EP2460250A2

EP2460250A2 - Device for storing electrical energy

Info

Publication number: EP2460250A2
Application number: EP10734698A
Authority: EP
Inventors: Conrad RÖSSEL
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2009-07-31
Filing date: 2010-07-16
Publication date: 2012-06-06
Also published as: CN102484378A; DE102009035862A1; WO2011012233A2; WO2011012233A3; US20120181956A1; KR20120052264A; RU2012102913A

Abstract

The invention relates to a device for storing electrical energy and comprises a plurality of storage cells. A switch and an electrical resistor in series thereto are connected parallel to each of the storage cells. At least one switch unit closes each individual switch as soon as the storage cell located parallel to said switch exceeds a specified voltage. There is additionally a time-switch unit that holds each closed switch closed for a specified time after closing has once occurred.

Description

Device for storing electrical energy

The invention relates to a device for storing electrical energy according to the closer defined in the preamble of claim 1. The invention also relates to a method for operating such a device.

Devices for storing electrical energy, and in particular for storing electrical traction energy in electric vehicles or in particular in hybrid vehicles, are known from the general state of the art. Typically, such devices for storing electrical energy by means of individual memory cells are formed, which are connected, for example, in series and / or in parallel with each other electrically. In principle, different types of accumulator cells or capacitors are conceivable as memory cells. Due to the comparatively high

Amounts of energy and performance in the storage and removal of energy, when used in powertrains for vehicles, and here in particular for commercial vehicles, are used as memory cells storage cells with sufficiently high energy content. These may be, for example, rechargeable battery cells in lithium-ion technology, or in particular but memory cells in the form of very powerful capacitors. These capacitors are also commonly referred to as supercapacitors, supercaps or ultracapacitors.

Regardless of whether supercapacitors or accumulator cells are used with high energy content, arises in such structures of a plurality of memory cells, which are connected in total or in blocks in series, the problem that the voltage of the individual memory cell due to design limited to an upper voltage value is. If this upper voltage value is exceeded, for example during charging of the device for storing electrical energy, the lifetime of the memory cell is generally drastically reduced. Due to predetermined manufacturing tolerances, the individual memory cells give way in their properties (For example, self-discharge) in practice typically small

from each other. As a result, individual memory cells have a slightly lower voltage than other memory cells in the device. However, since the maximum voltage for the entire device generally remains the same and which represents a typical driving criterion, in particular during loading, it inevitably results in a somewhat higher voltage for other memory cells and then exceeds those permitted during charging processes

Voltage limit to be charged. Such overvoltage leads, as already mentioned above, to a considerable reduction of the possible

Life of these individual memory cells and thus the device for storing electrical energy. Another problem is that individual memory cells sag due to a higher self-discharge faster in their voltage than other memory cells. In the longer term, this can lead to the memory cells increasingly divergence in their voltage potentials. In the worst case, there is a reversal of the bagged memory cell in the device for storing electrical energy. This would drastically reduce their lifespan and must be avoided at all costs.

In order to address these problems, the general state of the art essentially knows two different types of cell voltage balances, each of which has a centralized or decentralized structure. In a central electronics unit, for example, all the components are combined in a control unit, while in the decentralized structure of one to two memory cells, the individual components are mounted, for example, on a small board for specifically these one to two memory cells. The common terminology of the Zeilspannungsausgleichs is here a little misleading, since this does not compensate for the voltages or more specifically the energies of the individual memory cells with each other, but that only the cells are reduced with high voltages in their excessive voltages. Because the

Total voltages of the device for storing electrical energy remain constant, however, by the so-called cell voltage compensation a cell sagged in its tension over time in her again

Voltage can be increased, so that at least the risk of polarity reversal is reduced.

A first possibility for the cell voltage compensation is the so-called passive cell voltage compensation. In this case, an electrical resistance is connected in parallel with each individual memory cell. The electrical resistance is chosen comparatively high, but still leaves many times the typical

Selbstentladestroms the respective memory cell flow. As a result, an approximately equal voltage is established over time for each of the memory cells. However, this structure has the disadvantage that no electrical energy is present in the memory after a relatively short time, because due to the electrical resistance parallel to each cell constantly a small but still existing current flows and thus a constant discharge of

Device for storing electrical energy takes place. The problem is further exacerbated by the fact that by the power consumption in the

Heat generated by electrical resistors is generally undesirable in the area of a device for storing electrical energy and typically has to be cooled down. This results in this type of passive cell voltage compensation serious disadvantages, which can be seen in particular in the electrical losses and the unwanted heat development.

