JP2002006010A - Maximum charge/discharge electric-power calculating system for battery of electric automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a maximum charge/discharge electric-power calculating system for improved power calculation precision. SOLUTION: This is related to a maximum charge/discharge electric-power calculating system which repeats a sampling measurement and a power calculation following it. A sampling capacity Cx is so set that change in release voltage of a buttery is almost constant from starting through end of sampling measurement regardless of SOC, based on the release voltage provided by power calculation before the sampling measurement. By setting the sampling capacity Cx for each sampling measurement, variation in sampling data is suppressed to small even if the SOC is a small discharge end, for improved calculation precision at power calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maximum charge / discharge power calculation device used for an electric vehicle battery.

[0002]

2. Description of the Related Art Discharge power and charge power of a battery of an electric vehicle or the like are controlled to be equal to or less than a maximum discharge power and a maximum charge power, respectively. As a method of calculating the maximum charge / discharge power, there is a method disclosed in Japanese Patent Application Laid-Open No. H10-104325. The maximum charge / discharge power calculation disclosed in this publication is called a power calculation, and samples a voltage V and a current I of a battery while discharging a predetermined capacity (hereinafter, referred to as a sampling capacity) during traveling. The current dischargeable output of the battery is calculated from the sampling data. This power calculation is an effective means for estimating the remaining capacity of the battery. Further, the output of the vehicle is adjusted when the indication of the capacity meter becomes nearly empty at the end of discharge, but this is also effective in performing such output adjustment.

[0003]

The batteries mounted as driving batteries in electric vehicles include lithium-ion batteries and nickel-metal hydride batteries. The open-circuit voltage E0 and the SOC (state of chrage) of these batteries are known. Has a relationship as shown in FIG. That is, as the SOC decreases, the rate of decrease of the open circuit voltage E0 increases, and the open circuit voltage change ΔE0 per sampling capacity is as shown in FIG. When the SOC of the battery is about 100% (fully charged state) to about 50%, ΔE0 does not change so much and can be regarded as substantially constant, but it can be seen that ΔE0 increases when the SOC becomes smaller than 50%.

Therefore, as shown by reference numeral B1 in FIG.
When power calculation is performed in a state where OC is larger than 50%, sampling data (indicated by black circles) obtained during discharging by the sampling capacitance C has a distribution as shown in FIG. 9A. On the other hand, as shown by the symbol B2, the SOC is 5
The sampling data obtained in a state smaller than 0% has a distribution as shown in FIG. (A) of FIG.
In (b), d1 and d2, d11 and d21 and d
Numerals 12 and d22 denote data having substantially equal current values, d1, d11 and d12 are data obtained immediately after the start of sampling, and d2, d21 and d22 are data obtained immediately before the end of sampling. The voltage change during sampling is ΔV1 in the case of FIG.
In the case of (b), ΔV2 (> ΔV1).

In the power calculation, a regression line L1 is calculated from sampling data as shown in FIG. The regression line L1 is expressed by the following equation (1). The internal resistance R of the battery is calculated from the slope of the regression line L1, and the open circuit voltage E0 of the battery is calculated from the intercept of the vertical axis (V axis). At this time, the discharge end voltage Vmin, which is the lower limit voltage of the working voltage range in consideration of the battery life,
And the current Imax obtained from the regression line L1 gives an allowable discharge value. Then, the dischargeable power Pmax is calculated by the equation (2).
Given by

V = E0−I · R (1) Pmax = Vmin · Imax = Vmin · (E0−Vmin) / R (2)

However, if the change in the open-circuit voltage of the battery during sampling is large, the variation of the sampling data becomes large, as shown in FIG. 9 (b), and the calculation error of Pmax becomes large. .
For example, consider a case where high-load-side data d12 is sampled in the first half while discharging the sampling capacitor C, and low-load-side data d21 is sampled in the second half of discharging. In this case, a regression line as indicated by L21 in FIG. 9B is obtained, and the inclination of the regression line L21 is smaller than the inclination of the IV characteristic line L0 indicating the actual value of the battery. That is,
The internal resistance is calculated to be smaller than the actual value, and the dischargeable power Pmax of the battery is calculated to be larger than the actual value.

