EP2771959A2

EP2771959A2 - Battery having a plurality of accumulator cells and method for operating same

Info

Publication number: EP2771959A2
Application number: EP12773319.4A
Authority: EP
Inventors: Ralf Dittmann
Original assignee: Albright Deutschland GmbH
Current assignee: Albright Deutschland GmbH
Priority date: 2011-10-25
Filing date: 2012-10-16
Publication date: 2014-09-03
Also published as: DE202011110740U1; US20140349146A1; DE102011054790A1; WO2013060603A2; WO2013060603A3; CN103947071A

Abstract

The invention is based on a battery (100) having a plurality of accumulator cells, of which N first accumulator cells (111... 114) are connected to one another in series to form at least one cell line (110), wherein N second accumulator cells (121... 124) are each arranged such that said cells can be connected in parallel to individual cells of the N first accumulator cells (111... 114) by means of N+2 switching elements (131... 133', 134, 134'). According to the invention, in order to compensate the charge between the cells, the switching elements (131... 133', 134, 134') are capable of producing two-way connections (A, B) between the first and second accumulator cells, wherein each second accumulator cell (121) can be connected in parallel alternately either to a first accumulator cell (111) within the cell line (110) or to another adjacent firs accumulator cell (112). The switching elements (131... 133', 134, 134') are preferably controllable and alternately produce the two-way connections (A, B) between the first and second accumulator cells continuously at predefinable time intervals (TA, TB) in such a manner that each second accumulator cell (121) is connected in parallel to one first accumulator cell (111) in a first time interval (TA) and is connected in parallel to the other, adjacent first accumulator cell (112) in a second time interval (TB).

Description

The invention relates to a battery having a plurality of accumulator cells according to the preamble of claim 1 and to a method for operating such a battery according to the preamble of the independent claim. In particular, the invention relates to a battery having a plurality of similar accumulator cells (rechargeable secondary cells) connected in series with one or more strings to substantially define the desired operating voltage. In this case, several strands can in turn be connected in parallel with one another in order to increase the capacity and power of the battery. The invention is particularly directed to the construction of a high performance battery, such as a multicellular lithium-ion battery. Batteries with several accumulator cells, also called cells for short, are well known. Batteries have also been known for some years which have a flexible array structure which makes it possible to activate or deactivate individual cells within the array. For example, WO 03/041206 A1 discloses an array structure known as a "digital battery" in which a plurality of cells can be interconnected in series and in parallel via switching elements, for example N = 9 XM = 6 cells, each N A maximum of M = 6 strings can be formed and interconnected in parallel The switching elements are located between the cells and are arranged in the form of a matrix, which enables the activation of different switching paths, which allow a single failure Cells can be removed from the active circuitry to maintain operational readiness, and shorter or longer switching paths (paths) can be activated to provide different operating voltages and / or capacities. These can be tapped off on bus-shaped connecting cables.

Accordingly, a battery with several accumulator cells is known, of which N first accumulator cells are interconnected in series to a cell strand (eg the top strand), where N second accumulator cells (ie the cells of another strand) by means of Switching elements are each arranged in parallel switchable to each of the N first accumulator cells. Although this known battery has a flexible structure, which makes it possible to represent different voltages and capacities. In addition, defective cells can be deactivated. However, this type of battery, like any simple battery, also has the problem that even before the occurrence of defects in individual cells, care must be taken to ensure that each single intact cell is protected against overvoltage during charging and when it is being discharged against undervoltage ,

In order to achieve this, so-called charge balancing methods (charge balancing) are known, which ensure that the cells connected in series have as uniform a state of charge as possible. These methods are especially important in high power batteries, such as high power batteries. in lithium-ion batteries, which have a plurality of cells connected in series with one or more strings to achieve higher module voltages. So that the individual cells can be protected against overvoltage (overcharging) and undervoltage, so-called Zellbalancmg- methods and devices are used, which allow a charge equalization of the individual cells connected in series with each other.

