DE102011084473B4 - Method for balancing memory cells of a memory device and memory system for carrying out the method - Google Patents

Abstract

Method for balancing storage cells (102a, 102b, 102c, 102n) of a storage device (102), which is set up for storing electrical and/or chemical energy, in particular for storing energy for a motor vehicle drive, wherein charging states (214a, 214b , 214c, 214n) of the memory cells (102a, 102b, 102c, 102n) are determined and- cells to be balanced are selected from the memory cells (102a, 102b, 102c, 102n) and via discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) of a heat dissipation element (103) are at least partially discharged, with the discharging resistors being arranged in, on or on the heat dissipating element, and with the cells to be balanced being selected in such a way before discharging and/or being connected in such a way with the discharging resistors (106a, 106b , 106c, 106n, 107a, 107b, 107c, 107n) are electrically connected such that a temperature of the heat dissipation element (103) does not exceed a maximum temperature (505), and the selection of the cells to be balanced and/or the interconnection of the cells to be balanced with the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) are/is determined again before discharging until a dependent on the respectively determined Selection and/or a time profile (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat dissipation element (103) calculated as a function of the specific interconnection does not exceed the maximum temperature (505) within a balancing period (504), and that Discharging is then carried out with the last determined selection and / or interconnection.

Description

Motor vehicles that are fully or partially electrically driven are becoming increasingly important. The reasons for this are people's desire for mobility, the need to reduce CO ₂ emissions and the limited oil reserves. Such vehicles have at least one electrostatic or electrochemical energy storage device, which is set up to supply electrical energy to a starter, a drive or the on-board network of the vehicle. Typically, such energy stores in motor vehicles are in the form of batteries or double-layer capacitors and include a large number of storage cells, which can usually be connected in series. During operation, these storage cells are repeatedly charged and discharged.

During the production of such energy storage devices, fluctuations usually occur, which result in the individual storage cells of the energy storage device differing in their charging capacity, charging and/or discharging behavior. In the course of the operation of the energy store, such fluctuations in the properties of the storage cells even increase. As a result of the unequal charge states of the storage cells, individual cells can be overcharged when charging with a constant current. Accordingly, when the storage cells are discharged, there is a risk that individual storage cells will become totally discharged. Both can damage the storage cells, shorten their service life and/or reduce their charge capacity.

In order to prevent such damage, the charge states of the storage cells of the energy store are regularly matched to one another. Corresponding methods are called symmetrization methods or balancing methods. So-called passive balancing is widespread in this context. In this method, the states of charge of the memory cells with a higher state of charge are matched to the state of charge of the memory cell with the lowest state of charge by being discharged via discharge resistors. The excess energy stored in the storage cells with a higher state of charge is at least partially released at the discharge resistors in the form of thermal energy. This generation of heat can lead to damage to the energy store or to individual components of a storage system comprising the energy store.

DE 10 2009 041 005 A1 discloses a device for balancing an energy store, in particular an energy store in a motor vehicle electrical system, which is formed from a cell assembly from the series connection of a plurality of cell groups, a respective balancing circuit being connected to voltage terminals of a respective cell group and comprising a discharge resistor.

EP 1 513 249 A1 discloses a method for balancing a DC voltage circuit of a converter circuit for switching three voltage levels.

DE 10 2007 063 434 A1 discloses a PWM (pulse width modulation) control method for parallel connected self-commutated voltage source inverters, which can also be operated as rectifiers or active filters.

US 2011/0089897 A1 discloses a battery management system. Each of the battery modules contains multiple battery cells. The battery management system includes a plurality of first balancing units, a plurality of first controllers, a second balancing unit including a plurality of second balancing circuits, and a second controller coupled to the battery modules and the second balancing circuits. The first controllers are operable to control the first balancing units to adjust voltages of battery cells in the battery module when an imbalance between the battery cells occurs.

The second controller is operable to control the second balancing circuits to adjust voltages of the battery modules when an imbalance between battery modules occurs.

U.S. 2007/090788 A1 discloses a rechargeable battery with an internal microcontroller. The microcontroller includes a memory that stores data regarding the environment to which the battery is exposed. This data is read by a processor built into the charger used to charge the battery. If this data indicates that the battery has been exposed to a harsh environment for an excessive period of time, the charger will perform a full health assessment of the battery.

The present invention is therefore based on the object of proposing a method for balancing memory cells of a memory device for storing electrostatic and/or electrochemical energy, which allows damage to a memory system that can be caused by an amount of heat generated during balancing to be avoided as effectively as possible impede. The present invention is also based on the object of carrying out this Process to develop suitable storage system.

This object is solved by a method according to claim 1 and by a memory system for carrying out this method. Particular embodiments of the invention are described in the independent claims.

• - Ladezustände der Speicherzellen ermittelt werden und
• - aus den Speicherzellen zu symmetrierende Zellen ausgewählt und über Entladewiderstände eines Wärmeabgabeelements wenigstens teilweise entladen werden,

wobei die zu symmetrierenden Zellen vor dem Entladen derart ausgewählt und/oder derart mit den Entladewiderständen elektrisch verschaltet werden, dass eine Temperatur des Wärmeabgabeelements eine Maximaltemperatur nicht überschreitet.A method is therefore proposed for balancing storage cells of a storage device which is set up for storing electrical and/or chemical energy, in particular for storing energy for driving a motor vehicle, wherein

• - States of charge of the storage cells are determined and
• - cells to be balanced are selected from the storage cells and at least partially discharged via discharge resistors of a heat dissipation element,

wherein the cells to be balanced are selected prior to discharging and/or are electrically connected to the discharge resistors in such a way that a temperature of the heat dissipation element does not exceed a maximum temperature.