Conversely, during the first half of the discharge, the data d11 on the low load side
Is sampled, and the data d2 on the high load side
When 2 is sampled, the regression line becomes like L22. Therefore, the internal resistance is calculated to be larger than the actual value, and the dischargeable power Pmax of the battery is calculated to be smaller than the actual power. For example, if the dischargeable power Pmax is calculated to be larger than the actual value, a disadvantage occurs that the battery capacity becomes zero before the capacity meter indicates empty.

An object of the present invention is to provide a maximum charging / discharging power calculation device capable of improving power calculation accuracy.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 showing an embodiment of the present invention, the present invention comprises a voltage measuring means 4 for measuring a voltage V of a battery 1 while discharging a sampling capacity; A current measuring means 5 for measuring a current I flowing through the battery 1 while discharging the sampling capacity, and an open-circuit voltage of the battery 1 is obtained based on the measurement results of the voltage measuring means 4 and the current measuring means 5 to obtain chargeable / dischargeable power. Calculation means 6 for calculating
And applied to a maximum charge / discharge power calculation device for an electric vehicle battery that repeatedly performs sampling measurement by the voltage measurement unit 4 and the current measurement unit 5 and calculation of chargeable / dischargeable power by the calculation unit 6. Setting means 6 for setting the sampling capacity based on the open-circuit voltage calculated before the sampling measurement so that the change in the open-circuit voltage of the battery 1 from the start to the end of each sampling measurement is substantially constant. Thereby, the above object is achieved.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to facilitate understanding of the present invention. However, the present invention is not limited to the embodiment.

[0011]

According to the present invention, the sampling capacity at the time of calculating the chargeable / dischargeable power is set such that the change in the open-circuit voltage of the battery becomes substantially equal based on the open-circuit voltage calculated before the sampling measurement. Since it is set, the variation in the voltage of the sampling data can be reduced even at the end of discharge, and the calculation accuracy of the chargeable / dischargeable power calculation can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram illustrating an example of a traveling drive mechanism of an electric vehicle. A battery 1 composed of a plurality of single cells 101 supplies DC power to an inverter 2, which converts the DC power into AC power and drives a motor 3 to generate running energy.
At the time of regeneration, the traveling energy of the vehicle is converted back to electric energy via the motor 3 and the inverter 2,
The battery 1 is charged and the vehicle is regeneratively braked. The voltage sensor 4 detects a voltage V across the battery 1, and the current sensor 5 detects a current I flowing through the battery 1.

The battery controller 6, which monitors and controls the state of the battery 1, performs the above-described power calculation and charge / discharge control of the battery 1. For example, the voltage V and the current I are sampled by the voltage sensor 4 and the current sensor 5 while discharging only the sampling capacity during traveling, and the dischargeable power Pmax and the chargeable power PCmax of the battery 1 are calculated from the sampled data. The remaining capacity of the battery 1 is calculated based on the calculation result, and the remaining capacity is displayed on the capacity meter 7. Dischargeable power Pmax and chargeable power PCm
ax is sent to a TPC (Torque Processing Control) 8, which outputs an output control command and a regenerative control command to the motor controller 9 based on these data. The motor controller 9 controls the driving of the motor 3 by the inverter 2 according to a command from the TPC 8.

<< Method of Calculating Pmax and PCmax >> A method of calculating the dischargeable power Pmax and the chargeable power PCmax will now be described. When the battery 1 is in the discharging state, the voltage V and the current I of the battery 1 are sampled.
This sampling is performed during discharging by a predetermined sampling timing capacity. Then, as shown in FIG. 9A, a linear regression operation is performed on the IV characteristic from the obtained sampling data. As described above, the regression line L1 is expressed by equation (1), and the internal resistance R of the battery is calculated from the slope of the regression line L1, and the open-circuit voltage E0 of the battery is calculated from the intercept of the vertical axis (V axis).
Are calculated respectively.

## EQU2 ## V = E0-IR (1)

The current Imax at the intersection of the regression line L1 and the discharge lower limit voltage (lower limit voltage for use as a vehicle system) Vmin at the time of discharge gives an allowable discharge value, and the allowable maximum voltage Vm at the time of charge.
The current ICmax at the intersection with ax gives the allowable charging value. The dischargeable power Pmax and the chargeable power PCmax are given by the following equations (2) and (3).

