JPH10108301A - Travelable distance calculation for electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate a travelable distance exactly by ensuring the minimum output which an electric vehicle requires by the discharging end of a battery. SOLUTION: The total heating value and effective electric energy of batteries produced during the discharge of a fixed micro quantity of electricity is calculated from a constant power discharge curve determined in advance and heat absorption/generation value by an entropy change reactive to the batteries, and battery temperature at the next fixed micro electric energy discharge section is calculated from the total heating value and a predetermined battery specific heat. This process is repeated until the terminal voltage of the batteries exceeds final discharge voltage, and a travelable distance is calculated from a total of effective electric energy produced to that point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calculating a distance that an electric vehicle can travel while securing a required minimum output from that time to the end of battery discharge.

[0002]

2. Description of the Related Art As a method of calculating a distance that an electric vehicle can travel while securing a necessary minimum output from that time to the end of battery discharge, a method disclosed in Japanese Patent Application Laid-open No. -126777 and Japanese Patent Laid-Open No. 6-1
No. 74808, the maximum output of the battery at that time is calculated from the discharge current and the terminal voltage, and the dischargeable power of the battery is obtained from the correlation between the maximum power and the power amount of the battery experimentally obtained in advance. A method of calculating the amount and estimating the possible travel distance is conceivable.

[0003]

However, the temperature dependence of the internal resistance that determines the maximum output of the battery is not small, and when the battery temperature changes while the electric vehicle is running, the electric vehicle can secure the minimum output required. There is a possibility that the distance that can be traveled cannot be calculated accurately. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems and to enable an electric vehicle to accurately calculate a travelable distance by securing a required minimum output by the end of battery discharge.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present invention has been achieved. The basic concept of the present invention is to simulate the discharging process of the battery based on the discharge curve data in consideration of the temperature change of the battery, and more specifically, as follows. According to the first aspect of the present invention, in the method for calculating the travelable distance of the electric vehicle from the amount of remaining power of the secondary battery for the electric vehicle, the battery temperature and the open circuit voltage at that time are detected and experimentally determined in advance. From the relationship between the amount of discharged electricity at a constant temperature and constant power and the terminal voltage of the battery and the amount of heat absorbed and generated by the entropy change of the battery reaction, the total calorific value of the battery during discharging a small amount of micro electricity is calculated. The process of calculating the effective work amount and calculating the battery temperature in the next constant minute amount of electricity discharge section from the total calorific value and the specific heat of the battery determined in advance is repeated until the terminal voltage of the battery exceeds the discharge end voltage. The first characteristic is that the travelable distance is calculated from the total effective work amount up to that point. Also,
In a second aspect of the present invention, the second feature is that the secondary battery for an electric vehicle is a lithium ion battery.

[0005]

An embodiment of the present invention will be described below with reference to the drawings. First, prior to the calculation method, according to FIG. 2, the temperature dependence of the constant power discharge curve, and FIG.
The method of storing the experimental data obtained by measurement based on the curve will be described. FIG. 2 shows a constant output (power (P) while keeping the lithium ion battery at a constant temperature.
3 schematically shows the relationship (constant power discharge curve) between the amount of discharged electricity (Q) and the terminal voltage (E) of the battery when the battery is discharged in o)). The uppermost curve shows the open circuit voltage (E
4 shows the dependence of ocv) on the amount of discharged electricity. The constant output is an average output of the electric vehicle equipped with the battery in a constant running pattern.

[0006] The constant power discharge curve when the battery temperature is kept constant is based on the internal resistance (consisting of the reaction resistance of the positive electrode and the negative electrode, the solution resistance, the current collector resistance, etc.) when the battery temperature is low even in the same charged state. Polarization (△ Epol) due to concentration polarization and the like determined by the voltage drop (△ Eir) and the ion diffusion process in the active material increases, and the terminal voltage becomes Eocv.
Deviates greatly from the curve downward. For this reason, when the battery temperature is low, the discharge end voltage (Eend) is obtained with a smaller amount of discharged electricity.
To reach. To obtain a discharge curve with the battery temperature kept constant, construct a thin battery that easily dissipates heat using electrodes of the same structure as large batteries, attach cooling fins, etc., and forcibly cool in a constant temperature bath. Then, it can be estimated by discharging the battery with the output per unit electrode area being the same as that of the large battery.

On the other hand, if the battery is discharged without controlling the battery temperature, the temperature of the battery rises due to the heat generated by the battery itself due to the discharge, and gradually rises to the upper curve as shown by the thick short line in FIG. It shifts and follows a discharge process (discharge curve) different from that at a constant temperature.

[0008] When a large number of large batteries such as batteries for electric vehicles are compactly stored, the condition is close to a heat insulating state. Therefore, if the amount of heat generated from the battery itself due to the discharge is known, the temperature rise of the battery can be estimated by estimating the specific heat of the battery in advance. It is even better if the effective specific heat is used in consideration of the influence of the outside air temperature. In addition, if a battery storage case or a battery structure having a more adiabatic configuration is employed, the accuracy of the estimation can be improved.

The present invention predicts a discharge curve in the case where the battery temperature is not controlled from the data of the constant power discharge curve when the battery temperature is kept constant, and calculates the possible travel distance.

For this purpose, a constant power discharge curve at a constant temperature is divided for each constant minute electric quantity (ΔQ), and the i-th minute electric quantity ΔQi from the full charge and the average terminal voltage Ei in that section are calculated. The relationship and the relationship between △ Qi and Eocv, i are determined in advance. In the case of a lithium-ion battery, the temperature dependence of Eocv is small, so that the relationship at room temperature may be represented. In addition, data of the entropy change (△ S) i of the battery reaction in each section is measured in advance. For this purpose, the temperature coefficient of the electromotive force of the battery may be measured, or the battery may be thermally isolated from the outside to discharge a constant amount of electricity, and then estimated from the energy balance at that time. These experiment data may be stored in the storage device as shown in FIG.