The following different methods of charge balancing are known:

In the so-called shunting method, fully charged cells are bypassed with a bypass, which forms a discharge current for the respective bridged cell. The process is continued until the tensions of all cells within the strand are as close as possible and thus the charge of the cells is balanced (balanced). As advantages of this method are its inexpensive Realizability and the low EMC problems due to the low switching frequency. However, this method works only satisfactorily for accumulators with a cell chemistry which have a steep voltage charge characteristic (eg LiCoO 2), since the state of charge is estimated from the rest voltage. The method thus only works when the battery is at rest and the SOC (state of charge) has a high value. During operation of the battery, the shunting process is not applicable. Another disadvantage is that the charge balance is lossy because the excess charge is converted by a resistor (shunt) into heat energy.

In the so-called capacitive load-pump method, a proportion of the charge from cells with a higher state of charge (higher voltage) is removed via capacitors and transferred via switches to the neighboring cells. The method is relatively cheap and easy to implement. It assumes, however, that the charge differences between the cells are only small, since only relatively small amounts of energy can be transported via the capacitors. In addition, the switching frequency must be high in order to achieve a certain effectiveness. A compensation of larger cell asymmetries is hardly possible with this method. The inductive methods with coils or transformers work in different operating states of the battery. However, this approach is due to the inductive components quite expensive, complex and larger than in the shunt or the Charge pump method. In addition, the EMC problem increases due to the clocked circuit principle.

A method for operating a battery is known from US Pat. No. 6,157,165, in which switching elements are provided which have a capacitance (see "capacitor 111" in Fig. 1) optionally to individual battery cells of the battery (see "unit batteries 101a to 101c ") in parallel to charge the capacity with the current cell voltage of the accumulator cell. An interconnection with a voltage detector makes it possible to measure the cell voltage, wherein a further capacitor ("capacitor 104") is provided to eliminate voltage fluctuations, namely oscillating portions of the measuring voltage. The patent specification US Pat. No. 7,193,390 B2 discloses a method for operating a battery, in which switching elements are provided, the capacitances (see "capacitors Cl and C2" in FIG. 4) optionally parallel to individual battery cells of the battery (see "battery cells El and E2 ") or to each other. First, the first capacitance ("Cl") is switched in parallel with the first cell ("El") and charged with the cell voltage. Then, the capacitance is disconnected from the cell and connected in parallel with the second capacitance ("C2") so that both capacitors have the same voltage, after which the second capacitance is disconnected and connected to a voltage detecting circuit to measure the voltage. Since a terminal of the second capacitance is connected to ground potential, the voltage of the cell ("El") can be stably measured.

These known methods have the night part that additional components, such. Capacitors, coils or transformers, must be used, which can result in particular when used in the field of high-performance batteries, a large material and cost.

The charge balancing methods are particularly applied to batteries for industrial traction applications (such as electric mobility) and stationary energy storage, since these batteries are very high in terms of reliability, durability and safety. Often industrial applications run in uninterruptible continuous operation. A defined resting state, during which the cells can be balanced, is thus not present. In addition, in certain applications, the case occurs that the end of charge or the discharge state is not reached. This makes the state of charge determination via accounting methods difficult to impossible, since no cyclic recalibration can be done on the fully charged or empty state. It is therefore an object of the invention to develop a battery of the type mentioned so that the aforementioned disadvantages are overcome in an advantageous manner. In particular, a battery and a method for operating the battery can be proposed, which allow an effective and cost-effective charge balance within the cell structure.

The object is achieved by a battery having the features of claim 1 and by a method for operating such a battery having the features of the independent claim.

Thus, in the battery switching elements are used which are adapted to produce two-way circuits between the first and second accumulator cells, each second accumulator cell alternately either to a first accumulator cell within the cell strand or to an adjacent other first accumulator Cell is switchable in parallel, wherein the switched by means of the switching elements second accumulator cells connected in series with each other to a second cell strand, which is connected in parallel to the first cell strand. The second cell strand is thus formed as a strand with full energy storage function.

