JP3767422B2 - Charging method and charging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging method and a charging device for charging a driving secondary battery mounted on an electric vehicle or the like.
[0002]
[Prior art]
Generally, a secondary battery in which a plurality of cells are connected in series is used as a driving battery for an electric vehicle. When charging this secondary battery, multi-stage constant current charging, which reduces the charging current step by step by a constant current value, is carried out in the latter stage of charging in order to reduce the effect of voltage drop due to the cell internal resistance. Many. In multi-stage constant current charging, when the cell voltage of any cell reaches the charging target voltage, charging is performed by reducing the charging current by a predetermined current value, and then charging is performed again when the cell voltage reaches the charging target voltage again. Charging is performed by reducing the current by a predetermined current value. Such charging is repeated, and the charging is terminated when the charging current finally becomes equal to or lower than the charging end current.
[0003]
Moreover, it is preferable that the charging state of each cell is uniform, and even with the above-described multi-stage constant current charging, there is an effect of reducing voltage variation between the cells. However, in order to further enhance the reduction effect, the capacitance adjustment circuit is made to discharge at a constant current so that the cell voltage of all the cells becomes the same voltage as a reference cell (for example, a cell showing the lowest cell voltage). I have to. Actually, charging and discharging are performed simultaneously by bypassing part of the charging current of each cell.
[0004]
[Problems to be solved by the invention]
However, in the conventional charging method described above, since the reduction value of the charging current is constant or the discharge current value is constant, it is not possible to sufficiently suppress variation.
[0005]
The objective of this invention is providing the charging method and charging device which can suppress the dispersion | variation in the charge condition between cells in the charging method and charging device of a secondary battery comprised with a some cell.
[0006]
[Means for Solving the Problems]
  The embodiment of the invention will be described with reference to FIGS. 1, 2 and 6. FIG.
  (1) Describing in association with FIGS. 1, 2 and 6, the invention of claim 1 is directed to charging the secondary battery 1 composed of a plurality of cells C1 to Cn as the charging current I as the charging progresses.TheDecrease graduallyMakeCell of any cell that is applied to the charging method and that constitutes the secondary battery 1FruitEach time the voltage reaches the charge target cell voltage Vf,Charge target cell voltage Vf andLower than the lower limit voltage Vh of the target cell voltage variation rangeHas a valueCellCellVoltage VcmaxThe larger the difference ΔV,, Decrease charging current I step by stepIncrease the amount of reductionThis achieves the above-mentioned purpose.
  (2) Describing in association with FIG. 1, the invention according to claim 2 is the charging method according to claim 1,Bypassing a part of the charging current flowing into the cell to the cellThe charge state between the cells C1 to Cn is uniform.When adjusting capacity, increase the bypass current for cells with higher cell voltageIt is what I did.
  (3) Describing in association with FIGS. 1, 2 and 6, the invention of claim 3 applies the charging current I to the secondary battery 1 composed of a plurality of cells C1 to Cn as the charging progresses.TheDecrease graduallyMakeApplied to the charging device to charge the cells of cells C1 to CnFruitCell voltage detection devices B1 to Bn for detecting voltages respectively, and cells detected by the cell voltage detection devices B1 to BnFruitA determination device 4 for determining whether any one of the voltages has reached a charge target cell voltage Vf;FruitWhen it is determined that one of the voltages has reached the charge target cell voltage,Charge target cell voltage andLower than the lower limit voltage Vh of the target cell voltage variation rangeHas a valueCellCellVoltage VcmaxThe larger the difference ΔV,, Charging current IStep by stepDecreaseIncrease the amount of reductionThe charging current reducing device 4 is provided to achieve the above object.
  (4) Describing in association with FIG. 1, the invention of claim 4 is the charging device according to claim 3,Capacity adjusting devices A1 to An for bypassing a part of the charging current flowing into the cell are provided for each cell C1 to Cn, and the capacity adjusting devices A1 to An bypass a cell having a higher cell actual voltage. The current was increased.
  (5) When explained in association with FIG. 1 and FIG.3In the charging device described inCapacitance adjusting devices A1 to An that bypass a part of the charging current flowing into the cell with respect to the cell are provided for each of the cells C1 to Cn.Capacity adjustment device A1-An is a cellFruitIf the voltage is lower than the lower limit voltage Vh, the firstBypass only the current value,cellFruitIf the voltage is higher than the lower limit voltage Vh, the firstCurrent valueA larger secondBypass only the current valueIs.
