JP3754254B2 - Battery charge / discharge control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for charging and discharging while controlling the remaining capacity of a battery to be within a predetermined range.
[0002]
[Prior art]
When a battery is overcharged or overdischarged, its electrical performance is significantly reduced. In order to use the battery for a long period of time, in addition to preventing overcharge and overdischarge, stop charging when the remaining capacity is less than the maximum charge capacity, in other words, stop charging when it is not fully charged. In addition, it is important to stop the discharge before the remaining capacity becomes 0, that is, in a state where the discharge is not completely performed.
[0003]
In this specification, the “maximum charging capacity” of a battery means the maximum capacity that can be output when a fully charged secondary battery is completely discharged. For new batteries, the rated capacity is the maximum charge capacity. However, as the battery is charged and discharged, the battery deteriorates and the maximum charge capacity decreases.
[0004]
In order to prevent overcharge and overdischarge and prolong the life of the battery, for example, a battery used in an electric vehicle sets a discharge upper limit value and a charge lower limit value, and the remaining capacity is in this range. Thus, charging and discharging are performed while controlling. For example, the discharge upper limit value is set to about 30% of the maximum charge capacity of the battery, and the charge lower limit value is set to 70% of the maximum charge capacity. This charge / discharge control method has a feature that it can be used for a very long period of time without degrading the battery performance because the battery is charged / discharged in this range with 30-70% of the maximum charge capacity as the charge / discharge allowable range.
[0005]
[Problems to be solved by the invention]
A method of charging and discharging within this range by providing a discharge upper limit value and a charge lower limit value, for example, detects the maximum charge capacity when used for a certain period of time. This is because the maximum charge capacity of the battery decreases as it is used. The maximum charge capacity can be detected, for example, by fully discharging a fully charged battery. The discharge upper limit value and the charge lower limit value are set at a constant rate with respect to the maximum charge capacity. For this reason, when the maximum charge capacity decreases, the range of the discharge upper limit value and the charge lower limit value becomes narrow, and the actually usable capacity decreases.
[0006]
FIG. 1 shows this clearly. The upper graph in this figure shows the discharge upper limit value and the charge lower limit value of the new battery, and the lower graph shows the discharge upper limit value and the charge lower limit value of the battery that has deteriorated and the maximum charge capacity has decreased. As shown in this figure, when the maximum charge capacity of the battery is reduced, the charge / discharge allowable range is narrowed, and the user feels that the battery has been severely deteriorated and claims that the capacity is reduced.
[0007]
The present invention was developed with the object of solving these drawbacks, and an important object of the present invention is to prevent the range in which charging / discharging can be substantially reduced when the battery deteriorates. Another object of the present invention is to provide a battery charge / discharge control method that can be used effectively.
[0008]
[Means for Solving the Problems]
The charge / discharge control method of the present invention sets the discharge upper limit value and the charge lower limit value to charge / discharge. The discharge upper limit value is a capacity at which the remaining capacity of the battery 1 becomes larger than a fully discharged state, in other words, a value at which the remaining capacity is larger than zero. The charge lower limit value is a state in which the remaining capacity of the battery 1 is smaller than the fully charged state.
[0009]
Furthermore, the method of the present invention calculates the remaining capacity of the battery 1 and charges and discharges the remaining capacity while controlling the remaining capacity within a charge / discharge allowable range between the discharge upper limit value and the charge lower limit value. Furthermore, in the charge / discharge control method of the present invention, when the maximum charge capacity is reduced due to deterioration of the battery 1 or the like, the discharge upper limit value is decreased and the charge lower limit value is largely corrected. The correction for decreasing the discharge upper limit value and increasing the charge lower limit value is a correction for expanding the charge / discharge allowable range. Therefore, the charge / discharge control method of the present invention can reduce the allowable charge / discharge range from being narrowed when the battery 1 deteriorates and the maximum charge capacity decreases.
[0010]
The discharge upper limit value is preferably set to 10 to 40% of the maximum charge capacity. Further, the charging lower limit value is preferably set to 60 to 90% of the maximum charging capacity. The maximum charge capacity of the battery 1 is stored in the storage device as information for decreasing the maximum charge capacity of the battery 1, and the maximum charge capacity is calculated from the stored information. The stored information in which the maximum charge capacity of the battery 1 decreases is, for example, the relationship of the maximum charge capacity with respect to the internal resistance of the battery 1.