Also proposed is a method for operating such a battery, in which N first accumulator cells are connected to one another in series with at least one (first) cell strand (strand 110), and wherein N second accumulator cells are connected in parallel to each other by means of switching elements individual ones of the N first accumulator cells are arranged and form a second strand (strand 120) by making two-way circuits between the first cells of the strand 110 and the second cells of the strand 120 by means of the switching elements, each second accumulator cell alternately either to a first accumulator cell or to a within the cell strand (strand 110) adjacent the first accumulator cell is connected in parallel. In this case, the second accumulator cells connected by means of the switching elements are connected to one another in series with a second cell strand, which is connected in parallel with the first cell strand. By the invention, a charge balancing (balancing) is achieved, which can be performed only with the help of the accumulator cells themselves, in which the cells of one strand (strand 120) with the cells of the other strand (strand 110) are flexibly interconnected. Each cell of the strand 120 is alternately one particular Cell of the strand 110 and an adjacent cell of the strand 110 and may alternately be connected in parallel to one or the other cell in parallel, so that the alternating parallel circuit causes a balance of charge states between the cells of the strand 110 and also balances the strand 120. The battery according to the invention thus has two or more equivalent strands of N cells each. Each strand has the same number of cells and each has a full energy storage function. The cells of the second strand are alternately offset by one cell place connected to the at least one first cell strand. This results in a mutual balancing, without additional memory elements, such as capacitors or coils are needed. The cells of the strand 120 form a full galvanic series, which is arranged parallel to the strand 110 and thus fully contributes to the total capacity of the battery.

The battery according to the invention is particularly well suited for industrial traction applications and stationary energy storage. In this case, even in continuous operation of the battery, a balancing of the cells can be achieved, where appropriate, a state of charge determination is applied via balancing methods.

Preferred embodiments of the invention will become apparent from the dependent claims.

Accordingly, it is advantageous if the switching elements are controllable and if the two-way circuits between the first and second accumulator cells are continuously produced alternately at predetermined time intervals such that every second accumulator cell is parallel to the first one in a first time interval Accumulator cell is connected and connected in a second time interval in parallel to the adjacent first accumulator cell. This results in a constant switching back and forth as regards the assignment of the cells of the strand 120 to the cells of the strand 110. It is also advantageous if at least one cell of the second accumulator cells is connected to a plurality of switching elements which are arranged to separate this second accumulator cell from shading with the first and / or second accumulator cells at least for a predeterminable third time interval and with one Connecting measuring device. This allows this cell to be used temporarily for measurement purposes. In particular, charge state and capacity can be accurately determined to optimize battery management.

In the method for operating the battery, the switching elements are preferably controlled in particular by a processor-controlled unit, wherein at predetermined time intervals, in particular equally long time intervals, the two-way circuits between the first and second accumulator cells are produced alternately so that every second accumulator Cell (in strand 120) in a first time interval in parallel with the first accumulator cell (in the strand 110) is switched and in a second time interval in parallel with the adjacent first accumulator cell (in the strand 110) is switched. In this case, the second accumulator cells are connected to each other in series with a second cell strand (strand 120), which is connected in parallel to the first cell strand (strand 110).

In the following, the invention will be described in more detail by means of exemplary embodiments, reference being made to the enclosed figures, which reproduce the following schematic representations:

Fig. 1 shows the schematic structure and the structure of an inventive

Battery;

FIG. 2a shows the battery according to FIG. 1 in a first switching state; FIG.

FIG. 2b shows the battery according to FIG. 1 in a second switching state; FIG.

Fig. 2c shows to Fig. 2a / b schematically a timing diagram with the changing

Switching states;

FIG. 3 shows the battery according to FIG. 1 in the state during a measuring interval; FIG. and FIG. 4 shows schematically a time diagram with the changing FIG

Switching states.

Fig. 1 shows the structure of a battery 100 according to the invention with a first strand 110 (fixed series circuit), which consists of a plurality of serially connected first accumulator cells 111, 112, 113 and 114. By way of example, only N = 4 cells are connected in series here and form a first galvanic series with N times the number of cells. Tension. If, for example, you switch at least N = 100 lithium-ion cells in series can be reached by more than 300 volts, as is required for batteries for electric vehicles. It is also possible to connect several such rows (strands) in parallel. The cell voltages within such a strand may well differ from each other (eg by several hundred millivolts) and there may be a charge imbalance.

