JP2016201190A - Charging/discharging control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging/discharging control device capable of calculating a local reaction state inside a secondary battery by using a battery model, and calculating a protection current value of electrolytic solution on the basis of the battery state with a low calculation load.SOLUTION: A battery model unit 42 estimates the internal state of a battery cell 10 according to a battery model. By using the estimated internal state, the battery model unit 42 calculates predicted current or predicted power at which the concentration of the electrolytic solution of the battery cell 10 reaches an upper limit concentration or a lower limit concentration after a predetermined time, for example, t seconds have elapsed. By using the calculated predicted current or predicted power, the output unit 44 controls the charge/discharge state of the battery cell 10. Further, the battery model unit 42 executes the flow on a control-period basis. Therefore, each time the predicted current or predicted power is calculated, the internal state is estimated according to the battery model.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a charge / discharge control device that controls charging and discharging of a secondary battery.

  2. Description of the Related Art There is used a power supply system in which power is supplied to a load device by a chargeable / dischargeable secondary battery and the secondary battery can be charged even during operation of the load device as necessary. Typically, a hybrid vehicle, an electric vehicle, or the like equipped with an electric motor driven by a secondary battery as one of the driving force sources is equipped with such a power supply system.

  In the power supply system of a hybrid vehicle, the stored power of the secondary battery is used as the driving power of the motor as the driving force source, and the power generated when the motor generates regenerative power or the generator that generates power with the rotation of the engine. The secondary battery is charged by generated power or the like. In such a power supply system, it is necessary to grasp the state of charge of the secondary battery, for example, the SOC (State of Charge) indicating the remaining amount, and take care not to cause a severe use situation that would cause the battery to deteriorate. . In general, control for limiting excessive charging / discharging is performed by appropriately setting the input / output possible power of the secondary battery according to the battery state.

  In a specific SOC calculation method, the macroscopic remaining capacity of the entire secondary battery is estimated based on the integrated input / output current value from the secondary battery. In addition, as a method for accurately estimating the SOC based on the internal state of the secondary battery, modeling for estimating the battery state using a battery model capable of estimating the electrochemical reaction inside the battery in a lithium ion battery is disclosed in Patent Document 1 and Non-Patent Document 1 discloses this. In Patent Document 1, charge / discharge control of a secondary battery in which local deterioration inside the battery is prevented is performed based on a battery model whose internal state can be predicted.

  Patent Document 2 discloses a control device for a secondary battery that suppresses deterioration of a secondary battery that occurs during high-rate discharge while suppressing a decrease in power performance of the vehicle. Specifically, when the evaluation value based on the current history exceeds the threshold value, the power limit value is changed to a small value based on the maximum power limit value. The evaluation value is calculated from an average SOC and temperature map of the active material calculated by current integration or the like.

  Patent Document 3 discloses a charge / discharge control apparatus that performs charge / discharge control so that battery performance can be maximized while preventing overcharge and overdischarge. Specifically, the input / output possible time is estimated using a battery model that considers past charge / discharge history and local reaction of the battery.

JP 2007-141558 A JP 2009-123435 A JP 2008-42960 A

W.B.Gu and C.Y.Wang, “Thermo-electrochemical bond modeling of lithium ion batteries”, Electrochemical Society (ECS), 2000, pp 743-762.

  In the technique described in Patent Document 1 described above, power limitation is performed by paying attention only to the Li concentration of the active material and the voltage between terminals. During charging / discharging of the battery, the concentration of Li ions in the electrolytic solution is biased, and the internal resistance increases accordingly. In order to suppress battery deterioration, it is necessary to implement protection that prevents the Li ion concentration in the electrolyte from exceeding the upper and lower thresholds. Therefore, the technique described in Patent Document 1 reproduces a local battery reaction, but has a problem that it does not support protection of the electrolyte concentration.

  In the technique described in Patent Document 2, the evaluation value is calculated from an average SOC and temperature map of the active material calculated by current integration or the like. However, in actual charging / discharging, the outermost surface of the active material reacts locally with the electrolytic solution, and the state of the electrolytic solution cannot be accurately reproduced from the average SOC of the active material. Furthermore, when the same current flows in the same SOC state, the battery reaction differs depending on the current charge, discharge, and rest charge / discharge states. For this reason, the state of the electrolyte cannot be accurately expressed simply by accumulating the current history. The power limit value is calculated using the evaluation value calculated from the current history and does not directly use the concentration of the electrolyte, so the calculated power limit value must have a margin. Yes, there is a risk of limiting input / output power more than necessary. Therefore, the technique described in Patent Document 2 aims to protect the electrolyte concentration, but does not consider local reactions, and has a problem of restricting input / output power more than necessary.

