JP2000258513A - Method for calculating soc of secondary battery for electric automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for calculating SOC of secondary battery for electric automobile by which the charged-state SOC of a secondary battery can be calculated with accuracy. SOLUTION: The internal resistance (r) of a secondary battery 6 is calculated from a formula, r=r0.A2/A1, where the r0, A1, and A2 respectively represent a prescribed resistance value, a first resistance ratio based on the temperature T of the battery 6, and a second resistance ratio based on a prescribed standard charged state. Then the open-circuit voltage E of the battery 6 is calculated by using a formula, F=V+I.r, where the r, I, and V respectively represent the calculated internal resistance and the current and voltage of the battery 6. Thereafter, the SOC of the battery 6 is calculated from the open-circuit voltage E and the correlation between the voltage E and SOC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery SO for an electric vehicle used for an electric vehicle including a hybrid vehicle.
Related to C calculation method.

[0002]

2. Description of the Related Art In electric vehicles including hybrid vehicles, nickel-metal hydride batteries and lithium ion batteries are used as secondary batteries for driving motors. One of the quantities representing the state of charge of the secondary battery is an SOC (state of charge). A fully charged state is represented by SOC = 100%, and a state of zero charge is represented by SOC = 0%. In the above-mentioned nickel-metal hydride battery and lithium-ion battery, the open-circuit voltage Eo is independent of the battery temperature.
Has a predetermined correlation between the open circuit voltage Eo and the SOC.
Has a one-to-one correspondence. Therefore, the open circuit voltage Eo of the battery is estimated by measurement or calculation, and Eo−SO
The SOC corresponding to the open circuit voltage Eo can be obtained from the C correlation. In general, the open-circuit voltage E during charge / discharge is estimated from the following equation (5) from the total battery voltage V during charge / discharge, the load current I, and the internal resistance r of the battery.

E = V + I · r (5)

[0003]

Conventionally, when the open-circuit voltage E is calculated by using the equation (5), a constant set value r0 as the internal resistance r, for example, SOC = 100%, and the battery temperature 20
The calculation is made using the internal resistance at a temperature of ° C. However, since the internal resistance r depends on the battery temperature and the SOC at that time, an error occurs between the open-circuit voltage E calculated using the fixed set value r0 and the actual open-circuit voltage Eo, and the open-circuit voltage E There is a drawback that the SOC calculation accuracy is reduced by the error.

An object of the present invention is to provide an SOC calculation method for a secondary battery for an electric vehicle, which can accurately calculate a state of charge SOC.

[0005]

An embodiment of the present invention will be described with reference to FIG. According to the first aspect of the present invention, there is provided a vehicle for an electric vehicle, which calculates a state of charge of a battery from an open-circuit voltage of a battery by using an open-circuit voltage-to-SOC correlation indicating a correlation between an open-circuit voltage of a battery and an SOC indicating the state of charge of the battery. The battery open voltage E is applied to the SOC calculation method of the next battery, and (a) a first resistance ratio A1 based on the battery temperature T, a predetermined resistance value r0 given in advance for the battery 6, and a given reference charge state From the second resistance ratio A2 based on
The above-mentioned object is achieved by calculating from the battery internal resistance r calculated by the following equation (b) and (b) the current I and the voltage V of the battery 6 at the time of charging / discharging by the equation (7). As the reference state of charge, a state of charge calculated in the past from the state of charge calculation, a measured open circuit voltage, and the like are used.

R = r0 · A2 / A1 (6) E = V + I · r (7) According to the invention of claim 2, the open-circuit voltage indicating the correlation between the battery open-circuit voltage and the SOC indicating the state of charge of the battery 6. The present invention is applied to an SOC calculation method for an electric vehicle secondary battery that calculates the state of charge of the battery 6 from the battery open-circuit voltage using the SOC-correlation, and includes the battery temperature T, the battery voltage V during charging and discharging, and the current I. , A second step of calculating a first resistance ratio A1 depending on the battery temperature based on the battery temperature T detected in the first step, and a second step of calculating the first resistance ratio A1 depending on the state of charge of the battery 6. Second resistance ratio
The third step of calculating A2 based on a given reference state of charge, the reference resistance value r0 of the battery 6, the first resistance ratio A1 calculated in the second step, and the third step The fourth calculation of the battery internal resistance r from the second resistance ratio A2 according to equation (8)
Process and

R = r0 · A2 / A1 (8) a fifth step of calculating the battery open-circuit voltage E from the voltage V, the current I, and the battery internal resistance r according to the equation (9);

E = V + I · r (9) A sixth step of calculating the state of charge of the battery 6 from the battery open-circuit voltage E calculated in the fifth step and the correlation between the open-circuit voltage and the SOC, and a sixth step And a seventh step of setting the state of charge calculated in the above to a reference state of charge, and the above-described object is achieved by repeating a series of steps from the third step to the seventh step a plurality of times. As the reference state of charge, a state of charge calculated in the past from the time of calculation of the state of charge, a measured open circuit voltage, and the like are used.