Because the cells to be balanced are selected and/or electrically connected to the discharge resistors in such a way that a temperature of the heat dissipation element does not exceed a maximum temperature, in particular as a result of at least partial discharging, damage to a storage system caused by the amount of heat generated during balancing is avoided comprises at least the storage device and the heat dissipation element, effectively prevented. In particular, damage to the heat dissipation element or damage to components of the storage system arranged in or on the heat dissipation element are avoided.

The storage cells can be embodied, for example, as cells of a lead battery, as double-layer capacitors, as nickel-metal hydride, nickel-zinc, lithium-air, zinc-air or lithium-ion cells. Typically, the memory cells are connected in series. A cell voltage of about 4 V is usually present across the memory cells when they are fully charged. The state of charge of an individual storage cell or of the storage device as a whole is measured in each case as a percentage and relates to the maximum charge capacity of the respective storage cell or of the storage device. The state of charge is also referred to as SOC (State of Charge). Depending on the type of memory cell, there can be a characteristic relationship between the SOC of the memory cell and the quiescent voltage (OCV or Open Circuit Voltage) present at the respective memory cell. Based on a so-called SOC-OCV curve, the state of charge of the respective cell can then be determined by measuring the open-circuit voltage present at the cell. The determination of the charge states of the storage cells is consequently equivalent to the determination of the open-circuit voltages respectively present at the storage cells.

The term “balancing” should preferably be used here to designate balancing within the framework of the so-called passive balancing method. In the method described here, a target state of charge of the memory cells is preferably determined, which is usually set equal to the state of charge of that memory cell with the lowest state of charge. As part of the balancing method, the charge states of the memory cells should then be adjusted to the target charge state by at least partially discharging the memory cells via the discharge resistors.

The heat dissipation element is preferably different from the storage device. In particular, the heat dissipation element can be spaced apart from the storage device. For example, a shortest distance between the storage device and the heat releasing element is at least 1 cm, at least 5 cm, at least 10 cm, at least 20 cm, or at least 50 cm. The heat dissipation element can be made of metal. For example, the heat dissipation element can be designed as a printed circuit board.

The discharge resistors are arranged in, on or on the heat dissipation element. In particular, the discharge resistors can each be electrically connected to at least a subset of the storage cells. The connection can include both the electrical connection of the discharge resistors to the storage cells and the connection of the discharge resistors to one another. Each of the discharge resistors can typically be connected in parallel with at least one of the memory cells, with an ohmic resistance of the discharge resistors usually being between 10 Ω and 100 Ω in each case. However, the ohmic resistance of the discharge resistors can also assume any other value. The connection of the discharge resistors to the storage cells can preferably be carried out by means of electrical switches, which can be embodied as mechanical switches or, for example, as transistors. There are therefore preferably a large number of options for connecting the discharge resistors to the storage cells. In particular, it can be provided that the ohmic resistance of a a discharge resistor connected in parallel with a given memory cell or a discharge arrangement connected in parallel with the given memory cell can be varied. For example, it can be provided that a multiplicity of discharge resistors can be connected in parallel to a given storage cell independently of one another. A discharge current flowing away from the storage cell when this storage cell is discharged and a quantity of heat and/or power loss given off to the heat dissipation element when this storage cell is discharged can thus be controlled and/or monitored. Typically, a maximum value of the discharge current for a given memory cell is at most 1 A, preferably at most 500 mA, more preferably at most 200 mA.

In a specific embodiment, an initial temperature of the heat dissipation element is detected before the at least partial discharge of the cells to be balanced. This makes it possible to determine by how many degrees the temperature of the heat-emitting element can be increased until the maximum temperature is reached. The initial temperature is usually detected by means of at least one temperature sensor which is arranged in, on or on the heat-emitting element. This is preferably a large number of temperature sensors which are arranged in a regularly distributed manner in, on or on the heat dissipating element. In this way, a spatial temperature distribution of the heat-emitting element can be recorded at a given point in time. The at least one temperature sensor can be designed, for example, as a temperature-dependent electrical resistor.

The selection of the cells to be balanced and/or the interconnection of the cells to be balanced with the discharge resistors before discharging is determined again until a time profile of the temperature of the heat dissipation element calculated as a function of the specific selection and/or the specific interconnection exceeds the maximum temperature within of a balancing period. Discharging is then carried out with the selection and/or interconnection determined last.

The selection and the connection, which are determined prior to discharging and on the basis of which the calculation of the time profile of the temperature of the heat dissipation element is carried out, should also be called virtual selection and virtual connection. This choice of words is intended to express the fact that with the initially only virtual selection and/or virtual interconnection, no physical change in the interconnection, e.g. B. by flipping the electrical switch, is accompanied. The actual unloading is then with that actual, i. H. physical selection and/or interconnection made, which corresponds to the last determined virtual selection and/or the last determined virtual interconnection and for which the calculated course of the temperature of the heat dissipating element over time predicts that the temperature of the heat dissipating element will not exceed the maximum temperature within the balancing period. The virtual selection and/or the virtual interconnection are preferably changed in each case with the renewed determination. Instead of calculating the time profile of the temperature of the heat-emitting element, the corresponding time profile can also be read out from a database. If the time profile is calculated, it can then be stored in this database.

With this particular embodiment, it is possible to control and limit the rise in temperature of the heat-emitting element. Overheating of the heat dissipation element and damage caused thereby can be effectively prevented in this way.

