Core Temperature in a Cylindrical Energy Storage

Abstract

The core temperature (T ZK ) of the energy storage device (1) should be measured in a simple manner. To this end, the sheath temperature (T rA ) of the energy storage device (1) is measured. The current passing through the energy storage device (1) is also measured. With the aid of a thermal model, the core temperature (T rA ) of the energy storage device (1) is determined based on the measured sheath temperature (T ZK ) and the measured current.

Description

Field of the Invention

[0001] The present invention relates to a method for determining the core temperature in an energy storage device. Furthermore, the present invention also relates to an energy storage device having a control device for implementing such a method, a corresponding power tool, and a computer program product. Background Art

[0002] So far, regulation and control in the battery management system of lithium-ion batteries have been basically achieved based on current, voltage, and temperature, all of which are measured as measurement parameters. The problem is that temperature measurement is mainly carried out only by external thermal sensors and this temperature measurement is always slow.

[0003] The thermal energy introduced into a lithium-ion single cell is decisive for the electrochemical stress of the single cell because this thermal energy ultimately is responsible for forming a spatial temperature field across the three-dimensional single cell. Depending on the specific situation, that is, according to the previous load conditions or the set temperature field, further heat input will cause changes in the temperature field, just as the heat dissipated to the environment through the single cell housing will also change the temperature field. In addition to the potential level, which is a decisive driving factor for chemical and microphysical reactions, and the electrochemical substances or carrier materials (forming structures, providing support, etc.) present in the single cell, the local temperature is also an important factor in electrochemical reactions (here, for example, the reaction rate), but it can also assist, inhibit, or even change and damage the material structure in microphysical processes (such as the ion diffusion rate).

[0004] It is known from the published case DE 10 2011 080 512 A1 to determine the desired nominal temperature of the operating system for the current operating state in combination with model-based calculations, for example, in combination with a mathematical temperature model for a battery system. In this case, the value of the temperature model can be compared with the measured value of the temperature. In the operating mode where the temperature control system is not activated, the temperature model can dynamically calculate the temperature rise of the battery cell and the battery system and compare it with the measured value of the temperature sensor of this battery system.

[0005] Furthermore, the published case US 8 829 904 B2 relates to the modeling of the internal temperature of a lithium-ion single cell. The modeled internal temperature includes a three-dimensional temperature curve.

[0006] Furthermore, the published case CN 105206888A discloses a method for monitoring the internal temperature of a lithium-ion battery. Charge and discharge tests of the lithium-ion battery are carried out under different environmental conditions in order to obtain the change curve of the battery surface temperature. Relevant parameters are checked, such as the internal resistance of the battery and the open circuit voltage temperature coefficient. A thermal coupling model of the lithium-ion battery is established based on the heat generation rate. Therefore, the temperature change during the discharge process can be simulated. This temperature modeling is based on the solution of the corresponding differential equation.

[0007] The models shown above for simulating the internal temperature of individual cells are usually very complex and computationally intensive. Therefore, it is almost impossible to perform non-time-varying control of individual energy storage devices or the electrical equipment associated therewith within a fraction of a second. Summary of the Invention

[0008] Therefore, an object of the present invention is to propose an idea based on which rapid temperature control of an energy storage device can be performed.

[0009] The solution of the present invention to achieve the above object lies in a method, an energy storage device, a power tool, and a computer program product according to an embodiment. Advantageous further aspects of the present invention are described with reference to specific embodiments.

[0010] Therefore, according to the present invention, there is provided a method for determining the core temperature in an energy storage device, the method comprising

[0011] - measuring the sheath temperature of the energy storage device,

[0012] - measuring the current passing through the energy storage device, and

[0013] - determining the core temperature of the energy storage device by means of a thermal model based on the measured sheath temperature and the measured current.

[0014] The present invention is based on the idea that the determination of the temperature in the energy storage device is focused on the determination of the core temperature in the energy storage device, thereby enabling an increase in the simulation or modeling speed. This core temperature is usually the highest temperature within the energy storage. Therefore, the core of the energy storage device where the core temperature dominates will also be the area that ages fastest. In this regard, the core temperature is also the temperature that plays a decisive role in the temperature monitoring process. Most importantly, the core temperature, which is usually the highest temperature in the energy storage device, should not exceed a certain limit value. This limit value can be dynamically matched as appropriate.

[0015] In particular, the core temperature, i.e., the temperature in the core of the energy storage device, is determined in the proposed method. The core of this energy storage device is usually its geometric center point or the area around this geometric center point. In a wound energy storage device (such as a wound lithium-ion battery), this core or core area is located on the winding axis. This core is usually located in the axial center. However, asymmetry or non-uniformity in the structure may also cause the highest temperature not to be accurately anticipated at the geometric center point of the energy storage device. In such cases, this core may also be located approximately outside the geometric center. In the case of a wound energy storage device, this core may be slightly displaced axially relative to the center, for example.

