JP4494454B2 - In-vehicle secondary battery internal state detection device - Google Patents

Description

  The present invention relates to a technique for detecting an internal state of an in-vehicle secondary battery that can reduce the influence of battery polarization 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 of Patent Document 1 described above, the estimated charging current approximation function fluctuates due to variations in the polarization state of the battery and deviates from the actual charging current waveform, so that the charging current actually becomes a predetermined value (actual time point). There is a drawback that there is a large difference between the estimated time and the estimated time. For this reason, there has been a serious problem that the accuracy of the charge capacity (Ah) and the required charging time until the final value obtained on the basis of the estimated time point 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

  The present invention that solves the above-described problems includes a detection circuit unit that detects a terminal voltage and a current of a vehicle-mounted secondary battery that is converged and controlled to a predetermined adjustment voltage by a vehicle-mounted AC generator, and the vehicle-mounted 2D based on the calculated current. An internal state detection device for an in-vehicle secondary battery comprising an internal state detection circuit unit for estimating an internal state of the secondary battery, wherein the internal state detection circuit unit is configured to store the predetermined in-vehicle secondary battery immediately after starting the vehicle or during traveling of the vehicle. Constant voltage charging at a voltage value is continued for a predetermined time, and a polarization related amount P that is a parameter related to the polarization amount of the in-vehicle secondary battery after the start of the constant voltage charging is obtained based on a change in charging current data. It is determined whether or not the rate of change of the polarization related amount P is less than a predetermined threshold, and a plurality of the above-mentioned obtained at a predetermined time after determining that the rate of change of the polarization related amount P is less than the predetermined threshold. Charging current The charging current integrated value until the charging current value reaches a predetermined final value is obtained based on the data, and the internal state of the in-vehicle secondary battery is determined based on the obtained charging current integrated value. It is said.

  That is, the present invention confirms that the change in the polarization-related amount P after the start of constant voltage charging of the in-vehicle secondary battery has reached a slow stage, and then determines the future charging current from the transition of the charging current so far. And the internal state of the in-vehicle secondary battery is detected (determined) based on this estimation. In this way, when detecting the internal state of the in-vehicle secondary battery under constant voltage charging, it is possible to almost eliminate the influence of variations in the polarization state of the in-vehicle secondary battery, thereby realizing highly accurate internal state detection. be able to. The internal state detection referred to here includes SOC, SOH, or an amount related thereto (for example, an amount obtained by subtracting the current value of SOC or SOH from a full charge value).

  In a preferred aspect, the internal state detection circuit unit performs the steps in a constant voltage charging period immediately after engine startup. When the engine is stopped, the charge / discharge of the battery is very low due to the ignition switch being shut off, and as a result, it can be considered that the polarization of the in-vehicle secondary battery is almost zero, so that the calculation accuracy of the polarization related quantity P can be improved. As a result, the accuracy of the internal state determination can be improved.

  In a preferred aspect, the internal state detection circuit unit executes the internal state determination process during a constant voltage charging period during traveling of the vehicle in which a charging current of a predetermined value or more flows. Thereby, the internal state of a vehicle-mounted secondary battery can be detected frequently.

  In a preferred aspect, the internal state detection circuit unit executes the internal state determination process during the constant voltage charging period that is performed after a period in which the charging / discharging current is equal to or less than a predetermined value during vehicle travel continues for a predetermined time. . As a result, constant voltage charging can be started in a state in which the polarization of the in-vehicle secondary battery is sufficiently eliminated, so that the accuracy of the internal state determination can be improved.

  In a preferred embodiment, the internal state detection circuit unit has a current value of the polarization-related quantity P as Pn, its previous value as Pn−1, In as a current value of a charging current, and dt as a current detection interval during constant voltage charging, When τ is a predetermined time constant value, the polarization-related quantity P is obtained from the formula: Pn = Pn−1 + In * dt−1 / τ * Pn−1 * dt. Thereby, the amount of polarization (charge polarization) can be obtained with relatively high accuracy.