In a further specific embodiment, the balancing period is calculated as a function of the state of charge of at least the cells to be balanced and/or as a function of the connection of the cells to be balanced to the discharge resistors and/or as a function of a target state of charge. For example, the balancing period is that period of time that elapses until all the cells to be balanced have assumed the target state of charge as a result of the at least partial discharging. In this case, the balancing period is therefore equal to the maximum discharge period of the cells to be balanced. Alternatively, provision can be made for the balancing time period to be specified, e.g. as a time period specified by hardware and/or software. Expediently, the balancing time can also be set equal to the smaller of these two values, namely the maximum discharge time and the time specified by the software or hardware. By calculating the calculated course over time of the temperature of the heat dissipating element only for the balancing period, the calculation can be shortened and/or a physical memory for storing the course over time can be limited.

• - die virtuelle Auswahl der zu symmetrierenden Zellen und/oder die virtuelle Verschaltung der zu symmetrierenden Zellen mit den Entladewiderständen vor dem Entladen erneut bestimmt werden/wird oder
• - die zu symmetrierenden Zellen entladen werden.

In a further special embodiment, a heating period is determined as a function of the calculated time profile of the temperature of the heat-emitting element, which is typically given by the start of discharging and by a heating time at which the calculated time profile reaches the maximum temperature or a greatest temperature of the calculated time Ver reaches or exceeds the temperature of the heat-emitting element, depending on the specific heating period

• - the virtual selection of the cells to be balanced and/or the virtual interconnection of the cells to be balanced with the discharge resistors are/is determined again before discharging or
• - the cells to be balanced are discharged.

The first alternative, namely the renewed determination of the virtual selection and/or the virtual interconnection, is preferably selected when the determined heating time is shorter than the balancing time. In this first case, harmful overheating of the heat dissipation element is to be expected even before the maximum balancing time has elapsed. The second alternative, namely discharging the cells to be balanced, preferably for the balancing period, is preferably selected when the specific heating period is longer than the balancing period. In this second case, harmful overheating of the heat dissipation element is not to be expected within the balancing period. In this embodiment, harmful overheating of the heat dissipation element is thus effectively prevented.

• - das Berechnen des zeitlichen Verlaufs der Temperatur des Wärmeabgabeelements und/oder
• - das erneute Bestimmen und Verändern der virtuellen Auswahl und/oder der virtuellen Verschaltung abhängig von
• - elektrischen Eigenschaften wenigstens der jeweiligen virtuellen Auswahl der zu symmetrierenden Zellen und/oder
• - elektrischen und/oder geometrischen und/oder thermischen Eigenschaften der Entladewiderstände und/oder
• - thermischen und/oder geometrischen Eigenschaften des Wärmeabgabeelements.

In another specific embodiment

• - Calculating the time profile of the temperature of the heat-emitting element and/or
• - Determining and changing the virtual selection and/or the virtual interconnection again depending on
• - Electrical properties of at least the respective virtual selection of the cells to be balanced and/or
• - Electrical and/or geometric and/or thermal properties of the discharge resistors and/or
• - Thermal and/or geometric properties of the heat-emitting element.

The electrical properties of the respective virtual selection of the cells to be balanced can be an electrical voltage present at these cells and/or a state of charge and/or a charge capacity and/or a target state of charge and/or a calculated power loss emitted during discharging via the discharge resistors include. The electrical properties of the discharge resistors can in turn each include an ohmic resistance and/or a temperature dependency of the ohmic resistance and/or a discharge current flowing through the discharge resistors during discharge. The geometric properties of the discharge resistors and/or the heat dissipation element can include a geometric shape and/or an arrangement of the discharge resistors relative to the heat dissipation element. Finally, the thermal properties of the discharge resistors and/or the heat dissipation element can include a thermal conductivity and/or a heat capacity and/or a temperature and/or a spatial temperature distribution.

By taking these parameters into account when calculating the time profile of the temperature of the heat-emitting element, this time profile can be predicted with great accuracy. A possible overheating of the heat dissipation element with the associated damage can be detected in this way. By taking these parameters into account when determining and changing the virtual selection and/or the virtual interconnection again, an optimal selection and/or an optimal interconnection can be found as efficiently as possible. Computing and storage capacities can thus be effectively reduced.

In a further special embodiment, the selection and/or the interconnection or the virtual selection and/or the virtual interconnection are respectively determined and changed again before discharging in such a way that a calculated power loss delivered to the heat dissipation element via the discharge resistors is reduced as a result of the change . For example, the power loss can be reduced by reducing the number of cells to be balanced. It is also conceivable that the wiring is changed in such a way that the ohmic resistances of the discharge resistors are increased. Such storage cells can also be selected as cells to be balanced, at which a lower voltage is present. The calculated power loss is preferably reduced in each case by a predetermined value, e.g. by 1 W. Reducing the power loss reduces the amount of heat given off to the heat dissipation element via the discharge resistors during discharging and thus prevents the heat dissipation element from overheating.

In a further special embodiment, in a first step all memory cells of the memory device are selected as the cells to be balanced. Preferably, only the memory cell with the lowest state of charge is not selected as the cell to be balanced, since their state of charge usually already defines the target state of charge and no longer needs to be changed. This embodiment ensures that the memory cells are balanced as quickly as possible.

A storage system for carrying out the method described above is also proposed, comprising a storage device for storing electrical and/or chemical energy, in particular for storing energy for driving a motor vehicle, and a heat dissipation element, a measuring device and a control and computing unit.