[0016] In a first step of the method according to the invention, the jacket temperature of the energy storage device is measured. The energy storage device is, for example, cylindrical, and on the cylindrical jacket, i.e., on the outer surface of this energy storage device, the jacket temperature is measured. If the energy storage device has a geometry different from a cylinder, such as a cube, then this jacket temperature refers to the temperature on the surface of this energy storage device. That is to say, in this context, the term "jacket temperature" is synonymous with the term "surface temperature". By mounting a sensor on the outside of the energy storage device, the surface temperature or jacket temperature of the energy storage device can be obtained without high technical complexity.

[0017] In another step of the method for determining the core temperature, the current flowing through the energy storage device is measured. The total current generally flows through this energy storage device. Optionally, this total current can also be divided into partial currents. For determining the core temperature, it is only important to determine which current should be used. Either the total current for the measurement is used, or only one of the partial currents. The measured current represents the energy delivery into the energy storage device, which is only partially used for charge generation or charge decay. The energy storage device especially heats up due to ohmic losses.

[0018] In a subsequent step, the core temperature of the energy storage device is determined by means of a thermal model based on the measured jacket temperature and the measured current. This thermal model will generally not only take into account the geometric conditions of the energy storage device, such as the external shape, such as a cylindrical shape. This thermal model will generally also have material-specific parameters that take into account the individualized material of the energy storage device. An example of a material-specific parameter is the specific heat capacity. Another example is the density or the thermal conductivity. But in this thermal model, other physical parameters (such as mass and internal resistance of a single cell) and possible geometric variables (such as volume, radius, etc.) are also taken into account. Based on all these variables, but at least based on the measured jacket temperature and the measured current, the core temperature of the energy storage device is measured or estimated by means of the thermal model.

[0019] That is to say, advantageously, the core temperature, which is important for the energy storage device, is obtained by means of the method according to the invention using a model based on the jacket temperature. This shows that the temperature in the core of the energy storage device can be simply obtained by measuring the temperature on the jacket and taking into account the flowing current. Thereby, a very low simulation difficulty that can be accomplished by a relatively small processor is achieved.

[0020] In an advantageous embodiment of the method according to the invention, the energy storage device has the shape of a straight cylinder and the core temperature is measured at a position on the longitudinal axis of the energy storage device. In particular, lithium-ion accumulators usually have the shape of a straight cylinder because they are usually wound. In this case, the core of this cylindrical energy storage device lies on the cylinder axis or longitudinal axis. However, as has been shown above, this core does not have to be located precisely in the center of the energy storage device, i.e., in the center of the longitudinal axis, but can also be located at another position on the longitudinal axis. The advantage of the straight-cylinder shape of this energy storage device is that known thermal models can be used for straight cylinders. Such models are generally relatively simple and are based on analytical functions.

[0021] In a particular embodiment, the energy storage device has the shape of a straight cylinder and the core temperature is measured at a position on the longitudinal axis of the energy storage device. A straight cylinder is the most common cylindrical shape, but an inclined cylinder can also be used, the cylinder axis of which forms a non-zero angle with the normal to the cylinder end face. In this way, it is also possible to model the inclined-cut cylindrical energy storage device with respect to the core temperature, as the case may be.

[0022] In a particular further embodiment, it can be provided that the energy storage device has the shape of a cylinder, an elliptical cylinder or a prism, in particular the shape of a cube, and the core temperature is measured in the geometric center of the energy storage device. Thus, the end faces of the individual cylinders can have different shapes. These end faces can be not only circular or elliptical, but also any polygon. A corresponding thermal model must be selected for the respective cylinder shape.

[0023] Furthermore, it can be provided that the energy storage device is considered as a homogeneous body in the thermal model. This energy storage device is considered, for example, as a homogeneous body with an average specific heat capacity or an average thermal conductivity. Even if the actual energy storage device consists, for example, of a plurality of wound layers that can be made of different materials (such as anode, cathode, electrolyte, separator, conductor), for the sake of simplicity, it can be assumed to be a homogeneous body for this thermal model. This simplification makes it unnecessary, for example, to consider each single layer as a hollow cylinder. The computational effort in the modeling process is accordingly reduced.

[0024] In particular, for the thermal model, the average density and the average specific heat capacity of this energy storage device can be obtained based on the weighted material properties of the energy storage device. For the simplified model of the energy storage device, other physical parameters can also be determined with corresponding weights based on the material properties of the individual layers of this energy storage device.

[0025] In principle, the thermal model can include a heat conduction model, with which, for example, heat dissipation from the center of the energy storage device to the outside can be simulated. In addition, however, the thermal model can also include a heat loss model, which is used to determine the thermal energy generated from the current through ohmic losses. Furthermore, this thermal model can also include one or more functions that describe heat dissipation to the environment. However, this thermal model is not limited to this and can also include other functions.

