JP3817126B2 - Battery capacity calculation device considering the effect of polarization - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle battery capacity calculation device that takes into account the influence of polarization, which accurately estimates the current state of charge of the battery in consideration of polarization errors.
[0002]
[Prior art]
A battery controller such as an electric vehicle collects and averages a predetermined number of discharge currents and battery voltages from a battery at regular intervals. When a predetermined number of averaged data are collected, a correlation coefficient r of the data is collected. Ask for. Next, when the correlation coefficient r indicates a strong negative correlation, a regression line (also referred to as an approximate line) of the data is obtained by the least square method as shown in FIG. Y = aX + b) and an estimated voltage Vn, which is an estimated open circuit voltage of the current battery, was estimated from the reference current Io.
[0003]
That is, in an electric vehicle, voltage and current are collected while running and an approximate straight line (VI characteristic) is obtained to estimate how much discharge (running) can be performed. Such a method is very effective in an electric vehicle.
[0004]
[Problems to be solved by the invention]
However, the dischargeable capacity of the battery (indicating how much can be discharged if the discharge state at a certain moment continues as it is) varies depending on the temperature and the discharge current (load).
[0005]
Even if it changes in this way, in an electric vehicle, the amount of electricity charged in the battery during traveling does not exceed the amount of electricity discharged, and therefore, an approximate straight line (V-I) is collected by collecting voltage and current. It is not so much a problem to obtain the characteristic) and estimate how much discharge (running) can be performed.
[0006]
However, in recent years, high voltage vehicles, hybrid cars, and the like have been used. In such a vehicle, the amount of electricity charged to the battery while traveling can exceed the amount of electricity discharged, so now only know how much electricity (charged state) is left in the battery. In order to prevent overcharging of the battery, it is necessary to accurately know the chargeable capacity obtained by subtracting the remaining capacity from the full charge capacity.
[0007]
To accurately know the state of charge, it is necessary to know the influence of polarization due to battery characteristics. This polarization is a voltage drop that occurs due to an activation phenomenon or concentration change in the vicinity of the battery electrode. When the discharge current increases, the amount of voltage drop increases. Conversely, when the discharge current decreases, the voltage drop increases. Decreases in the direction of elimination.
[0008]
That is, the state of charge (which indicates how much electricity is charged) must take into account the effect of polarization. That is, an accurate charge state cannot be obtained unless the voltage drop due to polarization is offset.
[0009]
That is, when the battery voltage and current are measured from when the battery is in a neutral state (a state where no voltage drop due to polarization remains), the discharge current increases as shown in FIG. The polarization increases and the battery voltage decreases accordingly. In addition, when the discharge current decreases, the polarization decreases and the battery voltage also returns accordingly, but at this return, it takes time to cancel the polarization, so the polarization is canceled at the same time even if the discharge stops. However, compared with the response of the increase in the voltage drop with respect to the increase in current, the response of the decrease in the voltage drop with respect to the decrease in current is poor. For this reason, as shown in FIG. 6, there is a difference in voltage value at that time even when the current value is the same between going (when the current is increasing) and returning (when the current is decreasing).
[0010]
Accordingly, a predetermined number of discharge currents and battery voltages from the battery are collected and averaged every predetermined time, and when a predetermined number of the averaged data is collected, a correlation coefficient r of the data is obtained and this phase is obtained. When the relational number r shows a strong negative correlation, the discharge current is reduced compared with the case where the discharge current from the battery is increased even if the approximate straight line is obtained by the least square method. Since the approximate straight line to be obtained differs from that sometimes collected, it cannot be said that the approximate straight line correctly shows the VI characteristics of the current battery, and it is impossible to obtain a highly accurate charge state. was there.
[0011]
Moreover, the fact that the battery voltage is reduced due to polarization has a problem that it is determined that the battery voltage is reduced despite the fact that the amount of electricity is actually enough to enable traveling. It was.
