowing through a real energy storage element, and could be either the discharge current from the real energy storage element or the charging current to the real energy storage element. "Real voltage behavior" refers to the voltage behavior in a real energy storage element. The energy storage element model combines a voltage source of the energy storage element and circuit elements such as resistors and capacitors to simulate the charge and discharge behavior of the energy storage element. The energy storage element model may be an equivalent circuit model. The "parameters" may be circuit parameters in the ECM. The "model current" may be a discharge current from the energy storage element model or a charge current to the energy storage element model. The "model voltage behavior" means the voltage behavior in the energy storage element model.

[0011] When a real current (discharge current or charge current) flows through a real energy storage element over a predetermined period, the state of the energy storage element, such as the state of charge (SOC) and temperature, changes. When a discharge current flows, the SOC of the energy storage element decreases, and when a charge current flows, the SOC of the energy storage element increases. However, conventionally, the state transition of the energy storage element has not been considered when obtaining the circuit parameters in the ECM.

[0012] An example of a conventional method for obtaining circuit parameters in an ECM will be described. FIG. 1 is a diagram showing an example of an ECM of an energy storage element (hereinafter also referred to as a battery). The ECM shown in FIG. 1 includes, as circuit parameters, an OCV (Open Circuit Voltage) that simulates a battery (for example, a lithium-ion battery) and an R0 and a two-stage RC parallel circuit (R1, C1, R2, C2) that simulate overvoltage (polarization amount). In FIG. 1, Vocv is the electromotive force of the battery OCV, R0I is the initial ohmic resistance (less than 1 second or the first second when calculated at 1-second intervals), and u1 and u2 represent the subsequent non-ohmic resistances (after 1 second when calculated at 1-second intervals).

[0013] When current I is input to the ECM shown in FIG. 1, the voltage behavior can be expressed by the following equations (1) to (2).

[0014]

Equation

[0015] Here, Vcalc is the voltage (terminal voltage), and un is the voltage change due to the RC parallel circuit consisting of Rn and Cn.

[0016] When simulating current-voltage characteristics using the ECM described above, the circuit parameters (R0, R1, C1, R2, C2) that constitute the ECM are used. Each circuit parameter is set in advance based on measured data, etc., according to the purpose of the battery being simulated. Figure 2 is a conceptual diagram showing an example of table data for circuit parameters. As shown in Figure 2, the circuit parameters are stored as two-dimensional table data, for example, for the battery's SOC and temperature. The two-dimensional table stores R0, R1, C1, R2, and C2 for SOC and temperature at predetermined intervals.

[0017] Figure 3 is an explanatory diagram illustrating the method for obtaining circuit parameters in a conventional ECM. Below, as an example, we will explain how to obtain the circuit parameters (R0, R1, C1, R2, C2) of an ECM that simulates the transient voltage behavior of a lithium-ion battery when a discharge current is applied for 50 seconds from a temperature of 0°C and a state of charge of 40%. The calculation interval is assumed to be 1 second. The graph in Figure 3 shows the relationship between discharge time and voltage change. The horizontal axis of the graph is the time from the start of discharge (s), and the vertical axis is the voltage change ΔV (V) associated with discharge. In Figure 3, the dots indicate the voltage change obtained by measurement, and the solid line indicates the voltage change obtained by the fitting calculation described later. The voltage change corresponds to the polarization voltage.

[0018] First, R0 is set by dividing the voltage drop value at 1 second obtained from the measured data by the current value applied. Here, it is assumed that the SOC and temperature do not change during the 50 seconds of energization, and that the SOC and temperature at the start of energization are constant. Next, with R0 constant, the voltage behavior after 1 second is determined by fitting calculation. That is, the remaining four circuit parameters (R1, C1, R2, C2) are calculated by adjusting the voltage behavior of the ECM to approach the profile of connected dots. In this case, the remaining four circuit parameters are also calculated as constant values, similar to R0. The obtained R1, C1, R2, C2 and R0 are recorded in the two-dimensional table data shown in Figure 2. As a result, the circuit parameters corresponding to the temperature and SOC at the start of discharge are obtained.

[0019] The conventional method for obtaining circuit parameters described above does not take into account the progression of the battery's state. Even though discharging at a predetermined current for 50 seconds from a 40% SOC (State of Charge) decreases the battery's SOC and changes temperature, the circuit parameters are still set to those of a 40% SOC and 0°C temperature. In other words, the circuit parameters are determined under the assumption that the SOC and temperature do not change during energization. Furthermore, it is assumed that the battery's internal impedance does not change when the changes in SOC and temperature are small.

[0020] Figure 4 is a graph showing the relationship between DC resistance and SOC. In Figure 4, the horizontal axis is SOC (%) and the vertical axis is DC resistance R0 (mΩ). As shown in Figure 4, DC resistance is known to change significantly in response to changes in SOC, especially in the low SOC region. Conventional methods for obtaining circuit parameters do not take into account this SOC dependence of R0. R0 depends not only on SOC, but also on battery temperature and battery health (SOH: State of Health). Conventional methods for obtaining circuit parameters do not take into account these changes in battery state. When simulating current-voltage characteristics using an ECM that includes circuit parameters, the calculation accuracy may decrease, especially in regions where such changes in battery state are large.

[0021] The inventors of this invention have devised a method to adjust the parameters so that the transient model voltage behavior when a model current equivalent to the actual current is passed through the energy storage element model for a predetermined period of time approaches the actual voltage behavior, by changing the parameters in a way that simulates the state transition of the energy storage element model in conjunction with the flow of the model current. This allows for the generation of energy storage device models that accurately simulate the transient voltage behavior in response to current in real-world energy storage devices. Based on these models, it is expected that the design and development of systems using energy storage devices can be carried out more efficiently. In addition to the design and development phases, the energy storage device models can also be used for diagnosing the state of energy storage devices and for various control functions during their operation.