  (6) Describing in association with FIG. 1, the invention of claim 6 is the charging device according to claim 3,Provided for each of the cells C1 to Cn and bypass a part of the charging current flowing into the cells C1 to Cn to the cellCapacity adjustment circuits A1 to An and cells C1 to CnFruitVoltageThe larger theCapacitance adjustment circuits A1 to AnSo that the bypass time is longerAnd a controller 4 to be controlled.
  (7) Describing in association with FIG. 6, the invention of claim 7 is the charging device according to claim 6, wherein the controller is a cellFruitWhen the voltage is higher than the lower limit voltage VhbypassTime, cellFruitWhen the voltage is lower than the lower limit voltage VhbypassThe control is made to be longer than the time.
[0007]
In the section of means for solving the above problems, the drawings of the embodiments of the invention are used for easy understanding of the present invention. However, the present invention is not limited to the embodiments of the invention. Absent.
[0008]
【The invention's effect】
  (1) According to the invention of claim 1 and claim 3,Charge target cell voltage andLower than the lower limit voltage of the target cell voltage variation rangeHas a valueCellCellThe difference from the voltageThe bigger it is,Charge currentStep by stepDecreaseIncrease the amount of reductionSince it did in this way, the variation in the charge condition between each cell can be reduced efficiently.
  (2) According to the inventions of claims 2, 4 and 5, in addition to the effects of the inventions of claim 1 and claim 3 described above,Current to be bypassed during capacity adjustmentcellFruitVoltageBecause the larger the larger, Variation in the state of charge between cells can be further reduced.FruitThe voltage is almost equal.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a charging device according to the present invention, and shows a configuration of the charging device. The secondary battery 1 is obtained by connecting cells C1 to Cn in series. Each cell is provided with a capacity adjustment circuit A1 to An composed of a resistor 7 and a transistor 8, and voltage detection circuits B1 to Bn for detecting cell voltages Vc1 to Vcn of the cells C1 to Cn, respectively. The transistors 8 of the capacitance adjustment circuits A1 to An are turned on / off by a signal from the controller 4. The controller 4 receives the cell voltages Vcy (y = 1, 2,..., N) of the cells C1 to Cn detected by the voltage detection circuits B1 to Bn.
[0010]
When the transistor 8 of the capacity adjustment circuit A1 is turned on by a signal from the controller 4, a part of the charging current of the cell C1 is bypassed to the capacity adjustment circuit A1. As a result, the charging current flowing through the cell C1 is reduced, and the amount of charge per unit time is reduced as compared with the case where bypassing is not performed. The same applies to the other capacitance adjustment circuits A2 to An. Details of the capacity adjustment will be described later.
[0011]
A charger 6 is connected to the secondary battery 1 via a relay switch 5. The charger 6 incorporates a CPU or the like, receives control information corresponding to the state of the secondary battery 1 from the controller 4, and controls the charging current based on the control information. The relay switch 5 is turned on / off by the controller 4 and turned on when charging, and turned off when charging is completed. Reference numeral 2 denotes a temperature sensor that detects the temperature of the secondary battery 1. The charging current is detected by the current sensor 9, and the inter-terminal voltage of the secondary battery 1 is detected by the total voltage detection sensor 3.
[0012]
FIG. 2 is a diagram showing a charging pattern by the charging device according to the present embodiment. In the first half of charging, constant current charging is performed at a constant current value. In the second half of charging, secondary charging is performed by a method called multistage constant current charging. The battery 1 is charged. In FIG. 2, the horizontal axis represents time t, and the vertical axis represents the voltage V and charging current I of the secondary battery 1. FIG. 2 shows changes in the voltage V and the charging current I of the secondary battery 1 detected during charging. After charging starts, the charging current is I₀If it reaches, it will shift to constant current charging.
[0013]
After the transition to the constant current charging, if the cell voltage of the cells constituting the secondary battery 1 reaches a charging target voltage Vf described later, the transition to the multistage constant current charging is performed. If the multi-stage constant current charging is started, the charging current I is decreased by ΔIs, and the constant current value I₀Charge at -ΔIs. The details of the current value decrease width ΔIs will be described later. Thereafter, every time the cell voltage V reaches the charging target voltage Vf, the charging current I is decreased by ΔIs and the same charging is performed. Then, if the current value when it is decreased by ΔIs becomes smaller than the charging end current value Iend, the multistage constant current charging is stopped and the series of charging operations is ended.