[0012]
The present invention has been made to solve the above-described problems, and can obtain an accurate charged state (how much electricity is charged) by obtaining an accurate approximate straight line in consideration of the polarization of the battery. An object of the present invention is to obtain a battery capacity calculation device in consideration of polarization characteristics.
[0013]
[Means for Solving the Problems]
According to the present invention, a discharge current is supplied from a battery to a vehicle load to collect voltage and current to obtain a voltage-current characteristic, and a current estimated voltage of the battery is estimated using the voltage-current characteristic. In the battery capacity calculation device that determines the current state of charge of the battery from the voltage, the battery voltage and current are monitored after the vehicle starts running, and the current first reaches a large current that maximizes the polarization of the battery. And when the current first reaches a predetermined current value that is less than or equal to the large current, the battery voltage at this time is assumed to be the estimated voltage when the maximum polarization effect remains in the state where the maximum polarization effect remains, The gist is that the state of charge is corrected using the difference between the estimated voltage when the maximum polarization effect remains and the open circuit voltage of the battery at the start of traveling.
[0014]
In addition, when the ignition on of the vehicle is detected, an open circuit voltage holding unit that holds the battery voltage at the time of detection as an open circuit voltage of the battery, and after the ignition is detected, the battery current has the maximum polarization. A current monitoring unit that determines whether or not a large current has been reached first, and an estimation of when the maximum polarization effect remains when the current first reaches a predetermined current value after it is determined that the large current has been reached first A polarization-influenced voltage calculator that calculates the difference between the voltage and the open circuit voltage of the battery at the start of traveling, and an estimated value corrector that adds this differential voltage to the current estimated voltage of the battery based on the voltage-current characteristics Is the gist.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration diagram of a battery capacity calculation apparatus considering the polarization characteristics of the present invention.
[0016]
A battery capacity calculation device 1 shown in FIG. 1 includes a motor generator 5 connected to an engine 2 and a shaft mechanism 4 of a tire 3, and a battery 6 as a charging current by setting the electric power from the motor generator 5 to a predetermined voltage (for example, 42 V). Or a hybrid mechanism 8 including a charging / discharging circuit unit 7 for supplying predetermined power from the battery 6 to the motor generator 5, and calculating a charging state of the battery 6.
[0017]
The battery 6 is provided with a current sensor 9 and a voltage sensor 10 as shown in FIG.
[0018]
The battery capacity computing device 1 is connected to an input circuit unit 12 that shapes the detected current I and the detected voltage V from the current sensor 9 and the voltage sensor 10, and has at least the following program configuration.
[0019]
As shown in FIG. 1, the battery capacity calculation device (microcomputer) 1 includes an IV characteristic calculation unit 13, a voltage estimation unit 14, a charge state estimation unit 15, an open circuit voltage holding unit 18, and a current monitoring unit. 19, a polarization influence voltage calculation unit 20, and an estimated value correction unit 21.
[0020]
The IV characteristic calculation unit 13 collects the detected current (discharge) and voltage from the input circuit unit 12 on the current-voltage axis at regular intervals.
[0021]
The voltage estimator 14 averages each time a predetermined number of currents I and voltages V collected by the IV characteristic calculator 13 are collected, and when a predetermined number of the averaged data is collected, the correlation of the data When the number r is obtained and the correlation coefficient r indicates a strong negative correlation, a regression line (also referred to as an approximate line) of the data is obtained by the least square method, and this approximate line Y (Y = aX + b) And the current estimated voltage Vn of the battery 6 are estimated from the reference current Io.
[0022]
Each time the estimated voltage Vn is obtained, the charge state estimation unit 15 reads the estimated voltage Vn of the battery 6, the preset discharge end voltage Ve, and the full charge voltage Vs, and obtains the charge state SOC.
[0023]
The open circuit voltage holding unit 18 stores the voltage V when the ignition is turned on in the memory as the open circuit voltage OCV.
