JP2010231968A - Control device for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control charge and discharge of a secondary battery with high reliability. <P>SOLUTION: A control device for the secondary battery includes detection means 20, 22 for detecting conditions of the secondary battery at every designated time interval Δt, a calorific value estimation means 26 for calculating a calorific value of the secondary battery from conditions of the detected secondary battery, and a future internal temperature estimation means 28 for estimating internal temperature of the secondary battery after passing the time interval Δt from the present time on the basis of the calculated calorific value. Conditions of the secondary battery can be detected by the detection means 20, 22 whenever the internal temperature of the secondary battery is estimated by the future internal temperature estimation means 28. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control apparatus for a secondary battery that enables safe control of charging and discharging.

  Secondary batteries that can be charged and discharged are widely used for supplying electric power to electrical devices. For example, in a power source system of a hybrid vehicle or an electric vehicle, a secondary battery for driving a prime mover is used as a driving force source.

  Patent Document 1 discloses a charge / discharge control device that performs charge / discharge control of a secondary battery that prevents local deterioration inside the battery based on a battery model whose internal state can be predicted. In this technique, an electronic control unit (ECU) uses a battery model that calculates a predicted internal state value in a battery using a battery model that can dynamically estimate the internal state of a secondary battery. In order to prevent the predicted internal state value from locally deviating from the predetermined management range, the outputable power (discharge power upper limit value) and the input possible power (charge power upper limit value) from the secondary battery are calculated, Charge / discharge is limited within the range of power that can be input and output.

  Patent Document 2 discloses a protection control system that simply and sufficiently suppresses deterioration of a secondary battery. In this technique, at least one of the inter-terminal voltage, charge / discharge current, and resistance of the secondary battery to be controlled is detected, and the secondary battery is based on the detected voltage value, the detected current value, and at least one of the detected resistance value. It is determined whether or not it is in a predetermined deterioration promoting region. And when it is judged that a secondary battery exists in a deterioration promotion area | region, a secondary battery is avoided from a deterioration promotion area | region.

JP 2007-141558 A JP 2003-47159 A

W.B.Gu and C.Y.Wang, THERMAL-ELECTROCHEMICAL COUPLED MODELING OF A LITHIUM-ION CELL, ECS Proceedings Vol.99-25 (1), 2000, ECS (2000), pp 743-762

  By the way, as in Patent Document 1, a battery model is used to continuously estimate the internal state (ion concentration, potential, temperature, etc.) of the battery over a long period of time from the initial value, and control based on the estimated value. In the technique for performing the estimation, the accuracy of the estimated value decreases as time elapses from the time when the initial value is obtained. Therefore, the determination reference value used for determining the control of the secondary battery must be set to a value that allows for a considerable safety factor.

  Further, as in Patent Document 2, in the technology that only estimates the current state of the battery from the measured value of the state of the secondary battery and does not estimate the state of the future secondary battery, the state of the future secondary battery Considering a margin for the change, a considerable safety factor must be expected in the determination reference value used for determining the control of the secondary battery.

  For example, when controlling the temperature of the secondary battery, a temperature considerably lower than the actual thermal runaway start temperature is set as the determination reference value. For this reason, although sufficient discharge capacity is still left, control for suppressing discharge must be performed, and the secondary battery may not be sufficiently utilized.

  In view of the above problems, an object of the present invention is to provide a control apparatus for a secondary battery that can control charging and discharging with high reliability.

  One aspect of the present invention is a control device for a secondary battery, wherein the detection unit detects a state of the secondary battery at every predetermined time interval Δt, and the secondary battery is detected from the detected state of the secondary battery. A calorific value estimating means for calculating a calorific value at the time, and a future internal temperature estimating means for estimating the internal temperature of the secondary battery after the elapse of the time interval Δt from the present time based on the calculated calorific value, Each time the internal temperature of the secondary battery is estimated by the future internal temperature estimating means, the state of the secondary battery is detected by the detecting means.

  Here, the detection means includes a temperature detection means for detecting at least the external temperature of the secondary battery every predetermined time interval Δt, and uses the correspondence relationship between the external temperature and the internal temperature of the secondary battery obtained in advance. It is preferable that a current internal temperature estimating means for estimating the current internal temperature from the external temperature of the secondary battery detected by the temperature detecting means is provided.

