JP2009126278A - Internal state detection device of on-board secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate a charge current characteristic which appropriately includes relaxation phenomena of a charge current dropping characteristic at the end stage of constant voltage charging. <P>SOLUTION: The constant voltage charging is performed to a battery so as to obtain multiple pieces of current data at predetermined intervals. These pieces of the current data are used to obtain a charge current function being its approximate expression. The charge current function is compensated with, for example, a correction coefficient obtained by a map. Thus, a correction charge current function with few errors is obtained (S7). The correction charge current function is used to favorably estimate the internal state of the battery 101 (S8, S9). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an in-vehicle secondary battery internal state detection technique capable of reducing the influence of charging efficiency in estimating an internal state such as a storage state of the in-vehicle secondary battery.

  Increasing the capacity of in-vehicle secondary batteries and increasing the size of in-vehicle electric loads will improve the detection accuracy of internal conditions such as the capacity of in-vehicle secondary batteries to prevent overcharge and overdischarge. It is important.

Patent Document 1 discloses a point in time when a charging current reaches a predetermined final value (hereinafter referred to as a charging current approximation function) based on a charging current variation characteristic (hereinafter also referred to as a charging current approximation function) estimated from a charging current variation waveform immediately before constant voltage charging. , Which is also referred to as an estimation time point), and a technology for calculating a charge capacity (Ah) and a required charge time until the final value is reached is disclosed.
Japanese Patent No. 3249788

  However, in the technique for estimating the charging current characteristic based on the current data at the time of constant voltage charging described in Patent Document 1 described above, the effect of the charging efficiency of the battery is not taken into account, and the accuracy of the charging current approximation function is In particular, it was found that there was a problem that it decreased at the end of charging. For this reason, there has been a serious problem that the estimation accuracy of the charging capacity (Ah) and the required charging time from the estimation time point, that is, the constant voltage charging end time point to the final value is lowered.

  The present invention has been made in view of the above-described problems, and provides an internal state detection device for an in-vehicle secondary battery capable of accurately estimating when the charging current during constant voltage charging reaches a predetermined final value. Is the purpose.

Means for Solving the Problems and Effects of the Invention

  This invention made | formed in order to achieve the said subject is based on the detection circuit part which detects the terminal voltage and electric current of the vehicle-mounted secondary battery by which convergence control is carried out to the predetermined | prescribed adjustment voltage by the vehicle-mounted AC generator, and the calculated electric current. An internal state detection circuit unit that estimates an internal state of the in-vehicle secondary battery.

  The internal state detection circuit unit continues constant voltage charging at a predetermined voltage value of the in-vehicle secondary battery for a predetermined time immediately after starting the vehicle or during vehicle traveling, and a plurality of data of the charging current obtained after starting the constant voltage charging A charging current function that is a function that represents a change in the charging current over time is obtained, and a predetermined correction value or a correction function that is a numerical value or function that correlates with deterioration of the in-vehicle secondary battery is periodically obtained. Alternatively, a correction charging current function that is stored in advance by writing at the time of shipment and approximates an actual change in charging current at the time of constant voltage charging rather than the charging current function is the correction value or the correction function and the charging current function. The charging current integrated value until the charging current value reaches a predetermined final value is obtained based on the obtained corrected charging current function, and the previous charging current value is obtained based on the obtained charging current integrated value. It is set to its features to determine the internal state of the vehicle battery.

  That is, the present invention performs constant voltage charging for a predetermined time, samples a plurality of charging current values, obtains a charging current function indicating a future change characteristic of the charging current in constant voltage charging from each obtained data, A correction charging current function obtained by correcting the charging current function based on a correction value or a correction winding number stored in advance is obtained, and the internal state of the in-vehicle secondary battery is calculated from the correction charging current function. This correction value or correction function is a value or function that brings the charging current function closer to the actual charging current value at the end of charging after the end of the constant voltage charging. A specific method for deriving these correction values or correction functions will be described in the following embodiment. However, it is preferable that the correction value or the correction function reflects the variation due to the aging deterioration of the in-vehicle secondary battery.

  As a result, it has been found that the charging current integrated value calculation accuracy can be improved as compared with the case where the charging current function is not corrected. In addition, since it is not necessary to continue long-term constant voltage charging until the end of charging, the in-vehicle secondary battery is easy to use, and the in-vehicle secondary battery deteriorates due to frequent long-term constant voltage charging. Can be deterred.

