JP3376804B2 - Calculation device for maximum charge / discharge power of batteries - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maximum power dischargeable and chargeable power calculator for a battery.

[0002]

2. Description of the Related Art In general, a battery has a characteristic that, when discharged at a constant current, the voltage decreases with the lapse of time of the discharge reaction. FIG. 14 is a diagram showing changes in the terminal voltage V of the battery when discharged with a constant current. When the constant current I1 is discharged in the period from time t1 to t3, the terminal voltage V changes as shown in the figure. At the discharge start time t1, the terminal voltage V instantly drops from V0 to V1 at 0.1 mS or less.
This transient voltage VX is a voltage drop due to the liquid resistance and contact resistance of the battery. Next, a period T from time t1 to t2
At 1, the terminal voltage V drops sharply from V1 to V2. This decrease time is 100 mS or less, and the transient voltage V
Y is the voltage drop due to the charge transfer resistance of the battery. Further, in the period T2 from time t2 to time t3, the terminal voltage V gradually decreases from V2 to V3. This transient voltage VZ is a voltage drop due to concentration polarization of the electrolytic solution, and this region is generally called a diffusion region. After that, when the discharge stop time t3 has passed, the terminal voltage V recovers rapidly. Period T
1 and T3 are transient states that change in a short time, and the period T2
Is the normal use condition of the battery.

[0003]

As described above, the terminal voltage of the battery changes according to the discharge current, and also changes with the lapse of time of the discharge reaction. Therefore, when the maximum discharge power of the battery is calculated based on such a terminal voltage, an error may occur, and in some cases, the terminal voltage at the time of discharging may fall below the discharge end voltage of the battery. In addition,
The end-of-discharge voltage is the minimum allowable voltage of the battery, which is considered to accelerate the deterioration when the discharge is further continued.

An object of the present invention is to accurately calculate the maximum discharge power and the maximum charge power of a battery.

[0005]

(1) The invention of claim 1 is based on a voltage measuring means for measuring a terminal voltage of a battery, a current measuring means for measuring a current flowing through the battery, and a current measured value. Discharge start detection means for detecting the start time of the discharge reaction of the battery, and during the increase of the discharge current after the battery shifts to a stable diffusion state from the start time of the discharge reaction.
At a plurality of time points , sampling means for sampling the terminal voltage and discharge current of the battery by the voltage measuring means and the current measuring means, and the terminal voltage and discharge current of the battery sampled by the sampling means The voltage-current characteristics are linearly regressed, and an arithmetic means for arithmetically operating the maximum discharge power and the maximum charge power of the battery based on the regression line. (2) In the battery charging / discharging power calculation device according to the second aspect, the discharge start detection unit sets the discharge current measurement value and the rate of change thereof to be positive as the start time of the discharge reaction. It was done. (3) According to another aspect of the present invention, in the calculating device for the maximum charge / discharge power of the battery, the calculating means divides the range of the discharge current into a plurality of regions, and obtains the latest terminal voltage and the discharge current for each divided current region. A predetermined number of cells are stored, and the voltage-current characteristics of the battery are linearly regressed based on the stored terminal voltage and discharge current. (4) The maximum charging / discharging power calculation device for a battery according to claim 4, wherein the calculating means linearly determines the voltage-current characteristics of the battery based on at least three or more terminal voltages in the divided current region and the discharge current. It is designed to return.

[0006]

According to the invention of claim 1 and claim 2 as described above, according to the present invention, it is possible to obtain an average maximum charge-discharge electric power to the discharge time and the discharge current are different various discharge forms. In addition , the measurement of the terminal voltage and discharge current during the transient period when the discharge reaction of the battery is unstable can be avoided, and the terminal voltage and discharge current in the stable diffusion region can be measured. The maximum charge / discharge power can be calculated. According to the invention of claim 3, the voltage based on the measurement results of focus on the divided current region of JP <br/> constant - the linear regression of the current characteristic is avoided, based on the measurement result of the wide range of terminal voltage and the discharge current And an accurate regression line is obtained,
More accurate maximum charge / discharge power can be calculated. According to the invention of claim 4, it is possible to improve the straight-line regression accuracy.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to an electric vehicle will be described. Note that the present invention is not limited to application to electric vehicles, and the present invention can be applied to any device that charges and discharges a battery.