  In a preferred embodiment, the internal state detection circuit unit is configured such that when I is a charging current, a and b are constants, t is an elapsed time from the start of constant voltage charging, and K is a predetermined proportional constant, Based on a plurality of data of the charging current I obtained every predetermined time after determining that the rate of change is less than a predetermined threshold, an approximate expression (I = K + a * exp (b * t )) Is derived, and the charging current integrated value is obtained using the approximate expression. Thereby, the internal state of the in-vehicle secondary battery can be detected with high accuracy.

  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 referred to 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 an input buffer unit 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. Therefore, feedback control of the field current is performed, and the voltage of the battery 101 is set to this adjustment 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 control)
Next, the control operation that characterizes this embodiment will be specifically described below with reference to FIG. In FIG. 2, 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 value (S4). If not, the process returns to the main routine. The process proceeds to step S5 by determining that the current is stable, and reads the charging current values Icv1 to Icv31 that are sampled and stored during a predetermined time T (for example, 30 seconds) from when ΔP becomes equal to or less than the threshold value, An approximate expression (I = K + a * exp (b * t)) is obtained from each charging current value Icv1 to Icv31 using a known method (for example, the least squares method), and the time variation characteristic of the charging current is obtained (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.

  Next, a predetermined final charging current value Icv (final) is substituted into the obtained approximate expression to obtain a constant voltage charge control end time Tf at that time, and from this time until this constant voltage charge control end time Tf is reached. The total sum of the charging currents Icv during the period is integrated into a charging current integrated value (α = ∫I · dt) (S7).

  In this embodiment, the final charging current value Icv (final) is a charging current value at a value of SOC 90% of this battery when the constant voltage charging control is performed under the above conditions, and is a value obtained in advance through experiments or the like. . As a result, the current SOC can be accurately calculated by subtracting the charging current integrated value (α = ∫I · dt) from SOC 90%. In addition, it is possible to estimate how much capacity Ah is charged after the current time point to reach SOC 90% (S8). Then, constant voltage charge is complete | finished (S10).

(Example effect)
That is, in this embodiment, the capacity of the battery is reduced and the battery needs to be charged by charging with a predetermined capacity (Ah). This is suitable for accurately estimating the state of charge of the battery, for example, at the timing when the power generation of the generator 102 is increased to compensate for the decrease in SOC and the charging of the battery is enhanced. In further explanation, if constant voltage charging is continued in this charging process, if there is discharge polarization, it is quickly eliminated, and a constant amount of charge polarization corresponding to this charging voltage is restored from the start of constant voltage charging. Stabilizes after a predetermined time. In this embodiment, the time when this stabilization is completed is determined by whether or not the change in the polarization related amount P is less than a predetermined value.

  Further, in this embodiment, a required number of charge current values are sampled at a predetermined interval from the time when the charge polarization state of a certain amount is stabilized, and the charge current characteristics are obtained from the obtained data. Further, a charging current integrated value (α = ∫I · dt) necessary to reach a predetermined SOC value (for example, 90%) from the present time is calculated from the obtained charging current characteristics. This makes it possible to accurately estimate the current SOC value and the integrated charge value necessary for reaching the predetermined SOC value from the present time, excluding the influence of variations in the polarization state. It is also useful for detection of overcharge prevention.

  The effect of this embodiment will be described more specifically.

  First, the characteristics of the battery will be described with reference to FIG. FIG. 3 shows the characteristics of the charging current when constant voltage charging is performed on a battery that is not fully charged. When constant voltage charging is started, in the initial stage of charging, there is not only current droop due to capacity increase but also current droop due to generation of charge polarization, and the effect of polarization generation is particularly noticeable in lead storage batteries and the like. Conventionally, when obtaining an approximate expression of a charging current under constant voltage charging, no consideration has been given to the influence of variations in polarization state during polarization generation.

  In this embodiment, the charging current characteristic (approximate expression) is determined based on the charging current sampling data obtained after a predetermined time when the influence of the variation in polarization state can be satisfactorily eliminated from the start of constant voltage charging. Based on this, the internal state of the battery is estimated. This eliminates the influence of variations in polarization state during polarization generation in the initial stage of constant voltage charging, and realizes accurate estimation of charging current characteristics under constant voltage charging.