  After all, in the present invention, the correction current function is corrected with a correction value or a correction function commensurate with an increase in the charging current at the end of charging to obtain a corrected charging current function, and various battery states are obtained using this corrected charging current function. Is estimated. Thereby, it is possible to estimate the charging current with less error compared to the conventional charging current function obtained without using such a correction value or correction function. Conventionally, the need for such correction or determination of the charging current function has not yet been recognized.

  A preferred embodiment of the internal state detection device for an in-vehicle secondary battery of the present invention will be described below. However, the present invention should not be construed as being limited to the following embodiments, and it goes without saying that the technical idea of the present invention may be implemented by combining other known techniques and techniques having the same functions.

(Device configuration)
An SOC computing device for an in-vehicle secondary battery according to Embodiment 1 will be described with reference to a block diagram shown in FIG.

  101 is an in-vehicle power storage device (hereinafter also referred to as a battery), 102 is an in-vehicle generator (in-vehicle AC generator in the present invention) that is driven by an in-vehicle engine (not shown) and charges the battery 101, and 103 is a battery 101. 104 is a current sensor (detection circuit unit in the present invention) that detects the charging / discharging current of the battery 101 and outputs it in the form of a digital signal, 105 is the SOC of the battery 101, etc. It is a storage battery state detection device (an internal state detection device for an in-vehicle secondary battery referred to in the present invention) that is an electronic circuit device for calculation. The storage battery state detection device 105 includes a calculation process corresponding to the polarization calculation circuit unit referred to in the present invention. 106 is a buffer unit for input of the storage battery state detection device 105, 107 is an arithmetic processing unit of the storage battery state detection device 105, 108 is SOC from the arithmetic processing unit 107, engine state input from the outside, vehicle speed, generator speed, etc. This ECU calculates the power generation amount of the in-vehicle generator 102 based on the vehicle information 110 of the vehicle. Reference numeral 109 denotes a generator control device that controls the output of the field coil type on-vehicle generator. The generator control device 109 normally sets the difference between the voltage of the battery 101 and a predetermined adjustment voltage to 0 as in the conventional case. For this purpose, feedback control is performed on the field current, and the voltage of the battery 101 is set to this adjusted voltage. Further, the generator control device 109 causes the in-vehicle generator 102 to generate power corresponding to the power generation amount determined by the ECU 108 as necessary.

  The buffer unit 106 and the arithmetic processing unit 107 of the storage battery state detection device 105 are realized by software calculation by a microcomputer device, but of course may be configured by a dedicated hardware circuit. The buffer unit 106 samples and holds a pair (data pair) of the voltage V of the battery 101 and the current I from the current sensor 104 at a predetermined timing. The arithmetic processing unit 107 calculates the SOC by a method described later based on the input parameter input from the buffer unit 106. The battery 101 may be a secondary battery such as a lead storage battery, a nickel-hydrogen battery, or a lithium battery, but the type is not limited. In this embodiment, an ordinary vehicle lead-acid battery is employed.

(Constant voltage charging operation)
Next, the constant voltage charge control of the first embodiment will be specifically described below with reference to the flowcharts shown in FIGS. 2 and 3, the storage battery state detection device 105 is a subroutine showing constant voltage charging control that performs one of a number of processing operations that are sequentially executed at a predetermined short interval. This constant voltage charging control routine is started at a predetermined timing when the engine is started or while the vehicle is running.

  First, it is checked whether or not the constant voltage charge control operation is currently being executed (S1). If it is being executed, the process proceeds to step S2, otherwise constant voltage charge control for applying a constant voltage to the battery 101 is started ( S3). The constant voltage charging control is performed by maintaining the voltage of the battery 101 at a constant value by controlling the power generation of the in-vehicle generator 102.

  However, in step S1, it is checked whether there is a sudden change in the terminal voltage of the battery 101 due to a sudden load interruption or a sudden change in the power generation voltage due to a sudden change in the engine speed. Even if the constant voltage charge control is being executed, the constant voltage charge control operation is not regarded as being executed, and the process proceeds to step S3. This is because the time constant delay of the field current control of the generator 102 is taken into consideration. In addition, when the above-mentioned sudden change of the power generation situation or the load situation occurs, it is preferable to stop the constant voltage charging control shown in FIG. 2 and start it again after a certain period of time.

  In step S2, the charging current Icv of the battery 101 is read, and the polarization related quantity P and its differential value ΔP are calculated from the read charging current Icv (S3). In this embodiment, the polarization related amount P is obtained from the following equation.