Another approach from the general state of the art is the so-called active cell voltage compensation. It is additionally an electronic

Threshold switch connected in parallel with each of the memory cells and in series with the resistor. This construction, also referred to as bypass electronics, only ever allows a current to flow when the cell has a

Overvoltage, that is, a voltage above a predetermined limit for the single cell has. As soon as the voltage of the individual memory cell falls back into a range below the specified limit value, the switch is opened and no current flows. Because of that, a smaller one ohmic resistance can be used, the structure can also lead to a faster cell voltage compensation than the variant described above. Due to the fact that the electrical resistance across the switch is always overridden when the voltage of the individual

Memory cells is below the predetermined limit, an unwanted discharge of the entire device for storing electrical energy can be largely avoided. Also a permanent one

unwanted heat generation is not a problem with this approach of active voltage compensation.

However, here also the disadvantage remains that in particular in the

highly dynamic application of the device for storing electrical energy, only a possibly occurring damage is limited, while no long-term compensation of the individual voltage levels of the memory cells takes place. If it comes to a new charge, then so are just limited by the switch in their maximum voltage

Memory cells immediately operated again in this limit. This occurs, in particular in very dynamic charging and discharging cycles, which in principle continues to be damaging and only slowly via resistor and switch

mitigated scenario in a short time sequence at exactly the same

Memory cells again and again. Ultimately, therefore, this so-called active cell voltage compensation does not really equal the individual

Tensions of the cells with each other, but only when exceeding the damaging limit voltage, the memory cell is discharged with a small bypass current to slow degradation of the overvoltage

Exceed limit. The bypass current flows only until the device for storing electrical energy is discharged again, since in this case falls below the corresponding voltage limit and the switch is opened again. When re-loading the problem arises again. And the memory cell that has just been affected will still have a much higher voltage than, for example, a cell that has been lowered in voltage. In the two set forth and in the general state of the art

known possibilities for so-called cell voltage compensation, the goal is always to avoid the overvoltage and polarity reversal in individual memory cells. However, as stated, this does not succeed in all cases, especially not when a highly dynamic operation, ie a very fast

Succession of charging and discharging cycles, such as occur in a hybrid drive in city traffic occur in the device.

In particular, in such applications, so the life of

Device for storing electrical energy can be extended only conditionally by the cell voltage compensation.

Now, however, the life of the device for storing electrical energy in hybrid drives, and in particular in hybrid drives for commercial vehicles, such as buses in urban transport, from

crucial importance. Unlike conventional powertrains in the order of magnitude required for such applications

Performance, the device for storing electrical energy represents a significant part of the cost of the hybrid drive. Therefore, it is particularly important that in such applications very high lifetimes of the device for storing electrical energy can be achieved.

WO 2006/015083 A2 describes a method and an apparatus for performing cell-based balancing in a multi-cell lithium battery system. A discharge time parameter is calculated for each cell at the beginning of a charge cycle, and balancing is performed for each cell having a positive discharge time at the beginning of a charge cycle. Alternatively, the discharge time parameter is calculated during operation of the battery system and the equalization of the cells takes place in operation based on the discharge time values.

It is now the object of the present invention to provide an apparatus and a method for operating such a device, which the above avoid said disadvantages and ensures the best possible life of the individual memory cells in such a device for storing electrical energy with minimal effort.

This object is achieved by the features mentioned in the characterizing part of claim 1. A method according to the invention is indicated by the features in the characterizing part of claim 7.

Further advantageous embodiments of the device and the method are specified in the dependent subclaims.

In the device according to the invention for storing electrical energy, it is provided that the active

Zeilspannungsausgleich is extended by a timer unit, which closed each switch after closing for a predetermined time

closed. This ensures that each individual memory cell, after it has exceeded a predetermined voltage, with the switch closed always imperative for a predetermined time on the electrical

Resistance is discharged. The voltage present in this memory cell is thus reduced over a longer period of time. This can now lead in particular to the fact that in the next charging cycle for the device for storing electrical energy, precisely this one memory cell does not again reach the upper limit of its voltage and must be limited in its voltage via a renewed closing of the switch. On the contrary, the integration of a time function by the at least one time switching unit leads to a leveling of the voltage level of precisely this memory cell with respect to the other memory cells. Even in their voltage lowered memory cells are then increased in voltage again, so that in this way takes place a true cell voltage compensation in the literal sense.

