JP6927000B2 - Deterioration state estimation method for secondary batteries - Google Patents

Description

The present disclosure relates to a method for estimating a deterioration state of a secondary battery, and more specifically, to a method for estimating a deterioration state of a secondary battery for estimating the deterioration state of a secondary battery mounted on a vehicle.

In recent years, vehicles equipped with a secondary battery for traveling have become widespread. Since the secondary batteries mounted on these vehicles can deteriorate with the usage method or environment, or with the passage of time, it is required to estimate the deterioration state of the secondary batteries with high accuracy. Therefore, a method of estimating the deterioration state of the secondary battery based on the impedance (internal resistance) of the secondary battery has been proposed.

For example, according to the method disclosed in Japanese Patent Application Laid-Open No. 2005-221487 (Patent Document 1), the current value and the voltage value are measured in a state where charge / discharge currents having various waveforms having no periodicity flow through the secondary battery. Will be done. Then, by performing the Fourier transform of the measured current value and voltage value, the impedance component for each frequency is calculated from the current value and voltage value after the Fourier transform.

Japanese Unexamined Patent Publication No. 2005-221487

The present inventors have focused on the fact that the impedance component (reaction resistance described later) in a predetermined frequency range has current dependence and temperature dependence. If the current dependence and temperature dependence of the reaction resistance are not taken into consideration, it may not be possible to calculate the reaction resistance with high accuracy. As a result, the accuracy of estimating the deteriorated state of the secondary battery may decrease.

The present disclosure has been made to solve the above problems, and an object of the present invention is to use a deterioration state estimation method for estimating a deterioration state of a secondary battery mounted on a vehicle, in which the deterioration state of the secondary battery is determined. It is to improve the estimation accuracy.

The method for estimating the deterioration state of the secondary battery according to a certain aspect of the present disclosure is executed by the control device for the secondary battery mounted on the vehicle. The method for estimating the deterioration state of the secondary battery includes the first to sixth steps. The first step is a step of acquiring the voltage value and the current value of the secondary battery a plurality of times in a predetermined period and storing them in the memory. The second step is a step of calculating the current change width of the secondary battery, the temperature change width of the secondary battery, and the SOC change width of the secondary battery in a predetermined period. The third step is the permissible current change width indicating the permissible upper limit of the current change width and the permissible temperature change width indicating the permissible upper limit of the temperature change width, which are determined for each secondary battery temperature, current or SOC in a predetermined period. In addition, it is a step of acquiring the allowable SOC change width indicating the allowable upper limit of the SOC change width from the temperature, current, or SOC of the secondary battery. The fourth step is the current condition that the current change width is less than the permissible current change width, the temperature condition that the temperature change width is less than the permissible temperature change width, and the SOC change width is less than the permissible SOC change width. When all the SOC conditions are satisfied, the frequency of the secondary battery is converted from the frequency-converted voltage value and current value by performing frequency conversion of the voltage value and current value of the secondary battery stored in the memory multiple times. This is a step of calculating the impedance component for each region. The fifth step is a step of executing a correction process for correcting the reaction resistance, which is an impedance component corresponding to the predetermined frequency range, according to the temperature of the secondary battery in the predetermined period and the current value in the predetermined frequency range. The sixth step is a step of estimating the deterioration state of the secondary battery in the deterioration mode corresponding to each frequency range by using the impedance component for each frequency range. The correction process corrects the reaction resistance so that the smaller the current value in the predetermined frequency range, the lower the reaction resistance, and the lower the temperature of the secondary battery in the predetermined period, the lower the reaction resistance. It is a process to do.

According to the above method, paying attention to the fact that the smaller the current flowing through the secondary battery, the higher the reaction resistance, the reaction resistance is corrected based on the temperature in a predetermined period and the current in a predetermined frequency range (details will be described later). In this way, the accuracy of calculating the reaction resistance can be improved by considering the current dependence and the temperature dependence of the reaction resistance. Therefore, the accuracy of estimating the deteriorated state of the secondary battery can be improved.

According to the present disclosure, it is possible to improve the estimation accuracy of the deteriorated state of the secondary battery.

