EP2612394A1

EP2612394A1 - System for storing electrical energy

Info

Publication number: EP2612394A1
Application number: EP11748894.0A
Authority: EP
Inventors: Conrad RÖSSEL
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2010-08-31
Filing date: 2011-08-12
Publication date: 2013-07-10
Also published as: RU2013108761A; WO2012028256A1; US20130141052A1; KR20130100276A; CN103053064A; DE102010036002A1

Abstract

The invention relates to a system for storing electrical energy, comprising a plurality of storage cells having an operating voltage, wherein an electrical consumer and a switching element in series with the consumer are arranged in parallel with a storage cell, and wherein the switching element is closed when a threshold voltage is reached or exceeded, wherein the system comprises at least one module comprising a plurality of storage cells. The invention is characterized in that the system comprises a control device, which is designed to associate a temperature with individual storage cells and a module voltage with the module and to influence the threshold voltage of the individual storage cells depending on the associated temperature, whilst maintaining the module voltage.

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 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 systems are designed to store electrical energy by means of individual memory cells, which are electrically interconnected, for example, in series and / or in parallel.

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

Quantities of energy and performance in the storage and removal of energy, when used in powertrains for vehicles, and in particular for commercial vehicles, are preferably used as memory cells memory cells with a sufficient energy content and high performance. These may be, for example, rechargeable battery cells in lithium-ion technology, or in particular but memory cells in the form of very powerful

Double-layer 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, in such structures of a plurality of memory cells, which are connected in series or in blocks in series, the voltage of the individual memory cell due to design limited to an upper voltage value or a threshold voltage. Will this upper voltage value, for example when loading the Systems for storing electrical energy exceeded, 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, self-discharge) in practice typically slightly different from each other. As a result, individual memory cells have a slightly lower voltage than others

Memory cells in the system. However, since the maximum voltage for the entire system generally remains the same, and this is the driving criterion that is typical for charging in particular, other memory cells inevitably have a somewhat higher voltage and at

Charging then beyond the permitted voltage limit to be charged. Such overvoltage, as already mentioned above, leads to a considerable reduction in the possible lifetime of these individual memory cells and thus of the 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.

In order to address these problems, the general state of the art essentially knows two different types of so-called

Cell voltage equalization, which are each centrally or decentralized. In a central electronics all components are for example in one

Combined control unit, while the decentralized structure of each one to two memory cells, the individual components are mounted, for example, on a small board for specifically this one to two memory cells. The common terminology of the cell voltage compensation is a little misleading here, since this does not compensate for voltages or more specifically energies of the individual memory cells with each other, but it is the cells with high voltages in their excessive voltages reduced. Because the Whole voltage (s) of the system for storing electrical energy remain constant, but by the so-called cell voltage compensation, a lowered voltage in their cell over time in their

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

In addition to a passive cell voltage compensation, in which an electric

Resistor is connected in parallel with each individual memory cell and thus a constant unwanted discharge and heating of the system for

Storage of electrical energy takes place, is also an active

Cell voltage compensation used. In addition, an electronic threshold value switch is 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 always overridden when the voltage of the individual memory cells is below the predetermined limit, an undesirable

Discharge of the entire system for storing electrical energy

be largely avoided. Also a constant unwanted

Heat development in this approach is the active one

Cell voltage compensation no problem. However, it is done by the active

Cell voltage compensation no real compensation of the individual voltages of the cells with each other, but when the threshold voltage is exceeded, the memory cell is discharged with a small bypass current to limit by a slow reduction of the overvoltage the crossing. The bypass current only flows until the system for the storage of electrical energy is discharged again, since in this case the corresponding

Voltage limit is exceeded and the switch is opened again. The lifetime of the system for storing electrical energy is at

Hybrid drives, and especially in hybrid drives for commercial vehicles, such as buses in urban / suburban transport, crucial. 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 hybrid propulsion. Therefore, it is particularly important that very long lifetimes be achieved in such applications.

In addition to the mentioned circumstance that the operating voltage of individual

Memory cells in the charge / discharge cycle unintentionally exceeds a threshold voltage, the operating temperature of the memory cell is another the

Life of critical influencing parameters. The lifetime, for example, of double-layer capacitors is highly dependent on the

Operating temperature and the applied voltage. In particular, when using energy storage devices when operating a hybrid vehicle, different effective cooling options prevail for the individual storage cells. For example, some memory cells or modules reach cooling air that has already cooled other memory cells or modules. Since memory cells are connected in series, the memory cells connected in series conduct the same current and thus also generate the same heat loss per memory cell. Due to the unavoidable differences in the cooling of the memory cells, different temperatures occur from memory cell to memory cell.

It is an object of the invention to provide a system for storing electrical energy, the highest possible life and a low

Probability of default has. 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. The system according to the invention has the advantage that the strong

temperature-dependent life of the storage cells is taken into account. As memory cells age faster, thereby rendering the entire memory system inoperative, while most of the memory cells having a lower level temperature history are still functional, the invention contemplates that the voltage of cells actually or expected to be higher Temperature are exposed, a lower voltage is assigned. This is achieved, for example, by lowering the threshold voltage of the cells in question. The temperature differences of the individual memory cells include the different effective cooling of the individual memory cells

due. For example, part of the memory cells receives cooling air, which has already been heated by another part of the memory cells. But since memory cells of a module are connected in series, each memory cell of the module generates approximately the same heat loss. Due to the inevitable differences in the cooling arise different

Memory cell temperatures. The lifetime of the memory cells is highly age-dependent. Memory cells that operate at a higher temperature level age faster and lead to one after their failure

Total failure of the module or memory, although the memory cells operated at a lower temperature level are still functional.

This is particularly important in applications of the storage system of high relevance, where high amounts of energy in a short time from the memory cells

be taken or submitted. This occurs, for example, in the

Recuperation of braking energy or during acceleration (Boost) on. These charge / discharge cycles cause a rapid release of large amounts of waste heat through which the storage cells heat up.

The onset at high temperatures aging effects such as

Decrease in capacitance and increase in internal resistance are markedly self-boosting in such applications with regularly high power requirements, such as those found in hybrid buses in city buses. As the internal resistance increases, the heat loss increases further, which in turn causes the cell to heat up even more at an already higher temperature, allowing it to age more quickly progressively.

The solution according to the invention solves this problem by the in the

Temperature medium cells maintain their mean voltage, the cells with higher temperature is assigned a lower voltage and the cells with a lower temperature a higher voltage. The voltage of the module remains unchanged.

The required voltage drops and the required

Voltage increases compared to the middle cells arise

for example, from the absolute temperature level and / or the

Temperature differences between the memory cells.

The temperatures assigned to the individual memory cells can

be determined for example by means of sensors on each memory cell.

A particularly preferred embodiment of the invention results from the fact that the temperatures assigned to the individual memory cells

model-based calculations are determined. There is no measurement of the current temperature, which eliminates the associated effort in terms of sensors, cabling and evaluation. It will instead

for example, from a thermal model and a simulation of the structure, from life models of the memory cells and / or empirically determined from experiments, the possible temperature distribution between the individual memory cells. This results in a largely predictable temperature distribution due to the arrangement of the memory cells in a module. This is determined, for example, by the position of the memory cell within the module, such as a peripheral or center position, by the position of the module relative to others

Modules, by the location within a parent assembly or other thermally relevant components or by the

Direction of flow of the memory cells or the module through the air flow provided for the cooling. The air flow may also be caused by the speed of the vehicle, for example.

It can be used for setting the voltage values of the individual cells

give different strategies.

It is possible to select a lower voltage load in advance for memory cells for which a high thermal load is to be expected, so that it is not necessary to wait until a corresponding cell temperature is reached and then counteract this by lowering the voltage, but it always does set a voltage level corresponding to an expected temperature of the cell.

But it can also be the temperature determination in addition to the current operating state, expected operating situations and / or on

Environmental data are supported. When using the memory in a hybrid vehicle, this would be, for example, city driving or / overland travel,

Functionality of the cooling, measured outside temperature, climate or height of the site, etc. In this way, even better for the aging of individual cells unfavorable constellation of voltage and temperature counteracted and thus a not exactly predictable aging can be avoided. The different voltages of the memory cells can by default of the control unit to the switching elements or control inputs of the

Threshold of the individual cells can be realized. It can

For example, a CAN bus system can be used.

Thus, a strong homogenization of the aging of all cells is achieved, resulting in an overall optimized life and utilization of the memory. Further advantageous embodiments of the system according to the invention and / or of the method according to the invention also emerge from the

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

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

Figure 2 is a schematic representation of an inventive

Embodiment of a system 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 axis 3 is

exemplified a transmission 5, which shows 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 area of the driven 3 axis 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, in a use in a city bus as a vehicle 1 for braking operations from higher speeds, which will certainly be at a maximum of about 70 km / h in a city bus, a sufficient

In this case, an energy storage system 10 having an energy content of the order of 350 to 700 Wh must be provided. This can also be done

Energies, which are incurred, for example, in an approximately 10 seconds of braking 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 management. In this case, the energy flow between the electric machine 7 and the system 10 for storing the electrical energy is correspondingly coordinated via the converter 9 with the integrated control device. The control device ensures that when braking in the region of the then regeneratively driven electric machine 7 resulting power is stored as much as possible in the system 10 for storing the electrical energy, wherein a predetermined upper voltage limit of the system 10 may not be exceeded in general. 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, to drive the electric machine 7 by means of this extracted power. In addition to the hybrid vehicle 1 described here, which For example, a city bus may be a comparable structure would of course also conceivable in a pure electric vehicle.

FIG. 2 shows a schematic detail of a system 10 according to the invention for storing electrical energy. 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 can accumulator cells and / or

Supercapacitors, or any combination thereof. For the embodiment shown here, the memory cells 12 are all designed as supercapacitors, that is to say as double-layer capacitors, which are to be used in a system 10 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 the 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.

As already mentioned, the memory cells 12 can be seen in FIG. Only three serially connected memory cells 12 are shown. In the above embodiment and a corresponding electrical

Drive power of about 100 to 200 kW, for example 120 kW, this would be in a realistic design a total of about 150 to 250 memory cells 12. If these 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 of a

Given city bus. FIG. 2 shows an embodiment of the inventive concept. The electrical energy storage system 10 includes a plurality of memory cells 12 connected in series. These are structurally summarized in a module 13. Each of the memory cells 12 has a parallel to the respective memory cell 12 connected electrical load in the form of an ohmic resistor 14. This resistor 14 is connected in series with a switching element 16 in parallel with each of the memory cells 12. The switch 16 is designed as a threshold value. The individual switches 16 are provided with a control input 18.

Each of the control inputs 18 is connected via lines to a bus system 20, such as a CAN bus system. To the bus system 20 is a

Control unit 22 connected. The control device 22 is likewise connected to the bus system 20, sends information to the control inputs 18 of the threshold value switch 16 and thus makes it possible, for example, to increase or decrease the triggering voltage, that is to say the threshold voltage of the threshold value switch 16. Another possible parameter which can be influenced via the control unit 22 for example, the open time of

Threshold switch 16. Furthermore, it is possible not only to send information to the control inputs via the bus system 20, but also to receive data of the memory cells 12. The data which can be interrogated by the memory cells 12 may be, for example, the instantaneous voltage of the memory cells 12. A possible embodiment provides to determine the cell temperature of the memory cells 12. In operation, in the preferred embodiment of FIG. 2, the control unit determines the individual temperatures of the memory cells from assumptions about the temperature distribution within the module or module

Memory. The assumptions may come from model-based calculations such as a thermal model of the structure, memory cell life models, and / or experiments. Furthermore, the control unit 22, the total voltage of the module or the memory and the voltages of the individual memory cells 12 are known.

During operation of the system 10, memory cells 12 which have an average temperature are preferably assigned an average voltage, for example 2.5 V, by the control unit 22. High temperature memory cells 12 are assigned a lower voltage, for example, 2.42V. Low temperature memory cells 12 are assigned a higher voltage, for example 2.55V. The different voltages for the individual

Memory cells 12 are communicated by the control unit 22 to the control inputs 18 of the threshold value switch 16 via the bus system 20. The voltage for the system 10, for example for a hybrid drive, remains unchanged by this measure. It is thus achieved a homogenization of the aging of all memory cells 12, which leads to an overall maximized service life and utilization of the memory 10.

Claims

claims

System (10) for storing electrical energy, comprising

a plurality of operating voltage having memory cells (12), wherein parallel to a memory cell (12) an electrical load (14) and a switching element (16) are arranged in series with the consumer and wherein the switching member (16) upon reaching or exceeding a

Threshold voltage is closed, wherein the system (10) comprises at least one module (13) comprising a plurality of memory cells (12),

characterized in that

the system (10) comprises a control device (22) which is set up to assign a module voltage to individual memory cells (12) and to assign a module voltage to the module (13) and, depending on the assigned temperature, suppresses the threshold voltage of individual memory cells

Retention of the module voltage to influence.

The system of claim 1, wherein the control means (22) comprises the

Memory cells (12) associated temperatures determined from model-based calculations.

System according to claim 1 or 2, characterized in that the associated temperature is an expected temperature of the memory cell (12), which relates in particular to the current operating state, to expected operating situations and / or environmental data.

System according to one of the preceding claims, characterized

characterized in that the control device (22) that the middle

Temperature of the module (13) and / or the temperature differences between the memory cells (12) determined.

5. System according to any one of the preceding claims, characterized in that the threshold voltage by a default of the control device (22) is variable.

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

characterized in that the switching member (16) remains closed after closing for a certain time.

7. A method for controlling a for storing electrical energy

designed system (10) having a plurality of arranged in a module (13) and an operating voltage having memory cells (12), wherein parallel to each memory cell (12) an electrical load (14) and a switching element (16) arranged in series with the electrical load are, with the steps:

Charging the memory cells (12),

Determining the temperature of individual memory cells (12) of the module (13), comparing the determined temperatures,

Lowering the operating voltage in memory cells (12) with high

Temperature and raising the operating voltage of memory cells (12) at low temperature while maintaining the module voltage.