In this case, the memory device has a plurality of memory cells which are preferably connected or can be connected in series. The heat dissipation element comprises a plurality of electrical resistors that can be electrically connected to the storage cells and/or to one another and via which the storage cells can be at least partially electrically discharged, and at least one heat sensor for detecting a temperature of the heat dissipation element. The discharge resistors are arranged in, on or on the heat dissipation element. The measuring device is set up to detect states of charge of the storage cells and/or to detect electrical voltages present at the storage cells. Finally, the control and computing unit can be connected electrically and/or wirelessly to the heat dissipation element and the measuring device and is programmed to select storage cells to be balanced from the storage cells before discharging and/or to connect them to the resistors in such a way that the temperature of the heat dissipation element does not exceed a maximum temperature, in particular as a result of the at least partial discharge of the cells to be balanced.

The control and computing unit is designed to determine the selection of the cells to be balanced and/or the connection of the cells to be balanced to the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) again for as long as before the discharge , until a time profile (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat dissipation element (103) calculated as a function of the specific selection and/or depending on the specific interconnection, reaches the maximum temperature (505) within a balancing period (504) does not exceed, and then carry out the discharging with the last determined selection and/or interconnection.

• 1 ein Speichersystem, umfassend eine Speichervorrichtung mit einer Vielzahl von Speicherzellen, eine Messvorrichtung, ein Wärmeabgabeelement mit einer Vielzahl von Entladewiderständen sowie eine Steuer- und Recheneinheit,
• 2 schematisch einige der Speicherzellen aus 1 mit jeweils unterschiedlichen Ladezuständen,
• 3 das Speichersystem aus 1 mit einer ersten virtuellen Verschaltung der Entladewiderstände und der Speicherzellen,
• 4 das Speichersystem aus 1 mit einer weiteren virtuellen Verschaltung der Entladewiderstände und der Speicherzellen,
• 5 ein Temperatur-Zeit-Diagramm mit einer Vielzahl von berechneten zeitlichen Verläufen einer Temperatur des Wärmeabgabeelements aus 1 und
• 6 schematisch Schritte eines Verfahren zur Symmetrierung von Speicherzellen, in einem Ablaufdiagramm dargestellt.

Exemplary embodiments of the claimed method and of the claimed memory system are shown in the drawings and are explained in more detail on the basis of the following description. Show it

• 1 a storage system, comprising a storage device with a large number of storage cells, a measuring device, a heat dissipation element with a large number of discharge resistors and a control and computing unit,
• 2 schematically shows some of the memory cells 1 each with a different charging status,
• 3 the storage system off 1 with a first virtual interconnection of the discharge resistors and the memory cells,
• 4 the storage system off 1 with a further virtual interconnection of the discharge resistors and the storage cells,
• 5 a temperature-time diagram with a large number of calculated time curves of a temperature of the heat-emitting element 1 and
• 6 Schematic steps of a method for balancing memory cells, shown in a flowchart.

1 shows a storage system 101 with a storage device 102, a heat dissipation element 103, a measuring device 104 and with a control and computing unit 105. The storage device 102 comprises a large number of storage cells 102a to 102n, which in the present example are designed as lithium-ion cells and in are connected in series. The dashed line shown between the memory cells 102c and 102n is intended to indicate that a multiplicity of further memory cells of the same type are respectively arranged between these memory cells, but are not shown here. The storage cells 102a to 102n each have a charging capacity of 15 Ah (ampere hours). In the fully charged state, an electrical voltage present between the two poles of each of the storage cells 102a to 102n is approximately 4 V. The storage device 102 is an energy store for supplying electrical energy to an electrical drive of a motor vehicle.

The measuring device 104 comprises a multiplicity of strain gauges 111a to 111n. Voltage measuring devices 111a to 111n are set up to detect electrical voltages present between the poles of storage cells 102a to 102n. For example, with the voltmeter 111a, the electrical voltage present between the poles of the storage cell 102a measurable. The voltage measuring device 111b can be used to determine the electrical voltage present at the storage cell 102b, etc.

A multiplicity of discharge resistors 106a to 106n and 107a to 107n are arranged on the heat dissipation element 103, which is designed as a metal Printed Circuit Board (PCB). Furthermore, temperature sensors 110a to 110n are located on the heat dissipation element 103, which are spatially distributed uniformly over the heat dissipation element 103 and which are each temperature-dependent electrical resistances. In the exemplary embodiment shown here, the discharge resistors 106a to 106n and 107a to 107n are each configured identically, with an ohmic resistance of the discharge resistors 106a to 106n and 107a to 107n being 60 Ω in each case.

The discharge resistors 106a to 106n and 107a to 107n can be electrically connected to the storage cells 102a to 102n independently of one another via electrical switches 108a to 108n and 109a to 109n. In particular, each of the discharge resistors 106a to 106n and 107a to 107n can be connected in parallel to at least one of the storage cells 102a to 102n, independently of the other discharge resistors, so that the storage cells 102a to 102n are each independently connected via at least a subset of the discharge resistors 106a to 106n and 107a can be discharged up to 107n. For example, the memory cell 102a can be discharged via the discharge resistors 106a and/or 107a, the memory cell 102b can be discharged via the discharge resistors 106b and/or 107b, etc. When discharging the memory cells 102a to 102n, discharge currents flow via the discharge resistors 106a to 106n and/or via the discharge resistors 107a to 107n from the storage cells and are at least partially irreversibly converted into heat energy, which is given off to the heat dissipation element 103 and heats it. Because the storage cells 102a to 102n can each be discharged via only one or two of the discharge resistors, an amount of heat and/or power loss emitted by the storage cells 102a to 102n to the heat dissipation element 103 can be controlled and limited in each case. In embodiments that differ slightly from the one presented here, the amount of heat and/or power loss emitted by a given storage cell can be set and/or controlled in a much more finely graduated manner, e.g. B. by using sliding resistors, the value of which is continuously variable.

