JP2001157366A - Method of controlling charging and discharging of battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the relative remaining capacity of respective battery modules by preventing over-charging and over-discharging of the respective battery modules. SOLUTION: This method performs discharging while calculating the relative remaining capacity of a plurality of battery modules connected in series. This method, when any one of particular battery modules charged or discharged reaches a correction point, also corrects the calculated relative remaining capacity of the particular battery module to the standard capacity of the correction point. In addition, this method corrects the calculated relative remaining capacities of the other battery modules with the same correction value as for the particular battery module.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of charging and discharging a battery module while calculating the relative remaining capacity of a plurality of battery modules connected in series.

[0002] In the present specification, "relative remaining capacity" means a value indicating a ratio of a remaining capacity that is a dischargeable capacity to a maximum charging capacity that is a maximum charging capacity that can charge a battery module.

[0003]

2. Description of the Related Art An assembled battery in which a plurality of battery modules are connected in series is charged and discharged while preventing overcharging and overdischarging of each battery module, thereby effectively preventing battery deterioration. To realize this, it is necessary to calculate the relative remaining capacity of each battery module. Overcharging and overdischarging can be prevented by charging and discharging in a range where the relative remaining capacities of all the battery modules are 0 to 100%. Further, when the relative remaining capacity is used in a range of, for example, 20 to 80%, a decrease in battery performance can be extremely reduced.

A battery pack in which a plurality of battery modules are connected in series cannot be charged or discharged so that the relative remaining capacities of all the battery modules are the same. This is because as the battery is charged and discharged, the maximum charge capacity of each battery module and the calculated remaining capacity vary. A battery module having a large maximum charge capacity has a large remaining capacity even with the same discharge amount. In order to charge and discharge all the battery modules within a predetermined relative remaining capacity range, it is necessary to accurately detect the relative remaining capacity of each battery module and control the charging and discharging of the assembled battery.

The relative remaining capacity of each battery module is:
The voltage and current of each battery module can be detected and calculated. Also, by detecting the battery voltage, it can be detected that the battery is fully charged or completely discharged. When charging a completely discharged battery module until it is fully charged,
The maximum charging capacity can be detected by multiplying the integrated value of the charging current by the charging efficiency. Further, the maximum charge capacity of the battery module can be detected from the integrated value of the discharge current when the fully charged battery is completely discharged.

[0006]

However, the method of detecting the relative remaining capacity of each battery module by such a method is to prevent overcharging and overdischarging of all the battery modules while preventing the overcharging and overdischarging of each battery module. There is a disadvantage that the maximum charge capacity cannot be accurately detected. This is because when battery modules with different maximum charge capacities are connected in series and charged, the battery modules with smaller maximum charge capacities are fully charged first, so the battery modules with larger maximum charge capacities are charged until they are fully charged. Then, the battery module having a small maximum charge capacity is overcharged.

Conversely, when battery modules having a difference in maximum charge capacity are connected in series and discharged, a battery module with a small maximum charge capacity is completely discharged first, so that a battery module with a large maximum charge capacity is completely discharged. When the battery module is discharged until it is discharged, the battery module having a small maximum charge capacity is overdischarged.

[0008] The present invention has been developed for the purpose of solving such a conventional disadvantage. An important object of the present invention is to provide a battery pack charge / discharge control method capable of preventing overcharge and overdischarge of each battery module and accurately calibrating the relative remaining capacity of each battery module.

[0009]

A charge / discharge control method for a battery pack according to the present invention performs charge / discharge while calculating the relative remaining capacity of a plurality of battery modules connected in series. Further, the charge / discharge control method calibrates the calculated relative remaining capacity of the specific battery module to the standard capacity at the calibration point when any one of the specific battery modules being charged / discharged reaches the calibration point. Further, the calculated relative remaining capacities of the other battery modules are also calibrated with the same calibration values as those of the specific battery module.

According to the charge / discharge control method of the present invention, when a specific battery module reaches a charge calibration point, not all battery modules are calibrated, but some battery modules having a large relative remaining capacity are calculated. The relative remaining capacity can also be calibrated with a calibration value. Further, when the specific battery module reaches the discharge calibration point, the calculated relative remaining capacity of some battery modules having a small relative remaining capacity can be calibrated with the calibration value.

Further, according to the charge / discharge control method of the present invention, when the specific battery module reaches the charging calibration point, the calculated relative remaining capacity of half of the battery modules is calibrated in the order of the relative remaining capacity, When the specific battery module reaches the discharge calibration point, the calculated relative remaining capacity of half of the battery modules can be calibrated in ascending order of the relative remaining capacity.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below illustrate a charge / discharge control method of a battery pack for embodying the technical idea of the present invention, and the present invention does not specify the charge / discharge control method as follows.

