JP2013214371A - Battery system and estimation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect an open circuit voltage that does not include a voltage change amount due to polarization by estimating a time for which polarization of a battery unit is eliminated.
A battery system includes a battery unit (1) for charging / discharging, a voltage sensor (201, 201a) for detecting a voltage of the battery unit, a controller (300, 310) for estimating a state of the battery unit, Have The controller calculates the concentration distribution in the active material of the battery unit by using the diffusion equation, and assumes that the concentration distribution falls within an allowable range when it is assumed that the battery unit is not charged / discharged. Calculate the polarization elimination time. When the time during which the battery unit is not being charged / discharged is equal to or longer than the polarization elimination time, the controller acquires the open voltage of the battery unit using the voltage sensor.
[Selection] FIG.

Description

  The present invention relates to a battery system and an estimation method that can accurately acquire an open circuit voltage of a battery unit.

  The voltage of the secondary battery can be obtained using a voltage sensor. Here, during the charging / discharging of the secondary battery or immediately after stopping the charging / discharging of the secondary battery, the polarization of the secondary battery occurs, and the voltage acquired using the voltage sensor The amount of voltage fluctuation accompanying polarization is included.

JP 2008-243373 A

  The polarization of the secondary battery can be eliminated by leaving the secondary battery without charging / discharging. For this reason, if the voltage of a secondary battery is acquired using a voltage sensor after confirming that polarization has been eliminated, a voltage (so-called open circuit voltage) excluding the influence of polarization can be acquired. Here, when a fixed value is used as the time for eliminating the polarization, the time until the polarization is canceled may be excessively estimated. This reduces the opportunity to determine that polarization has been eliminated.

  The battery system according to the first invention of the present application includes a battery unit that performs charging and discharging, a voltage sensor that detects the voltage of the battery unit, and a controller that estimates the state of the battery unit. The controller calculates the concentration distribution in the active material of the battery unit by using the diffusion equation, and assumes that the concentration distribution falls within an allowable range when it is assumed that the battery unit is not charged / discharged. Calculate the polarization elimination time. Moreover, a controller acquires the open circuit voltage of a battery unit using a voltage sensor, when the time during which charging / discharging of a battery unit is not performed is more than polarization elimination time.

  In the first invention of this application, the concentration distribution in the active material is calculated using the diffusion equation (battery model equation described later), and the current concentration distribution of the battery unit can be acquired. If the current concentration distribution can be obtained, it is possible to calculate the time until the concentration distribution falls within the allowable range, in other words, the time until polarization is eliminated, based on the diffusion equation. By calculating the polarization elimination time in this way, the polarization elimination time reflecting the current state (concentration distribution) of the battery unit can be obtained, and the time until polarization is eliminated can be estimated appropriately. . And the opportunity to discriminate | determine that polarization is eliminated can be increased by estimating the elimination time of polarization appropriately.

  Also, when the time during which the battery unit is not being charged / discharged is equal to or longer than the polarization elimination time, in other words, when it is determined that the polarization is eliminated, the voltage associated with the polarization can be obtained by obtaining the voltage of the battery unit. A voltage that does not include a change amount can be acquired. Thereby, the open circuit voltage of a battery unit can be acquired accurately.

  For example, when the battery unit is a lithium ion secondary battery, the concentration distribution is a lithium concentration distribution. The concentration distribution can be calculated by setting the concentration at the center and interface of the active material as boundary conditions. When setting the polarization elimination time, a value obtained by adding the correction time to the polarization elimination time calculated from the concentration distribution can be used. When calculating the concentration distribution or calculating the polarization elimination time from the concentration distribution, a calculation error may occur. Therefore, by using a correction time considering the calculation error, it is possible to improve the accuracy when determining that the polarization has been eliminated.

  While the battery unit is being charged and discharged, the concentration distribution can be calculated and the state of charge (SOC) of the battery unit can be calculated. Specifically, a correspondence relationship between the average value of the concentration distribution and the charge state is obtained in advance, and the charge state can be estimated from the average value of the concentration distribution using this correspondence relationship. If the concentration distribution is calculated, the average value can be calculated from this concentration distribution.

  On the other hand, the full charge capacity of the battery unit can be estimated based on the state of charge of the battery unit. Specifically, when charging (or discharging) a battery unit, a charging state when charging (or discharging) is started, a charging state when charging (or discharging) is ended, and a battery unit is charged (or The full charge capacity can be calculated from the integrated current value during discharging.

  Here, the state of charge of the battery unit can be calculated using the correspondence between the open circuit voltage and the state of charge. Since the open voltage of the battery unit is acquired when the polarization is eliminated as described above, it is possible to improve the estimation accuracy of the open voltage. Since the state of charge is calculated based on this open circuit voltage, the accuracy of the state of charge can also be improved. If the accuracy of the state of charge is improved, the accuracy of the full charge capacity calculated from the state of charge can also be improved.

  On the other hand, when the plurality of battery units are connected in series, the voltage in the plurality of battery units can be equalized using the equalization circuit. In the present invention, since the open circuit voltage of each battery unit can be obtained with high accuracy, equalization processing can be performed with high accuracy.

  Here, the open circuit voltage of the battery unit can also be estimated from the average value of the concentration distribution. However, in this case, the estimated open-circuit voltage may contain an error, and to which side (higher side or lower side) the estimated open-circuit voltage is shifted relative to the true open-circuit voltage I can't figure out. In such a state, when equalizing the voltages in the plurality of battery units, it becomes difficult to perform equalization processing.

  That is, if it is not possible to grasp to which side the estimated open circuit voltage is deviated from the true open circuit voltage, the equalization process may be erroneously performed in the direction of increasing the voltage variation. Therefore, by using the present invention that can improve the estimation accuracy of the open-circuit voltage, the equalization process can be easily performed, and the equalization can be performed with high accuracy.

  The battery unit can be composed of single cells or a plurality of electrically connected single cells. In addition, the battery unit can be mounted on the vehicle, and the electric energy output from the battery unit can be converted into kinetic energy for running the vehicle.

  A second invention of the present application is an estimation method for estimating a state of a battery unit that is charged and discharged, and calculates a concentration distribution in the active material of the battery unit by using a diffusion equation, and charges and discharges the battery unit. When it is assumed that the concentration distribution is not performed, the polarization elimination time until the concentration distribution falls within the allowable range is calculated. When the time during which the battery unit is not being charged / discharged is equal to or longer than the polarization elimination time, the open voltage of the battery unit is acquired using a voltage sensor that detects the voltage of the battery unit. Also in the second invention of the present application, the same effect as that of the first invention of the present application can be obtained.

It is a figure which shows the structure of a battery system. It is a figure which shows the structure of a part of battery system. It is a figure which shows the structure of an equalization circuit. It is the schematic which shows the structure of a secondary battery. It is a figure which shows the list of variables etc. which are used with a battery model type | formula. It is a conceptual diagram explaining a battery model. It is a conceptual diagram which shows the active material model shown by the polar coordinate. It is a figure which shows the relationship between the terminal voltage of a secondary battery, and various average electric potential. It is a figure explaining the temperature dependence of a diffusion coefficient. It is a figure which shows the relationship between an open circuit voltage (positive electrode) and local SOC. It is a figure which shows the relationship between an open circuit voltage (negative electrode) and local SOC. It is the schematic which shows the structure of the battery state estimation part provided in the inside of a controller. It is a flowchart which shows the process of a battery state estimation part. It is a figure which shows the relationship between lithium average concentration and SOC. In an active material model, it is a figure which shows lithium concentration distribution of the state by which polarization was cancelled | released. It is a flowchart which shows equalization processing. It is a figure which shows the relationship between the remaining time until polarization cancellation, and a correction coefficient. It is a flowchart which shows the calculation process of a full charge capacity. It is a flowchart which shows the calculation process of a full charge capacity. It is a flowchart which shows the calculation process of a full charge capacity. It is a figure which shows the relationship between the remaining time until polarization cancellation, and a correction coefficient.

  Examples of the present invention will be described below.

  FIG. 1 is a diagram showing the configuration of the battery system of this example. The battery system shown in FIG. 1 can be mounted on a vehicle. Vehicles include HV (Hybrid Vehicle), PHV (Plug-in Hybrid Vehicle), and EV (Electric Vehicle).

  The HV includes other power sources such as an internal combustion engine or a fuel cell in addition to an assembled battery described later as a power source for running the vehicle. In PHV, an assembled battery can be charged using power from an external power source in HV. The EV includes only the assembled battery as a power source of the vehicle, and can receive the power supply from the external power source to charge the assembled battery. The external power source is a power source (for example, commercial power source) provided separately from the vehicle outside the vehicle.

  The assembled battery 100 includes a plurality of secondary batteries (corresponding to single cells or battery units) 1 connected in series. As the secondary battery 1, a secondary battery such as a nickel metal hydride battery or a lithium ion battery can be used. An electric double layer capacitor (capacitor) can be used instead of the secondary battery.

