JP2009159672A - Control system of charge/discharge circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control system of a charge/discharge circuit for deciding a target charge amount with which a leveling loss amount in the whole battery pack serves as minimum and controlling charging/discharging so that respective battery modules are appropriately charged or discharged with the target charge amount as reference. <P>SOLUTION: When the battery pack 3 is leveled with an average charging state of eight battery modules 2 as a target charging state if loss efficiency of a partial charging processing is smaller than that of a partial discharging processing, the leveling loss amount as the whole battery pack 3 does not become minimum. Thus, an optimum target charging state is decided so that the number of the battery modules 2 performing the partial discharging processing is reduced, and the number of the battery modules 2 performing the partial discharging processing is increased. The partial charging processing is performed on the battery module 2 whose charging state is smaller than the optimum target charging state and the partial discharging processing is performed on the battery module 2 whose state is larger than the optimum target charging state. Thus, the leveling loss amount is made minimum and leveling is performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control system for a charge / discharge circuit for leveling (uniformizing) the state of charge (SOC) of a battery module constituting an assembled battery.

  For vehicles that drive an electric motor, such as an electric vehicle, a hybrid vehicle, and a fuel cell vehicle, for example, a set in which a plurality of battery modules composed of a plurality of single cells are connected in series to obtain a required voltage. Batteries are loaded. Many single cells constituting the assembled battery are manufactured according to the same standard, but it is inevitable that there is some variation in electrical characteristics such as charge / discharge characteristics. Also, variations may occur depending on the environment during use, such as temperature. Therefore, in order to effectively utilize the capacity of the entire assembled battery, it has been considered to perform “leveling (equalization)” that reduces variations in the amount of charge between battery modules.

Conventionally, as a method of leveling the variation in the amount of charge of the batteries constituting the assembled battery, a discharge bypass circuit is connected in parallel for each unit of the battery to be leveled (for example, a cell obtained by dividing the battery module), There is known a method of selecting and discharging a cell having a larger amount of charge than others (see, for example, Patent Document 1).
In addition, a method is known in which a constant voltage power source is connected to each cell to perform charging more in a cell with a small amount of charge (see, for example, Patent Document 2).
Furthermore, as a method of using both partial discharge and partial charge, there is known a method of selectively discharging a cell with a large charge amount and selectively charging a cell with a small charge amount to level the cell voltage. (For example, refer to Patent Document 3).
In addition, using both partial charge and partial discharge, the power of a cell with a large amount of charge is input to a DC-DC converter circuit to discharge, and the obtained power is supplied to a cell with a small amount of charge to perform charging. Thus, a method of leveling the cell voltage is known (see, for example, Patent Document 4).

Japanese Patent Laid-Open No. 10-322925 (paragraphs [0011] to [0012], FIG. 2) JP-A-4-322131 (paragraphs [0004] to [0005], FIG. 2) JP 2001-339865 A (paragraph [0010], FIG. 1) Japanese Patent Laid-Open No. 10-32936 (paragraphs [0022] to [0031], FIG. 1)

When leveling the state of charge using both partial charge and partial discharge, energy loss occurs with the leveling operation.
For example, when a resistance bypass circuit is used as the partial discharge means, the amount of change in the state of charge is all converted to Joule heat at the resistance.
Further, when a DC / DC converter is used as the partial charging means, a conversion loss occurs in the DC / DC converter, but not all the amount of change in the charge state is lost.
When leveling a plurality of battery modules with arbitrarily varying charge amounts, it is desirable to set a target charge amount so that the sum of the loss due to partial discharge and the loss due to partial charge is minimized.
However, obtaining the target charge amount that minimizes the loss means obtaining the minimum value of the multivariable function having the target charge amount and the charge amount of each module as variables, and the calculation contents are complicated.
For example, although the method of calculating the change in the overall loss amount by slightly changing the target charge amount and further changing the target charge amount in the direction of reducing the loss amount is easily conceived, the optimum target value is determined. Until then, it is necessary to perform a large number of repetitive operations, and an expensive arithmetic processing unit is required.

  The present invention has been made in view of such circumstances, and a target charge amount that minimizes the leveling loss amount of the entire assembled battery by a simple search method without using an expensive arithmetic processing unit. It is an object of the present invention to provide a control system for a charge / discharge circuit that performs charge / discharge control so as to appropriately charge or discharge each battery module with reference to the target charge amount.