[0014]
Next, the charging operation will be described with reference to the flowcharts of FIGS. These flowcharts show the processing procedure of the charging operation program executed by the controller 4. In step S101, it is determined whether or not the secondary battery 1 may be charged. Here, whether or not charging is possible is determined from the battery temperature detected by the temperature sensor 2 and the open voltage of the secondary battery 1 detected by the total voltage detection sensor 3. For example, when the battery temperature is higher than a predetermined range immediately after using the battery, it is determined that charging is not possible. If it is determined that charging is possible, the process proceeds to step S102, and if it is determined that charging is not possible, the process proceeds to step S117 without performing charging.
[0015]
In step S102, the voltage detection circuits B1 to Bn detect the cell voltages Vcy of the cells C1 to Cn, respectively. Generally, the cell voltages Vcy of the cells C1 to Cn vary depending on the degree of deterioration of the cells. Therefore, the capacity of each cell is adjusted during charging. In step S103, settings relating to capacity adjustment are performed. As an example, as shown in FIG. 6 to be described later, when the cell voltage Vcy is within a predetermined voltage range H with the charging target voltage Vf as the upper limit, the transistors 8 of the capacity adjustment circuits A1 to An are turned on to adjust the capacity. When the cell voltage Vcy is lower than the predetermined voltage range H, the transistor 8 is turned off and the capacitance is not adjusted.
[0016]
For example, in the example shown in FIG. 5, the cell voltages Vc1 and Vcn of the cell C1 and the cell Cn are within a predetermined voltage range H, and the transistors 8 of the capacity adjustment circuits A1 and An are turned on to bypass the current i. . The bypass current i at this time is determined by the resistance value of the resistor 7.
[0017]
Thereafter, after the relay switch 5 is turned on in step S104, charging is started in step S105. After the start of charging, the voltage V and the charging current I of the secondary battery 1 rise as shown in FIG. In step S106, the charging current I of the secondary battery 1 is a predetermined current value I at which constant current charging starts.₀To determine whether I = I₀If it is determined, the process proceeds to step S107 and constant current charging is started.
[0018]
In step S108, the cell voltage Vcy of each of the cells C1 to Cn is detected. In step S109, it is determined whether or not the cell having the maximum cell voltage among the plurality of cells C1 to Cn has reached the charge target voltage Vf in FIG. If it determines with YES in step S109, it will progress to step S110, and if it determines with NO, it will progress to step S119. In step S119, it is determined whether or not the multistage charging flag is set. If YES is determined, the process proceeds to step S116, and if NO is determined, the process returns to step S108. In step S110, it is determined whether there is a cell voltage lower than a predetermined voltage range H with the charging target voltage Vf as an upper limit among the plurality of cell voltages Vcy detected in step S108. If it determines with YES in step S110, it will progress to step S111, and if it determines with NO, it will progress to step S120.
[0019]
FIG. 6 schematically shows the cell voltage distribution, where the horizontal axis represents the cell voltage, the vertical axis represents the number of cells, and each circle represents a cell. FIG. 6A shows the distribution when the cell voltage Vc1 of the cell C1 having the maximum cell voltage becomes the charge target voltage Vf. In the example shown in FIG. 6A, the cell voltage decreases in the order of the cell C1 and the cell C2. The predetermined voltage range H is a range between Vh and Vf, and the cell voltage Vc1 (= Vf) of the cell C1 is within the predetermined voltage range H, but the cell voltages Vcy (y = 3,4,. n) is lower than the predetermined voltage range H. That is, in the state of FIG. 6A, YES is determined in step S110, and the process proceeds to step S111.
[0020]
In step S111, a difference ΔV (= Vf−Vcmax) between the cell voltage Vf of the cell C1 and the maximum voltage Vcmax (cell voltage of the cell C2) within the cell voltage lower than the predetermined voltage range H is calculated. In step S112, the charging current reduction value ΔIs is calculated from the ΔV calculated in step S111 and the internal resistance R of the cell calculated in the controller 4 by the equation (1).