[0024]
The current monitoring unit 19 reads the current of the battery 6 in the IV characteristic calculation unit 13 from the start of a cell motor (not shown) used for starting the engine 2 when the ignition is turned on, and this current is stored in advance. It is determined whether or not a large current Imax (for example, 250 A) at which the generation of polarization associated with the start of the cell motor is maximized is reached first, and when the large current Imax is reached, it returns from this reaching point (the current decreases) It is determined whether or not the current I at the first time has reached a small current Imin (for example, 35 A) stored in advance.
[0025]
Here, as shown in FIG. 2, when the cell motor starts to start from the start / stop state of the motor generator 5 (no load, the battery is in a neutral state), the IV characteristic is the open circuit voltage OCV. Is gradually decreased linearly as a result of the influence of polarization as the discharge current increases.
[0026]
Thereafter, the current value of the IV characteristic becomes maximum (maximum current; for example, 250 A), the polarization becomes maximum, and the voltage value of the IV characteristic becomes maximum. Then, when the increase in the discharge current stops (in the case of discharge in which the capacity hardly changes) and the discharge current decreases, the voltage gradually returns (returns) linearly while leaving the influence of the maximum polarization.
[0027]
At the time of this return, the response of elimination of polarization or elimination of voltage drop due thereto is poor. For example, the voltage drop due to the influence of polarization is considerably eliminated until the discharge is stopped when the discharge current starts to decrease, but it takes about one day to eliminate 100% of the voltage drop due to the influence of polarization. Has been.
[0028]
In the present embodiment, the reference for ending the collection of the current I and the voltage V by the IV characteristic calculation unit 13 started when the discharge current is decreased from a predetermined large current is about 35 A in light of practical specifications. It is said.
[0029]
On the other hand, as shown in FIG. 3, the IV characteristic in a state where polarization is occurring has already occurred in the voltage drop due to polarization, and then the polarization increases as the discharge current increases. The current gradually decreases linearly, and when the polarization becomes maximum, the current becomes maximum. Here, the increase in the discharge current is stopped, and the voltage is linearly restored.
[0030]
Even in this case, the voltage drop due to the influence of polarization is substantially eliminated until the discharge is stopped when the discharge current starts to decrease. It is said that it will take some degree.
[0031]
Therefore, even when discharge is performed in a state where polarization is occurring, in the present embodiment, the current I and IV by the IV characteristic calculation unit 13 started when the discharge current is decreased from a predetermined large current. The reference for terminating the collection of the voltage V is about 35 A in light of practical specifications.
[0032]
The polarization influence voltage calculation unit 20 starts when the discharge current from the battery 6 determined by the current monitoring unit 19 first reaches the large current Imax and when the discharge current first decreases to 35 A due to the stop of the increase in discharge. The estimated voltage Vn of the battery 6 estimated by the voltage estimation unit 14 based on the collection result of the current I and the voltage V by the IV characteristic calculation unit 13 and the open circuit voltage holding unit 18 A difference voltage from the open circuit voltage OCV is obtained as a voltage eo indicating a residual voltage drop due to polarization when the discharge is stopped.
[0033]
The estimated value correcting unit 21 reads the voltage eo obtained by the polarization affecting voltage calculating unit 20 after the polarization affecting voltage calculating unit 20 obtains the voltage eo, and supplies the voltage eo to the estimated voltage Vn obtained by the voltage estimating unit 14. Is added.
[0034]
That is, the estimated voltage Vn is updated to an added value of Vn and eo. The effect of this addition will be described later in detail with reference to FIG.
[0035]
Each time the voltage estimation unit 14 estimates the current voltage of the battery 10, the charge state estimation unit 15 obtains the charge state SOC using the equation shown in Equation 1.
[0036]
[Expression 1]
SOC = [(Vn ² −Ve ² ) / (Vs ² −Ve ² )] × 100%
Where Vn: estimated battery voltage (Vn and eo)
Ve; End-of-discharge voltage Vs; Full-charge voltage Next, the operational effects of the processing of the estimated value correction unit 21 will be described with reference to FIG. For example, if the current estimated voltage Vn obtained using an approximate line as shown in FIG. 4 is the Ai point of the change line of Vn, the current actual discharge state is obtained by adding eo, which is a voltage difference due to polarization. Is located at Ap of the characteristic that the battery 10 is in a neutral state.