For charge balancing, now (N = 4) cells 121, 122, 123 and 124 are used, which are connected by means of (N + 2) switching elements 131, 132, 133, 133 'as well as 134 and 134' and another strand 120 form, in principle, the same galvanic series as the strand 110 and thus also contributes to the total capacity of the battery. The charge equalization takes place with the aid of these second cells 121 to 124; special compensating means and additional components, such as capacitors, coils, etc. are not required. The charge equalization takes place essentially by an alternately changing interconnection of the second cells (strand 120) with the first cells (strand 110) according to the method described in more detail below. It should be noted that in the strand 120 first Nl cells are connected in series (here, the cells 121 to 123) and that the other cell 124 via its associated switching elements 134 and 134 'to one end (above the cell 121 ) or to the lower end (behind cell 123). By means of the further switching elements 131 to 133 and one of the said switching elements 134 or 134 ', all the cells 121 to 124 of the strand 120 can then be connected in parallel to the cells of the strand 110. The principle of the mutual interconnection and the method for operating the battery operating thereafter will now be described in more detail, wherein reference is also made to FIGS. 2a and 2b and 2c. With reference to Figures 3 and 4 will also be described below, as with the battery structure of the invention, a determination of the state of charge of the battery can be performed. Thus, the invention allows both a balancing during operation and an accurate determination of the state of charge. According to the circuit principle presented here and illustrated in FIG. 1, the battery 100 is constructed from a plurality of individual cells 111-114 and 121-124 in series-parallel connection. The battery is divided into a strand 110 with the first cells 111-114 (fixed order) and a strand 120 with the additional (second) cells 121-124 (alternating shading). The strand 120 is connected to the strand 110 by switching elements 131-133 and 134 and 134 'as shown in FIG. Multiple strings may also be connected in parallel to increase the capacity of the battery 100. As switching elements, any type of switches can be used, preferably semiconductor switching elements, such as MOSFETs or mechanical switches, such as relays. Each switching element or each group of two switching elements can switch back and forth between the two switching states A and B in the manner of a two-way switch. This is symbolically illustrated in FIG. 1 by the individual switches A and B. By a phase-shifted switching of the switch elements (eg 131) in the state A or B, the strand 110 in a first phase (see time interval TA in Fig. 2c) with the cells of the strand 120 in a first position (see switch positions A in FIG. 2a), so that the cell 121 is connected in parallel to the cell 111 and the cell 122 is parallel to the cell 11, etc. Accordingly, the string 120 is connected in parallel to the string 110 so that the order of the cells in both strings is the same and starts with 111 and 121, respectively. In this case, the charge states between the cells connected in parallel (eg 111 and 121) are equal to each other. The strand 120 thus corresponds to the equivalent circuit diagram 120 'according to FIG. 2a. Then, in a second phase (see time interval TB in FIG. 2 c), the position of the cells of the strand 120 is shifted to a second position (see switch positions B in FIG. 2 b), so that cell 121 is now connected in parallel to cell 112 and cell 122 is parallel to cell 113, etc. Note that cell 124 is now connected in parallel to cell 111. Thus, the strand 120 is now in a parallel to the strand 110 parallel circuit, namely in a position offset by a position down. The order of cells in strand 110 begins with cell 111; however, the order in thread 120 begins with cell 124 and then proceeds to 121, 123 and 123 (see Fig. 2b). Thus, the strand 120 was shifted down by one position. The strand 120 thus corresponds to the equivalent circuit diagram 120 "according to Fig. 2b, and the charge states between the cells now connected in parallel to one another, ie the state of charge of the cell 111 to that of the cell 124, are now equalized by charge transfer to the respectively adjacent cells of the cell Stranges 110. The same applies to strand 120. The charge transfer ultimately leads to complete compensation of all cell charges.

Consequently, the charge balance can be carried out according to the charge pump principle, without having to use additional energy storage elements (capacitors, coils). Because the charge equalization takes place with the battery cells themselves. Accordingly, when using the invention, a battery with lOOAh in principle remains a 100Ah battery; However, with the essential difference that the battery structure according to the invention compared to a conventional structure, was internally divided into 2 strands and that no additional charge or energy storage (capacitors, coils) are needed for the loss-free charge equalization.

If the structure scheme of the battery in FIG. 1 is considered, then in the series connection of the strand 120 there is first one cell less (N-1 cells on the right side 121-123) than in the strand 110 (N = 4 cells 111) -114). The N-1 cells of the strand 120 are connected either parallel to the beginning or end of the strand 110 (see switch position A or B). This means that without additional measures, the lowermost or uppermost cells of the strand 110 are more current-charged than the others. In order to compensate for this asymmetry, a further cell 124 is added in line 120 as a parallel uppermost cell (see FIG. 2b) or as the lowest cell (see FIG. 2a).