  The detection means includes temperature detection means for detecting at least the external temperature of the secondary battery at every predetermined time interval Δt, and the external temperature of the secondary battery detected by the temperature detection means using a heat conduction equation. It is also preferable to include a current internal temperature estimating means for estimating the current internal temperature from the current internal temperature.

  The detection means includes charge / discharge detection means for detecting a charge / discharge amount, and the heat generation amount estimation means includes the current internal temperature of the secondary battery estimated by the current internal temperature estimation means and the charge / discharge detection. It is preferable to calculate the amount of heat generated in the secondary battery based on the charge / discharge amount detected by the means.

  Further, the difference between the present internal temperature of the secondary battery estimated by the present internal temperature estimation means and the future internal temperature of the secondary battery estimated based on the external temperature detected before the time interval Δt is It is preferable to include a pre-determination unit that determines that the secondary battery is abnormal without performing the process of the future internal temperature estimation unit when the difference is equal to or greater than a predetermined allowable temperature difference.

  In addition, it is preferable to include a determination unit that determines the safety of the secondary battery based on the future internal temperature of the secondary battery estimated by the future internal temperature estimation unit.

  According to the present invention, it is possible to control charging / discharging of a secondary battery with high reliability.

It is a figure which shows the block diagram of the secondary battery system which concerns on embodiment of this invention. It is a flowchart of the charging / discharging control process of the secondary battery in 1st Embodiment. It is a flowchart of the charging / discharging control process of the secondary battery in 2nd Embodiment. It is a figure which shows the block diagram of the secondary battery system which concerns on embodiment of this invention. It is a flowchart of the charging / discharging control process of the secondary battery in 2nd Embodiment.

  As shown in FIG. 1, the secondary battery system 100 according to the first embodiment of the present invention includes a secondary battery 102, a motor / generator 104, and an electronic control unit (ECU) 106. The

  The secondary battery 102 is a battery that can store energy by charging and can repeatedly charge and discharge. Examples of the secondary battery 102 include a nickel metal hydride battery and a lithium ion battery. The secondary battery 102 needs to perform charge / discharge control so as not to be overcharged or overdischarged according to its operating state.

  The output of the secondary battery 102 is connected to the motor / generator 104. The motor / generator 104 may include a control circuit such as an inverter for adjusting the output from the secondary battery 102. The secondary battery 102 is driven by supplying electric power to the motor / generator 104 in accordance with control from the ECU 106. The secondary battery 102 is charged by receiving regenerative power from the motor / generator 104 in accordance with control from the ECU 106. In this embodiment, the load of the secondary battery 102 is the motor / generator 104. However, the present invention is not limited to this.

  The secondary battery 102 is provided with a temperature sensor for measuring the temperature outside the casing of the secondary battery 102. The temperature sensor can be, for example, a thermocouple 10. The thermocouple 10 is used to measure the external temperature of the secondary battery 102 in order to estimate the temperature inside the battery in the control of the secondary battery system 100. The attachment position of the thermocouple 10 is a position suitable for measuring the internal temperature of the secondary battery 102, for example, an external temperature when a temperature map indicating the correspondence between the external temperature and the internal temperature of the secondary battery 102 is prepared in advance. It is preferable to attach to the position where the temperature is measured. The output of the thermocouple 10 is input to the ECU 106.

  Further, a current sensor 12 that measures the input / output current Iapp of the secondary battery 102 is provided. Further, a voltage sensor 14 that measures the output voltage Vb between the output terminals of the secondary battery 102 may be provided. Outputs from the current sensor 12 and the voltage sensor 14 are input to the ECU 106.

  ECU 106 receives outputs from thermocouple 10, current sensor 12, and voltage sensor 14, and controls charging / discharging of secondary battery 102 based on these signals. The ECU 106 includes a temperature detection unit 20, a charge / discharge detection unit 22, a current internal temperature estimation unit 24, a heat generation amount estimation unit 26, a future internal temperature estimation unit 28, and a determination unit 30.

  The ECU 106 can be configured to include a microcomputer. In this case, each means included in the ECU 106 is realized by executing a control program. Further, the ECU 106 can be configured to include a logic circuit. In this case, each means included in the ECU 106 is realized by a combination of logic circuits.

