JP2005065352A - Battery charge/discharge controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery charge/discharge controller capable of avoiding the influence of memory effect while preventing overdischarge of a battery. <P>SOLUTION: A battery is subjected to charge/discharge control such that the battery capacity falls within a use SOC range of a fixed width defined by an upper limit SOCmax and a lower limit SOCmin. When memory effect occurs in the vicinity of the lower limit SOCmin of the use SOC range, the use SOC range is altered by increasing the upper limit SOCmax and the lower limit SOCmin simultaneously by ΔSOC1. The use SOC range after alteration is represented by a formula SOCmax+ΔSOC1≥SOC≥SOCmin+ΔSOC1 and does not include a memory effect generating region. Since the battery is charged/discharged in the use SOC range after alteration, generation of memory effect is prevented and overdischarge of the battery can be avoided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery charge / discharge control device for a battery used in a hybrid vehicle or the like.
[0002]
[Prior art]
Conventionally, when a battery using a nickel compound, such as a nickel metal hydride battery, is used as a power source for a hybrid vehicle, it is actually possible to repeatedly charge the battery before full discharge or to discharge before full charge. The memory effect that the usable capacity is reduced occurs. In response to the occurrence of such a memory effect, a technique is known in which the memory effect is eliminated by changing the width of the SOC (State Of Charge) range of the battery to discharge the battery to near full discharge ( For example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-69608
[Problems to be solved by the invention]
However, in the above-described prior art, the memory effect is eliminated by expanding the range of the SOC usage range of the battery to the vicinity of complete discharge. However, since the voltage drop in the vicinity of complete discharge is abrupt in a battery using a nickel compound, such control may cause the battery to be in an overdischarge state, resulting in a decrease in battery life. It was.
[0005]
The present invention provides a battery charge control device capable of avoiding the influence of the memory effect while preventing overdischarge of the battery.
[0006]
[Means for Solving the Problems]
In the battery charge / discharge control device according to the present invention, the charge / discharge of the battery is controlled by the control means so that the battery capacity falls within a constant width capacity control range defined by the upper limit value and the lower limit value. Then, it is determined by the determining means whether or not the memory effect is generated in the battery in the capacity control range. When it is determined that the memory effect has occurred, the changing unit changes the capacity control range while maintaining a constant width so as not to include the memory effect generation range.
[0007]
【The invention's effect】
According to the present invention, when the memory effect occurs in the battery in the capacity control range, the capacity control range is changed while the capacity control range is kept constant so as not to include the memory effect generation range by the capacity control range changing means. The battery charge / discharge control is performed without using the memory effect occurrence region. As a result, the battery can be prevented from being overdischarged, and the battery can be charged and discharged without being affected by the memory effect.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining an embodiment of a battery charge / discharge control device according to the present invention, which is applied to a hybrid vehicle. The hybrid vehicle shown in FIG. 1 is a combination of a parallel system and a series system, and includes an engine 1 and an electric motor 2 as drive sources. The engine 1 is connected to the speed reducer 5 and the generator 4 via the power split mechanism 3, and the driving force of the engine 1 is divided into the driving force of the wheels 6 and the driving force of the generator 4 by the power split mechanism 3.
[0009]
The electric motor 2 is connected to a driving battery 8 via an inverter 7. Electric power is supplied from the battery 8 to the electric motor 2 when the motor is running, and the electric motor 2 is regeneratively generated during braking, and the battery 8 is charged by the regenerative power. The vehicle controller (HCM) 9 is an engine controller based on the accelerator pedal depression amount detected by the accelerator sensor 10, the brake pedal depression amount detected by the brake sensor 11, the vehicle traveling speed detected by the vehicle speed sensor 12, and the like. (E / C) 13, motor controller 14, battery controller 15 and brake controller 16 are controlled to control the driving force and braking force of the vehicle.
[0010]
The brake controller 16 controls the hydraulic pressure source 17 based on a command signal from the vehicle controller 9 to adjust a braking force by a hydraulic brake (not shown) provided on the wheel 6. The engine controller (E / C) 13 performs start / stop control of the engine 1 based on the start / stop signal of the engine 1 transmitted from the vehicle controller 9, and the engine torque is set to a torque command value from the vehicle controller 9. A throttle valve opening / closing device (not shown), a fuel injection device, and an ignition timing control device are controlled so as to match.
[0011]
The motor controller 14 controls the inverter 7 on the basis of the drive (power running) command, regenerative braking (power generation braking) command, and rotation speed command transmitted from the vehicle controller 9 to rotate the rotation speed of the electric motor 2. And adjust the torque. The battery controller 15 is based on the command signal from the vehicle controller 9, the battery voltage detected by the voltage sensor 18, the charge / discharge current detected by the current sensor 19, the battery temperature detected by the temperature sensor 20, and the like. Charge / discharge control and calculation of the state of charge (SOC).
