Method for heating a battery and battery, in particular for a motor vehicle

Abstract

Method for heating a battery comprising a plurality of battery cells (12a-c) and having a temperature which provides a predefinable electrical power with which at least one electrical consumer is operated, wherein by means of a circuit arrangement (10) of the battery at least a first subset of the battery cells (12a-c) is selected to provide the electrical power and at least a second subset of the battery cells (12a-c) is decoupled from the first subset and thereby excluded from providing the electrical power, such that the highest possible current strength, which remains below a maximum value provided for the temperature of the battery, is established to provide the electrical power.

Description

[0001] The invention relates to a method for heating a battery, in particular for a motor vehicle, and to a battery, in particular for a motor vehicle.

[0002] Batteries for storing electrical energy, especially electrical current, are already well known from the general state of the art. Such a battery comprises a plurality of battery cells, which serve to provide a predefined electrical power output. This electrical power output can supply and thus operate at least one electrical device that is electrically connected to the battery. Such batteries are used in various electronic devices, such as portable computers.

[0003] Furthermore, it is known from the general state of the art, and particularly from series production vehicles, to use at least one such battery in the form of a so-called traction battery. In this case, the vehicle, for example a passenger car, is designed as an electric or hybrid vehicle and includes at least one electric machine in the form of a so-called traction machine, by means of which the vehicle can be electrically driven. For electrical propulsion of the vehicle, the traction machine is supplied with electrical energy from the traction battery and is operated with a predefined electrical power output provided by the traction battery. The battery can be a lithium-ion battery.

[0004] Batteries typically have relatively narrow operating temperature ranges within which optimal operation—meaning maximum performance and energy utilization with minimal reduction in lifespan—is possible. If the battery cells reach a temperature outside this range, i.e., if the battery is too hot or too cold, direct damage from the battery's operation or from excessive heat or temperature is imminent. To maintain the battery within its optimal operating temperature range and thus operate it particularly efficiently, heating elements such as heating mats and cooling elements such as cooling plates are commonly used. These elements heat or cool the battery to ensure it operates within this optimal temperature range.

[0005] Furthermore, it is known to limit the battery's performance values, for example by a central control unit, when operating outside the permissible operating temperature range, in order to prevent undesirable damage. In this context, the electrical power available from the battery can be limited to zero percent in the event of overheating, i.e., when the battery reaches an undesirably high temperature. At particularly cold temperatures, limiting the power to a few percent is common. Limiting or reducing the power to zero percent is unusual in such cases.

[0006] Electrical consumers in a motor vehicle, such as a traction motor, very rarely require constant electrical power during operation, which is supplied by the battery designed as a traction battery. In other words, the electrical power used to operate electrical consumers, especially the traction motor, fluctuates during vehicle operation. Highly fluctuating load profiles are common, where power consumption can switch between minimum and maximum values ​​in fractions of a second.

[0007] Especially at very low or cold temperatures, the battery's performance is severely limited, necessitating heating. This is typically achieved through additional heating elements, primarily electric heating elements. These heating elements are powered by current drawn from the battery, thus discharging it during the heating process. Furthermore, these heating elements represent additional components, increasing the required installation space, weight, and overall cost.

[0008] DE 10 2013 203 320 A1 discloses a battery management system with a bidirectional charging circuit and a battery coupling node output configured to be coupled to a battery cell. The charging circuit has an input coupled to a common node of the battery management system. The battery management system further comprises a controller coupled to the bidirectional charging circuit, the controller being configured to operate the bidirectional charging circuit in a charging mode to transfer charge from the common node to the battery coupling node. The controller is also configured to operate the bidirectional charging circuit in a discharging mode to transfer charge from the battery coupling node to the common node.

[0009] German patent application DE 10 2011 004 610 A1 discloses a method for adjusting the electric current of an electrothermal converter used to control the temperature of an electrochemical energy storage device in a vehicle. The method includes a step of adjusting the electric current to a maximum current when the temperature of the electrochemical energy storage device is outside its operating temperature range. This maximum current results in maximum temperature control performance of the electrothermal converter.