  In order to solve the above-mentioned problem, the invention according to claim 1 charges and discharges an assembled battery formed by connecting a plurality of battery modules including one or more cells in series according to the charge state of each battery module. A control system for a charging / discharging circuit, a module voltage detecting circuit for detecting a charging state for each battery module, a charging state of an arbitrary battery module among a plurality of battery modules as a temporary target charging state, and other battery modules A loss amount calculating means for calculating a leveling loss amount for each battery module when leveling the charged state to a temporary target charged state, and leveling for each battery module calculated by the loss amount calculating means A temporary target charging state that minimizes the amount of loss is searched, and based on the searched temporary target charging state, the charging state of the battery module is temporarily determined for each battery module. For each battery module, the target charge state search means for calculating the charge / discharge amount for setting the charge state, the partial charge circuit for partially charging the charge amount calculated by the target charge state search means, and the target charge for each battery module And a partial discharge circuit that partially discharges the discharge amount calculated by the state search means.

  According to this configuration, when the charge state of an arbitrary battery module is set to the temporary target charge state, the loss amount calculation unit is charged or discharged so that the charge state of the other battery module becomes the temporary target charge state. The amount of charge / discharge loss is calculated. Then, the target charge amount search means compares the charge / discharge loss amount calculated by the loss amount calculation means in all the battery modules, searches for the battery module having the minimum charge / discharge loss amount, and the charge state of the battery module Is determined as the optimum target charging state. Thereby, the leveling loss amount at the time of charge / discharge for leveling the voltage module of the assembled battery can be minimized.

  The invention according to claim 2 is the invention according to claim 1, wherein the loss amount calculation means calculates the loss amount when the battery module in the charged state exceeding the temporary target charged state is discharged by the partial discharge circuit. Add as the amount of discharge loss, and add the amount of loss when charging by the partial charge circuit for the battery module in the charge state less than the temporary target charge state, based on the amount of discharge loss and the amount of charge loss The leveling loss amount is calculated.

  According to this configuration, the loss amount calculating means discharges the battery module having a charge amount exceeding the temporary target charge state, and the battery module having a charge amount less than the temporary target charge state. The total charge / discharge loss amount is calculated by adding the total charge loss amount when the battery is charged. Therefore, by comparing the total charge / discharge loss amount for each battery module, it is possible to uniquely find a battery module having a loss amount that minimizes the leveling loss amount.

  According to a third aspect of the present invention, in the first aspect of the invention, the loss amount calculating means is configured as a whole of the plurality of battery modules based on the charge states of the plurality of battery modules detected by the module voltage detection circuit. An average charge state is calculated, and a leveling loss amount is calculated using a battery module whose charge state is larger than the average charge state as a candidate for any battery module.

  According to this configuration, since the leveling loss amount is calculated using a battery module whose charging state is larger than the average charging state as a candidate for any battery module, the leveling loss amount can be calculated with a smaller calculation load. .

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the loss amount calculating means is configured as a whole of the plurality of battery modules based on the charge states of the plurality of battery modules detected by the module voltage detection circuit. An average charge state is calculated, and a leveling loss amount is calculated by setting a battery module whose charge state exceeds the average charge state and is not more than a predetermined range from the average charge state as a candidate for any battery module.

  According to this configuration, the leveling loss amount is calculated using any battery module whose charge state exceeds the average charge state and is less than or equal to the predetermined range from the average charge state as a candidate for any battery module. The amount of conversion loss can be calculated.

  According to the first aspect of the present invention, the charge / discharge loss amount is compared among all the battery modules constituting the assembled battery, the battery module having the minimum charge / discharge loss amount is searched, and the charge amount of the battery module is set to the optimum target. Since the charge amount is determined, the leveling loss amount of charge / discharge for leveling the voltage of the assembled battery can be minimized.

  According to the invention of claim 2, since the total charge loss amount and the total discharge loss amount of the plurality of battery modules are added to obtain the total charge / discharge loss amount, the battery module having the loss amount that minimizes the leveling loss amount Can be easily found.

Next, the best mode (referred to as an embodiment) for carrying out the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram showing a charge / discharge circuit control system 100 according to an embodiment of the present invention.
The charge / discharge circuit control system 100 is connected to the assembled battery 3. The assembled battery 3 is obtained by connecting a plurality of battery modules 2 in series, and one battery module 2 is obtained by connecting one or more cells 1 in series. That is, one or a plurality of (for example, three) cells 1 are connected in series to form a battery module 2, and a plurality of (for example, four) battery modules 2 are connected in series to form an assembled battery 3. It is configured. The cell 1 is composed of one unit cell or a plurality of unit cells connected in series or in parallel (none is shown).