[0022] In the method for generating the energy storage element model, the parameters at the point in time between the start and end of the predetermined period may be determined by interpolation calculation during the adjustment process.

[0023] With the above configuration, parameters that take into account the state transition of the energy storage element can be efficiently calculated by interpolation calculations using parameters at the start and end of a predetermined period. By having such parameters, it is possible to generate an energy storage element model that accurately simulates transient voltage behavior.

[0024] In the method for generating an energy storage element model, the energy storage element model is an equivalent circuit model that includes a resistor that simulates the DC resistance component of the energy storage element, and in the adjustment, the parameters related to the resistor may be changed.

[0025] According to the above configuration, the circuit parameter R0 related to the resistor that simulates the DC resistance component in the ECM is changed during parameter adjustment. By interpolating R0 at a predetermined time point using the R0 corresponding to the SOC of the energy storage element at the start and the R0 corresponding to the SOC of the energy storage element at the end, the SOC dependence of R0 can be reflected in the energy storage element model.

[0026] The method for generating the energy storage element model may involve changing the parameters to simulate the health state and / or temperature changes of the energy storage element model in conjunction with the flow of the model current.

[0027] According to the above configuration, the parameters are changed to correspond to the health state and / or temperature of the energy storage element, so the health state and / or temperature dependence of the parameters can be reflected in the energy storage element model. The parameters may be determined based on the amount of resistance degradation, which is a function of the health state and temperature of the energy storage element.

[0028] In the method for generating an energy storage element model, the energy storage element model may be an equivalent circuit model that includes a resistor that simulates the DC resistance component of the energy storage element and an RC parallel circuit that simulates the polarization characteristics of the energy storage element. In the adjustment of the method for generating the energy storage element model, the parameters relating to the resistor and the parameters relating to the RC parallel circuit may be changed.

[0029] With the above configuration, the state transitions of the energy storage element can be reflected in both the DC resistance component and the RC parallel circuit in the energy storage element model. By adjusting both the parameters related to the DC resistance component and the parameters related to the RC parallel circuit included in the energy storage element model, the accuracy of voltage behavior reproduction can be improved compared to adjusting only the parameters related to the DC resistance component.

[0030] In the method for generating an energy storage element model, the energy storage element model may be an equivalent circuit model that includes a resistor that simulates the DC resistance component of the energy storage element and a plurality of RC parallel circuits that simulate the polarization characteristics of the energy storage element. In the adjustment of the method for generating an energy storage element model, the parameters relating to at least one of the plurality of RC parallel circuits that represent the health state and / or temperature changes of the energy storage element model may be changed.

[0031] According to the above configuration, an RC parallel circuit containing parameters that represent the health status and / or temperature changes of the energy storage element model is added to the energy storage element model. To simulate the degradation characteristics of polarization voltage, only the parameters related to the added RC parallel circuit are changed among the multiple RC parallel circuits. This eliminates the need to adjust the parameters related to other RC parallel circuits for the purpose of simulating the degradation characteristics of polarization voltage, thereby enabling the generation of an energy storage element model with reduced computational load.

[0032] In the method for generating the energy storage element model, the parameters may be changed in the adjustment based on the amount of heat generated by the energy storage element model.

[0033] With the above configuration, the parameters are changed to correspond to the amount of heat generated by the energy storage element model, so the amount of degradation polarization that changes according to the amount of heat generated by the energy storage element model can be reflected in the energy storage element model.

[0034] The energy storage element model generation apparatus includes an adjustment unit that adjusts the parameters so that the transient model voltage behavior when a model current equivalent to the actual current is passed through an energy storage element model, which includes parameters, for a predetermined period of time, approaches the actual voltage behavior, in order to simulate the transient actual voltage behavior when an actual current is passed through an actual energy storage element for a predetermined period of time. In the energy storage element model generation apparatus, the adjustment unit changes the parameters in the adjustment so as to simulate the state transition of the energy storage element model in accordance with the flow of the model current.

[0035] The program adjusts the parameters of a storage element model, which includes parameters, so that the transient model voltage behavior when a model current equivalent to the actual current is passed through the storage element model for a predetermined period of time approaches the actual voltage behavior, in order to simulate the transient voltage behavior when a real current is passed through the storage element model for a predetermined period of time. In this adjustment, the program causes the computer to perform a process of changing the parameters so as to simulate the state transition of the storage element model in accordance with the flow of the model current.

[0036] The present disclosure will be described in detail below with reference to the drawings illustrating its embodiments.

[0037] (First Embodiment) Figure 5 is a conceptual diagram showing the overall picture of the lifetime prediction calculation for energy storage elements. First, we will use Figure 5 to explain the overall picture of the lifetime prediction calculation and the role of the ECM. When designing an energy storage system, it is common practice to perform calculations to predict the lifespan of the energy storage elements. Figure 5 schematically shows the calculation of how much the initial full charge capacity of an energy storage element will decrease (degrade) after 10 years. In the first step of the lifespan prediction calculation, an ECM (Electronic Voltage Measurement) is used, which outputs the transient voltage behavior of the energy storage element when a current is input to the energy storage element.

[0038] In the second step of the lifetime prediction calculation, a thermal circuit model is used that outputs the temperature of the energy storage element based on the current and voltage. In the third step of the lifetime prediction calculation, the amount of degradation of the energy storage element is calculated using methods such as the square root rule or the linear rule, based on the voltage behavior obtained in the first step and the temperature change obtained in the second step. Based on the obtained amount of degradation, the lifetime of the energy storage element is predicted. By repeating these first to third steps, the extent to which the energy storage element will degrade after 10 years is calculated. In this way, since ECM is used in the first step of the lifetime prediction calculation, improving the estimation accuracy in ECM can improve the accuracy of the final lifetime prediction of the energy storage element. In this embodiment, an ECM is generated that can properly simulate the voltage behavior of the energy storage element by adjusting the parameters described later.