This is also in dynamic applications, for example in a

Hybrid drive, in which by starting a large part of the stored electrical energy in the device is removed, and the next In turn, braking energy is stored in the device, a renewed exceeding the upper limit voltage of the affected memory cell avoided with high probability. This can be safely and reliably prevented with a very simple means that individual memory cells several times in a row reach the area of the overvoltage, what their

Life would affect massively. Rather, it comes through the inventive structure of the device very quickly to an adjustment of the cell voltages of the individual memory cells with each other, so reach even with highly dynamic charging and discharging much less memory cells in the problematic range of overvoltage.

In principle, the device can be represented in any memory cells which are typically connected in series with one another or in blocks in parallel and then in series with one another. In principle, accumulator cells are conceivable, for example, in the case of lithium-ion technology, the exceeding of a predetermined maximum voltage of the single cell has serious disadvantages and can possibly also lead to chemical and / or thermal damage to the memory cell up to an overpressure in the memory cell. For safety reasons, this pressure would have to escape via a pressure relief valve, which not only damages the memory cell in its lifetime, but directly destroyed. But also with other memory cell types,

In particular, in supercapacitors, exceeding the predetermined maximum voltage serious disadvantages and reduces their

Lifespan significantly.

According to a particularly favorable and advantageous development of

Device according to the invention, it is provided that the memory cells are at least partially formed as supercapacitors.

This structure of the device for storing electrical energy

exclusively or at least partially with supercapacitors has the advantage that this over any form of batteries or batteries as Memory cells with significantly higher currents at much lower internal resistance can be charged. This is the example

Storing very large amounts of energy, which occurs for example when braking a commercial vehicle in a very short time, possible with relatively low losses. In addition, such supercapacitors are much less complicated to use and maintain than, for example, lithium-ion batteries, since they can be discharged to 0 volts without any problem and are then available to the device for maintenance without voltage.

According to a very favorable and advantageous development of

According to the invention, it is further provided that the switching unit, the electrical resistance, the switch and the timer unit for each

Speicherzeire are formed as an independent arranged in the region of the memory cell electronic unit.

This purely decentralized structure offers the possibility of discharging individual memory cells over a predetermined threshold voltage over the resistor for a predetermined time. He is doing comparatively easy and compact to build. About an integrated circuit and a suitable resistor can be realized on a corresponding board of very small size for each memory cell, a corresponding structure. This can then be arranged in the area of the individual memory cell and works completely independently. By reacting for each individual memory cell in the manner described above, the device as a whole can be correspondingly charged or discharged without fear of damage, in particular damage to the individual memory cells that occurs several times in succession as a result of an overvoltage. Since a charging and discharging process is typically always controlled on the basis of the total voltage of the device, a balanced voltage level between the individual memory cells installed in the device occurs automatically in the device according to the invention over time, without this being the case requires a control of the individual memory cells from outside the device. Thus, the inventive structure of the device without a single cell monitoring, a cabling of each individual memory cell and / or a complex connected to each of the cells data bus system can get along. The structure of the device according to the invention is therefore

correspondingly easy. He can also use any inverter and

The same can be combined because besides loading and unloading the

Device no active control of the same is necessary. The

The device according to the invention thus operates autonomously and can be described as

integrate standardized components in different drive trains, without necessarily being integrated in their control electronics.

In a particularly advantageous embodiment of the invention

Device is the predetermined time in dependence of the voltage of the respective storage cases changeable. This variant of the device according to the invention offers the possibility of allowing the bypass current to flow for different amounts of time by adapting the predetermined time to each of the memory cells. The dependency can in particular be continuous or based on stages

be adjusted automatically according to the occurred overvoltage, for example in the respective electronics unit. This results automatically for each individual memory cell according to their voltage

variable value for the given time. Thus, the bypass current can flow according to this predetermined time and thus limit the exceeding of the limit voltage by targeted reduction of the overvoltage.

In the inventive method for operating such

Device is now provided that the charged into the device or removed from the device energy is controlled by a control device. This control takes place, in particular during charging, within predefined voltage limits, which, however, do not define voltage limits for each of the individual memory cells, but voltage limits of the device

Whole are. In addition, the voltage of at least some memory cells monitored in the device. This monitoring results in a maximum deviation of the detected voltage values among one another. As soon as this maximum deviation of the detected voltage values exceeds a predetermined limit value, during the next charging cycle the predetermined upper voltage limit during charging is activated or even slightly exceeded.

