JPH1138105A - Method for calculating residual capacity of battery and method for outputting alarm to insufficient residual capacity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the residual capacity of a battery with high accuracy by statistically finding a voltage-current relational expression from many pairs of discharge current values and terminal voltages of the battery measured during a measuring period by performing a primary regression analysis and estimating the residual capacity based on the dropping amount of the outputtable reference power of the battery. SOLUTION: A controller 5 calculates the residual capacity Ahr of a battery by reading the charging/discharge current I of the battery detected by means of a current sensor 2 at prescribed time intervals. The controller 5 calculates the residual capacity based on the outputtable reference power Pc of the battery after the controller 5 detects that the residual capacity Ahr drops to <=50% of the prestored fully charged capacity of the battery. The controller 5 finds a relational expression, V=V0 -R.I, between many sampled terminal voltages V and discharge currents of the battery by performing a primary regression analysis and the outputtable reference power Pc from the product of Vc and Ic found by substituting a reference terminal voltage value Vc and a reference discharge current value Ic into the expression. The controller 5 estimates the residual capacity by calculating the dropping amount ΔPc of the outputtable reference power Pc from the difference between the values of the outputtable reference power Pc calculated last time and this time. The controller 5 issues an alarm by estimating the insufficiency of the residual capacity.

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 remaining capacity of a battery and a method for outputting an insufficient remaining capacity alarm.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. Hei 5-341022 discloses that a charge / discharge current is periodically added and subtracted from an initial value to obtain a remaining capacity by current integration. Obtain the internal resistance, obtain the discharge rate of the battery from this internal resistance, obtain the remaining capacity by estimating the internal resistance based on this discharge rate, compare the above two remaining capacities, and when the error increases, the latter remaining capacity Has been proposed to calculate the remaining capacity of a nickel-based battery.

[0003]

However, the above-described conventional method for calculating the remaining capacity of a battery has a problem that an error increases due to the temperature of the battery, the degree of deterioration, and the like. After all, in the above-described conventional remaining capacity calculation method, the above-described internal resistance estimation is performed by a method in which the internal resistance is obtained from the terminal voltage and the discharge current, the discharge rate is obtained from the internal resistance, and the remaining capacity is obtained from the discharge rate. Is a technique for obtaining the remaining capacity from a three-way map of the terminal voltage, the discharge current, and the remaining capacity.

However, the relationship between the terminal voltage of the battery, the discharge current and the remaining capacity greatly changes depending on the degree of deterioration of the battery and its temperature state. Simply by inputting the following, the obtained remaining capacity includes a large error. The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for calculating the remaining capacity of a battery that can calculate the remaining capacity with high accuracy.

[0005]

According to the method for calculating the remaining capacity of a battery according to the present invention, a large number of pairs of a discharge current value and a terminal voltage value of a battery measured during a certain measurement period are obtained. A voltage-current relational expression V = Vo-RI is statistically obtained by linear regression analysis, and a predetermined reference terminal voltage value Vc or a predetermined reference discharge current value Ic is substituted into this expression,
A reference discharge current value Ic when the terminal voltage V is a predetermined reference terminal voltage value Vc, or a reference terminal voltage value Vc when the discharge current I is the reference discharge current value Ic, is calculated. Since the available output reference power Pc is calculated from the product of Vc and the reference discharge current value I, and the remaining capacity is estimated based on the decrease ΔPc of the available output power Pc, the remaining capacity can be estimated with high accuracy. .