  The number of secondary batteries 1 can be appropriately set based on the required output of the assembled battery 100 and the like. The assembled battery 100 can also include a plurality of secondary batteries 1 connected in parallel. A monitoring unit (corresponding to a voltage sensor) 201 detects a voltage between terminals of the assembled battery 100 or detects a voltage Vb of each secondary battery 1. The monitoring unit 201 outputs the detection result to the controller 300.

  The current sensor 202 detects the current Ib flowing through the assembled battery 100 and outputs the detection result to the controller 300. Here, the discharge current Ib is a positive value, and the charging current Ib is a negative value. The temperature sensor 203 detects the temperature Tb of the assembled battery 100 and outputs the detection result to the controller 300. By using the plurality of temperature sensors 203, it is possible to detect the temperature Tb of the secondary batteries 1 arranged at different positions.

  The controller 300 includes a memory 300a, and the memory 300a stores various types of information for the controller 300 to perform predetermined processing (for example, processing described in the present embodiment). In this embodiment, the memory 300a is built in the controller 300, but the memory 300a can be provided outside the controller 300.

  A system main relay SMR-B is connected to the positive terminal of the assembled battery 100. System main relay SMR-B is switched between ON and OFF by receiving a control signal from controller 300. A system main relay SMR-G is connected to the negative terminal of the assembled battery 100. System main relay SMR-G is switched between on and off by receiving a control signal from controller 300.

  A system main relay SMR-P and a current limiting resistor 204 are connected in parallel to the system main relay SMR-G. System main relay SMR-P and current limiting resistor 204 are connected in series. System main relay SMR-P is switched between ON and OFF by receiving a control signal from controller 300. The current limiting resistor 204 is used to suppress the inrush current from flowing when the assembled battery 100 is connected to a load (specifically, the inverter 205).

  When connecting the assembled battery 100 to the inverter 205, the controller 300 first switches the system main relay SMR-B from off to on and switches the system main relay SMR-P from off to on. As a result, a current flows through the current limiting resistor 204.

  Next, after switching the system main relay SMR-G from off to on, the controller 300 switches the system main relay SMR-P from on to off. Thereby, the connection between the assembled battery 100 and the inverter 205 is completed, and the battery system is in a start-up state (Ready-On). Information about on / off of the ignition switch of the vehicle is input to the controller 300, and the controller 300 activates the battery system in response to the ignition switch switching from off to on.

  On the other hand, when the ignition switch is switched from on to off, the controller 300 switches the system main relays SMR-B and SMR-G from on to off. As a result, the connection between the assembled battery 100 and the inverter 205 is cut off, and the battery system enters a stopped state (Ready-Off).

  The inverter 205 converts the DC power from the assembled battery 100 into AC power and outputs the AC power to the motor / generator 206. For example, a three-phase AC motor can be used as the motor / generator 206. Motor generator 206 receives AC power from inverter 205 and generates kinetic energy for running the vehicle. The kinetic energy generated by the motor / generator 206 is transmitted to the wheels so that the vehicle can run.

  When the vehicle is decelerated or stopped, the motor generator 206 converts kinetic energy generated during braking of the vehicle into electrical energy (AC power). The inverter 205 converts the AC power generated by the motor / generator 206 into DC power, and outputs the DC power to the assembled battery 100. Thereby, the assembled battery 100 can store regenerative electric power.

  In this embodiment, the assembled battery 100 is connected to the inverter 205, but the present invention is not limited to this. Specifically, the assembled battery 100 can be connected to the booster circuit, and the booster circuit can be connected to the inverter 205. By using the booster circuit, the output voltage of the assembled battery 100 can be boosted. Further, the booster circuit can step down the output voltage from the inverter 205 to the assembled battery 100.

  As shown in FIG. 2, the monitoring unit 201 includes voltage monitoring ICs (integrated circuits, corresponding to monitoring units) 201a as many as the number of secondary batteries 1 constituting the assembled battery 100, and each voltage monitoring IC 201a. Are connected to each secondary battery 1 in parallel. The voltage monitoring IC 201a detects the voltage of the secondary battery 1 and outputs the detection result to the controller 300.

  Moreover, the equalization circuit 207 is connected in parallel to each secondary battery 1, and the equalization circuit 207 is used in order to equalize the voltage (or SOC) in the some secondary battery 1. FIG. The operation of the equalization circuit 207 is controlled by the controller 300.

  For example, when the controller 300 determines that the voltage of a specific secondary battery 1 is higher than the voltages of other secondary batteries 1 based on the output of the voltage monitoring IC 207, the controller 300 is equivalent to the specific secondary battery 1. Only the specific secondary battery 1 is discharged by operating only the circuit 207. Thereby, the voltage of the specific secondary battery 1 falls and it can align with the voltage of the other secondary battery 1.

  A specific configuration (an example) of the equalization circuit 207 will be described with reference to FIG. FIG. 3 is a circuit diagram showing the configuration of the secondary battery 1 and the equalization circuit 207.

  The equalization circuit 207 includes a resistor 207a and a switch element 207b. The switch element 207b receives the control signal from the controller 300 and switches between on and off. When the switch element 207b is switched from OFF to ON, a current flows from the secondary battery 1 to the resistor 207a, and the secondary battery 1 can be discharged. Thereby, the voltage of each secondary battery 1 can be adjusted, and the voltage in the some secondary battery 1 can be equalized.

  In this embodiment, the equalization circuit 207 and the voltage monitoring IC 201a are provided for each secondary battery 1, but the present invention is not limited to this. For example, the plurality of secondary batteries 1 constituting the assembled battery 100 can be divided into a plurality of battery blocks (corresponding to battery units). Each battery block is composed of a plurality of secondary batteries 1 connected in series, and the plurality of battery blocks are connected in series. In this case, an equalization circuit 207 and a voltage monitoring IC 201a can be provided for each battery block. The voltage monitoring IC 201a detects the voltage of the corresponding battery block, and the equalization circuit 207 discharges the corresponding battery block. Each battery block can also include a plurality of secondary batteries 1 connected in parallel.

  In order to perform the equalization process with high accuracy, it is preferable to perform based on the OCV (Open Circuit Voltage) of the secondary battery 1. In the plurality of secondary batteries 1 constituting the assembled battery 100, variation in SOC (State of Charge) may occur. The SOC is the ratio of the current charge capacity to the full charge capacity. Here, the full charge capacity may decrease as the deterioration of the secondary battery 1 proceeds. For example, the charge capacity of the secondary battery 1 may decrease due to self-discharge or the like, but the decrease amount of the charge capacity may differ among the plurality of secondary batteries 1. As a result, SOC variation occurs in the plurality of secondary batteries 1.

  When the SOC variation occurs, it is preferable to reduce the SOC variation in order to continue using the secondary batteries 1 in an equivalent state. If a plurality of secondary batteries 1 are continuously used in different states, only a specific secondary battery 1 may be easily deteriorated. Here, since the SOC of the secondary battery 1 has a corresponding relationship with the OCV of the secondary battery 1, in order to reduce the variation in the SOC, the variation in the OCV may be reduced. For this reason, if OCV in the some secondary battery 1 is acquired and equalization processing is performed based on these OCV, the variation in SOC can be reduced.

  When the secondary battery 1 is charged and discharged, polarization occurs. If the polarization is eliminated, the OCV of the secondary battery 1 can be acquired. During charging / discharging of the secondary battery 1 or immediately after stopping charging / discharging of the secondary battery 1, the voltage (CCV: Closed Circuit Voltage) of the secondary battery 1 detected by the monitoring unit 201 is: Since the amount of voltage change due to polarization is also included, the OCV of the secondary battery 1 cannot be acquired in this state. On the other hand, if the voltage of the secondary battery 1 is detected in a state where the polarization is eliminated, the detected voltage does not include the voltage change amount due to the polarization.

  Polarization can be eliminated by leaving the secondary battery 1 without charging / discharging. That is, if the secondary battery 1 is left for a sufficient time, the polarization can be eliminated. Here, leaving means to leave the secondary battery 1 without charging / discharging. If an experiment or the like is performed in advance, the time for eliminating the polarization can be set. Thereby, it can be determined that the polarization is eliminated when the time during which the secondary battery 1 is left exceeds the polarization elimination time.

  When setting the polarization elimination time, a condition (for example, low temperature) where polarization is difficult to be eliminated may be considered. Since the elimination time set in this way is the maximum value in the range allowed as the elimination time, it takes time to determine that the polarization has been eliminated. For example, when a vehicle on which the assembled battery 100 is mounted is used as a taxi, it is difficult to take time to leave the assembled battery 100, and it is difficult to obtain an opportunity to determine that polarization has been eliminated.

