JP3391206B2 - Method for estimating initial value of regenerable power - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a regenerable power initial value in an electric vehicle such as an electric vehicle.

[0002]

2. Description of the Related Art In an electric vehicle such as an electric vehicle, a method of using the maximum regenerative power of the vehicle as an example of a method of setting an initial value of regenerative power for regenerative charging when the vehicle restarts after key-off during discharging. Can be given. At this time,
The regenerative electric power is regeneratively controlled so as to be equal to or less than the maximum regenerative electric power, but in that case, the regenerative electric power may become larger than the electric power that can be actually received by the regenerative electric power and may cause an overvoltage. In order to avoid such an overvoltage, there is a method of setting the regenerable power initial value based on the room temperature initial characteristics of the battery stored in the ROM of the charge control circuit. That is, the regenerative received power equivalent to full charge at the beginning of room temperature is corrected in consideration of the temperature and deterioration of the battery and the variation of each single cell constituting the battery, and the corrected value (the estimated received power at full charge is calculated). ) Is always used as the regenerable power initial value P0 regardless of the discharge depth of the battery.

FIG. 6 is a diagram for explaining the regenerative power initial value P0 calculated by the conventional method, in which the horizontal axis represents the discharge power amount (Wh) and the vertical axis represents the regenerative received power (kW). Figure 6
In, the curve L61 shows the room temperature initial characteristics of the battery, and P1 is the regenerative received power corresponding to the full charge at the room temperature initial. On the other hand, the curve L62 shows the actual battery characteristics (actual value of the regenerative received power) estimated in consideration of the temperature and deterioration of the battery, and P0 is the regenerative received power corresponding to the full charge. For example, the discharge power amount at the start of traveling is a (W
In the case of h), the regenerative power initial value is set to P0 (because it is set to P0 regardless of the depth of discharge) at the start of running, and is discharging after the start of running. Each time the power calculation based on the voltage and current is performed, the regenerable power is calculated, converges to the actual value (curve L62) along the curve as shown by the curve L63, and proper regenerative power can be obtained. .

[0004]

However, since the acceptable power value of the battery varies depending on the depth of discharge, the estimated acceptance value P0 at full charge is taken into consideration without considering the difference in acceptance depending on the depth of discharge as described above. In the method of always using the initial value, the initial value of the regenerable power after key-off during discharging becomes lower than the actual value. For this reason, it takes time to converge to the actual value after the start of traveling, and during that time, regenerative charging is controlled by regenerative power that is smaller than the power that can actually be accepted, so there is a problem that efficient regenerative charging cannot be performed. It was

An object of the present invention is to provide a method for estimating an initial value of regenerable power that can efficiently perform regenerative charging at the start of running after key-off in an electric vehicle such as an electric vehicle.

[0006]

(1) In the method for estimating the regenerative power initial value according to the invention of claim 1, the measured open circuit voltage of the electric vehicle battery is E, and the internal resistance reference value for the initial room temperature battery is R0. When the correction coefficient according to the battery state at the start of traveling is b and the upper limit voltage that is the initial value at the start of traveling of the receivable electric power in the regenerative charging control is Vh, traveling of the receivable electric power in the regenerative charging control is performed. The regenerative power initial value, which is the initial value at the start, is calculated by the following formula

(5) (Initial regenerative power value) = {Vh (Vh-E) / RO} b The above object is achieved by the calculation. (2) The invention of claim 2 is the method for estimating the regenerative power initial value according to claim 1, wherein the correction coefficient b is a temperature correction coefficient b1 indicating a change in internal resistance depending on the battery temperature, and deterioration of the battery. Deterioration correction coefficient b that represents the dependent internal resistance change
2 is used to calculate b = b1 · b2. (3) According to the invention of claim 3, in the method for estimating the regenerative power initial value according to claim 1, the correction coefficient b is a temperature correction coefficient b1 indicating a change in internal resistance depending on the battery temperature, and deterioration of the battery. Deterioration correction coefficient b that represents the dependent internal resistance change
2 and a variation correction coefficient b3 that corrects the variation of each single cell forming the battery, and is calculated by b = b1, b2, b3. (4) The invention according to claim 4 is the variation correction coefficient b3 in the method for estimating the regenerative power initial value according to claim 3.
Is the maximum value Rmax of the internal resistance of each single cell that constitutes the battery
And Rave the average value of the internal resistance of each unit cell, b
3 = Rmax / Rave