[0026] According to another aspect of the method for determining the core temperature according to the present invention, only the radial temperature distribution including the core temperature can be determined with the aid of the thermal model. Thus, the thermal model is simplified in such a way that only the radial temperature distribution including the core temperature can be determined with the aid of this thermal model. Therefore, the spatial temperature distribution or the temperature on a surface cannot be determined with the aid of this thermal model, but only a one-dimensional temperature distribution can be determined. In particular, when the outer contour of the energy storage device is cylindrical, this radial temperature distribution is very persuasive because of the corresponding point symmetry of this temperature distribution. Ideally, in a (infinitely long) cylindrical energy storage device, the temperature is independent of the axial position and the angular position. Depending on the situation, the temperature distribution can extend from the central axis of the energy storage device to the sheath. Due to the limitation of the thermal model only for the simulation of the radial temperature distribution, a very simple model is produced, and compared with the spatial model, the simulation speed can be further increased through this model.

[0027] In another embodiment, the radial temperature distribution and the axial temperature distribution in the energy storage device can be determined with the aid of the thermal model. In this case, this thermal model is used, for example, to obtain the spatial temperature distribution. This is particularly important when a temperature gradient is to be expected, for example, in the axial direction of a cylindrical energy storage device. This is usually the case because the end faces of the energy storage device itself dissipate heat, so for a cylindrical energy storage device, the temperature at the end faces is lower than the temperature in the center of the energy storage device. Although this three-dimensional temperature distribution also includes the core temperature, it is also possible to make statements about the temperature in the edge region of the energy storage device in all spatial directions. If temperature measurements are only carried out at specific (possibly thermally unfavorable) positions on the sheath surface, the above solution can be used, for example.

[0028] In a particularly advantageous use of the method according to the invention, the sheath temperature of the energy storage device is measured at the sheath position in the axial center of the energy storage device or at the hottest sheath position. In many cases, it can be inferred from a symmetric energy storage device that, in the case of current flow, the highest temperature occurs in the axial center of this energy storage device. Therefore, for this model, it is advantageous to also measure this sheath temperature at the axial center position. However, in other cases, this energy storage device can also be designed in an axially non-uniform manner. In such cases, it is advantageous to empirically determine the hottest sheath position and measure the sheath temperature there. In this case, usually at the same axial position, the core temperature will be the highest. In this case, when measuring the sheath temperature, an attempt should be made to find a point on the surface of the energy storage device that indicates the position of the core region with the highest temperature.

[0029] According to another embodiment, the energy storage device is simulated in the thermal model by means of a single RC element. If a thermal model is formed by means of an RC element, complex temperature curves can also be realistically simulated. A particular simplification is that this model only has a single RC element. This indicates that only a simple exponential function is simulated by means of this thermal model. However, in most cases, the accuracy of a simple exponential function is sufficient to estimate the temperature distribution. If the thermal simulation of the energy storage device is carried out by means of a single RC element, a very simple thermal model is preset, which requires the least amount of calculation.

[0030] In a further aspect of the method, the exponential function is approximated in the thermal model by one or more linear functions, and the linear functions have the exponent of the exponential function multiplied by the highest temperature as a term. Therefore, this exponential function is approximated by one or more linear functions. This significantly reduces the amount of calculation of the thermal model. The highest temperature can in particular be the limiting temperature that occurs under a specific load condition. Under a specific charging current or a specific discharging current, for example, this limiting temperature is generated after a stable stage. That is to say, this limiting temperature or highest temperature can be the thermal equilibrium state that occurs under a predetermined current.

[0031] Therefore, as described above, a method for controlling or regulating the operation of an energy storage device by measuring the core temperature of the energy storage device can also be provided. In this case, the operation of this energy storage device is controlled or regulated according to the measured core temperature. Since the core temperature can be simply obtained from the surface temperature or the sheath temperature, this energy storage device can also be indirectly controlled or regulated by the measured sheath temperature. As described above, this core temperature is estimated or derived from the sheath temperature and then used as a parameter for controlling or regulating the energy storage device.

[0032] In a further embodiment of the control or regulation method, the power output of the energy storage device to the electrical device or the charging current or charging voltage of the energy storage device is controlled based on the core temperature. That is to say, the discharge power of the energy storage device or the charging process of the energy storage device is controlled or regulated by means of this core temperature. The advantage is that the aging process of the energy storage device caused by the charging process and the discharge process can be optimized in combination with the corresponding core temperature of the energy storage device. That is, the core temperature or temperature distribution under the current conditions (such as the current total voltage and the current discharge current of the energy storage device) is known. Therefore, it is also known at which position (such as the electrode, the separator, etc.) the critical temperature is generated. Based on the corresponding temperature preset value, the operation (such as discharge) of the energy storage device can be controlled or regulated accordingly. When a predetermined temperature is reached at a certain position or before reaching this predetermined temperature, for example, the discharge process can be stopped or reduced in a timely manner. In this way, the operation of the energy storage device can be automatically adjusted in a certain way so that certain maximum temperatures are not exceeded. A similar situation also applies to the minimum temperature.