It is a figure which shows schematic the whole structure of the vehicle which mounted the secondary battery system which concerns on this Embodiment. It is a figure which shows the structure of a battery and a monitoring unit in more detail. It is a figure which shows an example of the time change of the current, temperature and SOC of a battery while the vehicle is running. It is a figure for demonstrating the impedance component of a battery. It is a figure for demonstrating the frequency dependence of the impedance component of a battery. It is a conceptual diagram for demonstrating the calculation method of the impedance component for every frequency domain by Fourier transform. It is a figure which shows an example of the calculation result of an impedance component. It is a figure for demonstrating the current dependence of a reaction resistance. It is a flowchart which shows the determination method of the deterioration state of the battery in this embodiment. It is a figure which shows an example of the map MP1. It is a figure which shows an example of the correction map MP2. It is a figure for comparing the calculation result of the reaction resistance in the comparative example and this embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

[Embodiment]
<Configuration of secondary battery system>
FIG. 1 is a diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to the present embodiment. With reference to FIG. 1, vehicle 1 is a hybrid vehicle. However, the vehicle on which the battery system according to the present disclosure can be mounted is not limited to a hybrid vehicle (including a plug-in hybrid vehicle). The battery system according to the present disclosure can be mounted on all vehicles that generate driving force by using the electric power supplied from the secondary battery system. Therefore, the vehicle 1 may be an electric vehicle or a fuel cell vehicle.

The vehicle 1 includes a secondary battery system 2, a power control unit (PCU) 30, motor generators 41 and 42, an engine 50, a power dividing device 60, a drive shaft 70, and drive wheels 80. To be equipped. The secondary battery system 2 includes a battery 10, a monitoring unit 20, and an electronic control unit (ECU) 100.

The engine 50 is an internal combustion engine that outputs power by converting the combustion energy generated when the air-fuel mixture is burned into the kinetic energy of movers such as pistons and rotors.

The power splitting device 60 includes, for example, a planetary gear mechanism (not shown) having three rotating shafts of a sun gear, a carrier, and a ring gear. The power dividing device 60 divides the power output from the engine 50 into a power for driving the motor generator 41 and a power for driving the drive wheels 80.

Each of the motor generators 41 and 42 is an AC rotating electric machine, for example, a three-phase AC synchronous motor in which a permanent magnet (not shown) is embedded in a rotor. The motor generator 41 is mainly used as a generator driven by the engine 50 via the power dividing device 60. The electric power generated by the motor generator 41 is supplied to the motor generator 42 or the battery 10 via the PCU 30.

The motor generator 42 mainly operates as an electric motor and drives the drive wheels 80. The motor generator 42 is driven by receiving at least one of the electric power from the battery 10 and the electric power generated by the motor generator 41, and the driving force of the motor generator 42 is transmitted to the drive shaft 70. On the other hand, when the vehicle is braking or the acceleration is reduced on a downward slope, the motor generator 42 operates as a generator to generate regenerative power generation. The electric power generated by the motor generator 42 is supplied to the battery 10 via the PCU 30.

The battery 10 is an assembled battery including a plurality of cells. Each cell 12 is a secondary battery such as a lithium ion secondary battery or a nickel metal hydride battery. The battery 10 stores electric power for driving the motor generators 41 and 42, and supplies electric power to the motor generators 41 and 42 through the PCU 50. Further, the battery 10 is charged by receiving the generated power through the PCU 30 when the motor generators 41 and 42 generate power.

The monitoring unit 20 includes a voltage sensor 21, a current sensor 22, and a temperature sensor 23. The voltage sensor 21 detects the voltage VB of the battery 10. The current sensor 22 detects the current IB input / output to / from the battery 10. The temperature sensor 23 detects the temperature TB of the battery 10. Each sensor outputs a signal indicating the detection result to the ECU 100. The configurations of the battery 10 and the monitoring unit 20 will be described in more detail with reference to FIG.

The PCU 30 executes bidirectional power conversion between the battery 10 and the motor generators 41 and 42 according to the control signal from the ECU 100. The PCU 30 is configured so that the states of the motor generators 41 and 42 can be controlled separately. For example, the motor generator 42 can be put into a power running state while the motor generator 41 is in a regenerative state (power generation state). The PCU 30 includes, for example, two inverters provided corresponding to the motor generators 41 and 42, and a converter (neither shown) that boosts the DC voltage supplied to each inverter to a voltage equal to or higher than the output voltage of the battery 10. Consists of.