[0010] From DE 10 2011 077 264 A1, an energy storage device for generating an n-phase supply voltage for an electric machine is known, wherein n ≥ 1, with n parallel connected energy supply branches, each of which can be connected to one of n phase lines, wherein each of the energy supply branches has a plurality of series-connected energy storage modules, each comprising: an energy storage cell module, which has at least one energy storage cell, and a coupling device, which is designed to selectively switch or bridge the energy storage cell module in the respective energy supply branch, wherein at least one of the energy storage modules also has a heating element for the at least one energy storage cell;and a heating device which is connected to the heating elements and which is designed to control the heating elements to warm the energy storage cells of the groups of energy storage modules.

[0011] From US patent 2014 / 0197777A1, an electrical supply system for heating a battery group is known, comprising: a battery module comprising at least two series modules, each series module comprising at least two battery groups connected in series; a control module connected to the battery module, comprising: a module with an insulated-gate bipolar transistor; a relay module comprising multiple relays, each series module being connected to the relay module, and the relay module being connected to the insulated-gate bipolar transistor module; a relay control module configured to control the ON or OFF state of each relay by selecting one or more series modules to be connected to the insulated-gate bipolar transistor module; and a distribution box connected to the control module.

[0012] The object of the present invention is to create a method and a battery which enable a particularly simple and, in particular, cost-, weight- and space-saving heating of the battery.

[0013] This problem is solved by a method with the features of claim 1 and by a battery with the features of claim 6. Advantageous embodiments with expedient further developments of the invention are specified in the remaining claims.

[0014] The method according to the invention serves to heat a battery comprising a plurality of battery cells and having a specific temperature. The battery provides a predefinable electrical power with which at least one electrical load is operated. Within the framework of the method according to the invention, at least a first subset of the battery cells is selected to provide the electrical power by means of a circuit arrangement of the battery, and at least a second subset of the battery cells is decoupled from the first subset and thereby excluded from providing the electrical power. In other words, the electrical power is provided by the selected first subset of the battery cells, that is, by the selected battery cells or by at least one selected battery cell. The second subset of the battery cells is not used to provide the electrical power.In other words, the battery cells of the second subset do not participate in providing electrical power.

[0015] The selection of the first subset and the decoupling and exclusion of the second subset are achieved by means of the circuit arrangement such that the highest possible current, which remains below a maximum value specified for the current temperature of the battery, is used to provide the electrical power. The underlying insight of the invention is that heat losses in the battery depend quadratically on the current and can be used for heating purposes, i.e., to warm or heat the battery. In order to heat the battery particularly effectively using these heat losses, the well-known dependence of the electrical power to be provided by the battery, in particular by the selected battery cells, on the current and the voltage is utilized. This dependence is expressed by the following well-known formula: P=U×I

[0016] Here, P denotes electrical power, I the current, and U the voltage. The voltage is the sum of the individual voltages of the selected battery cells. If the number of selected battery cells is very small, the voltage U will also be low. However, if the required electrical power P, which the battery must supply via the selected battery cells, is high, a large current I is required. This high current I results in significant heat losses, which effectively heat the battery.

[0017] In this process, a maximum current value I is assigned to the current temperature or temperature range of the battery. This represents the maximum current that the battery may supply at that temperature through the selected battery cells without causing damage to the battery, particularly to the individual battery cells. Within the framework of the inventive method, a sufficient number of battery cells are selected, and consequently decoupled and thus switched off, to maximize the electrical current or current value according to the temperature-dependent maximum value, which represents a limit, in order to meet the specified power requirement. This allows the battery to be heated effectively without causing undesirable damage.Furthermore, no additional heating elements, particularly electrical ones, are provided or required to heat the battery, thus keeping the weight, costs, and installation space requirements especially low. The rationale for heating the battery is that the thermal power, and therefore the heat losses, of any ohmic resistance, including parasitic resistances such as cables and the battery cells themselves, can be calculated using the formula P. th =I 2 ×R can be calculated. Here, P denotes... th the thermal power or heat losses and R the ohmic resistance.

[0018] In an advantageous embodiment of the invention, the battery temperature is detected by means of at least one temperature sensor. This makes the current battery temperature available, so that the battery can be heated in a particularly demand-oriented manner.

[0019] Another embodiment is characterized by the fact that the battery temperature is calculated using a model. This model represents the physical properties of the battery and is stored, for example, in a storage device of a computer, particularly in the form of a control unit. The model is, in particular, a thermal model that allows the temperature of the battery, especially the battery cells, to be calculated in real time.