[0033] In particular, it can be set that the power output of the energy storage device to the electrical device or the charging current or charging voltage of the energy storage device is controlled based on the core temperature. This means that not only can the energy storage device itself be adjusted or controlled in this way, but also the corresponding electrical device or charging device can be adjusted and controlled. Therefore, based on the core temperature measured in the energy storage device, a control or regulation signal can be provided for an external device located outside the energy storage device.

[0034] Furthermore, the solution of the present invention for achieving the above object also lies in an energy storage device having a control device for implementing the above method. This energy storage device or its control device can be improved in terms of function in the same way as the above method. In this regard, the advantages of the energy storage device also apply to the method.

[0035] The energy storage device can particularly have a plurality of single cells, and each of the single cells is individually modeled by means of the same thermal model. In this case, the corresponding core temperature of each single cell of the energy storage device is individually measured. Specifically, the corresponding sheath temperature of the single cell and the current passing through this single cell are measured, and the corresponding core temperature is determined by means of the thermal model based on these measured variables. However, it is not necessary to measure the core temperature for each individual single cell. Rather, in some cases, it is sufficient to representatively measure the core temperature for a specific single cell in the single cell complex and control or regulate a plurality of single cells based on this core temperature.

[0036] In another aspect of the method according to the invention, numerical simulation is carried out when determining the corresponding core temperature. Such numerical simulation is generally more advantageous compared to analytical solutions. In particular, real-time conditions can thus be maintained, under which, for example, switching processes must be carried out within a fraction of a second (in particular 0.1 s to 1 s). Such numerical simulation can be implemented in the management system of the energy storage device. A corresponding processor can be used in particular for the above numerical simulation.

[0037] In particular, one or more parameters for the numerical simulation can be determined by combining artificial intelligence with temperature measurement. The artificial intelligence can be based, for example, on neural networks, support vector machines, decision trees, Bayesian networks, kinetic algorithms, and / or association rules, etc. The neural network or other algorithms can be trained accordingly for the numerical simulation. In this way, for example, temperature measurements can also be carried out inside the energy storage device in the laboratory, and the temperature measurements can be used to train the artificial intelligence. Then, the artificial intelligence trained in the laboratory can be used to perform the simulation in order to determine the required core temperature in the energy storage device in the shortest possible time during the operation of the energy storage device. Therefore, the numerical simulation performed by the artificial intelligence can be trained by temperature measurement, especially in the laboratory, where the corresponding parameters or weights of the artificial intelligence are obtained.

[0038] As already pointed out above, the energy storage device can have a control device in order to implement the above method. Therefore, a lithium-ion battery can in particular have specific control or monitoring electronics. This control device can be part of a so-called battery management system, which is provided as an integrated electronic device in the energy storage device.

[0039] According to the invention, in particular, an electric tool is provided, which has the above energy storage device including the control device in order to implement the above method. Such battery-operated electric tools are, for example, rechargeable screwdrivers, rechargeable drills, rechargeable circular saws, rechargeable gardening tools, etc.

[0040] The solution of the present invention for achieving the above object also lies in a computer program product, which includes commands for causing the above energy storage device or the above electric tool to execute the above method steps. Such a computer program product can include a storage medium, on which a corresponding computer program including the above commands is stored. The storage medium can be, for example, a DVD, RAM, SSD memory, or any other suitable memory for computer programs.

[0041] Regarding the energy storage device or the electric tool, the advantages and variant embodiments described above in connection with the method according to the invention can be similarly achieved. This also applies to the corresponding feature combinations. Description of the Drawings

[0042] The present invention is described in detail below in conjunction with the accompanying drawings, wherein:

[0043] Figure 1 is a model of a cylindrical energy storage device for determining the core temperature;

[0044] Figure 2 A battery pack for a power tool or garden tool;

[0045] Figure 3 For power tools, and

[0046] Figure 4 The following is a schematic processing procedure of an embodiment. DETAILED DESCRIPTION

[0047] The embodiments described in detail below are preferred embodiments of the present invention.

[0048] Thermal energy (heat) is loaded into the energy storage device in a physically calculated manner, in particular by a current passing through two internal resistances of a dielectric and an electrochemical capacitor. The dielectric capacitance is generated by the layer structure, and the electrochemical capacitance is generated by the charge storage in the electrochemical structure. The energy input is spatially carried out according to the layer structure of the energy storage device. The energy input in a wound cell is different from the energy input in a stacked cell. The energy input into the cell is usually achieved in a manner distributed to the individual layers. As long as a uniform current is generated flowing through the electrode path and its surface, at least the above scheme is applicable. If an uneven current path is generated when the current load is very high, more heat dissipation is achieved at fixed points along these current paths.

[0049] In the case of wound cells, the introduced heat is distributed by radial heat conduction from the center of the cell to the radial closure of the cell (cell jacket) and by axial heat conduction from the center of the cell to the two pole caps. This heat is stored in the cell volume by all mass elements of the cell according to their thermal capacity. Such mass elements are in particular electrodes, electrolytes, separators, housings and conductors.