The control and computing unit 105, which is presently embodied as a programmable microcontroller, is connected or can be connected to the measuring device 104 via a connection 112 and to the heat dissipating element 103 via a connection 113. Here, the connections 112 and 113 are each designed as electrical connections. In a slightly modified embodiment, the connections 112 and 113 can be e.g. B. be radio connections. Voltage measuring devices 111a to 111n and temperature sensors 110a to 110n can be read out and/or controlled via connections 112 and 113. The control and computing unit 105 is also set up to control the electrical switches 108a to 108n and 109a to 109n independently of one another via the connection 113 . The control and processing unit 105 can thus bring the electrical switches 108a to 108n and 109a to 109n independently of one another, as desired, into the open or into the closed switch position.

In the present exemplary embodiment, the storage device 102 and the heat dissipation element 103 are designed as separate components and are spatially separated from one another. A smallest spatial distance 120 between the storage device 102 and the heat dissipation element 103 is 30 cm. A transfer of heat from the heat dissipation element 103 to the storage device 102 is thus prevented or reduced in a simple manner.

In the following, a means of the storage system 101 is to be 1 A feasible method for balancing the memory cells 102a to 102n of the memory device 102 will be described.

In a first step of the method, the voltage measuring devices 111a to 111n are used to determine charge states 214a to 214n of the memory cells 102a to 102n, which are shown schematically in 2 are shown. Here and in the following, recurring features are each provided with identical reference symbols. The charge states 214a to 214n of the memory cells 102a to 102n can be derived from open-circuit voltages present at the memory cells 102a to 102n using an SOC-OCV curve stored in the control and computing unit 105, which is characteristic of the cell type of the memory cells 102a to 102n . The charge states 214a to 214n are each specified as a percentage and each relate to the charge capacities 216a to 216n of the corresponding memory cell. 2 it can be seen that the state of charge 214c of the memory cell 102c is lower than the states of charge of the remaining memory cells. The charge state 214c should also be lower than the charge states 214d to 214n-1 of memory cells 102a to 102n-1 (not shown here). The control and computing unit 105 is used to compare the charge states 214a to 214n carried out, wherein the state of charge 214c is identified as the target state of charge 215, which in 2 is shown in the form of a dashed line.

The task of the balancing method is therefore to charge those of the memory cells 102a to 102n of the memory device 102 whose state of charge is greater than the target state of charge 215 via the discharge resistors 106a to 106n and/or 107a to 107n or via at least a subset of the discharge resistors 106a to 106n and/or 107a to 107n to be at least partially discharged until their state of charge corresponds as closely as possible to the target state of charge 215. The storage cells 102a to 102n should be discharged in such a way that a temperature of the heat dissipation element 103 reaches a maximum temperature 505 (see 5 ) as a result of discharging. This is intended to prevent damage to the heat dissipation element 103 or damage to components arranged in, on or on the heat dissipation element 103 .

In the next step, the temperature of the heat dissipation element 103 is first determined with the aid of the temperature sensors 110a to 110n. In this way, a spatial temperature distribution of the heat dissipation element 103 is determined. The control and processing unit 105 then selects cells to be balanced from the storage cells 102a to 102n in a first virtual selection, the charge states of which are to be matched to the setpoint charge state 215 first. In the present example, with the exception of memory cell 102c, whose state of charge 214c defines target state of charge 215, all other memory cells 102a, 102b and 102d to 102n are initially selected as cells to be balanced with the first virtual selection. In this context, the term "virtual" is intended to indicate that "virtually" selected cells are not actually symmetrical at first. Rather, initially only calculations and/or simulations are carried out for the first virtual selection of the cells to be balanced.

Furthermore, a discharging process is simulated with the aid of the control and computing unit 105 for the first virtual selection of the memory cells to be balanced. For this purpose, first a first virtual interconnection 301 of the discharge resistors 106a to 106n and 107a to 107n with the memory cells 102a to 102n is selected (see FIG 3 ) . An interconnection, and thus also the first virtual interconnection 301, corresponds to exactly one configuration of the electrical switches 108a to 108n and 109a to 109n. The configuration is determined in that it is determined for each of the electrical switches 108a to 108n and 109a to 109n whether the respective switch is in the open or in the closed switch position. The term “virtual interconnection” is intended to mean that the corresponding interconnection is initially not implemented by actually driving the electrical switches 108a to 108n and 109a to 109n by the control and computing unit 105a. Rather, the first virtual interconnection 301 in this step serves only as a basis for the simulation or calculation of the discharging process and a time profile of the temperature of the heat dissipating element 103 as a result of this discharging process carried out by the control and computing unit 105 .

With the exception of the electrical switches 108c and 109c, all the electrical switches in the first virtual interconnection 301 are in the closed switch position. The first virtual interconnection 301 is therefore selected in such a way that the total resistances via which the cells to be balanced are to be discharged each assume the smallest possible value. So is in 3 For example, the total resistance of discharge resistors 106a and 107a, each connected in parallel to memory cell 102a, totals 30 Ω. If, for example, the electrical switch 109a were brought from the closed switch position into the open switch position, then the corresponding total resistance of the discharge resistors 106a and 107a, via which the storage cell 102a would be discharged, would be 60 Ω.

for the inside 3 In the first virtual interconnection 301 shown, the control and computing unit 105 calculates a first virtual power loss that would be dissipated to the heat dissipation element 103 via the discharge resistors 106a to 106n and 107a to 107n if the partial discharge of the storage cells 102a to 102n were carried out with an actual interconnection , which corresponds to the first virtual interconnection 301. The first virtual power loss is given by the sum of the individual first virtual power losses emitted by the individual cells to be balanced according to the first virtual selection to the heat dissipation element 103 . The individual first virtual power losses are in turn given by the previously determined electrical voltages present at the individual cells to be balanced and by the total resistance of those discharge resistors via which the respective cells to be balanced are to be discharged. If adjacent memory cells are discharged, discharge currents that flow between these adjacent memory cells or that flow between the discharge resistors that are assigned to the adjacent memory cells can be ignored. Eg can in 3 Discharge currents generated by a discharge formed of the discharge resistors 106a and 107a Order flow to a further discharge arrangement formed from the discharge resistors 106b and 107b, are not taken into account when calculating the first virtual power loss.