  Hereinafter, charge / discharge control of the secondary battery 102 in the secondary battery system 100 will be described. The charge / discharge control process is executed according to the flowchart shown in FIG. The charge / discharge control process is performed every predetermined time interval Δt. That is, the following processing is executed at each time interval Δt to perform charge / discharge control.

  In step S10, the charge / discharge rate Iapp is acquired. The process of step S10 corresponds to the charge / discharge detection means 22. The ECU 106 acquires the current input / output current Iapp from the current sensor 12.

  In step S12, the external temperature of the secondary battery 102 is acquired. The ECU 106 acquires the battery stack temperature estimated value Tstack, mes of the secondary battery 102 from the thermocouple 10, that is, the external temperature (hereinafter referred to as Tout). The process of step S12 corresponds to the process in the temperature detection means 20.

In step S14, the internal temperature _TN of the secondary battery 102 at the present time (step: N) is estimated based on the external temperature Tout of the secondary battery 102. The processing in step S14 corresponds to the processing in the current internal temperature estimation means 24. Usually, it is impossible to insert a temperature sensor such as a thermocouple into the inside of the commercially available secondary battery 102, and the internal temperature _TN of the secondary battery 102 cannot be directly measured. Therefore, from the external temperature Tout of the secondary battery 102 The internal temperature _TN is estimated.

In this embodiment, the internal temperature T _N, the corresponding relationship between the internal temperature T _N of the external temperature Tout and the secondary battery 102 of the previously measured in the same test apparatus and the like and the secondary battery 102 to implement the secondary battery 102 Is used to obtain an internal temperature _TN corresponding to the acquired external temperature Tout of the secondary battery 102.

In step S16, based on the charge and discharge rate Iapp state of charge _SOC N: calculating the (SOC State of Charge). The process of step S16 corresponds to a part of the heat generation amount estimation means 26.

The ECU 106 obtains the amount of current charged / discharged at the time interval Δt from the difference between the charge / discharge rate Iapp previously measured before the time interval Δt and the charge / discharge rate Iapp measured at step S10 this time, and the current value ( Step: Obtain the state of charge SOC _N of the secondary battery 102 in N). In calculating the state of charge SOC _N , the detected values of the external temperature Tout and the output voltage Vb of the secondary battery 102 may be appropriately reflected.

  In step S18, the potential gradient and concentration gradient of the secondary battery 102 are obtained using the battery internal state model formula. The processing in step S18 corresponds to a part of the heat generation amount estimation means 26.

The ECU 106 obtains the potential gradient and the concentration gradient by introducing the internal temperature _TN of the secondary battery 102 obtained in step S14 and the state of charge SOC _N of the secondary battery 102 obtained in step S16 into the battery internal state model equation. .

  In the secondary battery control device in the embodiment of the present invention, the internal state distribution of the battery is estimated using battery model equations M1 to M15 described below. The battery model formula used in the battery model unit of the ECU 106 will be described below. Table 1 shows a list of variables and constants used in the battery model equations M1 to M15.

Formulas M1 to M3 are formulas indicating an electrode reaction (Butler Volmer formula). The exchange current density i ₀ is expressed by the formula M1, and is given as a function of the ion concentration at the interface of the active material. Η in the equation M1 is obtained by the equation M2, and U in the equation M2 is obtained by the equation (M3).

Expressions M4 to M6 indicate the ion conservation law in the electrolysis solution. The effective diffusion coefficient in the electrolysis solution is expressed by Equation M5. Reaction current j ^Li, as shown in Equation M6, given by the product of active material surface area a _s per unit electrode volume transport current density / i _nj. The volume integral of the reaction current j ^{Li over} the entire electrode corresponds to the charge / discharge rate Iapp.

Formulas M7 and M8 show the ion conservation laws in the solid phase. Formula M7 represents a diffusion equation in an active material that is a sphere. The active material surface area a _s per electrode unit volume is obtained by the equation M8.

Based on the law of conservation of electric charge in the electrolysis solution, equations M9 to M11 indicating the potential in the electrolysis solution are obtained. The effective ionic conductivity κ ^eff is obtained by the equation M10. Further, the diffusion conductivity coefficient κ _D ^eff is expressed by the equation M11.