[0039] Figure 6 is a block diagram of the generation device 1 according to this embodiment. The generation device 1 comprises a control unit 10, a storage unit 11, and a communication unit 12.

[0040] The control unit 10 is an arithmetic circuit equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc. The CPU in the control unit 10 executes various computer programs stored in the ROM and memory unit 11, and controls the operation of the hardware components described above, thereby making the entire device function as a generation device of this disclosure. The control unit 10 may also be equipped with functions such as a timer for measuring the elapsed time from the time a measurement start instruction is given until a measurement end instruction is given, a counter for counting numbers, and a clock for outputting date and time information.

[0041] The storage unit 11 is a storage device such as a hard disk or an SSD (Solid State Drive). Various computer programs and data are stored in the storage unit 11. The computer programs stored in the storage unit 11 include a generation program 111 for generating an energy storage element model ECM. The data stored in the storage unit 11 includes generation data 112 used for generating the energy storage element model ECM. The generation data 112 may include measured data for generating the energy storage element model ECM, configuration information showing the circuit configuration of the energy storage element model ECM, etc.

[0042] The computer program (computer program product) stored in the storage unit 11 may be provided on a non-temporary recording medium 1A on which the computer program is recorded in a readable format. The recording medium 1A is a portable memory such as a CD-ROM, USB memory, or SD (Secure Digital) card. The control unit 10 reads the desired computer program from the recording medium 1A using a reading device (not shown) and stores the read computer program in the storage unit 11. Alternatively, the computer program may be provided via communication. The generated program 111 can be deployed on a single computer or at one site, or distributed across multiple sites and run on multiple computers interconnected by a communication network.

[0043] The communication unit 12 is a communication interface for communicating with external devices. External devices are terminal devices such as personal computers and smartphones used by users and administrators. The control unit 10 transmits information about the generated energy storage element model ECM from the communication unit 12 to the external device. The external device receives the information transmitted from the communication unit 12 and performs various simulations using the energy storage element model ECM based on the received information.

[0044] The generating device 1 may also include an input unit for receiving other operational inputs, a display unit for displaying images, and the like.

[0045] Figure 7 is an explanatory diagram illustrating the method for obtaining circuit parameters in the energy storage element model ECM of this embodiment. Below, we will describe an example of determining the circuit parameters of the ECM that simulate the transient voltage behavior of the energy storage element when a discharge current is flowed for a predetermined period from the start of discharge to the end of discharge. The calculation interval is set to every 1 second. The graph in Figure 7 shows the relationship between discharge time and voltage change, similar to Figure 3. The horizontal axis of the graph is the time from the start of discharge (s), and the vertical axis is the voltage change amount ΔV (V) due to internal impedance, which is the voltage change amount associated with discharge minus the change in open circuit voltage associated with the change in SOC. The dots in Figure 7 indicate the voltage change amount obtained by actual measurement, and the solid line indicates the voltage change amount obtained by fitting calculation described later.

[0046] The measured voltage change can be determined, for example, by measuring the voltage of the energy storage element when discharging from a full charge (SOC 100%) at predetermined SOC intervals (e.g., every 10%) using a constant current discharge test, and then subtracting the previously acquired OCV from the measured voltage.

[0047] Let X be the state of charge (SOC) of the ECM at the start of discharge and X be the SOC of the ECM at the end of discharge. If the discharge is performed every 10% of the SOC in a constant current discharge test, X2 may also be X1 - 10.

[0048] As described above, in the conventional method, fitting calculations were performed by preparing five circuit parameters R0, R1, C1, R2, and C2. In this embodiment, as elements constituting the ECM, ten circuit parameters are obtained: R0(X1), R1(X1), C1(X1), R2(X1), and C2(X1) corresponding to the SOC value X1 of the energy storage element, and R0(X2), R1(X2), C1(X2), R2(X2), and C2(X2) corresponding to the SOC value X2 of the energy storage element.

[0049] First, the initial voltage drop value (at 1 second from the start) obtained from the measured data is divided by the current value applied to set R0(X1). Referring to the correlation between R0 and SOC, the R0 of the SOC value Xe% calculated based on R0(X1) is set to R0(X2).

[0050] Based on R0(X1) and R0(X2), the voltage behavior after 1 second is determined by fitting calculations. By adjusting the ECM voltage behavior to approximate the dotted profile, the remaining eight parameters R1(X1), C1(X1), R2(X1), C2(X1), R1(X2), C1(X2), R2(X2), and C2(X2) are calculated by fitting calculations. In this case, R0 corresponding to the SOC value after 1 second is calculated by interpolation calculations using R0(X1) and R0(X2), and the calculated R0 is used to perform fitting calculations for the eight circuit parameters.

[0051] Optimization calculations may be used to adjust the circuit parameters. For example, nonlinear programming may be used as the optimization calculation. Specifically, methods such as generalized reduced gradient descent (GRG) or genetic algorithms may be used to adjust the circuit parameters. The obtained R0(X1), R1(X1), C1(X1), R2(X1), and C2(X1) are associated with the initial SOC value X1 and temperature and recorded in a two-dimensional table data. R0(X2), R1(X2), C1(X2), R2(X2), and C2(X2) are associated with the final SOC value X2 and temperature and recorded in a two-dimensional table data.

