JPH05341022A - Residual capacity calculating method for nickel type battery - Google Patents

Abstract

PURPOSE:To calculate the residual capacity of a battery precisely independently from the degree of deterioration of the battery by determining the rate of electric discharge corresponding to the internal resistance determined from the battery voltage and the discharge current, and presuming and calculating the residual capacity. CONSTITUTION:A residual capacity meter 1 measures the terminal voltage of a Ni-Cd battery 3, and the resultant is subjected to a computation process with the discharge current value measured by an ammeter 4. Therein the data of residual capacity A when the battery 3 is charged fully is assumed as 100%, and the current I and terminal voltage V are sampled, for example at 10-msec intervals, If it is in discharged condition when judged from the current direction, the electric quantities measured at this time are cumulated on the discharge electric quantity cumulation value B, and this cycle is repeated, for example for 60sec. If the measured current I is large (for example, I>=50A) and the capacity A is for example below 40%, the internal resistance of the battery is calculated from the current I and voltage V, and the residual capacity A' is calculated presumatively from the rate of discharge corresponding to the obtained internal resistance. If there is an error for example exceeding 10Ah between the two capacity values A' and A, a correction is made to change the capacity A to A'.

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 the remaining capacity of a nickel-based battery, and more particularly to an apparatus for displaying the remaining capacity of a nickel-based battery such as Ni-Cd or nickel-hydrogen used as a power source for electric vehicles. Can be applied.

[0002]

2. Description of the Related Art Lead batteries have been generally known as a power source for electric vehicles. In the case of this type of battery, there is a correlation between the remaining capacity of the battery and the terminal voltage. Therefore, the remaining capacity can be roughly estimated by monitoring the terminal voltage. However, the residual capacity obtained by this method has an error of ± 20 to 25%, which is not a highly accurate method.

On the other hand, in nickel-based Ni-Cd batteries which have begun to be adopted as a power source for electric vehicles, the amount of change in the terminal voltage in proportion to the discharge amount is extremely small. Therefore, it is necessary to estimate the remaining capacity of the battery from the terminal voltage. Is very difficult. For this reason, in the Ni-Cd battery, the remaining capacity is 10
The initial value is set to 0%, and the amount of electricity used is subtracted from this to calculate the remaining capacity. The amount of electricity used can be obtained by integrating the measured discharge current every unit time. Of course, if the battery becomes charged in the middle, the amount of electricity is added to the remaining capacity.

The remaining capacity of a nickel-based battery can also be determined by measuring the terminal voltage when there is no load. This requires that the battery be left for a certain period of time, for example, 24 hours, and the polarization effect in the battery will be observed. Since it can be obtained only when it runs out, the remaining capacity cannot be known while driving the electric vehicle, which is not practical.

[0005]

By the way, in the method of calculating the remaining capacity of the nickel-based battery based on the integrated value of the discharge current, when the battery is charged, the charging which has reached the completion of charging (full charge) is always performed. Charging is not necessarily completed in this state, and therefore, if charging and discharging are repeated in such a state, the error of the integrated value may increase and the accuracy of the remaining capacity may deteriorate.

When the battery deteriorates, the chargeable capacity decreases, and the actual remaining capacity becomes different from the calculated remaining capacity, which also contributes to the decrease in accuracy. ing.

The remaining capacity of the battery is
It is an extremely important information for predicting the mileage or the mileage as well as for the safe driving, as it is an index showing how long the drivable state can last.
Therefore, the calculated remaining capacity is desired to be as accurate as possible.

The present invention has been made in view of the above circumstances. Even if the integrated calculation is repeatedly performed in a charged state where the charging is not completed, the error does not increase, and even if the battery deteriorates, the capacity decrease due to the deterioration is considered. It is an object of the present invention to provide a method for calculating the remaining capacity of a nickel-based battery that can obtain a highly accurate remaining capacity.