[0037]
That is, since the actual estimated voltage is a voltage Ap higher than Ai, the voltage drop accompanying the occurrence of polarization is taken into consideration.
[0038]
For this reason, since the actual charge state of the battery 10 is obtained, overcharge can be prevented.
[0039]
【The invention's effect】
As described above, according to the present invention, the voltage and current of the battery that flows the discharge current to the vehicle load are collected to obtain the voltage-current characteristic, and the current estimated voltage of the battery is estimated using this voltage-current characteristic. The current state of charge of the battery is determined from the estimated voltage, while the collected current first reaches the large current at which the battery has the maximum polarization, and after that, the current first reaches a predetermined current value that is less than or equal to the large current. The battery voltage at this time is assumed to be the estimated voltage when the maximum polarization effect remains with the maximum polarization effect remaining, and the estimated voltage when the maximum polarization effect remains and the open circuit of the battery at the start of traveling The state of charge is corrected using the difference from the voltage.
[0040]
For this reason, the estimated state of charge increases by the amount of residual voltage drop due to polarization, so that the actual state of charge can be obtained accurately.
[0041]
Therefore, it is not determined that the voltage of the battery has dropped despite the fact that the amount of electricity is enough to actually travel, so that the charging state can be accurately obtained even in hybrid cars and high voltage vehicles. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a battery capacity calculation device according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining current values determined to return to a neutral state according to the present embodiment;
FIG. 3 is an explanatory diagram illustrating a current value that is determined to return from the occurrence of polarization according to the present embodiment.
FIG. 4 is an explanatory box for explaining the effect of addition of the difference voltage according to the present embodiment.
FIG. 5 is an explanatory diagram illustrating collection of battery voltage and current.
FIG. 6 is an explanatory diagram illustrating a problem.
[Explanation of symbols]
2 Engine 3 Tire 5 Motor generator 8 Hybrid mechanism 13 IV characteristic calculation unit 14 Voltage estimation unit 15 Charging state estimation unit 18 Open circuit voltage holding unit 19 Current monitoring unit 20 Polarization influence voltage calculation unit 21 Estimated value correction unit

Claims (2)

A discharge current is supplied from a battery to a vehicle load to collect voltage and current to obtain a voltage-current characteristic, and the current estimated voltage of the battery is estimated using the voltage-current characteristic, and the battery is estimated from the estimated voltage. In the battery capacity calculation device for determining the current charging state of
The battery voltage and current are monitored thereafter from the start of travel of the vehicle, and the current first reaches a large current that maximizes the polarization of the battery,
And when the current first reaches a predetermined current value equal to or less than the large current after the arrival, the voltage of the battery at this time is set as the estimated voltage when the maximum polarization influence remains in the state where the influence of the maximum polarization remains. ,
A battery capacity calculation device considering the influence of polarization, wherein the charged state is corrected using a difference between the estimated voltage when the maximum polarization influence remains and the open circuit voltage of the battery at the start of traveling. An open circuit voltage holding unit for holding the voltage of the battery at the time of detection as an open circuit voltage of the battery when the ignition on of the vehicle is detected;
A current monitoring unit that determines whether or not the current of the battery first reaches a large current at which the polarization is maximized after detection of the ignition on;
After it is determined that the large current has been reached first, when the current first reaches the predetermined current value, the estimated voltage when the maximum polarization effect remains and the open circuit voltage of the battery at the start of traveling A polarization influence voltage calculation unit for obtaining a difference;
2. The battery capacity calculation device considering the influence of polarization according to claim 1, further comprising an estimated value correction unit that adds the difference voltage to a current estimated voltage of the battery based on the voltage-current characteristics.

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