In the method according to the invention, therefore, this intentional activation of the upper voltage limit of the device as such safely leads to an exceeding of the limit voltage of some of the memory cells, since these, if a correspondingly large deviation between the individual

Memory cells is already at such a high voltage level that when charging the upper limit voltage of some single cells is exceeded. In this or these individual memory cells, which with the

inventive design of switch, resistor and time switching unit are provided, then it comes to a response of the switch, so that in this memory cell for a predetermined time, a discharge current flows across the parallel to the memory cell arranged electrical resistance. On the basis of the method according to the invention, it can therefore be known that some of the

Memory cells deviate very much from the voltage level of other memory cells, deliberately activation of the switches and the time switching units of the upwardly diverging memory cells can be achieved. There is no

Single cell monitoring or no control of the individual memory cells necessary, but it is only approached the upper voltage limit when loading the entire device or slightly exceeded. The fact that a current flows over the time switching units for a certain time over the parallel connected to the critical memory cells resistors, it comes "automatically" to an approximation of the voltage levels of the individual interconnected memory cells.

According to a very advantageous variant of the method according to the invention, it is further provided that for the after such a charging cycle, in which the predetermined upper voltage limit when charging controlled or slightly was exceeded, the upper voltage limit is no longer controlled for the subsequent charging cycles during the time specified by the timer unit time. This means that during the time in which the discharge due to the actuation of the switches and the keep closed the switch for the time specified by the timer unit for those cells which have reached an overvoltage, the upper voltage limit for charging the entire device no longer approached. The voltage is thus kept lower in order to give the individual memory cells of the device time to level their voltage levels without disturbing them by re-triggering the threshold switches. It makes sense for the entire device predetermined voltage slightly below the upper

Limit, for example, to 80 or 90% of this limit for the known, since fixed time, in which the closed switches are kept closed set up. The memory cells, which previously had a high

Voltage experienced are thus lowered in voltage accordingly and adapted to the voltage level of the other memory cells. As a result, the affected memory cells in the following

Charging cycles spared accordingly, which has a positive effect on their lifespan.

In a particularly favorable embodiment of the method according to the invention, it is provided that the voltage of all memory cells is detected by combining the memory cells into at least two blocks whose block voltages are detected and then used as voltage values. With this construction of at least two blocks, depending on the number of

Memory cells but typically also more blocks, it can be achieved that as soon as one of the blocks has a corresponding voltage difference with respect to the others, a leveling of the voltage values of the individual memory cells by the coming charging cycle is initiated via the above-described method. The monitoring of memory cells combined in blocks, for example eight to twelve of the individual memory cells as a block, is considerably less complicated than this Single cell voltage monitoring would be. In contrast to the possibility set out above in principle of monitoring only individual memory cells, in block-by-block monitoring it can also be avoided that individual cells, as they are not monitored by chance, have a corresponding overvoltage and are damaged, which in turn damages the entire system Device would entail.

In a further very advantageous embodiment of the invention

Method is provided that the device for storing

electrical energy is used as traction energy storage in an at least partially electrically powered vehicle. This preferred

Application form of the device and the method in an electric vehicle or in particular a hybrid vehicle, has the particular advantage that in such applications very dynamic charging and discharging cycles occur, which, as already described, to a considerable

Can cause stress on the individual memory cells of the device. Due to the inventive structure of the device and the method according to the invention, precisely this can be prevented, so that the advantages already described above when used as traction energy storage in a

Electric vehicle or hybrid vehicle are particularly advantageous advantage.

Further advantageous embodiments of the device according to the invention and / or the method according to the invention will be apparent from the

Embodiment, which is described below with reference to the figures.