[Expression 1]
ΔIs = ΔV / R (1)
[0021]
Here, a method for calculating the internal resistance R will be described. FIG. 7 is a diagram illustrating the IV characteristics of the secondary battery 1. V₀Is the open circuit voltage of the secondary battery 1, but when the discharge current Id (> 0) flows, the terminal voltage decreases to Vd due to the influence of the internal resistance R. Conversely, when the charging current Ic (<0) flows, the terminal voltage increases to Vcy due to the influence of the internal resistance R. The internal resistance R is calculated from the current value Id and terminal voltage Vd detected during discharging and the current value Ic and terminal voltage Vc detected during charging according to Equation (2).
[Expression 2]
R = (Vc−Vd) / (Id−Ic) (2)
[0022]
Returning to FIG. 4, in step S113, the charging current value I is set to I as shown in FIG.₀To I₀Decrease to -ΔIs. The decrease amount of the current value at this time is ΔIs calculated in step S112. As can be seen from the IV characteristics in FIG. 7, when the charging current is decreased, the cell voltage Vcy of each cell decreases. FIG. 6B shows a distribution when the charging current value is decreased by ΔIs from the state of FIG. 6A, and the distribution is on the left side of the drawing as compared with the case of FIG. It's off. Next, in step S114, a multistage charging flag is set. That is, the charging current value I₀I₀From the point of time when it is decreased to −ΔIs, the process shifts to multi-stage constant current charging.
[0023]
In step S115, the capacity adjustment is reset. For example, the charging current is I₀When the state before the decrease to −ΔIs is the state shown in FIG. 6C, for the cells C1 and C2 within the predetermined voltage range H, the transistors 8 of the capacity adjustment circuits A1 and A2 are turned on to supply current. Bypass. On the other hand, for cells having a cell voltage lower than the predetermined voltage range H, that is, cells on the left side of the predetermined voltage range H in the figure, the transistor 8 of each capacitance adjusting circuit A is turned off so as not to bypass the current.
[0024]
In step S116, it is determined whether or not the charging current value I is equal to or less than the charging end current value Iend. If YES is determined, the process proceeds to step S117, and if NO is determined, the process returns to step S108. That is, until the charging current I becomes equal to or lower than the charging end current value Iend, the processing from step S108 to step S116 is repeatedly executed, and the charging current I decreases every time the cell voltage of any cell reaches the charging target voltage Vf. It is reduced by the width ΔIs.
[0025]
FIG. 6C shows the charging current I from the state of FIG.₀It is a figure when it charges by-(DELTA) Is and the cell voltage of the cell C1 reaches Vf. At this time, the cell voltage Vcy of the cell C2 is in the predetermined voltage range H, the cell voltage is smaller than the predetermined voltage range H, and the cells having the maximum cell voltage are the cells C3 and C4. In this case, ΔV is calculated using the voltages of the cells C3 and C4 as Vcmax, and the charging current reduction width ΔIs is calculated based on this ΔV. Therefore, ΔIs in the case of (a) in FIG. 6 is different from ΔIs in the case of (c), and ΔIs is larger in (a) having a larger variation.
[0026]
When such multi-stage constant current charging is performed, even if the cell voltage at the beginning of the transition to multi-stage constant current charging varies greatly as shown in FIG. 6A, the variation gradually decreases. Then, when all the cell voltages Vcy of the cells C1 to Cn are within the predetermined voltage range H as shown in FIG. 8, NO is determined in step 110 of FIG. 4, and the process proceeds to step S120. In step S120, the charging current is changed to ΔIs.₀Decrease, and then the process proceeds to step S114. That is, as shown in FIG. 8, when the variation in the cell voltage becomes small, the reduction amount of the charging current is set to a predetermined constant ΔIs as in the conventional multi-stage constant current charging.₀And
[0027]
If such multi-stage charging is performed and the charging current I becomes equal to or less than the charging end current value Iend, the process proceeds from step S116 to step S117, the multi-stage charging flag is reset, and the charging is terminated. Then, it progresses to step S118 and the switch 5 of FIG. 1 is turned off, and a series of charging work is complete | finished.
[0028]
<Modification of capacity adjustment method>
In the above-described embodiment, whether or not the adjustment by the capacity adjustment circuits A1 to An is performed is determined depending on whether or not the cell voltage Vcy when the charging current is reduced is within the predetermined voltage range H. The capacity adjustment method is not limited to the above-described method, and there are various methods. Hereinafter, modified examples of the capacity adjustment method will be described.