FIG. 1 is a block diagram showing the configuration of one embodiment. The battery 11 supplies DC power to the inverter 12, and the inverter 12 converts the DC power into AC power to generate running energy. During regeneration, the running energy of the vehicle is converted back into electric energy via the motor 13 and the inverter 12, the battery 11 is charged, and the vehicle is regeneratively braked. Voltage sensor 1
4 detects the voltage V across the battery 11, and the current sensor 15
Detects the current I flowing through the battery 11. The current I
Indicates that the direction from the battery 11 to the inverter 12 is positive when the motor is driven, and the direction from the inverter 12 to the battery 11 is negative during the regenerative charging. The controller 16 calculates the maximum discharge power and the maximum charge power of the battery 11 based on the voltage V and the current I detected by the voltage sensor 14 and the current sensor 15, and controls the output of the inverter 12 based on the calculation result. Performs regeneration control, etc.

Here, the characteristics of the battery will be described. Certain types of batteries, such as lithium-ion batteries and nickel-hydrogen batteries, have the following characteristics. (1) As shown in FIG. 2, the depth of discharge of the battery (hereinafter, D
OD (Depth of Discharge) is low (~ 60)
%), The internal resistances during charging and discharging are almost the same. (2) The linearity of the voltage V-current I characteristic during charge / discharge is good. By utilizing such characteristics of the battery of this type, it is possible to accurately calculate the maximum discharge power and the maximum charge power according to the state of the battery such as DOD and temperature. The battery is not limited to a lithium ion battery or a nickel hydrogen battery,
Any battery having the above characteristics may be used.

Next, a method of calculating the maximum discharge power and the maximum charge power of the battery will be described. First, the V-I characteristic of the battery being discharged is sampled, and as shown in FIG. 3, the sampling result is plotted on a V-I graph (indicated by X in the figure). As described above, in this type of battery, since the internal resistances during charging and discharging are almost the same and the VI characteristic has a good linearity, the VI characteristic of the sampling result can be linearly regressed, and further regressed. The straight line can be extended to the charge side and the discharge side. In the figure, the V-axis intercept Eo of the regression line
Represents the open circuit voltage of the battery, and the slope of the regression line represents the internal resistance R of the battery. The regression line is

[Equation 1] V = Eo-IR Can be expressed as

The current ICmax at the intersection A between the regression line and the maximum allowable voltage Vmax during charging gives a charge allowable value, and at the intersection A, the following equation is established.

## EQU00002 ## Vmax = Eo-ICmax.R Similarly, the current IDmax at the intersection B between the regression line and the discharge end voltage Vmin at the time of discharge gives a discharge allowable value, and at the intersection B, the following equation is established.

[Equation 3] Vmin = Eo-IDmax · R

The maximum charging power PC can be calculated by the above equation 2

[Equation 4] PC = Vmax ・ ICmax = Vmax ・ (Eo-Vmax) / R The maximum discharge power PD is

## EQU00005 ## PD = Vmin.IDmax = Vmin. (Eo-Vmin) / R. The sampling value of the VI characteristic during discharging is a value according to the battery state such as the DOD and temperature of the battery, and the maximum charging power PC and the maximum discharging power PD obtained by linear regression of such sampling values. Is, of course, electric power according to the state of the battery such as DOD and temperature. Note that FIG.
As shown in, when the DOD exceeds 60%, the difference between the internal resistance R at the time of discharging and the internal resistance R at the time of charging becomes large, and the calculated maximum charging power PC includes a large error. But,
When the DOD exceeds 60%, the true maximum charging power of the battery is sufficiently larger than the maximum power regenerated from the inverter 12, so that there is no problem even if the calculated value PC of the maximum charging power has a large error.

By the way, the discharge end voltage Vmin of a battery mounted on an electric vehicle is usually

[Formula 6] Vmin ≧ Eo / 2. On the other hand, in general, the maximum output P of a battery, that is, the maximum discharge power P is

## EQU7 ## It is known that V = Eo / 2 is obtained. Therefore, the discharge end voltage Vmin of the electric vehicle battery is

## EQU00008 ## When set in the range of Vmin> Eo / 2, the maximum discharge power PD calculated by the above-mentioned method is the maximum discharge power P of the general battery described above.
Will be smaller than. In this specification, the discharge end voltage Vmi
Set n within the range of Equation 6, and set the discharge end voltage Vm
The discharge power calculated for in is the maximum discharge power of the battery.

