JP2002272011A - Charging and discharging control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging and discharging control unit using power inputted and outputting considering the internal resistance of a unit battery for controlling the charging and discharging of an assembly battery. SOLUTION: When discharging, the total voltage and current of a battery 4 are sampled by a voltage sensor 7 and a current sensor 8. A battery controller 6 carries out a regression operation based on the sampled data for calculating power that can be inputted and outputted. When discharging, the voltage of each cell for composing the battery 4 is detected by a cell controller 5. In the battery controller 6, a regression operation on each cell is carried out based on the sampled cell voltage and current, and a cell having the maximum internal resistance is obtained. Then, the power that can be inputted and outputted is corrected based on the regression operation result of the cell having the maximum internal resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge / discharge control device for a battery pack used as a drive battery of an electric vehicle or the like.

[0002]

2. Description of the Related Art Conventionally, as a battery mounted on an electric vehicle, an assembled battery in which a plurality of unit cells called cells are connected in series is used. Japanese Patent Application Laid-Open No. 11-41711 describes a method for calculating the input / output available power of such a battery.
Is disclosed in Japanese Patent Application Laid-Open Publication No. H10-26095. In the conventional calculation method, the total voltage and the discharge current value of the battery are sampled at the time of discharging, and the input / output available power is obtained by regression calculating the VI characteristic based on the sampled data.

[0003] For example, when obtaining the inputtable power, a regression line is calculated based on sampling data obtained during discharging. Next, the current value Icmax at the battery upper limit voltage Vmax which is the target voltage of the inputtable voltage is obtained from the regression line, and the inputtable power Pcmax is calculated by the following equation. For example, in the regenerative control during braking, control is performed so that the charging power becomes the inputtable power Pcmax.

## EQU1 ## Pcmax = Icmax × Vmax

In the regenerative control, regenerative control is performed so that each cell does not exceed a predetermined upper limit charging voltage for battery protection. In the discharge control, the output is limited so that each of the cells does not fall below a predetermined discharge lower limit voltage.

[0005]

However, in the conventional input / output available power calculation method, the input / output available power is calculated based on the voltage and current of the entire assembled battery as described above, and the internal resistance of each cell is calculated. Was not taken into account. If the variation in the internal resistance is large, for example,
When the cell having the maximum internal resistance reaches the lower discharge limit voltage during the running control, the discharge is limited so that the discharge current does not increase any more.

Therefore, until immediately before such discharge limitation is performed, power corresponding to the accelerator operation is output based on the calculated available output power, but the cell having the maximum internal resistance reaches the discharge lower limit voltage. Then the discharge limit is executed,
The output is limited to a power smaller than the required output power. Therefore, for example, if the output is limited when the driver steps on the accelerator for a predetermined time to accelerate, the output intended by the driver is not increased, and the driver may feel uncomfortable.

An object of the present invention is to provide a charging / discharging control device for controlling charging / discharging of a battery pack by using input / output available power in consideration of the internal resistance of a unit battery.

[0008]

An embodiment of the present invention will be described with reference to FIGS. 1 and 3. FIG. (1) Explaining in association with FIG. 1, the charge / discharge control device 6 according to the first aspect of the present invention detects a current detector 8 for detecting a current value of the battery pack 4 and a total voltage value of the battery pack 4. A total voltage detector 7, a unit battery voltage detector 5 for detecting each voltage value of a plurality of unit batteries constituting the assembled battery 4, and a regression of the voltage / current characteristics of the assembled battery 4 based on the current value and the total voltage. A regression calculation unit 6 that calculates and regressively calculates the voltage and current characteristics of each battery pack based on the current value and the voltage value of the unit battery, and a battery pack based on the calculation result of the regression calculation unit 6 regarding the battery pack 4 4 based on the voltage / current characteristics of the unit battery having the largest internal resistance calculated by the regression calculation unit 6 and the input / output possible power calculation unit 6 for calculating the input possible power and the output possible power. Or a correction function to correct the output power And a section 6, to achieve the above object by charging and discharging control of the battery pack 4 based on the calculation result of the input and output electric power calculating unit 6 and the correction calculating unit 6. (2) When described in association with FIGS. 1 and 3, the invention according to claim 2 is characterized in that, in the charge / discharge control device 6 according to claim 1, the variation in the voltage value detected by the unit battery voltage detection unit 5 is reduced. When the voltage value is equal to or smaller than the predetermined voltage value Y and the magnitude of the current value is equal to or smaller than the predetermined current value (X / 2), the regression calculation unit 6 performs the calculation. (3) In the third aspect of the present invention, in the charge / discharge control device 6 according to the first or second aspect, when the internal resistance of the unit battery having the largest internal resistance is equal to or more than a predetermined value, the unit battery is determined to be abnormal. The determination unit 5 is provided.