[0029]
[Modification 1]
In the capacity adjustment method of the first modification, for the cell whose cell voltage Vcy is within the predetermined voltage range H, the bypassed current is increased more than the cell whose cell voltage is lower than the predetermined voltage range H. For example, in the case of FIG. 6A, when the bypass currents for the cells C1 and C2 are i1 and i2, respectively, the base current of the transistor 8 is adjusted to change the bypass current i1 to 2 of the bypass current i2. Set to double. That is, the charging currents I1 and I2 of the cells C1 and C2 are expressed by the following equation (3) based on the charging current reduction width ΔIs and the bypass currents i1 and i2. Not only the cell C2, but all cells lower than the predetermined voltage range H in FIG. 6A are set to the charging current I2. When the process proceeds from step S110 in FIG. 4 to step S120, the decrease width ΔIs is ΔIs.₀Is replaced by
[Equation 3]
I1 = I₀-ΔIs-2 × i2
I2 = I₀-ΔIs-i2 (3)
[0030]
[Modification 2]
The magnitude of the bypass current is set according to the magnitude of the cell voltage Vcy. For example, when the cell voltage Vcy having the smallest voltage value is Vcmin, the bypass current value is set to be proportional to the difference (Vcy−Vcmin) between the cell voltage Vcy and the voltage Vcmin. If the proportionality constant at this time is k, the charging current I of each cell is expressed by the following equation (4).
[Expression 4]
I = I₀−ΔIs−k × (Vcy−Vcmin) (4)
[0031]
[Modification 3]
On / off of the bypass current flowing through the capacity adjustment circuits A1 to An is controlled by the on / off operation of the transistor 8 serving as a switching element. In the third modification, the capacity of each cell is adjusted by setting the switching on duty ratio according to the cell voltage Vcy. That is, the duty ratio is set in the capacity adjustment settings in steps S103 and S115 in FIGS.
[0032]
FIG. 9 is a flowchart showing a detailed procedure for setting the duty ratio in steps S103 and S115. In step S201, the cell voltage Vcy of each cell C1 to Cn constituting the secondary battery 1 is detected. In step S202, the maximum cell voltage Vcmax and the minimum cell voltage Vcmin within the cell voltage lower than the predetermined voltage range H with the charging target voltage Vf as the upper limit in the cell voltage Vcy detected in step S201 are obtained. In step S203, using the cell voltage-charge capacity characteristic (V-Ah characteristic) shown in FIG. 10, a charge capacity CAPMIN (Ah) corresponding to the maximum cell voltage Vcmin and a charge capacity CAPMAX (corresponding to the maximum cell voltage Vcmax). Ah) is obtained.
[0033]
In FIG. 10, a characteristic curve L0 represents an initial characteristic of the cell, and a characteristic curve L represents a characteristic at the time of battery deterioration. The initial characteristic L0 is stored in advance in a storage unit (not shown) of the controller 4 (see FIG. 1). When obtaining the charge capacities CAPMIN and CAPMAX, first, the charge capacities CMIN and CMAX when the cell voltages are Vcmin and Vcmax are calculated using the initial characteristic L0. By correcting the calculated charging capacities CMIN and CMAX with the capacity deterioration coefficient α as in the following equations (5) and (6), the charging capacities CAPMIN and CAPMAX are obtained.
[Equation 5]
CAPMIN = CMIN × α (5)
CAPMAX = CMAX × α (6)
[0034]
The capacity deterioration coefficient α is calculated by the controller 4 while the vehicle is traveling. A specific calculation method will be described later. Next, in step S204 of FIG. 9, the absolute value DCAP of the difference between CAPMAX and CAPMIN is calculated. In step S205, the charge capacity CACLy (y = 1, 2,..., N) after deterioration correction for each cell voltage Vcy is calculated. In step S206, the switching on duty ratio ONDUTYy (%) at the time of capacity adjustment is calculated by the following equation (7).
[Formula 6]
ONDUTYy = {(CAPCLy−CAPMIN) / DCAP} × 0.50 × 100 (7)
[0035]
In the subsequent step S207, the switching on duty ratio ONDUTYy (%) for the cells within the predetermined voltage range H is all set to 100%. In this way, a series of processing relating to the duty ratio setting ends. When charging, a charging current bypass process is performed based on the duty ratio setting.