According to the method for calculating the remaining capacity of a battery according to the second aspect of the present invention, a number of pairs of the discharge current value and the terminal voltage value of the battery measured within a certain measurement period are statistically analyzed by linear regression analysis. The voltage-current relational expression V = Vo-R.
I is determined, and a predetermined reference terminal voltage value Vc or a predetermined reference discharge current value Ic is substituted into this equation to obtain a reference discharge current value I when the terminal voltage V is the predetermined reference terminal voltage value Vc.
c or a reference terminal voltage value Vc when the discharge current I is the reference discharge current value Ic, and an outputable reference power Pc is calculated from a product of the reference terminal voltage value Vc and the reference discharge current value Ic. , The amount of decrease ΔPc in the outputable reference power Pc
, The warning is output by estimating the shortage of the remaining capacity, so that the shortage of the remaining capacity can be warned with high accuracy.

The effects of the above two inventions will be described in more detail below. First, for example, in a battery for supplying power for driving a vehicle, the discharge current I and the terminal voltage V frequently fluctuate due to frequent changes in load current. If the discharge current I fluctuates, the electrochemical reaction speed inside the battery, that is, the battery reaction speed varies, and this is reflected in the internal resistance R of the battery.
= Vo−R · I, the terminal voltage V, the initial voltage value Vo, and the discharge current I are input to determine the internal resistance R. However, the determined internal resistance R is the current value, its recent change history, and surrounding conditions. For example, when the remaining capacity is estimated from the internal resistance, an error increases.

On the other hand, in the present invention, a large number of pairs of the terminal voltage V and the discharge current I are sampled, and the relationship between the current terminal voltage V and the discharge current I of the battery is determined based on the linear regression equation. Since the determination is made and the remaining capacity is calculated or the remaining capacity is detected based on the determined value, it is possible to prevent the above-described variation in the internal resistance specific to the battery from being reflected in the remaining capacity estimation. A much more accurate estimation of the remaining capacity is now possible.

Next, according to the present invention, the output possible reference at that time is obtained from a relational expression between the terminal voltage V of the battery and the discharge current I at a certain time statistically obtained by the above method using the least square method or the like. The power Pc is calculated, similarly, the outputable reference power Pc ′ at different time points is calculated, and the remaining capacity is estimated based on the relationship between the difference Pc−Pc ′ and the discharge amount ΔAh between these time points. Since the remaining capacity is determined to be insufficient, the remaining capacity can be estimated and the remaining capacity can be determined with high accuracy. This will be described in more detail with reference to examples.

According to a third aspect of the present invention, in the battery remaining capacity shortage warning output method according to the second aspect, the battery remaining capacity detected by the integration of the discharge current is reduced to a predetermined rate or less. Since the output of the capacity shortage alarm is prohibited, it is possible to prevent a sudden drop in the reference output power Pc at the beginning of the battery discharge from being mistaken for a sudden drop in the reference output power Pc at the end of the battery discharge, and to issue an alarm. can do.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the following examples using a nickel-metal hydride battery. However, 2 regarding the remaining capacity estimation of the present invention.
The two methods can be applied to batteries other than nickel-metal hydride batteries.

[0012]

The preferred embodiments of the present invention will be described in detail in the following examples. FIG. 1 is an equivalent circuit diagram showing a power supply circuit for an electric vehicle, wherein 1 is a battery, 2 is a current sensor for detecting its charging / discharging current, 3 is a running motor, and 4 is a decompression D.
A constant-voltage power supply device 5 including a C / DC converter is a controller having a microcomputer configuration supplied with a power supply voltage from the constant-voltage power supply device 4.

A method of calculating the remaining capacity of the battery 1 and outputting a low-capacity warning by the controller 5 will be described with reference to the flowchart of FIG. First, the power is turned on and reset (S100), and the remaining capacity is calculated by current integration (S102 to S106). More specifically, the charging / discharging current I is read every predetermined time (for example, one second) specified in S104 (S102), and the capacitance change amount ΔAh, which is the product of the detected charging / discharging current I and the above-mentioned predetermined time, is calculated. The remaining capacity Ahr is calculated by adding / subtracting the remaining capacity Ah (S106).