  In this embodiment, the polarization elimination time is not set in advance, but by using the battery model described below, the polarization is eliminated in consideration of the current usage state of the secondary battery 1. I am trying to estimate the time.

  First, the battery model will be described. FIG. 4 is a schematic diagram showing the configuration of the secondary battery 1. Here, a lithium ion secondary battery is used as an example of the secondary battery 1. A coordinate axis x shown in FIG. 4 indicates a position in the thickness direction of the electrode.

  The secondary battery 1 includes a positive electrode 141, a negative electrode 142, and a separator 143. The separator 143 is located between the positive electrode 141 and the negative electrode 142 and contains an electrolytic solution. The positive electrode 141 has a current collecting plate 141 a made of aluminum or the like, and the current collecting plate 141 a is electrically connected to the positive electrode terminal 11 of the secondary battery 1. The negative electrode 142 includes a current collector plate 142 a made of copper or the like, and the current collector plate 142 a is electrically connected to the negative electrode terminal 12 of the secondary battery 1.

Each of the negative electrode 142 and the positive electrode 141 is composed of an aggregate of spherical active materials 142b and 141b. When the secondary battery 1 is discharged, a chemical reaction that releases lithium ions Li ⁺ and electrons e ⁻ is performed on the interface of the active material 142 b of the negative electrode 142. In addition, a chemical reaction that absorbs lithium ions Li ⁺ and electrons e ⁻ is performed on the interface of the active material 141 b of the positive electrode 141. The secondary battery 1 is charged and discharged by the exchange of lithium ions Li ⁺ between the negative electrode 142 and the positive electrode 141, and a charging current Ib (<0) or a discharging current Ib (> 0) is generated.

  The basic battery model formula used in this embodiment is represented by a basic equation consisting of the following formulas (1) to (11). FIG. 5 shows a list of variables and constants used in the battery model equation.

  Regarding the variables and constants in the model formula described below, the subscript e indicates a value in the electrolytic solution, and s indicates a value in the active material. The subscript j distinguishes between the positive electrode and the negative electrode. When j is 1, the value at the positive electrode is indicated. When j is 2, the value at the negative electrode is indicated. When the variables or constants in the positive electrode and the negative electrode are described comprehensively, the suffix j is omitted. In addition, the notation (t) indicating that it is a function of time, the notation (T) indicating the dependency of the battery temperature, the (θ) indicating the dependency of the local SOC θ, and the like are indicated in the specification. Sometimes omitted. The symbol # attached to a variable or constant represents an average value.

  The above formulas (1) and (2) are formulas indicating an electrochemical reaction in the electrode (active material), and are called Butler-Volmer formulas.

  The following formula (3) is established as a formula for the conservation law of lithium ion concentration in the electrolytic solution. As an equation relating to the law of conservation of lithium concentration in the active material, a diffusion equation of the following equation (4) and boundary condition equations shown in the following equations (5) and (6) are applied. The following formula (5) represents the boundary condition at the center of the active material, and the following formula (6) represents the boundary condition at the interface between the active material and the electrolyte (hereinafter also simply referred to as “interface”).

The local SOC θ _j that is a local lithium concentration distribution (concentration distribution) at the interface of the active material is defined by the following formula (7). C _sej in the following formula (7) indicates the lithium concentration at the active material interface between the positive electrode and the negative electrode, as shown in the following formula (8). c _{sj, max} indicates the limit lithium concentration in the active material.

The following equation (9) is established as an equation relating to the charge conservation law in the electrolytic solution, and the following equation (10) is established as an equation relating to the charge conservation law in the active material. As an electrochemical reaction formula at the active material interface, the following formula (11) indicating the relationship between the current density I (t) and the reaction current density j _j ^Li is established.

  The battery model formula represented by the basic equations of the above formulas (1) to (11) can be simplified as described below. The simplification of the battery model formula can reduce the calculation load and the calculation time.

  It is assumed that the electrochemical reaction in each of the negative electrode 142 and the positive electrode 141 is uniform. That is, it is assumed that the reaction in the x direction occurs uniformly in each of the electrodes 142 and 141. Further, since it is assumed that the reactions in the plurality of active materials 142b and 141b included in the electrodes 142 and 141 are uniform, the active materials 142b and 141b of the electrodes 142 and 141 are handled as one active material model. Thereby, the structure of the secondary battery 1 shown in FIG. 4 can be modeled into the structure shown in FIG.

  In the battery model shown in FIG. 6, the electrode reaction on the surfaces of the active material model 141b (j = 1) and the active material model 142b (j = 2) can be modeled. Further, in the battery model shown in FIG. 6, it is possible to model the diffusion (diameter direction) of lithium inside the active material models 141b and 142b and the diffusion (concentration distribution) of lithium ions in the electrolytic solution. Furthermore, potential distribution and temperature distribution can be modeled in each part of the battery model shown in FIG.

As shown in FIG. 7, the lithium concentration c _s inside each of the active material models 141b and 142b is expressed by the coordinate r in the radial direction of the active material models 141b and 142b (r: distance from the center of each point, r _s : active It can be expressed as a function on the radius of the material. Here, it is assumed that there is no position dependency in the circumferential direction of the active material models 141b and 142b. The active material models 141b and 142b shown in FIG. 7 are used to estimate the lithium diffusion phenomenon inside the active material due to the electrochemical reaction at the interface. The lithium concentration c _{s, k} (t) is estimated according to the diffusion equation described later for each region (k = 1 to N) divided into N (N: natural number of 2 or more) in the radial direction of the active material models 141b and 142b. Is done.

  According to the battery model shown in FIG. 6, the basic equations (1) to (6) and (8) can be expressed by the following equations (1 ') to (6') and (8 ').

In the above equation (3 ′), it is assumed that c _ej (t) is a constant value by assuming that the concentration of the electrolytic solution does not change with time. For the active material models 141b and 142b, the diffusion equations (4) to (6) are transformed into diffusion equations (4 ′) to (6 ′) considering only the distribution in the polar coordinate direction. In the above formula (8 ′), the lithium concentration c _{sej at} the interface of the active material corresponds to the lithium concentration c _si (t) in the outermost region of the N-divided regions shown in FIG.

The above formula (9) relating to the law of conservation of electric charge in the electrolysis solution is simplified to the following formula (12) using the above formula (3 ′). That is, the potential φ _{ej of the} electrolytic solution is approximated as a quadratic function of x. The average potential φ _ej # in the electrolytic solution used for calculating the overvoltage η _j # is obtained by the following formula (13) obtained by integrating the following formula (12) with the electrode thickness L _j .

For the negative electrode 142, the following formula (14) is established based on the following formula (12). Therefore, the potential difference between the electrolyte average potential φ _e2 # and the electrolyte potential at the boundary between the negative electrode 142 and the separator 143 is expressed by the following equation (15). For the positive electrode 141, the potential difference between the electrolyte average potential φ _e1 # and the electrolyte potential at the boundary between the positive electrode 141 and the separator 143 is expressed by the following formula (16).

The above formula (10) relating to the law of conservation of charge in the active material can also be simplified to the following formula (17). That is, the potential φ _sj of the active material is also approximated as a quadratic function of x. The average potential φ _sj # in the active material used for calculating the overvoltage η _j # is obtained by the following formula (18) obtained by integrating the following formula (17) with the electrode thickness L _j . Therefore, with respect to the positive electrode 141, the potential difference between the active material average potential φ _s1 # and the active material potential at the boundary between the active material model 141b and the current collector plate 141a is expressed by the following formula (19). Similarly, the following formula (20) is established for the negative electrode 142.

FIG. 8 shows the relationship between the terminal voltage V (t) of the secondary battery 1 and each average potential obtained as described above. In FIG. 8, since the reaction current density j _j ^Li is 0 in the separator 143, the voltage drop at the separator 143 is proportional to the current density I (t), and L _s / κ _s ^eff · I (t) Become.

In addition, by assuming that the electrochemical reaction in each electrode is uniform, the current density I (t) per unit area of the electrode plate and the reaction current density (lithium generation amount) j _j ^Li are as follows. Formula (21) is materialized.

  Based on the potential relationship shown in FIG. 8 and the above equation (21), the following equation (22) is established for the battery voltage V (t). The following equation (22) is based on the potential relational equation of equation (23) shown in FIG.

Next, an average overvoltage η # (t) is calculated. ^Assuming that j _j ^Li is constant and the charge / discharge efficiency is the same in the Butler-Bolmer relational expression and α _aj and α _cj are 0.5, the following equation (24) is established. The average overvoltage η # (t) is obtained by the following equation (25) by inversely transforming the following equation (24).

The average potentials φ _s1 and φ _s2 are obtained using FIG. 8, and the obtained values are substituted into the above equation (22). Further, the average overvoltages η ₁ # (t) and η ₂ # (t) obtained from the above equation (25) are substituted into the above equation (23). As a result, a voltage-current relationship model formula (M1a) according to the electrochemical reaction model formula is derived based on the formulas (1 ′), (21) and the formula (2 ′).