[0020] To calculate the temperature with particular precision using the model, it is preferably provided that the temperature calculated by the model is verified against at least one recorded temperature, which is measured by at least one temperature sensor. In other words, it is possible to verify the thermal model, particularly at predetermined time intervals, using temperature sensors, also known as thermal sensors, and thereby calibrate it as needed. This makes it possible, for example, to determine the individual temperatures of the battery cells—that is, the so-called cell temperatures of a complex structure consisting of a large number of individual cells—using only a few thermal sensors, and to apply current to the battery cells based on their state, particularly for a limited time.This makes it possible to select or decouple the respective battery cells depending on the temperature, and thus exclude or switch them off.

[0021] To enable the targeted selection and disconnection of battery cells, these are equipped with switches, which are designed as individual cell switches. Opening a switch disconnects the corresponding battery cell from the other cells, whose switches are closed, thus preventing it from supplying electrical power—in other words, it switches it off. Closing the switch selects the corresponding battery cell, which then uses it to supply electrical power. For example, opening the switch electrically disconnects the respective battery cell from a circuit and thus from the electrical load.By closing the switch, the battery cell is electrically connected to the line and thus, for example, to the electrical consumer, so that the battery cell belonging to the closed switch is used to provide the required or requested electrical power.

[0022] When several battery cells are connected by closing their respective switches and thus used to provide electrical power, these connected battery cells form a network, also known as a cell array. Those battery cells whose switches are open are disconnected from the cell array, meaning they are removed from the network and cannot contribute to providing the required electrical power.

[0023] Finally, it has proven particularly advantageous to use a traction battery from a motor vehicle, especially an electric or hybrid vehicle. Such a traction battery is typically subject to high temperature fluctuations, and this method allows the traction battery to be effectively heated and thus kept within its optimal operating temperature range.

[0024] To achieve particularly advantageous heating behavior, the individual battery cells can be switched off depending on differences in their internal resistance and / or their maximum current ratings. For example, those battery cells that contribute the least heat to the overall system, i.e., the battery, are always switched off. Furthermore, if particularly heat-generating battery cells—that is, those capable of contributing especially high heat to the system—are unsuitable for normal driving, these cells can be switched off again after a heating phase by opening their respective individual cell switches.

[0025] Closing the respective switches connects the selected and interconnected battery cells in series, meaning they are connected in series, forming, for example, a cell stack. Opening the switches bypasses the corresponding battery cells, thus removing them from the cell array. The disconnected battery cell therefore does not contribute to power output, and the overall voltage of the cell array drops by the voltage of the disconnected cell. If the electrical load requires a defined amount of power, this is compensated for by an increased current, i.e., a higher amperage, according to the law P=U×I mentioned above. This increased current is used to heat the battery.

[0026] The invention also includes a battery, particularly for a motor vehicle, with a plurality of battery cells for providing a predefinable electrical power with which at least one electrical consumer can be operated. The battery comprises a circuit arrangement which, for heating the battery, is configured to select at least a first subset of the battery cells for providing the electrical power and to decouple at least a second subset of the battery cells from the first subset and thereby exclude them from providing the electrical power, such that the highest possible current, which remains below a maximum value provided for the battery temperature, is established for providing the electrical power. In other words, the battery is configured to carry out the method according to the invention.Advantageous embodiments of the method according to the invention are to be regarded as advantageous embodiments of the battery according to the invention and vice versa.

[0027] Finally, the invention also includes a motor vehicle, which is designed, for example, as an electric vehicle or hybrid vehicle and comprises at least one battery according to the invention or at least one battery designed for carrying out the method according to the invention. The battery is preferably designed as a traction battery and serves to supply at least one electrical consumer in the form of an electric machine, which is designed as a traction machine, by means of which the motor vehicle can be electrically driven.

[0028] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and / or shown in the single figure alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0029] The drawing shows in the single figure a schematic representation of a battery, in particular for a motor vehicle, with a plurality of battery cells for providing a predeterminable electrical power with which at least one electrical consumer is operated, wherein by means of a circuit arrangement of the battery the battery cells are coupled to each other or decoupled from each other as required, so that a particularly high current is generated for heating the battery.