  Although an example in which the battery modules 2 are connected in four stages in series is illustrated, the battery module 2 may constitute the assembled battery 3 by connecting fewer or more stages in series. Thereby, the terminal voltage at both ends of the assembled battery 3 can be set to a desired value. In the present embodiment, the term “terminal of the assembled battery 3” simply refers to terminals at both ends of the assembled battery 3, that is, terminals where the largest potential difference is obtained in the assembled battery 3.

  The assembled battery 3 is typically mounted on an electric vehicle, a hybrid vehicle, a fuel cell vehicle, and the like, and is connected to a load (not shown) of an electric motor drive circuit and various in-vehicle electrical devices. . Furthermore, a charging mechanism (none of which is shown) including a charging stand, an alternator (including a rectifier) and the like is temporarily or always connected to the assembled battery 3. As described above, when the assembled battery 3 is used, charging and discharging are performed through the terminals at both ends of the assembled battery 3, so that the charge state is not uniform between the battery modules 2 constituting the assembled battery 3, and variation occurs. Sometimes.

  The charge / discharge circuit control system 100 includes a partial discharge circuit CD connected in parallel to each battery module 2, a partial charge circuit CC connected in parallel to each battery module 2, and each of these elements. And a voltage monitoring device DD connected to both terminals of the assembled battery 3, and the voltage monitoring device DD is used to charge the partial charging circuit CC by the DC / DC conversion circuit based on the power from both terminals of the assembled battery 3. Supply power.

  The partial discharge circuit CD has a function of discharging the connected battery module 2 in accordance with the control of the voltage monitoring device DD. At this time, the energy of the discharge current is converted into Joule heat by a load such as a resistor and a power FET included in the partial discharge circuit CD, and is released into the atmosphere via a heat sink attached to the load, resulting in a loss ( Neither is shown).

  The partial charging circuit CC has a function of charging the connected battery module 2 in accordance with the control of the voltage monitoring device DD. At this time, in order to generate charging power to be supplied to the partial charging circuit CC, a conversion loss occurs in the DC / DC conversion circuit and is consumed as Joule heat in the conversion circuit component. The ratio of energy that is lost to the energy that is effectively charged is called loss efficiency and is expressed as a percentage.

The module voltage detection circuit MV detects the terminal voltage of the battery module 2 to be connected, and sends a voltage detection signal representing this terminal voltage to the voltage monitoring device DD.
The voltage monitoring device DD is typically configured to include a microcomputer (not shown) loaded with a control program and storing data for control, and based on a voltage detection signal from the module voltage detection circuit MV. And has a function of controlling the corresponding partial discharge circuit CD and partial charge circuit CC. That is, in the assembled battery 3, the battery module 2 is a minimum control unit related to charging / discharging.

  FIG. 2 is a graph showing a concept of charging or discharging each battery module 2 of the assembled battery 3 toward the optimum target charging state p by the control system 100 of the charging / discharging circuit. In this graph, time is shown in the horizontal axis direction, and the state of charge (%) of the battery module 2 is shown in the vertical axis direction.

  The charged state is a ratio of the amount of electricity that is charged (stored as chemical energy in the battery module 2 and can be normally taken out) with respect to the electric capacity of the battery module 2. Further, in this description, the charge amount means an amount of electricity normalized with the standard capacity of one battery module 2 as 1.

  In this example, the assembled battery 3 is composed of eight battery modules 2, and the charging states of these battery modules 2 are 30%, 40%, 43%, 45%, 45%, 47%, 50, respectively. %, 60%. In this example, when the average value of the state of charge of each battery module 2 (hereinafter referred to as the average state of charge) is calculated, it is 45%.

An example in which the battery modules 2 of the assembled battery 3 are leveled to the average charge state (45%) will be described.
In this example, partial charging is performed on the battery module 2 having a charge state lower than the average charge state (45%) (that is, the battery module 2 having a charge state of 30%, 40%, 43%), and the average charge is performed. A partial discharge is performed on the battery module 2 in a charged state greater than 45% (that is, the battery module 2 in which the charged state is 47%, 50%, 60%), and the charged state of each battery module 2 of the assembled battery 3 Leveling is performed so that the average charge state (45%) is obtained.

  In this case, the electric energy which is not effectively charged in the battery module 2 in the partial charging process and becomes a charging loss in the form of Joule heat, and the electric energy which is lost as Joule heat in the partial discharging process are the same amount. . That is, in the partial charge, a part of the electric energy is stored in the battery module 2 (that is, it is not lost), and the remainder is lost as Joule heat, whereas in the partial discharge, substantially all of the electric energy is lost. Is converted into Joule heat and lost.