The ECU 100 includes a CPU (Central Processing Unit) 101, a memory (ROM (Read Only Memory) and RAM (Random Access Memory)) 101, and an input / output port (not shown) to which various signals are input / output. It is composed. The ECU 100 executes various processes for controlling the vehicle 1 to a desired state based on the signals received from each sensor and the programs and maps stored in the memory 102.

More specifically, the ECU 100 controls the charging and discharging of the battery 10 by controlling the engine 50 and the PCU 30. Further, the ECU 100 estimates the SOC (State Of Charge) of the battery 10. For the estimation of SOC, a known method such as a current integration method or a method using an OCV-SOC curve can be used. Further, the ECU 100 calculates the impedance (internal resistance) of the battery 10. The impedance of the battery 10 can be calculated from the ratio of the voltage VB to the current IB (= VB / IB). The calculation of impedance will be described in detail later.

FIG. 2 is a diagram showing the configuration of the battery 10 and the monitoring unit 20 in more detail. With reference to FIGS. 1 and 2, the battery 10 includes M blocks 11 connected in series. Each block 11 contains N cells 12 connected in parallel. M and N are natural numbers of 2 or more.

The voltage sensor 21 detects the voltage of each block 11. The current sensor 22 detects the current IB flowing through all the blocks 11. The temperature sensor 23 detects the temperature of the battery 10. However, the monitoring unit of the voltage sensor is not limited to the block, and may be for each cell 12 or for each of a plurality of adjacent cells (the number less than the number of cells in the block). Further, the monitoring unit of the temperature sensor 23 is not particularly limited, and for example, the temperature of each block (or each cell) may be detected.

The internal configuration of the battery 10 and the monitoring unit of the monitoring unit 20 are merely examples, and are not particularly limited. Therefore, in the following, the plurality of blocks 11 are not distinguished from each other or the plurality of cells 12 are not distinguished from each other, and are simply referred to comprehensively as the battery 10. Further, it is described that the monitoring unit 20 monitors the voltage VB, the current IB, and the temperature TB of the battery 10.

<Changes in voltage and current while the vehicle is running>
While the vehicle 1 configured as described above is running, the voltage VB, the current IB, the temperature TB, and the SOC of the battery 10 may change with the passage of time. The term "running" of the vehicle 1 may include a state in which the vehicle 1 is temporarily stopped, as long as the vehicle 1 is in a state in which the ignition is turned on and the vehicle can run.

FIG. 3 is a diagram showing an example of time changes in the current IB, temperature TB, and SOC of the battery 10 while the vehicle 1 is traveling. In FIG. 3 and FIG. 12 described later, the horizontal axis indicates the elapsed time. The vertical axis shows the current IB, the temperature TB, and the SOC in order from the top. The voltage VB may change irregularly like the current IB, but the voltage VB is not shown below in order to prevent the drawings from becoming complicated.

With reference to FIG. 3, it takes a certain amount of time for the temperature TB and SOC to change, and the temperature TB and SOC often change relatively smoothly. On the other hand, while the vehicle 1 is traveling, the discharge current from the battery fluctuates as the driving force generated by the motor generator 42 is adjusted, and the charging current in the battery 10 due to the regenerative power generation of the motor generator 42. The current IB may change irregularly due to the flow of electric current. When calculating the impedance of the battery 10 based on the irregularly changing current IB, the frequency dependence of the impedance component is taken into consideration in the present embodiment as described below.

<Impedance calculation>
FIG. 4 is a diagram for explaining the impedance component of the battery 10. FIG. 4 shows an example of an equivalent circuit diagram of a positive electrode, a negative electrode, and a separator of the battery 10 (more specifically, each cell 12). Generally, the impedance component of the secondary battery is roughly classified into a _{DC resistance R DC} , a reaction resistance R _c, and a diffusion resistance R _d.

The DC resistance R _DC is an impedance component related to the movement of ions and electrons between the positive electrode and the negative electrode. The DC resistance R _DC increases due to a bias in the salt concentration distribution of the electrolytic solution when a high load is applied to the secondary battery (when a high voltage is applied or a large current flows). The DC resistance R _DC is represented in the equivalent circuit diagram shown in FIG. 4 as the active material resistance Ra1 of the positive electrode, the active material resistance Ra2 of the negative electrode, and the electrolyte resistance R3 of the separator.