[0011]
The maximum charge capacity can be detected when the maximum capacity detection timing is set by a timer and the maximum capacity detection timing is reached. In order to detect the maximum charge capacity at the maximum capacity detection timing, the fully charged battery 1 is completely discharged and calculated from the integrated value of the discharge current. Further, the maximum capacity detection timing can be set to a timing at which the remaining capacity of the battery 1 becomes the discharge upper limit value or the charge lower limit value for the set number of times without using the timer. In this method, when the remaining capacity of the battery 1 reaches the charging lower limit value for the set number of times, the battery 1 is fully charged to detect the maximum charging capacity, and the number of times that the remaining capacity of the battery 1 reaches the charging lower limit value is set. When the calculated value is reached, the remaining capacity calculated by completely discharging the battery 1 is corrected, and the remaining capacity can be calculated more accurately.
[0012]
The remaining capacity of the battery 1 can be calculated by detecting the charging current and the discharging current, or by detecting the battery voltage.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify the battery charge / discharge control method for embodying the technical idea of the present invention, and the present invention does not specify the battery charge / discharge control method as the following method. .
[0014]
Further, in this specification, in order to facilitate understanding of the scope of claims, the numbers corresponding to the members shown in the examples are referred to as “the scope of claims” and “the means for solving the problems”. It is added to the member shown by. However, the members shown in the claims are not limited to the members in the embodiments.
[0015]
FIG. 2 shows a circuit used in the charge / discharge control method of the present invention. The apparatus of this figure is set in the battery 1, the arithmetic circuit 2 that detects the maximum charge capacity and the remaining capacity of the battery 1, the deterioration information storage device 3 that stores information that the battery 1 deteriorates, and the arithmetic circuit 2. A remaining capacity indicator 4 for displaying the remaining capacity of the battery 1 and a charge / discharge control device 5 for controlling charge / discharge of the battery 1.
[0016]
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. A battery 1 used in an electric vehicle has a large 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.
[0017]
The arithmetic circuit 2 detects the voltage, current, and temperature of the battery 1. The temperature of the battery 1 is detected by a temperature sensor 6. The temperature sensor 6 is disposed close to the battery 1 or is in contact with the battery 1. The current flowing through the battery 1 is detected by amplifying a voltage generated in a current detection resistor (not shown) connected in series with the battery 1. Since the charging current and the discharging current are reversed from + − generated in the current detection resistor, charging and discharging can be identified by the polarity of + −. A battery 1 in which a plurality of secondary batteries are connected in series detects the voltage and temperature of each secondary battery separately, or a battery unit in which a plurality of secondary batteries are connected in series is regarded as one unit. Detect voltage and temperature.
[0018]
The arithmetic circuit 2 calculates the maximum charge capacity of the battery 1 from the deterioration information stored in the deterioration information storage device 3 or by completely discharging the fully charged battery 1. The method of calculating the maximum charge capacity from the deterioration information does not require the battery 1 to be fully charged and does not need to be completely discharged, and can quickly calculate the maximum charge capacity with the remaining capacity as a charge / discharge allowable range.
[0019]
In order to calculate the maximum charge capacity from the deterioration information, for example, the internal resistance of the battery 1 is detected, and the maximum charge capacity is calculated from the internal resistance. When the battery 1 deteriorates, the internal resistance increases and the maximum charge capacity decreases. Since the internal resistance of the battery 1 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 device 3. The arithmetic circuit 2 detects the internal resistance of the battery 1 and compares the internal resistance with deterioration information to calculate the maximum charge capacity.
[0020]
The internal resistance of the battery 1 can be detected from the current and voltage flowing through the battery 1. This is because the voltage drop due to the internal resistance reduces the output voltage of the battery 1. 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 1 and the output voltage when a predetermined current flows through the battery 1. The internal resistance is calculated by dividing the voltage drop by the current.
[0021]
Further, the arithmetic circuit 2 can calculate the maximum charge capacity by completely discharging the fully charged battery 1. The method of calculating the maximum charge capacity by this method is suitable, for example, for a battery whose maximum charge capacity temporarily decreases due to the memory effect, for example, a nickel-cadmium battery or a nickel-hydrogen battery. This is because when the fully charged battery 1 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 2 that fully charges and discharges the battery 1 controls the charge / discharge control device 5 to fully discharge the battery 1 and then completely discharges it. Then, the maximum charging capacity is calculated by integrating the discharge current until the fully charged battery 1 is completely discharged.
[0022]
The arithmetic circuit 2 that calculates the maximum charge capacity by completely discharging the fully charged battery 1 sets the timing for detecting the maximum charge capacity by the timer, that is, the maximum capacity detection timing. When the timer reaches the maximum capacity detection timing, the battery 1 is fully charged and then completely discharged to calculate the maximum charge capacity.