Pmax = Vmin · Imax = Vmin · (E0−Vmin) / R (2) PCmax = Vmax · ICmax = Vmax · (E0−Vmax) / R (3) The discharge lower limit voltage Vmin is as follows. (A) and (b), and Vmin ≧ E0 / 2. (A) Lower limit voltage of operating voltage range considering battery life (discharge end voltage) (b) Lower limit voltage of operating voltage range capable of guaranteeing performance and function of vehicle mounted unit

By the way, as described above, the SOC is 50
% Or less and the open-circuit voltage change ΔE0 increases, Pm
There has been a problem that the calculation error of ax and PCmax increases and the calculation accuracy decreases. Therefore, in the present embodiment, the sampling capacity is set so that the open-circuit voltage change ΔE0 is substantially constant in each sampling, specifically, the open-circuit voltage change in the fully charged state where the value of ΔE0 is small. I set it.

<< How to set sampling capacity >>
FIG. 2 is a flowchart showing a procedure of power calculation and setting of a sampling capacity performed by the battery controller 6. In the flowchart shown in FIG. 2, the process is started from step S1 with a fully charged state as an initial state. In an initial state, the sampling capacity is set to a specified sampling capacity C0. In step S1, the voltage V and the current I are sampled while discharging the sampling capacitor C0. In step S2, a predetermined power calculation is performed based on the sampling data obtained in step S1. That is, FIG.
The regression line L1 of FIG.
01, the dischargeable power Pmax, the chargeable power PCmax, and the like are calculated. In step S3, the calculated open circuit voltage E01 is stored.

In step 4, the sampling capacity C
While discharging 0, the voltage V and the current I are sampled. Next, after performing power calculation in step S5,
In step S6, the open circuit voltage E02 calculated in step S5 is stored. In step S7, the corrected sampling capacitance Cx is calculated by equation (4) based on the stored open-circuit voltages E01 and E02, a predetermined specified open-circuit voltage change ΔE0x, and the sampling capacitance C0. In step S8, while discharging the sampling capacitance Cx calculated in step S7, the voltage V and the current I
Is sampled.

## EQU4 ## C0.times..DELTA.E0x / (E01-E02) = Cx (4)

Thereafter, returning to step S7, power calculation is performed based on the data sampled in step S8. Thereafter, the processing of steps S5 to S8 is repeatedly executed, and the power calculation is repeatedly executed. At that time, every time the power calculation is performed, the sampling capacity Cx is determined in step S7.
Is set, and the sampling capacity Cx is adopted at the time of sampling at the next timing.

Next, as described above, the sampling capacity C
A description will be given of the fact that, by setting x, the open-circuit voltage changes at each sampling become substantially equal. As the open-circuit voltage change ΔE0x in the equation (4), for example, as shown in FIG. 3, a voltage change during discharging of the sampling capacitor C0 in the almost fully charged state G1 is used. FIG. 3 is a graph showing the relationship between the open-circuit voltage of the battery 1 and the SOC. When the SOC is smaller than 50% as indicated by reference numeral G2, the change in the open-circuit voltage E0 increases. FIG. 4 shows G2 in FIG.
It is an enlarged view of the part shown by.

In FIG. 4, E03 is a sampling capacity C
This is an open circuit voltage obtained by power calculation based on sampling data during discharging of x. Prior to this power calculation, the open circuit voltage E02 was obtained by the previous power calculation, and the open circuit voltage E01 was obtained by the power calculation two times before. Cx '
Is a sampling capacity used at the time of the previous power calculation, and the sampling capacities Cx and Cx 'are set by the above equation (4). Since the slope of the curve in FIG. 3 increases with decreasing SOC, E01−E02> ΔE
It is 0x.

In FIG. 4, when the curve of the portion E01 to E02 is regarded as a straight line, the slope of the straight line is expressed by the following equation (5). , It is equal to ΔE0x. That is, in the present embodiment, the sampling capacitance Cx at the time of each power calculation is set such that the change in the open-circuit voltage from the start to the end of sampling is substantially equal to ΔE0x. Actually, the curve representing the relationship between the open-circuit voltage and the SOC is a curve whose slope increases as the SOC decreases, so that E02-E03 is slightly larger than ΔE0x.