Next, a method of sampling the V-I characteristic of the battery will be described. The relationship between the voltage V and the current I of the battery is expressed by the above mathematical expression 1. However, as described above, the terminal voltage V of the battery changes over time of the discharge reaction,
Even if the voltage is sampled at the same discharge current, the same voltage cannot be obtained if the reaction steps are different. Conversely, even if the current is sampled at the same voltage, the same current cannot be obtained if the reaction steps are different. That is, since the terminal voltage V and the discharge current I change depending on the stage of the chemical reaction of the battery itself, in order to accurately estimate the capacity of the battery every moment,
It is necessary to sample the VI characteristic in consideration of the reaction stage of the battery.

FIG. 4 shows a terminal voltage V and a discharge current I during discharging.
5 is a diagram illustrating the sampling timing of FIG. Generally, a battery has a property that a change in voltage is delayed with respect to a change in current when the discharge current decreases. Therefore, when sampling the terminal voltage V and the discharge current I, a transient phenomenon between different reaction modes such as discharge reaction to charge reaction, discharge reaction to discharge stop, or equilibrium state to discharge reaction or charge reaction and discharge current decrease. In order to exclude the time, the rise of the discharge current is detected, and the terminal voltage V and the discharge current I when the discharge current increases are sampled. In addition, the transient region (the period T1 in which the transient voltages VX and VY in FIG. 14 are generated)
In order to avoid the unstable sampling of the terminal voltage V and the discharge current I at, the terminal voltage V and the discharge current I are sampled after a predetermined time from the rise of the discharge current.

Here, the discharge current rises when the current I and its rate of change dI / dt are both positive. The rising point of this discharge current is the starting point of the discharge reaction of the battery. In the example of FIG. 4, t1, t3, t5 are the rising points of the discharge current, and the terminal voltages V1, V2, V3 and the discharge current I1, respectively, at the points of t2, t4, t6 after a predetermined time Δt from those points. Sample I2 and I3. This avoids measurement in an unstable transient region where the state of the battery changes abruptly, and the terminal voltage and discharge current of the battery in a stable diffusion region can be measured. When sampling the V-I characteristic, if there is a new rise of the discharge current within a predetermined time from the rise of the discharge current, timing is restarted from that point, and after a predetermined time, the terminal voltage V and the discharge current are increased. I
To sample.

By the way, if the sampling timing of the VI characteristic is set to only one point after a predetermined time from the rise of the discharge current, the following problems occur. FIG. 5 shows how the discharge current I and the terminal voltage V are sampled after a predetermined time Δt from the rise of the discharge current. In addition, FIG.
Is a plot of the sampling results on a VI graph and linear regression. The maximum discharge power PD of this battery is
It is obtained by the above-mentioned formula 5. The calculated maximum discharge power PD is obtained based on the sampling result after the predetermined time Δt from the rising of the discharge current, and is therefore the maximum power that can be discharged for the predetermined time Δt. However, when the discharge is performed with the maximum discharge power PD for more than Δt time, the characteristics of the battery deteriorate as shown by the straight line C in FIG. 6, and the discharge end voltage Vmin drops to Vmin ′ along the equal output line. .

That is, since the dischargeable power of the battery differs depending on the reaction stage, it is necessary to sample the VI data according to the required discharge time. Therefore, after the discharge current rises, the VI characteristic is sampled at a plurality of times. FIG. 7 shows how the discharge current I and the terminal voltage V are sampled after a predetermined time Δt1 and Δt2 from the rising of the discharge current. Also, FIG.
Is a plot of the sampling results on a VI graph and linear regression. In FIG. 8, the straight line D is a regression line based on the sampling data (x mark) after the predetermined time Δt1 from the rising of the discharge current, and the straight line E is the sampling data (◯ mark) after the predetermined time Δt2 from the rising of the discharge current. It is a regression line based on this. The straight line F is
It is a regression line based on sampling data (both × and ◯) after a predetermined time Δt1 and Δt2 from the rising of the discharge current. If the maximum discharge power PD is obtained from this regression line F, it is possible to obtain the average maximum power for various discharge forms with different discharge currents and discharge times.