In the meantime, in the section of the means for solving the above problems, the drawings of the embodiments of the present invention are used to make the present invention easy to understand, but the present invention is not limited to the embodiments of the present invention. Not something.

[0010]

According to the first aspect of the present invention, the voltage / current characteristics of the unit battery having the largest internal resistance are calculated by regression calculation, and based on the calculation result, the inputtable power and / or power of the battery pack are calculated. Since the available output power is corrected, and the charge / discharge control of the battery pack is performed based on the corrected available input power and / or the available output power, the input power is set when the unit battery having the maximum internal resistance reaches the limit voltage. And the output power is not sharply limited. (2) According to the second aspect of the present invention, the same effects as those of the first aspect are obtained, and when the variation of the voltage value of each unit battery is equal to or less than a predetermined voltage value and the current value is equal to or less than the predetermined current value. Since the regression calculation is performed for each unit battery, the influence of the variation in the battery state (SOC) of each unit battery can be reduced, and the correction accuracy of the correction calculation unit can be improved. (3) According to the third aspect of the invention, the same effects as those of the first and second aspects can be obtained, and the abnormality of the unit battery can be detected with high accuracy.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram illustrating a hybrid electric vehicle (HEV) including a charge / discharge control device according to the present invention, and is a diagram illustrating a schematic configuration of a drive system of a parallel HEV. The rotor of the electric motor 2 is directly connected to the main shaft of the engine 1. The driving force of the engine 1 and / or the motor 2 is transmitted to the axle via a drive system (not shown). The inverter 3 converts DC power from a battery 4 composed of a secondary battery into AC power and supplies the AC power to the motor 2, and converts AC power from the motor 2 into DC power in a power generation mode described later to convert the AC power into DC power. Supply to

As the battery 4, a battery called an assembled battery in which a plurality of single cells are connected in series is used. The cell voltage of each single cell constituting the assembled battery is detected by the cell controller 5, and the detected value is stored in the battery controller 6.
Is output to. For example, a lithium ion battery or the like is used for the single cell. The battery controller 6 includes:
The cell voltage value sent from the cell controller 5, the total voltage value of the battery 4 detected by the voltage sensor 7, and the charge / discharge current value detected by the current sensor 8 are input. A battery controller 6 composed of a microcomputer and its peripheral components controls charging and discharging of the battery 4 based on these values. The indicator 9 displays a cell state (cell abnormality or the like) detected by the battery controller 6.

The operation modes of the motor 2 in the parallel HEV include a drive mode for driving the axle and a power generation mode for charging the battery 4. When the battery 4 for supplying electric power to the motor 2 is in a sufficiently charged state when the vehicle is driven, that is, when accelerating, traveling on a flat road, climbing a hill, or the like, the motor 2 is driven in the drive mode to start the engine 1. The vehicle travels with the driving force of both the motor and the motor 2. However, when the state of charge of the battery 4 is low, the motor 2 is operated in the power generation mode, the vehicle is driven by the driving force of the engine 1, the rotor of the motor 2 is rotated, and the power is generated by the motor 2. Charge.

On the other hand, when the vehicle is braking, that is, when decelerating or going down a hill, the engine 1 and the motor 2 are driven by the rotational force of the wheels via the drive system. At this time, the motor 2 is operated in the power generation mode, and the battery 4 is charged by absorbing regenerative energy.

Next, a method of calculating the input / output available power of the battery 4 during the charge / discharge control will be described. First, during discharge, the voltage V,
The current I is sampled, and a regression line of the VI characteristic is obtained based on the sampled data. FIG.
It is a figure which shows I characteristic, "x" has shown sampling data and L1 has shown each regression line. Regression line L1
Represents the internal resistance R of the battery 4, and the value E at the intersection of the regression line L1 and the V axis is the open voltage of the battery 4.

Using the current value Icmax at the intersection A between the straight line indicating the charging upper limit voltage Vmax and the regression line L1, the inputtable power Pcmax of the battery 4 is calculated by the following equation (1).