[0030] The single figure shows a schematic representation of a battery in the form of a traction battery of a motor vehicle, for example, an electric or hybrid vehicle, particularly a passenger car. The motor vehicle comprises at least one electric machine in the form of a traction machine, by means of which the motor vehicle can be electrically driven. The traction machine is an electrical load that is operated with a predetermined electrical power, this electrical power being supplied by the traction battery. The electrical power, i.e., the power consumption of the traction machine, can fluctuate considerably during operation, particularly, for example, during deceleration and acceleration.

[0031] The battery (traction battery) comprises a plurality of battery cells 12a-c, with three battery cells 12a-c being provided in this case. Of course, it is possible for the battery to have a smaller or a significantly larger number of battery cells. The battery also has a circuit arrangement, designated as a whole by 10, which includes switches SW1 arranged in series with each battery cell 12a-c, switches SW2 arranged in parallel with each battery cell 12a-c, and control devices 14. In other words, each switch SW1 is arranged in series with its corresponding battery cell 12a-c, with each switch SW2 arranged in parallel with its corresponding battery cell 12a-c. The respective control device 14 serves to switch the respective switches SW1 and SW2.Switches SW1 and / or SW2 can be configured, for example, as field-effect transistors and / or as bipolar transistors, particularly with an insulated gate electrode. By opening the first switch SW1 and closing the corresponding switch SW2, the respective battery cell 12a-c can be bypassed and thus decoupled from the rest of the system, i.e., from the other battery cells 12a-c. This arrangement of the battery cells 12a-c with a so-called single-cell topology allows for the separate switching on and off of the individual battery cells 12a-c, for example, to protect the respective battery cells 12a-c from damage if they are in an unsuitable condition for operation.

[0032] The battery has an operating temperature range within which optimal operation is possible, maximizing performance and energy utilization while minimizing reduction in lifespan. It is therefore desirable to operate the battery within this optimal temperature range. However, due to its use in a motor vehicle, the battery is subject to significant temperature fluctuations, meaning it may be exposed to particularly low ambient temperatures and consequently reach temperatures significantly below the advantageous operating temperature range. In such cases, it is desirable to warm or heat the battery to bring it into the advantageous operating temperature range and maintain it there even at low ambient temperatures.

[0033] To achieve particularly effective battery heating in a simple, cost-effective, space-saving, and lightweight manner, a method is provided for heating the battery in a way that utilizes the battery's current temperature. This current temperature is measured, for example, by at least one temperature sensor and / or calculated using a model, which is stored, for example, in a memory unit of a control unit for regulating and / or controlling the battery. The temperature is then calculated by the control unit based on this model.

[0034] As part of the process, the battery provides the predetermined electrical power with which the traction machine is operated, whereby this electrical power can fluctuate.

[0035] Within the framework of the method, at least a first subset of the battery cells 12a-c is selected for providing electrical power by means of the circuit arrangement 10, by appropriately opening and closing switches SW1 and SW2, wherein the selected battery cells 12a-c are connected in series with one another. Furthermore, within the framework of the method, at least a second subset of the battery cells 12a-c, different from the first subset, is decoupled from the first subset and thereby excluded from providing electrical power. In other words, the second subset is switched off so that the battery cells 12a-c belonging to the second subset do not participate in providing the electrical conductivity. The selected battery cells 12a-c of the first subset, which are coupled together and connected in series with one another, form a cell assembly from which the excluded battery cells 12a-c are decoupled.This selection and exclusion of the respective battery cells 12a-c is carried out by means of the circuit arrangement 10 in such a way that the highest possible current strength, which remains below a maximum value intended for the current temperature of the battery, is set to provide the electrical power.

[0036] The procedure is explained in more detail using the following example: In this example, the traction battery comprises 100 battery cells, each with an electrical voltage of 3.7 volts and capable of delivering a maximum current of 200 amperes. This maximum current of 200 amperes can be supplied by the individual battery cells as long as the battery or battery cell temperature is within the operating temperature range, ensuring that no undesirable damage occurs to the individual battery cells when supplying 200 amperes. Currently, however, the battery has a temperature of, for example, minus 10 degrees Celsius. This temperature of minus 10 degrees Celsius corresponds to a maximum current of 10 amperes. This means that each battery cell at minus 10 degrees Celsius can supply a maximum current of 10 amperes without being damaged.