[0050] However, for a model that is accurate enough in most cases, it can be assumed that the maximum temperature of the energy store is reached when the current flows into its core. In the case of a cylindrical energy store, this is in the longitudinal axis of the cylinder. In this case, under simplified assumptions, it can be inferred that heat is input by means of the current in the center or on the axis and that this heat is dissipated to the outside, in particular in the radial direction. The corresponding surface or jacket temperature can be measured on the surface of the energy store, for example on the jacket of the single cell. This then allows inferences to be drawn about the core temperature of the energy store from the flowing current.

[0051] For solid-phase control of, for example, a lithium-ion single cell, especially in a dynamic situation (quasi-steady operating state), the ambient temperature at all spatial points of the single cell must be taken into account. If only external temperature measurement points are used, sufficient heat buffering must always be provided to ensure the safe operation of the single cell, and at the same time, the current flow must be limited so that the temperature in the core region of the single cell does not exceed a critical threshold. The single cell cannot exhibit its actual electrochemical performance in this way. For this purpose, according to the present invention, a simple (numerical) simulation model is provided, which preferably simulates the actual core temperature or temperature situation in the single cell in a high-resolution manner over time, so as to be able to safely and timely shut down adjacent electrical devices, but at the same time provide the maximum power from the single cell to this electrical device.

[0052] In Figure 1 the specific example shown, it is assumed that the energy storage device is a wound cylindrical single cell. Such a single cell can be a lithium-ion battery monomer. The single cell has a side surface 2 equivalent to a cylindrical sleeve. This side surface is the outer surface of the single cell or the energy storage device. As an alternative, the energy storage device 1 can also be, for example, a cubic layered memory. In this case, the outer side of this cube is the surface of the energy storage device. The single cell chemistry is in principle arbitrary.

[0053] In Figure 1 the specific example shown, the cylindrical single cell has a cylindrical axis or longitudinal axis 3. From this, it can be concluded that the highest temperature is generated when the current flows onto this axis 3. In addition, it can be assumed that the highest temperature is generated in the axial center, which is shown by a center line 4 perpendicular to the longitudinal axis 3 in the figure. The intersection of the center line 4 and the longitudinal axis 3 is the center or the single cell core 5. Optionally, this single cell core can also be a spatial region around this center, and this spatial region is approximately 10% of the extent of the energy storage device in each spatial direction.

[0054] In Figure 1 a schematic radial temperature distribution 6 is shown, which extends from the longitudinal axis 3 along the center line 4 to the side surface 2. This temperature distribution 6 includes the core temperature T ZK , and includes the surface temperature T rA on the side surface 2. An approximately exponential decrease occurs between the two.

[0055] For temperature measurement, temperature sensors 7 can be provided on the side surface 2. It is easier to measure the temperature on the surface or the side surface 2 than, for example, on the longitudinal axis 3 of the single cell.

[0056] The purpose of the thermal simulation is to determine the single cell core temperature T ZKAs shown above, it is assumed that, for example, the temperature on the longitudinal axis 3 of a cylindrical single cell is the highest. To avoid damaging the single cell, the highest temperature in the single cell is used as a limiting factor during the charging or discharging process. For example, the cell core temperature T is determined based on measurable parameter values ZK :

[0057] - Current (charging or discharging current amount)

[0058] - Single cell sheath temperature T rA

[0059] - Single cell impedance

[0060] In this case, the single cell impedance can also be set as a variable that is at least temporarily fixed in time. However, this single cell impedance can also be indirectly incorporated into the determination of the single cell core temperature through a constant

[0061] When performing simulations using a thermal model, multiple assumptions and simplifications can be made to ensure fast calculations with limited resources. In the following embodiments, the simulation is performed in three optional steps a) to c). The division of these steps is one of multiple schemes

[0062] To determine the single cell core temperature, the following processing method can be used as a recursion. The derivation of the listed equations is as follows

[0063] a) First, in the first step, the temperature distribution on the single cell radius is determined. For this purpose, it is assumed that heat is generated, which is caused by the static power consumption in the cell monomer in a non-adiabatic system. This heat generation causes a temperature gradient on the single cell radius according to the power consumption and material properties. When this system is in thermal equilibrium, for a specific load case, this temperature gradient or temperature curve is fixedly present between the single cell core and the single cell surface. In this thermal equilibrium state, the cell core temperature T ZK corresponds to the highest temperature

[0064]

[0065] Where:

[0066] T Max = The highest temperature of the single cell core, in [°C]

[0067] T rA = The temperature on the single cell surface, in [°C]

[0068] P = Power, in [W]

[0069] V = Volume, in [m 3

[0070] ​λ = thermal conductivity, unit: [W / (m*K)]

[0071] r = radius

[0072] b) In a further step, the temperature of the single cell is determined based on the work done. In this case, it should be considered that in the assumed adiabatic system, the measured power consumption will cause a time-dependent, dynamic and uniform temperature rise of the cell unit. Observing the temperature development of the single cell surface considering the measured power consumption and the characteristics of the single cell material provides information about the actual heat dissipation of the cell unit to the environment. The temperature development of the single cell surface (the difference in the recursive step: T rA -T rA-1 ) and the ratio K 2 of the dynamic temperature rise of the single cell (proportional to the power I P * R) affect the simulated temperature rise of the single cell core. A part of the generated heat is released to the environment, and the remaining part remains in the single cell. Therefore, it can be concluded that:

[0073]

[0074] Where:

[0075] k p = ratio

[0076] c = specific heat capacity, unit: [J / K]

[0077] m = mass, unit: [kg]

[0078] I = current, unit: [A]

[0079] R = internal resistance of the single cell, unit: [ohm]

[0080] c) In the third step, the equilibrium of the single cell core temperature is determined. For this purpose, an equivalent circuit diagram composed of RC elements (preferably a single RC element) is used in the simulation of the cell unit. That is, the temperature development of the single cell core is similar to the exponential function of the voltage in the RC element. The maximum temperature value of the single cell core is equivalent to the single cell sheath temperature plus the maximum temperature difference calculated in a). The time constant of this exponential function is obtained from the heat capacity and the thermal resistance according to the ratio of the temperature development of the single cell surface measured in b) to the dynamic temperature rise of the single cell in the adiabatic system.

[0081] If the single cell heats up based on an increasing current intensity, then when T Max >T ZK it applies that:

[0082]

[0083] In contrast, if the single cell cools down when the current decreases, then when TMax <T ZK is applicable when:

[0084]

[0085] Where:

[0086] T ZKn = the single cell temperature calculated in the recursive step n, in [°C]

[0087] K1 = system constant

[0088] The above equation is differentiated below.

[0089] In the first step a) of determining the temperature distribution on the single cell radius, the following assumptions are made:

[0090] - The axial temperature distribution is not taken into account in the simulation for the time being. Only the radial temperature distribution is considered below. In this case, the temperature sensor can be set centrally at the axial center or the hottest point of the sheath.

[0091] - For the radial thermal conductivity, the helical layer of the coil is simply regarded as a concentric ring shell for simplicity. To determine the single cell thermal conductivity, the single cell is regarded as a homogeneous body with corresponding material properties.

[0092] - The density p and specific heat capacity c of the single cell are described by the weighted average material properties of the cell components. In this case, the density as a volume ratio variable is related to the volume fraction, while the mass specific heat capacity is averaged in terms of the mass fraction.

[0093] The thermal conductivity of the single cell can be expressed as follows:

[0094]

[0095] λ r = radial thermal conductivity

[0096] D = total layer thickness of the material layer

[0097] The following heat conduction equation can be established:

[0098]

[0099] Where:

[0100] s = heat source density:

[0101] c = heat capacity:

[0102] p = density:

[0103] T = Temperature: K

[0104] t = Time: s

[0105] = Heat flux density:

[0106] According to Fourier's law of heat conduction:

[0107] and λ = Thermal conductivity

[0108] For a cylindrical single cell, cylindrical coordinates apply:

[0109]

[0110] Assume: Since it is expected that there is no heat flow in the circumferential direction and axial heat flow is neglected, and i z can be set to zero. It follows that:

[0111]

[0112] Because in this case, the temperature distribution related to power on the radius of the single cell is sought, this case can be regarded as steady-state.

[0113] Applies in the steady-state case

[0114]

[0115] Integrate over the radial extent of the cylinder:

[0116]

[0117] Assume: To calculate the integration constant C, assume that for a hollow cylinder, the heat dissipation density at the inner radius ri is equal to the negative of the heat dissipation density at the outer radius r a at.

[0118]

[0119] For a solid cylinder, the inner radius = 0. It follows that C = 0.

[0120]

[0121] For the heat flux density at the outer edge, j = j A and r = r A

[0122]

[0123] According to Fourier [3], for steady-state considerations in the spatial coordinates limited to the radial dimension (also for the gradient in cylindrical polar coordinates), the following applies:

[0124] Where the following applies:

[0125]

[0126] Insert [5]:

[0127]

[0128] Keeping s and λ constant, integrating over the radius r gives:

[0129]

[0130] In this case, the integration constant C is the external temperature T = T RA (r = R A ). Thus, the steady-state temperature field of a single cell can be described by the following formula:

[0131]

[0132] Using the heat source density s = heating power P / volume, we get:

[0133]

[0134] Based on the power consumption P inside the single cell, T (r) Here corresponds to the maximum possible temperature. T rA Corresponds to the sheath temperature. Therefore, at r = 0, for the maximum single cell core temperature T MAX , we get:

[0135]

[0136] Next, for step d), the equation [9] for determining the temperature of a single cell based on the work done is differentiated.

[0137] Only ohmic losses are considered. Reversible losses such as reaction entropy, mixing enthalpy, or side reactions are not considered.