## EQU2 ## Pcmax = Icmax × Vmax (1)

When the current value Icmax at the intersection B between the straight line indicating the discharge lower limit voltage Vmin and the regression line L1 is used, the outputable power Pdmin of the battery 4 is calculated by the following equation (2).

## EQU3 ## Pdmax = Idmax × Vmin (2)

The inputtable power P calculated as described above
The cmax and the outputtable power Pdmin are corrected according to the variation in the internal resistance of each cell. FIGS. 3 and 4 are diagrams for explaining the correction method, and show the VI characteristics for each cell. FIG. 4 is an enlarged view of a portion of the charging area in FIG.

In FIG. 3, L12 is a regression line for a cell having a maximum internal resistance r of rmax, and L13 is a regression line for a cell having a minimum internal resistance r of rmin. That is, the cell internal resistance r varies in the range of rmin ≦ r ≦ rmax. L11 is a regression line related to the average value of the cell internal resistance. The regression line L11 may be obtained by performing a regression operation based on the cell voltage of each cell, or may be a regression line of the battery 4 using the total voltage for each cell. E0 and F0 are open-circuit voltages obtained from the regression lines L11 and L12. When the current is Icmax, the internal resistance r
The voltage of the max cell is F1 and the average voltage is E1. Current Id
At the time of max, the voltage of the cell having the internal resistance rmax is F2, and the average voltage is E2.

In FIG. 4, E1 is E1 = Vmax / (number of cells). Here, Vmax / (number of cells) is represented by vmax.
Expressed by Now, if the charging current is gradually increased from zero,
The cell of the maximum internal resistance rmax represented by the regression line L12 is
At the current I3 (<Icmax), the charging upper limit voltage vmax of the cell is reached. Therefore, the outputable power per cell ΔPcm
If ax is corrected from "Icmax.times.vmax" to "I3.times.vmax", the cell having the maximum internal resistance rmax does not exceed the charging upper limit voltage vmax.

At this time, the charge correction coefficient K1 is given by the following equation (3).
Is calculated. And the battery 4 calculated from the total voltage
Is calculated by the charge correction coefficient K1 as shown in equation (4), and the corrected power K1 × Pcmax
And the regenerative control of the battery 4 is performed with the inputtable power P′cmax.

K1 = (I3.times.vmax) / (Icmax.times.vmax) = (E1-F0) / (F1-F0) (3) P'cmax = K1.times.Pcmax (4)

On the other hand, the same applies to the case of the outputable power.
The output correction coefficient K2 is calculated by the following equation (5), and discharge control is performed using the power K2 × Pdmax calculated by the equation (6) as the outputable power P′dmax.

K2 = (F0−E2) / (F0−F2) (5) P′dmax = K2 × Pdmax (6)

The flowcharts shown in FIG. 5 and FIG.
FIG. 6 shows a processing procedure of input / output power calculation performed by the battery controller 6, and FIG. 6 is a view showing a procedure following FIG. A series of processes shown in FIGS. 5 and 6 are repeatedly performed at a predetermined timing during charging and discharging. In step S1, each cell voltage of the battery 4 is detected by the cell controller 5, and the detected values are transmitted to the battery controller 6. In step S2, the average voltage Eave of the cell voltages detected in step S1 is calculated. In step S3, the current between the battery 4 and the inverter 3 is detected by the current sensor 8.

In step S4, it is determined whether or not the detected cell voltage is within a predetermined range Y of FIG. This predetermined range Y ranges from the voltage (Eave-Y / 2) sandwiching the average voltage Eave calculated in step S2 to the voltage (Eave + Y / 2).
Range. If it is determined in step S4 that it is within the predetermined range Y, the process proceeds to step S5, while if it is determined that it is out of the range, the process returns to step S1. In the following step S5, it is determined whether or not the current value detected in step S3 is within the predetermined range X in FIG. 3, that is, whether or not the current value ≦ X / 2. If it is determined in step S5 that it is within the predetermined range X, the process proceeds to step S6, while if it is determined that it is out of the range, the process returns to step S1.

In a lithium ion battery used for a vehicle drive battery, there is a correlation between the cell open circuit voltage and the SOC as shown in FIG. 7, and the SOC can be grasped from the open circuit voltage. On the other hand, between the cell internal resistance and SOC, FIG.
The internal resistance changes with SOC. Therefore, in order to more accurately perform the correction operation due to the variation in the internal resistance, it is necessary to eliminate the influence of the variation in the SOC on the variation in the internal resistance.