The remaining capacity obtained by the current integration is as follows:
For example, the initial capacity is set to a predetermined value at the time of full charge, but can be periodically corrected to a value determined by another remaining capacity measurement method. Therefore, the description is omitted. The calculation of the remaining capacity by the current integration is performed until the remaining capacity Ahr decreases to 50% or less of the full capacity, that is, the full charge capacity.

When it is detected that the state of charge Ahr has dropped to 50% or less of the full charge capacity stored in advance (S10).
8), the remaining capacity determination routine based on the decrease amount ΔPc of the outputable reference power Pc (S110 to S110), which is a feature of this embodiment.
S122) is executed. Hereinafter, the remaining capacity determination routine will be described with reference to the flowcharts of FIGS.

First, the terminal voltage V and the charge / discharge current I are read (S110), and it is checked whether or not the charge / discharge current I is a charge current (S112). 0 (S111), and S1
Return to 10, if the discharge current, discharge amount integrated value Σ
Ah, the product of the discharge current I × the predetermined time t is added (S11
4) It is checked whether the integrated discharge amount 量 Ah is 1 Ah or more (S116), and if not, the predetermined time t '
And then returns to S110. By waiting for the predetermined time t 'in S118, the reading of the terminal voltage V and the discharge current I in S110, and the integration of the discharge amount integrated value ΣAh in S114 are executed every predetermined time t.

The predetermined time t is equal to the integrated discharge amount 積 算
By the time Ah becomes 1 Ah, the terminal voltage V and the discharge current I are set to values at which the terminal voltage V and the discharge current I can be read at least three times even in the maximum discharge current state. In S116, the discharge amount integrated value ΣAh is 1
If Ah or more, the output available reference power Pc is calculated based on the data of the terminal voltage V and the discharge current I read in S110 (S120).

The method of calculating the outputable reference power Pc will be further described. During the measurement period defined as the period from when the previous outputable reference power Pc was calculated or after the last state of charge was completed to when the discharge amount integrated value ΣAh reached 1 Ah, the number of samples sampled in S110 Is introduced into a first-order regression analysis subroutine (not shown), and a relational expression V = Vo−R · I, which is a linear model, is determined using the least squares method. The terminal voltage V and the discharge current I are variables, and the open terminal voltage Vo and the battery resistance R are constants. To determine the above relational expression means that the open terminal voltage value Vo and the battery resistance value R, which are constants, are calculated. It is to be.

Next, a predetermined reference terminal voltage value Vc (for example, 100 V) is substituted for the obtained variable V in the above equation, a reference discharge current value Ic at that time is calculated, and Vc and Ic are integrated and output. The possible reference power Pc is calculated. Therefore, the outputable reference power Pc indicates the power that the battery can output at the present time. Next, a decrease ΔPc in the outputable reference power Pc is calculated by subtracting the previous value of the outputable reference power Pc calculated in the previous step S120 from the previous value of the outputable reference power Pc calculated in the step S120. (S122). Although not shown in the flowchart of FIG. 2, the previous value is 0 for the first time after the execution of the routine, and in this case, the decrease amount Δ which is the subtraction result is used.
Since Pc is negative, in this case, S122 to S11
Return to 0.

Next, the calculated decrease amount ΔPc of the outputable reference power Pc and the predetermined threshold value ΔPc stored in advance
is compared with the threshold value th (S124). If the decrease amount ΔPc exceeds the threshold value ΔPcth, a warning is issued as a judgment that the remaining capacity is insufficient (S126). Otherwise, the discharge amount integrated value ΣAh is reset to 0. Then (S128), the process proceeds to S130.

In step S130, the remaining amount is obtained by substituting the amount of reduction .DELTA.Pc calculated in step S122 into a table in which the relationship between the amount of decrease .DELTA.Pc of the outputable reference power Pc and the remaining capacity is stored in advance. Returning, the routine for calculating the remaining capacity shortage alarm output and the remaining capacity calculation described above is repeatedly executed. Hereinafter, the function and effect that can be realized by the control routine will be described.