[0052] Using a similar procedure, each circuit parameter is obtained for the next period (the period corresponding to the SOC value X2 to SOC value X3 of the energy storage element). If discharge occurs every 10% of SOC in a constant current discharge test, X3 = X2 - 10 may also be used. Let X2 be the SOC value at the start of the predetermined period and X3 be the SOC value at the end, and determine each circuit parameter by fitting. In this case, R0(X3) is determined based on the voltage drop value obtained from the measured data. R0(X2), R1(X2), C1(X2), R2(X2), and C2(X2) have already been obtained. Therefore, based on these six circuit parameters, the remaining four circuit parameters R1(X3), C1(X3), R2(X3), and C2(X3) can be calculated by fitting calculations. In this way, the circuit parameters corresponding to each SOC value are obtained sequentially.

[0053] According to the method described above, in order to simulate the transient real voltage behavior (measured data) when a real current is passed through a real energy storage element for a predetermined period of time, circuit parameters are obtained that are adjusted so that the transient model voltage behavior when a model current equivalent to the real current is passed through the energy storage element model ECM, which includes parameters, for a predetermined period of time approaches the real voltage behavior.

[0054] Figure 8 is a flowchart showing an example of the procedure for generating an energy storage element model ECM. The control unit 10 of the generation device 1 executes the following process according to the generation program 111. In the following steps, an ECM is generated as an energy storage element model ECM, which includes a resistor that simulates the DC resistance component of the energy storage element, a first RC parallel circuit that simulates the first polarization characteristic of the energy storage element, and a second RC parallel circuit that simulates the second polarization characteristic of the energy storage element.

[0055] The control unit 10 of the generation device 1 refers to the generated data 112 of the storage unit 11 to acquire configuration information and measured data of the ECM to be generated, and prepares 10 circuit parameters for the ECM (step S11). The circuit parameters include R0(Xi), R1(Xi), C1(Xi), R2(Xi), and C2(Xi) corresponding to the SOC value Xi% at the start of a predetermined period to be calculated, and R0(Xe), R1(Xe), C1(Xe), R2(Xe), and C2(Xe) corresponding to the SOC value Xe% at the end of the predetermined period.

[0056] The control unit 10 acquires R0(Xi) and R0(Xe) (step S12). Specifically, the control unit 10 acquires R0(Xi) by calculating the voltage drop value less than 1 second or at 1 second from the start time based on the measured data. The control unit 10 acquires R0(Xe) corresponding to the SOC value Xe% based on the correlation between R0 and SOC.

[0057] The control unit 10 performs a fitting calculation based on R0(Xi) and R0(Xe) so that the voltage behavior after 1 second matches the measured data (step S13). In this case, the control unit 10 calculates R0 corresponding to the SOC value after 1 second by interpolation calculation using R0(Xi) and R0(Xe), and performs a fitting calculation of the eight circuit parameters based on the calculated R0 corresponding to the SOC value after 1 second. The control unit 10 may adjust the circuit parameters using methods such as the generalized reduced gradient descent (GRG) or a genetic algorithm.

[0058] The control unit 10 obtains circuit parameters R1(Xi), C1(Xi), R2(Xi), C2(Xi), R1(Xe), C1(Xe), R2(Xe), and C2(Xe) according to the fitting (step S14).

[0059] The control unit 10 determines whether or not to terminate the process (step S15). The control unit 10 determines to terminate if it has acquired circuit parameters for all predetermined periods (SOC values), for example. If it determines not to terminate (step S15: NO), the control unit 10 returns the process to step S11 and repeats the acquisition of circuit parameters for the next period.

[0060] When acquiring circuit parameters for the next period, the control unit 10 may use the already acquired R1(Xe), C1(Xe), R2(Xe), and C2(Xe). The control unit 10 sets the five circuit parameters corresponding to the SOC value at the end of the previous period as the circuit parameters corresponding to the SOC value at the start of the next period. The control unit 10 also sets R0(Xe) at the end of the next period according to the measured data. Based on the six set circuit parameters, the control unit 10 performs a fitting calculation and acquires R1(Xe), C1(Xe), R2(Xe), and C2(Xe) at the end of the next period.

[0061] If it determines that the process is complete (step S15: YES), the control unit 10 stores the ECM configuration information, a two-dimensional table including each circuit parameter, etc., in the storage unit 11 (step S16), and terminates the series of processes. The control unit 10 may also transmit the generated ECM information to an external device, etc., via the communication unit 12.

[0062] In the process described above, the control unit 10 may determine the estimation accuracy of the generated ECM. The control unit 10 uses the ECM, which includes each acquired circuit parameter, to calculate the voltage response to the model current and determines whether the error between the obtained voltage response and the measured data is less than a preset threshold. If the error is not less than the threshold, the control unit 10 may perform the process from step S12 onward again and readjust the circuit parameters.

[0063] Figure 9 is a graph showing the verification results of the ECM generated by the method of this embodiment. In the graph shown in Figure 9, the horizontal axis represents the time from the start of discharge (s), and the vertical axis represents the voltage change ΔV (V) associated with the discharge. The simulation conditions were an ambient temperature of 10°C for the energy storage element, a state of charge (SOC) of 20% at the start of discharge, and a discharge time of 100 seconds. For reference, Figure 9 also shows a graph of the measured values ​​and the reproduction results of a conventional ECM. When the circuit parameters were changed considering the fluctuation of SOC (the present invention's method), it was possible to improve the accuracy of the reproduction of the measured values ​​compared to when the circuit parameters were not changed (the conventional method). Here, the average error was used as a parameter that reflects the accuracy of the reproduction. The average error was defined as Σ{(measured voltage)-(calculated voltage)} / (number of data points). The average error of the voltage change between the reproduction results by the conventional ECM and the measured values ​​was 73.9mV, while the average error of the voltage change between the reproduction results by the present invention's ECM and the measured values ​​was -9.6mV.