  Specifically, partial charge processing is performed for charging the three battery modules 2 whose charge states are less than the average charge state pv (45%) by subtracting the charge amount from the average charge state pv. The amount of charge increased by the partial charging process is 0.45-0.3 = 0.15, 0.45-0.4 = 0.05, and 0.45-0.43 = 0.02, respectively. It is assumed that the loss efficiency in the partial charging process is 30%. That is, if 1 of the amount of electric energy is charged in the battery module 2, 0.3 is converted into Joule heat and becomes a loss. Therefore, since the capacity of the battery module 2 is 1, 0.15 × 0.3 = 0.045, 0.05 × 0.3 = 0.015, 0.02 × 0.3 = 0.006, respectively. Is a loss. That is, the total loss in the partial charging process is 0.045 + 0.015 + 0.006 = 0.066, where the capacity of one battery module 2 is 1.

  On the other hand, there are three battery modules 2 that have more charged states than the average charged state (45%). For these three battery modules 2, 0.47−0.45 = 0.02,. When the discharge of 5-0.45 = 0.05 and 0.6-0.45 = 0.15 is performed, the loss efficiency in the partial discharge treatment is 100%, so that 0.02 × 1 = 0. 02, 0.05 × 1 = 0.05 and 0.15 × 1 = 0.15. That is, the total loss in the partial discharge process is 0.02 + 0.05 + 0.15 = 0.22.

  That is, when the partial charging process or the partial discharging process is performed on each battery module 2 so that the charging state of each battery module 2 becomes the average charging state pv (45%), the total loss due to the partial charging process is 0.066. And the total loss due to the partial discharge treatment is 0.22. Therefore, the total loss due to the partial charge process and the partial discharge process is calculated to be 0.286. As described above, when the average value of the charge states of all the battery modules 2 (that is, the average charge state pv) is the temporary target charge state px, the difference between the total loss in the partial discharge process and the total loss in the partial charge process. However, the sum of the total loss in the partial charge process and the total loss in the partial discharge process becomes large, and the leveling loss amount s in the entire assembled battery 3 becomes large. In other words, if the average charge state pv is the temporary target charge state px, the leveling loss amount s in the entire assembled battery 3 cannot be minimized.

  That is, when the loss efficiency (70%) in the partial charge process is smaller than the loss efficiency (100%) in the partial discharge process, the partial discharge process is performed in order to minimize the leveling loss amount s in the entire assembled battery 3. The temporary target charge state px is determined so as to reduce the number of battery modules 2 to be applied and increase the number of battery modules 2 that perform the partial discharge process, and the charge state of the battery module 2 that is the temporary target charge state px is the optimum target. The charging state p is set, the partial charging process is performed on the battery module 2 in the charging state lower than the optimum target charging state p, and the partial discharging process is performed on the battery module 2 in the charging state higher than the optimum target charging state p. You can see that

  FIG. 3 is a graph showing a relationship example of the leveling loss amount (normalized value) sn with respect to the target charge state px. In this graph, the level of the target charge state px (%) is shown in the horizontal axis direction, and the leveling loss sn normalized by assuming that the target charge state px is 50 (%) in the vertical axis direction is “1”. The size of is shown. In this example, when the same amount of energy is effectively charged and discharged with respect to the battery module 2, it is assumed that there is a relationship of (loss in partial charge processing) :( loss in partial discharge processing) = 0.3: 1. . That is, the loss efficiency is 30% in the partial charging process.

  Referring to this graph, when the target charge state px is at least in the range of 45 (%) to 55 (%) and the target charge state px is 50%, the leveling loss amount (normalized value) sn is 1.00. It can be seen that the leveling loss amount sn increases both when the target charge state px is higher and lower than this value. For example, the leveling loss amount sn when the target charging state px is the average charging state pv (45%) is 1.14, and for example, the leveling loss amount sn when the target charging state px is 55% Is 1.22, and it can be seen that the leveling loss amount sn is larger than that when the target charge state px is 50%. Therefore, in order to perform leveling between the battery modules 2 while minimizing the leveling loss amount sn under these conditions, the target charge state px may be set to 50%.

Returning to FIG. 2, when the optimum target charging state p is set to 50% as described above, leveling is performed as in the following (1) to (3).
(1) For the battery module 2 whose charging state is equal to the optimum target charging state p (that is, the battery module 2 whose charging state is 50%), charging / discharging for leveling is not performed.
(2) For the battery module 2 whose charge state is lower than the optimum target charge state p (50%) (that is, the battery module 2 whose charge state is 30%, 40%, 43%, 45%, 45%, 47%) Then, partial charging is performed until the state of charge reaches 50%.
(3) For the battery module 2 having a higher charge state than the optimum target charge state p (50%) (that is, the battery module 2 having a charge state of 60%), partial discharge is performed until the charge state reaches 50%. .