In addition, for the first virtual selection of the cells to be balanced, the control and computing unit 105 calculates respective first virtual discharge durations, which a discharge down to the target state of charge would require in each case. The first virtual discharge durations are dependent on the state of charge of the respective memory cell before discharging, on the target state of charge 215 and on the first virtual interconnection.

The control and computing unit 105 then compares the first virtual discharge durations calculated in this way with a hardware duration specified by the control and computing unit 105 . In the present example, the calculated first virtual discharge durations of the cells to be balanced should each amount to several hours according to the first virtual selection. They are each much larger than the hardware duration, which should be 2000 seconds here. The control and processing unit 105 then selects the hardware time period of 2000 seconds as the balancing time period 504 (see 5 ) out. In the following, all simulations and/or calculations of the discharging process or the time profile of the temperature of the heat dissipation element 103 carried out by the control and computing unit 105 are only carried out for a time interval which is given by the balancing period 504 or is only slightly longer than the balancing period 504

Starting from the in 3 shown first virtual selection of the cells to be balanced and the first virtual interconnection 301, the control and processing unit 105 now calculates a first time profile 506a (see 5 ) the temperature of the heat dissipation element 103. Input variables for this calculation are the first virtual power loss transmitted from the discharge resistors 106a to 106n and 107a to 107n to the heat dissipation element 103, a spatial arrangement of the discharge resistors 106a to 106n and 107a to 107n on the heat dissipation element 103, a geometric shape of the heat dissipation element 103 and a thermal conductivity of the heat dissipation element 103.

For example, the control and computing unit 105 calculates the first time curve 506a of the temperature of the heat dissipation element 103 by solving the heat conduction equation for the heat dissipation element 103 with the aid of finite element methods. It can also be provided that a decrease in the discharge currents flowing from the first virtual selection of the cells to be balanced in the course of the discharging process and an associated decrease in the first virtual power loss are taken into account. Another input variable for the calculation is the initial temperature of the heat dissipation element 103 or the spatial initial temperature distribution of the heat dissipation element 103. It can also be provided that the control and computing unit 105 does not carry out the calculation itself, but instead uses the first time profile 506a, e.g database reads. Various temperature curves over time can be stored in such a database as a function of different values of the input parameters. These input parameters include, for example, the virtual power loss given off to the heat dissipation element 103, the initial temperature of the heat dissipation element 103, the respective virtual selection of the cells to be balanced and/or the respective virtual interconnection selected.

5 FIG. 5 shows a temperature-time diagram 501 with different time curves 506a to 506f of the temperature of the heat-emitting element 103. The time is plotted on the X-axis 502, with the point in time t=0 corresponding to a start of the discharging process. The temperature change of the heat-emitting element 103 is plotted on the Y-axis 503 . This temperature difference relates in each case to the greatest temperature of the heat dissipation element 103 calculated for a given point in time and to the greatest temperature of the heat dissipation element 103 at the beginning point in time, ie before the beginning of the discharging process. The balancing time period 504 specified by the hardware time period is 2000 seconds. The maximum temperature 505 is also emphasized by a dashed line. This is a temperature value that the heat dissipation element 103 should not overwrite in order to avoid damage to the heat dissipation element 103 or damage to components arranged on the heat dissipation element 103 .

After the control and processing unit 105 has calculated the first time profile 506a, the control and processing unit 105 determines a first heating point in time 507a at which the first time profile 506a reaches the maximum temperature 505. In the present case, the first heating time 507a is approximately 350 s. In a next method step, the control and computing unit 105 compares a first heating time 508a given by the first heating time 507a with the balancing time 504. In the present case, the first heating time 508a of 350 s is less than the Symmetrierzeitdauer 504 of 2000 s. If the discharge of the cells to be balanced with the first virtual Interconnection 301 according to 3 carried out, the heat dissipation element 103 would exceed the maximum temperature 505 at the first heating time 507a. Therefore, the actual discharging of the cells to be balanced is not performed with an interconnection that corresponds to the first virtual interconnection 301 3 is equivalent to.

Instead, the control and computing unit 105 determines a second virtual selection of the cells to be balanced and/or a second virtual interconnection 401 (see 4 ) of the cells to be balanced with the discharge resistors 106a to 106n and 107a to 107n. The virtual selection of the cells to be balanced and/or the virtual interconnection of the cells to be balanced with the discharge resistors 106a to 106n and 107a to 107n is changed in such a way that according to the second virtual selection and/or the second virtual interconnection 401 via the discharge resistors 106a to 106n and 107a to 107n delivered to the heat dissipation element 103 second virtual power loss is less than the first virtual power loss. Here the first virtual power loss should be 20 W, but the second virtual power loss is only 19 W.