Based on the law of conservation of charge in the active material, the potential in the solid phase is expressed by the formulas M12 and M13.

  The thermal energy conservation law inside the battery is expressed by equations M14 and M15. Thereby, it becomes possible to analyze the local temperature change inside the secondary battery due to the charge / discharge phenomenon.

  Based on the above model, the boundary condition for each point of the interelectrode distance x (for example, x = 0 at the negative electrode end, x = L at the positive electrode end) and the electrode longitudinal coordinate y (for example, y = 0 to y = H). Is appropriately set, and the battery model equations of equations M1 to M15 can be sequentially solved as a difference equation. Thereby, it is possible to estimate the temporal transition of the positional distribution (such as the positional gradient of the potential and the positional gradient of the concentration) for the internal state of the secondary battery 102.

That is, the internal state estimated values at each point inside the secondary battery 102 can be sequentially calculated using the battery model expressions of the expressions M1 to M15. As shown in the equations M1 to M15, the estimated internal states include ion concentrations c _s (in the active material) and c _e (in the electrolyte) averaged by volume, potential distribution ψ _e (in the electrolyte) ) And ψ _s (within the active material), absolute temperature T, ion generation amount j ^{Li and the} like. Further, the local ion concentration c _e and the ion concentration C _se at the interface of the active material are obtained, and the ratio C _se / C _{s, max} to the ion concentration C _{s, max} is obtained, so that The local charge rate SOC can be obtained. In this way, the internal state of the secondary battery 102 is obtained.

  The ion concentration in the active material is a function of the active material radius r, and the ion concentration is uniform in the circumferential direction.

  The details of the battery model formulas M1 to M15 are described in Non-Patent Document 1, and the detailed description uses Non-Patent Document 1. The battery model is not limited to Non-Patent Document 1 and can be used as long as the same physical quantity (power generation amount) can be calculated.

In step S20, obtaining the calorific value _{Q N} of the secondary battery 102 at the present time. Calorific value Q _N is obtained from the secondary battery 102 inside the potential gradient and the concentration gradient calculated in step S18. Step S20 corresponds to part of the heat generation amount estimation means 26.

In step S22, it estimates the increase value [Delta] T _N of the internal temperature of the secondary battery 102. ECU106 is the calorific value _{Q N} calculated in step S20 are substituted into Equation M16 estimates the increase value [Delta] T _N of the internal temperature of the secondary battery 102. Here, ρ is the density of the secondary battery 102, and Cp is the constant pressure specific heat of the secondary battery 102. The process of step S22 corresponds to a part of the future internal temperature estimation means 28.

In step S24, the start time of the next charge / discharge control process, that is, the internal temperature T _{N + 1, predict} (hereinafter referred to as T _{N + 1} ) of the secondary battery 102 after the time interval Δt from the present time is estimated. The process of step S24 corresponds to a part of the future internal temperature estimating means 28. ECU106 is the rise value [Delta] T _N of the internal temperature of the secondary battery 102 estimated by substituting the equation M17 in step S22, estimates the internal temperature _{T N + 1} of the secondary battery 102 after a time interval Δt from the current time.

In step S26, charge / discharge control of the secondary battery 102 is performed based on the internal temperature _{TN + 1} of the secondary battery 102 after the time interval Δt from the current time. In the present embodiment, when the internal temperature T _{N + 1 of the} secondary battery 102 after the time interval Δt from the current time reaches a predetermined temperature reference value T _{thermal_runaway} (hereinafter referred to as T _th ), the _{ECU 106} Assuming that there is a possibility that the thermal runaway 102 may occur, the process proceeds to step S28 to perform avoidance processing. The avoidance process can be, for example, a process of stopping charging / discharging of the secondary battery 102. On the other hand, if the internal temperature T _{N + 1} is smaller than the predetermined temperature reference value T _th , it is assumed that the secondary battery 102 has a low possibility of thermal runaway, and after a time interval Δt, the process returns to step S10 and the charge / discharge control process is repeated. The process of step S26 corresponds to the determination unit 30.

Note that the charge / discharge control for the secondary battery 102 in step S26 is not limited to this, and may be performed based on the internal temperature _{TN + 1} of the secondary battery 102 after the time interval Δt from the present time.

