EP2471157A2

EP2471157A2 - System for storing electrical energy

Info

Publication number: EP2471157A2
Application number: EP10747410A
Authority: EP
Inventors: Conrad RÖSSEL
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2009-08-27
Filing date: 2010-07-16
Publication date: 2012-07-04
Also published as: US20120229099A1; KR20120073247A; WO2011023265A2; RU2012111677A; CN102754300A; WO2011023265A3; DE102009039161A1

Abstract

A system for storing electrical energy comprises a plurality of storage cells with respective operating voltages. An electrical consumer and a switch member are serially connected in parallel to a storage cell. The switch member is closed when a threshold voltage is reached or exceeded. The system further comprises a control device which is adapted to adjust the threshold voltage depending on a voltage value determined from operating voltages of the plurality of storage cells. The invention further relates to a storage cell for storing electrical energy and to a method for controlling a system deigned to store electrical energy.

Description

System for storing electrical energy

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

Systems for the storage of electrical energy, and in particular for the storage of electric traction energy in electric vehicles or

especially in hybrid vehicles, are known from the general state of the art. Typically, such systems for storing electrical energy comprise individual memory cells, which are interconnected, for example, in series and / or in parallel electrical connection with one another.

In principle, different types of accumulator cells or capacitor cells are conceivable as memory cells. Due to the comparatively high

Quantities of energy and in particular the high performance of the storage and extraction of energy when used in powertrains of

Vehicles and especially commercial vehicles occur, are preferably used as memory cells with sufficient energy content and high performance. For example, accumulator cells in lithium-ion technology or, in particular, memory cells in the form of very powerful double-layer capacitors can be used. These capacitors are also referred to in the art as supercapacitors, supercaps or ultracapacitors. Regardless of whether

Supercapacitors or accumulator cells of conventional type with high

Energy content are used in such structures of a plurality of memory cells, which can be connected in total or in blocks in series with each other, the voltage of the individual memory cell due to the design limited to an upper voltage value or a threshold voltage. If this upper voltage value is exceeded, for example when charging the system for storing electrical energy, the life of the memory cell is generally drastically reduced. Due to given manufacturing tolerances the individual give way

Memory cells in their properties, for example in terms of

Self-discharge in practice is typically slightly different. As a result, a slightly lower operating voltage may result for individual memory cells in operation than for other memory cells in the system. However, since the maximum voltage for the entire system generally remains the same and the maximum total voltage, especially during charging, is the typical driving criterion, this inevitably leads to others

Memory cells, which are connected in series with the memory cells with lower operating voltage, have a slightly higher voltage and at

Charging then beyond the allowed individual maximum voltage limit to be charged. Such overvoltage leads, as already mentioned above, to a considerable reduction in the possible lifetime of these individual memory cells and thus also of the entire system for storing electrical energy.

On the other hand, in their voltage greatly reduced memory cells can be reversed in the system for storing electrical energy in cyclic operation, which also drastically reduces the life.

To address this problem, the general state of the art essentially knows two different types of so-called

Cell voltage balancing. The generally common terminology of "cell voltage compensation" is somewhat misleading here, but not here

Strains or, more precisely, energy contents of the individual memory cells are compensated for each other, but the cells are reduced with high voltages in their too high voltages. Because the

Total voltage (s) of the system for storing electrical energy remains constant, however, can be increased by the so-called cell voltage compensation a lowered in voltage cell over time in their voltage, so that at least the risk of polarity reversal is excluded. In addition to a passive voltage compensation, in which an electric

Resistor is connected in parallel to each individual memory cell and thus a constant unwanted discharge and also a heating of the system for storing electrical energy takes place, is also an active

Tension compensation used. In this case, in addition to the each memory cell connected in parallel resistor is an electronic

Threshold switch connected in parallel with the memory cell and in series with the resistor. This construction, also referred to as bypass electronics, always allows a current to flow when the operating voltage of the cell is above a predetermined threshold voltage. As soon as the voltage of the individual memory cell falls back into a range below the predetermined threshold voltage, the switch is opened and no current flows. Due to the fact that the electrical resistance across the switch is overridden whenever the voltage of the individual memory cells is below the predetermined limit, an unwanted discharge of the entire system for storing electrical energy may also occur

be largely avoided. Also a constant unwanted

Heat development in this approach is the active one

Cell voltage compensation no problem.