[0037] The rest of the vehicle, especially the traction motor, is also at a temperature of minus 10 degrees Celsius. In this example, the traction motor first requests an electrical power of 3700 watts for a duration of two seconds, followed by an electrical power of 1850 watts for another two seconds. This respective electrical power must be supplied by the traction battery.

[0038] With a cell voltage of 3.7 volts, this means that all battery cells must be switched on in the first two seconds. Therefore, using the circuit arrangement, all 10 battery cells are selected and connected in series. This allows the battery to provide an electrical power of 3700 watts via its cells. This power is calculated by multiplying the 100 battery cells by their respective cell voltages of 3.7 volts and their respective maximum currents of 10 amperes at minus 10 degrees Celsius. In the following two seconds, the power could be halved by halving the current, the voltage, or a combination of both. If the voltage is halved by switching off several battery cells, and the current is thus kept constant at 10 amperes, then, according to the formula P... th =I 2×R, the thermal power loss is four times greater than when the current is halved to 5 amperes. In the formula mentioned, P denotes... th the thermal power loss or heat losses, where I denotes the current and R the electrical resistance.

[0039] The example shows that, for instance, during a battery warm-up phase, the battery cells are switched by means of the circuit arrangement 10, and in particular by means of the switches SW1 and SW2 representing the individual cell switches, in such a way that the electrical power required by the traction motor or the electrical consumers and supplied by the battery is provided at a current maximized according to the temperature-dependent current limits. This maximizes the waste heat generated by each cell and can be used as heating energy to warm the battery cells and thus the battery as a whole. This eliminates the need for additional heating systems such as electric heating elements.In other words, the procedure provides that the battery cells are selected and switched off by means of the circuit arrangement 10 in such a way that the current supplied by the battery, which is required to provide the total electrical power, corresponds to the stated maximum current value or is as close as possible to this maximum value without exceeding the maximum value, so that damage to the battery cells can be avoided.

[0040] Optimized battery cell load management with demand-based individual cell shutdown can be achieved with optional additional or independent temperature monitoring using thermal simulation of the battery, particularly the individual battery cells. Model correction based on defined temperature sensors allows the model to be adjusted to reflect the current real-world conditions. In other words, it is possible to verify the temperature calculated by the model using at least one measured temperature, which is recorded by at least one temperature sensor at at least one predefined location on the battery. This allows for a particularly precise calculation of the battery temperature, enabling simple and demand-based heating of the battery without the need for additional electrical heating elements.

Claims

[1] Method for heating a battery comprising a plurality of battery cells (12a-c) and having a temperature which provides a predefinable electrical power with which at least one electrical consumer is operated, wherein by means of a circuit arrangement (10) of the battery at least a first subset of the battery cells (12a-c) is selected to provide the electrical power and at least a second subset of the battery cells (12a-c) is decoupled from the first subset and thereby excluded from providing the electrical power, such that the highest possible current strength, which remains below a maximum value provided for the temperature of the battery, is established to provide the electrical power. [2] Method according to claim 1, characterized by that the battery temperature is measured by means of at least one temperature sensor. [3] Method according to claim 1, characterized by that the battery temperature is calculated using a model. [4] Method according to claim 3, characterized by that the temperature calculated using the model is verified by means of at least one recorded temperature, which is recorded using at least one temperature sensor. [5] Method according to any one of the preceding claims, characterized by , that the battery used is a traction battery of a motor vehicle, in particular an electric vehicle or a hybrid vehicle. [6] Battery, in particular for a motor vehicle, comprising a plurality of battery cells (12a-c) for providing a predefinable electrical power with which at least one electrical consumer can be operated, and comprising a circuit arrangement (10) which is designed to heat the battery, to select at least a first subset of the battery cells (12a-c) for providing the electrical power and to decouple at least a second subset of the battery cells (12a-c) from the first subset and thereby exclude it from providing the electrical power, such that the highest possible current strength, which remains below a maximum value provided for the temperature of the battery, is established for providing the electrical power. [7] Motor vehicle, with at least one battery according to claim 6, which is designed to carry out the method according to any one of claims 1 to 5.

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