[0138] Calculation of the internal resistance R of a single cell:

[0139]

[0140] Where:

[0141] U t1 / t2 = terminal voltage at time points t1 and t2

[0142] I t1 / t2 = Electric current at time points t1 and t2

[0143] The single cell is considered as a combination of multiple RC elements. For reasons of computational power, an attempt is made to implement the simulation using only a single RC element (first basic approximation step):

[0144]

[0145] Where:

[0146] ΔT (t) = Change in single cell core temperature over time

[0147] P = Power consumption

[0148] R th = Thermal resistance of the single cell

[0149] t = Time

[0150] τ = Time constant

[0151]

[0152] Where:

[0153] ΔT Max = ΔT Max - T rA

[0154] C = Heat capacity

[0155] ΔT = Temperature change

[0156] For the homogeneous body assumed in this case, it applies: C = c * m

[0157] Where:

[0158] c = Specific heat capacity

[0159] m = Mass

[0160] In order to be able to respond dynamically to load jumps, calculations are performed for T Max - T ZK at constant time intervals according to the power P.

[0161]

[0162] Where:

[0163] T ZK = Temperature in the single cell core

[0164] K1 = System constant 1

[0165]

[0166] In the first round of calculations, it is

[0167] By performing calculations at constant time intervals, the exponential function can be omitted for the corresponding small steps (second basic approximation step), and this function is as follows:

[0168]

[0169] To take into account the heat dissipation to the environment, the non-adiabatic heat generation of the single-cell sheath is compared with the theoretically adiabatic heat generation of the single cell.

[0170] The heat generation of the single-cell sheath is calculated successively:

[0171] T rA -T rA-1 The theoretically adiabatic heat generation of the single cell per unit time t = 1 ms:

[0172]

[0173] The power K remaining for the temperature rise of the single-cell core P component

[0174]

[0175] If the following conditions are applicable during the temperature rise of the single cell, this calculation is performed:

[0176] T Max >T ZK

[0177] The equations

[10] and

[12] for determining the approximate value of the single-cell core temperature in step c) can be differentiated in the following manner:

[0178] The "single-cell core temperature" increases up to the "maximum single-cell core temperature" at most. If the "highest temperature" drops below the single-cell core temperature due to lower power consumption, a cooling effect occurs in the single-cell core.

[0179] As described above, the temperature drop in the single cell is similar to the voltage drop in an RC element. Its calculation method is as follows:

[0180]

[0181] Where:

[0182] ΔT Max =T ZK-升温 -T Max

[0183] TZK-升温 = The temperature of a single cell core during the warming-up period. This value remains constant during the cooling-down process.

[0184]

[0185] As described in [8], the exponential function is omitted and it results in:

[0186]

[0187] If the following conditions are applicable during the cooling-down of a single cell, this calculation is carried out:

[0188] T Max <T ZK

[0189] Figure 2 Figure 8 shows the battery pack 8, which can be used, for example, in a power tool 9 (see Figure 3 ), such as a rechargeable screwdriver or a rechargeable gardening tool. This battery pack has a socket 10 by means of which it can be attached to the corresponding power tool 9. Inside the housing 11 of this battery pack, for example, a plurality of cylindrical energy storage devices 1 are provided. Each energy storage device 1 can be, for example, a wound lithium-ion single cell. The respective associated thermal models can be similar in terms of their geometric design to Figure 1 's thermal model.

[0190] A battery management system having an interface 12 for the operator can also be integrated into this battery pack. The interface 12 can, for example, display the charge state of the battery pack 8 or implement an operating scheme.

[0191] This battery management system can have suitable sensing means for detecting the charging current, the discharging current, the single cell voltage, the total voltage of the battery pack, the temperature of one or more single cells of the energy storage device, etc. In this way, one or more of the above-mentioned set of parameters can be detected and further processed as appropriate. In particular, the change in the single cell voltage or the total voltage and the change in the charging current and the discharging current can be determined in this way. In this case, a suitable temperature model based on the geometric structure, for example as Figure 1 shown, allows the determination of the core temperature inside each energy storage device or each single cell. The temperature model of this battery management system can provide the core temperature according to the current operating parameters, and this core temperature can be used to control the energy storage device and / or the operation of the electrical equipment operating with the aid of the energy storage device.

[0192] Figure 4 Figure 9 schematically shows a processing procedure according to which an electrical equipment can be operated. In this case, the method steps for determining the core temperature are an essential component.

[0193] In a first step S1, the sheath temperature of the energy storage device is measured. This measurement is carried out, for example, by means of a temperature sensor located on the outer side of the cylindrical energy storage device. This sensor can be placed in the axial center, but it can also be placed at the empirically determined hottest point on the sheath surface.

[0194] In a second step S2, the current flowing through the energy storage device is measured. In this case, this current can be a charging current or a discharging current. Both currents cause the energy storage device or the battery to heat up.

[0195] In a third step S3, which can be optionally carried out, the highest temperature occurring in the single cell core in a thermal equilibrium state is determined. In another optional step S4, the current-dependent relative temperature rise can be determined.

[0196] In a fifth step S5, the core temperature is determined at least based on the measured sheath temperature and the measured current. Optionally, the above determination is carried out based on the sheath temperature measured in steps S3 and S4 and the measured current-dependent relative temperature rise.