In other words, by positional offset of the series connection of the N-1 cells 121-123, there is a space at the top or at the bottom for the addition of the Nth cell 124. Thus, a full-value string 120 or 120 'or 120 "always results. (see FIGS. 2a and 2b), which is connected in parallel to the strand 110.

All battery cells are thus charged equally. The battery structure shown (see Fig. 1 and Fig. 2a and 2b) consisting of a combination of at least one strand 110 with another strand 120 or 120 'or 120 "(including the auxiliary cell 124) is quasi with a symmetrical series-parallel connection (N cells in series each to one strand, P strands parallel) identical.

The method of alternately connecting the cells 121-124 includes i.a. the particular advantage that a charge balance in each operating condition of the battery (charging, discharging, rest and full load) is feasible. The excess energy of individual cells is - without intermediate storage - redistributed to other cells and not converted into heat. The here proposed balancing method is virtually lossless. Overloading of individual cells is in principle not possible with the method. The battery and its circuitry in string 110 has no switching elements (MOSFETs, relays) in series, thereby achieving minimum internal resistance.

The switching elements 131-134 / 134 'and optionally the controller (not shown) are also referred to herein as "balancers" and can be fully or partially integrated into the battery or can also be designed separately The balancer circuit contains no inductive components for energy transfer, but uses the battery cells for this purpose (double benefit) .The circuit has very good EMC properties because of the inherent low switching frequency, eg in the hertz state. Range can be applied and so steep current peaks are avoided.

The balancing method described here relieves weaker cells due to the principle. The total energy content of the series-parallel connection of the cells is fully exploited by the circuit principle.

In the prior art, the capacity of the weakest cell determines the total capacity of the battery. This is not the case with the present invention. This results in further advantages:

- The individual cells of the battery need not necessarily be classified and sorted prior to assembly in order to achieve the maximum pack capacity.

- The overall life of the battery increases due to the relief of weaker cells In addition to the balancing function, the invention can also be used due to the circuit topology without further circuitry to determine the exact state of charge of the battery during operation. This allows a recalibration of the current balance measurement and will be described in detail below with reference to FIGS. 3 and 4:

FIG. 3 shows the battery according to FIG. 1 in a state in which the cell 124 is separated from the strand 120 and separately connected to a measuring device M. This state is assumed during the operation of the battery during a measuring interval TO (see FIG. 4), wherein the switch positions A 'and B' do not correspond to the switch positions A and B during the measuring interval TO. The cell 124 serves as a reference cell for a measurement for determining battery state variables.

Because the reliable operation of battery systems requires accurate knowledge of the condition of the battery system used. Both the current state of charge (still removable amount of charge) and the state of aging (loss of capacity or change in internal resistance) provide information about the operational readiness and operational capability of a battery system. While the measurement of the battery state variables in the laboratory under defined conditions poses few problems, the determination during operation encounters considerable difficulties. An interruption of the operation for measuring, for example, the capacity is not permitted or possible in most applications. In the prior art, the state of charge during operation is determined either by charge balance, at certain intervals must be recalibrated so that the value does not run away, or it is estimated using a battery model based on the terminal voltage, the open circuit voltage and the sleep voltage characteristic to the state of charge closed. However, both methods do not allow an exact determination of the state of charge and can lead to considerable uncertainties and highly fluctuating results. For LiFePO cells, for example, the charge state estimation is extremely inaccurate due to the flat UQ characteristic in the middle range. The measuring method according to the invention described below does not show these deficiencies. The compensation cell 124 (see FIG. 3), which serves for charge equalization between top and bottom cells of a series connection in normal operation (compare FIG. 1 and FIG. 2 a / b), is now also used to determine the cell characteristics. By opening at least 3 of the 4 switches of the cell 124 (see FIG. 3), it is decoupled from the battery for a certain period of time (see in FIG. 4 the illustrated switch states A 'and B' in the time interval T0 during the decoupling of the cell 124 ).