[0023]
Further, the arithmetic circuit 2 for calculating the maximum charge capacity by completely discharging the fully charged battery 1 is the number of times that the remaining capacity becomes the discharge upper limit value or the number of times that the charge lower limit value is set. It is also possible to calculate the maximum charge capacity at the timing when the number of times is reached. In this method, when the remaining capacity of the battery 1 reaches the lower limit of charge for the set number of times, the battery 1 is fully charged exceeding the lower limit of charge, and then fully discharged to detect the maximum charge capacity. be able to. Further, when the number of times the remaining capacity of the battery 1 reaches the lower limit of charging becomes a set value, the battery 1 is completely discharged exceeding the upper limit of discharge, and the maximum charging capacity is calculated. It is also possible to correct the remaining capacity.
[0024]
Further, the arithmetic circuit 2 shown in the figure also calculates the remaining capacity and outputs it to the remaining capacity indicator 4. The remaining capacity is calculated by subtracting the discharge capacity from the charge capacity of the battery 1. The charging capacity is calculated by the product of the integrated value of charging current and charging efficiency. The discharge capacity can be calculated by the integrated value of the discharge current.
[0025]
In addition, the arithmetic circuit 2 controls the charge / discharge control device 5 so that the remaining capacity of the battery 1 is larger than the discharge upper limit value and smaller than the charge lower limit value, that is, the charge / discharge allowable range. The discharge upper limit value and the charge lower limit value are stored in a storage element (not shown) such as a semiconductor memory built in the arithmetic circuit 2.
[0026]
The discharge upper limit value is a state in which the remaining capacity is larger than the fully discharged state, and is a value that can minimize the deterioration of the battery 1 when the battery 1 is discharged, for example, 10 to 40 of the maximum charge capacity. %, More preferably 20-30%. As the discharge upper limit value is set lower, the capacity that can actually discharge the battery 1 increases. Conversely, when the discharge upper limit value is increased, the substantial discharge capacity of the battery 1 is reduced, but the deterioration of the battery 1 can be reduced.
[0027]
The charge lower limit value is a state in which the remaining capacity is smaller than the fully charged state, and is a value that can minimize deterioration when charging the battery 1, for example, 60 to 90% of the maximum charge capacity, preferably 70. Set to ~ 80%. The higher the charge lower limit value is set, the greater the capacity that can actually charge the battery 1. On the contrary, when the lower limit of charging is lowered, the substantial discharge capacity of the battery 1 is reduced, but the deterioration of the battery 1 can be reduced.
[0028]
The discharge upper limit value and the charge lower limit value are optimally set within the above-mentioned range in consideration of the life required for the battery 1 and the required discharge capacity. Further, the arithmetic circuit 2 changes the discharge upper limit value and the charge lower limit value according to the maximum charge capacity of the battery 1 without making the discharge upper limit value and the charge lower limit value constant. This is to reduce deterioration of the battery 1 while maintaining a large capacity of the battery 1 that can be substantially discharged.
[0029]
FIG. 3 shows a state in which the discharge upper limit value and the charge lower limit value are changed according to the maximum charge capacity. As shown in this figure, when the maximum charge capacity of the battery 1 decreases as indicated by an arrow, the arithmetic circuit 2 decreases the discharge upper limit value and increases the charge lower limit value to widen the charge / discharge allowable range. In this figure, when the maximum charge capacity decreases, the arithmetic circuit 2 changes the discharge upper limit value from 30% to 20% of the maximum charge capacity, and changes the charge lower limit value from 70% to 80%.
[0030]
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 1 is reduced to 2/3, the capacity that can be substantially charged and discharged does not decrease. When the maximum charge capacity decreases, how much the discharge upper limit value and the charge lower limit value are changed depends on the battery application, battery type, maximum charge capacity, discharge current, charge current, etc. To do. However, in any application, the discharge upper limit value is set so that the battery 1 is not completely discharged, and the charge lower limit value is set smaller than 100% of the maximum charge capacity. This is to prevent sudden deterioration of the battery 1.
[0031]
The charge / discharge control device 5 stores the maximum charge capacity with respect to the internal resistance in a semiconductor memory or the like. The maximum charge capacity for the internal resistance is stored as a function having the internal resistance as a parameter, or is stored as a maximum charge capacity value for a specific range of the internal resistance.
[0032]
The remaining capacity indicator 4 displays the remaining capacity output from the arithmetic circuit 2 on a monitor such as a liquid crystal, or displays the number of light emitting diodes and the light emission color. The remaining capacity indicator 4 displays the remaining capacity as a relative value with respect to the maximum charge capacity.