Showing:

FIG. 1 shows an exemplary construction of a hybrid vehicle; and

Figure 2 shows a detail of the structure of the device for storing electrical energy. 1 shows an example of a hybrid vehicle 1 is indicated. It has two axles 2, 3 each with two wheels 4 indicated by way of example. The axle 3 is intended to be a driven axle of the vehicle 1, while the axle 2 merely travels in a manner known per se. To drive the axle 3, a transmission 5 is shown by way of example, which is the power of a

Internal combustion engine 6 and an electric machine 7 receives and directs in the area of the driven axle 3. In the drive case, the electric machine 7 alone or in addition to the drive power of

Internal combustion engine 6 drive power in the region of the driven axle 3 and thus drive the vehicle 1 or support the drive of the vehicle 1. In addition, when braking the vehicle 1, the electric machine 7 can be operated as a generator, so as to recover the braking power and store it accordingly. For example, when used in a city bus as a vehicle 1 for

Braking from higher speeds, which will certainly be at a maximum of about 70 km / h in a city bus, a sufficient

To be able to provide energy content in this case, an apparatus 8 for storing electrical energy must be provided which a

Energy content of the order of 350 to 700 Wh has. In this way, it is also possible to convert energies which, for example, originate from such a speed during a braking process of about 10 seconds, into electrical energy via the electric machine 7, which will typically have a magnitude of approximately 150 kW, and these in the device 8 save.

For driving the electric machine 7 and for charging and discharging the device 8 for storing electrical energy, the structure according to FIG. 1 has an inverter 9, which is designed in a manner known per se with an integrated control device for the energy management. About the inverter 9 with the integrated control device is doing the

Energy flow between the electric machine 7 and the device 8 for Storage of electrical energy coordinated accordingly. The controller ensures that when braking in the area then

as far as possible in the device 8 for storing the electrical energy generated generator-driven electric machine 7

is stored, wherein a predetermined upper voltage limit of the device 8 may generally not be exceeded. In the drive case, the control device in the inverter 9 coordinates the removal of electrical energy from the device 8 in order to drive the electric machine 7 by means of this extracted power in this reverse case. In addition to the hybrid vehicle 1 described here, which may be for example a city bus, a comparable structure would of course also be in a pure

Electric vehicle conceivable.

The device 8 for storing electrical energy can be constructed in a variety of ways. In principle, various types of device 8 for storing electrical energy are conceivable. Typically, this will be constructed so that a plurality of memory cells 10

are typically connected in series in the device 8. These

Memory cells 10, which can be seen in FIG. 2, can thereby

Accumulator cells and / or supercapacitors, or any combination thereof. For the embodiment shown here, the memory cells 10 should all be designed as supercapacitors, which are to be used in a single device 8 for storing electrical energy in the vehicle 1 equipped with the hybrid drive. The structure can preferably be used in a commercial vehicle, such as a bus for Stadtwnahverkehr. This is due to frequent starting and braking maneuvers in conjunction with a very high

Vehicle mass achieved a particularly high efficiency of storage of electrical energy through the supercapacitors, since comparatively high currents flow. Since supercapacitors as memory cells 10 have a much lower internal resistance than, for example, accumulator cells, they are to be preferred for the exemplary embodiment described in more detail here. As already mentioned, the memory cells 10 can be seen in FIG. Only three of the series-connected memory cells 10 are shown. In the above embodiment and a corresponding electrical drive power of about 100 to 200 kW, for example, 12O kW, this would be in a realistic design about 150 to 250 memory cells 10. If these as supercapacitors with a current upper voltage limit of about 2, 7 V per supercapacitor and a capacity of 3000 Farad are formed, would be a realistic application for the hybrid drive of a city bus is given.

The problem with the use of such memory cells 10 in the device 8 for storing electrical energy, it is now that, as mentioned above, in particular due to manufacturing tolerances, individual memory cells 10 in their voltage level of a mean voltage level of the device 8 and against the voltage of others Memory cells 10 may differ. Therefore, in spite of the charging voltage predetermined as a whole for the device 8, in the region of precisely this voltage cell 10, which deviates upward in voltage versus the other memory cells 10, the limit voltage predetermined for the respective type of memory cells 10 is exceeded. It is particularly disadvantageous if individual of the

Memory cells 10 exceed a maximum predetermined voltage, in the above example, the 2.7 V per single supercapacitor, comparatively often. Each exceeding of this limit voltage significantly reduces the lifetime of the individual memory cell 10 to be achieved. A reduced lifetime of the individual memory cells 10 leads after a certain

Operating time to a failure of the corresponding memory cell 10, which then, at least in the medium term, to a failure of the entire device 8 for

Storage of electrical energy will result. Therefore, it is necessary to achieve a long service life, especially in the very dynamic charging and discharging cycles, as they occur in a city bus, if possible prevent the individual memory cells 10 from exceeding this upper limit voltage frequently or at least frequently in succession.