FIG. 1 shows a circuit used in the charge / discharge control method of the present invention. The device shown in this figure detects the battery pack 1 and the relative remaining capacity of the battery pack 1,
A charge / discharge control device 3 for controlling the charge / discharge of the battery, and a remaining capacity display 4 for displaying the relative remaining capacity detected by the charge / discharge control device 3.

The charge / discharge control method of the present invention is used for an electric vehicle. However, it can also be used for applications other than electric vehicles. An assembled battery used in an electric vehicle has a number of secondary batteries connected in series. The secondary battery is a nickel-cadmium battery, a nickel-hydrogen battery, a lithium ion secondary battery, or the like.

The charge / discharge control device 3 has a built-in arithmetic circuit 5, control circuit 6, and deterioration information storage circuit 7. Arithmetic circuit 5
Calculates the relative remaining capacity by detecting the battery voltage, current, and temperature. The relative remaining capacity is calculated based on the remaining capacity with respect to the maximum charging capacity that is the maximum capacity that can be charged in each battery module 2. The temperature of the battery is detected by a temperature sensor. The temperature sensor is disposed close to each battery module 2 or provided in contact with each battery module 2. The current flowing through the battery is detected by amplifying a voltage generated at a current detection resistor (not shown) connected in series with the battery. Since the charge current and the discharge current have the opposite polarity of +-generated in the current detection resistor, the charge and discharge can be distinguished by the polarity of +-. The assembled battery in which a plurality of secondary batteries are connected in series detects the voltage and temperature of each secondary battery separately, or one battery module 2 in which a plurality of secondary batteries are connected in series. Detects voltage and temperature.

The arithmetic circuit 5 completely discharges the fully charged battery module 2 from the deterioration information stored in the deterioration information storage circuit 7 or at predetermined time intervals, or
The fully charged battery module 2 is fully charged, and the maximum charge capacity of the battery is calculated. The method of calculating the maximum charge capacity from the deterioration information does not require the battery module 2 to be fully charged and does not need to be completely discharged, and can quickly calculate the maximum charge capacity.

To calculate the maximum charge capacity from the deterioration information, for example, the internal resistance of the battery module 2 is detected, and the maximum charge capacity is calculated from the internal resistance. When the battery module 2 deteriorates, the internal resistance increases and the maximum charge capacity decreases. The internal resistance of the battery module 2 is
Since it is related to the state of deterioration, the maximum charge capacity can be calculated from the internal resistance. The deterioration information for the internal resistance is stored in the deterioration information storage circuit 7. Arithmetic circuit 5
Detects the internal resistance of the battery module 2 and compares the internal resistance with the deterioration information to calculate the maximum charging capacity.

The internal resistance of the battery module 2 can be detected from the current and voltage flowing through the battery module 2. This is because the voltage drop due to the internal resistance lowers the output voltage of the battery module 2. The voltage drop due to the internal resistance can be calculated from the difference between the output voltage when no current flows through the battery module 2 and the output voltage when a predetermined current flows through the battery module 2. The internal resistance is calculated by dividing the voltage drop by the current.

Further, at a predetermined timing, the arithmetic circuit 5 can calculate the maximum charge capacity by discharging all battery modules 2 from a fully charged state to a completely discharged state. The method of calculating the maximum charge capacity by this method is suitable for, for example, a battery in which the maximum charge capacity is temporarily reduced by a memory effect, for example, a nickel-cadmium battery or a nickel-hydrogen battery. This is because when the fully charged battery is completely discharged and the maximum charge capacity is calculated, the temporary decrease in capacity due to the memory effect can be recovered.
The arithmetic circuit 5 for fully charging and completely discharging the battery controls the charge / discharge control device 3 to fully charge the battery and then completely discharge the battery. Then, the maximum charging capacity is calculated by integrating the discharge current until the fully charged battery is completely discharged.

The arithmetic circuit 5, which calculates the maximum charge capacity by completely discharging the fully charged battery, sets the timing for detecting the maximum charge capacity with a timer, that is, the maximum capacity detection timing. When the timer reaches the maximum capacity detection timing, the battery is fully charged and then fully discharged to calculate the maximum charge capacity.

In the method of detecting the maximum charge capacity by the above method, the battery module 2 having a small maximum charge capacity may be overcharged or overdischarged. However, this method does not actually charge the battery module 2 fully until the relative remaining capacity reaches 100%, and does not completely discharge the battery module 2 until the relative remaining capacity becomes 0%. Can be calculated, the battery module 2 having a small maximum charge capacity is not always overcharged or overdischarged. This is because, for example, the fact that the relative remaining capacity of the battery module 2 has become about 80% or about 20% can be detected relatively accurately by detecting the battery voltage.