The reaction resistance R _c is an impedance component related to charge transfer (charge transfer) at the interface between the electrolytic solution and the active material interface (the surface of the positive electrode active material and the negative electrode active material). The reaction resistance R _c increases due to the growth of a film at the active material / electrolyte interface when the secondary battery in a high SOC state is in a high temperature environment. The reaction resistance R _c is represented as a positive electrode resistance component Rc1 and a negative electrode resistance component Rc2 in the equivalent circuit diagram.

The diffusion resistance R _d is an impedance component related to the diffusion of a salt in an electrolytic solution or a charge transporting substance in an active material. The diffusion resistance R _d increases due to cracking of the active material when a high load is applied. The diffusion resistance R _d is the equilibrium voltage Veq1 generated in the positive electrode, the equilibrium voltage Veq2 generated in the negative electrode, and the salt concentration overvoltage Vov3 generated in the cell (overvoltage caused by the salt concentration distribution of the active material in the separator). ) And it is decided.

Where the impedance of the battery 10 includes various impedance components as described above, the response time to a change in the current IB differs for each impedance component. The impedance component, which has a relatively short response time, can follow changes in the voltage VB at high frequencies. On the other hand, the impedance component having a relatively long response time cannot follow the change of the voltage VB at a high frequency. Therefore, as described below, there is a dominant impedance component of the battery 10 in each of the low frequency range, the middle frequency range, and the high frequency range.

FIG. 5 is a diagram for explaining the frequency dependence of the impedance component of the battery 10. In FIG. 5, the horizontal axis represents the frequency of the current IB (or voltage VB), and the vertical axis represents the impedance of the battery 10.

Hereinafter, the impedance measured when the frequency of the current IB is included in the high frequency region is referred to as a “high frequency impedance component”. The impedance measured when the frequency of the current IB is included in the medium frequency range is referred to as a "medium frequency impedance component". The impedance measured when the frequency of the current IB is included in the low frequency region is referred to as a "low frequency impedance component".

As shown in FIG. 5, the DC resistance R _{DC of the} battery 10 is mainly reflected in the high frequency impedance component. The medium frequency impedance component mainly reflects _{the reaction resistance R c} and the DC resistance R _{DC of the battery 10. Therefore, the reaction resistance R c} can be obtained from the difference between the medium frequency impedance component and the high frequency impedance component. The low-frequency impedance component reflects _{the reaction resistance R c} , the DC resistance R _DC, and the diffusion resistance R _{d of the battery 10. Therefore, the diffusion resistance R d} can be obtained from the difference between the low frequency impedance component and the medium frequency impedance component.

By calculating the impedance component for each frequency range in this way, each of the DC resistance R _DC , the reaction resistance R _c, and the diffusion resistance R _d can be separated. Then, each of these resistors corresponds to a different deterioration factor (deterioration mode) of the battery 10. Therefore, by determining (or the rate of increase) how much the current resistance (DC resistance R _DC , reaction resistance R _c, or diffusion resistance R _d ) has increased from the resistance in the initial state of the battery 10. The cause of deterioration of the battery 10 can be estimated, and the degree of deterioration of each factor can be estimated. That is, it becomes possible to estimate the deteriorated state of the battery 10 with high accuracy.

<Fourier transform>
In the present embodiment, the Fourier transform is used to calculate the impedance component for each frequency range as described above.

FIG. 6 is a conceptual diagram for explaining a method of calculating an impedance component for each frequency domain by Fourier transform. As shown in FIG. 6, by applying a Fourier transform to the current IB (and voltage VB), the current IB can be decomposed into a low frequency component, a medium frequency component, and a high frequency component. The impedance component can be calculated for each frequency range based on the voltage VB and the current IB decomposed in this way.

In the following, an example of calculating the impedance component by performing a fast Fourier transform (FFT) on the voltage VB and the current IB will be described. However, the Fourier transform algorithm is not limited to the FFT, and may be a Discrete Fourier Transform (DFT).

FIG. 7 is a diagram showing an example of the calculation result of the impedance component. In FIG. 7, the horizontal axis indicates the frequency on a logarithmic scale. The low frequency range is, for example, a frequency range of 0.001 Hz or more and less than 0.1 Hz. The medium frequency range is, for example, a frequency range of 1 Hz or more and less than 10 Hz. The high frequency range is, for example, a frequency range of 100 Hz or more and less than 1 kHz. The vertical axis of FIG. 7 shows impedance.