As shown in FIG. 2, each individual one of the memory cells 10 has an electrical, ohmic resistor 11 connected in parallel with the respective memory cell 10. This is connected in series with a switch 12 in parallel with each of the memory cells 10, in this case in parallel with each of the supercapacitors 10. The switch 12 is designed as a threshold value switch and is controlled by a corresponding switching unit 13, which essentially contains two functionalities. Thus, the switching unit 13 comprises a

Voltage monitoring U of the supercapacitor 10. As soon as it exceeds an upper limit voltage, the switch 12 is closed so that a current can flow from the supercapacitor 10 via the resistor 11. Thus, the charge in it and thus also the voltage is reduced accordingly, so that a renewed exceeding of the Grenzspan voltage value in the same supercapacitor 10 as before, is avoided.

In order to prevent now, as soon as the voltage under the

Limit voltage value drops, the switch 12 is opened again and thus a very high voltage in the respective supercapacitor 10 remains, a time switching unit T is also provided. In a pure circuit via the voltage detection U of the switching unit 13, the switch 12 would be opened again after falling below the limit voltage. The supercapacitor 10 would then continue to be at a very high voltage level. If the device 8 is charged again, precisely this supercapacitor 10 would immediately be charged again beyond the voltage limit, which then leads to a renewed closing of the switch 12. By the integration of the timer function T, which the switch 12, once it has been closed via the voltage detection U, for a predetermined time

holds closed, more charge from the supercapacitor 10 is degraded, as without the timer unit T. Thus, the voltage in the

Supercapacitor 4 reduced so that this after a discharge, for example, by a start of the vehicle 1 and a thereafter

re-loading the device 8 does not return to above the upper limit voltage during braking. At best, others are now

Supercapacitors 10 are in a correspondingly high voltage range and learn the procedure just described in turn. Overall, it comes with the integration of the time switching function T over the operating time away to a rapid equalization of the voltages of the individual

Supercapacitors 10 of the device 8.

The time switching unit T can be designed in particular so that a fixed time of, for example, a few minutes is given. Together with the size of the respective individual memory cell 10 and the value of the electrical resistance 11, this results in a corresponding discharge. There are

Discharges of the order of 3 - 5% of the nominal charge of the

appropriate supercapacitor 10 makes sense. When reloading is then achieved that this supercapacitor 10 is not the default again

Exceeds limit voltage. As a result of at least preventing one of the supercapacitors 10 from repeatedly exceeding the limiting voltage several times in a very rapid change, a significant increase in the life of the supercapacitors 10 and thus of the device 8 is already achieved. If the above-mentioned numerical example is repeated, the voltage of the corresponding supercapacitor would have decreased by about 0.1 V in five minutes at a leakage current of 1 A. In a leakage current of 250 mA accordingly in about 20 minutes. Depending on the size of the memory cell 10 and the possible leakage current, which can be passed through the resistor 11, this results in a period of about 5 to 20 minutes, over which the switch 12 is kept closed via the time switching unit T. At other magnitudes of the resistors, the currents and the used

Memory cells 10, this value can of course be adapted analogously.

The thus constructed device 8 for storing electrical energy can therefore also be used in highly dynamic charging and discharging cycles, without the service life of the memory cells 10 being correspondingly reduced by unnecessarily high voltages in the region of the memory elements 10.

In this case, the structure of the switching unit 13, the electrical resistance 11, the switch 12 and the time switching unit T can be realized as an integrated electronic unit 14 so that it is constructed independently for each of the memory cells 10. For this purpose, a small integrated circuit is generally sufficient, which monitors the voltage U in the memory cell 10 accordingly and actuates the switch 12, which is integrated, for example, as an electronic switch 12 into the component. The resistor 11 can then be placed on this mini-board in a conventional manner. Since the time switching unit T typically keeps the switch 12 closed for a predetermined time after it has been activated due to the voltage U, this time can also be permanently integrated in the time switching unit T or the integrated electronic unit 14. This can be done for example by programming a fixed time in an integrated circuit. It would also be conceivable to solve this by circuitry in that in the electronics unit 14 via a suitable component,

In particular, a capacitor at an output of the switching unit 13 this time is fixed. The structure can thus be realized very easily, since no activation of the electronic unit 14 from outside the device 8 is necessary. The device 8 is rather automatically for a

Cell voltage compensation, which also allows highly dynamic charging and discharging ensure. This structure with decentralized electronic units 14 is very simple and can be realized completely self-sufficient. An activation of the device 8 is then only necessary as a whole, for example during

Discharging and especially when loading within a given

Voltage window.