For example, when a nickel-hydrogen battery or a nickel-cadmium battery is rapidly charged, the voltage changes depending on the charging current. When the relative remaining capacity becomes about 80 to 90%, the battery voltage reaches a peak voltage. For this reason, it can be accurately detected that the relative remaining capacity of the battery module 2 has reached 80 to 90%. Further, the relative remaining capacity is 10 to 20%.
Can also be detected relatively accurately, although it varies depending on the discharge current. For this reason, the battery module can be charged to a state close to full charge, and discharged to a state close to complete discharge, and the maximum charge capacity can be detected. Or overdischarge. However, since this method charges and discharges a battery module with a small maximum charge capacity deeply, it is not preferable in terms of using the battery for an extremely long life, so detection is performed at long time intervals unless an error is a problem. Good to do.

Further, the arithmetic circuit 5 for calculating the maximum charge capacity by completely discharging the fully charged battery becomes the set number of times when the relative remaining capacity becomes the discharge upper limit, or the charge lower limit. The maximum charge capacity can be calculated at the timing when the number of times reaches the set number. In this method, when the relative remaining capacity of the battery reaches the charging lower limit for a set number of times, the battery is fully charged beyond the charging lower limit, and then fully discharged to detect the maximum charging capacity. Can be. Also, when the number of times that the relative remaining capacity of the battery reaches the lower limit of charge reaches a set value, the battery is completely discharged beyond the upper limit of discharge, and the maximum charge capacity is calculated. The relative remaining capacity can be corrected.

Further, the arithmetic circuit 5 shown in the figure calculates the remaining capacity by subtracting the discharge capacity from the charge capacity. The charge capacity is calculated by the product of the integrated value of the charge current and the charge efficiency. The discharge capacity can be calculated from the integrated value of the discharge current. When the remaining capacity is calculated, the relative remaining capacity is calculated by the remaining capacity / maximum charging capacity.

With the above method, the arithmetic circuit 5 calculates the relative remaining capacity, and the calculated relative remaining capacity becomes larger as time elapses due to accumulation of errors. The error in the relative remaining capacity occurs due to, for example, a change in charging efficiency due to a variation in the battery module 2 or the like. The charging efficiency is not always a constant value, and varies depending on, for example, the temperature of the battery module 2 and the amount of heat generated by a battery that is almost fully charged.

The arithmetic circuit 5 calibrates the relative remaining capacity of each battery module 2 to reduce the accumulated error. The arithmetic circuit 5 calibrates the relative remaining capacity when charging and discharging the battery pack 1. However, the relative remaining capacity can be calibrated only when charging or only when discharging.

The method of calibrating the relative remaining capacity of the battery module 2 by charging the battery pack 1 is as follows. When any one of the specific battery modules reaches the charge calibration point while the battery pack 1 is being charged, The relative remaining capacity of the battery module is calibrated to the capacity at the charging calibration point. The capacity of the charging calibration point is, for example, 80 to 90%. Nickel-cadmium batteries and nickel-hydrogen batteries, when charged rapidly, have a relative remaining capacity of 80-90%.
The battery voltage becomes the peak voltage, and this state can be accurately detected. In addition, since the battery voltage of a lithium ion secondary battery increases as the relative remaining capacity increases, the battery voltage can be detected, and the capacity at the charging calibration point can be accurately specified.

When the specific battery module reaches the charging calibration point, the relative remaining capacity of this battery module is calibrated to the standard capacity at the charging calibration point, and the relative remaining capacities of the other battery modules are also calibrated with the same calibration value. For example, when the specific battery module reaches the charging calibration point of 80%, if the calculated relative remaining capacity is 75%, the calibration value is added to + 5% and calibrated to 80%.
Therefore, other battery modules are calibrated by adding + 5% of the same calibration value to the calculated relative remaining capacity. For example, if the calculated relative remaining capacity of another battery module is 73
%, 72%, and 71%, the relative remaining capacities of these battery modules are 78%, 77%, 7
Calibrate to 6%. However, the calibrated relative remaining capacity is 1
If it exceeds 00%, calibrate to 100%.

The method of calibrating the relative remaining capacity of the battery module 2 by discharging the battery pack 1 is as follows. When any one of the specific battery modules reaches the discharge calibration point while the battery pack 1 is being discharged, Calibrate the relative remaining capacity of the battery module to the standard capacity at the discharge calibration point. The standard capacity at the discharge calibration point is, for example, 10 to 20%. Reaching the discharge calibration point is determined by detecting the voltage of the battery module.