       Pn = Pn-1 + In * dt-1 / .tau. * Pn-1 * dt (.tau .: time constant) In the above equation, n represents the current value and n-1 represents the previous value. Therefore, Pn is the current value of the polarization related quantity P, Pn-1 is the previous value of the polarization related quantity P, and In is the current value of the charging current Icv. The time difference between the current value and the previous value is set to a predetermined constant value dt.

  However, in the first calculation of this equation, it is preferable that the previous value Pn−1 of the polarization related amount P be 0. In this embodiment, for simplicity, dt is set equal to the routine period and the current sampling period (S2). τ is a charge diffusion time constant of the battery electrolyte, and is a predetermined value obtained in advance by experiments. The current value Pn of the polarization state quantity is an increase amount In · dt of the polarization state quantity generated from the previous sampling time to the current sampling time, and a polarization state quantity attenuated from the previous sampling time to the current sampling time. The attenuation amount Pn−1 · dt / τ is calculated by adding or subtracting from the previous value Pn−1 of the polarization state quantity at the previous sampling time. The differential value ΔP of the polarization related amount P is expressed by the following equation.

ΔP = (Pn−Pn−1) / dt = In−1 / τ * Pn−1
Next, it is checked whether or not the differential value ΔP of the polarization related amount P has decreased to less than a predetermined threshold (S4). If not, the process returns to the main routine, and if it has decreased, the polarization is sufficiently eliminated. The process proceeds to step S5, and the charging current values Icv1 to Icv31 sampled and stored for a predetermined time T (for example, 30 seconds) from the time when ΔP becomes equal to or lower than the above threshold value are read. An approximate expression (I = K + a * exp (b * t)) is obtained from the current values Icv1 to Icv31 using a known method (for example, the least square method), and the time variation characteristic of the charging current, that is, the charging current function referred to in the present invention. (S6).

  In this approximate expression, I is a charging current, K, a, and b are constants, and t is an elapsed time from the start of constant voltage charging. These constants are determined by experiment. K may be 0. However, the charging current function referred to in the present invention is not limited to the above approximate expression, and it is naturally possible to adopt various known approximate expression creation methods that approximate each current data obtained during the constant voltage charging period. Needless to say.

  Next, the approximate expression (charging current function) obtained in step S6 is corrected based on the correction coefficient stored in advance to obtain a corrected charging current function (S7). Of course, this correction charging function may be described in a map format instead of a mathematical expression. However, this correction coefficient will be described later.

  Next, a predetermined final charging current value Icv (final) is substituted into the obtained correction charging function to obtain a constant voltage charging control end time Tf at that time, and if constant voltage charging is continued from the present time, The sum of the charging current Icv during the period until reaching the time point Tf to be completed is integrated to obtain a charging current integrated value (α = ∫I · dt) (S8). In this embodiment, the final charge current value Icv (final) is a charge current value corresponding to 90% of the battery's SOC when the constant voltage charge control is performed under the above conditions, and the current value obtained in advance through experiments or the like. It was.

  As a result, the current SOC can be accurately calculated by subtracting the charging current integrated value (α = ∫I · dt) from SOC 90%, and how much capacity Ah is charged after the current time becomes SOC 90%. It can be estimated whether it will be reached (S9). Then, constant voltage charge is complete | finished (S10). The constant voltage charging may be terminated after step S5 for current data sampling.

(Calculation of correction coefficient)
Next, correction coefficients for correcting the above-described charging current function (approximate expression) will be described. As described above, this correction coefficient is for correcting the slowdown of the charging current droop at the end of the constant voltage due to, for example, deterioration of the in-vehicle secondary battery, and employs a number of methods as described below. can do.

(1st plan)
The charging current increase ratio based on the charging current value obtained from the charging current function at each time in constant voltage charging has a positive correlation with the cumulative charging / discharging time of the in-vehicle secondary battery for the reason described above, and charging / discharging. The larger the cycle life, the larger.

  For the charging current function (I = K + a * exp (b * t)), the corrected charging current function Iγ is (Iγ = K ′ + a ′ * exp (b ′ * t)). The coefficients K ′, a ′, and b ′ are respectively a coefficient or a function in which the original coefficient K is a variable, a ′ is a coefficient or function of the original coefficient a, and b ′ is an original coefficient b. It is a coefficient or function. In order to simplify the calculation, the function is preferably a linear expression, or a map may be adopted.

  When a function or map is employed instead of a constant value, this function or map can be created by the following method.