Hereinafter, a method of calculating the travelable distance will be described with reference to the flowchart of FIG.

First, a scheduled driving mode of an electric vehicle is selected, and an average discharge power Po corresponding to the selected mode is determined (S1). Next, the battery temperature Tr and the open circuit voltage Eocv,
r is measured (S2). From these and the relationship between △ Qi and Eocv, i previously obtained experimentally in advance, the amount of discharge electricity from the fully charged state is estimated, and the corresponding minute electricity amount section △ Qr (rth from full charge) is determined. (S
3). Next, the average terminal voltage Er is read from the discharge curve data at the temperature Tr (S4). In this section, the active power amount ({Hr = Er △}) is calculated from the area of the shaded area below Er.
Q) is calculated and stored (S5). From the area of the upper black portion, the heat generated by the internal resistance and polarization of the battery ({qr, r = 0.24 (Eocv, r−Er))}
Q) is calculated (S6). Next, the entropy change (△ S) i of the battery reaction in this section is read (S7), and the resulting heat value (△ qs, r = −Tr · (△ S) r · △).
Q) is calculated (S8). The sum of these is considered to be the calorific value of the battery in this section. The next minute electricity section △ Q
At r + 1, it is considered that the battery temperature has increased by an amount corresponding to this heat generation, and the effective specific heat of the battery at Tr (Cp, e)
ff (Tr)) is read from the table (S9), and the battery temperature (Tr + 1 = Tr + (△ qr, r + △ qs,
r) / Cp, eff (Tr)) is calculated (S10).
In this section, the average terminal voltage Er + 1 and the average open circuit voltage Eocv, r + 1 are calculated from the discharge curve data at the calculated temperature.
Is read, and the same estimation is performed (S11). This process is repeated until the read average terminal voltage Er + 1 becomes equal to or lower than the discharge end voltage Eend (S12). The sum of the active power amounts immediately before the terminal voltage becomes equal to the end-of-discharge voltage Eend is calculated, and the effective remaining power amount (Heff) is calculated (S13). ) To calculate the distance (L) that can travel by the end of discharge (S14).

Here, when there is no discharge curve data at the corresponding temperature, for example, Eocv and E may be linearly approximated to the temperature and interpolated.

If the electric vehicle is provided with a method for accurately measuring the amount of discharged electricity from the fully charged state, the minute electric amount section △ Qr can be determined at any time during the operation of the electric vehicle by the method. Needless to say, it can be applied.

When the battery deteriorates, the Eocv-Q curve is compressed in the Q direction, and the ΔEir and ΔEpo
As l increases, the constant power discharge curve goes further down,
By having the above-mentioned discharge curve data package corresponding to the state of deterioration of the battery, the present invention can be applied to a deteriorated battery.

Furthermore, by selecting a data package of a deteriorated battery identified by a parameter defining the discharge performance of the battery, it is possible to apply the data package with high accuracy in accordance with the state of deterioration and to save storage capacity. Become.

In addition, the Eocv-
The Q curve is approximated and expressed as a function, and the voltage drop due to internal resistance (△ Eir) and the polarization due to concentration polarization determined by the ion diffusion process in the active material (△ Epol)
Is expressed as a function as an approximate expression, the accuracy of the present invention can be improved and the storage capacity can be saved.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. If so, they are included in the present invention.

[0019]

As described above, according to the present invention, the distance that can be traveled with the minimum output required by the end of discharging of the battery is calculated in consideration of the battery temperature change due to the running of the electric vehicle. it can. Further, if the discharge curve of the deteriorated battery under an arbitrary condition is approximated, the amount of data that the system needs to have is drastically reduced and the prediction accuracy is improved. In addition, a practical and highly accurate remaining capacity meter can be configured by measuring the temperature of the battery at regular intervals during traveling and repeating this simulation to sequentially update the possible travel distance. At the same time, the battery temperature rise can be predicted, which is useful for predicting the necessity time of the battery cooling mechanism. Further, by using the discharge data at various temperatures corresponding to the extreme driving modes, it is possible to cope with more realistic driving in which the driving mode changes halfway. In addition, a driving simulation of an electric vehicle can be performed in combination with the navigation system. If the map of the navigation system has the necessary power information in the typical driving mode of the electric vehicle, it leads to a more realistic simulation. In addition, if the electric vehicle is provided with a mechanism for learning and storing the mode and the required power amount in the actual running, the driving simulation of the electric vehicle can be further enhanced. As described above, the present invention greatly promotes the spread of electric vehicles, and greatly contributes to the industry.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature dependence of a constant power discharge curve and a relationship between an open circuit voltage and a discharge electricity amount.

FIG. 3 is an example of a method of storing experimental data.

Claims (2)

[Claims] In a method for calculating a travelable distance of an electric vehicle from an amount of remaining power of an electric vehicle secondary battery, a battery temperature and an open circuit voltage at that time are detected and experimentally obtained in advance. From the relationship between the amount of discharged electricity and the terminal voltage of the battery at a constant temperature and constant power, and the amount of heat generated by the entropy change of the battery reaction, the total amount of heat and the effective work amount of the battery during discharging a small amount of small electricity are calculated. The process of calculating and calculating the battery temperature in the next constant minute amount of electricity discharge section from the total calorific value and the previously determined specific heat of the battery is repeated until the terminal voltage of the battery exceeds the discharge end voltage, and at that time A travelable distance calculation method for calculating the travelable distance from the total sum of the effective work load up to the vehicle. 2. The method according to claim 1, wherein the secondary battery for an electric vehicle is a lithium ion battery.