  Further, in the technique described in Patent Document 3 described above, the input / output possible time is estimated using a battery model in consideration of past charge / discharge history and local reaction of the battery. However, the host system requires information on the input / output possible electric power value (current value) that can flow for a fixed time, for example, 5 seconds, from the input / output available time. Virtually input various electric power values into the battery model and create a map of electric power and input / output possible time can calculate the input / output possible power, but the calculation load on the battery model is very large. Therefore, although the technique described in Patent Document 3 reproduces a local battery reaction, there is a problem that sequential prediction is difficult from the viewpoint of calculation load by repeatedly using a battery model.

  Therefore, the present invention has been made in view of the above-described problems, and calculates a local reaction state inside a secondary battery using a battery model, and calculates a protection current for the electrolyte with a low calculation load. It aims at providing the charging / discharging control apparatus which can do.

  The present invention employs the following technical means in order to achieve the aforementioned object.

  The present invention provides an estimation means (42) for estimating the internal state of the secondary battery (10) according to the battery model using the battery information detected by the detection means (20, 30), and the internal state estimated by the estimation means. And calculating means (42) for calculating a predicted current or predicted power at which the concentration of the electrolyte of the secondary battery reaches a preset upper limit concentration or lower limit concentration after elapse of a predetermined time. The charge / discharge control apparatus is characterized in that the internal state is estimated according to the battery model only once each time the calculation means calculates the predicted current or the predicted power.

  According to the present invention as described above, the internal state of the secondary battery is estimated by the estimating means according to the battery model. Therefore, the internal state of the secondary battery can be reflected in the charge / discharge control. Further, the calculation means calculates the predicted current or the predicted power at which the concentration of the electrolyte solution of the secondary battery reaches the upper limit concentration or the lower limit concentration after elapse of a predetermined time, using the estimated internal state. The concentration of the electrolyte varies depending on the charge / discharge time and current. Therefore, the predicted current or predicted power that reaches the set upper limit concentration and lower limit concentration can be calculated. Using the predicted current or predicted power calculated in this way, the control means controls the charge / discharge state of the secondary battery. Therefore, reaching the upper limit concentration or lower limit concentration of the electrolytic solution can be prevented. Thereby, excessive charge / discharge of the secondary battery can be suppressed, and deterioration of the secondary battery can be suppressed.

  Thus, by utilizing the battery model, the local reaction state inside the secondary battery is faithfully calculated, and the protection current value of the electrolytic solution based on the battery state is calculated. The estimation means estimates the internal state only once according to the battery model every time the calculation means calculates the predicted current or the predicted power. Therefore, since charge / discharge control can be performed by calculating the predicted power or the predicted current once, the calculation load can be reduced as compared with the conventional technique that performs the sequential calculation. Therefore, in the present invention, a charge / discharge control device capable of calculating a local reaction state inside a secondary battery using a battery model and calculating a protection current value of the electrolyte based on the battery state with a low calculation load. Can be realized.

  In addition, the code | symbol in the bracket | parenthesis of each above-mentioned means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a block diagram showing an assembled battery system 100. FIG. It is a graph which shows the cation density | concentration in 1A. It is a graph which shows the cation density | concentration in 10A. It is a graph which shows the cation density | concentration in 100A. It is a graph which shows the cation density | concentration in 1A and 100A. It is a graph which shows the relationship between an electric current and a density | concentration change. It is a flowchart which shows the calculation method of protection current.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. The assembled battery 1 is configured by connecting battery cells 10 of a plurality of lithium ion secondary batteries in series. The assembled battery 1 is used as a vehicle storage battery mounted on, for example, an electric vehicle (EV) that runs only by an electric motor, a plug-in hybrid vehicle (PHV) that uses a motor and an internal combustion engine as a driving force, and the like. it can. The assembled battery 1 can be used as a stationary storage battery for a storage battery in a house.

  The assembled battery system 100 is mounted on a hybrid vehicle and connected to an electric motor for traveling. As shown in FIG. 1, the assembled battery system 100 includes an assembled battery 1, a current detection device 30, a voltage detection device 20, and a charge / discharge control device 40. Here, the assembled battery 1 includes a plurality of battery cells 10 as an example thereof. The assembled battery 1 is configured by connecting a plurality of battery cells 10 in series. The battery cell 10 may have a configuration in which a plurality of battery cells are connected in parallel.