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 in order to make the present invention easier to understand. However, the present invention is not limited to the embodiment.

[0007]

According to the present invention, the battery internal resistance r used for calculating the battery open-circuit voltage E is set to a predetermined resistance value r0, a first resistance ratio A1 based on the battery temperature, and a second resistance ratio A1 based on the reference state of charge. Since the battery state is calculated from the resistance ratio A2, the battery internal resistance r reflecting the battery state more accurately is calculated, and the accuracy of the state of charge SOC calculated from the battery open-circuit voltage and the open-circuit voltage-SOC correlation is improved. be able to. In particular, in the second aspect of the present invention, the second resistance ratio A2 is calculated based on the calculated state of charge SOC, and the calculation processing of calculating the state of charge SOC again using the second resistance ratio A2 is performed a plurality of times. Since the repetition is performed, a more accurate state of charge SOC can be calculated.

[0008]

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 showing a configuration of a parallel hybrid vehicle. The rotor of the electric motor 3 is directly connected to the main shaft of the engine 2, and the driving force of the engine 2 and / or the motor 3 is transmitted to the axle 1 via the drive system 4. The motor 3 is driven by a secondary battery 6. At this time, the secondary battery 6 is
Is converted to AC power.

The driving modes of the motor 3 in the parallel hybrid vehicle include a driving mode for driving the axle 1 and a power generation mode for charging the secondary battery 6. When the secondary battery 6 that supplies power to the motor 3 is in a sufficiently charged state in the drive mode of the vehicle itself, that is, when accelerating, traveling on a flat road, or climbing a hill, the motor 3 is operated in the drive mode. Then, the vehicle travels with the driving force of both the engine 2 and the motor 3.
However, when the state of charge of the secondary battery 6 is low, the motor 3
Is operated in the power generation mode, the vehicle runs with the driving force of the engine 2, rotates the rotor of the motor 3 with the driving force of the engine 2, generates power by the motor 3, and charges the secondary battery 6. In the power generation mode, the inverter 5 converts AC power from the motor 3 into DC power and supplies the DC power to the secondary battery 6.

On the other hand, in the vehicle braking mode, that is, during deceleration or downhill, the engine 2 and the motor 3 are driven by the rotational force of the wheels via the drive system 4. At this time, the motor 3 is operated in the power generation mode to absorb the regenerative energy and charge the secondary battery 6. 7 calculates the SOC of the secondary battery 6 based on the terminal voltage V, the charging / discharging current I, the battery temperature T, and the like detected by the voltage sensor 8, the current sensor 9, and the temperature sensor 10;
It is a battery controller that performs output control, regenerative control, etc., and has a CPU, RAM, ROM, etc. A main controller 11 performs overall control of the engine 2, motor 3, battery controller 7, and the like.

FIG. 2 is a diagram showing an example of the correlation between the open-circuit voltage Eo of the secondary battery 6 and the SOC. If the open-circuit voltage E 'of the battery 6 is known as shown in FIG. SO
C 'can be obtained. The Eo-SOC correlation is stored in the battery controller 7 in the form of a correlation equation in advance. As described above, the open circuit voltage E during charging and discharging is calculated using the following equation (10).

E = V + I · r (10) In equation (10), V is the total voltage under load, I is the load current, r is the internal resistance of the battery, and V and I are the voltage sensor 8 of FIG. And the current sensor 9.

FIG. 3 is a graph showing the characteristics of the internal resistance r of the battery. The vertical axis represents the internal resistance r, and the horizontal axis represents the DOD (depth of discha).
rge). DOD = 0% is SOC = 10
Corresponding to 0%, DOD = 100% corresponds to SOC = 0%.
In FIG. 3, L (0) indicates the internal resistance characteristics when the battery temperature T = 0 ° C., and L (20) and L (40) indicate T = 20 ° C. and T = 20 ° C.
The graph shows the internal resistance characteristics at 40 ° C. As can be seen from FIG. 3, the characteristics L (0), L (20), and L (40) can be regarded as straight lines parallel to each other except for a region where the DOD at the end of discharge is large.