As described above, the electric capacity per battery module 2 is assumed to be 1, and the amount of electricity applied to the battery module 2 is normalized and described.
In this case, the charge amount of the battery module 2 in the optimum target charge state p (50%) is 0.5. There are six battery modules 2 in the charged state lower than the optimal target charged state p (50%), and the charged amounts thereof are 0.3, 0.4, 0.43, 0.45, 0.45, 0.47.

  For these six battery modules 2, 0.5-0.3 = 0.2, 0.5-0.4 = 0.1, 0.5-0.43 = 0.07, Charging is performed with an amount of electricity of 0.5−0.45 = 0.05, 0.5−0.45 = 0.05, and 0.5−0.47 = 0.03. In this case, it is assumed that the loss in the partial charge process is 30% of the loss in the partial discharge process. Then, 0.2 × 0.3 = 0.06, 0.1 × 0.3 = 0.03, 0.07 × 0.3 = 0.021, 0.05 × 0.3 = 0. 015, 0.05 × 0.3 = 0.015, 0.03 × 0.3 = 0.09. That is, the leveling loss amount s in the partial charging process is 0.06 + 0.03 + 0.021 + 0.015 + 0.015 + 0.009 = 0.15.

  On the other hand, there is one battery module 2 in a charged state greater than the optimum target charged state p (50%). In order to make the charged state (60%) of this one battery module 2 50%, 10% of discharge is performed. Is performed, the loss efficiency in the partial discharge treatment is 100%, so the loss amount in the partial discharge treatment is 0.1. That is, the sum of the loss amount due to the partial charge process and the loss amount due to the partial discharge process is 0.15 + 0.10 = 0.25. Therefore, the leveling loss amount s when the above average charge state pv is the target charge state px is 0.286, whereas the optimum target charge state p (50%) is set to the target charge as in this example. Since the leveling loss amount s in the state px is 0.25, if the battery modules 2 are charged or discharged with respect to the optimum target charging state p (50%), the leveling loss amount s is further increased. The voltage of the assembled battery 3 can be leveled by reducing the voltage.

  Therefore, when the loss amount in the partial charge process is smaller than the loss amount in the partial discharge process, the battery module 2 that performs the partial discharge process is used to minimize the leveling loss amount s in the entire assembled battery 3. The charging state of the battery module 2 serving as a reference is determined as the target charging state px so as to increase the number of battery modules 2 that perform partial discharge processing, and the charging state of the battery module 2 is the optimum target. The charge state p is set, the partial charge process is performed on the battery modules 2 smaller than the optimum target charge state p, and the partial discharge process is performed on the battery modules 2 larger than the optimum target charge state p.

  That is, in the assembled battery 3 composed of n battery modules 2 (that is, the number n of battery modules), the optimum target charge state is p, and the number of battery modules 2 having more charge states than the optimum target charge state p. M, and the state of charge of the battery module 2 closest to the optimum target state of charge p is q. In addition, the number of battery modules 2 having a smaller charge state than the optimum target charge state p is nm, and the charge state of the battery module 2 closest to the optimum target charge state p is r. That is, r <p <q. Further, the ratio between the discharge loss and the charge loss is set to 1: z. Although the case where the charge loss efficiency ratio z is smaller than 1 will be described, z may be larger or smaller than 1. When z = 1, the optimum target charging state can be arbitrarily selected within a chargeable / dischargeable range.

  Here, when the optimum target charging state p is changed by Δp, the leveling loss change amount Δs, which is the change amount of the leveling loss amount s, is expressed by the following equation (1).

Δs = Δp × (n−m) × z−Δp × m
= Δp × (nz−m (1−z)) (1)

  As can be seen from the equation (1), the slope of the leveling loss change amount Δs includes the number n of battery modules 2 constituting the assembled battery 3, the number m of battery modules 2 having a higher charge state than the optimum target charge state p, And charging loss efficiency ratio z.

  Here, the number n is the number of the battery modules 2 and can be regarded as a constant. Further, the value of the charge loss efficiency ratio z is substantially constant regardless of the state of the assembled battery 3. Therefore, since the number m of the battery modules 2 having a higher charged state than the optimum target charged state p does not change within the range of r <p <q (that is, n, z, m are constant), the equation ( As can be seen from the fact that 1) is a linear expression, the slope of the leveling loss variation Δs is uniform. Therefore, the value of the optimal target charging state p is not an intermediate value between the charging state r immediately below and the charging state q immediately above, and the optimal target charging state p is the charging state r immediately below or the charging immediately above. Equal to either state q. In other words, the optimum target charging state p is equal to the charging state of any one of the n battery modules 2.