[0009]

To solve the above problems, according to the present invention, the charging / discharging current of a battery is measured, and the charging / discharging electricity quantity is integrated every unit time, and the integrated electricity quantity is preset. In the method of calculating the remaining capacity of the battery by adding or subtracting to the initial value of the remaining capacity of the battery, when the calculated remaining capacity is less than a predetermined value and the discharge current and the charging current are more than the predetermined value, the discharge The internal resistance of the battery is obtained from the current and the terminal voltage of the battery measured at the same time, and the remaining capacity is estimated and calculated from the discharge rate corresponding to this internal resistance, and the estimated remaining capacity and the calculated remaining capacity are calculated. There is provided a method for calculating the remaining capacity of a nickel-based battery, which is characterized in that the calculated remaining capacity is changed to the estimated remaining capacity when the difference is greater than or equal to a predetermined value.

[0010]

According to the above means, the internal resistance of the nickel-based battery is not very low even though it is very low. Therefore, when a large discharge current of a predetermined value or more flows, it can be obtained as a relatively large change in the terminal voltage. You can At this time, it is possible to obtain a relatively accurate value of the internal resistance from the discharge current and the terminal voltage. From the value of the internal resistance, the discharge rate having a correlation with this can be obtained, and the residual capacity at that time is estimated. When a difference of more than a predetermined value occurs between this remaining capacity and the calculated remaining capacity, the calculated remaining capacity is changed to an estimated remaining capacity that is close to the actual value, and the remaining capacity data is always calculated. The value is corrected.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings showing a preferred embodiment of the present invention.

FIG. 1 illustrates a method according to the invention, for example Ni--
FIG. 2 is a block diagram showing a calculation processing flow when applied to a remaining capacity display device for a Cd battery, and FIG. 2 is a block diagram showing a configuration example of the remaining capacity display device.

The battery remaining capacity display device is composed of a remaining capacity meter 1 and a display unit 2, and the remaining capacity meter 1 is Ni-C.
It is connected to the d battery 3 so as to measure its terminal voltage, and is also connected to an ammeter 4 that measures the charging / discharging current of the Ni—Cd battery 3. Reference numeral 5 is an electric motor controller for controlling the drive electric motor of the electric vehicle.

The remaining capacity meter 1 is not shown in the drawing, but is made of Ni-C.
d Analog-to-digital converter that converts the terminal voltage of the battery 3 and the analog value of the discharge current measured by the ammeter 4 into a digital signal, a read-only memory and a random access memory that store programs for performing the arithmetic processing of FIG. , A central processing unit, various interfaces and a power supply.

Next, a method for calculating the remaining capacity of the Ni-Cd battery 3 will be described.

In step 10 of FIG. 1, the remaining capacity (A) data is set to 100% when the Ni-Cd battery is completely charged (fully charged). In steps 11 and 12, the battery current (I) and terminal voltage (V) are sampled, for example, every 10 milliseconds. In step 13, it is determined from the direction of the current whether the battery is in a charging state or a discharging state.

If the battery is in a discharged state, in step 14, the accumulated electricity quantity (B) is integrated with the electricity quantity measured this time, and this is repeated for 60 seconds, for example. Then, in step 15, it is determined whether the measured current (I) is a large current. In this embodiment, it is determined whether or not the current consumed by the electric motor during traveling, for example, exceeds 50 A. If the current is large, it is determined in step 16 whether the remaining capacity (A) is 40% or less. to decide. Here, if the remaining capacity (A) is 40% or less,
In step 17, the remaining capacity is estimated and calculated based on the measured current (I) and terminal voltage (V).

That is, first, the internal resistance of the battery is calculated from the current (I) and the terminal voltage (V). The calculation of the internal resistance can be more accurately obtained as the current (I) is larger. That is, for example, a small current consumed when the vehicle is stopped causes the internal resistance to be too small, so that the terminal voltage (V) hardly changes. Therefore, this small current cannot be used at all for calculating the internal resistance, but the discharge current is The larger the value, the larger the change in the terminal voltage of the battery, and the more accurate the obtained voltage change amount. Therefore, the calculated value of the internal resistance due to the discharge current and the terminal voltage can also be obtained with relatively high accuracy. Further, since the internal resistance changes according to the discharge rate as shown in FIG. 3, it is possible to obtain the discharge rate at that time by obtaining the internal resistance. However, the higher the calculated internal resistance is, the higher the accuracy becomes. A high discharge rate, that is, a remaining capacity will be obtained.