<Second Embodiment>
The charging / discharging control process of the secondary battery 102 in 2nd Embodiment is shown as a flowchart of FIG. In the charge / discharge control process of the secondary battery 102 in the second embodiment, as shown in FIG. 3, the process of step S14 is performed with respect to the charge / discharge control process of the secondary battery 102 in the first embodiment. This is replaced with the processing of S14a. The processing of other steps is the same as the charging / discharging control processing of the secondary battery 102 in the first embodiment, and thus description thereof is omitted.

In step S14 of the charge / discharge control process in the first embodiment, the measured external temperature is measured using a map showing the correspondence between the external temperature Tout and the internal temperature _TN of the secondary battery 102 measured in advance in a test apparatus or the like. The internal temperature _TN corresponding to Tout was determined. In step S14a, the internal temperature _TN is calculated from the external temperature Tout measured based on an empirical equation or a heat conduction equation.

The empirical formula refers to the external temperature Tout based on the correspondence between the external temperature Tout of the secondary battery 102 and the internal temperature _TN of the secondary battery 102 measured in advance in a test device similar to the mounted secondary battery 102. Is an approximate function that indicates the internal temperature _TN of the secondary battery 102. By introducing the external temperature Tout of the secondary battery 102 acquired in step S10 into this empirical formula, the current internal temperature _TN of the secondary battery 102 can be obtained.

In addition, the heat conduction equation is determined based on the shape of the secondary battery 102 and the heat conduction characteristics of each part, and the current temperature is determined by introducing the external temperature Tout of the secondary battery 102 acquired in step S10 as a boundary condition. The internal temperature _TN of the secondary battery 102 can be obtained.

<Third Embodiment>
As shown in FIG. 4, the secondary battery system 110 according to the third embodiment of the present invention includes a secondary battery 102, a motor / generator 104, and an electronic control unit (ECU) 106 a. The As shown in FIG. 4, the secondary battery system 110 according to the third embodiment is obtained by replacing the ECU 106 of the secondary battery system 100 according to the first embodiment with an ECU 106a. Since other configurations are the same as those of the secondary battery system 100 in the first embodiment, description thereof will be omitted.

  The ECU 106a receives outputs from the thermocouple 10, current sensor 12, and voltage sensor 14, and controls charging / discharging of the secondary battery 102 based on these signals. The ECU 106a includes a temperature detection unit 20, a charge / discharge detection unit 22, a current internal temperature estimation unit 24, a heat generation amount estimation unit 26, a future internal temperature estimation unit 28, a determination unit 30 and a pre-determination unit 32. The components other than the pre-determination means 32 are the same as those of the ECU 106 in the first embodiment.

  The charging / discharging control process of the secondary battery 102 in 3rd Embodiment is shown as a flowchart of FIG. As shown in FIG. 5, the charge / discharge control process of the secondary battery 102 in the third embodiment is the same as the charge / discharge control process of the secondary battery 102 in the first embodiment. It is inserted between S14 and S16. The processing of other steps is the same as the charging / discharging control processing of the secondary battery 102 in the first embodiment, and thus description thereof is omitted.

  In step S30, a pre-determination process is performed before the final determination in step S26. The process of step S30 corresponds to the pre-determination means 32.

The ECU 106a determines whether or not the secondary battery 102 is normal based on the current internal temperature _TN of the secondary battery 102 obtained in step S14. For example, ECU106a the future internal temperature _{T N} of the secondary battery 102 calculated in the internal temperature _{T N} and step N-1, which is started before the time interval Δt from the current time of _current, the difference between the _predict, i.e. current internal temperature T _If the difference _obtained by subtracting the future internal temperature T _{N, predict} from _N is equal to or greater than the reference value ε, it is determined that the secondary battery 102 is abnormal, the process proceeds to step S32, and the secondary battery 102 is abnormal. Perform avoidance processing. On the other hand, if the difference is smaller than the reference value ε, it is assumed that there is a high possibility of being in a normal state as a pre-determination, and the process proceeds to step S16.