[0197] In another optional step S6, the temperature distribution within the energy storage device can be determined. In this case, this temperature distribution can be, for example, the radial temperature distribution in a cylindrical single cell. Optionally, the axial temperature distribution can also be determined. A part of this temperature distribution is always the core temperature in the core of the energy storage device.

[0198] Finally, in a seventh step S7, the operation of the energy storage device is controlled or regulated based on the determined core temperature or temperature distribution. Optionally, the power tool powered by the energy storage device can also be directly controlled or regulated by means of the determined core temperature.

[0199] In this way, for example, it is possible to decouple in a timely manner the electrical equipment driven by the single cell and, for example, disconnect the applied charging voltage or adapt the charging current to the calculated temperature within the single cell (for example, carry out charging at a lower temperature).

[0200] List of reference numerals

[0201] 1 Energy storage device

[0202] 2 Side

[0203] 3 Longitudinal axis

[0204] 4 Center line

[0205] 5 Single cell core

[0206] 6 Temperature distribution

[0207] 7 Temperature sensor

[0208] 8 Battery pack

[0209] 9 Electric tool

[0210] 10 Socket

[0211] 11 Housing

[0212] 12 Interface

[0213] T Max Highest temperature in a single cell

[0214] T rA Sheath temperature

[0215] T ZK Core temperature

[0216] S1 First step

[0217] S2 Second step

[0218] S3 Third step

[0219] S4 Fourth step

[0220] S5 Fifth step

[0221] S6 Sixth step

[0222] S7 Seventh step

Claims

1. A method for measuring the core temperature (T ZK ) in a storage device (1), - Measure (S1) the sheath temperature (T rA ) of the energy storage device (1) - Measuring (S2) the current passing through the energy storage device (1), and -Determine (S5) the core temperature (T rA ) of the energy storage device (1) based on the measured sheath temperature (T ZK ) and the measured current by means of a thermal model; wherein the energy storage device (1) is simulated by means of a single RC element, characterized in that in the thermal model, the exponential function is approximated by one or more linear functions, and the linear functions have the exponent of the exponential function multiplied by the highest temperature in the battery core in thermal equilibrium as a term.

2. The method according to claim 1,[[]]END]] characterized in that The accumulator (1) has the shape of a straight cylinder and the core temperature (T ZK ) is measured at a position on the longitudinal axis (3) of the accumulator (1).

3. The method according to claim 1 or 2,[[]]END]] characterized in that The accumulator (1) has the shape of a cylinder, an elliptical cylinder, a prism or a cube, and the core temperature (T ZK ) is measured in the geometric center of the accumulator (1).

4. The method according to claim 1 or 2,[[]]END]] characterized in that in the thermal model, the energy storage device (1) is regarded as a homogeneous body.

5. The method according to claim 4,[[]]END]] characterized in that for the thermal model, the average density and average specific heat capacity of the energy storage device (1) are obtained according to the weighted material properties of the energy storage device (1).

6. The method according to claim 2,[[]]END]] characterized in that With the aid of the thermal model, only the radial temperature distribution (6) including the core temperature (T ZK ) can be determined.

7. The method according to claim 2,[[]]END]] characterized in that measuring (S5) the radial temperature distribution (6) and the axial temperature distribution in the energy storage device (1) by means of the thermal model.

8. The method according to claim 1 or 2 above,[[]]END]] characterized in that Measure the sheath temperature (T rA ) of the accumulator (1) at the sheath position in the axial center of the accumulator (1) or at the hottest sheath position 9. A method according to claim 1 or 2 above, for determining (S5) the core temperature (T ZK ) of the accumulator (1) to control or regulate (S7) the operation of the accumulator (1), and for controlling or regulating (S7) the operation of the accumulator (1) based on the determined core temperature (T ZK ).

10. The method according to claim 9, wherein the power output of the energy storage device (1) to the electrical device or the charging current or charging voltage of the energy storage device (1) is controlled according to the core temperature (T ZK ). (S7) 11. An energy storage device (1), comprising: A first sensor device for measuring (S1) the sheath temperature (T rA ) of the energy storage device (1) a second sensor device for measuring (S2) the current passing through the energy storage device (1); and A battery management system for determining (S5) a core temperature (T rA ) of the energy storage device (1) based on a measured sheath temperature (T ZK ) and a measured current, wherein simulating the energy storage device (1) by means of a single RC element in the thermal model of the energy storage device (1), wherein in the thermal model, the exponential function is approximated by one or more linear functions, and the linear functions have the exponent of the exponential function multiplied by the highest temperature in the battery core in thermal equilibrium as a term.

12. The energy storage device (1) according to claim 11, wherein the energy storage device has a plurality of single cells, and each of the single cells is modeled separately by the same thermal model.

13. A power tool (9) having the energy storage device (1) according to claim 11 or 12.

14. A computer program product, the computer program product comprising instructions for causing the energy storage device (1) according to claim 11 or 12 or the power tool (9) according to claim 13 to perform the steps of the method according to any one of claims 1 to 10.

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