Therefore, the predetermined range Y is, for example, SOC
Is intended to be in the range of 3%. However, as shown in FIG. 7, since the change amount of the open-circuit voltage is not proportional to the change amount of the SOC, the change depends on the value of the open-circuit voltage. That is, for example, when the SOC is about 80%, the voltage width corresponding to 3% of the SOC is as small as 30 mV, and when the SOC is about 20%, the voltage width corresponding to 3% of the SOC is as large as 50 mV. Will be. Therefore, the predetermined range Y is changed based on the Eave calculated in step S2 in consideration of the open-circuit voltage-SOC characteristic shown in FIG.

Next, a description will be given of the above-mentioned predetermined range X. It is desirable that the difference between the open circuit voltage and the load voltage be minimized in all the temperature ranges. In this embodiment, the difference is, for example, within ± 2.5 A. .

The variation in the SOC can be estimated from the variation in the open circuit voltage.
It can be determined whether or not C varies. Also, by determining whether or not the current value satisfies the current value ≦ X / 2 in step S5, by adopting only the current value close to zero, the cell voltage used in the determination in step S4 is determined. Is limited to a value close to the open circuit voltage. As a result, the influence of the variation in SOC in the correction calculation is reduced, and the correction accuracy is improved. Further, by performing the correction calculation only when the discharge current value is small, it is possible to reduce an error in the calculation.

Next, in step S6, a plurality of samples are taken of the total voltage detected by the voltage sensor 7, the current value detected by the current sensor 8, and the cell voltage of each cell detected by the cell controller 5. In step S7, based on the current value detected in step S6, it is determined whether or not sampling has been performed during discharging. If it is determined in step S7 that the battery is in the discharge state, step S8 is performed.
Proceed to and acquire sampling data as correction calculation data. On the other hand, if NO is determined in the step S7, the process returns to the step S6, and data sampling is performed again.

In step S9 of FIG. 6, a regression line for each cell as shown in FIG. 3 is calculated based on the plurality of cell voltages and current values obtained in step S8. In step S10, a regression line for the entire battery 4 is calculated based on the plurality of total voltages and current values sampled in step S6. In step S11, the battery 4
An average internal resistance rave, which is an average of the internal resistance of each cell, is calculated based on the entire regression calculation. In step S12, each internal resistance is calculated from the regression calculation of each cell, and the cell having the maximum internal resistance rmax is obtained.
This maximum internal resistance rmax is represented by F0, F2 and Idmax in FIG.
And is calculated by the following equation (7).

Rmax = (F0−F2) / Idmax (7)

In step S13, it is determined whether or not the maximum internal resistance rmax calculated in step S12 is equal to or greater than a predetermined value r0. The predetermined value r0 is 2 when the battery is new.
値 3 times, for example, 1.2Ω. Step S1
If it is determined in step 3 that rmax ≧ r0, the process proceeds to step S14, where a warning indicating that a cell abnormality has occurred is displayed on the indicator 9 in FIG. 1, and then the process proceeds to step S15. on the other hand,
If it is determined in step S13 that rmax <r0, the process proceeds to step S15, where the output correction coefficient K2 is calculated by the above equation (5), and in the next step S16, the charge correction coefficient K1 is calculated by the equation (3). And step S
After calculating the possible output power K2 × Pcmax of the equation (6) in 17, the possible input power K1 × Pdmax is calculated by the following equation (4) in a succeeding step S18, and a series of processing ends.

FIG. 9 is a diagram showing an output example by the charge / discharge control device according to the present invention in comparison with a conventional example. (A) shows the required output according to the accelerator depression amount,
(B) shows the output power when the conventional output possible power calculated using only the regression calculation of the battery 4 is used,
(C) shows the output power when the corrected available output power of the present embodiment is used. In the example shown in FIG. 9, the required output eventually becomes P1, but in (B) and (C), the final output is limited to P2 due to the variation in the internal resistance of the cell.