  The active material diffusion model equation (M2a) for the active material models 141b and 142b is obtained by the above equation (4 ′) and boundary condition equations (5 ′) and (6 ′) which are the lithium concentration conservation law (diffusion equation). .

The first term on the right side of the model formula (M1a) represents the open circuit voltage (OCV) determined by the concentration of the reactant (lithium) on the active material surface, and the second term on the right side represents the overvoltage (η ₁ # −η ₂ # ), And the third term on the right side indicates a voltage drop due to current flowing through the secondary battery. That is, the DC pure resistance of the secondary battery 10 is represented by Rd (T) in the formula (M2a).

In the formula (M2a), diffusion coefficients D _s1 and D _s2 used as parameters for defining the diffusion rate of lithium as a reactant have temperature dependence. Therefore, the diffusion coefficients D _s1 and D _s2 can be set using, for example, the map shown in FIG. The map shown in FIG. 9 can be acquired in advance. In FIG. 9, the battery temperature T on the horizontal axis is a temperature acquired using the temperature sensor 203. As shown in FIG. 9, the diffusion coefficients D _s1 and D _s2 decrease as the battery temperature decreases. In other words, the diffusion coefficients D _s1 and D _s2 increase as the battery temperature increases.

Regarding the diffusion coefficients D _s1 and D _s2 , not only the temperature dependency but also the local SOC θ dependency may be considered. In this case, a map indicating the relationship between the battery temperature T, the local SOC θ, and the diffusion coefficients D _s1 and D _s2 may be prepared in advance.

  As shown in FIG. 10A, open circuit voltage U1 included in equation (M1a) decreases as local SOC θ increases. Further, as shown in FIG. 10B, open circuit voltage U2 rises as local SOCθ rises. If the maps shown in FIGS. 10A and 10B are prepared in advance, the open-circuit voltages U1 and U2 corresponding to the local SOC θ can be specified.

Exchange current densities i ₀₁ and i ₀₂ included in formula (M1a) have a dependence on local SOC θ and battery temperature T. Therefore, if a map showing the relationship between the exchange current densities i ₀₁ and i ₀₂ , the local SOC θ and the battery temperature T is prepared in advance, the exchange current densities i ₀₁ and i ₀₂ are specified from the local SOC θ and the battery temperature T. Can do.

  The DC pure resistance Rd has temperature dependence. Therefore, if a map showing the relationship between the DC pure resistance Rd and the battery temperature T is prepared in advance, the DC pure resistance Rd can be specified from the battery temperature T. In addition, about the map mentioned above, it can create based on experimental results, such as the well-known alternating current impedance measurement regarding the secondary battery 1. FIG.

  The battery model shown in FIG. 6 can be further simplified. Specifically, a common active material model can be used as the active material of the electrodes 142 and 141. By treating the active material models 141b and 142b shown in FIG. 6 as one active material model, the following equation (26) can be replaced. In the following formula (26), the suffix j indicating the distinction between the positive electrode 141 and the negative electrode 142 is omitted.

The model formulas (M1a) and (M2a) can be expressed by the following formulas (M1b) and (M2b). In the battery model using one active material model, the following formula (21 ′) is applied instead of the above formula (21) as the relational expression of the current density I (t) and the reaction current density j _j ^Li. The

  The following equation (M1c) is obtained by first-order approximation (linear approximation) of the arcsinh term in the above equation (M1a). By performing linear approximation in this way, it is possible to reduce the calculation load and the calculation time.

In the above formula (M1c), as a result of the linear approximation, the second term on the right side is also represented by the product of the current density I (t) and the reaction resistance Rr. The reaction resistance Rr is calculated from the exchange current densities i ₀₁ and i ₀₂ depending on the local SOC θ and the battery temperature T, as shown in the above equation (27). Therefore, when the above formula (M1c) is used, a map showing the relationship between the local SOC θ, the battery temperature T, and the exchange current densities i ₀₁ and i ₀₂ may be prepared in advance. According to the above formula (M1c) and the above formula (27), the above formula (28) is obtained.

  If the arcsinh term of the second term on the right side in the above equation (M1b) is linearly approximated, the following equation (M1d) is obtained.

  The above formula (M1b) can be expressed as the following formula (M1e).

  The above formula (M1e) is expressed by the following formula (M1f) by performing linear approximation.

  Next, a configuration for estimating the state of the secondary battery using the battery model formula described above will be described. FIG. 11 is a schematic diagram showing the internal configuration of the controller 300. The battery state estimation unit 310 includes a diffusion estimation unit 311, an open circuit voltage estimation unit 312, a current estimation unit 313, a parameter setting unit 314, and a boundary condition setting unit 315. In the configuration shown in FIG. 11, battery state estimation section 310 calculates current density I (t) by using equation (M1f) and equation (M2b).

  In this embodiment, the current density I (t) is calculated using the above formula (M1f), but the present invention is not limited to this. Specifically, the current density I (t) is calculated based on any combination of the above formula (M1a) to the above formula (M1e) and the above formula (M2a) or the above formula (M2b). Can do.

  The diffusion estimation unit 311 calculates the lithium concentration distribution inside the active material based on the boundary condition set by the boundary condition setting unit 315 using the above formula (M2b). The boundary condition is set based on the above formula (5 ') or the above formula (6'). Diffusion estimation unit 311 calculates local SOC θ based on the calculated lithium concentration distribution using equation (7). Diffusion estimation unit 311 outputs information on local SOC θ to open-circuit voltage estimation unit 312.

  The open-circuit voltage estimation unit 312 specifies the open-circuit voltages U1 and U2 of the electrodes 142 and 141 based on the local SOC θ calculated by the diffusion estimation unit 311. Specifically, the open-circuit voltage estimation unit 312 can specify the open-circuit voltages U1 and U2 by using the maps shown in FIGS. 10A and 10B. The open-circuit voltage estimation unit 312 can calculate the open-circuit voltage of the secondary battery 1 based on the open-circuit voltages U1 and U2. The open circuit voltage of the secondary battery 1 is obtained by subtracting the open circuit voltage U2 from the open circuit voltage U1.

Parameter setting unit 314 sets parameters used in the battery model equation according to battery temperature Tb and local SOC θ. The temperature Tb detected by the temperature sensor 203 is used as the battery temperature Tb. The local SOC θ is acquired from the diffusion estimation unit 311. Parameters set by the parameter setting unit 314 include the diffusion constant D _{s in} the above formula (M2b), the current density i ₀ in the above formula (M1f), and the DC resistance Rd.

The current estimation unit 313 calculates (estimates) the current density I (t) using the following formula (M3a). The following formula (M3a) is a formula obtained by modifying the above formula (M1f). In the following formula (M3a), the open circuit voltage U (θ, t) is the open circuit voltage U (θ) estimated by the open circuit voltage estimation unit 312. The voltage V (t) is the battery voltage Vb acquired using the monitoring unit 201. Rd (t) and i ₀ (θ, T, t) are values set by the parameter setting unit 314.

  Note that even when any one of the above formulas (M1a) to (M1e) is used, the current density I (t) can be calculated by the same method as the above formula (M3a). .

The boundary condition setting unit 315 calculates the reaction current density (lithium generation amount) j _j ^Li from the current density I (t) calculated by the current estimation unit 313 using the above formula (21) or the above formula (21 ′). calculate. Then, the boundary condition setting unit 315 updates the boundary condition in the equation (M2b) using the equation (6 ′).

  Next, the process of the battery state estimation part 310 is demonstrated using the flowchart shown in FIG. The process shown in FIG. 12 is executed at a predetermined cycle.

  In step S101, the battery state quantity estimation unit 310 acquires the voltage (battery voltage) Vb of the secondary battery 1 based on the output of the monitoring unit 201. In addition, in step S102, the battery state quantity estimation unit 310 acquires the temperature (battery temperature) Tb of the secondary battery 1 based on the output of the temperature sensor 203.

  In step S103, battery state estimation unit 310 (diffusion estimation unit 311) calculates local SOC θ based on the lithium concentration distribution at the time of the previous calculation using equation (M2b). In step S104, battery state estimation unit 310 (open voltage estimation unit 312) calculates open voltage U (θ) from local SOC θ obtained in step S103.

  In step S105, the battery state estimation unit 310 (current estimation unit 313) calculates (estimates) the current density Im (t) using the above formula (M1f). For the estimated current density Im (t), the battery voltage Vb, the open circuit voltage U (θ) obtained in step S103, and the parameter value set by the parameter setting unit 314 are substituted into the above equation (M3a). Obtained by.