  The thermal runaway of the secondary battery 102 due to overcharge or the like occurs when the internal temperature of the secondary battery 102 gradually increases and reaches a certain temperature. Therefore, it can be avoided if appropriate charge / discharge control is performed. If the charge / discharge control in the first and second embodiments is applied, it is possible to cope with a failure of the secondary battery 102 such as thermal runaway with higher reliability than the conventional charge / discharge control.

  However, even if the internal temperature of the secondary battery 102 is relatively low, an unexpected sudden thermal runaway may occur. For example, in a lithium ion battery, thermal runaway due to abnormal heat generation due to a partial short circuit due to lithium deposition, foreign matters mixed in the manufacturing process, or a short circuit due to an unexpected force applied from the outside can occur.

  In the charge / discharge control according to the third embodiment, when the pre-determination process in step S30 is performed, when there is a sudden temperature change, it is assumed that the secondary battery 102 is abnormal and a quick response process is performed. It becomes possible.

  As described above, in the charge / discharge control of the secondary battery in the first to third embodiments, the temperature of the secondary battery is obtained every predetermined time interval Δt, and the internal state of the secondary battery is based on the temperature. Is estimated and controlled. Therefore, the accuracy of the estimated value of the internal state can be improved compared to the control in which the temperature estimation is performed once in a time sequence as in the prior art, and the reliability is more reliable. Charge / discharge control is possible.

  In addition, the internal temperature of the future secondary battery is estimated based on the current internal temperature of the secondary battery, and control is performed based on the estimated value. It is.

  DESCRIPTION OF SYMBOLS 10 Thermocouple, 12 Current sensor, 14 Voltage sensor, 20 Temperature detection means, 22 Charge / discharge detection means, 24 Current internal temperature estimation means, 26 Heat generation amount estimation means, 28 Future internal temperature estimation means, 30 Judgment means, 32 Pre-determination Means, 100, 110 Secondary battery system, 102 Secondary battery, 104 Motor generator, 106, 106a ECU.

Claims (6)

A control device for a secondary battery,
Detecting means for detecting the state of the secondary battery every predetermined time interval Δt;
A calorific value estimating means for calculating a calorific value in the secondary battery from the detected state of the secondary battery;
A future internal temperature estimating means for estimating the internal temperature of the secondary battery after the elapse of the time interval Δt from the current time, based on the calculated calorific value;
With
The secondary battery control device, wherein the detection means detects the state of the secondary battery every time the future internal temperature estimation means estimates the internal temperature of the secondary battery. The control apparatus for a secondary battery according to claim 1,
The detection means includes a temperature detection means for detecting at least an external temperature of the secondary battery every predetermined time interval Δt,
Provided with a current internal temperature estimation means for estimating the current internal temperature from the external temperature of the secondary battery detected by the temperature detection means, using the correspondence relationship between the external temperature and internal temperature of the secondary battery determined in advance. A control device for a secondary battery. The control apparatus for a secondary battery according to claim 1,
The detection means includes a temperature detection means for detecting at least an external temperature of the secondary battery every predetermined time interval Δt,
An apparatus for controlling a secondary battery, comprising: current internal temperature estimation means for estimating a current internal temperature from an external temperature of the secondary battery detected by the temperature detection means using a heat conduction equation. A control device for a secondary battery according to claim 2 or 3,
The detection means includes charge / discharge detection means for detecting a charge / discharge amount,
The calorific value estimation unit is configured to generate a calorific value in the secondary battery based on the current internal temperature of the secondary battery estimated by the current internal temperature estimation unit and the charge / discharge amount detected by the charge / discharge detection unit. A control apparatus for a secondary battery, wherein A control device for a secondary battery according to any one of claims 2 to 4,
The difference between the current internal temperature of the secondary battery estimated by the current internal temperature estimation means and the future internal temperature of the secondary battery estimated based on the external temperature detected before the time interval Δt is a predetermined value. A control apparatus for a secondary battery, comprising: a pre-determination unit that determines that the secondary battery is abnormal without performing the process of the future internal temperature estimation unit when the difference is greater than an allowable temperature difference. The secondary battery control device according to any one of claims 1 to 4,
A control apparatus for a secondary battery, comprising: determination means for determining safety of the secondary battery based on a future internal temperature of the secondary battery estimated by the future internal temperature estimation means.

Images