  Therefore, it is not necessary to analytically obtain an arbitrary numerical value for the optimum target state of charge p. That is, since the candidate of the optimal target charging state p always exists in the charging state of any one of the charging states of the n battery modules 2, all the batteries constituting the assembled battery 3 are present. The leveling loss amount s is calculated by sequentially applying the state of charge of the module 2, and the value of the state of charge that minimizes the leveling loss amount s may be selected and set to the optimum target state of charge p.

  In this way, since the optimum target charging state p is higher than the average charging state pv, even if the optimum target charging state p is calculated based on the charging state of the battery module 2 having a higher charging state than the average charging state pv. Good. Furthermore, the optimum target charging state p may be calculated based on the charging state of the battery module 2 in a charging state that is larger than the average charging state pv and within a predetermined range from the average charging state pv.

FIG. 4 is a flowchart showing the procedure of the optimum target charge state search process in the control system 100 for the charge / discharge circuit according to the present invention.
In this procedure, in order to search for the optimum target charging state p, the charging state of the first battery module 2 (for example, the charging state in FIG. A leveling loss amount s (hereinafter simply referred to as a loss amount) when the battery module 2) is set to the temporary target charging state px is calculated, and this loss amount is set to Xmin (step S1).
Further, the index j is set to 1 (j = 1), and the charging state of the second battery module 2 (i = 2) (for example, the battery module 2 having a charging state of 40% shown in FIG. 2) is targeted. Loss amount is calculated, and if it is smaller than Xmin, the value is substituted into Xmin (step S2). The procedure for calculating the loss amount Xmin will be described later in detail with reference to FIG.

  In this way, when the loss amount is sequentially obtained for each battery module 2 and the target is the state of charge of the i-th battery module 2 (for example, 50% of the battery modules 2 in the state of charge shown in FIG. 2). Loss amount Xi is calculated (step S3).

Then, it is determined whether or not the loss amount Xi is smaller than Xmin (Xi <Xmin?) (Step S4).
When the loss amount Xi is smaller than Xmin (Yes in step S4), the loss amount Xi is substituted into Xmin, and the index j is set to i (step S5).
If the loss amount Xi is not smaller than Xmin, that is, if the loss amount Xi is equal to or greater than Xmin (No in step S4), the process proceeds to step S6.

Such a search operation is repeated, and it is determined whether or not all search operations for the state of charge of n battery modules 2 have been completed (i = n?) (Step S6).
If all search operations for the state of charge of the n battery modules 2 have not been completed (No in step S6), i is incremented by 1 (i = i + 1) (step S7), and the process returns to step S3 described above. The subsequent processing is repeated.

In this way, when all the search operations for the charging states of the n battery modules 2 are completed, that is, when i = n (Yes in step S6), the loss of the j-th battery module 2 indicated by the index j. Since the amount Xj is Xmin, the state of charge of the jth battery module 2 is set to the optimum target state of charge p (step S8).
Then, the process returns to step S1 as appropriate according to the change in the state of charge, etc., and the above processing is repeated.

Next, the procedure for obtaining the above-described loss amount calculation will be described in detail with reference to FIG.
FIG. 5 is a flowchart showing a procedure for obtaining the leveling loss amount s due to charging / discharging in the procedure shown in FIG.
Specifically, this procedure is executed as a subroutine for obtaining the loss amount Xmin in step S1 (see FIG. 4) and a subroutine for obtaining the loss amount Xi in step S3 (see FIG. 4).

  In addition, each code | symbol in the flowchart shown in FIG. 5 is as follows. px is the temporary target charging state, Yi is the charging state of the i-th battery module 2 (therefore, Y1 is the charging state of the first battery module 2, Y2 is the charging state of the second battery module 2,... Yn is the nth. Xp is a discharge side loss amount, Xn is a charge side loss amount, z is a charge loss ratio (where z <1), and X is a total loss amount.

  First, the first battery module 2 (for example, the battery module 2 with the least charged state of 30% in FIG. 2 is defined as the first battery module 2) is set to i = 1, and the battery module 2 is discharged. The side loss amount Xp is reset to zero (Xp = 0) and the charge side loss amount Xn is reset to zero (Xn = 0) (step S11).