In step S106, the battery state estimation unit 310 (boundary condition setting unit 315) calculates a reaction current density (lithium generation amount) j _j ^Li from the estimated current density I (t) obtained in step S105. Moreover, the battery state estimation part 310 (boundary condition setting part 315) sets the boundary condition (active material interface) in the active material interface of said Formula (M2b) using the calculated reaction current density.

  In step S107, the battery state estimation unit 310 (diffusion estimation unit 311) calculates the lithium concentration distribution inside the active material model using the above formula (M2b), and updates the estimated value of the lithium concentration in each region. . Here, the lithium concentration (updated value) in the outermost peripheral divided region is used for calculation of the local SOC θ in step S103 when the process shown in FIG. 12 is performed next time.

By calculating the lithium concentration distribution, the SOC of the secondary battery 1 can be estimated. Specifically, the average lithium concentration c _save is calculated based on the lithium concentration distribution by using the following formula (29). Further, by using the following formula (30), the SOC of the secondary battery 1 can be calculated based on the average lithium concentration c _save .

As shown in FIG. 7, the lithium concentration c _{s1, k} (t) (k = 1 to N) shown in the above formula (29) is the lithium concentration in each region obtained by dividing the active material models 141b and 142b into N parts in the radial direction. The concentration is estimated by the diffusion model equations (M2a) and (M2b). ΔVk indicates the volume of each divided region, and V indicates the volume of the entire active material. Moreover, when the active material model in the positive electrode and the negative electrode is made common, the average value of the lithium concentration c _{s, k} (t) (k = 1 to N) in each region in the common active material model is By obtaining in the same manner as the above equation (29), the average lithium concentration c _save (t) can be obtained.

FIG. 13 shows, as an example, the relationship between the average lithium concentration c _save in the active material of the positive electrode 141 and the estimated SOC value SOCe. As shown in FIG. 13, the estimated value SOCe decreases as the average lithium concentration c _save in the active material of the positive electrode 141 increases. For this reason, first, an average lithium concentration Cf when fully charged (SOC = 100%) and an average lithium concentration CO when fully discharged (SOC = 0%) are obtained in advance. Then, by linearly interpolating between the lithium average concentration Cf when the SOC is 100% and the lithium average concentration CO when the SOC is 0%, the SOC can be estimated using the above equation (30). That is, if the lithium average concentration c _save (t) is obtained as described above, the SOC corresponding to the lithium average concentration c _save (t) can be specified using the relationship shown in FIG.

  In the process shown in FIG. 12, the lithium concentration distribution can be calculated, and this lithium concentration distribution represents the state of polarization. For this reason, if the lithium concentration distribution is made uniform, polarization is eliminated. FIG. 7 shows a state when polarization is occurring, but when the polarization is eliminated, the lithium concentration distribution becomes the state shown in FIG.

According to the battery model described above, the time until the lithium concentration distribution is eliminated (elimination time) is calculated based on the above formulas (M1a) and (M2a) or the above formulas (M1b) and (M2b). Can do. Here, the lithium concentration c _{s, k} (t + Δt) in the active material can be calculated by using the above formulas (M1a) and (M2a) or the above formulas (M1b) and (M2b). Δt is a calculation cycle for calculating the lithium concentration distribution and the estimated value SOCe. Since polarization decreases when the secondary battery 1 is left unattended, assuming that the current of the secondary battery 1 is zero and increasing the number of cycles Δt, the above formulas (M1a) and (M2a) ) Or a change in lithium concentration distribution can be estimated based on the above formulas (M1b) and (M2b).

  Here, as the number of cycles Δt increases, the lithium concentration distribution changes in the elimination direction. Therefore, the number of cycles Δt until the lithium concentration distribution falls within the allowable range is counted. The allowable range is a range where it can be determined that polarization (lithium concentration distribution) has been eliminated, and can be set as appropriate. If the polarization is completely eliminated, the lithium concentration becomes constant regardless of the position in the active material. However, since the lithium concentration distribution may occur due to an error or the like when calculating the lithium concentration distribution, the allowable range can be appropriately set in consideration of this point. A value obtained by multiplying the count number of the period Δt by the period Δt, in other words, a cumulative value of the period Δt according to the count number is a time (resolving time) until the lithium concentration distribution falls within the allowable range.

  In this example, it is assumed that the concentration distribution in the electrolytic solution is unchanged, but when it is better to consider the concentration distribution in the electrolytic solution, the polarization elimination time based on the lithium concentration distribution in the electrolytic solution is It is preferable to calculate together with the depolarization time based on the lithium concentration distribution in the active material.

  According to the present embodiment, as described above, when the SOC of the secondary battery 1 is estimated using the battery model equation, the lithium concentration distribution is calculated. Based on this lithium concentration distribution, the polarization ( The time until the lithium concentration distribution is eliminated can be calculated. That is, the polarization elimination time can be estimated while estimating the SOC of the secondary battery 1. Since the SOC of the secondary battery 1 is estimated at a predetermined cycle, the polarization elimination time can also be estimated at a predetermined cycle.

  When calculating the lithium concentration distribution and the polarization elimination time using the battery model formula, there is a possibility that the calculated value includes an error. Therefore, a time obtained by adding a correction time in consideration of an error to the estimated polarization elimination time can be used as the polarization elimination time. The correction time can be set in consideration of at least one of the calculation error of the lithium concentration distribution and the calculation error of the elimination time.

  For example, the polarization elimination time estimated from the battery model equation can be compared with the polarization elimination time obtained from an experiment or the like, and can be determined in advance based on the comparison result. On the other hand, if errors are likely to occur in the calculated values of the lithium concentration distribution and polarization elimination time under specific conditions, the correction time should be added to the estimated polarization elimination time only when the specific conditions are satisfied. Can do.

  Moreover, in the some secondary battery 1 which comprises the assembled battery 100, deterioration and variation in temperature may generate | occur | produce. In this case, the plurality of secondary batteries 1 may vary in polarization elimination time. Therefore, when it is determined that polarization is eliminated in the entire assembled battery 100, the secondary battery 1 having the largest lithium concentration distribution, in other words, the secondary battery 1 having the longest polarization elimination time is determined as a reference. can do.

  Specifically, when each of the lithium concentration distributions in the plurality of secondary batteries 1 is calculated, the largest lithium concentration distribution can be identified, and the polarization elimination time can be calculated based on the lithium concentration distribution. On the other hand, for each secondary battery 1, the polarization elimination time is calculated from the lithium concentration distribution, and the longest elimination time among the polarization elimination times in the plurality of secondary batteries 1 is the polarization elimination time in the assembled battery 100. can do.

  As described above, in the configuration in which the voltage of the battery block is detected instead of the voltage of the secondary battery 1, the SOC of each battery block is estimated or the polarization elimination time in each battery block is estimated. Can do. Further, when the assembled battery 100 is composed of a plurality of battery blocks, the entire assembled battery 100 is polarized on the basis of the battery block having the largest lithium concentration distribution, in other words, the battery block having the longest polarization elimination time. It is possible to determine whether or not the problem is solved.

  As described above, when the polarization elimination time is calculated, the time after the secondary battery 1 is left standing is measured, and when the measurement time exceeds the polarization elimination time, the polarization is eliminated. Can be determined. After confirming that the polarization has been eliminated, the monitoring unit 201 can detect the voltage of the secondary battery 1 that is not affected by the polarization. Here, when detecting the voltage of the secondary battery 1, it is preferable to pass a current through the secondary battery 1 so that the amount of voltage change caused by the internal resistance of the secondary battery 1 can be ignored. Thereby, the voltage of the secondary battery 1 detected by the monitoring unit 201 can be regarded as the OCV of the secondary battery 1.

  If the OCV variation occurs in the plurality of secondary batteries 1, the OCV variation can be reduced using the equalization circuit 207 (see FIG. 2) as described above. That is, the OCV in the plurality of secondary batteries 1 can be equalized by discharging the secondary battery 1 on the higher OCV side.

  Next, the process of calculating the polarization elimination time and the equalization process will be described with reference to the flowchart shown in FIG. The process shown in FIG. 15 is executed by the controller 300.

  In step S201, the controller 300 (battery state estimation unit 310) calculates the lithium concentration distribution of the secondary battery 1. As described above, the controller 300 (battery state estimation unit 310) calculates the lithium concentration distribution inside the active material by using the above formulas (M1a) and (M2a) or the above formulas (M1b) and (M2b). can do. In step S202, the controller 300 calculates a change in the lithium concentration distribution when it is assumed that the secondary battery 1 is left based on the lithium concentration distribution calculated in the process of step S201. When it is assumed that no current flows through the secondary battery 1 due to leaving the secondary battery 1, the lithium concentration distribution changes in the elimination direction.