[0036]
In the modified example 3 described above, a duty ratio of 0 to 50% is assigned to cells having cell voltages Vcmin to Vcmax, and a duty ratio of 100% is assigned to cells within a predetermined voltage range H. The cell voltage variation is effectively reduced by charging with a larger current. A 50% duty ratio may be uniformly assigned to cells having cell voltages Vcmin to Vcmax. In this way, when a uniform duty ratio of 50% is assigned, the bypass current of the cell within the predetermined voltage range H is set to 2 × i2 and the bypass current of the cell outside the predetermined voltage range H is set to i2 as in Modification 1. Same result as setting.
[0037]
(Calculation method of capacity degradation coefficient α)
Here, a method of calculating the capacity deterioration coefficient α described above will be described. As a calculation method, there is a method as disclosed in Japanese Patent Laid-Open No. 2000-261901. Here, an outline of the calculation method will be described. FIG. 11 (a) is a diagram showing the discharge IV characteristics of secondary batteries with different amounts of discharge electricity. The straight line f10 represents the case where the discharge electricity amount Ah = 0, that is, SOC = 100% (at the time of full charge), and the discharge electricity amount Ah in the case of the straight lines f11, f12 and f13 is Ah1, Ah2, Ah3 ( However, Ah1 <Ah2 <Ah3). That is, as the discharge electricity amount Ah increases from 0 → Ah1 → Ah2 → Ah3, the IV characteristic changes from f10 → f11 → f12 → f13, and the estimated open circuit voltage at that time also changes from E0 → E1 → E2 → E3.
[0038]
FIG. 11B is a diagram showing the relationship between the amount of discharge electricity Ah and the open circuit voltage E, and shows the initial battery characteristics and deterioration characteristics of the lithium ion battery. By the way, the capacity deterioration coefficient α can be expressed by the ratio between the battery capacity Cd at the time of deterioration of the secondary battery and the initial battery capacity C0 as in the following equation (8). The battery capacity is the charge capacity when SOC = 100%.
[Expression 7]
α = Cd / C0 (8)
Here, assuming that the amount of discharge electricity Ah until the open circuit voltage reaches a predetermined discharge capacity regulation voltage Ve is the battery capacity C of the secondary battery, the battery capacities C0 and Cd are a straight line E = Ve, an initial characteristic curve, and a deterioration time. It can be expressed by the amount of discharge electricity at the intersection with the characteristic curve.
[0039]
In FIG. 11 (b), black circles indicate data (Ah, E) at the initial stage of the battery, white circles indicate data (Ah, E) at the time of deterioration, and f20 is a regression obtained from the initial data by linear regression calculation. A straight line, f21 is a regression line obtained from deterioration data. In addition, a regression curve closer to the battery characteristics can be obtained by performing a linear regression calculation or more, but in the case of a lithium ion battery, except for the end of discharge (region where the discharge electricity amount Ah is large) in which the open-circuit voltage E significantly decreases. Thus, battery characteristics can be obtained with high accuracy by linear regression calculation. Therefore, the discharge electric quantities Ah0 and Ahd at the intersections of the regression lines f20 and f21 and the straight line E = Ve can be used as the battery capacities C0 and Cd.
[0040]
Incidentally, these regression lines f20 and f21 are expressed by the following equation (9). K is the slope of the characteristic line, Vf is the voltage intercept of the characteristic line, the slope of the regression line f20 is K0, and the slope of the regression line f21 is Kd. As can be seen from the regression lines f20 and f21 in FIG. 11B, Ah0 / Ahd = K0 / Kd is satisfied. That is, the capacity deterioration coefficient α is obtained by the following equation (10).
[Equation 8]
E = Vf−Ah · K (9)
α = Ah0 / Ahd = K0 / Kd (10)
[0041]
The charging device according to the above-described embodiment has the following effects.
In the multi-stage constant current charging, the charging current reduction value ΔIs when the cell voltage of an arbitrary cell reaches the charging target voltage Vf is set to the charging target voltage Vf and the maximum voltage Vcmax within the cell voltage lower than the predetermined voltage range H. Difference ΔV = Vf−Vcmax. As a result, the variation in cell voltage can be quickly reduced as compared with the conventional case where the charging current is reduced by a constant reduction value ΔIs0.