In a very favorable variant, however, it may be provided that the

Voltage of some of the memory cells 10, in particular of a plurality of each connected to blocks memory cells 10, is detected. This voltage value from the interior of the device 8 then, for example, the control device in the inverter 9 can be made available. There the tensions between each other are compared. If one notes that a very large deviation of the voltage values of the individual memory cells or cell blocks occurs, it must be assumed that some of the memory cells 10 or the blocks of memory cells 10 will come across the limiting voltage in the near future. This can now be actively triggered by charging the device 8 at the next charging cycle via the control device in the converter 9 with a voltage which is at the upper limit or slightly above the upper voltage typically specified for charging. In this way, it is possible to consciously initiate a minimum exceeding of the threshold voltage in the memory cells 10 which deviate very much upwards.

Due to the integrated electronic unit 14 with the time switching unit T can then by this slight exceeding of the threshold voltage a

Leveling of the voltages within the device 8 between the individual memory cells 10 are triggered from outside the device 8, without the need for a targeted control of single cells or blocks of single cells within the device 8 would be necessary.

This applies accordingly to accumulator cells, in particular accumulator cells in lithium-ion technology.

The hitherto based on the supercapacitors 10 in the device. 8

Comparatively generally described embodiment will now be

It should be pointed out that the values apply very concretely for the numerical example presented here and for different capacities or future developments with regard to the maximum stresses of

Supercapacitors must be adjusted analogously.

Claims

claims

1. Device for storing electrical energy with

1.1 multiple memory cells;

1.2 each one electrical resistance parallel to each of the memory cells;

1.3 each a switch in series with the electrical resistance and parallel to the memory cell; uηd

1.4 at least one switching unit which closes each of the switches as soon as the memory cell located parallel to this switch exceeds a predetermined voltage;

characterized in that

1.5 at least one time switching unit (T) is provided, which each

closed switch (12) keeps closed after closing for a predetermined time.

2. Apparatus according to claim 1, characterized in that the

Memory cells (10) are at least partially formed as supercapacitors.

3. Apparatus according to claim 1 or 2, characterized in that the memory cells (10) at least partially as accumulator cells,

especially in lithium-ion technology, are formed.

4. Device according to claim 1, 2 or 3, characterized in that the switching unit (13), the electrical resistance (11), the switch (12) and the time switching unit (T) for each memory cell (10) as independent in the field of Memory cell (10) arranged electronic unit (14) are formed.

5. Apparatus according to claim 4, characterized in that the

predetermined time in the region of the electronic unit (14) via a suitable component, in particular a capacitor, is fixed.

6. Device according to one of claims 1 to 4, characterized in that the predetermined time in dependence of the voltage of the respective memory cell (10) is variable.

7. Device according to one of claims 1 to 6, characterized in that all memory cells (10) of the same type are formed and interconnected in series.

8. A method of operating a device according to one of claims 1 to 7,

characterized in that

8.1 loaded in the device (8) and out of the device (8)

extracted energy is controlled by a control device; in which

8.2 the control device, in particular when loading, the device (8)

loads or discharges within specified voltage limits; in which

8.3 the voltage of at least some memory cells (10) is detected, from which a maximum deviation of the detected voltage values with one another is determined; which

8.4 in the next charging cycle, the predetermined upper voltage limit is activated during charging or slightly exceeded when the maximum deviation exceeds a predetermined limit value.

9. The method according to claim 8, characterized in that for the after such a charging cycle, in which the predetermined upper

Voltage limit was activated during charging or slightly exceeded, for the subsequent charging cycles during by the

Time switching unit (T) predetermined time, the upper voltage limit is no longer activated.

10. The method according to claim 8 or 9, characterized in that the

Voltage of all memory cells (10) is detected by the memory cells (10) are combined to form at least two blocks whose

Block voltages detected and then used as voltage values.

11. The method according to claim 8, 9 or 10, characterized in that the device (8) for storing electrical energy as

Traction energy storage in an at least partially electric

driven vehicle is used.

12. The method according to any one of claims 8 to 11, characterized in that as controller a converter (9) or in a converter (9) integrated control is used.

13. The apparatus of claim 11 or 12, characterized in that the loading by recuperation of braking energy via a then used as a generator electric drive machine (7).

14. The method according to any one of claims 8 to 13, characterized in that as a vehicle (1) a commercial vehicle, in particular a bus in city / local traffic, is used.