When the specific battery module reaches the discharge calibration point, the relative remaining capacity of this battery module is calibrated to the standard capacity at the discharge calibration point, and the relative remaining capacities of the other battery modules are calibrated with the same calibration value. For example, when the specific battery module reaches the discharge calibration point of 20%, if the calculated relative remaining capacity is 23%, it is corrected to 20% by adding a calibration value of -3%. Therefore, other battery modules are calibrated by adding -3% of the same calibration value to the calculated relative remaining capacity. For example, if the calculated relative remaining capacities of the other battery modules are 22% and 21%, the relative remaining capacities of these battery modules are calibrated to 19% and 18%, respectively. However, if the calibrated relative remaining capacity is less than 0%, calibrate to 0%.

FIG. 2 shows a flowchart in which the arithmetic circuit 5 calibrates the maximum charge capacity. This flowchart calibrates the calculated relative remaining capacity in the following steps. [Step S1] In this step, the arithmetic circuit 5 detects the current, voltage and temperature of each battery module 2. [Step S2] In this step, the arithmetic circuit 5 determines whether any of the battery modules 2 has reached the calibration point. Steps S1 and S2 are looped until one of the battery modules 2 reaches the calibration point. [Step S3] When the specific battery module reaches the calibration point, the calculated relative remaining capacity (SOC of the detection module) of the specific battery module is subtracted from the standard capacity (calibration SOC) of the calibration point to obtain the calibration point. A calibration value (SOC difference value) that is a difference from the capacity is calculated. [Steps S4 and S5] Calibration is performed by adding a calibration value to the calculated relative remaining capacities of all the battery modules 2. [Steps S6 and S7] The corrected SOC is 100%
If it exceeds, it is corrected to 100%. [Steps S8 and S9] When the corrected SOC becomes 0% or less, the correction is made to 0%. [Step S10] The above steps are repeatedly executed, and the process ends.

In the above flowchart, calibration is performed by adding a calibration value to the calculated relative remaining capacities of all the battery modules 2. However, the arithmetic circuit 5 does not always need to add a calibration value to the calculated relative remaining capacity of the battery module 2 to perform calibration. For example, when charging, the relative remaining capacity of half of the battery modules can be calibrated in descending order of relative remaining capacity, and when discharging, the relative remaining capacity of half of the battery modules having smaller relative remaining capacity can be calibrated.

The arithmetic circuit 5 controls the control circuit 6 to charge and discharge the battery pack 1. The arithmetic circuit 5 controls the control circuit 6 so that the relative remaining capacities of all the battery modules 2 are larger than the upper discharge limit and smaller than the lower charge limit,
That is, charging and discharging are performed so as to be within the charging and discharging allowable range.
The upper discharge limit and the lower charge limit are stored in a storage element (not shown) such as a semiconductor memory built in the arithmetic circuit 5.

The discharge upper limit value is a value that can minimize battery deterioration when the battery module 2 is discharged, for example,
10 to 40% of the maximum charging capacity, more preferably 20 to
Set to 30%. The lower the discharge upper limit is set, the more the battery can actually discharge. Conversely, increasing the upper discharge limit decreases the actual discharge capacity of the battery,
Battery deterioration can be reduced.

The lower limit of charge is a state in which the relative remaining capacity is smaller than the state of full charge, and a value that can minimize deterioration when charging the battery, for example, 60 to 90% of the maximum charge capacity. Preferably, it is set to 70 to 80%.
As the charging lower limit is set higher, the capacity that can actually charge the battery increases. Conversely, lowering the lower charging limit reduces the actual discharge capacity of the battery, but can reduce the deterioration of the battery.

The upper discharge limit and the lower charge limit are optimally set within the above-mentioned ranges in consideration of the required life of the battery and the required discharge capacity. Further, the arithmetic circuit 5 can change the upper limit of discharge and the lower limit of charge according to the maximum charge capacity of the battery without setting the upper limit of discharge and the lower limit of charge to fixed values. This method is intended to reduce the deterioration of the battery while maintaining a large dischargeable capacity of the battery.

FIG. 3 shows a state in which the upper discharge limit and the lower charge limit are changed according to the maximum charge capacity. As shown in this figure, when the maximum charge capacity of the battery decreases as indicated by the arrow, the arithmetic circuit 5 decreases the discharge upper limit value and increases the charge lower limit value to widen the allowable charge / discharge range. In this figure, when the maximum charge capacity decreases, the arithmetic circuit 5 changes the discharge upper limit value from 30% of the maximum charge capacity to 20%,
The lower limit of charge is changed from 70% to 80%.