[0064] According to this embodiment, by adjusting the circuit parameters in consideration of fluctuations in the state of charge (SOC) of the energy storage element, it is possible to generate an ECM that takes into account the SOC dependence of the circuit parameters. When using the ECM to calculate the current-voltage response when, for example, the energy is discharged from SOC 20% to SOC 30%, the circuit parameters at intermediate points in the discharge period are estimated by interpolation calculation from the circuit parameters at SOC 20% and SOC 30%. Since the circuit parameters are adjusted in consideration of SOC dependence (assuming that the circuit parameters used in the calculation differ as the SOC of the energy storage element changes from 20% to 30%), the accuracy of reproduction during current-voltage response calculation can be improved.

[0065] (Second Embodiment) In the second embodiment, in addition to the circuit parameter R0 related to the DC resistance component, the circuit parameters R1 and R2 related to the RC parallel circuit are changed. The following mainly describes the differences from the first embodiment, and components common to the first embodiment are denoted by the same reference numerals and their detailed descriptions are omitted.

[0066] It has been known that there is a correlation between the DC internal resistance (DCR) and state of health (SOH) of energy storage elements. Figure 10 is a graph showing the relationship between the DC internal resistance and the state of health of a lithium-ion battery. In the graph shown in Figure 10, the horizontal axis is the state of health (SOH) (%), and the vertical axis is the DC internal resistance (DCR) (ohm resistance at less than 1 second or at 1 second when calculated at 1-second intervals, in Ω). The state of health corresponds to the health of the energy storage element. As shown in Figure 10, DCR increases as SOH decreases. When this correlation between SOH and DCR is expressed as a function, the following equation (3) holds. ΔR=(SOH,T)…(3) Here, ΔR is the amount of resistance degradation of the energy storage element.

[0067] Conventionally, methods have been used that ignore the degradation of the energy storage element and do not change the circuit parameters of the ECM once they have been determined. However, in order to simulate the state transition of a battery, which is degradation, one method is to add the amount of resistance degradation to the circuit parameter R0 related to the DC resistance component in the ECM shown in Figure 1. The voltage behavior in the ECM using this method can be expressed by equations (4) to (5) below.

[0068]

number

[0069] The above ECM does not take into account degradation in the RC parallel circuit. When using the above relational equations (4) and (5), only R0' changes as the energy storage element degrades, resulting in a decrease in the representation performance of the RC parallel circuit that expresses the nonlinear polarization curve. In this embodiment, in order to more appropriately represent the polarization behavior that takes into account degradation over time, the circuit parameters R1 and R2 related to the RC parallel circuit are changed in addition to R0'.

[0070] Figure 11 shows an example of an ECM of an energy storage element in the second embodiment. The ECM includes an OCV that simulates a battery, R0′ that simulates an overvoltage, and a two-stage RC parallel circuit (R1′, C1, R2′, C2) as circuit parameters. The voltage behavior in the ECM shown in Figure 11 can be expressed by the following equations (6) to (8).

[0071]

number

[0072] Here, Vcalc is the model voltage (terminal voltage), un' is the voltage change due to the RC parallel circuit consisting of Rn' and Cn, and kn(T) is a temperature-dependent correction coefficient. For simplicity, kn(T) will be simply written as kn below.

[0073] Figure 12 is an explanatory diagram illustrating the method for obtaining circuit parameters in the energy storage element model ECM of the second embodiment. In the graph shown in Figure 12, the horizontal axis represents the time (s) from the start of discharge, and the vertical axis represents the absolute value of the voltage change ΔV (V) associated with discharge. In Figure 12, the solid line represents the measured value, the dashed line represents the fitting result by the ECM of this embodiment, and the dashed line represents the fitting result by the conventional ECM.

[0074] As shown in Figure 12, the conventional method of changing only R0 results in a discrepancy with the measured value. In this embodiment, this discrepancy ΔV′ (the difference between the value obtained by the conventional method and the measured value) is expressed by R1′ and R2′.

[0075] The generation device 1 uses the conventional circuit parameters R0, R1, C1, R2, and C2 expressed by equations (4) and (5) to determine R0', R1', and R2', taking degradation into account. The generation device 1 has previously acquired each circuit parameter from the conventional ECM and stores a two-dimensional table of the acquired circuit parameters in the generated data 112.

[0076] Figure 13 is a flowchart showing an example of the energy storage element model ECM generation process in the second embodiment. The control unit 10 of the generation device 1 executes the following processes according to the generation program 111.

[0077] The control unit 10 of the generation device 1 refers to the generated data 112 of the storage unit 11 to acquire configuration information of the ECM to be generated, circuit parameters R0(Xi), R1(Xi), C1(Xi), R2(Xi), C2(Xi) in a conventional ECM, measured data, etc., and prepares the circuit parameters for the ECM (step S21). The circuit parameters include R0′(Xi), R1′(Xi), C1(Xi), R2′(Xi), C2(Xi), k1(Xi), and k2(Xi) corresponding to the SOC value Xi% at the start of a predetermined period to be calculated.

[0078] The control unit 10 obtains the value R0′(Xi) by adding the resistance degradation amount ΔR(SOH,T), which is determined from the SOC value and temperature at the start, to R0(Xi) (step S22). The control unit 10 calculates the degradation polarization amount ΔV′ at each point in time from the start to the end of a predetermined period using the following relational expression (9) (step S23). ΔV′=ΔV-ΔVcalc…(9) Here, ΔV is the polarization amount (the change in voltage due to discharge), and ΔVcalc is the calculated value of the polarization amount obtained by equations (4) and (5) above. ΔV′ represents the difference between the measured value and the calculated value when only R0(Xi) is changed.