As shown in FIG. 7, a large number of impedance components having different frequencies are calculated in each frequency range. Therefore, the ECU 100 determines a representative value from a large number of impedance components for each of the low frequency region, the medium frequency region, and the high frequency region.

For example, when the maximum value of the impedance component is used as a representative value, the ECU 100 determines the maximum value of the impedance component in the low frequency region as the low frequency impedance component Z _L. Further, the ECU 100 determines the maximum value of the impedance component in the medium frequency region as the medium frequency impedance component Z _M, and determines the maximum value of the impedance component in the high frequency region as the high frequency impedance component Z _H. It should be noted that the maximum value may be used as a representative value, and the average value of the impedance components in each frequency range may be used as the representative value, or the intermediate value may be used as the representative value.

<Data acquisition period>
In order to ensure the accuracy of the FFT, it is required to store the data (voltage VB and current IB) repeatedly acquired for each sampling cycle in the memory 102 of the ECU 100 for a certain period of time before performing the FFT. The period for acquiring data and storing the data in the memory 102 in this way is also referred to as a “data acquisition period”. The data acquisition period corresponds to the “predetermined period” according to the present disclosure.

The impedance of the battery 10 (impedance component in each frequency range) may have current dependence, temperature dependence and SOC dependence. Therefore, if any of the current IB, temperature TB, and SOC of the battery 10 changes excessively during a certain data acquisition period, a certain period (the period before the change) and another period (change) during the data acquisition period. Since the Fourier transform (FFT) is performed collectively even though the influence of the dependence (current dependence, temperature dependence or SOC dependence) is different from that of the later period), the impedance is highly accurate. May not be able to be calculated.

In view of such circumstances, the data subject to the FFT is subject to the condition that the current IB, the temperature TB, and the SOC of the battery 10 have not changed significantly during the data acquisition period. Whether or not this condition is satisfied is determined based on the current change width ΔIB, the temperature change width ΔTB, and the SOC change width ΔSOC.

More specifically, the current change width ΔIB is the current IB after considering both the charging direction and the discharging direction of the battery 10 in a certain data acquisition period (n is a natural number _{and is described as the data acquisition period P n).} It can be calculated from the change width (difference between the maximum current in the charging direction and the maximum current in the discharging direction). The temperature change width ΔTB can be calculated from the difference between the maximum temperature (the maximum value of the temperature TB) and the minimum temperature (the minimum value of the temperature TB) in the _{data acquisition period Pn.} The SOC change width ΔSOC can be calculated from the difference between the highest SOC and the lowest SOC in the _{data acquisition period Pn.}

<Current dependence and temperature dependence of reaction resistance>
As described above, the impedance components (low-frequency impedance component Z _L , medium-frequency impedance component Z _M, and high-frequency impedance component Z _H ) for each frequency of the battery 10 are calculated by FFT, and each impedance component is compared. The DC resistance R _DC , the reaction resistance R _c, and the diffusion resistance R _d of the battery 10 can be obtained. Specifically, the DC resistance R _DC is calculated from the high-frequency impedance component Z _{H (R DC} = Z _H ). _{The reaction resistance R c} is calculated from the difference between the medium frequency impedance component Z _M and the high frequency impedance component Z _{H (R c} = Z _M −Z _H ). _{The diffusion resistance R d} is calculated from the difference between the low frequency impedance component Z _L and the medium frequency impedance component Z _{M (R d} = Z _L −Z _M ).

Here, the present inventors have _{focused on the fact that the reaction resistance R c} has current dependence and temperature dependence as described below.

FIG. 8 is a diagram for explaining the current dependence of the reaction resistor Rc. In FIG. 8, the horizontal axis represents the current IB and the vertical axis represents the reaction resistance R _c . _{The characteristics of the reaction resistance R c} shown in this figure are measured by adjusting the current IB while maintaining the temperature TB of the battery 10 at −30 ° C. As shown in FIG. 8, when the battery 10 is at a low temperature (for example, below freezing point), the smaller the current IB, the higher the _{reaction resistance R c.}

Therefore, in the present embodiment adopts a configuration of correcting the reaction resistance R _c in consideration of the current dependence and temperature dependence of the reaction resistance Rc. More specifically, the calculated value of the reaction resistance R _c based on a comparison of the impedance component of each frequency component _{(i.e., R c = Z M -Z H} ) as a reference, the current frequency range in corresponding to the reaction resistance Rc The reaction resistance R _c is corrected so that the smaller the value (hereinafter, also referred to as “medium frequency current component”), the lower the reaction resistance R _{c. Further, the reaction resistance R c} is corrected so that the lower the average temperature TB _ave in the data acquisition period P _{n, the lower the reaction resistance R c} (in other words, the larger the correction amount of the reaction resistance R _c ). As a result, the calculation accuracy of the reaction resistance R _c is improved, so that the estimation accuracy of the deteriorated state of the battery 10 can be improved.