(Equation 5)

As described above, when the sampling capacitance Cx is determined as in the present embodiment, the change in the open-circuit voltage during the discharge of Cx is substantially constant regardless of the SOC of the battery at each sampling. At this time, each open-circuit voltage change has a value substantially equal to the specified open-circuit voltage change ΔE0x. As a result, FIG.
As shown in FIG. 5, even at the end of discharge where the SOC is smaller than 50%, the voltage variation of data having the same current value is represented by ΔE.
It can be set to about 0x, and the accuracy of power calculation can be improved. In the above-described embodiment, the sampling capacitance Cx is calculated by the equation (4). However, a calculation method based on the open-circuit voltage calculated before the sampling may include various equations other than the equation (4). Can be

When the battery 1 is in a low temperature state or deteriorates, the curve representing the relationship between the open circuit voltage and the SOC changes from L50 to L51 as shown in FIG. With such a change, the rate of change in the open-circuit voltage increases at room temperature or before deterioration. As a result, the change in the open-circuit voltage at the time of sampling becomes larger, and the power calculation accuracy is significantly reduced due to variation in sampling data. Even in such a case, by setting the sampling capacitance Cx as in the above-described embodiment, it is possible to prevent a decrease in calculation accuracy.

In the above-described embodiment, Cx is set based on the open circuit voltage calculated for each sampling. However, the SOC and the open circuit voltage for various battery states such as deterioration and low temperature are set. A map indicating the relationship may be prepared in advance, and the sampling capacity Cx may be set to an optimum value according to the battery temperature, the battery deterioration state, and the SOC. However, when Cx is calculated based on the open-circuit voltage calculated in real time as described above, the detected open-circuit voltage reflects the battery temperature, the deterioration state, and the like. Can be lightened.

In the correspondence between the embodiment described above and the elements of the claims, the voltage sensor 4 functions as voltage measuring means, the current sensor 5 functions as current measuring means, and the battery controller 6 functions as calculating means and setting means. Constitute.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a traveling drive mechanism of an electric vehicle.

FIG. 2 is a flowchart illustrating a procedure of power calculation and setting of a sampling capacity.

FIG. 3 is a diagram showing a relationship between an open circuit voltage of a battery 1 and an SOC.

FIG. 4 is an enlarged view of a portion G2 in FIG. 3;

FIG. 5 is a diagram showing a sampling data distribution at the end of discharge in the case of the present embodiment.

FIG. 6 is a diagram showing the relationship between the open circuit voltage and the SOC when the battery temperature decreases or the battery deteriorates.

FIG. 7 is a diagram showing a relationship between open circuit voltage E0 and SOC.

FIG. 8: Open-circuit voltage change ΔE0 per sampling capacity
FIG.

FIG. 9 is a diagram showing a relationship between sampling data and a regression line, where (a) shows a case where the SOC is greater than 50%;
(B) shows a case where the SOC is smaller than 50%.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery 2 Inverter 3 Motor 4 Voltage sensor 5 Current sensor 6 Battery controller 8 Torque processing controller 9 Motor controller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/00 H02J 7/00 X F term (Reference) 2G016 CA03 CB11 CB12 CB13 CB21 CB24 CC01 CC03 CC04 CC13 CC27 CC28 5G003 AA07 BA01 DA07 EA05 FA06 GC05 5H030 AA06 AS08 BB01 BB21 FF43 FF44 5H115 PC06 PG04 PI16 PI29 PU08 PV09 TI02 TI05 TI06 TO14 TR19 TU01 TU04

Claims (1)

[Claims] 1. A voltage measuring means for measuring a voltage of a battery while discharging a sampling capacity, a current measuring means for measuring a current flowing through the battery while discharging the sampling capacity, the voltage measuring means and a current Calculating means for calculating the open-circuit voltage of the battery based on the measurement result of the measuring means and calculating chargeable / dischargeable power; sampling measurement by the voltage measuring means and current measuring means; and chargeable / dischargeable power by the calculating means. In the maximum charge / discharge power calculation device for an electric vehicle battery, which repeats the calculation, for each of the sampling measurements, based on the open-circuit voltage calculated before the sampling measurement, from the start to the end of each of the sampling measurements. Setting means for setting the sampling capacity so that the change in the open-circuit voltage of the battery is substantially constant; Maximum discharge power calculation apparatus for an electric vehicle battery, characterized.