Therefore, in the present embodiment, the internal resistance r is calculated using the following equation (11).

R = r0 · A2 / A1 (11) where r0 is the initial set value of the internal resistance, and the battery temperature T
= 20 ° C, SOC = 100%. Also,
A1 is the internal resistance ratio of the battery depending on the battery temperature T, and A2 is the
This is the battery internal resistance ratio depending on the SOC.
(B) shows an example of A1 and A2. Note that A1 and A2 relating to the secondary battery 6 are previously input to the battery controller 7 (FIG. 1) as a table as shown in Table 1. Equation (11)
According to the formula, when the battery temperature is 20 ° C and the SOC = 100%, A1 =
Since A2 = 1, r = r0. For example, when the battery temperature is 30
When SOC = 80% at ° C., A1 = 0.9 and A2 = 1.10, so r1.22 · r0.

[Table 1]

Next, the procedure of the SOC calculation performed by the battery controller 7 will be described. —SOC Calculation Example 1— A first example of the SOC calculation will be described with reference to the flowchart shown in FIG. This flowchart is started by turning on the vehicle power supply and starting up the vehicle.
Proceed to 1. In step S1, the voltage at the time of the load current I = 0 immediately after the vehicle power is turned on, that is, the open voltage E0 of the battery 6 in FIG. In step S2,
From the Eo-SOC correlation shown in FIG. 2, the SOC at the time of starting the vehicle (hereinafter referred to as SOC1) corresponding to the open circuit voltage E0 obtained in step S1 is calculated, and this SOC1 is provided in a memory (not shown) in the battery controller 7. Is stored in the specified memory area M1. In the following step S3, the battery temperature T, voltage V, and current I are read.

Step S4 is a step of performing the SOC calculation, and the detailed procedure is shown in the flowchart of FIG. FIG.
In step S41, the internal resistance ratio A1 (T) corresponding to the battery temperature T and the SOC1 of the memory area M1 are corresponded using the internal resistance ratio A1 table and the internal resistance ratio A2 table stored in the battery controller 7 in advance. A2 (SOC1)
Is calculated. In step S42, an internal resistance r is calculated from the internal resistance ratios A1 (T) and A2 (SOC1) calculated in step S41 and the above-described initial set value r0 using equation (11). In step S43, the open-circuit voltage E is calculated from the voltage V, the current I, and the internal resistance r calculated in step S42 using Expression (10). Next, in step S44, Eo-S
When the SOC2 corresponding to the open circuit voltage E obtained in step S42 is calculated from the OC correlation and stored in the memory area M2 of the battery controller 7, the SOC calculation routine of FIG. 5 ends, and the process proceeds to step S5 of FIG.

Step S5 in FIG. 4 is a step for judging whether or not an instruction to turn off the vehicle power has been received. If YES, a series of processes relating to the SOC calculation is ended. On the other hand, if NO is determined in step S5, the process proceeds to step S5.
Proceeding to 6, the SOC2 of the memory area M2 is stored as a new SOC1 in the memory area M1. Thereafter, the process proceeds to step S3, and the process from step S3 to step S5 is repeated until an instruction to turn off the vehicle power is received. In this way, the SOCs after startup are calculated one after another, and the SOC 1 in the memory area M 1 is used as the SOC of the battery 6.

-SOC Calculation Example 2 In the above-described SOC calculation method, the internal resistance ratio A2 (SOC1) when calculating the internal resistance r is based not on the SOC2 at the time of calculation but on the SOC1 obtained before. is there. Therefore, the calculated SOC2 does not accurately reflect the battery state at the time of calculation, and includes an error due to the internal resistance ratio A2 (SOC1). Therefore, SOC that minimizes the effects of such errors
The calculation method will be described with reference to the flowchart in FIG.

In FIG. 6, steps S1 to S
The processes up to 4 are the same as steps S1 to S4 of the flowchart in FIG. If SOC2 is calculated in step S4, step S4
It is determined whether or not an instruction to turn off the vehicle power has been received at 10; if YES, a series of processes related to the SOC calculation is terminated,
If NO, proceed to step S11. In step S11, the magnitude | SOC2−SOC1 | of the difference between SOC2 stored in the memory area M2 and SOC1 stored in the memory area M1 is equal to the set value Δ
This is a step of determining whether or not it is equal to or less than S. If YES, the process proceeds to step S14, and if NO, the process proceeds to step S12. || represents an absolute value symbol.