(Experimental result)
FIG. 4 shows the experimental results of estimating the charging capacity by constant voltage charging in a vehicle lead-acid battery. FIG. 4 shows a case where the constant voltage charging is started, and the current value for 30 seconds is stored from the point that the differential value of the polarization related quantity (polarization index) obtained from the charging current value becomes 0 or less. The approximate expression I (t) = A * exp (B * t) was obtained. The accumulated capacity until the current value obtained by the approximate expression reaches the predetermined value 5A is 6.4 Ah, which is almost equal to the actually measured charge capacity 6.5 Ah, and it can be seen that the charge capacity can be estimated with high accuracy.

  In the same vehicle lead battery, the charging current characteristic (B) obtained in this embodiment, the charging current characteristic (A) obtained by a known technique not considering polarization, and the measured charging current characteristic (C) As shown in FIG. In this known technique, constant voltage charging is continued for a predetermined time T, and an approximate expression is obtained from the charging current and relative time during this period. In this case, it cannot be approximated more accurately than the actually measured current. On the other hand, in this embodiment, an approximate expression is obtained from the charging current and the relative time in the predetermined period Tp from the point of change ΔP <0 in the polarization index, and the measured charging current characteristic (C) is obtained. It was found that the approximation accuracy was greatly improved.

(Reduction of polarization before starting constant voltage charging)
The above formula (Pn = Pn-1 + In * dt-1 / τ * Pn-1 * dt) for calculating the current value of the polarization-related amount P that can be regarded as the polarization amount (charge polarization amount) of the in-vehicle secondary battery ) Requires determination of the previous value Pn-1 of the polarization-related quantity P. However, the current value Pn (= Pn-1 + In * dt-1 / τ * Pn-1 * dt) of the first polarization-related quantity P using the first and second current data or the differential value (Pn-Pn -1) / dt = In-1 / τ * Pn-1), the previous value Pn-1 of the polarization-related quantity has not yet been calculated. However, if the current charge / discharge current is a substantially constant predetermined value or very small, the previous value Pn−1 of the polarization-related amount can be regarded as a constant value or zero.

  Therefore, immediately after the engine is started, the discharge current integrated value of the battery consumed at the time of starting the engine can be regarded as almost constant, and until then, the polarization of the in-vehicle secondary battery is eliminated by leaving it for a long time. Can be considered. Therefore, it can be considered that a certain amount of discharge polarization occurs every time immediately after the on-vehicle secondary battery is discharged immediately after the engine is started, and this value can be a predetermined value examined in advance. Moreover, immediately after the engine is started, the in-vehicle secondary battery always discharges a predetermined amount from its fully charged state, and after that, if constant voltage charging is performed, at least a predetermined amount of charge current integrated value should be obtained. It is. This is an advantage of constant voltage charging immediately after the engine is started.

  In addition, the current value of the polarization amount (discharge polarization amount) can also be calculated using the above equation during discharge for starting the engine. The current value of the polarization-related amount at the start of constant voltage charging of the discharge polarization amount calculated in this way can be used. Therefore, the current value of the polarization related amount (discharge polarization amount) may be used as the previous value Pn−1 of the polarization related amount under constant voltage charging performed when the second charge current data is obtained.

  Next, when the vehicle is traveling, the SOC of the in-vehicle secondary battery takes various values. However, after the in-vehicle secondary battery is in a discharged state for a certain period due to an increase in load or a decrease in the amount of power generation, the in-vehicle secondary battery must be charged for replenishing the lowered SOC. Therefore, it is preferable to start the constant voltage charging after the discharge tendency for a predetermined period has continued.

  Moreover, if the above-mentioned discharge tendency for a predetermined period continues, a predetermined amount of discharge polarization occurs in the in-vehicle secondary battery. Therefore, it is preferable to start the constant voltage charging after the discharge tendency for a predetermined period has continued and after the charge / discharge current has maintained a small value for a predetermined period in order to eliminate the discharge polarization generated at this time.

  Also, if the charge / discharge current is small and the polarization can be considered to have been eliminated before the discharge tendency of the predetermined period continues, the polarization at the start of the discharge tendency of the predetermined period is set to 0. The amount of discharge polarization due to the discharge tendency for a predetermined period is obtained by the above formula (the sign is reversed), and this is the polarization related amount at the start of constant voltage charge, that is, at the time of the second charge current sampling after the start of constant voltage charge The previous value Pn−1 of the polarization related amount P may be used.