FIG. 9 shows an example in which the VI characteristic is sampled at a plurality of points in a normal driving pattern of an electric vehicle. In this example, sampling is performed 1 second and 3 seconds after the rise of the discharge current. Further, FIG. 10 is a graph obtained by plotting the sampling results on a VI graph and performing linear regression. In FIG. 10, a straight line G is a regression line based on sampling data (x mark) one second after the rise of the discharge current, and a straight line H is regression based on sampling data (circle mark) three seconds after the rise of the discharge current. It is a straight line. The straight line J is a regression line based on the sampling data (both x and ◯) 1 second and 3 seconds after the rise of the discharge current.

FIG. 11 shows the sampling data shown in FIGS. 9 and 10 classified by sampling timing Δt and discharge current I. 5 after 1 second sampling
3 pieces of data were collected and 3 pieces of data were collected in the sampling after 3 seconds. However, as shown in FIG.
The sampling data after 1 second where Δt is small is likely to concentrate in the low current region, and therefore the accuracy of the regression calculation based on these data is low. On the other hand, although the sampling data after 3 seconds in which Δt is large is distributed in a wide current range, the number of data tends to be small, and the regression calculation accuracy is also low. However, the sampling data at a plurality of points after the rise of the discharge current, that is, after 1 second and 3 seconds, naturally has a large number of data, and since the current I and the voltage V are distributed in a wide range, the regression calculation accuracy is high. Become. Therefore, by calculating the maximum discharge power PD from the regression line J based on these data, it is possible to obtain the ideal average maximum power for various discharge forms with different discharge currents and discharge times. Further, if the accuracy of the regression calculation is improved based on the sampling data at a plurality of time points, the calculated regression line can be extended to the charging side to obtain the accurate maximum charging power PC, as shown in FIG.

In the sampling examples shown in FIGS. 7 to 10, the sampling is performed at two points after the discharge current rises, but the sampling timing may be three or more. Further, when sampling the V-I characteristic, if there is a new rise of the discharge current within a predetermined time from the rise of the discharge current, timing is restarted from that time point, and after a predetermined time, the terminal voltage V and the discharge current are increased. Sample I.

The data sampled at a plurality of timings described above are stocked by the following method. The range of the discharge current I is divided into a plurality of areas, and a predetermined number of stock memories are prepared for each area. For example, as shown in FIG.
The range of discharge current is divided into 5 areas, 3 for each area.
Prepare stock memory individually. Then, during a predetermined sampling time, the current in and the voltage vn (n indicates the sampling order) are sampled at the above-described timing, and are classified and stocked for each current region. When the number of data in the current region reaches a predetermined number, the oldest data is erased and the latest data is stocked. For example, in FIG.
In the above example, if the data of (i8, v8) is sampled and the data is included in the I2 to I3 area, the oldest data (i3, v3) in the area is erased and the latest data ( i8, v8) is memorized. According to this sampling data stocking method, since only a predetermined number of data sufficient for linear regression is stocked for each divided current region, a straight line of the VI characteristic based on the sampling data concentrated in a specific divided current region is stocked. Avoiding regression
Accurate linear regression is possible based on a wide range of sampling data of terminal voltage and discharge current, and accurate maximum charge / discharge power PD, PC can be estimated. Also, because a predetermined number of sampling data is stocked for each divided current area,
Accurate linear regression can be performed using sampling data in a wide range within the discharge current range, accurate maximum charge / discharge powers PD and PC can be estimated, and it is not necessary to secure a huge memory capacity in the controller. .

The V-I characteristic is sampled within a predetermined time or at a predetermined discharge electricity amount, and the maximum discharge power PD and the maximum charge power PC are calculated based on the data stocked by the above method. Maximum discharge power PD and maximum charge power PC
When the calculation of is finished, all the sampling data stored in the memory are erased, and the data is stored again at the next sampling time. Thereby, the terminal voltage V and the discharge current I in the latest state of the battery can be sampled, and the accurate maximum discharge power PD and maximum charge power PC can be calculated based on the sampling data in the latest battery state.