By the way, at present (during step S11)
Is the SOC2 of the memory area M2, and the SOC1 stored in the memory area M1 is the SOC calculated one time before the SOC2. Here, the internal resistance ratio A2 (SOC1) used for calculating SOC2 is calculated based on SOC1 calculated last time. Therefore, if the SOC has not changed since the SOC1 calculation, for example, the SOC1
If SOC2 is calculated before the vehicle starts traveling in SOC, SOC2 should be SOC1.Therefore, the internal resistance ratio A2 (SOC1) used for SOC2 calculation is based on SOC1, but A2 ( SOC1) = A2 (SOC2).

That is, if the SOC has not changed, the calculated values SOC1 and SOC2 satisfy SOC2 = SOC1 and the process proceeds to step S2.
The process proceeds from step 11 to step S14. And step S
If the value of the memory area M1 is rewritten to the value of SOC2 of the memory area M2 and stored as SOC1 in step 14,
Returning to step 3, the SOC at the next timing is calculated.

On the other hand, if the SOC at the time of calculating SOS2 is different from SOC1, the calculated SOC2 is SOC2 ≠ SOC1.
Also, since SOS2 is calculated using the internal resistance ratio A2 (SOC1), SOS22SOC2 'also holds for the true value SOC2'. Here, SOS2 becomes a value closer to SOC2 'than SOC1, so that A2 (SOC2) is used instead of the internal resistance ratio A2 (SOC1).
If C is calculated, the true value SOC2 ′ is even more than SOS2 described above.
Can be calculated.

Therefore, if NO is determined in the step S11, the process proceeds to a step S12, in which the SOC1 of the memory area M1 is changed.
Is rewritten to the value of SOC2, and in the next step S13, the SOC calculation is performed using the rewritten SOC1. Note that the SOC calculation in step S13 is the same as the calculation in step S4, and a description thereof will be omitted. If SOC2 is calculated in step S13, the process returns to step S11, and the calculated SOC2 is | SOC2
It is determined whether or not −SOC1 | ≦ ΔS. Then, the processing from step S11 to step S13 is repeated until SOC2 satisfies | SOC2−SOC1 | ≦ ΔS in step S11 and proceeds to step S14.

As described above, steps S11 to S
When the processing up to 13 is repeatedly performed, the calculated SOC2 asymptotically approaches the true value SOC2 ′, and | SOC2−SOC1 | gradually decreases. Therefore, the reference value ΔS at the end of the repetitive processing is set so as to obtain an SOC with a predetermined accuracy, and | SOC2
If −SOC1 ≦ ΔS, the process proceeds to step S14 to rewrite the value of the memory area M1 to the value of SOC2, and then returns to step S3 to calculate the SOC at the next timing.

By repeating the processing from step S3 until the vehicle power is turned off, the SOC
Are calculated one after another. It is stored in the memory area M1.
SOC1 is used as the SOC indicating the battery state. In this calculation example 2, S is calculated until SOC2 satisfies | SOC2−SOC1 | ≦ ΔS.
Calculation example 1 because OC2 is calculated repeatedly
As a result, an SOC with higher accuracy can be obtained.

-SOC Calculation Example 3-In the above-described SOC calculation example 2, when the SOC changes, | SO
The SOC calculation was repeated until C2−SOC1 | became equal to or less than the set value ΔS. However, in the calculation example 3 shown in the flowchart of FIG. 7, the SOC calculation was performed a specified number of times (M times ) Repeatedly. In the flowchart of FIG. 7, steps having the same contents as in FIG. 6 are denoted by the same reference numerals as in FIG. The following description focuses on the differences from the flowchart of FIG.

Step S20 is a step for judging whether or not the calculated SOC2 is equal to the SOC1 of the memory area M1. If YES, the process proceeds to step S14 to proceed to the memory area M1.
After rewriting SOC1 of 1 to the value of SOC2, the process returns to step S3. If NO, that is, if the SOC has changed, the process proceeds to step S21. Next, if the variable N indicating the number of repetitions is set to 1 in step S21, the process proceeds to step S22, where SOC1 of the memory area M1 is rewritten to the value of SOC2. Step S23 is the same as step S4 in FIG.
This is the step of performing the SOC calculation as shown in FIG. 4. If SOC2 is calculated in step S23, the process proceeds to step S24. Step S24 is a step of judging whether or not the value of the variable N is equal to the prescribed number of repetitions M. If N <M, the process proceeds to step S25, and after increasing the value of the variable N by 1, returns to step S22. . Then, the variable N becomes N
The processing of steps S22 to S25 is repeated until M = M. Then, if N = M, the process proceeds from step S24 to step S14, where the SO of the memory area M1 is
After rewriting C1 to the value of SOC2, the process returns to step S3.