FIG. 4 shows a change in the terminal voltage V during normal running of the electric vehicle, and FIG. 5 shows a change in the charge / discharge current I at that time. As can be seen from these figures, the terminal voltage V and the charge / discharge current I of the battery 1 of the electric vehicle fluctuate very frequently with time. This problem becomes more remarkable because the battery 1 is frequently charged. Such a terminal voltage V
Since the fluctuation of the discharge current I causes the fluctuation of the battery reaction environment, the internal resistance of the battery is affected by the recent fluctuation history. Cause significant fluctuations. Therefore, when the respective data input in S110 are plotted in a two-dimensional coordinate space using the terminal voltage V and the discharge current I as coordinate axes, they are not aligned in a straight line, but are, for example, shown in FIG.
Disperse as exemplified in

Therefore, in the present embodiment, the relational expression V = Vo−R · I shown by the characteristic line L in FIG. 6 is obtained by executing a linear regression analysis in step S120. The gradient of the characteristic line L in FIG. This makes it possible to calculate the internal resistance very accurately even in a battery such as a battery for supplying running energy of an electric vehicle, which has a drastic load variation and which also supports regenerative charging. it can.

Further, in this embodiment, the above relational expression V = Vo
By substituting the reference terminal voltage Vc for −R · I,
A reference discharge current I is obtained, and an outputable reference power P defined as a product of the reference terminal voltage Vc and the reference discharge current I
c, and the amount of decrease Δ in the calculated outputable reference power Pc
The remaining capacity Ahr of the battery 1 is estimated from Pc.

As another modified example, the relational expression V =
By substituting the reference discharge current Ic for Vo−R · I, the reference terminal voltage Vc is obtained, and the outputtable reference power Pc is calculated as the product of the reference terminal voltage Vc and the reference discharge current I. This is quite equivalent to calculating the outputtable reference power Pc by substituting the reference terminal voltage Vc into the relational expression V = Vo-RI.

FIG. 7 shows the relationship between the outputable reference power Pc and the depth of discharge DOD of the new battery and the deteriorated battery, and FIG. 8 shows the relationship between the outputable reference power Pc of the battery and the depth of discharge DOD at each temperature. Show. From these characteristic diagrams, it can be considered that the above-described characteristics of the battery 1 are substantially parallel-shifted in the direction in which the outputable reference power Pc fluctuates depending on the degree of deterioration or the temperature state. Therefore, it can be seen that the relationship between the amount of decrease ΔPc in the outputable reference power Pc and the depth of discharge DOD of the battery 1 can be regarded as substantially constant regardless of the degree of deterioration or the temperature state. The depth of discharge DOD is the ratio of the discharge capacity to the full charge capacity, and the remaining capacity A
Since hr is a value obtained by subtracting the discharge capacity from the full charge capacity, it can be seen that the residual capacity Ahr and the decrease ΔPc of the outputable reference power Pc have a fixed relationship.

Therefore, as in the present embodiment, the relationship between the reduction amount ΔPc of the outputable reference power Pc and the remaining capacity Ahr is stored in advance as a table, and the calculated reduction of the outputable reference power Pc is stored. It can be seen that, by substituting the amount ΔPc, the remaining capacity Ahr of the battery can be estimated with high accuracy regardless of battery deterioration or battery temperature.

As can be seen from FIGS. 7 and 8, at the end of discharge, the decrease ΔPc per unit change in the depth of discharge DOD (remaining capacity Ahr) sharply increases. Therefore, by detecting that the amount of decrease ΔPc has exceeded a predetermined value, it is possible to accurately warn of the shortage of the remaining capacity of the battery. Furthermore, as can be seen from FIGS. 7 and 8, even at the beginning of the discharge, the decrease ΔPc per unit change in the depth of discharge DOD (remaining capacity Ahr) increases sharply.