Next, it is determined whether or not the charging state Yi of the i-th battery module 2 is larger than the temporary target charging state px (px <Yi?) (Step S12).
Here, when the charging state Yi of the i-th battery module 2 is larger than the temporary target charging state px (px <Yi) (Yes in step S12), the charging state Yi of the i-th battery module 2 is set to the temporary target charging state px. Therefore, the first battery module 2 is divided into the side to be discharged. Then, with respect to the previous discharge side loss amount Xp (the discharge side loss amount Xp of the first battery module 2 is Xp = 0), the charging state Yi of the i-th battery module 2 and the temporary target charging state A difference (Yi−px) from px is added to obtain a new discharge side loss amount Xp. That is, Xp = Xp + (Yi−px) is calculated (step S13).

  On the other hand, when the charging state Yi of the i-th battery module 2 is not greater than the temporary target charging state px (px ≧ Yi) (No in step S12), the charging state Yi of the first battery module 2 is the temporary target charging state px It is determined whether it is smaller (px> Yi?) (Step S14).

  Here, when the charging state Yi of the i-th battery module 2 is smaller than the temporary target charging state px (px> Yi) (Yes in step S14), the charging state Yi of the i-th battery module 2 is set to the temporary target charging state px. Therefore, the i-th battery module 2 is classified into the side to be charged. And the temporary target charge state px and the charge state of the i-th battery module 2 with respect to the charge-side loss amount Xn so far (the charge-side loss amount Xn of the first battery module 2 is Xn = 0). The difference (px−Yi) from Yi is added to obtain a new charge side loss amount Xn. That is, Xn = Xn + (px−Yi) is calculated (step S15).

  If px> Yi is not satisfied in step S14 (No in step S14), the charging state Yi of the i-th battery module 2 is the temporary target charging state px (that is, px = Yi), and it is necessary to perform the discharging operation and the charging operation. Therefore, the process of calculating the loss amount of the first battery module 2 (i = 1) is terminated.

Thus, for the i-th battery module 2, when the calculation of the discharge side loss amount Xp is completed in step S13, or when the calculation of the charge side loss amount Xn is completed in step S15, 1 is incremented to i. (I = i + 1) (step S16), it is determined whether i has reached n (step S17).
For example, in the example shown in FIG. 2 (see FIG. 5 as appropriate), since the number of battery modules 2 is n = 8, it is determined whether or not the calculation for eight battery modules 2 has been completed (step) S17).
When i = n is not true, that is, for example, when the calculation for the eight battery modules 2 has not been completed yet (No in step S17), the process returns to step S16 to perform the calculation for the i + 1-th battery module 2 as described above. .

Returning to FIG. 5, it is determined whether or not processing has been performed up to the nth (i = n?) (Step S17).
When the calculation for the n-th battery module 2 is completed (Yes in step S17), the discharge-side loss amount Xp of the battery module 2 up to i = n calculated in step S13, that is, the total of the eight battery modules 2 is calculated. The charge loss efficiency ratio z is set to the discharge side loss amount Xp and the charge side loss amount Xn of the battery module 2 up to i = n calculated in step S15, that is, the total charge side loss amount Xn of the eight battery modules 2. The multiplied value is added to obtain a total loss amount X for leveling processing. That is, X = Xp + Xn × z is calculated (step S18).

  That is, the magnitude relationship between the charging state Yi of the i-th battery module 2 and the target charging state px is examined (step S12 and step S14). If the charging state Yi of the i-th battery module 2 is larger (in step S12). (Yes), (Yi−px) is added to the discharge side loss amount Xp (step S13). If the target charge state px is larger (Yes in step S14), (px−Yi) is added to the charge side loss amount Xn. to add. The process of performing such calculation up to the nth battery module 2 (the eighth battery module 2 in FIG. 2) is repeated. The value obtained by multiplying the total charge side loss amount Xn by the charge loss efficiency ratio z and the total discharge side loss amount Xp is charged or discharged to the temporary target charge state px for each battery module 2. This is the minimum loss amount X (minimum leveling loss amount s) when the battery module 2 voltage is leveled.

  When the above processing is completed, a value is returned to the optimum target charging state search processing (step S1 or step S3) shown in FIG. 4, and when the next value is input, the processing after step S11 is repeated.

  In the present embodiment, the loss amount is calculated for all the battery modules 2, and the state of charge of the battery module 2 that minimizes the loss amount is determined as the optimum target charge state p. However, in practice, even if the loss amount is not calculated for all the battery modules 2, the optimum target charge state p can be obtained by calculating the loss amount only for the battery modules 2 in the charge state higher than the average charge state pv. it can. The reason is that, when the loss efficiency is lower in the charging process than in the discharging process, the charged state of the battery module 2 in the charged state that is higher than the average value of the charged state of all the battery modules 2 is always the optimum target charged state p. Because the minimum leveling loss amount s is given as follows, the optimum target charging state p may be searched for from the battery module 2 in the charging state higher than the average charging state pv.