[0012]
The hybrid vehicle shown in FIG. 1 travels by driving the electric motor 2 with the electric power of the battery 8 when starting or when traveling at a very low speed. During normal travel, the engine power is divided into two paths by the power split mechanism 3, and one of the split power directly drives the wheels 5. The other side drives the generator 4 to generate electric power, and the electric motor 2 is driven by the electric power to assist the driving force. Electric power is also supplied from the battery 8 to the electric motor 2 during full-open acceleration that requires a larger driving force.
[0013]
During such power running, as described above, the driving force of the vehicle is determined based on the accelerator operation amount, the brake operation amount, and the vehicle speed. Further, it is determined whether or not power generation is necessary based on the calculated SOC of the battery 1, and the engine 1, the electric motor 2, and the generator 4 are determined based on the information such as the driving force and the necessity for power generation described above. The generated torque is calculated, and the engine 1, the electric motor 2, and the generator 4 are controlled. For example, when the SOC of the battery 8 becomes too small, the generator 4 is driven by the power of the engine 1 to charge the battery 8.
[0014]
At the time of braking and deceleration, the electric motor 2 is driven by the driving force of the wheels 5, and the electric motor 2 is operated as a generator to perform regenerative power generation. Then, the battery 8 is charged with the regenerative power. At this time, the engine 1, the electric motor 2, and the generator 4 are controlled in consideration of the regenerative braking force of the vehicle, and the braking force obtained by subtracting the regenerative braking force corresponding to the maximum chargeable power of the battery 8 from the required braking force. Is generated by an engine brake or a hydraulic brake.
[0015]
As described above, in the hybrid vehicle, the battery 8 is charged by regenerative power generation during deceleration and braking. However, when the battery 8 is in a state near the full charge, the controllability is poor. Charge / discharge control is performed within a predetermined SOC range that does not include the vicinity. For example, charge / discharge control is performed so that the SOC is in the range of 40% to 80%. However, in a nickel-based secondary battery such as a nickel metal hydride battery, when charging and discharging are repeatedly performed in the SOC range (40% to 80%) as described above, a memory effect that a capacity that can be actually used is reduced occurs. .
[0016]
FIG. 3 is a diagram for explaining the memory effect of the battery 8 composed of a nickel metal hydride battery. In FIG. 3, the horizontal axis represents the SOC of the battery, and the vertical axis represents the battery voltage. A solid line L10 indicates a voltage-SOC characteristic before the memory effect occurs, and a broken line L20 indicates a voltage-SOC characteristic when the memory effect occurs. The range “SOCmax ≧ SOC ≧ SOCmin” in FIG. 3 indicates a normal SOC range in which the memory effect does not occur. For example, SOCmin = 40% and SOCmax = 80% are set. When the battery 8 is discharged, the SOC of the battery 8 decreases and moves to the right side in the figure within the SOC range of use in FIG. On the contrary, when charging is performed, the SOC increases and moves to the left in the used SOC range.
[0017]
Before the memory effect occurs (L10), the battery voltage at the lower limit SOCmin of the used SOC range is Vmin, but after the memory effect occurs, it decreases to V′min (<Vmin). When the charge / discharge control is actually performed, the control is performed based on the battery voltage. Therefore, it is determined that the battery cannot be used below the lower limit voltage Vmin. Therefore, normally, as shown by the solid line L10 in FIG. 3, it can be used up to SOC = SOCmin, but when it changes as shown by the broken line L20, the remaining capacity below SOC = SOC1 is regarded as an unusable capacity. The usable capacity is reduced by (SOC1-SOCmin). In this way, the state where the capacity that can actually be used is reduced is called the memory effect.
[0018]
As can be seen from FIG. 3, when the SOC of the battery 8 becomes smaller than the SOC 1, the battery voltage tends to decrease rapidly. For this reason, if the battery 8 is used with the SOC range expanded as in the prior art described above, the battery 8 may be overdischarged. In the present embodiment, the memory effect control at the time of charging / discharging to avoid such overdischarge is performed, and control is performed so as to eliminate the generated memory effect. .
[0019]
<Control when memory effect occurs>
Next, control when the memory effect occurs will be described. FIG. 2 is a flowchart for explaining control for avoiding the influence of the memory effect of the battery 8 and eliminating the memory effect, and shows processing executed by the battery controller 15. A series of processes shown in the flowchart of FIG. 2 is started when the ignition switch of the vehicle is turned on, and thereafter repeatedly executed at predetermined time intervals until the ignition switch is turned off.