  In step S203, the controller 300 determines whether or not the changed lithium concentration distribution calculated in the process of step S202 is within the allowable range described above. Here, the controller 300 repeats the processes of steps S202 and S203 until the lithium concentration distribution falls within the allowable range. When the lithium concentration distribution is within the allowable range, the controller 300 calculates the polarization elimination time TimeV in step S204. Here, the calculation of the lithium concentration distribution (the process of step S202) is performed until the lithium concentration distribution falls within the allowable range, and the accumulated value of this calculation cycle Δt becomes the elimination time TimeV.

  In step S205, the controller 300 determines whether or not the ignition switch of the vehicle is off. If the ignition switch is on, the process returns to step S201. While the ignition switch is on, the processes from step S201 to step S205 are repeated. Thereby, the polarization elimination time TimeV is calculated in a predetermined cycle while the ignition switch is on.

  On the other hand, when the ignition switch is OFF, the controller 300 sets the cancellation time TimeV as the timer time Time in step S206. As the elimination time TimeV here, the elimination time TimeV calculated in the process of step S204 immediately before the ignition switch is turned off is used. In step S207, when the time has elapsed, the controller 300 decreases the time Time (TimeV) of the timer.

  In step S208, the controller 300 determines whether or not the timer time Time is zero. That is, the controller 300 determines whether or not the time from when the ignition switch is turned off has reached the elimination time TimeV.

  When the timer time Time is not 0, the controller 300 performs the process of step S207. That is, until the timer time Time reaches 0, the controller 300 decreases the timer time Time each time. When the timer time Time is 0, in other words, when the elimination time TimeV has elapsed, the controller 300 acquires the voltage of the secondary battery 1 based on the output of the monitoring unit 201 in step S209.

  When the process of step S209 is performed, since the elimination time TimeV has elapsed, the voltage detected by the monitoring unit 201 does not include the amount of voltage change due to polarization. Therefore, it is possible to obtain the voltage of the secondary battery 1 that does not include the amount of voltage change due to polarization, more specifically, the OCV of the secondary battery 1. The OCV is acquired for all the secondary batteries 1 constituting the assembled battery 100.

  In step S210, first, the controller 300 specifies an OCV that indicates the minimum value among the OCVs in the plurality of secondary batteries 1. Then, the controller 300 determines whether or not the difference ΔV between the OCV (minimum value) and the OCV of each secondary battery 1 is greater than or equal to the threshold value ΔVth. The threshold value ΔVth is a reference for determining whether or not OCV variation occurs in the plurality of secondary batteries 1. That is, when the OCV difference ΔV is equal to or greater than the threshold value ΔVth, it is determined that OCV variation has occurred. Further, when the OCV difference ΔV is smaller than the threshold value ΔVth, it is determined that the variation in the OCV is acceptable. The threshold value ΔVth can be determined in advance, and information regarding the threshold value ΔVth can be stored in the memory 300a.

  When the OCV difference ΔV is equal to or greater than the threshold value ΔVth, the controller 300 performs equalization processing in step S211. That is, the controller 300 operates the equalization circuit 207 (see FIG. 2) to discharge the secondary battery 1 on the side with a higher OCV, thereby reducing the variation in OCV. By performing the equalization process in this way, the OCV in the plurality of secondary batteries 1 can be aligned with the OCV (minimum value).

  The specific content of the equalization process is not limited to the method described above. That is, in the plurality of secondary batteries 1, it is only necessary to reduce the variation in OCV, and based on this point, the content of the equalization process may be determined. For example, in the present embodiment, the equalization process is performed based on the OCV (minimum value), but the OCV that is the reference for performing the equalization process can be selected as appropriate.

  According to this example, the lithium concentration distribution in the active material is estimated, and the polarization elimination time TimeV is estimated from the estimated lithium concentration distribution. Therefore, the polarization elimination time TimeV is determined according to the state of the lithium concentration distribution. Changes. If the polarization elimination time TimeV is set to a predetermined fixed value, as described above, it takes time to determine that the polarization has been eliminated.

  On the other hand, in this embodiment, since the polarization elimination time TimeV corresponding to the current lithium concentration distribution can be acquired, the polarization elimination time TimeV can be appropriately estimated. In addition, by estimating the lithium concentration distribution using the battery model equation, the use state, deterioration state, and use environment (particularly temperature) of the secondary battery 1 can be reflected in the estimated lithium concentration distribution. For this reason, it is possible to estimate the polarization elimination time TimeV according to the use state, deterioration state, and use environment of the secondary battery 1.

  Furthermore, in this embodiment, when determining the state of elimination of polarization, there is no need to leave the secondary battery 1 unnecessarily, and the chances of determining that polarization has been eliminated can be increased. In other words, when there are variations in the SOC of the plurality of secondary batteries 1, it is possible to increase the opportunities for performing the equalization process, and it is possible to efficiently reduce the variation in the SOC.

On the other hand, as described with reference to FIG. 13, the SOC of the secondary battery 1 can be estimated from the lithium average concentration c _save (t). Since SOC and OCV have a corresponding relationship, the OCV of the secondary battery 1 can be estimated from the lithium average concentration c _save (t). For this reason, it is conceivable to perform equalization processing based on the estimated OCV.

  However, the estimated OCV may include an error, and it is unknown whether the estimated OCV is located on the high side or the low side with respect to the true OCV. For this reason, if an equalization process is to be performed based on an OCV (estimated value) that includes an error, it is difficult to set an OCV that serves as a reference for performing the equalization process. That is, even if an OCV (estimated value) including an error is acquired in a plurality of secondary batteries 1, it is difficult to specify which secondary battery 1 can be discharged. For this reason, depending on the secondary battery 1 to be discharged, there is a possibility that the dispersion of the OCV spreads.

  In this embodiment, even if an error is included in the lithium concentration distribution and the polarization elimination time TimeV, as described above, the polarization elimination state can be determined by simply adding the correction time. Then, after determining that the polarization has been eliminated, if the OCV (actually measured value) of the secondary battery 1 is obtained using the monitoring unit 201, the OCV of the secondary battery 1 will not include an estimation error. The equalization process can be performed efficiently. That is, in the present embodiment, the accuracy of OCV can be improved, and it becomes easy to specify which secondary battery 1 can be discharged. Then, the equalization process can be performed without widening the variation of the OCV.

  A second embodiment of the present invention will be described. In the present embodiment, the description of the contents described in the first embodiment will be omitted, and differences from the first embodiment will be mainly described.

  In Example 1, the polarization elimination time is calculated based on the lithium concentration distribution, and the equalization process is performed when the polarization elimination time has elapsed. On the other hand, in the present embodiment, as in the first embodiment, the polarization elimination time is calculated, and based on the voltage (OCV) of the secondary battery 1 obtained after the polarization elimination time has elapsed, Calculate (estimate) the full charge capacity.

  If the full charge capacity of the secondary battery 1 is estimated, the deterioration state of the secondary battery 1 can be confirmed. As the deterioration of the secondary battery 1 proceeds, the full charge capacity of the secondary battery 1 decreases, so that the deterioration state of the secondary battery 1 can be specified according to the decrease of the full charge capacity.

  In PHV and EV, as described in the first embodiment, the assembled battery 100 can be charged by supplying power from the external power source to the assembled battery 100. This charging is called external charging. When external charging is performed, the SOC_s of the secondary battery 1 at the time of starting external charging and the SOC_e of the secondary battery 1 at the time of ending external charging are acquired, and the current integration during the external charging is performed If the value is acquired, the full charge capacity of the secondary battery 1 can be estimated.

  Specifically, the full charge capacity CAPn of the secondary battery 1 can be calculated using the following formula (31). The full charge capacity CAPn can be calculated every time external charging is performed.

  In the above equation (31), ΣI is a current integrated value during external charging, and is obtained by integrating the current value detected by the current sensor 202 during external charging. SOC_s is the SOC of the secondary battery 1 when external charging is started, and can be estimated based on the OCV of the secondary battery 1 when external charging is started. SOC_e is the SOC of the secondary battery 1 when external charging is terminated, and can be estimated based on the OCV of the secondary battery 1 when external charging is terminated.

  By performing external charging, SOC_e becomes higher than SOC_s. When estimating the SOC_s and SOC_e of the secondary battery 1, as described in the first embodiment, the SOC_s and SOC_e can be estimated by measuring the OCV of the secondary battery 1 after the polarization is eliminated. .

  Here, even if the voltage of the secondary battery 1 is measured when the time for leaving the secondary battery 1 does not reach the polarization elimination time, the measured voltage includes the voltage change amount due to the polarization. The OCV of the secondary battery 1 may deviate. Therefore, when the full charge capacity is calculated in a state where the polarization is not eliminated, the full charge capacity may deviate from the actual full charge capacity, and the accuracy may be reduced. Therefore, as described below, the shift of the full charge capacity can be corrected by using the correction coefficient.

  First, the full charge capacity can be corrected based on the following equation (32).