However, this active cell voltage compensation does not actually compensate the individual voltages of the cells with one another, but when the threshold voltage is exceeded, the memory cell is discharged with a small bypass current in order to limit the overshoot by slowly reducing the overvoltage. The bypass current only flows until the system for storing electrical energy is discharged again, as this falls below the corresponding voltage limit and the switch is opened again. This arises in particular in applications with cyclical operation, such as hybrid drives, since in these applications, the threshold voltage for the individual memory cell is only very short or even for a long time not achieved, if lack of recuperation and strong Boost operation of the memory is not fully loaded. This prevents operation of the Zeilspannungsausgleichs and in particular carries the risk of over-discharge or polarity reversal of individual memory cells with low operating voltage while the other cells are operated with too high voltage.

The life of the system for storing electrical energy is in the described hybrid drives and especially in hybrid drives for commercial vehicles such as buses in urban / suburban traffic of crucial importance. Unlike conventional powertrains in the power class suitable for such applications, the system for storing electrical energy represents a significant portion of the cost of the hybrid drive. Therefore, it is particularly important that very high lifetimes can be achieved in such applications.

It is therefore an object of the invention to provide a system for storing electrical energy, which at least partially avoids the disadvantages described and, in particular, provides for efficient cyclic voltage compensation in a cyclical mode of operation.

This object is achieved by a system and a method having the features of the independent claims. Further embodiments of the invention are specified in the dependent claims. In particular, the invention provides a system for storing electrical energy, comprising a plurality of memory cells, each having a

Operating voltage, wherein parallel to a memory cell

electrical load and a switching element are arranged in series with the consumer, wherein the switching element is closed when reaching or exceeding a threshold voltage. The system is characterized in that it comprises a control device which is adapted to the Set threshold voltage as a function of a voltage determined from operating voltages of the plurality or all memory cells voltage value.

According to the invention, it is thus possible to set the threshold voltage of, for example, each of the memory cells by means of the control device to a voltage value which can be derived from the instantaneous operating state of the memory cells, ie from their operating voltages. In the majority of

Memory cells may, for example, be a module or a submodule of a larger memory system or the entirety of all memory cells of an electrical energy storage system. The voltage value determined from operating voltages of the plurality or also of all memory cells may be, for example, the average

Cell voltage or to the average cell voltage changed by a certain fixed or variable value. Such a dynamic adjustment of the threshold voltage as a function of the instantaneous state of charge of the system for storing electrical energy or a module of the system, for example, always set the threshold voltage 0.1 V above the currently prevailing average voltage. Such a tracking of the threshold voltage causes individual memory cells are discharged with increased cell voltage, regardless of the state of charge of the module or the entire system.

The amount of voltage added to the average voltage value may be a fixed amount. He can also, for example, in

Depending on the absolute total voltage or depending on the current operating mode or depending on environmental or other parameters are selected. For example, it may be provided that a comparatively large voltage value is added at an overall low voltage level of the memory system, whereas a smaller amount of voltage is added in the vicinity of the upper absolute threshold voltage limit value. This ensures that too little energy is used for cell voltage balance at a low overall voltage level while in the voltage range near the maximum voltage of the single memory cell Exceeding the same is prevented. In addition to the setting of

Threshold voltage in response to operating voltages of the plurality of memory cells may also be provided that additionally one of the

Operating voltages of the plurality of memory cells independent

Threshold voltage value is used, which ensures an exceeding of a maximum operating voltage regardless of the voltage derived from the plurality of memory cells voltage value. Again, this absolute upper maximum threshold voltage value may in turn depend on the operating state of the

Entire system, individual modules or even the currently required requirement profile to the storage system or of environmental and other system parameters such as an ambient temperature or a

System temperature dependent.

In one embodiment of the system according to the invention, a central control device may be provided for a plurality of memory cells. Thus, with regard to the definition of the threshold voltage, one or more centrally controlled memory modules can be formed whose threshold voltage is uniform within the module but, for example, for each module

is different controllable.