This can be done, for example, by reducing the number of cells to be balanced. For example, the memory cell 201b according to the first virtual interconnection 301 in 3 selected as the memory cell to be balanced, but not according to the second virtual interconnection 401 in 4 . Compare the switch positions of the electrical switches 108b and 109b in FIGS 3 and 4 . However, the virtual power loss can also be reduced if, for example, the ohmic resistance through which a given memory cell is to be discharged is greater according to the second virtual interconnection than according to the first virtual interconnection. For example, the memory cell 102a according to the first virtual interconnection 301 in 3 discharged via an ohmic resistance of 30 Ω, according to the second virtual interconnection 401 in 4 however, via an ohmic resistance of 60 Ω. Compare the switch positions of the electrical switch 109a in FIGS 3 and 4 .

In the example implemented here, the initially determined initial temperature distribution of the heat dissipation element 103 is taken into account during the transition from the first to the second virtual selection of the cells to be balanced or from the first virtual interconnection 301 to the second virtual interconnection 401 . For example, in the case of the second virtual selection 401, those memory cells are no longer selected whose discharge would further heat a region of the heat dissipation element 103 with a particularly high temperature. When the storage cells are partially discharged, the heat dissipation element 103 usually heats up particularly quickly in a central area of the heat dissipation element 103 . When changing the virtual selection of the cells to be balanced, those storage cells are typically initially no longer selected as cells to be balanced, to which discharge resistors in the central region of the heat dissipation element are assigned for discharging. When changing the virtual selection and/or the virtual interconnection, the arrangement of the discharge resistors 106a to 106n and 107a to 107n on the heat dissipation element 103 is also taken into account.

After the control and computing unit 105 has changed the virtual selection and/or the virtual interconnection, a second virtual power loss is calculated for the second virtual selection and/or the second virtual interconnection 401, which would be emitted to the heat dissipation element 103 during discharging. Then for the second virtual selection and/or for the second virtual interconnection 401 a second time course 506b (see 5 ) of the temperature of the heat releasing element 103 is calculated. It can be clearly seen that the temperature increase of the heat dissipation element 103 according to the second time profile 506b turns out to be lower than in the case of the first time profile 506a. A second heating point in time 507b, at which the second time profile 506b reaches the maximum temperature 505, is then also determined for the second virtual interconnection 401 or for the second time profile 506b. Since the second virtual power dissipation (19 W) is smaller than the first virtual power dissipation (20 W), the temperature of the heat dissipation member 103 increases more slowly. This is accompanied by the fact that the second heating time period 508b given by the second heating time point 507b is longer than the first heating time period 508a given by the first heating time point 507a. As already described in connection with the first time curve 506a, the second heating duration 508b is also compared to the balancing duration 504. Since the second heating period 508b is also shorter than the balancing period 504, the actual discharging is not performed with a selection and/or interconnection that corresponds to the second virtual selection and/or the second virtual interconnection 401.

Instead, the control and evaluation unit 105 determines a third virtual selection of the cells to be balanced and/or a third virtual connection of the discharge resistors 106a to 106n and 107a to 107n to the memory cells 102a to 102n, with a third virtual power loss being small ner is than the second virtual power dissipation. As before, a third time course 506c of the temperature of the heat dissipation element 103 is calculated. The corresponding third heating period 508c is in turn longer than the second heating period 508b.

This process is continued until the calculated heating time is greater than the balancing time 504. In 5 further time curves 506d and 506d are shown with corresponding heating times 507d and 507e and heating durations 508d and 508e. For a sixth time curve 506f, the sixth heating duration 508f is finally longer than the balancing duration 504. Therefore, the control and processing unit 105 controls the electrical switches 108a to 108n and 109a to 109n in such a way that an actual selection of the cells to be balanced and/or or an actual connection of the discharge resistors 106a to 106n and 107a to 107n to the memory cells 102a to 102n corresponds to the last determined sixth virtual selection and/or sixth virtual connection (not shown here). A corresponding sixth virtual power loss should be 15 W. The discharging of the cells to be balanced that have been selected in this way begins with the actual actuation of the electrical switches. The cells to be balanced are discharged for the balancing period 504 .

The method described above prevents the temperature of the heat dissipation element 103 from exceeding the maximum temperature 505 within the balancing period 504 . Damage to the heat dissipation element 103 as a result of overheating is thus successfully avoided. After the balancing period 504 has elapsed, the method just described can be carried out again until the states of charge 214a to 214n of all memory cells 102a to 102n are adjusted to the target state of charge 215 .

In 6 the balancing procedure described here is shown again schematically in the form of a flowchart. In a first method step 601, a first virtual selection of cells to be balanced and/or a first virtual interconnection 301 of the memory cells 102a to 102n with the discharge resistors 106a to 106n and 107a to 107n is determined, first virtual discharge durations being calculated for the first virtual selection will. In a second method step 602, a first virtual power loss is determined. In a third method step 603, a first time profile of a temperature of the heat dissipation element 103 is calculated. In addition, a first heating point in time and a first heating time period determined by this point are calculated as a function of the first course over time. In a fourth method step 604, the first heating period is compared to the balancing period 504. If the first heating duration is shorter than the balancing duration 504, the process moves to method step 605.

In method step 605, a new virtual selection and/or a new virtual interconnection are determined, with a virtual power loss calculated for the new virtual selection and/or for the new virtual interconnection being reduced, e.g. B. by 1 W. In the next method step 606 for the new virtual selection and / or for the new virtual interconnection, a new time curve of the temperature of the heat dissipating element 103 is calculated. In addition, a new heating time and a new heating duration are determined. Then the process goes to method step 604 again. Method steps 604, 605 and 606 are repeated until the currently calculated heating duration is greater than the balancing duration 504.