<Battery deterioration status judgment flow>
FIG. 9 is a flowchart showing a method of determining a deteriorated state of the battery 10 in the present embodiment. This flowchart is called and executed from the main routine every time a predetermined cycle elapses while the vehicle 1 is traveling. Each step (abbreviated as S) is basically realized by software processing by the ECU 100, but may be realized by hardware processing by an electronic circuit manufactured in the ECU 100.

With reference to FIG. 9, the ECU 100 acquires the voltage VB and the current IB from each sensor in the monitoring unit 20 of the battery 10 at a predetermined sampling cycle in _{a certain data acquisition period Pn (S1).} All the data (acquisition result of voltage VB and current IB) acquired by the ECU 100 is temporarily stored in the memory 102. The length of the data acquisition period _Pn can be set to, for example, about several seconds to several tens of seconds. The sampling period can be set, for example, from the order of milliseconds to the order of several hundred milliseconds.

In S2, ECU 100 calculates the current change width ΔIB showing the variation width of the current IB in the data obtaining period _{P n.} Further, the ECU 100 calculates a temperature change width ΔTB indicating a change width of the temperature TB _{during the data acquisition period Pn.} Further, ECU 100 calculates the SOC variation ΔSOC indicating the SOC variation width of the battery 10 in the data acquisition period _{P n.}

The memory 102 of the ECU 100 non-volatilely stores the map MP1 in which the correspondence between the average temperature TB _{ave in the data acquisition period Pn} and the permissible current change width ΔIB _{max is defined.} The permissible current change width ΔIB _max is a parameter that serves as a criterion for determining whether or not the data stored in the memory 102 in S1 is used for impedance calculation, and indicates the permissible upper limit of the current change width ΔIB.

FIG. 10 is a diagram showing an example of the map MP1. As shown in FIG. 10, the map MP1, each range of the average temperature _{TB ave} of the battery 10 in the data acquisition period _{P n,} the allowable current variation? IB _max in the data obtaining period _{P n} are defined. In the map MP1, the permissible temperature change width ΔTB _max and the permissible SOC change width ΔSOC _max are also defined for each range of the average temperature TB _ave. It should be noted that the specific numerical values shown in FIG. 10 are merely examples for facilitating the understanding of the map MP1.

In S3, the ECU 100 acquires the permissible current change width ΔIB _{max from the average temperature TB ave by referring to the map MP1.} Similarly, for the temperature change width ΔTB and the SOC change width ΔSOC, the ECU 100 acquires the permissible temperature change width ΔTB _max and the permissible SOC change width ΔSOC _{max from the average temperature TB ave} by referring to the map MP1, respectively.

Returning to FIG. 9, in S4, the ECU 100 determines whether or not the _{current change width ΔIB is less than the allowable current change width ΔIB max.} Further, the ECU 100 determines whether or not the temperature change width ΔTB is _{less than the allowable temperature change width ΔTB max} , and determines whether or not the SOC change width ΔSOC is less than the _{allowable SOC change width ΔSOC max.}

When the current change width ΔIB, the temperature change width ΔTB and the SOC change width ΔSOC are all less than the corresponding allowable change widths, that is, the current condition of _{ΔIB <ΔIB max} is satisfied and the temperature is _{ΔTB <ΔTB max.} When the condition is satisfied _{and the SOC condition of ΔSOC <ΔSOC max} is satisfied (YES in S4), the ECU 100 executes FFT on the data (voltage VB and current IB) stored in the memory 102 in S1. (S5).