[0079] The control unit 10 performs a fitting calculation so that the amount of degradation polarization after 1 second is in line with the calculated ΔV′ (step S24), and obtains k1(Xi) and k2(Xi) (step S25). In detail, the control unit 10 adjusts k1(Xi) and k2(Xi) so that the sum of k1(Xi) × ΔR(SOH,T) and k2(Xi) × ΔR(SOH,T) is in line with ΔV′.

[0080] The control unit 10 obtains R1'(Xi) and R2'(Xi) based on the acquired k1(Xi) and k2(Xi) (step S26). Specifically, the control unit 10 calculates R1'(Xi) by substituting R1(Xi), k1(Xi), and ΔR(SOH,T) into equation (8) and performing the calculation process of equation (8). Similarly, it calculates R2'(Xi) based on R2(Xi), k2(Xi), and ΔR(SOH,T).

[0081] The control unit 10 determines whether or not to terminate the process (step S27). The control unit 10 determines to terminate if it has acquired circuit parameters for all predetermined periods (SOC values), for example. If it determines not to terminate (step S27: NO), the control unit 10 returns the process to step S21 and repeats the acquisition of circuit parameters for the next period.

[0082] If it determines that the process is complete (step S27: YES), the control unit 10 stores the ECM configuration information, a two-dimensional table including various circuit parameters, etc., in the storage unit 11 (step S28), and terminates the series of processes.

[0083] In the process described above, the control unit 10 may determine whether the acquired k1(Xi) and k2(Xi) are temperature-dependent. If the correlation between the temperature of the energy storage element and k1(Xi) and k2(Xi) does not satisfy the predetermined conditions, the control unit 10 may repeat the process from step S24 onwards to readjust k1(Xi) and k2(Xi).

[0084] According to this embodiment, the circuit parameters R1' and R2' make it possible to generate an ECM that reflects the health status of the ECM and changes in the amount of resistance degradation in response to temperature.

[0085] (Third embodiment) In the third embodiment, a new RC parallel circuit is added to represent the resistance degradation of the energy storage element. Below, the differences from the first and second embodiments will be mainly described, and components common to the first and second embodiments will be given the same reference numerals and their detailed descriptions will be omitted.

[0086] Figure 14 shows an example of an ECM of an energy storage element in the third embodiment. The ECM includes an OCV that simulates a battery, R0' that simulates an overvoltage, and a three-stage RC parallel circuit (R1, C1, R2, C2, R3, C3) as circuit parameters. The voltage behavior in the ECM shown in Figure 14 can be expressed by the following equations (10) to (13).

[0087]

number

[0088] Here, Vcalc is the model voltage (terminal voltage), un is the voltage change due to an RC parallel circuit consisting of Rn and Cn, and kn(SOC,T) is a correction coefficient that is dependent on SOC and temperature.

[0089] As shown in equations (10) to (13), R3 depends on the SOC, temperature, and SOH of the energy storage element. C3 also depends on the SOC and temperature of the energy storage element. Of the circuit parameters related to the three RC parallel circuits, the only circuit parameters that change with the degradation of the energy storage element are R3 and C3 related to the newly added third stage RC parallel circuit. In this embodiment, ΔV′ (the difference between the value obtained by the conventional method and the measured value) shown in Figure 12 is represented by the RC parallel circuit equipped with R3 and C3.

[0090] Figure 15 is a flowchart showing an example of the energy storage element model ECM generation process in the third embodiment. The control unit 10 of the generation device 1 performs the following processing according to the generation program 111.

[0091] The control unit 10 of the generation device 1 refers to the generated data 112 of the storage unit 11 to acquire configuration information, measured data, etc. of the ECM to be generated, and prepares the circuit parameters for the ECM (step S31). The circuit parameters include R0'(Xi), R1(Xi), C1(Xi), R2(Xi), C2(Xi), R3(Xi), C3(Xi) corresponding to the SOC value Xi% at the start of the predetermined period to be calculated, and R0'(Xe), R1(Xe), C1(Xe), R2(Xe), C2(Xe), R3(Xe), C3(Xe) corresponding to the SOC value Xe% at the end of the predetermined period.

[0092] The control unit 10 uses equation (9) above to calculate the degradation polarization amount ΔV′ at each point in time from the start to the end of a predetermined period (step S32). ΔV′ represents the difference between the measured value and the calculated value when using an ECM that does not include the third stage RC parallel circuit (an RC parallel circuit with circuit parameters that change with degradation).

[0093] The control unit 10 performs a fitting calculation so that the amount of degradation polarization after 1 second aligns with the calculated ΔV′ (step S33), and obtains R3(Xi), C3(Xi), R3(Xe), and C3(Xe) (step S34). In detail, the control unit 10 adjusts the above four circuit parameters so that the third stage RC parallel circuit u3 aligns with ΔV′.

[0094] The control unit 10 performs a fitting calculation based on the four circuit parameters above so that the voltage behavior after 1 second elapses conforms to the measured data (step S35). In this case, the control unit 10 calculates R3 and C3 corresponding to the SOC value after 1 second elapses by interpolation calculation using the four circuit parameters above, and performs a fitting calculation of the remaining circuit parameters using the calculated R3 and C3. The method for calculating the remaining circuit parameters may be the same as in the first embodiment.

[0095] The control unit 10 obtains circuit parameters R0'(Xi), R1(Xi), C1(Xi), R2(Xi), C2(Xi), R0'(Xe), R1(Xe), C1(Xe), R2(Xe), and C2(Xe) according to the fitting (step S36).