[0033]
The charge / discharge control device 5 is controlled by the arithmetic circuit 2 to control the charge / discharge of the battery 1. When the remaining capacity of the battery 1 is in the charge / discharge allowable range, the charge / discharge control device 5 turns on both the discharge switch and the charge switch to allow charging and discharging. When the remaining capacity is equal to or lower than the discharge upper limit value, the discharge switch is turned off to prohibit discharge, and the charge switch is turned on to allow charging. Further, when the remaining capacity of the battery 1 is equal to or higher than the charging lower limit value, the discharging switch is turned on to allow discharging, and the charging switch is turned off to prohibit charging.
[0034]
Since the discharge upper limit value and the charge lower limit value change depending on the maximum charge capacity, the charge / discharge control device 5 is controlled by a signal from the arithmetic circuit 2 to charge / discharge the battery 1 within the charge / discharge allowable range.
[0035]
As described in detail above, the circuit of FIG. 2 detects the maximum charge capacity of the battery 1 with the arithmetic circuit 2, changes the discharge upper limit value and the charge lower limit value according to the maximum charge capacity of the battery 1, and The charge / discharge control device 5 controls the charge / discharge of the battery 1 so that the capacity is within the charge / discharge allowable range.
[0036]
【The invention's effect】
The charge / discharge control method of the present invention has an advantage that when a battery is deteriorated, it can be effectively used while preventing the range in which charge / discharge can be substantially reduced from being narrowed, and the deterioration of the battery can be minimized. That is, when the charge / discharge control method of the present invention controls the remaining capacity of the battery to a charge / discharge allowable range between the discharge upper limit value and the charge lower limit value, and when the maximum charge capacity of the battery decreases, This is because the discharge upper limit value is reduced and the charge lower limit value is corrected so as to widen the charge / discharge allowable range.
[0037]
The charge / discharge control method of the present invention can reduce the decrease in the actual usable capacity when the battery deteriorates and the maximum charge capacity decreases. There is.
[0038]
Furthermore, the charge / discharge control method of the present invention also has an advantage that the battery can be used effectively until it is deteriorated and discarded. The conventional charge / discharge control method is used while being sufficiently protected by charging / discharging within a narrow charge / discharge allowable range until the battery is discarded. Since the charge / discharge control method of the present invention is used effectively by expanding the allowable charge / discharge range as the battery deteriorates and the maximum charge capacity decreases, the deterioration of the battery increases, but it can be used effectively. Can increase capacity. For this reason, there is a feature that the battery can be effectively used until it is completely deteriorated.
[Brief description of the drawings]
FIG. 1 is a graph showing a battery discharge upper limit value and a charge lower limit value in a conventional charge / discharge control method. FIG. 2 is a circuit diagram showing a circuit used in the battery charge / discharge control method of the present invention. The graph which shows the discharge upper limit of a battery and the charge lower limit in the charging / discharging control method of an Example of [Example]
DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Arithmetic circuit 3 ... Degradation information storage device 4 ... Remaining capacity indicator 5 ... Charge / discharge control device 6 ... Temperature sensor

Claims (7)

Set a discharge upper limit value in which the remaining capacity becomes larger than the fully discharged state and a charge lower limit value in which the remaining capacity of the battery (1) becomes smaller than the fully charged state, and the remaining battery (1) In the charge / discharge control method of the battery, which calculates the capacity and charges / discharges while controlling the remaining capacity within the charge / discharge allowable range between the discharge upper limit value and the charge lower limit value,
A charge / discharge control method for a battery, characterized in that, when the maximum charge capacity of the battery (1) decreases due to deterioration , the discharge upper limit value is decreased and the charge lower limit value is largely corrected.   The charge / discharge control method according to claim 1, wherein the discharge upper limit value is 10 to 40% of the maximum charge capacity, and the charge lower limit value is 60 to 90% of the maximum charge capacity.   The battery charge / discharge control method according to claim 1, wherein information for decreasing the maximum charge capacity of the battery (1) is stored in a storage device, and the maximum charge capacity of the battery (1) is calculated from the stored information.   The battery charge / discharge control method according to claim 1, wherein the maximum capacity detection timing is set by a timer, and the maximum charge capacity is detected when the maximum capacity detection timing is reached.   The battery according to claim 1, wherein a maximum capacity detection timing for detecting a maximum charge capacity is set at a timing when the remaining capacity of the battery (1) reaches a set number of times, a discharge upper limit value or a charge lower limit value. Charge / discharge control method.   6. The battery charge / discharge control method according to claim 5, wherein when the remaining capacity of the battery (1) reaches the set number of times and the charge lower limit value, the battery (1) is fully charged and the maximum charge capacity is detected.   The charge / discharge of the battery according to claim 5, wherein when the number of times the remaining capacity of the battery (1) reaches the lower limit of charging reaches a set value, the remaining capacity calculated by completely discharging the battery (1) is corrected. Control method.

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