[0020]
In step S10, it is determined whether or not the memory effect has occurred in the battery 8. If it is determined that the memory effect has not occurred, the flowchart of FIG. That is, the initial setting SOCmax ≧ SOC ≧ SOCmin is used as the use SOC range, and charge / discharge control of the battery 8 is performed. On the other hand, if it is determined in step S10 that the memory effect has occurred, the process proceeds to step S20. Here, there are various methods for determining whether or not the memory effect has occurred. For example, the determination is made as in the following (a) and (b).
[0021]
(A) When the voltage of the battery 8 detected by the voltage sensor 18 during charging / discharging reaches the voltage Vmin at the lower limit SOCmin of the used SOC range, it is determined that the memory effect has occurred. When charge / discharge control is performed in the normal use SOC range (SOCmax ≧ SOC ≧ SOCmin), the memory effect is not generated because the battery 8 is controlled to be charged when the SOC approaches SOCmin. When the battery voltage does not reach the lower limit value Vmin. However, when the memory effect occurs and the characteristics change to L20 in FIG. 3, the voltage Vmin is detected when the SOC of the battery 8 becomes SOC1 even when charge / discharge control is performed within the normal SOC range. Is done.
[0022]
(B) The battery voltage and the battery current are detected at a plurality of points during discharging, the IV characteristic line is regressed from the sampling data, and the internal resistance of the battery 8 is obtained from the IV characteristic line. Then, the internal resistance is obtained for each of a plurality of different SOCs, and it is determined that the memory effect has occurred when the internal resistance in the vicinity of the lower limit SOCmin of the SOC is larger than the internal resistances of other SOC regions.
[0023]
Hereinafter, the case of (a) will be described as an example. When it is determined that the memory effect has occurred and the process proceeds from step S10 to step S20, the range width (SOCmax−SOCmin is set so as to avoid the memory effect occurrence range greatly deviated from the original characteristic L10 as shown in FIG. ) Is maintained, and the use SOC range of charge / discharge control is increased from the normal use SOC range (SOCmax ≧ SOC ≧ SOCmin) to the one where the SOC increases. That is, the SOC range in which SOCmax ≧ SOC ≧ SOCmin is increased to SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1 as a whole by + ΔSOC1.
[0024]
The magnitude ΔSOC1 to be raised may be set so as not to include an area where the deviation between the solid line L10 and the broken line L20 is large (area where the memory effect occurs), as in ΔSOC1 of FIG. Since the broken line L20 can be obtained in advance as a battery characteristic by actual measurement or the like, ΔSOC1 may be set based on the actual measurement value. When increasing the SOC range to be used by + ΔSOC1 such as SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1, it is desirable to reduce the rate of increase in SOC in order to prevent sudden changes in vehicle behavior. Is preferred.
[0025]
By the process of step S20, there is almost no deviation between the solid line L10 and the broken line L20 within the newly set SOC range (SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1). Therefore, as long as charge / discharge control is performed within this range, the SOC range in which the memory effect is generated is not used, so that there is no inconvenience that the actually usable remaining capacity is reduced.
[0026]
Next, in step S30, it is determined whether or not the battery voltage detected by the voltage sensor 18 has reached a preset upper limit voltage Vu (see FIG. 3). If it is determined that the upper limit voltage Vu has been reached, step S30 is performed. The process proceeds to S40, and if it is determined that the upper limit voltage Vu has not been reached, the process returns to Step S10. The upper limit voltage Vu defines a charging voltage at which the battery 8 is overcharged. When returning from step S30 to step S10, it is determined again whether the memory effect has occurred. In this case, since the used SOC range is changed to “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1” in step S20, it is determined whether or not the memory effect has occurred depending on whether or not the voltage value corresponding to the lower limit SOCmin + ΔSOC1 has been detected.
[0027]
At the beginning of the change in which the used SOC range is changed to “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1” in step S20, the memory effect does not occur. Therefore, it is determined as NO in step S10, and the process of the flowchart of FIG. That is, the charge / discharge control of the battery 8 is performed based on the use SOC range “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”. Thereafter, when a predetermined time elapses, the control of FIG. 2 is executed again.
[0028]
As described above, when the use SOC range is changed to “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”, the memory effect does not occur, and NO is always determined in step S10, and the use SOC range is maintained as “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”. The However, if charging / discharging is repeated in this range, as shown in FIG. 4, the memory effect may occur again in the vicinity of the control lower limit SOCmin + ΔSOC1 of the used SOC range “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”. In such a case, it is determined in step S10 that a memory effect has occurred, and the process proceeds to step S20.
[0029]
FIG. 4 shows battery characteristics (broken line L20) when the memory effect occurs when charge / discharge control is performed in the SOC range “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”. In the vicinity of the lower limit SOCmin + ΔSOC1 of the used SOC range, the broken line L20 is greatly deviated from the solid line L10, and the memory effect occurs. In step S20, the entire current use SOC range “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1” is increased by + ΔSOC2, and “SOCmax + ΔSOC1 + ΔSOC2 ≧ SOC ≧ SOCmin + ΔSOC1 + ΔSOC2” is set as a new use SOC range. When the voltage corresponding to SOCmax + ΔSOC1 + ΔSOC2 exceeds the upper limit voltage Vu of the battery 8, the upper limit of the used SOC range is set to SOCu corresponding to the upper limit voltage Vu.