[0096] The control unit 10 determines whether or not to terminate the process (step S37). The control unit 10 determines to terminate if it has acquired circuit parameters for all predetermined periods (SOC values), for example. If it determines not to terminate (step S37: NO), the control unit 10 returns the process to step S31 and repeats the acquisition of circuit parameters for the next period.

[0097] If it determines that the process is complete (step S37: YES), the control unit 10 stores the ECM configuration information, a two-dimensional table including various circuit parameters, etc., in the storage unit 11 (step S38), and terminates the series of processes.

[0098] According to this embodiment, the ECM is equipped with a new RC parallel circuit for representing the health status of the ECM and changes in the amount of resistance degradation according to temperature. Since the degradation of the ECM can be represented by this RC parallel circuit, the amount of work required can be reduced compared to the case in the second embodiment where the circuit parameters R1' and R2' are changed.

[0099] (Fourth Embodiment) In the fourth embodiment, circuit parameters are obtained that take into account the heat generated by the energy storage element. Below, the differences from the first to third embodiments will be mainly explained, and components common to the first to third embodiments will be given the same reference numerals and their detailed explanation will be omitted. The ECM in the fourth embodiment, like in the third embodiment, includes an OCV that simulates a battery, R0′ that simulates overvoltage, and a three-stage RC parallel circuit (R1, C1, R2, C2, R3, C3) as circuit parameters.

[0100] Figure 16 is an explanatory diagram illustrating the method for obtaining circuit parameters in the energy storage element model ECM of the fourth embodiment. In the graph shown in Figure 16, the horizontal axis represents the time (s) from the start of discharge, and the vertical axis represents the absolute value of the voltage change ΔV (V) associated with discharge. In Figure 16, the solid line represents the measured value, the dashed line represents the fitting result by the ECM of this embodiment, the dashed line represents the voltage behavior assuming constant heat generation of the energy storage element, and the dashed line represents the voltage behavior considering heat generation of the energy storage element.

[0101] As shown in Figure 16, the voltage behavior when temperature changes due to heat generation from the energy storage element are considered differs from the voltage behavior when the heat generation from the energy storage element is assumed to be constant. Therefore, when acquiring circuit parameters R3 and C3 using the method of the third embodiment, the accuracy of ECM reproduction can be further improved by using the voltage change amount when temperature changes due to heat generation from the energy storage element are considered when calculating the difference ΔV′ between the voltage change amount using the conventional method and the measured value.

[0102] The generating device 1, for example, when using a conventional ECM expressed by equations (3) and (4), changes ΔR(SOH,T) according to the temperature of the energy storage element at each time point and obtains the circuit parameter R0′ corresponding to ΔR(SOH,T) at each time point. The generating device 1 divides the ΔVcalc obtained in this way from ΔV and takes the value obtained as ΔV′. This ΔV′ is represented by a third-stage RC parallel circuit.

[0103] Figure 17 is a flowchart showing an example of the energy storage element model ECM generation process procedure in the fourth embodiment. The control unit 10 of the generation device 1 performs the following processing according to the generation program 111.

[0104] The control unit 10 of the generation device 1 refers to the generated data 112 of the storage unit 11 to acquire configuration information, measured data, etc. of the ECM to be generated, and prepares the circuit parameters for the ECM (step S41). The circuit parameters include R0'(Xi), R1(Xi), C1(Xi), R2(Xi), C2(Xi), R3(Xi), C3(Xi) corresponding to the SOC value Xi% at the start of a predetermined period to be calculated, and R0'(Xe), R1(Xe), C1(Xe), R2(Xe), C2(Xe), R3(Xe), C3(Xe) corresponding to the SOC value Xe% at the end of the predetermined period.

[0105] The control unit 10 calculates the degradation polarization amount ΔV′ at each point in time from the start to the end of a predetermined period (step S42). In this case, the control unit 10 calculates ΔV′ that takes into account the temperature change of the energy storage element at each point in time by using ΔR(SOH,T) which takes into account the temperature change of the energy storage element at each point in time. Thereafter, the generation device 1 performs the energy storage element model ECM generation process by executing the same process as steps S33 to S38 shown in Figure 15.

[0106] Figure 18 is a graph showing the verification results of the ECM generated by the method of the fourth embodiment. In the graph shown in Figure 18, the horizontal axis represents the time (s) from the start of discharge, and the vertical axis represents the absolute value of the voltage change ΔV (V) associated with discharge. The simulation conditions were an ambient temperature of 10°C for the energy storage element, a state of charge (SOC) of 20% at the start of discharge, and a discharge time of 85 seconds. For reference, Figure 18 also shows a graph of the measured values ​​and the reproduction results of the conventional ECM. When circuit parameters R3 and C3 were calculated considering the heat generation of the energy storage element (the present method), it was possible to improve the accuracy of the reproduction of the measured values ​​compared to when the heat generation of the energy storage element was not considered (the conventional method). The average error in the voltage change between the reproduction results of the conventional ECM and the measured values ​​was -10.5mV, while the average error in the voltage change between the reproduction results of the present ECM and the measured values ​​was -0.3mV.

[0107] According to this embodiment, the ECM makes it possible to simulate current-voltage characteristics that take into account changes in the amount of resistance degradation due to heat generation in the energy storage element.

[0108] The examples shown in each of the embodiments described above can be combined with all or part of the configurations shown in each embodiment to realize other embodiments. Furthermore, the sequences shown in each of the embodiments described above are not limiting, and the order of each processing step may be changed and executed within the scope that does not contradict the processing content, and multiple processes may be executed in parallel.