In a further embodiment according to the invention, the control device is set up to form a common voltage value from a plurality of operating voltages of memory cells and to set the threshold voltage of the plurality of memory cells to a value into which the common voltage value is received. In addition to the already explained possibility of forming an average value of the operating voltage values of the plurality of memory cells and this in itself or by a fixed

or add variable component added, other parameters can be included in the calculation of the threshold voltage in addition to these operating voltage values per se. For example, the current

Power delivery or intake profile, a past or a past future expected performance profile in the calculation of the threshold voltage value.

In the system according to the invention can be provided that the

Control device sets the threshold voltage at certain intervals. Such a temporal scanning of the system or the detected module allows for a low control effort, a still improved voltage control of the memory cells. It can, for example, the

Time interval between two scans are adapted to the profile of the total voltage of the system or the module or to the height of the total voltage.

Alternatively, it can be provided in one embodiment that the

Control means continuously controls the threshold voltage. Such a real-time adjustment of the threshold voltage ensures compliance with the specified threshold voltage at all times and thus directly reduces any possibly too high voltage of individual memory cells. The

Adjustment of the threshold voltage value can in particular be realized not only as a control, but in particular also as a closed control loop.

A likewise advantageous embodiment of the invention provides that the switching element has a control input, via which the threshold voltage is controlled. By means of the control input, a control of the switching element via the possibly centrally arranged control device is made possible.

A preferred embodiment provides that the control device is connected to the memory cell by means of a bus line. This enables efficient driving of a plurality of memory cells, wherein not only the transmission of a changed threshold voltage value from the

Control device to the memory cell is possible, but also the transmission of the current operating voltage value from the memory cell to the Control device. This allows the creation of an accurate image of the storage state of the electrical energy storage system

or the module of the system detected. In a simple embodiment, the load is a resistor, but alternatively, other means for dissipating electrical energy, such as by means of directed radiation, may be provided. The memory cell can be designed as a so-called supercapacitor, ie as a double-layer capacitor. In a simple embodiment, the switching element may be a threshold value switch. The threshold of the threshold switch is then adjustable via the control device by means of a signal or data bus. In particular, the control input of the switching element can be used.

The control of the switching element by a control device may comprise a contactless transmission device, in particular a buffer amplifier. The isolation amplifier can be realized, for example, by an optocoupler or by an inductive coupling and thus enable galvanically separated from the memory cells control of the switching elements. In this case, either the threshold voltage directly to the memory cell or a

Actuating signal for the switching element to be transmitted.

The above-mentioned object is also achieved by a memory cell for

Storage of electrical energy with an arranged parallel to the memory cell electrical load and a switching element in series with the consumer, wherein the switching element is closed when reaching or exceeding a threshold voltage. According to the invention, it is provided that the switching element has a control input for controlling the threshold voltage. By means of the control input, the instantaneous operating voltage of the memory cell and possibly arranged in a further module

Memory cells supplied to a central control device, processed there and based on the detected operating voltages, the threshold voltage of

Memory cell via the control input are set accordingly. The above-mentioned object is also achieved by a method for controlling a system for storing electrical energy with a plurality of memory cells, each having a memory voltage, wherein parallel to each memory cell, an electrical load and a switching element are arranged in series with the consumer, with the steps of charging the memory cells, comparing the operating voltage of a memory cell with a threshold voltage and the closing of the switching element, if the operating voltage reaches or exceeds threshold voltage.

According to the invention, it is provided in the method that the

Threshold voltage is set in response to one of operating voltages of the plurality of memory cells enabled voltage value.

Further advantageous embodiments of the system according to the invention, the memory cell according to the invention and / or the method according to the invention will become apparent from the exemplary embodiment, which is described in more detail below with reference to FIGS.

Show it:

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

Figure 2 is a schematic representation of an embodiment of a

Systems 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. When driving, the electrical 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 using the vehicle 1 as a city bus for

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

To provide energy content, a system 10 for storing electrical energy must be provided in this case, which is a

Energy content in the order of 350 - has 700 Wh. This can be energies, which, for example, in an approximately 10 seconds long

Braking process arise from such a speed, via the electric machine 7, which will typically have an order of about 150 kW, convert into electrical energy and store them in the system 10.

For driving the electric machine 7 and for charging and discharging the system 10 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 manager. The energy flow between the electric machine 7 and the system 10 for storing electrical energy is correspondingly coordinated via the converter 9 with the integrated control device. The control device ensures that when braking in the area of then driven by a generator

electric power is stored 7 as far as possible in the system 10 for storing electrical energy, wherein a predetermined upper voltage limit of the system 10 may generally not be exceeded. In the drive case, the control device in the inverter 9 coordinates the removal of electrical energy from the system 10 in order to

reverse case, the electric machine 7 removed by means of this

Power to power. In addition to the hybrid vehicle 1 described here, as is For example, be designed as a city bus, a comparable structure would of course also conceivable in a pure electric vehicle.

Figure 2 shows schematically a section of an inventive

System 10 for storing electrical energy according to ejner embodiment. In principle, various types of system 10 for storing electrical energy are conceivable. Typically, such a system 10 is constructed such that a plurality of memory cells 12 are typically connected in series in the system 10. These memory cells may be accumulator cells and / or supercapacitor cells or any combination thereof. For the embodiment shown here, the memory cells 12 are all designed as supercapacitors, that is, as double-layer capacitors, which are used in a system 10 for storing electrical energy in the equipped with the hybrid drive vehicle 1. However, the structure can preferably be used in a commercial vehicle, for example a bus for city / local traffic.

This is achieved by frequent start-up and braking maneuvers in conjunction with a very high vehicle mass, a particularly high efficiency of storage of electrical energy through the supercapacitors, since comparatively high currents flow. Since supercapacitors as memory cells 12 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 12 can be seen in FIG. Only three of several serially connected memory cells 12 are shown. These form a first module A in a series of further non-imaged memory cells. Further modules B, C are also shown schematically. The exact number of modules varies depending on the purpose of the system. In the above embodiment and a corresponding electrical

Drive power of about 100 - 200 kW, for example, 120 kW, this would be in a realistic design a total of about 150 - 250 memory cells 12. If These are designed as supercapacitors with a current upper voltage limit of about 2.7 V per supercapacitor and a capacity of 3000 Farad, would be a realistic application for the hybrid drive

Given city bus.

As shown in FIG. 2, each of the memory cells 12 has an electrical load connected in parallel to the respective memory cell 12 in the form of an ohmic resistor 14. This is connected in series with a switching element 16 in parallel with each of the memory cells 12, in this case in parallel with each of the supercapacitors 12. The switch 16 is designed as a threshold value and has a control input 18. The switching element 16 comprises a voltage monitoring of the supercapacitor 12. As soon as the

Supercapacitor 12 exceeds an upper threshold voltage, the switch 16 is closed, so that via the resistor 14, a current from the

Supercapacitor 12 can flow. Thus, the charge in it and thus also the voltage is reduced accordingly, so that a renewed

Exceeding the threshold voltage value in the same supercapacitor 12 is avoided. Furthermore, a central control device 22 is provided. It is connected to a bus 20, to which in turn all memory cells 12 are connected. The control device 22 is adapted to by means of the bus 20 to the

Memory cells arranged switching elements 16 via the respective control input 18 to the effect that the threshold voltage for each memory cell 12 can be adjusted. Conversely, the control device 22 can detect the current operating voltage of each memory cell 12 via the bus 20 via the operating voltage detection of the switching member 16 by the control input, a corresponding signal or corresponding data to the bus 20 and thus to the controller 22 are forwarded.

Now occur during ongoing operation of the system 10, for example, by different internal resistance or constructive other differences between the memory cells 12 significantly different operating voltages, they are transmitted via the bus 20 to the controller 22. The control device 22 determines from these individual operating voltage values of the individual memory cells 12 in each case one average operating voltage value valid for one of the modules A, B or C. This will be one for the

Memory cells in the respective module A, B, C valid threshold voltage determined, for example, characterized in that the average value of a fixed or a dependent on the current operating mode voltage value amount is added. Alternatively, only the arithmetically determined

Average value to be used. This determined so

Threshold voltage value is transmitted from the controller 22 via the bus 20 to the memory cells 12 of the respective module. If individual memory cells 12 are now above this threshold voltage value, the respective switching element 16 closes and the charge located in the memory cell 12 is reduced via the ohmic resistor 14, which also reduces the operating voltage of the memory cell 12. If a larger number of memory cells 12 in the respective module A, B, C are above the threshold voltage determined from the average operating voltage value, the average value is reduced by discharging individual memory cells 12. From this reduced average value, the control unit 22 again calculates a lower threshold voltage, transmits these via the bus 20 and the control input 18 to the respective switching element 16. In this way, if necessary, iteratively results in an adaptation of the operating voltages of memory cells 12 to the average value of a module A, B, C.

In this way, a permanent synchronization of all the memory cells 12 substantially at any time, which allows maximum memory utilization without sacrificing the life of the system for storing electrical energy 10.

This is particularly advantageous when in applications with cyclic operation, such as in hybrid drives, a threshold voltage for the Overall system or the entire module is achieved only very briefly. It can also occur that this threshold voltage is not reached for a long time, because the memory is no longer filled up to the threshold voltage for lack of recuperation with simultaneous strong boost operation. The solution according to the invention solves this problem, since the switching element 16 designed as a threshold value switch has the appropriate function

Control input 18 with respect to its threshold, ie also during cyclic operation, for example in a Rekuperationsvorgang in which increases the voltage by energy storage is adjusted in real time, for example, the average cell voltage resulting from the total voltage and the number of all cells or from the average

Cell voltage of a module or submodule results.

Claims

claims

A system (10) for storing electrical energy, comprising

A plurality of memory cells (12), each having an operating voltage, wherein parallel to a memory cell (12) an electrical

Consumer (14) and a switching element (16) are arranged in series with the consumer (14) and wherein the switching member (16) is closed when reaching or exceeding a threshold voltage,

characterized in that

the system (10) comprises a control device (22) which is set up to set the threshold voltage as a function of a voltage value determined from operating voltages of the plurality of memory cells (12).

2. System according to claim 1, characterized in that a central control device (22) for a plurality of memory cells (12) is provided.

3. System according to claim 1 or 2, characterized in that the

Control device (22) is adapted to a common

Voltage value from a plurality of operating voltage values of

Form memory cells (12) and set the threshold voltage of the plurality of memory cells (12) to a value in which the

common voltage value is received.

4. System according to one of the preceding claims, characterized

in that the control device (22) sets the threshold voltage at specific time intervals.

5. System according to one of claims 1 to 3, characterized in that the control device (22) continuously controls the threshold voltage.

6. System according to one of the preceding claims, characterized

in that the switching element (16) has a control input (18) via which the threshold voltage is controlled.

7. System according to one of the preceding claims, characterized

in that the control device (22) is connected to the memory cell (12) by means of a bus line (20).

8. System according to any one of the preceding claims, characterized

characterized in that the consumer is a resistor (14) and / or the

Memory cell is a supercapacitor (12).

9. System according to one of the preceding claims, characterized

in that the switching element is a threshold value switch (16).

10. System according to one of the preceding claims, characterized

in that the control device (22) actuates the switching element (12) by means of a contactless transmission device.

11. System according to claim 10, characterized in that the contactless transmission device comprises a buffer amplifier.

12. System according to one of the preceding claims, characterized

in that the system (10) is used in an energy store, in particular for hybrid drives.

13. memory cell for storing electrical energy with a parallel to the memory cell arranged electrical load (14) and a switching element (16) in series with the consumer (14), wherein the switching member (16) is closed when reaching or exceeding a threshold voltage,

characterized in that the switching element (16) has a control input (18) for controlling the threshold voltage.

14. A method for controlling an electrical energy storage

designed system with a plurality of memory cells, each one

Operating voltage, wherein parallel to each memory cell, an electrical load and a switching element in series with the

Consumers are arranged, with the steps: - charging the memory cells,

Compare the operating voltage of a memory cell with a

Threshold voltage as well

Closing of the switching element, if the operating voltage the

Threshold voltage reached or exceeded, characterized by the step:

Adjusting the threshold voltage in dependence on a voltage value determined from operating voltages of the plurality of memory cells.