JP2001161037A - Charging/discharging control method for battery group driving electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a capacity, which can be substantially discharged, by reducing differences between residual capacities of a large number of battery modules. SOLUTION: Relative residual capacities of battery modules, connected in series to each other, are calculated. The battery modules are charged/discharged while the relative residual capacities of the battery modules are controlled to be within an actual use region. Further, if differences between the relative residual capacities of the respective battery modules are increased, calibration charging is applied until the relative residual capacities reach a charging prohibiting region. The battery modules with large substantial battery capacities are fully charged in the order of capacities, and the battery modules with small substantial battery capacities are charged to have differences between the substantial battery capacities reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the charging and discharging of a battery group for driving a motor of an electric vehicle, and more particularly to a method for controlling the charging and discharging of a battery group.
The present invention relates to a charge / discharge control method optimal for a hybrid car that drives a generator by an engine.

[0002]

2. Description of the Related Art A battery group for driving a motor for driving an electric vehicle has a number of battery modules connected in series. This is because the output voltage of the battery group is increased to increase the output of the motor.

A battery group in which a number of battery modules are connected in series can be charged and discharged while preventing overcharge and overdischarge of each battery module, thereby effectively preventing battery deterioration. In order to realize this, the battery group of the electric vehicle is charged and discharged while controlling the relative remaining capacity of each battery module to the actual use area between the charge inhibition area and the discharge inhibition area shown in FIG. ing.

[0004] 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.

[0005] A battery group in which a large number of battery modules are connected in series cannot be charged or discharged so that all the battery modules have the same capacity. 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 remaining capacity range, it is necessary to accurately detect the remaining capacity of each battery module and control the charging and discharging of the battery group.

[0006] When the variation in the remaining capacity of a large number of battery modules becomes large, the capacity that can be substantially charged and discharged becomes extremely small. The relative remaining capacity of all battery modules is
This is because charge and discharge are performed while being controlled to be in the actual use area. Charging is limited by the battery module with the maximum remaining capacity,
Since the discharge is limited by the battery module having the minimum remaining capacity, if the difference between the maximum and the minimum of the relative remaining capacity is large, both charging and discharging are stopped early, and the capacity that can be substantially discharged is significantly reduced.

FIG. 1 shows the calculated relative remaining capacity of the battery module on the upper side and the actual battery capacity of the actual battery module on the lower side. However, since the actual battery capacity of the battery module cannot be calculated, it is shown in the figure,
I don't really know.

[0008]

The difference between the relative remaining capacities of the battery modules can be reduced by discharging a battery module having a large remaining capacity. To achieve this, first,
The battery module having the maximum remaining capacity is fully charged, and which battery module has the higher remaining capacity is specified.

Thereafter, the battery module specified as the maximum remaining capacity is discharged to reduce the difference in the relative remaining capacity.
However, in a battery group in which a large number of battery modules are connected in series, it is extremely difficult to forcibly discharge a specific battery module. This is because no output terminal is connected to each of the battery modules, so that a specific battery module is not discharged. In addition, if an output terminal is connected to all the battery modules and a discharge load is connected to the output terminals, it is difficult to radiate heat generated in the discharge load. Further, there is a disadvantage that a switching circuit for connecting a specific battery module to a discharge load becomes extremely complicated.

[0010] The present invention has been developed to solve such disadvantages. An important object of the present invention is to provide a charge / discharge control method for a battery group for driving an electric vehicle, which can easily reduce the difference between the substantial battery capacities of a large number of battery modules and increase the capacity that can be substantially discharged. It is in.

[0011]

According to a charge / discharge control method of the present invention, a relative remaining capacity of battery modules connected in series is calculated, and a relative remaining capacity of each battery module is calculated as follows.
The battery pack is charged and discharged while being controlled to be in an actual use area provided between the charge prohibition area and the discharge prohibition area. Further, when the difference in the relative remaining capacity of each battery module exceeds a predetermined range, calibration charging is performed until the relative remaining capacity of the battery module is in the charge prohibition region, and the battery having the maximum real battery capacity of the battery is charged. While the module is being fully charged, the capacity of the battery module with the smallest actual battery capacity is increased to reduce the difference between the capacities of the battery modules with the maximum remaining capacity and the minimum remaining capacity.

Further, according to the charge / discharge control method of the present invention, for example, in calibration charging, charging can be stopped by detecting a temperature gradient of a battery module having a minimum relative remaining capacity. In addition, it is possible to prevent the characteristics of a fully charged battery module from deteriorating by performing calibration charging while forcibly cooling the battery group.