In S6, the ECU 100 calculates an impedance component for each frequency based on the voltage component and the current component after the FFT (see, for example, Patent Document 1 for a detailed calculation formula of the impedance component). _{Further, the ECU 100 calculates the DC resistance R DC} , the reaction resistance R _c, and the diffusion resistance R _d of the battery 10 from the impedance components for each frequency range. Since this calculation method has been described in detail in FIG. 5, the description will not be repeated here.

In S7, the ECU 100 corrects the reaction resistance R _c calculated in S6 by referring to the correction map MP2. This process corresponds to the "correction process" according to the present disclosure.

FIG. 11 is a conceptual diagram showing an example of the correction map MP2. As shown in FIG. 11, in the correction map MP2, the average temperature TB _{ave in the data acquisition period Pn} and the medium frequency current component (current in the medium frequency range) are based on the preliminary experimental results (AC impedance measurement results). And the correspondence between the correction coefficient are defined. By referring to the correction map MP2, the _{correction coefficient is calculated from the average temperature TB ave} and the medium frequency current component. Then, by multiplying the correction factor to the reaction resistance R _c calculated in S6, the reaction resistance R _c is corrected.

Incidentally, an example will be described using the average temperature _{TB ave} in the map MP2 the data acquisition period _{P n,} instead of the average temperature _{TB ave,} for example, may be used the maximum temperature or minimum temperature in the data obtaining period _{P n} The mode value of temperature TB may be used. Further, instead of the correction map MP2, the reaction resistance R _c can be corrected by using a function or a conversion formula.

After that, the ECU 100 discards the data (acquisition result of voltage VB and current IB) stored in the memory 102 (S8). In S4, when at least one of the current change width ΔIB, the temperature change width ΔTB, and the SOC change width ΔSOC is equal to or greater than the corresponding allowable change width (NO in S4), that is, the current during the data acquisition period Pn. When the IB, the temperature TB, or the SOC fluctuates to some extent, the ECU 100 advances the process to S8 without executing the processes of S5 to S7, and discards the data stored in the memory 102.

In S9, the ECU 100 estimates the deteriorated state of the battery 10 based on each resistance component (DC resistance R _DC , reaction resistance R _c, and diffusion resistance R _{d) calculated in S7.} Specifically, ECU 100 compares the DC resistance _{R DC} and tolerance _{X H,} compares the reaction resistance _{R c} and tolerance _{X M,} compares the allowable value _{X L} with diffusion resistance _{R d.} Then, when at least one resistance component is higher than the permissible value, the ECU 100 determines that the deterioration of the battery 10 is progressing. On the other hand, when all the resistance components are equal to or less than the permissible values, the ECU 100 determines that the deterioration of the battery 10 has not progressed.

The process of estimating the deterioration state of the battery 10 in S10 may be executed in a separate flow. That is, the processes S5 to S7 may be repeatedly executed until the calculation results of the resistance components are accumulated, and the deterioration state of the battery 10 may be estimated after the calculation results of the resistance components are accumulated.

Further, when it is determined in S10 that the deterioration of the battery 10 is progressing, the ECU 100 can suppress the charging / discharging of the battery 10. Specifically, the ECU 100 has a limit upper limit value (charge power control upper limit value and discharge power control) of the charge / discharge power of the battery 10 as compared with the normal time (when it is determined that the deterioration of the battery 10 has not progressed). Set the upper limit) low. As a result, it is possible to suppress the further progress of deterioration of the battery 10 and reduce the deterioration rate of the battery 10. Further, the ECU 100 may execute control for promptly stopping the charging / discharging of the battery 10. For example, the ECU 100 transitions the vehicle 1 to a fail-safe mode, thereby informing the user of the vehicle 1 to bring the vehicle 1 to a dealer (or a repair shop or the like) for appropriate inspection.

FIG. 12 is a diagram for comparing the calculation results _{of the reaction resistance R c} in the comparative example and the present embodiment. In FIG. 12, the horizontal axis indicates the elapsed time. The vertical axis shows the reaction resistance R _c of the battery 10. In FIG. 12, the reaction resistance R _c precisely obtained by a general AC impedance measurement is shown by a broken line as a “true value”.

With reference to FIG. 12, there is an error between _{the calculation result of the reaction resistance R c} in the comparative example, that is, the reaction resistance R _{c when the correction in S7 is not performed and the true value.} On the other hand, in the present embodiment, as a result of performing the treatment of S7, _{it can be seen that the corrected reaction resistance R c} and the true value are in good agreement.