[0042]
FIG. 12 qualitatively shows the effect of reducing variation. FIG. 12 shows changes in the cell voltage and charging current of the cells C1 and C2 during multi-stage constant current charging. A broken line arrow shows a change in the conventional case where the charging current reduction value is constant, and a solid line An arrow indicates a change in the present embodiment. The example shown in FIG. 12 shows a case where the charging current reduction value ΔIs is twice the conventional reduction value ΔIs0.
[0043]
In the conventional case, constant current charging (current value I₀), When the cell voltage of the cell C1 reaches the charging target voltage Vf, the current value is reduced by ΔIs0, and the states of the cells C1 and C2 move to the left on the IV characteristic line. When the cell voltage of the cell C1 reaches the charging target voltage Vf again by charging the current value I−ΔIs0, the current value is reduced by ΔIs0. Thereafter, charging is performed with the current value I−2 × ΔIs0. Note that there is a relationship as shown in FIG. 13 between the cell voltage Vc and the SOC (or charge capacity), and the same SOC change ΔS is smaller than the cell voltage change ΔVc ′ when the SOC is large. The cell voltage change ΔVc is greater. Therefore, since the cell voltage of the cell C2 in FIG. 12 is lower than that of the cell C1, in the charging with the current values I−ΔIs0 and I−2 × ΔIs0, the voltage increase of the cell C2 is larger than the voltage increase of the cell C1. Become.
[0044]
On the other hand, in the present embodiment, the current value I₀When the cell voltage of the cell C1 reaches the charging target voltage Vf by charging, the charging current value is reduced by ΔIs (= 2 × ΔIs0). Then, the cell 1 is charged with the current value I−2 × ΔIs0 until it reaches the charging target voltage Vf. In this case, since the charging current is reduced by 2 × ΔIs0 in one stage, the charging time becomes longer, and the cell voltage rise in the cell C2 becomes larger than the two-stage cell voltage rise in the conventional case. As a result, the voltage variation Δ when the cell C1 reaches the charging target voltage Vf again becomes smaller than the conventional variation Δ ′.
[0045]
As a second effect, when the charge current is bypassed to the capacity adjustment circuits A1 to An for the purpose of capacity adjustment, the bypass current value of the cell outside the range than the cell within the predetermined voltage range H or the time of bypass Since the switching on-duty ratio is reduced, the variation reduction effect due to the capacity adjustment can be further improved as compared with the case where the bypass current is constant.
[0046]
14A and 14B are diagrams for explaining the capacity adjustment effect. FIG. 14A shows the case where the bypass current is set according to the cell voltage, and FIG. 14B shows the case where the bypass current is constant regardless of the cell voltage. . The left side of FIGS. 14A and 14B shows the cell voltage distribution before the start of charging, and the right side shows the cell voltage distribution when charging is interrupted halfway. In the above-described embodiment, charging and capacity adjustment are performed at the same time. However, when charging and capacity adjustment are considered separately, capacity adjustment can be considered as discharge by bypass current. That is, in the capacity adjustment, an operation is performed in which the cell voltage is lowered by discharging so that each cell voltage becomes the adjustment target voltage. In FIG. 14, the cell voltage moves to the left in the figure by adjusting the capacity.
[0047]
When the bypass current is constant as shown in FIG. 14B, the distribution gradually moves to the left side. Therefore, when charging is stopped halfway, the cell voltage distribution moves toward the adjustment target voltage, but the variation (interval of distribution) is not improved so much. On the other hand, in the case of FIG. 14A, since the bypass current is larger in the cell having a larger cell voltage, the movement to the left side due to the capacity adjustment is larger when the cell voltage is larger. As a result, the distribution interval is narrowed and the variation is improved as a whole.
[0048]
In the above-described embodiment, charging and discharging related to capacity adjustment are performed simultaneously, but charging and discharging may be performed separately. Further, the difference between the charging target voltage Vf and the maximum voltage Vcmax among the cell voltages lower than the predetermined voltage range H is used as ΔV, but the difference between the charging target voltage Vf and any of the cell voltages lower than the predetermined voltage range H is used. May be ΔV.
[0049]
  In the correspondence between the embodiment described above and the elements of the claims, the voltage detection circuits B1 to Bn are cell voltage detection devices, the controller 4 is a determination device and a charging current reduction device, and the bypass current i2 is the first.CurrentThe bypass current i1 is the secondCurrentRespectively.