[0007]

(1) According to the inventions of claims 1 to 4, based on the measured open circuit voltage of the battery, the internal resistance reference value for the initial room temperature battery, and the correction coefficient according to the battery state at the start of running, In other words, since the regenerative power initial value is calculated based on the battery characteristics according to the depth of discharge at the start of travel, it is possible to obtain a highly accurate initial regenerative power value, and efficient regenerative charging from the start of travel. It can be carried out. (2) According to the inventions of claims 3 and 4, since the variation in the internal resistance of each single cell constituting the battery is corrected by the variation correction coefficient b3, a more accurate regenerative possible power initial value is obtained. Can be calculated.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. FIG. 4 is a block diagram showing a configuration of a traveling drive mechanism of an electric vehicle to which the method for estimating the regenerative power initial value according to the present invention is applied. The battery 11 supplies DC power to the inverter 12, and the inverter 12 converts the DC power into AC power to generate running energy. During regeneration, the running energy of the vehicle is converted back into electric energy via the motor 13 and the inverter 12, the battery 11 is charged, and the vehicle is regeneratively braked. The voltage sensor 14 detects the voltage V across the battery 11, and the current sensor 15 detects the current I flowing through the battery 11. A temperature sensor 18 detects the temperature T of the battery 11. The current I is positive when flowing from the battery 11 to the inverter 12 when driving the motor, and is negative when flowing from the inverter 12 to the battery 11 during regenerative charging.

The controller 16 calculates the maximum discharge power and the maximum charge power of the battery 11 based on the voltage V, the current I and the temperature T detected by the voltage sensor 14, the current sensor 15 and the temperature sensor 18, and the calculation result. The output control and regenerative control of the inverter 12 are performed based on the above. Then, at the start of running after the key is turned off, the regenerative possible power initial value obtained by the estimation method to be described later is used as the value at the start of running of the regenerable power that is the power that can be accepted when performing regenerative charging. Performs regenerative control. The cell controller 17 controls charging / discharging of each of the unit cells 111 to 11n of the battery 11 and detects a terminal voltage (hereinafter, referred to as a cell voltage) vc of each of the unit cells 111 to 11n.

FIG. 1 is a diagram for explaining a method for estimating a regenerative power initial value. In FIG. 1, the vertical axis represents voltage and the horizontal axis represents current. The positive region of the current I indicates the discharge side, while the negative region indicates the charge side. First, the open circuit voltage E is measured before the start of travel, that is, when the motor is stopped. From the open circuit voltage E and the internal resistance R of the battery, the battery characteristic at the start of running is determined (straight line L1 in FIG. 1). Since the actual internal resistance cannot be known until after the start of running, the internal resistance reference value R0 stored in the ROM as the room temperature initial value was corrected for the temperature and deterioration according to the battery state. Estimates are used. Further, the open circuit voltage E is measured before turning on a heavy electric load such as a DC / DC converter in order to minimize the calculation error, as in the case of the pre-charge open circuit voltage check.

Next, the characteristic straight line L1 is extended to the charging side,
When the current at the intersection C between the straight line L1 and the regenerative upper limit voltage Vh is Ic, the following equation (1) is established.

## EQU6 ## Vh = E-Ic.multidot.R (1) Then, the regenerable power given by the following equation (2) is set as the regenerable power initial value at the start of traveling.

[Formula 7] Vh (Vh-E) / R (2) Note that the regenerative upper limit voltage Vh is set such that the upper limit voltage of the vehicle at the time of regenerative charging has a margin for an error in the calculation of the regenerative power initial value. It is a value.

In the above equation (2), the internal resistance R is R = bR0 using the internal resistance reference value R0 and the correction coefficient b.
Then, the initial value of the regenerable power is expressed by the following equation (3).