As described above, in the present embodiment, the internal resistance r of the battery 6 is calculated by using the internal resistance ratios A1 and A2 according to the equation (11).
, The internal resistance r reflecting the battery state can be calculated. Then, the open circuit voltage E is calculated by the equation (10) using the internal resistance r, and the SOC is calculated using the open circuit voltage E and the Eo-SOC correlation. Therefore, the SOC can be calculated with high accuracy. . Further, in the above-described SOC calculation examples 2 and 3, the calculated
Since the resistance ratio A2 is calculated based on the SOC2 and the SOC2 is repeatedly calculated while correcting the resistance ratio A2 in this manner, a more accurate SOC can be calculated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a parallel hybrid vehicle.

FIG. 2 is an Eo-SOC correlation diagram.

FIG. 3 is a battery internal resistance characteristic diagram.

FIG. 4 is a flowchart showing a procedure of SOC calculation in SOC calculation example 1;

FIG. 5 is a flowchart illustrating a calculation process in step S4 of the flowchart shown in FIG. 4;

FIG. 6 is a flowchart illustrating a procedure of an SOC calculation in SOC calculation example 2;

FIG. 7 is a flowchart illustrating a procedure of an SOC calculation in SOC calculation example 3;

[Explanation of symbols]

 6 Secondary battery 7 Battery controller 8 Voltage sensor 9 Current sensor 10 Temperature sensor A1, A2 Battery internal resistance ratio

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H02J 7/00 H02J 7/00 X F term (reference) 2G016 CA03 CB06 CB11 CB12 CB13 CB21 CB31 CC01 CC13 CC27 CC28 CD01 CD02 CD03 5G003 BA01 CA01 CA11 CB01 FA06 5H030 AA08 AA10 AS08 FF22 FF42 FF43 FF44 5H115 PG04 PI16 PI22 PI29 PO17 PU08 PU23 PU25 PV09 QE06 QE10 QI04 QN03 TI01 TI05 TI06 TI10

Claims (2)

[Claims] 1. SO representing the open-circuit voltage of a battery and the state of charge of the battery
A SOC calculation method for a secondary battery for an electric vehicle, which calculates a state of charge of a battery from an open-circuit voltage of a battery using an open-circuit voltage versus SOC correlation indicating a correlation with C. A battery internal resistance calculated by equation (1) from a predetermined resistance value r0 given in advance for the battery, a first resistance ratio A1 based on the battery temperature, and a second resistance ratio A2 based on a given reference state of charge. r and
(B) An SOC calculation method for a secondary battery for an electric vehicle, wherein the SOC is calculated from the current I and the voltage V of the battery at the time of charge / discharge by Expression (2). R = r0 · A2 / A1 (1) E = V + I · r (2) 2. SO representing the open-circuit voltage of the battery and the state of charge of the battery.
In an SOC calculation method for a secondary battery for an electric vehicle, which calculates a state of charge of a battery from an open-circuit voltage of a battery using an open-circuit voltage vs. SOC correlation indicating a correlation with C, the battery temperature and the battery voltage V during charging and discharging A second step of calculating a first resistance ratio A1 dependent on the battery temperature based on the battery temperature detected in the first step; and charging the battery. A third step of calculating a second resistance ratio A2 depending on the state based on a given reference state of charge; and a reference resistance value r0 of the battery, the first step calculated in the second step.
A fourth step of calculating the battery internal resistance r from equation (3) from the resistance ratio A1 of the above and the second resistance ratio A2 calculated in the third step; and r = r0 · A2 / A1 (3) a fifth step of calculating a battery open-circuit voltage E from the voltage V, the current I, and the battery internal resistance r according to the equation (4), and E = V + I · r (4) Calculating the state of charge of the battery from the battery open circuit voltage E calculated in the fifth step and the open circuit voltage versus SOC correlation;
And a seventh step of setting the state of charge calculated in the sixth step to the reference state of charge, wherein a plurality of series of steps from the third step to the seventh step are performed. A SOC calculation method for a secondary battery for an electric vehicle, wherein the SOC calculation is performed repeatedly.