  According to the control system 100 for the charge / discharge circuit of this embodiment, the difference between the charge state of each battery module 2 and the target charge state px is multiplied by the loss in the partial charge process and partial discharge process of each battery module 2. Thus, the optimum target charging state p is set so that the sum is minimized. Thereby, the leveling loss amount s in the entire assembled battery 3 constituted by the battery modules 2 can be minimized.

  That is, according to the control system 100 for the charge / discharge circuit of the present embodiment, when the battery module 2 is partially discharged, the electric energy discharged from the battery module 2 is converted into Joule heat, and the electric energy is substantially reduced. All are lost, but when the battery module 2 is partially charged, part of the electrical energy used for charging is effectively charged to the battery module 2, so this amount is not lost and the rest is It is converted into Joule heat and lost. Therefore, not only the charging state of each battery module 2 but also the charging loss efficiency ratio z at the time of partial charging is taken into account to search for the target charging state px, and each battery module 2 is partially charged so as to reach this target charging state px. By discharging, the leveling loss amount s can be reduced, and the assembled battery 3 can be leveled.

It is a whole lineblock diagram showing the control system of the charge and discharge circuit of one embodiment by the present invention. It is a graph which shows the concept which charges or discharges each battery module of the assembled battery 3 toward the optimal target charge state by the control system of a charging / discharging circuit. It is a graph which shows the example of a relationship of the leveling loss amount (normalization value) sn with respect to a target charge state. It is a flowchart which shows the procedure of the optimal target charge condition search process in the control system of the charging / discharging circuit which concerns on this invention. 5 is a flowchart showing a procedure for obtaining a leveling loss amount due to charging / discharging in the procedure shown in FIG. 4.

Explanation of symbols

1 cell 2 battery module 3 assembled battery CD partial discharge circuit CC partial charge circuit DD voltage monitoring device MV module voltage detection circuit 100 charge / discharge circuit control system CC partial charge circuit CD partial discharge circuit DD voltage monitoring device MV module voltage detection circuit

Claims (4)

A control system for a charge / discharge circuit that performs charge / discharge according to the state of charge of each battery module, with respect to an assembled battery formed by connecting a plurality of battery modules composed of one or more cells in series,
A module voltage detection circuit for detecting the state of charge for each battery module;
The charging state of an arbitrary battery module among the plurality of battery modules is set as a temporary target charging state, and the battery modules other than the arbitrary battery module are charged and discharged to level the charging state to the temporary target charging state. Loss amount calculating means for calculating the leveling loss amount for each of the arbitrary battery modules;
The temporary target charge state that minimizes the leveling loss amount for each of the battery modules calculated by the loss amount calculating means is searched, and the battery module of each battery module is searched for based on the searched temporary target charge state. A target charge state search means for calculating a charge / discharge amount for changing the charge state to the temporary target charge state; and a partial charge circuit for partially charging the charge amount calculated by the target charge state search means for each of the battery modules. When,
For each battery module, a partial discharge circuit that partially discharges the discharge amount calculated by the target charge state search means;
A control system for a charge / discharge circuit, comprising: The loss amount calculating means includes
For the battery module in a charged state exceeding the temporary target charged state, add a loss amount when discharged by the partial discharge circuit as a discharge loss amount,
For the battery module in a charged state less than the temporary target charged state amount, add a loss amount when charged by the partial charging circuit as a charge loss amount,
The charge / discharge circuit control system according to claim 1, wherein the leveling loss amount is calculated based on the discharge loss amount and the charge loss amount. The loss amount calculating means includes
Based on the state of charge of the plurality of battery modules detected by the module voltage detection circuit, the average state of charge as a whole of the plurality of battery modules is calculated,
The leveling loss amount is calculated by setting a battery module whose charge state is larger than the average charge state as a candidate for the arbitrary battery module,
The charge / discharge circuit control system according to claim 1. The loss amount calculating means includes
Based on the state of charge of the plurality of battery modules detected by the module voltage detection circuit, the average state of charge as a whole of the plurality of battery modules is calculated,
The leveling loss amount is calculated with the battery module exceeding the average charge state and the battery module having a predetermined range or less from the average charge state as a candidate for the arbitrary battery module,
The charge / discharge circuit control system according to claim 1.

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