  The charge / discharge control device 40 includes an input unit 41, a battery model unit 42, an input / output power calculation unit 43, an output unit 44, and the like. The current detection device 30 detects a current value flowing through the plurality of battery cells 10 constituting the assembled battery 1. The voltage detection device 20 detects the voltage between the terminals of each battery cell 10. The voltage detection device 20 is used to calculate the SOC of the assembled battery 1 by detecting the voltage between the terminals of one battery cell 10 when a predetermined condition is satisfied when the assembled battery 1 is charged or discharged. To do.

  The current value detected by the current detection device 30 and the voltage between terminals detected by the voltage detection device 20 at the time of charging or discharging are input to the input unit 41. The SOC state of the assembled battery 1 is calculated by the battery model unit 42 using, for example, a program stored in the input / output power calculation unit 43. The program is, for example, an arithmetic program using a battery model that represents the specific charge / discharge characteristics of the battery cell 10. For example, for each battery cell 10, the battery model unit 42 can calculate the SOC of each cell from the internal state terminal voltage detected by the voltage detection device 20, and can calculate the SOC of the entire assembled battery 1.

  The output unit 44 controls charging / discharging of the assembled battery 1 based on the calculation result. Therefore, the charge / discharge control device 40 controls charging / discharging of the assembled battery 1 using the current value detected by the current detection device 30 and the voltage between terminals detected by the voltage detection device 20. The charge / discharge control device 40 calculates the charge capacity or discharge capacity of the assembled battery 1 using the inter-terminal voltage detected by the voltage detection device 20 and the charge / discharge characteristics using the battery model, and is stored in the assembled battery 1. Find the electrical capacity.

  The battery cell 10 includes a positive electrode including a positive electrode active material, a negative electrode including a hard carbon, soft carbon, or a negative electrode active material mainly composed of a material obtained by mixing these active materials and graphite, and is interposed between the positive electrode and the negative electrode. And an electrolyte that is a medium to be used. Further, the battery cell 10 includes a separator interposed between the positive electrode and the negative electrode so that they are not electrically short-circuited, and an outer case including the positive electrode, the negative electrode, the electrolyte, and the separator inside. .

Next, the relationship between the current value and the electrolyte concentration will be described. 2 to 4 show a current value of 1 A / m ² (FIG. 2), 10 A / m ² (FIG. 3), and 100 A / m ² (FIG. 4) for a battery model of SOC 85% for 10 seconds, The concentration distribution of the electrolytic solution after flowing for 20 seconds, 30 seconds, 40 seconds, and 50 seconds is shown. The vertical axis represents the cation concentration, and the horizontal axis represents the position inside the battery cell 10. Among the positions, 0 to 70 are negative electrodes, 70 to 90 are separators, and 90 to 185 are positive electrodes. These numerical values are the results of calculations using a battery model described later.

  Before the current is applied, the cation concentration is constant at 1000 μm at any position. As shown in FIGS. 2 to 4, after the current is passed, the absolute value of the cation concentration distribution is different for each current value, but any current value has the same distribution, and the negative electrode centering on the separator. The cation concentration increases toward the side (left side). The cation concentration decreases toward the positive electrode side (right side) centering on the separator. Moreover, the shorter the time, the smaller the difference between the maximum value and the minimum value of the cation concentration. Further, when the current value is increased, the change width of the cation concentration is increased.

Next, the result of comparing the cation concentration waveforms in 1A and 100A will be described with reference to FIG. In FIG. 5, the cation concentration distribution at 1A is shown using the left axis, and the cation concentration distribution at 100A is shown using the right axis. The left and right axes are aligned at a height of an initial concentration of 1000 mol / m ³ . One scale on the right axis of 1A is 100 times the left axis of 100A. The curves for each time are well overlapped at 1A and 100A. Therefore, it can be seen that the tendency of change in concentration is similar at any electrode position regardless of the current value.

Next, the relationship between the change in cation concentration and the current value will be described with reference to FIG. FIG. 6 shows the relationship between the current at position = 0 and the electrolyte concentration change after 10 seconds. In FIG. 6, the vertical axis indicates the concentration change, and the horizontal axis indicates the current value. As shown in FIG. 6, it can be seen that the concentration change of the electrolytic solution, that is, the cation concentration-initial concentration is proportional to the current value at all times. This relationship can be expressed by the following equation (1).

  The left side of Equation (1) divides the concentration change ΔCl for t seconds by the average current Iav for t seconds. The right side of Equation (1) is obtained by dividing the value obtained by subtracting the current concentration Cl from the upper limit concentration Clmax of the electrolyte by the predicted current Isim.