  Furthermore, the constant voltage charging is performed with an adjustment voltage value Vref + ΔV that is slightly higher than the adjustment voltage Vref of a normal generator. In this case, if the charge / discharge current is equal to or less than a predetermined value during a predetermined period immediately before the start of constant voltage charging while the vehicle is traveling, it can be considered that polarization has been eliminated. The previous value Pn−1 of the polarization-related amount P at the time of collection can be set to zero. In addition, when the constant voltage charging is performed at an adjustment voltage value Vref + ΔV that is slightly higher than the adjustment voltage Vref of a normal generator, it is advantageous that a charging current corresponding to the charging voltage difference ΔV always flows during constant voltage charging. .

(Modification)
In the above embodiment, the charging current characteristic in the constant voltage charging control is estimated using the approximate expression. However, the absolute value of the charging currents Icv1 to Icv31, the decrease dIcv of the charging current within a predetermined time (for example, 30 seconds), the integrated capacity, The relationship may be derived using a pre-stored table or equation.

1 is a block diagram illustrating a control device for an in-vehicle secondary battery according to Embodiment 1. FIG. 3 is a flowchart illustrating constant voltage charging control according to the first embodiment. It is a characteristic view which shows the typical example of the charging current characteristic at the time of constant voltage charge. It is a characteristic view which shows the characteristic of the charging current obtained by the constant voltage charge of this embodiment, a polarization index, and its differential value. It is a characteristic view which shows embodiment and the conventional charging current characteristic, and the measured charging current characteristic.

Explanation of symbols

101 Battery 102 On-vehicle generator (generator)
104 Current sensor 105 Storage battery state detection device (internal state detection circuit unit)
106 Buffer 107 Operation Processing Unit 109 Generator Control Device

Claims (6)

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 polarization-related amount P that is a parameter related to the polarization amount of the in-vehicle secondary battery after the start of the constant voltage charging based on at least a change in charging current data,
It is determined whether or not the rate of change of the obtained polarization related quantity P is less than a predetermined threshold
Charge current integration until the charge current value reaches a predetermined final value based on a plurality of the charge current data obtained in a predetermined time after determining that the rate of change of the polarization related amount P is less than the predetermined threshold value Find the 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. In the in-vehicle secondary battery internal state detection device according to claim 1,
The internal state detection circuit unit is
A device for detecting an internal state of a vehicle-mounted secondary battery that executes the determination of the internal state during a constant voltage charging period immediately after engine startup. In the in-vehicle secondary battery internal state detection device according to claim 1,
The internal state detection circuit unit is
A device for detecting an internal state of an in-vehicle secondary battery, wherein the internal state is determined during a constant voltage charging period during traveling of a vehicle in which a charging current of a predetermined value or more flows. In the in-vehicle secondary battery internal state detection device according to claim 1,
The internal state detection circuit unit is
A device for detecting an internal state of a vehicle-mounted secondary battery that performs the above steps during the constant voltage charging period that is performed after a period in which the charging / discharging current is equal to or less than a predetermined value during traveling of the vehicle. In the in-vehicle secondary battery internal state detection device according to claim 1,
The internal state detection circuit unit has a current value of polarization related amount P as Pn, a previous value as Pn−1, In as a current value of charging current, dt as a current detection interval during constant voltage charging, and τ as a predetermined time. A device for detecting an internal state of an in-vehicle secondary battery, wherein the polarization-related amount P is obtained from an expression of Pn = Pn-1 + In * dt-1 / τ * Pn-1 * dt when a constant value is used. In the in-vehicle secondary battery internal state detection device according to claim 1,
The internal state detection circuit unit has a predetermined rate of change of the polarization-related quantity P when I is a charging current, a and b are constants, t is an elapsed time from the start of constant voltage charging, and K is a predetermined proportional constant. An approximate expression (I = K + a * exp (b * t)) of the charging current I is derived based on a plurality of data of the charging current I obtained every predetermined time after determining that the threshold value is less than the threshold value, An internal state detection device for an in-vehicle secondary battery that obtains the charge current integrated value using the approximate expression.