  For example, these coefficients K ′, a ′, and b ′ are stored in advance as a linear function or map in which the charge / discharge cumulative time T of the in-vehicle secondary battery is a variable, and the charge / discharge cumulative time T is substituted for this. The coefficients K ′, a ′, and b ′ may be obtained.

  The charge / discharge cumulative time T can be estimated by various methods. For example, when the on-time of the ignition key, the accumulated time equal to or greater than a predetermined charge / discharge current value of the in-vehicle secondary battery (battery), and the like are counted by a counter, this count value can be regarded as substantially the charge / discharge accumulated time.

  In addition, any one or two of the coefficients K ′, a ′, and b ′ may be corrected. For example, the correction coefficient k can be a ′ = γ · a.

  The above correction coefficient may be written at the time of shipment from the factory, or by a calculation formula stored in advance from a state signal (for example, voltage, current, temperature, operation time, etc.) detected from the in-vehicle secondary battery during operation of the in-vehicle secondary battery. It may be calculated. Furthermore, long-term constant voltage charging control at the end of charging of the in-vehicle secondary battery (for example, up to SOC 90%) is sometimes performed, and the above coefficient is derived from an equation or map stored in advance using the charging current value obtained thereby. May be.

(2nd plan)
The charging current increase amount and rate based on the charging current value obtained from the charging current function in constant voltage charging have a positive correlation with the increase in the elapsed time of constant voltage charging for the reasons described above, and constant voltage charging. The longer the elapsed time, the larger.

  Therefore, the correction charging current function Iγ is (Iγ = K ′ + a ′ * exp (b ′ * t)) with respect to the charging current function (I = K + a * exp (b * t)). The coefficients K ′, a ′, and b ′ are respectively a coefficient or a function in which the original coefficient K is a variable, a ′ is a coefficient or function of the original coefficient a, and b ′ is an original coefficient b. It is a coefficient or function. In order to simplify the calculation, the function is preferably a linear expression, or a map may be adopted.

  When a function or map is employed instead of a constant value, this function or map can be created by the following method.

  For example, these coefficients K ′, a ′, and b ′ are stored in advance as a linear function or map in which the charge / discharge cumulative time T of the in-vehicle secondary battery is a variable, and the charge / discharge cumulative time T is substituted for this. The coefficients K ′, a ′, and b ′ may be obtained.

  The charge / discharge cumulative time T can be estimated by various methods. For example, when the on-time of the ignition key, the accumulated time equal to or greater than a predetermined charge / discharge current value of the in-vehicle secondary battery (battery), and the like are counted by a counter, this count value can be regarded as substantially the charge / discharge accumulated time.

  In addition, any one or two of the coefficients K ′, a ′, and b ′ may be corrected. For example, the correction coefficient k can be a ′ = γ · a.

  The above correction coefficient may be written at the time of shipment from the factory, or by a calculation formula stored in advance from a state signal (for example, voltage, current, temperature, operation time, etc.) detected from the in-vehicle secondary battery during operation of the in-vehicle secondary battery. It may be calculated. Furthermore, long-term constant voltage charging control at the end of charging of the in-vehicle secondary battery (for example, up to SOC 90%) is sometimes performed, and the above coefficient is derived from an equation or map stored in advance using the charging current value obtained thereby. May be.

(Test results)
Next, FIG. 4 shows the result of examining the charge capacity at the time of constant voltage charging using an ordinary vehicle lead-acid battery and the estimated result.

  In FIG. 4, constant voltage charging is performed for 480 seconds, a large number of charging current values and elapsed time from the start of constant voltage charging are sampled at a constant interval, and a charging current function (I ( t) = A * exp (B * t)). Next, the correction charging current function (Iγ (t) = γ * A * exp (B * t)) was obtained by applying correction according to the correction coefficient γ. Therefore, the differential coefficient (dIγ (t)) of the corrected charging current function (Iγ (t) = γ * A * exp (B * t)) is expressed by the following equation. Note that Iγ (t) is the current value of the corrected charging current, Iγ (t−1) is the previous value of the corrected charging current function, and the sampling period of the corrected charging current function is dt.

dIγ (t) = γ * A * B * exp (B * t))
= Iγ (t) -Iγ (t-1)
Using this corrected charging current function, a charging current accumulated value (integrated capacity) until the charging current reaches a final charging current value Icv (final) that is a charging current value equivalent to SOC 90% set in advance is obtained as 5.8. Ah. On the other hand, it was found that the final charging current value Icv (final) actually measured by constant voltage charging was 6.2 Ah, and the error was only 0.4 Ah, which can be estimated with high accuracy.

