JP7183577B2 - Battery capacity estimation device and battery capacity estimation method - Google Patents

Description

The present invention relates to a battery capacity estimation device and a battery capacity estimation method for estimating the capacity of a battery mounted on a hybrid electric vehicle (HEV) or the like.

A battery mounted in a hybrid electric vehicle or the like is repeatedly charged and discharged frequently. Along with this, deterioration such as a decrease in battery capacity progresses. Therefore, it is required to estimate the battery capacity with high accuracy for charge/discharge control of the battery, determination of necessity of battery replacement, and the like.

As a technology related to estimating battery capacity, a technology is known in which the capacitance is obtained by dividing the time integral value of the current value that flows during an arbitrary time interval by the amount of change in the terminal voltage during the time interval. (See Patent Document 1, for example).

In addition, a technology is known in which an SOC (State Of Charge) value is obtained based on the terminal voltage at the timing at which charge and discharge are switched, and the capacitance value is obtained by dividing the integrated value of the charge/discharge current by the difference between the successive SOC values. (See Patent Document 2, for example).

Also, in order to determine the function of the battery, there is known a technique of periodically detecting voltage changes and current changes and determining the dynamic internal resistance of the battery based on the ratio of the two (for example, Patent Document 3 reference.).

Also, there is known a technique of sampling an offset current value in a charging/discharging stopped state and estimating a detected current value based on the sampled value (see, for example, Patent Document 4).

Also, there is known a technique of obtaining an integrated value component of an offset error of a current sensor by integrating detected currents during successive full-charge times (see, for example, Patent Document 5).

JP 2014-81258 A WO2008/026477 Japanese Patent Publication No. 2004-527076 JP-A-2000-137062 Japanese Patent Application Laid-Open No. 2001-078365

However, even if the terminal voltage is obtained during an arbitrary time interval or at the timing at which charging and discharging are switched to obtain the battery capacity, etc., there are various cases where charging and discharging are frequently repeated, such as in a hybrid vehicle. However, it is difficult to suppress the influence of noise and errors, and it is difficult to obtain the battery capacity with high accuracy. Regarding this point, it has been difficult to greatly improve the estimation accuracy even by using the methods of detecting the dynamic internal resistance and the offset current as described in Patent Documents 3 to 5.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to enable estimation of battery capacity with high accuracy.

To achieve the above objectives,
The first invention is
A battery capacity estimation device for estimating the capacity of a battery,
a current sensor that detects the charge/discharge current of the battery;
a current integration unit that integrates the charge/discharge currents to obtain an integrated current value;
a voltage sensor that detects the terminal voltage of the battery;
an electromotive force calculation unit that calculates electromotive force of the battery based on the terminal voltage, the charge/discharge current, and an equivalent circuit model of the battery;
an SOC value generating unit that obtains an SOC value based on the electromotive force and a preset relationship between the electromotive force of the battery and the SOC value that is the state of charge of the battery;
The estimated capacity of the battery is obtained by dividing the current integrated value during the charging period or during the discharging period by ΔSOC, which is the difference between the SOC value at the start of the integration of the charging/discharging current and the SOC value at the end of the integration. a battery capacity estimator that obtains
characterized by comprising

As a result, the electromotive force of the battery is calculated based on the equivalent circuit model, and the SOC value and ΔSOC are obtained based on the electromotive force. Even if it is detected, it is possible to obtain a better estimate of the battery capacity.

The second invention is
A battery capacity estimation device of the first invention,
The start and end of integration of the charging/discharging current are performed immediately after switching between discharging and charging and immediately before switching to the next,
The calculation of the electromotive force is performed based on the terminal voltage of the battery detected immediately after the switching between discharging and charging and immediately before the next switching.

As a result, it is possible to easily improve the estimation accuracy of the capacity by increasing the integrated current value and the value of ΔSOC.

The third invention is
A battery capacity estimation device according to any one of the first invention and the second invention,
Furthermore, it is characterized by comprising an averaging processing unit for averaging the estimated values of the battery capacity.

As a result, it is possible to easily improve the estimation accuracy by reducing various errors caused by the influence of noise and the like.

The fourth invention is
A battery capacity estimation device of a third invention,
The averaging unit is characterized by using a Kalman filter with an observation matrix H(t)=1.

As a result, it is possible to easily perform an averaging process that avoids the overflow of arithmetic processing and quickly converges the estimated value of the capacity.

The fifth invention is
A battery capacity estimation device of a third invention,
The averaging processing unit estimates the battery capacity during charging and discharging such that the product of ΔSOC during charging and the current integration time during discharging is equal to the product of ΔSOC during discharging and the current integration time during charging. is configured to average

This makes it possible to easily suppress the influence of the offset current error.

According to the present invention, it is possible to estimate the battery capacity with high accuracy.