[0030]
If the process in step S20 is performed several times, the upper limit of the SOC range used becomes SOCu, and the battery voltage detected by the voltage sensor 18 may reach the upper limit voltage Vu. In such a case, YES is determined in step S30, and the process proceeds to step S40. In step S40, it is determined whether or not the memory effect has occurred as in step S10. If the memory effect has occurred near the lower limit of the used SOC range as shown in FIG. 5, the process proceeds to step S50.
[0031]
In step S50, the lowering of the lower limit of the used SOC range in FIG. 5 is started. Also in this case, it is gradually lowered at a rate of about 1% / min. In step S60, the median of the used SOC range during the descent is compared with the actual SOC of the battery 8, and “median> actual SOC” and “(median−actual SOC) <(median of 5 %) ”Is determined. If “YES” is determined in the step S60, the process proceeds to a step S70 to stop the lowering of the lower limit. That is, as the battery 8 is discharged and the actual SOC decreases, the lower limit of the used SOC range moves to the right side of FIG. The amount of descent until the stop is SOCu- (SOCmax-SOCmin) -SOC3. If SOC3 at the stop position is smaller than SOCmin, which is the lower limit of the initial value, the lower limit is set to SOCmin.
[0032]
In step S80, the lower limit of the used SOC range is fixed to the value stopped in step S70, and the upper limit of the used SOC range is lowered by the same value as the lower limit. Also in this case, it is gradually lowered at a descending speed of about 1% / min. In step S90, it is determined whether or not the use SOC range is equal to the initial use SOC range “SOCmax ≧ SOC ≧ SOCmin”. If it is determined that the use SOC range is equal, the series of processing ends, and if it is determined that they are different. Returning to step S50, the descent process from step S50 to step S80 is performed again.
[0033]
In the lower limit lowering process from step S50 to step S70, charging / discharging is performed in a region where the battery voltage is lower than the region where the memory effect occurs. As a result, the memory effect is eliminated. Furthermore, since the battery voltage is sufficiently higher than V′min in FIG. 3 when the memory effect is eliminated, there is no possibility that the battery 8 will be overdischarged.
[0034]
In addition to the above-described determination methods (a) and (b) for occurrence of the memory effect, there are determination methods as described in the following (c) and (d).
(C) When the charge / discharge time reaches a predetermined time, it is determined that the memory effect has occurred. (D) When the charge / discharge capacity reaches a predetermined capacity, it is determined that the memory effect has occurred.
[0035]
In the correspondence between the embodiment described above and the elements of the claims, the battery controller 15 is a control means, a judgment means and a change means, the voltage sensor 18 is a voltage detection means, and a drop amount “SOCu− (SOCmax−SOCmin ) -SOC3 "each constitutes a predetermined decrease value. In the above-described embodiment, the charging / discharging control of the traveling battery of the hybrid vehicle has been described as an example. However, if the battery has a memory effect due to repeated charging / discharging in the middle capacity range, The present invention can be applied. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an embodiment of a battery charge / discharge control device according to the present invention.
FIG. 2 is a flowchart showing control when a memory effect occurs.
FIG. 3 is a diagram for explaining a memory effect of a battery 8 composed of a nickel metal hydride battery.
FIG. 4 is a diagram showing battery characteristics when a memory effect occurs when charge / discharge control is performed in a use SOC range “SOCmax + ΔSOC1 ≧ SOC ≧ SOCmin + ΔSOC1”.
FIG. 5 is a diagram illustrating a lower limit lowering operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 2 Electric motor 7 Inverter 8 Battery 9 Vehicle controller 13 Engine controller 14 Motor controller 15 Battery controller 18 Voltage sensor 19 Current sensor

Claims (2)

Control means for controlling charging / discharging of the battery so that the battery capacity is within a constant width capacity control range defined by the upper limit value and the lower limit value;
Determination means for determining whether or not a memory effect is generated in the battery in the capacity control range;
And changing means for changing the capacity control range while maintaining the constant width so as not to include the generation range of the memory effect when it is determined that the memory effect is generated. Battery charge / discharge control device. The battery charge / discharge control device according to claim 1,
Voltage detecting means for detecting the voltage of the battery;
If the voltage detected by the voltage detection means after the change of the capacity control range reaches a predetermined upper limit voltage, the changing means decreases the lower limit value by a predetermined decrease value according to the capacity of the battery, and thereafter The battery charge / discharge control apparatus, wherein the upper limit value is decreased by the predetermined decrease value.

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