If this is the case, then there is a transition to method step 607. In method step 607, cells to be balanced are actually selected or memory cells 102a to 102n are actually connected to discharge resistors 106a to 106n and 107a to 107n by appropriately driving electrical switches 108a to 108n and 109a to 109n. The actual selection or the actual interconnection correspond to the last determined virtual selection or the last determined virtual interconnection. The corresponding selection of the cells to be balanced is then at least partially discharged for the balancing period 504 . The method can be repeated until the states of charge 214a to 214n of all memory cells 102a to 102n are adjusted to the target state of charge 215 .

Claims (9)

Method for balancing storage cells (102a, 102b, 102c, 102n) of a storage device (102), which is set up for storing electrical and/or chemical energy, in particular for storing energy for driving a motor vehicle, wherein - charging states (214a, 214b , 214c, 214n) of the memory cells (102a, 102b, 102c, 102n) are determined and - cells to be balanced are selected from the memory cells (102a, 102b, 102c, 102n) and via discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) of a heat dissipation element (103) are at least partially discharged, the discharge resistors being arranged in, on or on the heat dissipation element, and wherein the cells to be balanced are selected prior to discharging and/or are electrically connected to the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) in such a way that a temperature of the heat dissipation element (103) reaches a maximum temperature (505 ) does not exceed, and the selection of the cells to be balanced and/or the connection of the cells to be balanced to the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) are/is determined again before discharging as long as until a time curve (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat dissipation element (103) calculated as a function of the particular selection and/or a time profile (506b, 506c, 506d, 506e, 506f) within a balancing period ( 504) does not exceed, and the discharge is then carried out with the last selection and/or interconnection determined. Method according to one of the preceding claims, characterized in that an initial temperature of the heat-emitting element (103) is detected before discharging. procedure after claim 1 , characterized in that the balancing period (504) - depending on the state of charge of at least the cells to be balanced and/or depending on the interconnection of the cells to be balanced with the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n ) is calculated and/or - is specified. procedure after claim 1 , characterized in that a heating period (508a, 508b, 508c, 508d, 508e, 508f) is determined depending on the calculated time profile (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat-emitting element (103), wherein depending on the determined heating period - the selection and/or the interconnection are/is determined again before discharging or - the cells to be balanced are discharged. procedure after claim 1 , characterized in that - calculating the time course (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat dissipation element and/or - determining and changing the selection and/or the connection again depending on - electrical properties at least the respective selection of the cells to be balanced and/or - electrical and/or geometric and/or thermal properties of the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) and/or - thermal and/or geometric properties of the heat dissipation element (103) is carried out. procedure after claim 5 , characterized in that - that the electrical properties of the respective selection of the cells to be balanced in each case an electrical voltage applied to these cells and/or a state of charge (214a, 214b, 214c, 214n) and/or a charge capacity (216a, 216b, 216c, 216n) and/or a target state of charge (215) and/or a calculated power loss emitted during discharging via the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) - and/or that the electrical properties of the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) each have an ohmic resistance and/or a temperature dependency of the ohmic resistance and/or during discharging via the discharge resistors (106a, 106b, 106c, 106n, 107b, 107c, 107n) include flowing discharge current - and / or that the geometric properties of the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) and / or the heat dissipation element (103) a geometric ical shape and/or an arrangement of the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) relative to the heat dissipating element (103) - and/or that the thermal properties of the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) and/or the heat dissipation element (103) include a thermal conductivity and/or a thermal capacity and/or a temperature. procedure after claim 1 , characterized in that the selection and / or the interconnection before discharging are respectively determined and changed again / is that via the discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) to the heat dissipation element (103) the calculated power loss is reduced as a result of the change. Method according to one of the preceding claims, characterized in that in a first step all memory cells (102a, 102b, 102c, 102n) of the memory device (102) are selected as the cells to be balanced. Storage system (101) for performing the method according to one of the preceding claims, comprising - a storage device (102) for storage electrical and / or chemical energy, in particular for storing energy for a drive of a motor vehicle, - a heat dissipation element (103), - a measuring device (104) and - a control and computing unit (105), wherein - the storage device (102) a plurality of storage cells (102a, 102b, 102c, 102n), - the heat dissipation element (103) comprises a plurality of discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) which are connected to the storage cells (102a, 102b , 102c, 102n) and/or can be electrically interconnected and via which the storage cells (102a, 102b, 102c, 102n) can be at least partially electrically discharged, and at least one heat sensor (110a, 110b, 110c, 110n) for detecting a temperature of the Heat dissipation element (103), wherein the discharge resistors are arranged in, on or on the heat dissipation element, - the measuring device (104) for detecting charge states (214a, 214b, 214c, 214n) of the storage cells (102a, 102b, 102c, 102n) and/or is set up to detect electrical voltages present at the storage cells (102a, 102b, 102c, 102n) and wherein - the control and computing unit (105) with the heat dissipation element (103) and the measuring device (104) electrically and/or can be connected via radio and is set up in terms of programming to select cells to be balanced from the storage cells (102a, 102b, 102c, 102n) before discharging in such a way and/or with the discharging resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) in such a way that a temperature of the heat dissipation element (103) does not exceed a maximum temperature (505), the control and computing unit being designed to select the cells to be balanced and/or to connect the cells to be balanced to the Discharge resistors (106a, 106b, 106c, 106n, 107a, 107b, 107c, 107n) to be determined again before discharging until a depending on the particular selection and/or depending on the depending because the time profile (506a, 506b, 506c, 506d, 506e, 506f) of the temperature of the heat dissipation element (103) calculated for the specific connection does not exceed the maximum temperature (505) within a balancing period (504), and then discharging with the last selection determined and /or make the connection.

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