Further, the charge / discharge control method of the present invention further comprises:
The electric vehicle can be stopped and the generator can be driven by the idling engine to perform calibration charging. Further, the calibration charge is set to a low rate charge, so that the performance of a fully charged battery module can be prevented from deteriorating. In the low-rate charging, the battery pack can be charged by the emergency charger mounted on the electric vehicle.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below illustrate a method of controlling the charge and discharge of a battery group that drives an electric vehicle to embody the technical idea of the present invention. Not specific.

FIG. 2 is a block diagram of an electric vehicle running with a motor and an engine. The electric vehicle shown in FIG. 1 includes a battery group 1, an engine 2 having a generator (not shown) for charging the battery group 1, and an arithmetic circuit for calculating the relative remaining capacity of the battery group 1 to control charging and discharging. 3, a motor 4 driven by the battery group 1, and an operation circuit 3
A motor control device 5 that controls the operation of the engine 2 with a signal of the arithmetic circuit 3
And an electric battery 6 charged by the generator of the engine 2
And an emergency charger 7 for charging the battery group 1 with the battery 6 for electrical equipment.

The battery group 1 has a number of battery modules connected in series. The battery module contains one or more secondary batteries. The secondary battery of the battery module is a nickel-cadmium battery, a nickel-hydrogen battery, a lithium ion secondary battery, or the like.

The arithmetic circuit 3 calculates the remaining capacity by detecting the voltage, current and temperature of the battery. 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.

The temperature of the battery is detected by a temperature sensor.
The temperature sensor is disposed close to each battery module battery or is provided in contact with each battery module. 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 battery group 1 in which a plurality of secondary batteries are connected in series detects the voltage and temperature of each secondary battery separately, or one battery unit in which a plurality of secondary batteries are connected in series. Detects voltage and temperature.

The arithmetic circuit 3 calculates the maximum charge capacity of the battery from the deterioration information stored in the deterioration information storage device 9. The method of calculating the maximum charge capacity from the deterioration information does not require the battery module to be fully charged and does not need to be completely discharged, and can quickly calculate the maximum charge capacity.

In order to calculate the maximum charge capacity from the deterioration information, for example, the internal resistance of the battery module is detected and
Calculate the maximum charge capacity from the internal resistance. When the battery module deteriorates, the internal resistance increases and the maximum charge capacity decreases. Since the internal resistance of the battery module 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 9. The arithmetic circuit 3 detects the internal resistance of the battery module, compares the internal resistance with the deterioration information, and calculates the maximum charge capacity.

The internal resistance of the battery module can be detected from the current and voltage flowing through the battery module. This is because the voltage drop due to the internal resistance lowers the output voltage of the battery module. 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 and the output voltage when a predetermined current flows through the battery module. The internal resistance is calculated by dividing the voltage drop by the current.

Further, the arithmetic circuit 3 shown in the figure calculates the remaining capacity by subtracting the discharging capacity from the charging 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.

The arithmetic circuit 3 calculates the relative remaining capacity of each battery module in the above-described manner. As time elapses, the difference in the relative remaining capacity of each battery module increases. In addition, the calculated relative remaining capacity also increases as errors accumulate. 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. The charging efficiency is not always a constant value, and changes depending on, for example, the temperature of the battery module, the amount of heat generated by a battery that is almost fully charged, and the like.

When the difference between the calculated relative remaining capacities of the respective battery modules increases, the arithmetic circuit 3 charges by the following method to reduce the difference between the substantial battery capacities. Arithmetic circuit 3
Performs a calibration charge that reduces the difference between the actual battery capacities when detecting that the difference between the maximum remaining capacity and the minimum remaining capacity of each battery module is, for example, 10 to 50% of the full charge capacity. I do. This is because the electrical characteristics of some battery modules may be degraded by the calibration charging.

FIGS. 3 and 4 show a state in which the actual battery capacity of the battery module changes in the calibration charging for reducing the difference in the actual battery capacity of the battery module.
The arithmetic circuit 3 controls the motor control device 5 and the engine control device 8 to charge and discharge the battery group 1 so that the relative remaining capacity of each battery module is in the actual use area in a normal state. The arithmetic circuit 3 controls the charging and discharging of the battery pack based on the calculated relative remaining capacity so that the relative remaining capacity becomes the actual use area. When the difference between the relative remaining capacities of the respective battery modules becomes larger and exceeds a predetermined range, as shown in FIG. 3, calibration charging is performed until the relative remaining capacities of the battery modules enter the charging prohibited area. In this drawing, the area indicated by dots on the upper side shows the range of the calculated relative remaining capacity of each battery module, and the lower side shows the range where the actual battery capacity of the actual battery module is distributed. However, since the actual battery capacity of the battery module cannot be calculated, the control of the assembled battery is controlled by the calculated relative remaining capacity.