As described above, when the discharge upper limit value and the charge lower limit value are changed, even if the maximum charge capacity of the battery is reduced to 2/3, the chargeable / dischargeable capacity does not substantially decrease. When the maximum charge capacity decreases, the extent to which the upper discharge limit and the lower charge limit are changed depends on the use of the battery, battery type, maximum charge capacity, discharge current, charge current, etc. I do. However, in any application, the discharge upper limit is set so that the battery is not completely discharged, and the charge lower limit is set to be smaller than 100% of the maximum charge capacity. This is for preventing a rapid deterioration of the battery.

The remaining capacity display 4 displays the relative remaining capacity output from the arithmetic circuit 5 on a monitor such as a liquid crystal display, or displays the number of light emitting diodes or the color of light emitted. The remaining capacity display 4 displays the relative remaining capacity as a relative value to the maximum charging capacity.

The control circuit 6 is controlled by the arithmetic circuit 5 to control charging and discharging of the battery. When the relative remaining capacity of the battery is within the allowable charging / discharging range, the control circuit 6 turns on both the discharging switch and the charging switch to allow charging and discharging. When the relative remaining capacity falls below the upper discharge limit, the discharge switch is turned off to prohibit discharge, and the charge switch is turned on to allow charging. When the relative remaining capacity of the battery is equal to or greater than the lower charging limit, the discharging switch is turned on to permit discharging, and the charging switch is turned off to prohibit charging.

Since the discharge upper limit value and the charge lower limit value change depending on the maximum charge capacity, the control circuit 6 is controlled by a signal from the arithmetic circuit 5 to charge and discharge the battery within the allowable charge and discharge range.

As described in detail above, the circuit shown in the figure detects the maximum charge capacity of the battery module 2 by the arithmetic circuit 5, and changes the upper discharge limit and the lower charge limit according to the maximum charge capacity of the battery module 2. The control circuit 6 controls the charging and discharging of the battery pack 1 so that the relative remaining capacity of the battery falls within the allowable charging and discharging range.

[0043]

According to the charge / discharge control method for a battery pack of the present invention, the overcharge and the overdischarge of each battery module can be prevented.
The feature is that the relative remaining capacity of each battery module can be accurately calibrated. That is, the charge / discharge control method of the present invention is such that when any one specific battery module that is charging / discharging reaches the calibration point, the calculated relative remaining capacity of the specific battery module is calibrated to the standard capacity of the calibration point. ,
This is because the calculated relative remaining capacities of the other battery modules are also calibrated with the same calibration value as the specific battery module. The method of calibrating the relative remaining capacity of each battery module by this method is that when one of the battery modules is charged or discharged to the calibration point, charging or discharging is stopped, so that a battery having a small maximum charging capacity is used. The module is not overcharged or overdischarged.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit used for a method of controlling charge and discharge of a battery pack according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a process in which an arithmetic circuit calibrates a maximum charging capacity.

FIG. 3 is a graph showing a state in which a discharge upper limit value and a charge lower limit value are changed according to a maximum charge capacity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery pack 2 ... Battery module 3 ... Charge / discharge control device 4 ... Remaining capacity display 5 ... Operation circuit 6 ... Control circuit 7 ... Deterioration information storage circuit

Claims (4)

[Claims] 1. A method for charging and discharging a plurality of battery modules connected in series while calculating a relative remaining capacity, wherein when one of the charged and discharged specific battery modules reaches a calibration point, the specific battery is charged. The calculated relative remaining capacity of the module is calibrated to the standard capacity at the calibration point, and the calculated relative remaining capacity of the other battery modules is calibrated with the same calibration value as the specific battery module. Charge and discharge control method. 2. The set according to claim 1, wherein when the specific battery module reaches a charging calibration point, the calculated relative remaining capacity of some of the battery modules having a large relative remaining capacity is calibrated with a calibration value. Battery charge / discharge control method. 3. The set according to claim 1, wherein when the specific battery module reaches a discharge calibration point, the calculated relative remaining capacity of some of the battery modules having a small relative remaining capacity is calibrated with a calibration value. Battery charge / discharge control method. 4. When the specific battery module reaches a charging calibration point, the calculated relative remaining capacity of half of the battery modules is calibrated in order of increasing relative remaining capacity, and the specific battery module reaches a discharge calibration point. 4. The charge / discharge control method for an assembled battery according to claim 2, wherein the calculated relative remaining capacity of half of the battery modules is corrected in ascending order of the relative remaining capacity.