  In the above formula (32), CAP is the full charge capacity after correction, CAPn-1 is the full charge capacity calculated last time (nearest), and CAPn is the full charge capacity calculated this time. . The full charge capacities CAPn−1 and CAPn are values calculated based on the above formula (31). When the full charge capacity CAPn is calculated for the first time, an initial value obtained in advance through experiments or the like is used as the full charge capacity CAPn-1. The full charge capacity as the initial value can be stored in the memory 300a.

  K in the above equation (32) is a correction coefficient. The correction coefficient k is a value in the range of 0-1. The correction coefficient k can be determined based on the time when the secondary battery 1 is left, in other words, the remaining time until the polarization is eliminated. The remaining time until the polarization is eliminated corresponds to the timer time Time described in the first embodiment.

  According to the above equation (32), when calculating the corrected full charge capacity CAP, the full charge capacity CAPn−1, CAPn is taken into account and the correction coefficient k is used to calculate these full charge capacity CAPn−1, CAPn is weighted. Here, when the correction coefficient k is 1, only the full charge capacity CAPn calculated this time is used, and when the correction coefficient k is 0, only the full charge capacity CAPn−1 calculated last time is used.

  For example, if the map shown in FIG. 16 is prepared in advance, the correction coefficient k can be specified from the remaining time until the polarization is eliminated. In the map shown in FIG. 16, the correction coefficient k is made smaller as the remaining time becomes longer. Here, when the remaining time is 0, the correction coefficient k is 1. When the remaining time is longer than the threshold value tr_th, the correction coefficient k is set to 0.

  The threshold value tr_th can be appropriately set in consideration of the state of polarization, in other words, the remaining time until the polarization is eliminated. The longer the remaining time, the more polarization is not eliminated, and the full charge capacity CAPn calculated in such a state deviates from the actual full charge capacity. Therefore, it is preferable not to consider the full charge capacity CAPn calculated this time as the remaining time is longer. Considering this point, the threshold value tr_th can be set. Information regarding the threshold value tr_th can be stored in the memory 300a.

  In the above formula (32), the full charge capacity of the secondary battery 1 is corrected, but the present invention is not limited to this. For example, the OCV for correcting SOC_s and SOC_e when calculating the full charge capacity or specifying SOC_s and SOC_e by the same method (correction method using the correction coefficient k) as when correcting the full charge capacity Can also be corrected. Then, the full charge capacity can be calculated from the corrected SOC_s and SOC_e, or the SOC_s and SOC_e can be specified from the corrected OCV, and the full charge capacity can be calculated from the SOC_s and SOC_e.

  In this embodiment, the full charge capacity of the secondary battery 1 is calculated when external charging is performed. However, the present invention is not limited to this. For example, the full charge capacity of the secondary battery 1 can be calculated also when the electric power of the assembled battery 100 is supplied to an electronic device (such as a home appliance) arranged outside the vehicle. Here, supplying the electric power of the assembled battery 100 to the electronic device is referred to as external discharge.

  If the SOC_s of the secondary battery 1 when starting the external discharge and the SOC_e of the secondary battery 1 when ending the external discharge are acquired, and the current integrated value ΣI during the external discharge is acquired The full charge capacity of the secondary battery 1 can be estimated. The full charge capacity of the secondary battery 1 can be calculated using the above formula (31). Since SOC_e becomes lower than SOC_s due to external discharge, the absolute value of the above equation (31) becomes the full charge capacity.

  Next, the process of calculating the full charge capacity will be described using the flowcharts shown in FIGS. 17A to 17C. The processing illustrated in FIGS. 17A to 17C is executed by the controller 300.

  In step S301, the controller 300 determines whether or not the battery system shown in FIG. 1 is in an externally charged state. The external charging state is a state in which external charging is started, and power is not yet supplied to the assembled battery 100 from the external power source. For example, when power from an external power supply is supplied to the assembled battery 100 using a wired cable, whether or not a plug connected to the external power supply via a cable is connected to an inlet connected to the battery system. It is possible to determine whether or not the battery is in the external charging state.

  The determination of whether or not the battery is in the external charging state can be appropriately set according to the system that supplies power from the external power source to the assembled battery 100. When the battery system is in the external charging state, the process proceeds to step S302. When the battery system is not in the external charging state, the process proceeds to step S312 (FIG. 17B).

  In step S302, the controller 300 sets the external charging mode as the battery system mode. In step S303, the controller 300 sets the current time Time as time Time_s when starting external charging. Here, the time Time is the remaining time until the polarization is eliminated. As will be described later, when the time until polarization is eliminated is calculated (estimated), the polarization elimination time is reduced each time the secondary battery 1 is allowed to stand. For example, if the polarization elimination time is 0, 0 is set as the time Time_s. If the elimination time of polarization is longer than 0, this time is set as the time Time_s.

  In step S304, based on the output of the monitoring unit 201, the controller 300 acquires the voltage of the secondary battery 1 when starting external charging. Here, if the time Time_s is 0, the OCV of the secondary battery 1 can be obtained as described in the first embodiment. On the other hand, if the time Time_s is longer than 0, the voltage of the secondary battery 1 detected by the monitoring unit 201 includes a voltage change amount associated with the polarization.

  In step S305, the controller 300 sets the current integrated value ΣI to 0. The process of step S305 is performed before the power of the external power source is supplied to the assembled battery 100. By setting the current integrated value ΣI to 0 before performing external charging, the current integrated value ΣI during external charging can be acquired.

  In step S306, the controller 300 sets the current mode as the previous mode. For example, if the current mode is the external charging mode, the external charging mode is set as the previous mode. As will be described later, when the current mode is the travel mode, the travel mode is set as the previous mode.

  In step S307, the controller 300 acquires the current of the assembled battery 100 (secondary battery 1) based on the output of the current sensor 202. Then, the controller 300 sets, as the current integrated value ΣI, a value obtained by adding the current I acquired this time to the previously calculated current integrated value ΣI. When the current I is acquired for the first time, the previous current integrated value ΣI becomes zero.

  In step S308, the controller 300 calculates the lithium concentration distribution in the active material using the battery model equation. The method for calculating the lithium concentration distribution is the same as the method described in Example 1, and the lithium concentration distribution can be calculated using the above formula (M2a) or (M2b). In step S309, the controller 300 calculates a change in the lithium concentration distribution based on the lithium concentration distribution calculated in step S308. That is, as described in the first embodiment, the lithium concentration distribution after the lapse of the period Δt is calculated while the period δt is calculated.

  In step S310, the controller 300 calculates a time Time V until the polarization is eliminated based on the change in the lithium concentration distribution calculated in the process of step S309. That is, the elimination time TimeV is calculated based on the accumulated value of the period Δt until the lithium concentration distribution calculated in the process of step S309 falls within the allowable range. The method for calculating the elimination time TimeV is the same as the method described in the first embodiment.

  In step S311, the controller 300 determines whether or not external charging has ended, or determines whether or not the ignition switch is off. For example, when the plug connected to the external power source is removed from the inlet connected to the battery system, the external charging is finished. On the other hand, when the vehicle finishes traveling, the ignition switch may be switched from on to off in response to an instruction from the driver. When the ignition switch is turned off, the battery system is activated and stopped.

  In the case where external charging is performed, if external charging has not been completed, the processes in steps S307 to S311 are repeated. If the ignition switch remains on, the processes in steps S307 to S311 are repeated. Thereby, the integrated current value ΣI during external charging can be acquired by the process of step S307, or the lithium concentration distribution can be acquired by the processes of steps S308 and S309. Further, the polarization elimination time TimeV corresponding to the current lithium concentration distribution can be calculated by the process of step S310. On the other hand, when external charging is finished or the ignition switch is off, the process proceeds to step S320 (FIG. 17C).

  When the process proceeds from step S301 to step S312, the controller 300 sets the travel mode as the battery system mode because the battery system is not in the externally charged state. In step S313, the controller 300 determines whether or not the previous mode is the external charging mode. The previous mode is a mode (external charging mode or traveling mode) set in the process of step S306. When the previous mode is the external charging mode, the process proceeds to step S314. On the other hand, when the previous mode is the traveling mode, the process proceeds to step S306 (FIG. 17A).

  In step S314, the controller 300 determines whether or not the timer time Time is zero. As described above, the time Time is the remaining time until the polarization is eliminated. When the time Time is 0, the controller 300 determines that the polarization of the secondary battery 1 has been eliminated, and performs the process of step S316. On the other hand, when the time Time is not 0, in other words, when the polarization of the secondary battery 1 is not eliminated, the process proceeds to step S315.

  In step S315, the controller 300 acquires the voltage of the secondary battery 1 based on the output of the monitoring unit 201. In the process of step S315, when the time Time is not 0, the voltage of the secondary battery 1 after the external charging is completed can be acquired. In step S316, the controller 300 sets the current time Time as the time Time_e when the external charging is finished. Time Time is the remaining time until polarization is eliminated. For example, if the polarization elimination time Time is 0, 0 is set as the time Time_e. If the polarization elimination time Time is longer than 0, this time is set as the time Time_e.