[0109] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the claims and equivalents thereof. [Explanation of symbols]

[0110] 1 generator 10 Control Unit 11 Storage section 12 Communications Department 111 Generation Program 112 Generated data 1A Recording medium

Claims

1. In order to simulate the transient voltage behavior when a real current is passed through a real energy storage element for a predetermined period, the parameters are adjusted so that the transient model voltage behavior when a model current equivalent to the real current is passed through an equivalent circuit model including the parameters for a predetermined period approaches the real voltage behavior. In the adjustment described above, the parameters are changed to simulate the state transitions, including the transitions of the SOC and health state of the equivalent circuit model in accordance with the flow of the model current. The equivalent circuit model includes a plurality of RC parallel circuits that simulate the polarization characteristics of the energy storage element, each including an RC parallel circuit that includes parameters dependent on the health state of the energy storage element and an RC parallel circuit that does not include parameters dependent on the health state of the energy storage element. In the adjustment described above, the parameters relating to the RC parallel circuit, which includes parameters that depend on the health status of the energy storage element, are changed among the plurality of RC parallel circuits. Method for generating an energy storage element model.

2. In the adjustment described above, the parameters at the point in time between the start and end of the predetermined period are determined by interpolation. A method for generating an energy storage element model according to claim 1.

3. The equivalent circuit model includes a resistor that simulates the DC resistance component of the energy storage element. In the adjustment described above, the parameter relating to the resistor is changed. A method for generating an energy storage element model according to claim 2.

4. In the adjustment described above, the parameters are changed to simulate the temperature changes of the equivalent circuit model associated with the flow of the model current. A method for generating an energy storage element model according to any one of claims 1 to 3.

5. The equivalent circuit model includes a resistor that simulates the DC resistance component of the energy storage element and an RC parallel circuit that simulates the polarization characteristics of the energy storage element. In the adjustment described above, the parameters relating to the resistor and the parameters relating to the RC parallel circuit are changed. A method for generating an energy storage element model according to claim 4.

6. In order to simulate the transient real voltage behavior when a real current is passed through a real energy storage element for a predetermined period of time, the parameters are adjusted so that the transient model voltage behavior when a model current equivalent to the real current is passed through an equivalent circuit model including the parameters for a predetermined period of time approaches the real voltage behavior. The equivalent circuit model includes a resistor that simulates the DC resistance component of the energy storage element and an RC parallel circuit that simulates the polarization characteristics of the energy storage element. In the adjustment described above, the parameters relating to the resistor and the parameters relating to the RC parallel circuit are changed to simulate the state transitions, including the transitions in the SOC of the equivalent circuit model associated with the flow of the model current. In the above adjustment, The parameters relating to the resistor at the start of the first predetermined period are obtained, The parameters relating to the resistor corresponding to the SOC and temperature of the energy storage element at the end of the first predetermined period are obtained. Based on the parameters relating to the resistor at the start and end of the first predetermined period obtained, the parameters relating to the RC parallel circuit at the start and end of the first predetermined period are obtained. The parameters for the resistor and the parameters for the RC parallel circuit in the second predetermined period following the first predetermined period are adjusted using the parameters for the resistor and the parameters for the RC parallel circuit at the end of the first predetermined period as initial values. Method for generating an energy storage element model.

7. In the above adjustment, the parameters are changed based on the amount of heat generated by the equivalent circuit model. A method for generating an energy storage element model according to any one of claims 4 to 6.

8. In order to simulate the transient voltage behavior when a real current is passed through a real energy storage element for a predetermined period, the parameters are adjusted so that the transient model voltage behavior when a model current equivalent to the real current is passed through the energy storage element model, including the parameters, for a predetermined period approaches the real voltage behavior. In the adjustment described above, the parameters are changed based on the heat generation of the energy storage element model so as to simulate the state transitions, including the transition of the state of temperature (SOC) of the energy storage element model in accordance with the flow of the model current, and the transition of the health state and / or temperature. Method for generating an energy storage element model.

9. In order to simulate the transient voltage behavior when a real current is passed through a real energy storage element for a predetermined period, the equivalent circuit model, which includes parameters, is equipped with an adjustment unit that adjusts the parameters so that the transient model voltage behavior when a model current equivalent to the real current is passed through the equivalent circuit model for a predetermined period approaches the real voltage behavior. The adjustment unit, in the adjustment, changes the parameters to simulate the state transitions, including the state of control (SOC) and health status of the equivalent circuit model, associated with the flow of the model current. The equivalent circuit model includes a plurality of RC parallel circuits that simulate the polarization characteristics of the energy storage element, each including an RC parallel circuit that includes parameters dependent on the health state of the energy storage element and an RC parallel circuit that does not include parameters dependent on the health state of the energy storage element. The adjustment unit, in the adjustment, changes the parameters related to the RC parallel circuit among the plurality of RC parallel circuits, which include parameters that depend on the health status of the energy storage element. A device for generating energy storage element models.

10. In order to simulate the transient voltage behavior when a real current is passed through a real energy storage element for a predetermined period, the parameters are adjusted so that the transient model voltage behavior when a model current equivalent to the real current is passed through an equivalent circuit model including the parameters for a predetermined period approaches the real voltage behavior. In the adjustment described above, the parameters are changed to simulate the state transitions, including the transitions of the SOC and health state of the equivalent circuit model in accordance with the flow of the model current. The equivalent circuit model includes a plurality of RC parallel circuits that simulate the polarization characteristics of the energy storage element, each including an RC parallel circuit that includes parameters dependent on the health state of the energy storage element and an RC parallel circuit that does not include parameters dependent on the health state of the energy storage element. In the adjustment described above, the parameters relating to the RC parallel circuit, which includes parameters that depend on the health status of the energy storage element, are changed among the plurality of RC parallel circuits. A program that causes a computer to perform a process.

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