FIG. 13 is a flowchart showing the processing of the controller 16. The operation of this embodiment will be described with reference to this flowchart. The controller 16 repeatedly executes this processing while the electric vehicle is in operation. In step 1, the voltage V is increased at several points when the discharge current is increased.
And the current I are sampled, and the sampling data is stocked by the method described above. This sampling is performed within a predetermined time or every predetermined amount of discharged electricity. After the sampling is completed, in step 2, it is checked whether or not sampling data is stocked in three or more divided current regions in order to prevent regression calculation in a narrow current range and improve calculation accuracy. If data is stocked in three or more areas, the process proceeds to step 3 and the VI characteristic is linearly regressed by the stock data. On the other hand, when the sampling data is not stocked in the three or more divided current regions in step 2, the maximum charge / discharge powers PD and PC are not calculated. In step 4, the current IDmax at the discharge end voltage Vmin is obtained from the regression line, the maximum discharge power PD is calculated by the above equation 5, and the current ICmax at the allowable maximum voltage Vmax is obtained.
The maximum charging power PC is calculated by Continued Step 5
Then, the calculated maximum discharge power PD and maximum charge power PC are output to the inverter 12, and the power during power running is the maximum discharge power PD.
The output control is performed as follows, and the regeneration control is performed so that the electric power at the time of regeneration becomes the maximum charging power PC or less.

In the configuration of the above embodiment, the voltage sensor 14 and the current sensor 15 constitute a measuring means, and the controller 16 constitutes an arithmetic means.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment.

FIG. 2 is a diagram showing the relationship between the depth of discharge (DOD) of a battery and the internal resistance.

FIG. 3 is a diagram showing a regression line based on sampling data of a terminal voltage V and a discharge current I at the time of discharging.

FIG. 4 is a diagram illustrating sampling timings of a terminal voltage V and a discharge current I during discharging.

FIG. 5 is a diagram showing a case where the discharge current I and the terminal voltage V are sampled after a predetermined time Δt from the rise of the discharge current.

FIG. 6 is a diagram obtained by plotting the sampling results shown in FIG. 5 on a VI graph and performing linear regression.

FIG. 7 is a diagram showing a case where the discharge current I and the terminal voltage V are sampled after a predetermined time Δt1 and Δt2 from the rising of the discharge current.

FIG. 8 is a diagram obtained by plotting the sampling results shown in FIG. 7 on a VI graph and performing linear regression.

FIG. 9 is a diagram showing an example in which VI characteristics are sampled at a plurality of points in a normal traveling pattern of an electric vehicle.

FIG. 10 is a diagram obtained by plotting the sampling results shown in FIG. 9 on a VI graph and performing linear regression.

FIG. 11 is a diagram in which the sampling data shown in FIGS. 9 and 10 are classified according to sampling timing Δt and discharge current I.

FIG. 12 is a diagram illustrating a method of stocking sampling data.

FIG. 13 is a flowchart showing the operation of one embodiment.

FIG. 14: Terminal voltage V of the battery when discharged at a constant current
FIG.

[Explanation of symbols]

11 batteries 12 inverter 13 motor 14 Voltage sensor 15 Current sensor 16 controller

Continuation of front page (56) Reference JP-A-6-34727 (JP, A) JP-A-56-126777 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 31 / 36 G01R 21/00-21/14 H02J 7/00-7/12

Claims (4)

(57) [Claims] 1. A voltage measuring means for measuring a terminal voltage of a battery, a current measuring means for measuring a current flowing through the battery, and a discharge start for detecting a start time point of a discharge reaction of the battery based on the measured current value. Detecting means, after the discharge reaction start time after the battery transitioned to a stable diffusion state, at a plurality of times during the increase of the discharge current ,
Sampling means for sampling the terminal voltage and discharge current of the battery by the voltage measuring means and the current measuring means, and a linear voltage-current characteristic of the battery by the terminal voltage and discharge current of the battery sampled by the sampling means. An arithmetic unit for calculating a maximum charging / discharging power of a battery, comprising: a calculating unit that regresses and calculates the maximum discharging power and the maximum charging power of the battery based on the regression line. 2. The apparatus for calculating the maximum charge / discharge power of a battery according to claim 1, wherein the discharge start detection means defines a time point at which the measured discharge current value and its change rate are both positive as a discharge reaction start time point. A device for calculating the maximum charge / discharge power of a battery, characterized in that 3. The battery maximum charge / discharge power calculation device according to claim 1 or 2, wherein the calculation means divides the discharge current range into a plurality of regions, each divided current region having the latest value. The terminal voltage and the discharge current of the battery are stored by a predetermined number each, and the voltage-current characteristic of the battery is linearly regressed based on the stored terminal voltage and discharge current. Arithmetic unit. 4. The battery maximum charging / discharging power computing device according to claim 3, wherein the computing means calculates a voltage of the battery based on a terminal voltage and a discharging current of at least three or more divided current regions. A device for calculating the maximum charge / discharge power of a battery, which is characterized by linear regression of current characteristics.