As described above, according to the present embodiment, when the temperature TB of the battery 10 is a low temperature such as below freezing point, the smaller the current IB (more specifically, the medium frequency current component), the higher the _{reaction resistance R c.} Focusing on the point, _{the reaction resistance R c} is corrected based on the average temperature TB _ave and the medium frequency current component _{in the data acquisition period Pn} (see the correction map MP2 shown in FIG. 11). Thus, taking into account the current dependence and temperature dependence of the reaction resistance R _c, it is possible to improve the calculation accuracy of the reaction resistance R _c. As a result, it is possible to improve the estimation accuracy of the deteriorated state of the battery 10.

Further, according to the present embodiment, at least one of the current IB, the temperature TB and the SOC of the battery 10 changes significantly more than the _{corresponding allowable change width (ΔIB max} , ΔTB _max , ΔSOC _{max) during the data acquisition period.} If so, the data (voltage VB and current IB) acquired during the data acquisition period is excluded from the target of FFT and is not used for impedance calculation. As a result, the current dependence, the temperature dependence, and the SOC dependence can be appropriately reflected in the calculation result of the impedance of the battery 10, so that the estimation accuracy of the deteriorated state of the battery 10 can be improved.

In the present embodiment, a configuration for calculating the impedance component of the battery 10 using an irregular current waveform (and voltage waveform) generated during traveling of the vehicle 1 which is a hybrid vehicle has been described. Although not shown, when the vehicle 1 is a plug-in hybrid vehicle or an electric vehicle, that is, a configuration in which the battery 10 can be charged by the electric power supplied from a power source (external power source) provided outside the vehicle (so-called external charging is possible). When the vehicle 1 has such a configuration, the impedance component may be calculated from the current waveform supplied from the external power source at the time of external charging. In each frequency range, instead of supplying power with a constant current waveform from an external power source, the frequency range is a current waveform (sine wave, square wave, triangle wave, etc.) extending from the low frequency range to the high frequency range. It becomes possible to calculate the impedance component.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the description of the embodiment described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 vehicle, 2 rechargeable battery system, 10 batteries, 11 blocks, 12 cells, 20 monitoring units, 21 voltage sensors, 22 current sensors, 23 temperature sensors, 30 PCUs, 41, 42 motor generators, 50 engines, 60 power dividers. , 70 drive shafts, 80 drive wheels, 100 ECUs, 101 CPUs, 102 memories.

Claims (1)

It is a method of estimating the deterioration state of the secondary battery, which is executed by the control device for the secondary battery mounted on the vehicle.
A step of acquiring the voltage value and the current value of the secondary battery a plurality of times in a predetermined period and storing them in the memory.
A step of calculating the current change width of the secondary battery, the temperature change width of the secondary battery, and the SOC change width of the secondary battery in the predetermined period, and
The permissible current change width indicating the permissible upper limit of the current change width, the permissible temperature change width indicating the permissible upper limit of the temperature change width, and the permissible temperature change width indicating the permissible upper limit of the current change width, which are determined for each of the temperature, current or SOC of the secondary battery in the predetermined period. The step of acquiring the permissible SOC change width indicating the permissible upper limit of the SOC change width from the temperature, current or SOC of the secondary battery, and
The current condition that the current change width is less than the allowable current change width, the temperature condition that the temperature change width is less than the allowable temperature change width, and the SOC change width are less than the allowable SOC change width. When all the SOC conditions are satisfied, the frequency conversion of the voltage value and the current value acquired a plurality of times of the secondary battery stored in the memory is performed, and the frequency-converted voltage value and the current value are used. Steps to calculate the impedance component for each frequency range of the secondary battery,
A step of executing a correction process for correcting the reaction resistance, which is an impedance component corresponding to the predetermined frequency range, according to the temperature of the secondary battery and the current value in the predetermined frequency range in the predetermined period.
It includes a step of estimating the deterioration state of the secondary battery in the deterioration mode corresponding to each frequency range by using the calculated impedance component for each frequency range and the reaction resistance after the correction by the correction process.
In the correction process, the reaction resistance is corrected so that the smaller the current value in the predetermined frequency range is, the lower the reaction resistance is, and the lower the temperature of the secondary battery in the predetermined period is, the lower the reaction resistance is. A method for estimating a deterioration state of a secondary battery, which is a process of correcting the reaction resistance so as to be.

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