The calibration charge preferably comprises
The battery group 1 is charged with a constant current. In the battery group 1 charged in this state, first, the battery module having the maximum substantial battery capacity is fully charged. Thereafter, the battery modules are fully charged one after another in the order of the real battery capacity. A fully charged battery module has a capacity of 10
It is kept at 0%. Since the battery module having a small real battery capacity is charged in a state where the battery module having a large real battery capacity is fully charged, the real battery capacity of the battery module is reduced as shown in FIG. This is because a fully charged battery module is in a fully charged state, and a battery module having a substantially small battery capacity approaches full charge.

In calibration charging, it is important to reduce deterioration of a fully charged battery module. The battery can be further charged in a fully charged state by low-rate charging in which the battery is charged with a small current, so that deterioration in performance can be reduced. In order to realize this, the apparatus shown in the drawing performs calibration charging of the battery group 1 with the emergency charger 7. The emergency charger 7 is provided in the electric vehicle to charge the battery group 1 with the battery for electrical equipment 6 when the remaining capacity of the battery group 1 becomes low and the engine 2 cannot be started. The emergency charger 7 is suitable for charging the battery group 1 with a small-capacity electrical battery 6, reducing the charging current, and charging the battery group 1 at a low rate. The emergency charger 7 performs, for example, calibration charging of the assembled battery with a charging current of 0.1 to 0.5C.

The battery group 1 is charged by the emergency charger 7 before the electric battery 6 is over-discharged.
Is started to charge the electric battery 6. The engine 2 can sufficiently charge the electric battery 6 in the idling state. This is because the charging current is small. Therefore, this method prevents the electrical battery 6 from being over-discharged,
A battery group can be charged at a low rate by an electric battery. In this method, when the electric vehicle is stopped, the engine 2 can be started to charge the electric battery 6.

The arithmetic circuit 3 stops the calibration charging when the difference between the actual battery capacities of the respective battery modules decreases. The timing at which the calibration charging is stopped is determined by detecting the battery voltage of each battery module, detecting the gradient at which the temperature of each battery module rises, or using a timer. The voltage or temperature rise gradient is detected by detecting that the voltage of the battery module with the lowest relative remaining capacity has risen to the set voltage or that the temperature rise gradient has reached the set value, and then performing calibration charging. To stop. The timer method starts counting the timer when the battery module is first fully charged, and stops the calibration charging when the timer times out.

In the method of charging the battery group 1 at a low rate by the emergency charger 7, the calibration charging can be stopped by any of the methods described above.

Further, the battery group 1 to be calibrated and charged can be directly charged by the generator of the engine 2 while forcibly cooling. This method also allows the battery group 1 to be charged while the engine 2 is idling. This method
A fully charged battery is charged while being cooled while being charged with a larger current than low-rate charging, so that deterioration in battery performance can be reduced. This method performs calibration charging while forcibly cooling all battery modules. The battery module can be forcibly cooled by blowing cooling air.

According to this method, the calibration charging is stopped by detecting a gradient in which the temperature of the battery module having the minimum relative remaining capacity rises. Further, the voltage of the battery module having the minimum relative remaining capacity is detected, and the calibration charging can be stopped when the voltage reaches the set voltage. The set voltage for stopping the calibration charge can be constant, but can be changed according to the temperature. This is because, when the temperature increases, the set voltage is lowered to reduce the performance degradation of the battery module.

Further, the arithmetic circuit 3 controls the motor control device 5 and the engine control device 8 to charge and discharge the battery group 1 in a normal state. The arithmetic circuit 3 is configured such that the relative remaining capacities of all the battery modules are larger than the discharge prohibition area and smaller than the charge prohibition area except for the calibration charge for correcting the difference in the actual battery capacity to be small, that is, in a normal state. Charge / discharge is controlled so as to be in a range, that is, an actual use area. The discharge inhibition area and the charge inhibition area are stored in a storage element (not shown) such as a semiconductor memory built in the arithmetic circuit 3.

The discharge prohibition region is a value that minimizes battery deterioration when the battery module is discharged, for example,
10 to 40% of the maximum charging capacity, more preferably 20 to
Set to 30%. The lower the discharge prohibition area, the more
The capacity that can actually discharge the battery increases. Conversely, when the discharge prohibition region is increased, the actual discharge capacity of the battery decreases, but the deterioration of the battery can be reduced.

The charge prohibition region is a state in which the relative remaining capacity is smaller than the fully charged state, and is 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 charge prohibition region is set higher, the capacity that can actually charge the battery increases. Conversely, when the charge prohibition region is lowered, the actual discharge capacity of the battery decreases, but the deterioration of the battery can be reduced.

The discharge prohibition region and the charge prohibition region 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 3 can change the discharge prohibition region and the charge prohibition region according to the maximum charge capacity of the battery without setting the discharge prohibition region and the charge prohibition region to fixed values. This method is intended to reduce the deterioration of the battery while maintaining a large dischargeable capacity of the battery.