(Equation 8) (Regenerative power initial value) = {Vh (Vh−E) / R0} · b (3) The straight line L0 shown in FIG. 1 is a battery obtained from the internal resistance reference value R0 and the open circuit voltage E. The characteristic shows that the regenerative power at the intersection D with the regenerative upper limit voltage Vh is

## EQU9 ## Vh (Vh-E) / R0 (4) The straight line L1 is obtained by correcting the battery characteristic with the correction coefficient b.

The correction coefficient b is a temperature correction coefficient b1 that is a parameter that represents a change in internal resistance due to temperature, a deterioration correction coefficient b2 that is a parameter that is a parameter that represents a change in internal resistance due to deterioration of the battery, and each of the constituent elements of the battery 11. Using the variation correction coefficient b3 for correcting the variation of the single cell, b =
It is represented as b1, b2, and b3.

Here, the variation correction coefficient b3 is the ratio of the maximum internal resistance of the internal resistance of each single cell to the average internal resistance, and the calculation method will be outlined below. The internal resistance of each single cell forming the battery 11 varies due to a deterioration state and the like, and even if the same current flows, the cell voltages do not become the same. The open circuit voltage e of each unit cell
If 0 is within a predetermined discharge amount, the self controller 17
By equalizing the voltage variation due to, it is possible to make the values almost equal. Assuming that the internal resistance of a single cell exhibiting an average voltage drop is Rave and the internal resistance of the deteriorated cell having the largest voltage drop is Rmax, the average single cell with respect to the discharge current I has an open voltage e0 to I · Rave. The cell voltage drops by a certain amount, and in the deteriorated cell, the cell voltage drops by I · Rmax from the open voltage e0.

In any one of the n unit cells, the cell voltage vc becomes a predetermined voltage (for example, 3.4 V) or less,
The maximum internal resistance Rmax of the deteriorated single cell and the average internal resistance Ra of the single cell are calculated based on the total voltage Vt when the state continues for a predetermined time or more and the measured open circuit voltage E.
The ratio with ve is calculated and used as the variation correction coefficient b3.
For example, when the predetermined voltage is 3.4 V, the calculation is performed using the following equation (5).

[Equation 10]     b3 = Rmax / Rave = (I · Rmax) / (I · Rave)         = (E-3.4n) / (E-Vt) (5)

In the calculation of the regenerative power initial value described above, the calculation is performed on the assumption that the internal resistance has little dependency on the depth of discharge. For example, in a lithium ion battery, the depth of discharge is within a predetermined value (the depth of discharge is Almost 60%
If it is within), such a condition is satisfied. However, as shown in FIG. 2, which shows the relationship between the internal resistance and the depth of discharge, there is a high discharge depth region where an inflection point appears in the change of the internal resistance with respect to the depth of discharge, and a change of the internal resistance with respect to the progress of discharge such as a lead acid battery. In a large battery, the estimation error of the initial value of regenerable power increases as the depth of discharge increases. In FIG. 2, L21 indicates the temperature and the calculated value for the initial value before the deterioration correction, and L31 indicates the temperature and the calculated value when the deterioration is corrected. Low depth of discharge area (area Q in FIG. 2)
In 1), the calculated value almost represents the actual value, and in this area Q1, high accuracy can be guaranteed for the calculation of the internal resistance. On the other hand, as described above, in the high discharge depth region (region Q2 in FIG. 2), the calculated values L21 and L31 and the respective actual value L
A large deviation (calculation error) occurs between 22 and L32.

FIG. 3 is a diagram showing the relationship between the regenerative power initial value and the depth of discharge. Corresponding to L21 and L31 in FIG.
L41 is the calculated value for the initial value before temperature and deterioration correction,
51 indicates the calculated value at the time of deterioration. On the other hand, L42, L52
Indicates the initial value and the actual value at the time of deterioration. The region Q3 where the depth of discharge is small is a region corresponding to the region Q1 in which the internal resistance can be accurately guaranteed as shown in FIG. 2, and in this region Q3, the calculation accuracy of the regenerative power initial value is high. On the other hand, in the high discharge depth range, the accuracy of calculation of the regenerable power initial value is reduced due to the reason described above.