The internal resistance characteristics of FIG. 3 are calculated in advance by calculating the terminal voltage characteristics of the battery at each discharge rate shown in FIG. 5 based on the basic discharge characteristics of the used battery shown in FIG. It was obtained by.

Now, in step 18, it is judged whether or not the remaining capacity (A ') estimated and calculated from the discharge rate corresponding to the calculated internal resistance is different from the remaining capacity (A). If there is an error of, the remaining capacity (A) is corrected in step 19 to the estimated remaining capacity (A ′).

For example, during charging or regenerative braking,
If it is determined in step 13 that the battery is in the charged state, in step 20, the measured current (I) and voltage (V)
A process for integrating the charge electricity amount obtained from the above into the charge electricity amount integrated value (C) is repeated for 60 seconds, for example.

In step 21, an interval for updating the display of the remaining capacity of the battery is set, and is set to, for example, 60 seconds to prevent the display output from flickering. In step 22, a new remaining capacity is calculated by considering the discharge integrated value (B) and the charge integrated value (C) with respect to the remaining capacity (A),
In step 23, the discharge integrated value (B) and the charge integrated value (C) are reset to zero, and in step 24, the corrected new remaining capacity is displayed and output.

In the remaining capacity estimation calculation, the temperature of the battery may be added as one of the parameters to eliminate the influence of the temperature. In this case, in step 12,
The temperature of the battery is also measured at the same time, and in step 17,
The temperature value is used for temperature correction of the battery current and voltage simultaneously measured.

[0024]

As described above, according to the present invention, when the remaining capacity of a nickel-based battery is obtained by subtracting the integrated value of the discharge current from the initial value at the completion of charging, the calculated remaining capacity is, for example, When it is 40% or less, for example, 50
When a large current of A or more flows, that is, at the time of large current discharge in which the remaining capacity decreases to a range where the motor may stop due to calculation error and the terminal voltage changes relatively,
The remaining capacity is estimated from the discharge current and terminal voltage by calculation, and when this deviates from the calculated value from the initial value by a predetermined value or more, the estimated remaining capacity is set as a new remaining capacity. The error can be reduced to ± 10% or less, and by positively correcting the remaining capacity data when the electric motor is actually used, the remaining capacity is not affected by the degree of deterioration of the battery. It is possible to accurately calculate the remaining capacity when the amount becomes small.

[Brief description of drawings]

FIG. 1 is a diagram showing a remaining capacity calculation processing flow in a remaining capacity display device to which a remaining capacity calculation method for a nickel-based battery according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration example of a remaining capacity display device to which a method for calculating a remaining capacity of a nickel-based battery according to the present invention is applied.

FIG. 3 is a diagram showing an example of calculating internal resistance characteristics of a battery.

FIG. 4 is a diagram showing an example of discharge characteristics of a battery.

FIG. 5 is a diagram showing an example of calculating a terminal voltage characteristic of a battery.

[Explanation of symbols]

 1 Remaining capacity meter 2 Display section 3 Ni-Cd battery 4 Ammeter 5 Motor controller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyasu Suzuki 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Kazuo Natori 2-4-1 Nishitsujikeoka, Chofu-shi, Tokyo Tokyo (72) Inventor Noboru Fujiwara 2-4-1, Nishitsutsujigaoka, Chofu-shi, Tokyo Inside the Technical Research Institute, Tokyo Electric Power Co., Inc.

Claims (1)

[Claims] 1. A battery is obtained by measuring a charge / discharge current of a battery, adding up an amount of charge / discharge electricity every unit time, and adding / subtracting the added amount of electricity to a preset initial value of the remaining capacity of the battery. In the method of calculating the remaining capacity of the battery, when the calculated remaining capacity is less than a predetermined value and the discharge current and the charging current are more than the predetermined values, the internal resistance of the battery is calculated from the discharge current and the simultaneously measured terminal voltage of the battery. Then, the discharge rate corresponding to this is calculated from this internal resistance and the remaining capacity is estimated and calculated.If the difference between the estimated remaining capacity and the calculated remaining capacity is equal to or more than a predetermined value, the remaining capacity is estimated by the calculation. A method for calculating the remaining capacity of a nickel-based battery, characterized in that the calculated remaining capacity is changed.