FIG. 2 is a circuit diagram showing a connection relationship between a battery or the like and a battery capacity estimating device; 4 is a graph showing an example of changes in charge/discharge current, inter-terminal voltage, and SOC; FIG. 3 is a circuit diagram showing an example of an equivalent circuit model of a battery; 7 is a graph showing an example of adjustment of current integration intervals; FIG. 4 is a block diagram showing an example of a battery capacity sequential averaging processing unit; 7 is a graph showing an example of results of sequential averaging of battery capacities; 7 is a graph showing an example of selection of a current integration section;

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

The battery 110 to be capacity-estimated in this embodiment is mounted in a vehicle such as an HEV. For example, as shown in FIG. It is connected to a power supply 160 and a voltage sensor 120 is connected to positive and negative electrode terminals. Battery capacity estimating device 210 is connected to voltage sensor 120 and current sensor 130, functions as a current integrating section, an electromotive force calculating section, an SOC value generating section, a battery capacity estimating section, and an averaging section, and performs the following: The capacity of the battery 110 is estimated as follows.

(Summary of battery capacity estimation)
First, charging and discharging are repeated in the battery 110, and charging and discharging current Isense and terminal voltage Vbat as shown in FIGS. 2A and 2B are detected. is integrated (integrated) to obtain an integrated current value.

On the other hand, the electromotive force of the battery is calculated based on the charging/discharging current Isense, the terminal voltage Vbat, and the equivalent circuit model of the battery. More specifically, as the equivalent circuit model, for example, as shown in FIG. is applied, and based on this, the electromotive force V0 at the start and end of the current integration is calculated. Further, based on a preset relationship between the electromotive force V0 of the battery and the SOC (State Of Charge) value, which is the state of charge of the battery, the SOC value is obtained, for example, as shown in FIG. ΔSOC, which is the difference between the SOC values at the start and end of the integration, is obtained.

Then, the current integrated value is divided by .DELTA.SOC as shown in (Equation 1) below to obtain an estimated value of the capacity of the battery.

As described above, the electromotive force of the battery is calculated based on the terminal voltage of the battery, the charging/discharging current, and the equivalent circuit model, and the SOC value and ΔSOC are obtained based on the electromotive force. Even if the terminal voltage is detected when the inside of the is not in a stable state, it is possible to obtain a more appropriate estimated value of the battery capacity.

(Regarding the start and end timing of current integration)
In principle, the capacity estimation value as described above can be obtained by starting and ending the current integration at any timing. Easy to keep small. In this regard, the numerator and denominator of (Formula 1) are maximized by setting the start and end time of current integration to the zero cross point of the current, that is, from the start time to the end time of charging and discharging at which the charging and discharging current becomes 0. It becomes easy to improve the estimation accuracy of the capacity by using In practice, when the current or voltage is detected discretely by sampling, it is preferable to set the timing immediately after the switching between charging and discharging and immediately before the next switching. The timing at which the current becomes 0 may be obtained by interpolating the current and voltage, and these may be set as the start and end timings of the current integration.

In addition, the timing at which the current becomes 0 is not limited, and the start and end timing of the current integration may be set so that the charging and discharging currents become equal. In this case, as shown in the following (Equation 2), it is possible to suppress the influence of the error of the resistor R0 set in the equivalent circuit model of the battery. In other words, even if the value of the resistor R0 contains an error due to deterioration of the battery, temperature change, etc., it is possible to avoid the influence of the error of the resistor R0. Note that, in (Equation 2), since the effect of the offset current error is the same at the start and end of the integration, the effect of the error of the resistor R0 due to the offset current error can be ignored, so the effect is omitted.

here,
SOCerr: SOC error Isens: charge/discharge current R0err: resistor R0 error EPerr: SOC error caused by resistor R1 and capacitor C1 ΔSOCerr: SOC difference error at the start and end of integration.

In practice, when currents and voltages are discretely detected by sampling, sampling is not always performed at such timings that charging and discharging currents are equal as described above. In such a case, as shown in FIG. 4 and Table 1 below, the charging/discharging current Isens, terminal voltage Vbat, electromotive force V0, or SOC value at one or both of the start and end of current integration are obtained by interpolation. You may do so. Moreover, the charge/discharge current at the time when the integration starts and ends may all become 0 by interpolation as described above.

(Regarding averaging of capacity estimates, etc.)
The capacitance estimated value obtained as described above contains various errors due to the influence of noise and the like. To reduce such errors, the resulting capacity estimates may be averaged. In particular, by averaging the estimated capacity values obtained during charging and discharging, it becomes easier to reduce the offset current error during current detection. In cases such as when arithmetic processing overflows when a plurality of capacitance values are simply totaled in order to average the estimated capacitance values, sequential averaging processing may be performed. For example, as shown in FIG. 5, by setting the observation matrix H(t)=1 in the Kalman filter, that is, by subtracting the feedback value directly from the value input to the Kalman gain, the averaging process can be easily performed. It can be carried out. By such averaging processing, for example, as shown in FIG. 6, the capacitance estimated value can be converged in a relatively short period of time.

When averaging the estimated capacity values, it is not necessary to use all the estimated capacity values obtained based on the measured values for the averaging calculation. Conceivable measured values and the like may be excluded from the calculation. In this regard, the same applies to the case where the capacity estimation value is selected as described below.