  Next, without performing the above correction, the integrated capacity integrated using the charging current function was 4.9 Ah, and the error from the actual measurement value was as large as 1.3 Ah.

  FIG. 5 shows the relationship between the correction coefficient γ and the measured charging current value in constant voltage charging. The correction coefficient γ is a square between the measured charge current value obtained at each measurement time point of the same elapsed time and the calculated value obtained from the corrected charge current function after performing constant voltage charging with a battery mounted on the vehicle in advance. The determination is made in FIG. 5 so that the error is minimized.

  In addition, as described above, characteristics (charging efficiency, internal resistance, etc.) of the storage battery for a vehicle are deteriorated due to the usage method or operation time, and the charging current drooping characteristic (for example, FIG. 4) during constant voltage charging changes. . For this reason, it is preferable to further correct the correction coefficient γ according to the current state of the battery depending on, for example, the operation time. An example of this correction will be described with reference to FIG.

  In FIG. 6, a map of a plurality of charging currents vs. correction coefficients γ is prepared in advance, and immediately after the constant voltage charging is performed, the obtained current measured values and the charging current functions obtained from the current measured values are expressed as follows: A square error between each measured current value and each current calculation value obtained at the same time by calculating each correction charging current function obtained by correction using each correction coefficient map m1 to m4 shown in FIG. A map having the smallest value may be selected and adopted as the current correction coefficient γ. Thereby, even when the battery state changes, the charge capacity can be accurately estimated.

  In the embodiment described above, the battery capacity is reduced and the battery SOC is required immediately after starting the engine, which needs to be charged with a predetermined capacity (Ah), or while the vehicle is running. This is suitable for accurately estimating the state of charge of the battery, for example, at a timing when the power generation of the generator 102 is enhanced to compensate for this and the charging of the battery is enhanced.

(Modification)
In the above embodiment, the exclusion of the influence of polarization (charging polarization) that occurs in constant voltage charging was not mentioned, but current sampling was performed after a predetermined time ΔT from the start of constant voltage charging, or the predetermined time ΔT was determined as the charging current. However, the influence of the polarization may be reduced by performing current sampling at a time when a predetermined rate is decreased from the time when constant voltage charging is started.

It is a block diagram which shows the control apparatus of the vehicle-mounted secondary battery of embodiment. It is a flowchart which shows the constant voltage charge control in embodiment. It is a flowchart which shows the constant voltage charge control in embodiment. FIG. 7 is a characteristic diagram showing an actual measurement characteristic line A of charging current during constant voltage charging, a characteristic line B calculated with a corrected charging current function, and a characteristic line C calculated with a charging current function. It is a figure which shows the relationship between a charging current and a correction coefficient. It is a figure which shows four maps which show a mutually different relationship between a charging current function and a correction coefficient.

Explanation of symbols

101 Battery 102 On-vehicle generator (generator)
104 Current sensor 105 Storage battery state detection device 106 Buffer unit 107 Arithmetic processing unit 109 Generator control device 110 Vehicle information

Claims (1)

A detection circuit unit that detects the terminal voltage and current of the in-vehicle secondary battery that is converged and controlled to a predetermined adjustment voltage by the in-vehicle AC generator, and an internal state that estimates the internal state of the in-vehicle secondary battery based on the calculated current In the in-vehicle secondary battery internal state detection device comprising a detection circuit unit,
The internal state detection circuit unit is
Continue constant voltage charging at a predetermined voltage value of the in-vehicle secondary battery for a predetermined time immediately after starting the vehicle or during vehicle traveling,
Obtaining a charging current function that is a function representing a time change of the charging current based on a plurality of data of the charging current obtained after the start of the constant voltage charging,
A predetermined correction value or correction function that is a numerical value or a function having a correlation with deterioration of the in-vehicle secondary battery is stored in advance by periodically obtaining or writing at the time of shipment,
A correction charging current function that is a function that approximates an actual change in charging current during the constant voltage charging rather than the charging current function is obtained based on the correction value or the correction function and the charging current function,
Based on the corrected charging current function that has been obtained, to determine a charging current integrated value until the charging current value reaches a predetermined final value,
An internal state detection device for an in-vehicle secondary battery, wherein the internal state of the in-vehicle secondary battery is determined based on the obtained charging current integrated value.