  In step S317, the controller 300 calculates the full charge capacity CAPn of the secondary battery 1 using the above equation (31). Here, the value calculated in the process of step S307 (FIG. 17A) is used as the integrated current value ΣI shown in the above equation (31).

  Moreover, as SOC_s shown in the above formula (31), the SOC corresponding to the voltage of the secondary battery 1 when external charging is started is used. The voltage of the secondary battery 1 when external charging is started is obtained by the process of step S304 (FIG. 17A). If the correspondence between the voltage of the secondary battery 1 and the SOC is obtained in advance, the SOC of the secondary battery 1 can be specified from the voltage of the secondary battery 1. As SOC_e shown in the above equation (31), the SOC corresponding to the voltage of the secondary battery 1 when the external charging is finished is used. The voltage of the secondary battery 1 when the external charging is finished is obtained by the process of step S315 or the process of step S324 (FIG. 17C) described later.

  In step S318, the controller 300 calculates the correction coefficient k. In the present embodiment, the correction coefficient k is specified using the map (example) shown in FIG. The map shown in FIG. 18 shows the relationship between each of the times Time_s and Time_e and the correction coefficient k. If the map shown in FIG. 18 is used, the correction coefficient k can be specified by specifying the times Time_s and Time_e.

  The relationship between the time Time_s and the correction coefficient k and the relationship between the time Time_e and the correction coefficient k are the same as those shown in FIG. That is, the longer the time Time_s, the smaller the correction coefficient k. Further, the correction coefficient k becomes smaller as the time Time_e becomes longer. In the map shown in FIG. 18, even when at least one of the times Time_s and Time_e is different, the correction coefficient k may be the same.

  In step S319, the controller 300 calculates the full charge capacity CAP of the secondary battery 1 using the above equation (32). As the full charge capacities CAPn and CAPn−1 shown in the above equation (32), the values calculated in the process of step S317 are used. Here, CAPn is the full charge capacity calculated in the current process, and CAPn−1 is the full charge capacity calculated in the previous process. Further, as the correction coefficient k shown in the above equation (32), the value calculated in the process of step S318 is used.

  For example, when the correction coefficient k is 1, the full charge capacity CAPn calculated this time is equal to the full charge capacity CAP calculated from the above equation (32). When the correction coefficient k is other than 1, the full charge capacity CAP is calculated by weighting the full charge capacities CAPn and CAPn−1.

  After the process of step S319 is completed, the process proceeds to step S306 (FIG. 17A). On the other hand, when the process proceeds from the process of step S311 (FIG. 17A) to the process of step S320 (FIG. 17C), the controller 300 sets the polarization elimination time TimeV calculated in the process of step S310 as the timer time Time. .

  In step S321, the controller 300 decreases the time Time (TimeV) of the timer when the time has elapsed. In step S322, the controller 300 determines whether or not the timer time Time is zero. That is, the controller 300 determines whether or not the elimination time TimeV has elapsed.

  When the timer time Time is not 0, the controller 300 performs the process of step S321. That is, until the timer time Time reaches 0, the controller 300 decreases the timer time Time each time. When the timer time Time is 0, in other words, when the elimination time TimeV has elapsed, the controller 300 determines in step S323 whether the previous mode is the external charging mode. The previous mode is a mode set in the process of step S306 (FIG. 17A).

  If the timer time Time reaches 0, 0 is set as the time Time. On the other hand, if charging / discharging of the assembled battery 100 (secondary battery 1) is started before the timer time Time becomes 0, the time Time at this time is held. The time Time is used in the processing of step S303, step S314, and step S316.

  When the previous mode is the external charging mode, the process proceeds to step S324, and when the previous mode is not the external charging mode, in other words, when the previous mode is the traveling mode, this process is terminated. In step S324, the controller 300 acquires the voltage of the secondary battery 1 based on the output of the monitoring unit 201. Here, since the elimination time TimeV has elapsed, the voltage detected by the monitoring unit 201 does not include a voltage change amount due to polarization. Therefore, the OCV of each secondary battery 1 can be acquired after the external charging is finished.

  According to the present embodiment, it is possible to acquire the voltage of the secondary battery 1 at the start and end of external charging after confirming that the polarization of the secondary battery 1 has been eliminated. Since the voltage of the secondary battery 1 does not include the amount of voltage change due to polarization, the OCV of the secondary battery 1 can be acquired. If the OCV of the secondary battery 1 is obtained, the SOC of the secondary battery 1 can be specified. Therefore, based on the SOC of the secondary battery 1 at the start and end of external charging, the full charge capacity of the secondary battery 1 CAP can be calculated. Since the SOC of the secondary battery 1 can be calculated in a state where the influence of polarization is eliminated, the accuracy of estimating the full charge capacity CAP of the secondary battery 1 can be improved.

  Also in the present embodiment, as in the first embodiment, since an appropriate time corresponding to the lithium concentration distribution in the active material is specified as the polarization elimination time, the opportunity to determine that the polarization is eliminated is increased. be able to. Along with this, it is possible to increase opportunities to calculate the full charge capacity CAP with high accuracy.

  Further, in this embodiment, even when the polarization of the secondary battery 1 is not eliminated, the full charge capacity CAP of the secondary battery 1 can be calculated by using the correction coefficient k. Thereby, even if the voltage of the secondary battery 1 at the start and end of external charging is acquired in a state where polarization is not eliminated, the full charge capacity CAP of the secondary battery 1 is estimated based on these voltages. be able to.

1: secondary battery, 100: assembled battery, 201: monitoring unit, 201a: voltage monitoring IC,
202: current sensor, 203: temperature sensor, 204: current limiting resistor,
205: inverter, 206: motor generator, 207: equalization circuit,
207a: resistor, 207b: switch element, 300: controller, 300a: memory,
141: positive electrode, 141a: current collector plate, 141b: active material, 142: negative electrode,
142a: current collector plate, 142b: active material, 143: separator, 11: positive electrode terminal,
12: Negative terminal 310: Battery state estimation unit, 311: Diffusion estimation unit,
312: Open-circuit voltage estimation unit, 313: Current estimation unit, 314: Parameter setting unit,
315: Boundary condition setting part

Claims (10)

A battery unit for charging and discharging;
A voltage sensor for detecting a voltage of the battery unit;
A controller for estimating the state of the battery unit,
The controller is
By calculating the concentration distribution in the active material of the battery unit by using a diffusion equation, and assuming that the battery unit is not charged / discharged, the concentration distribution is within an allowable range. Calculate the depolarization time,
When the time during which the battery unit is not charged or discharged is equal to or longer than the polarization elimination time, the voltage sensor is used to obtain the open voltage of the battery unit.
A battery system characterized by that.   The battery system according to claim 1, wherein the controller sets concentrations at the center and interface of the active material as boundary conditions, and calculates the concentration distribution using the diffusion equation.   3. The controller according to claim 1, wherein the controller adds a correction time determined in advance according to a calculation error in at least one of the concentration distribution and the polarization elimination time to the polarization elimination time. Battery system.   The controller calculates the concentration distribution while charging / discharging the battery unit, and calculates a charge state of the battery unit using a correspondence relationship between an average value of the concentration distribution and a charge state. The battery system according to any one of claims 1 to 3. The controller is
Using the correspondence between the open-circuit voltage and the charge state, calculate the charge state corresponding to the acquired open-circuit voltage,
The charging state when charging or discharging of the battery unit is started, the charging state when charging or discharging of the battery unit is finished, and an integrated current value during charging or discharging of the battery unit The battery system according to claim 1, wherein a full charge capacity of the battery unit is calculated using A plurality of the battery units connected in series;
An equalization circuit that discharges each of the battery units and equalizes voltages in the plurality of battery units, and
6. The battery system according to claim 1, wherein the controller operates the equalization circuit when a difference in open voltage among the plurality of battery units is equal to or greater than a threshold value.   The battery system according to claim 1, wherein the battery unit is a single battery.   The battery system according to claim 1, wherein the battery unit includes a plurality of unit cells electrically connected.   The battery system according to any one of claims 1 to 8, wherein the battery unit outputs electrical energy converted into kinetic energy for running the vehicle. An estimation method for estimating a state of a battery unit that performs charging and discharging,
By calculating the concentration distribution in the active material of the battery unit by using a diffusion equation, and assuming that the battery unit is not charged / discharged, the concentration distribution is within an allowable range. Calculate the depolarization time,
When the time during which the battery unit is not charged or discharged is equal to or longer than the polarization elimination time, a voltage sensor that detects the voltage of the battery unit is used to obtain the open voltage of the battery unit.
An estimation method characterized by that.