Therefore, in the present embodiment, until the discharge has advanced to some extent (here, 50%), an alarm is not executed for the remaining capacity shortage using the above-mentioned decrease ΔPc of the outputable reference power Pc. Thereby, a false alarm can be prevented. (Modification) In the above embodiment, the sampling in S110 is performed continuously during the measurement period in which the discharge is continuous, but can be performed in the measurement period including the charge state period. However, data during charging is not used. Therefore,
In this case, the measurement period is extended by the amount of charge, and more data is sampled.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram showing a power supply circuit for an electric vehicle used in an embodiment.

FIG. 2 is a flowchart showing a method of calculating a remaining capacity of a controller 5 of FIG.

FIG. 3 is a flowchart showing a method of calculating a remaining capacity of a controller 5 of FIG. 1 and outputting a remaining capacity shortage alarm.

FIG. 4 is a timing chart showing a change in terminal voltage V during general running of an electric vehicle.

FIG. 5 is a timing chart showing a change in charge / discharge current I during a general running of the electric vehicle.

FIG. 6 shows each data input in S110 shown in FIG.
The relational expression V = Vo-R obtained by the linear regression analysis
It is a figure showing an example with I.

FIG. 7 is a characteristic diagram showing a relationship between an outputable reference power Pc and a depth of discharge DOD in a new battery and a deteriorated battery.

FIG. 8 is a characteristic diagram showing a relationship between a battery outputable reference power Pc and a depth of discharge DOD at each temperature.

[Explanation of symbols]

 1 is a battery, 5 is a controller

Claims (3)

[Claims] 1. A discharge current measurement value and a terminal voltage measurement value of a battery are detected at every n (n is an integer of 3 or more) measurement time points within a predetermined measurement period, and each of the discharge current measurement value and the terminal voltage is detected. Based on the measured values, the terminal voltage V as a variable and the open terminal voltage V as a constant
o, a relational expression V = Vo−R · I between a discharge current I as a variable and a battery resistance R as a constant is determined using a regression analysis method, and the terminal voltage V is a predetermined reference terminal voltage value Vc. The reference discharge current value Ic, or the reference discharge current value Ic when the terminal voltage V is a predetermined reference terminal voltage value Vc.
Is calculated, and the output possible reference power Pc defined as the product of the Vc and Ic is calculated. The output possible reference power Pc is sequentially calculated for each predetermined discharge amount ΔAh. Based on the reference discharge amount Δ
Amount of decrease ΔPc in outputable reference power Pc per Ah
Calculating the relationship between the amount of decrease ΔPc and the remaining capacity in advance, and calculating the remaining capacity based on the calculated amount of decrease ΔPc and the relationship. , 2. A discharge current measurement value and a terminal voltage measurement value of a battery are detected at each of n (n is an integer of 3 or more) measurement points within a predetermined measurement period, and each of the discharge current measurement value and the terminal voltage is detected. Based on the measured values, the terminal voltage V as a variable and the open terminal voltage V as a constant
o, a relational expression V = Vo−R · I between a discharge current I as a variable and a battery resistance R as a constant is determined using a regression analysis method, and the terminal voltage V is a predetermined reference terminal voltage value Vc. The reference discharge current value Ic, or the reference discharge current value Ic when the terminal voltage V is a predetermined reference terminal voltage value Vc.
Is calculated, and an outputable reference power Pc defined as a product of the Vc and Ic is calculated. The outputable reference power Pc is sequentially calculated for each predetermined discharge amount ΔAh. Based on the reference discharge amount Δ
Amount of decrease ΔPc in outputable reference power Pc per Ah
And outputting an insufficient battery warning when the amount of decrease ΔPc exceeds a predetermined threshold value stored in advance. 3. The battery output method according to claim 2, wherein the output of the alarm is inhibited until the remaining capacity detected by integrating the discharge current of the battery reaches a predetermined ratio or less. Characteristic low battery capacity warning output method.