In addition, it is possible to improve the estimation accuracy by selectively using the averaged capacitance estimated value for calculation. For example, the product of ΔSOC during charging and the accumulated time is equal to the product of ΔSOC during discharging and the accumulated current time. As shown, the influence of the offset current error can be suppressed. Further, the average value of the estimated capacity values during charging and discharging is further averaged, or a plurality of sets of estimated capacity values having the relationship of charging and discharging time as described above are collectively averaged. may Also, in order to obtain an estimated capacity value that satisfies the charge/discharge time relationship as described above, the start/end timing of current integration may be adjusted.

here,
CAP _C , CAP _D : Estimated capacity values during charge and discharge _{IC_ref} , _{ID_ref} : Charge/discharge current without offset current error I _err : Offset current error (equal during charge/discharge)
ΔSOC_C, ΔSOC_D: ΔSOC during charging and discharging
is.

In addition, as shown in FIG. 7, the current for the charge section and the discharge section in which the sum of the multiple (one or more) charging current integration times and the sum of the multiple (one or more) discharge current integration times are equal Selectively use the integrated value, ΔSOC, etc. for calculation, and divide the sum of the absolute values of each integrated current value by the sum of the absolute values of each ΔSOC during charging and discharging to obtain an estimated capacity value. may As a result, the influence of the offset current error may be suppressed as shown in (Equation 4) below.

here,
CAP: estimated capacity I _{C_ref} , I _{D_ref} : charge/discharge current without offset current error I _err : offset current error (equal when charging/discharging)
ΔSOC_C, ΔSOC_D: ΔSOC during charging and discharging
is.

Note that the effect of improving the capacity estimation accuracy by performing the above-described averaging process, etc., is obtained when the electromotive force of the battery is calculated based on the terminal voltage of the battery, the charge/discharge current, and the equivalent circuit model. However, it is possible to obtain the SOC value directly based on the terminal voltage.

Also, the constituent elements described in the above examples may be combined in various ways as long as it is logically possible.

110 Battery 120 Voltage Sensor 130 Current Sensor 140 Switch 150 Load 160 Charging Power Supply 210 Battery Capacity Estimating Device

Claims (4)

A battery capacity estimation device for estimating the capacity of a battery,
a current sensor that detects the charge/discharge current of the battery;
a current integration unit that integrates the charge/discharge currents to obtain an integrated current value;
a voltage sensor that detects the terminal voltage of the battery;
an electromotive force calculation unit that calculates electromotive force of the battery based on the terminal voltage, the charge/discharge current, and an equivalent circuit model of the battery;
an SOC value generating unit that obtains an SOC value based on the electromotive force and a preset relationship between the electromotive force of the battery and the SOC value that is the state of charge of the battery;
The estimated capacity of the battery is obtained by dividing the current integrated value during the charging period or during the discharging period by ΔSOC, which is the difference between the SOC value at the start of the integration of the charging/discharging current and the SOC value at the end of the integration. a battery capacity estimator that obtains
an averaging unit that averages the estimated values of the battery capacity;
with
The averaging processing unit estimates the battery capacity during charging and discharging such that the product of ΔSOC during charging and the current integration time during discharging is equal to the product of ΔSOC during discharging and the current integration time during charging. A battery capacity estimating device characterized in that it is configured to average . The battery capacity estimation device according to claim 1,
The start and end of integration of the charging/discharging current are performed immediately after switching between discharging and charging and immediately before switching to the next,
The battery capacity estimating apparatus, wherein the calculation of the electromotive force is performed based on the terminal voltage of the battery detected immediately after switching between discharging and charging and immediately before switching to the next switching. The battery capacity estimating device according to any one of claims 1 and 2 ,
The battery capacity estimating device, wherein the averaging unit is configured using a Kalman filter with an observation matrix H(t)=1. A battery capacity estimation method for estimating the capacity of a battery, comprising:
current integration processing for obtaining an integrated current value by integrating charging/discharging currents of the battery detected by the current sensor;
electromotive force calculation processing for calculating the electromotive force of the battery based on the terminal voltage of the battery detected by the voltage sensor, the charge/discharge current, and an equivalent circuit model of the battery;
SOC value generation processing for obtaining an SOC value based on the electromotive force and a preset relationship between the electromotive force of the battery and the SOC value, which is the state of charge of the battery;
The estimated capacity of the battery is obtained by dividing the current integrated value during the charging period or during the discharging period by ΔSOC, which is the difference between the SOC value at the start of the integration of the charging/discharging current and the SOC value at the end of the integration. and a battery capacity estimate that finds
and an averaging process for averaging the estimated values of the battery capacity,
In the averaging process, the estimated value of the battery capacity during charging and discharging is calculated so that the product of ΔSOC during charging and the accumulated current time during discharging is equal to the product of ΔSOC during discharging and the accumulated current time during charging. A battery capacity estimation method characterized by averaging .

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