However, as shown in FIG. 3, both the calculated regenerative power initial value and the actual value are sufficiently larger than the maximum regenerative power of the vehicle in the high depth of discharge range, and the regenerative power initial value is low. It can be seen that it is sufficient to guarantee a high calculation accuracy only in the depth of discharge area (area Q3).

FIG. 5 is a diagram for explaining the regenerative power initial value estimated by the method according to the present embodiment and the conventional value, and is an enlarged view of the vicinity of point B in FIG. In FIG. 5, point C indicates the regenerative possible power initial value (value is P2) at the start of travel (discharged power amount a) calculated by the above-described method. As described above, according to the method for estimating the regenerable power initial value of the present embodiment, the correction coefficient for temperature, deterioration, etc. according to the open circuit voltage and the battery state at the start of running after key-off is used, Since the regenerative power initial value is calculated from the VI characteristic (that is, the idea of the power calculation method is applied) according to the depth of discharge of the battery shown in FIG. 1,
An accurate initial value of regenerable power can be obtained. That is, the value P2 is close to the actual value of the battery, and its error Δ
P is very small. Therefore, after traveling, the vehicle quickly converges to the curve L62 along the curve shown by L64, and regenerative charging can be efficiently performed from the start of traveling.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of a method for estimating a regenerable power initial value according to the present invention.

FIG. 2 is a diagram for explaining an estimation error of a regenerative power initial value, showing a relationship between an internal resistance and a depth of discharge.

FIG. 3 is a diagram for explaining an estimation error of a regenerable power initial value, showing a relationship between a regenerable power initial value and a discharge depth.

FIG. 4 is a block diagram showing a configuration of a traveling drive mechanism of the electric vehicle.

FIG. 5 is a diagram for explaining an initial value of regenerable power by the method of the present embodiment and an initial value of regenerable power by the conventional method.

FIG. 6 is a diagram for explaining a conventional initial value of regenerable power.

[Explanation of symbols]

11 batteries 13 motor 14 Voltage sensor 15 Current sensor 16 Battery controller 17 cell controller 18 Temperature sensor 111-11n single cell

Continuation of front page (51) Int.Cl. ⁷ identification code FI H02J 7/00 H02J 7/00 P (56) References JP-A-9-98508 (JP, A) JP-A-7-264709 (JP, A ) JP-A-5-284608 (JP, A) JP-A-6-105405 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60L 3/00 B60L 7/12 B60L 11 / 18 G01R 31/36 H01M 10/48 H02J 7/00

Claims (4)

(57) [Claims] 1. An actual open circuit voltage of an electric vehicle battery is set to E, an internal resistance reference value for an initial room temperature battery is set to R0,
When the correction coefficient according to the battery state at the start of travel is b and the upper limit voltage at the time of regenerative charging is Vh, the regenerative power initial value which is the initial value at the start of the acceptable power in the regenerative charging control is A method for estimating an initial value of regenerable power, characterized in that the initial value of regenerable power is calculated by the following equation: (initial value of regenerable power) = {Vh · (Vh−E) / RO} · b. 2. The method for estimating an initial value of regenerable power according to claim 1 , wherein a temperature correction coefficient indicating a change in internal resistance depending on a battery temperature is b1, and a deterioration correction indicating an internal resistance change depending on deterioration of the battery is set. A method for estimating a regenerable power initial value, characterized in that when the coefficient is b2, the correction coefficient b is calculated by the following equation b = b1 · b2. 3. The method for estimating an initial value of regenerable power according to claim 1 , wherein a temperature correction coefficient indicating an internal resistance change depending on a battery temperature is b1, and a deterioration correction indicating an internal resistance change depending on a deterioration of the battery is set. When the coefficient is b2 and the variation correction coefficient for correcting the variation of each single cell that constitutes the battery is b3,
The regenerative possible power initial value estimation method characterized in that the correction coefficient b is calculated by the following equation: b = b1, b2, b3. 4. The method for estimating a regenerable power initial value according to claim 3 , wherein the maximum value of the internal resistance of each single cell forming the battery is Rma.
x and the average internal resistance of each unit cell is Rave, the variation correction coefficient b3 is calculated by the following equation b3 = Rmax / Rave. Value estimation method.