  As shown in FIG. 6 described above, since the concentration change of the electrolyte is proportional to the current value, the rate of change, which is the value obtained by dividing the concentration change of the molecule in equation (1) by the current, is equal. Every time calculation is performed according to the battery model, the input / output power calculation unit 43 stores the calculation result. Accordingly, the density change over the past t seconds can be obtained by reading information from the input / output power calculator 43. Similarly, the average current during the past t can be detected by the current detection device. Therefore, the left side of equation (1) can be obtained by detection and calculation.

  Moreover, the molecule | numerator of a right side is the upper limit density | concentration of the electrolyte solution set beforehand. Thus, the upper limit concentration predicted current Isim can be obtained by solving the equation (1) with the predicted current Isim. Similarly, when obtaining the predicted current of the lower limit concentration, on the right side of the equation (1), the value obtained by subtracting the lower limit concentration Clmin from the current concentration Cl of the electrolytic solution may be divided by the predicted current Isim. Such calculation is performed by the calculation unit. Accordingly, the calculation unit functions as a calculation unit, and calculates the predicted current using a calculation formula that formulates the relationship between the concentration change of the electrolytic solution and the current value.

  Next, a series of processes in which the calculation unit calculates the predicted current will be described with reference to FIG. The flowchart shown in FIG. 7 is executed for each control cycle determined in advance by the calculation unit.

  In step S1, the cation concentration distribution of the electrolytic solution is calculated using the battery model using the battery state detected by the voltage detection device 20 and the current detection device 30, and the process proceeds to step S2. The battery model is an equation showing the electrode reaction called the Butler-Volmer equation, the law of conservation of lithium ions in the electrolysis solution, the law of conservation of lithium ions in the solid phase, the law of conservation of charge in the electrolysis solution, the law of conservation of thermal energy Etc. are used. Since such battery model formulas are based on Non-Patent Document 1, Non-Patent Document 1 is used for detailed description of each model formula. Thereby, the predicted value of the internal state in the battery cell 10 can be calculated sequentially. The predicted internal state includes, for example, the potential distribution in the electrolytic solution and in the active material, the absolute temperature, and the amount of cation generated in addition to the cation concentration in the electrolytic solution. In step S1, the cation concentration of the electrolytic solution is calculated for all the battery cells 10 according to the battery model.

  In step S2, the concentration change for the past t seconds is calculated for each position in the battery cell 10, and the process proceeds to step S3. Since the calculation result in step S1 is stored in the input / output power calculation unit 43, the concentration change is obtained by reading the concentration t seconds before from the input / output power calculation unit 43 and comparing it with the calculation result in step S1. Can be calculated.

  In step S3, an average current value for the past t seconds is calculated, and the process proceeds to step S4. Similarly, since the current value detected in the past is stored in the input / output power calculation unit 43 in association with the time, the average current value can be calculated by reading these time-series data. it can.

  In step S4, a predicted current that reaches the upper limit concentration and the lower limit concentration after t seconds is calculated using a relationship in which the density change and the current value are proportional, and the process proceeds to step S5. As described above, since the density change and the current value are in a proportional relationship, the predicted current can be calculated using Equation (1).

  In step S5, information is transmitted to the output unit 44 so as to protect the battery cell 10 using information on the predicted current, and this flow ends.

  Thus, the output unit 44 performs charge / discharge control so as not to reach the predicted current. If the predicted current is not reached, exceeding the upper limit concentration can be suppressed, and similarly, falling below the lower limit concentration can be suppressed.

  In this way, while calculating the concentration distribution of the electrolyte in the battery model, the current value is calculated so that the concentration of the electrolyte reaches the upper limit or the lower limit after t seconds based on the concentration transition, and the calculated predicted current value is input. The battery is protected as a current that can be output. Here, the predicted current is calculated, but power may be calculated instead of current and controlled as predicted power.

  As described above, the battery model unit 42 of the present embodiment functions as an estimation unit, and estimates the internal state of the battery cell 10 according to the battery model. Therefore, the internal state of the battery cell 10 can be reflected in charge / discharge control. Further, the battery model unit 42 also functions as a calculation unit, and uses the estimated internal state to predict a predicted current at which the concentration of the electrolytic solution in the battery cell 10 reaches the upper limit concentration or the lower limit concentration after elapse of a predetermined time, for example, t seconds. Alternatively, the predicted power is calculated. The concentration of the electrolyte varies depending on the charge / discharge time and current. Therefore, the predicted current or predicted power that reaches the set upper limit concentration and lower limit concentration can be calculated. Using the predicted current or the predicted power calculated in this way, the output unit 44 that functions as a control unit controls the charge / discharge state of the battery cell 10. Therefore, reaching the upper limit concentration or lower limit concentration of the electrolytic solution can be prevented. Accordingly, excessive charging / discharging of the battery cell 10 can be suppressed, and deterioration of the battery cell 10 can be suppressed.