In the case of the conventional output (B), the variation in the internal resistance of the cell is not taken into account in the available output power.
Until the output reaches P2, it increases in accordance with the required output. However, when the output reaches P2, the maximum internal resistance r
Since the cell voltage of max reaches the upper limit voltage, the cell upper and lower limit voltage protection function of the cell controller 5 is activated, and the output P2
Output is limited to Therefore, what was output as requested until time t0, output suddenly stops at time t0. On the other hand, in the output (C), the available output power is corrected by the output correction coefficient K2 as shown in Expression (6), so that the output correction coefficient K
An output of a predetermined ratio according to 2 is output from the start of output. Therefore, the output changes in proportion to the change in the amount of depression of the accelerator until the output B is reached, so that the driver does not feel uncomfortable.

In the above-described embodiment, the open voltage calculated from the regression lines L11 and L12 is used as E0 and F0, but the total voltage and the cell voltage detected in the predetermined range X may be used. Further, although the maximum internal resistance of the unit battery is calculated using the regression calculation, the correction may be performed by calculating the maximum internal resistance by a method other than the regression calculation.

In the above-described embodiment, the voltage V and the current I are sampled by the voltage sensor 7 and the current sensor 8 during discharging. However, the voltage V and the current I are sampled during charging.
The current I may be sampled or both during discharging and during charging. In particular, when the battery pack is made of lithium ions, discharge and charging are particularly effective because there is little change in current and voltage characteristics.

In the above-described embodiment, the driving battery mounted on the hybrid electric vehicle has been described as an example. However, the charge / discharge control device of the present invention can be applied to other batteries.

In the correspondence between the embodiment described above and the elements of the claims, the battery controller 6 includes a charge / discharge control device, a correction calculation unit, an input / output power calculation unit, and a regression calculation unit. The detection unit and the determination unit are respectively configured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a drive system of a hybrid electric vehicle (HEV) including a charge / discharge control device according to the present invention.

FIG. 2 is a diagram showing VI characteristics of a battery 4.

FIG. 3 is a diagram showing VI characteristics for each cell.

FIG. 4 is an enlarged view of a charging region having a VI characteristic shown in FIG. 3;

FIG. 5 is a flowchart showing a processing procedure of input / output power calculation performed by the battery controller 6;

FIG. 6 is a flowchart showing a procedure following FIG. 5;

FIG. 7 is a diagram showing a correlation between open-circuit voltage and SOC.

FIG. 8 is a diagram showing a correlation between internal resistance and SOC.

FIG. 9 is a diagram showing an output example of the charge / discharge control device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 engine 2 motor 3 inverter 4 battery 5 cell controller 6 battery controller 7 voltage sensor 8 current sensor 9 indicator K1 charge correction coefficient K2 output correction coefficient L1, L11 to L13 regression line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/00 ZHV H02J 7/00 ZHVY F-term (Reference) 5G003 AA07 BA01 CA01 CA11 DA15 EA08 FA06 GB06 5H030 AA03 AA04 AA06 AS08 BB01 BB21 FF42 FF43 FF44 5H115 PA01 PC06 PG04 PI16 PO02 PO10 PO17 PU25 PV09 QN02 SE06 TI05 TI06 TI10

Claims (3)

[Claims] A current detecting unit for detecting a current value of the battery pack; a total voltage detecting unit for detecting a total voltage value of the battery pack; and detecting each voltage value of a plurality of unit batteries constituting the battery pack. A unit battery voltage detection unit, and a voltage / voltage of the battery pack based on the current value and the total voltage.
A regression calculation unit for performing a regression calculation on the current characteristic, and a regression calculation unit for performing a regression calculation on the voltage / current characteristics of each battery pack based on the current value and the voltage value of the unit battery; An input / output available power calculation unit for calculating an input available power and an output available power of the battery pack, based on a voltage / current characteristic of a unit battery having the largest internal resistance calculated by the regression calculation unit. A correction operation unit that corrects input possible power and / or output possible power, and performs charge / discharge control of the battery pack based on each calculation result of the input / output possible power calculation unit and the correction calculation unit. Charge and discharge control device. 2. The charge / discharge control device according to claim 1, wherein the regression calculation unit is configured such that a variation in a voltage value detected by the unit battery voltage detection unit is equal to or less than a predetermined voltage value, and
A charge / discharge control device, wherein the regression calculation is performed when the magnitude of the current value is equal to or smaller than a predetermined current value. 3. The charge / discharge control device according to claim 1, further comprising: a determination unit that determines that the unit battery is abnormal when the internal resistance of the unit battery having the largest internal resistance is equal to or greater than a predetermined value. A charge / discharge control device, characterized in that: