DE102010051011A1 - Method for balancing voltage between individual cells of energy store for electric vehicle, involves discharging voltage of memory cell having preset voltage across switches, and storing energy after discharge in buffer memory - Google Patents

Abstract

The individual voltages of memory cells (2) are detected. The switches (S) are provided in each memory cell for loading and unloading of the respective memory cell. The voltage of the memory cell above a predetermined upper voltage value is discharged across the switches, and the energy resulting after the discharge is stored in a buffer memory (5). The memory cells with a voltage below a predetermined voltage value are loaded by suitable actuation of the switch. An independent claim is included for energy store.

Description

The invention relates to a method for cell voltage compensation according to the closer defined in the preamble of claim 1. The present invention also relates to an energy storage, which is constructed so that it is suitable for carrying out the method, for example. Furthermore, the present invention relates to the use of such a method with the energy storage.

Energy storage for storing electrical energy are known from the prior art. Energy storage devices for storing high-capacity electrical energy and the ability to store electrical energy over an extended period of time are generally batteries. Such batteries are usually composed of a plurality of individual memory cells typically connected in series. The individual memory cells of the batteries can be designed in different technologies. In order to achieve batteries with high storage capacity, memory cells in lithium-ion technology or in nickel-metal hydride technology are typically used for the individual memory cells.

Such memory cells, in particular memory cells in lithium-ion technology, now have the disadvantage that they must be kept within a comparatively small predetermined voltage band in order to achieve the highest possible life and high performance. It is important that all memory cells, which are typically connected in series in the energy store, within this predetermined comparatively narrow voltage band whose bandwidth is, for example, 30 mV, are.

Therefore, systems for cell voltage compensation are known from the prior art. These are also called balancing systems. They serve to keep in the electrical energy storage all individual memory cells as possible at a same voltage level. In principle, two different options are used to influence the voltages of the individual memory cells. Both options are based on the assumption that, as is customary in the general state of the art, the individual voltages of the individual memory cells are respectively detected and present as measured values, for example in a data bus system. The first option of cell voltage compensation is often referred to as dissipative or passive equalization or balancing. It consists essentially in that via resistors, which are connected via switches with the individual memory cells, a discharge of the memory cells with high or above a threshold voltage lying. The problem with this is that the energy released during discharging is converted into thermal energy in the electrical resistors and is lost or has to be cooled down. The second alternative, in contrast, provides that the cells with the lowest voltage or a voltage below a predetermined limit value are recharged accordingly until they are within the specified voltage band. In contrast to the procedure described above, this process is also referred to as active balancing. He has the disadvantage that it can be done only during a charging process of the overall battery, and that while a relatively high cost in the distribution of energy accumulating during charging is necessary.

The object of the present invention is now to provide a method for cell voltage compensation, which avoids these disadvantages. Moreover, it is the object of the present invention to provide an energy store which is suitable for such a method.

The above object is achieved by a method having the features in the characterizing part of claim 1. A suitable for solving the task energy storage results from the features in the characterizing part of claim 5.

The inventive method now provides that individual memory cells are discharged with a voltage above a predetermined upper voltage value via the switches in a conventional manner. However, the energy generated during discharging is not thermally converted to electrical resistors, but is stored in a buffer. Thereafter, by appropriate operation of the switches, the discharge may be terminated and the energy present in the buffer may be used to charge other individual memory cells whose voltage is below a lower voltage value.

Thus, the method according to the invention provides for a cell voltage equalization in which individual memory cells are deliberately discharged with too high a voltage and other cells with too low a voltage are deliberately charged. The energy removed from the memory cells with too high a voltage is buffered and can be used to charge the individual memory cells with too low a voltage. The method of cell voltage compensation therefore works very energy efficient, since only the power losses incurred in the buffer are lost while a large part of the energy discharged from the memory cells with too high a voltage can be used again for charging other memory cells with too low a voltage. This cell voltage compensation is always possible, even if the energy storage device as a whole is in the idle state or is just being charged or discharged. Unlike the prior art active cell voltage compensation, functionality is not limited to those times when the energy store is actively charged.

According to a particularly favorable and advantageous development of the method according to the invention, a capacitive or an inductive intermediate store can be used as the buffer store.

The energy store according to the invention now provides that, as usual in the prior art, each individual memory cell is associated with switches. In addition, the energy store has a cache. Each of the poles of each memory cell is connected to two switches, wherein the first switch is connected to a respective first terminal of the electrical buffer and the second switch is in each case connected to a second terminal of the electrical buffer. As a result, each individual memory cell in one or the other polarity can be connected to the electrical buffer via targeted activation of the switches. Depending on the terminal polarity of the individual memory cell to the electrical buffer and its control, the memory cell is then discharged and the energy is stored in the buffer or the memory cell is charged in the other polarity with energy from the electrical buffer. A suitable activation of the switches thus makes it possible to discharge and charge individual memory cells, for example by means of their voltage, as described above, so as to realize cell voltage compensation without or with minimal loss of energy.

According to a particularly favorable and advantageous development, the memory cells of the energy store can be embodied in lithium-ion technology. Especially with energy storage in lithium-ion technology, which allow a very high energy density, the cell voltage compensation between the individual memory cells plays a correspondingly high role, since the exact adherence of the lowest possible voltage band for each of the memory cells of the energy storage a very positive impact on performance and lifetime of memory cells in lithium-ion technology has.

A particularly preferred use of the method, as described above, it now provides that this method is used with a designed according to the invention energy storage. This structure is particularly efficient for carrying out the method according to the invention.

Further advantageous embodiments of the method according to the invention and / or of the energy store according to the invention will become apparent from the remaining dependent subclaims and will be apparent from the embodiment, which will be explained in more detail with reference to the figures.

Showing:

1 a schematic outline of a possible structure of the energy storage device according to the invention;

2 a first possible embodiment for an electrical buffer; and

3 a second possible embodiment for an electrical buffer.

In the presentation of the 1 is a trained example of lithium-ion technology battery as energy storage 1 indicated in principle. This energy storage 1 consists of a large number of individual memory cells 2 , which in series with each other to the electrical energy storage 1 are interconnected.

In a manner known per se and therefore not illustrated here, the voltages of each individual memory cell are thereby determined 2 recorded and are available as measured values for control electronics 3 to disposal. In the presentation of the 1 this is via an arrow marked U, which is in the field of control electronics 3 leads, shown. Each one of the memory cells 2 now has at each of its poles on a connection with two switches, which in the representation of 1 denoted by S ₁ to S _{2n + 2} . The switches can be via a dashed control line 4 through the control electronics 3 to target specifically. The switches S ₁ and S ₂ , for example, connect the first pole of the first memory cell 2 with a connection x ₁ or x _{2 of} a later described in more detail electrical buffer 5 , The other pole of the memory cell 2 is a switch pair S ₃ and S ₄ in a comparable manner with the buffer 5 connected. If necessary, the individual memory cell can be activated via a suitable control of the switches 2 So in one or the other polarity with the electrical buffer 5 get connected. This applies to every single memory cell 2 in the electrical energy storage 1 , wherein the control of the switches S ₁ to S _{2n + 2} via the control electronics 3 he follows.

The control electronics 3 controls via another control line 6 at a designated z terminal and the electrical buffer 5 , The structure now makes it possible to use the available voltage values U of the individual memory cells 2 those memory cells 2 be selected, the voltage is above a predetermined upper voltage value. Such a memory cell 2 is then discharged by a suitable control of their switches, wherein the energy accumulating during discharging in the electrical buffer 5 is stored. In the electrical buffer 5 This energy can then be released again at a later time. This is done via the control electronics 3 set by a suitable setting of the switches, a state which is used to load individual memory cells 2 whose voltage U is below a predetermined lower voltage value allows. About the electrical cache 5 which is also from the control electronics 3 via the control line 6 is driven, then with the stored electrical energy in these memory cells 2 getting charged. This allows for cell voltage compensation without the need for energy to be converted to heat during discharge and generally left unused. In addition, recharging the memory cells 2 with a voltage below the predetermined lower voltage value also take place when the energy storage 1 is in a state of rest and / or not reloaded from the outside.

In the presentation of the 2 is a first variant of the electrical buffer 5 to recognize. About the designated z terminal can via the controller 3 a control of the switches S _A and S _B take place. The electrical buffer 5 is essentially designed as a step-down and step-up converter. By activating the switch S _A in the form of a high-frequency switching, the energy at the terminals X ₁ and X ₂ in a capacitor C _{1 is} cached. This corresponds to the functionality of a buck converter. This variant is used when a memory cell 2 is discharged with a voltage above a predetermined upper voltage value and the energy in the region of the buffer 5 should be cached.

In the other use, so if cached energy from the cache 5 for loading a memory cell 2 is to be used with a voltage below a lower predetermined voltage value, then in the capacitor C ₁ stored energy and deactivated switch S _A, the switch S _{B is} closed or activated to deliver the energy at the terminals X ₁ and X ₂ again. This is the functionality of a boost converter.

In the 3 is an alternative embodiment of the electrical buffer 5 shown. This fulfills essentially the same task, although with a higher circuit complexity, but with a correspondingly higher efficiency and better electromagnetic compatibility, than those in the field of 2 described variant of the electrical buffer 5 , In the 3 illustrated variant of the electrical buffer allows a currentless switching as well as correspondingly small switching frequencies with low duty cycle. By closing the switch S _A energy is also stored here in a capacitor C ₁ , which is then discharged by driving the switch S _B again. In this case, the voltage at the capacitor C _{1 is} first lowered by the transformer designated T ₁ and then raised again, so that ultimately the same functionality when charging or discharging individual memory cells 2 of the energy store 1 arises, as in the variant of the electric buffer 5 according to 2 ,

Claims (10)

Method for cell voltage compensation between individual memory cells of an electrical energy store consisting of at least two memory cells, with a device for detecting the voltage of each individual memory cell, and with each individual memory cell associated switches for charging and discharging the respective memory cell, wherein memory cells with a voltage above a predetermined upper Voltage are discharged through the switch, characterized in that the energy arising during discharging in a buffer ( 5 ) and by appropriate actuation of the switches ( 5 ) Memory cells ( 2 ) are charged with a voltage lower than a predetermined lower voltage value. A method according to claim 1, characterized in that as a buffer ( 5 ) a capacitive buffer is used. A method according to claim 1, characterized in that as a buffer ( 5 ) an inductive buffer is used. Method according to claim 1, 2 or 3, characterized in that the voltages of the individual memory cells ( 2 ) in a control electronics ( 3 ) and evaluated, with the Control electronics ( 3 ) the switches (S) and switching elements (S _{A ,} S _B ) in the region of the intermediate memory ( 5 ) in a suitable temporal. Sequence drives to individual memory cells ( 2 ), to temporarily store the energy and thus save other memory cells ( 2 ) to load specifically. Energy storage with at least two individual memory cells, with each individual memory cell associated switches, characterized in that an electrical buffer ( 5 ), each of the poles of each individual memory cell ( 2 ) is connected to two switches (S), wherein the first switch in each case with a first terminal (X ₁ ) of the electrical buffer ( 5 ) and the second switch each with a second terminal (X ₂ ) of the electrical buffer ( 5 ) connected is. Energy store according to claim 5, characterized in that the temporary storage ( 5 ) is designed as a buck and boost converter. Energy store according to claim 5 or 6, characterized in that the temporary storage ( 5 ) is designed as an inductive storage with at least one transformer (T ₁ ). Energy store according to claim 5, 6 or 7, characterized in that the individual memory cells ( 2 ) are formed in lithium-ion technology. Energy store according to one of claims 5 to 8, characterized by its use as traction energy storage in an at least partially electrically driven vehicle. Use of the method according to one of claims 1 to 4, with an energy store ( 1 ) according to any one of claims 5 to 9.

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