  Thus, by utilizing the battery model, the local reaction state inside the battery cell 10 is faithfully calculated, and the protection current value of the electrolytic solution based on the state of the battery cell 10 is calculated. Moreover, the battery model part 42 performs the flow shown in FIG. 7 for every control period. Therefore, every time the predicted current or the predicted power is calculated, the internal state is estimated according to the battery model only once. As described above, since the output unit 44 can perform the charge / discharge control by calculating the predicted power or the predicted power once, it is possible to reduce the calculation load as compared with the conventional technique that performs the sequential calculation. Therefore, in the present embodiment, the battery cell 10 can calculate the local reaction state inside the battery cell 10 using the battery model, and calculate the protection current value of the electrolytic solution based on the battery state with a low calculation load. The charge / discharge control apparatus can be realized.

  In the present embodiment, the battery model unit 42 calculates the predicted power or the predicted current using a calculation formula that formulates the relationship between the concentration change of the electrolytic solution and the current value. Therefore, in this embodiment, the current value that protects the upper and lower limits of the electrolyte concentration is calculated. In addition, the current limit value is not determined by a map created in advance, but the protection current value is determined from the protection current formula using the characteristics of the current value and the electrolyte transition. Thus, by introducing the formula for calculating the predicted current or the predicted power from the electrolyte concentration, it is possible to reduce the calculation load.

  Further, in the present embodiment, the battery model unit 42 estimates the internal state of the plurality of battery cells 10 according to the same number of battery models as the battery cells 10. As a result, the cation concentration can be calculated with high accuracy. Thereby, it is possible to further suppress the occurrence of excessive charging / discharging in the battery cell 10.

(Other embodiments)
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  The structure of the said embodiment is an illustration to the last, Comprising: The scope of the present invention is not limited to the range of these description. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  In the first embodiment described above, in step S1, the cation concentration of the electrolytic solution is calculated according to the battery model for all the battery cells 10, but the cation concentration may not be calculated for all the battery cells 10. The battery model unit 42 may estimate the internal state of the secondary battery according to the battery model of one representative battery cell 10 among the plurality of battery cells 10. Therefore, the internal state of the secondary battery is estimated on the assumption that there are the same battery models as the number of battery cells 10. As a result, the calculation load can be reduced compared to estimating the internal state of all the battery cells 10.

  In the first embodiment described above, the battery cell 10 is a lithium ion battery. However, the battery cell 10 may be composed of another secondary battery such as a nickel metal hydride battery.

  In the first embodiment described above, the detection means is realized by the current detection device 30 and the voltage detection device 20, but it is not necessary to use both, and either one may be used. In other words, the detection means may be any device that detects at least one of current and voltage among the battery information of the battery cell 10.

1 ... assembled battery 10 ... battery cell (secondary battery)
20 ... Voltage detection device (detection means) 30 ... Current detection device (detection means)
DESCRIPTION OF SYMBOLS 40 ... Charge / discharge control apparatus 41 ... Input part 42 ... Battery model part (estimation means, calculation means) 43 ... Input / output calculating part 44 ... Output part (control means) 100 ... Assembly battery system

Claims (4)

Detection means (20, 30) for detecting at least one of current and voltage among battery information of the secondary battery (10);
Estimating means (42) for estimating an internal state of the secondary battery according to a battery model using the battery information detected by the detecting means;
A calculating means for calculating a predicted current or a predicted power at which the concentration of the electrolyte of the secondary battery reaches a preset upper limit concentration or lower limit concentration after elapse of a predetermined time, using the internal state estimated by the estimating means. 42)
Control means (44) for controlling the charge / discharge state of the secondary battery so as not to reach the predicted current or the predicted power calculated by the calculating means,
The charging / discharging control apparatus according to claim 1, wherein the estimating unit estimates the internal state only once according to the battery model every time the calculating unit calculates the predicted current or the predicted power.   2. The charge / discharge control according to claim 1, wherein the calculation unit calculates the predicted power or the predicted current using a calculation formula that formulates a relationship between a change in concentration of the electrolytic solution and a current value. apparatus. The secondary battery includes a plurality of battery cells (10),
The charge / discharge control apparatus according to claim 1, wherein the estimation unit estimates the internal state of the secondary battery according to the same number of battery models as the battery cells. The secondary battery includes a plurality of battery cells (10),
3. The charge / discharge control according to claim 1, wherein the estimation unit estimates the internal state of the secondary battery according to the battery model of one of the plurality of battery cells. apparatus.

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