[0050]
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a charging device according to the present invention, and is a block diagram showing a configuration of the charging device.
FIG. 2 is a diagram showing a charging pattern by the charging device of the present embodiment.
FIG. 3 is a flowchart illustrating a charging operation.
FIG. 4 is a flowchart showing a processing procedure following FIG. 3;
FIG. 5 is a block diagram showing a part of FIG. 1;
FIG. 6 is a schematic diagram of cell voltage distribution, and the charging operation proceeds in the order of (a) to (c).
7 is a graph showing IV characteristics of the secondary battery 1. FIG.
FIG. 8 is a diagram showing a cell voltage distribution at the end of charging.
FIG. 9 is a flowchart showing a detailed procedure for setting a duty ratio.
FIG. 10 is a diagram showing a cell voltage-charge capacity characteristic of a cell.
11A and 11B are diagrams for explaining a capacity deterioration coefficient α, where FIG. 11A is a diagram showing discharge IV characteristics with different discharge electric quantities, and FIG. FIG.
FIG. 12 is a diagram qualitatively showing a variation reducing effect.
FIG. 13 is a diagram showing a relationship between a cell voltage Vc of a cell and SOC (or charge capacity).
14A and 14B are diagrams for explaining a capacity adjustment effect, in which FIG. 14A shows a case where a bypass current is set according to the cell voltage, and FIG. 14B shows a case where the bypass current is constant regardless of the cell voltage. Show.
[Explanation of symbols]
1 Secondary battery
2 Temperature sensor
3 Total voltage detection sensor
4 Controller
5 Relay switch
6 Charger
9 Current sensor
A1 to An capacitance adjustment circuit
B1-Bn Cell voltage detection circuit
C1-Cn cells
Vf Charge target voltage
α Capacity degradation coefficient

Claims (7)

The secondary battery composed of a plurality of cells, the charging method for charging to make reduce the charge current stepwise according to the progress of the charging,
Each time the cell actual voltage of any cell constituting the secondary battery reaches the charge target cell voltage, the cell actual voltage of the cell having a value lower than the charge target cell voltage and the lower limit voltage of the target cell voltage variation range. The charging method characterized by increasing the amount of reduction when the charging current is reduced stepwise as the difference from the voltage increases . The charging method according to claim 1,
When the capacity adjustment is performed so that a part of the charging current flowing into the cell is bypassed to the cell and the charging state between the cells is uniform, the larger the cell actual voltage, the larger the bypass current. The charging device characterized by performing. The secondary battery composed of a plurality of cells, the charging device for charging to make reduce the charge current stepwise according to the progress of the charging,
A cell voltage detection device for detecting each cell actual voltage of the cell;
A determination device for determining whether any of the cell actual voltages detected by the cell voltage detection device has reached a charge target cell voltage;
When it is determined by the determination device that any one of the cell actual voltages has reached the charge target cell voltage, the cell actual of a cell having a value lower than the charge target cell voltage and the lower limit voltage of the target cell voltage variation range. A charging device comprising: a charging current reducing device that increases a reduction amount when the charging current is reduced stepwise as the difference from the voltage increases . The charging device according to claim 3,
A capacity adjustment device that bypasses a part of the charging current flowing into the cell with respect to the cell is provided for each cell,
The capacity adjustment device increases a current to be bypassed as a cell has a higher cell actual voltage . The charging device according to claim 3 ,
A capacity adjustment device that bypasses a part of the charging current flowing into the cell with respect to the cell is provided for each cell,
The capacity adjustment device, the cell when the actual voltage is lower than the lower limit voltage to bypass by a first current value, larger second than the first current value when the cell the actual voltage is greater than the lower limit voltage A charging device characterized by bypassing only the current value . The charging device according to claim 3,
A capacity adjustment circuit that is provided for each cell and bypasses a part of the charging current flowing into the cell with respect to the cell ;
More cells actual voltage of the cell is large, the charging device characterized by comprising a controller for controlling so that the bypass time becomes longer to perform by Ri bypass the capacity adjustment circuit. The charging device according to claim 6,
Wherein the controller is charging the cell the actual voltage and controls so that the bypass time if it is the lower limit voltage or higher, the cell actual voltage longer than the bypass time is lower than the lower limit voltage apparatus.

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