FIG. 5 shows a state in which the discharge prohibition area and the charge prohibition area 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 increases the charge-discharge allowable range by reducing the discharge-prohibited area and increasing the charge-prohibited area. In this figure, when the maximum charge capacity decreases, the arithmetic circuit
The discharge prohibited area is changed from 30% to 20% of the maximum charge capacity, and the charge prohibited area is changed from 70% to 80%.

As described above, when the discharge prohibition area and the charge prohibition area are changed, even if the maximum charge capacity of the battery is reduced to 2/3, the capacity that can be discharged does not substantially decrease. When the maximum charge capacity decreases, the extent to which the discharge prohibition area and the charge prohibition area 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 battery is not completely discharged in the discharge prohibited area, and the charge prohibited area is set to be smaller than 100% of the maximum charge capacity. This is for preventing a rapid deterioration of the battery.

[0039]

The charging / discharging control method of a battery group for driving an electric vehicle according to the present invention has a feature that the difference in the remaining capacity of a large number of battery modules can be reduced and the capacity that can be charged / discharged substantially can be increased. It is the charge / discharge control method of the present invention,
When the difference in the remaining capacity of the battery module increases,
The battery is not charged in the normal state, the calibration charging is performed up to the charging prohibition region, the battery module with the substantial battery capacity is fully charged in order, and the battery module with the small real battery capacity is charged to increase the real battery capacity. is there. A battery module with a large real battery capacity is fully charged and the capacity does not increase, but a battery module with a small real battery capacity is charged. For this reason, the capacity difference between the battery modules is reduced. When the difference in relative remaining capacity decreases,
The capacity of the battery pack that can be charged and discharged substantially increases.

Further, according to the charge / discharge control method of the present invention, when it is detected that the difference between the relative remaining capacities is large, the battery modules having substantially larger battery capacities are sequentially fully charged. There is also a feature that the relative remaining capacity of the can be accurately corrected.

[Brief description of the drawings]

FIG. 1 is a graph showing a state in which a battery module is charged and discharged in an actual use area.

FIG. 2 is a circuit diagram of an electric vehicle used in the charge / discharge control method of the present invention.

FIG. 3 is a graph showing a state in which a battery module having a large relative remaining capacity is fully charged by the method of the present invention.

FIG. 4 is a graph showing a state in which a battery module having a small relative remaining capacity is charged to increase a relative remaining capacity while sequentially charging a plurality of battery modules having a large relative remaining capacity by the method of the present invention.

FIG. 5 is a graph showing a state in which a discharge prohibition region and a charge prohibition region are changed according to a maximum charge capacity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery group 2 ... Engine 3 ... Arithmetic circuit 4 ... Motor 5 ... Motor control device 6 ... Battery for electrical equipment 7 ... Emergency charger 8 ... Engine control device 9 ... Deterioration information storage device

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H02J 7/00 B60K 9/00 C F-term (Reference) 2G016 CA03 CB12 CB21 CB22 CB31 CB32 CC01 CC02 CC13 CC23 CC27 CC28 5G003 AA07 BA03 CA02 CA14 CB01 DA04 DA12 EA05 EA09 FA06 5H030 AA03 AA04 AA08 AS08 BB01 BB10 DD20 FF22 FF41 5H115 PG04 PI16 PI22 PI29 PU01 PU26 QN12 SE06 TI02 TI05 TI06 TI10 TR19 TU17

Claims (6)

[Claims] A relative remaining capacity of battery modules connected in series is calculated, and a relative remaining capacity of each battery module is controlled in an actual use area provided between a charge inhibition area and a discharge inhibition area. In the charge / discharge control method for a battery group that drives an electric vehicle that is charged / discharged, the difference in the relative remaining capacity of each battery module exceeds a predetermined range. Calibration charging until the battery module with the largest real battery capacity is fully charged, while increasing the real battery capacity of the battery module with the smallest real battery capacity, A charge / discharge control method for a battery group that drives an electric vehicle that corrects a difference in capacity to be small. 2. The charge / discharge control method for a battery group for driving an electric vehicle according to claim 1, wherein in the calibration charging, the charging is stopped by detecting a temperature gradient of the battery module having the minimum relative remaining capacity. 3. The charge / discharge control method for a battery group for driving an electric vehicle according to claim 1, wherein the calibration charge is performed while forcibly cooling the battery group. 4. The charge / discharge control method for a battery group for driving an electric vehicle according to claim 1, wherein the electric vehicle is stopped, and the generator is driven by the engine in an idling state to perform calibration charging. 5. The method according to claim 1, wherein the calibration charging is a low-rate charging. 6. The charge / discharge control method for a group of batteries for driving an electric vehicle according to claim 5, wherein low-rate charging is calibrated by an emergency charger mounted on the electric vehicle.