The parameters can thus be used without additional aids, e.g. be determined by simple rest voltage measurement for SOC determination (state of charge). This can also be done with auxiliaries (discharge current sink, charging source for SOC, capacitance and internal resistance determination). During measurement on the cell 124, the entire battery may continue to operate. The asymmetry caused by temporary decoupling of the cell 124 is already compensated by the continuous balancing with the remaining cells 121-123. After the measurement, the cell 124 is coupled back into the balancing process. With the measurement result of the SOC of the cell 124, the SOC of the whole battery can be reliably recalibrated taking into account the charge balance. This provides a method for the precise determination of the state of charge and the state of aging of a battery module during operation.

The invention is applicable to all types of battery cells and modules, especially those used in high power batteries.

The invention is therefore particularly suitable for the construction and operation of high-performance batteries.

Claims

1. Battery (100) with a plurality of accumulator cells, of which N first accumulator cells (111 ... 114) are interconnected in series with each other to at least one cell strand (110), wherein N second accumulator cells (121 ... 124) by means of

Switching elements (131 ... 133, 134, 134 ') are each arranged in parallel switchable to each of the N first accumulator cells (111 ... 114),

characterized in that

the switching elements (131 ... 133, 134, 134 ') are arranged to produce two path circuits (A, B) between the first and second accumulator cells, each second accumulator cell (121) being alternately connected either to a first accumulator cell. Cell (111) within the cell strand (110) or to a neighboring other first accumulator cell (112) is connected in parallel, and that the means of the switching elements (131 ... 133, 134, 134 ') connected to the second accumulator Cells (121 ... 124) are connected in series with each other to a second cell string (120, 120 ', 120 ") connected in parallel with the first cell string (110).

2. Battery (100) according to claim 1, characterized in that the switching elements (131 ... 133, 134, 134 ') are controllable and at predetermined time intervals (TA, TB) continuously the Zweiweggeschaltungen (A, B) between the first and second accumulator cells alternately so that each second accumulator cell (121) in a first time interval (TA) parallel to the one first

Accumulator cell (111) is connected and in a second time interval (TB) in parallel with the adjacent other first accumulator cell (112) is connected.

3. Battery (100) according to any one of the preceding claims, characterized in that at least one (124) of the second accumulator cells (121 ... 124) is connected to a plurality of switching elements (134, 134 ') which are arranged, these second accumulator cell (124) at least for a predeterminable third time interval (TO) of interconnections with the first and / or second accumulator cells disconnect and connect with a measuring device (M).

A method of operating a battery (100) having a plurality of accumulator cells, of which N first accumulator cells (111 ... 114) are connected to one another in series with at least one cell string (110), wherein N second accumulator cells (110) 121 ... 124) by means of switching elements (131 ... 133, 134, 134 ') each in parallel switchable to each of the N first accumulator cells (111 ... 114) are arranged,

characterized in that

two-way circuits (A, B) between the first and second accumulator cells are produced by means of the switching elements (131 ... 133, 134, 134 '), wherein each second accumulator cell (121) alternately either to a first accumulator cell ( 111) is connected in parallel within the cell string (110) or to another adjacent first accumulator cell (112), and that the second accumulator cells connected by means of the switching elements (131 ... 133, 134, 134 ') (121 ... 124) are connected in series with each other to a second cell string (120, 120 ', 120 ") connected in parallel with the first cell string (110).

A method according to claim 4, characterized in that the switching elements (131 ... 133, 134, 134 ') are controlled, in particular by a processor-controlled unit, wherein in predetermined first and second time intervals (TA, TB) continuously the two-way circuits ( A, B) between the first and second accumulator cells are alternately made so that every other

Accumulator cell (121) in a first time interval (TA) in parallel with the first accumulator cell (111) is switched and in a second time interval (TB) in parallel with the adjacent other first accumulator cell (112) is switched.

Method according to one of claims 4 or 5, characterized in that at least one (124) of the second accumulator cells (121 ... 124) is connected to a plurality of switching elements (134, 134 ') which are arranged to supply this second accumulator Cell (124) at least for a predefinable third time interval (TO) disconnect from interconnections with the first and / or second accumulator cells and connect to a measuring device (M).

7. The method according to any one of claims 4 to 6, characterized in that the vorgebaren first and second time intervals (TA, TB) are the same length, in particular between 0.1 seconds and 120 seconds long.

8. The method according to any one of claims 4 to 7, characterized in that the vorgebare third time interval (TO) is longer than the first and second time intervals (TA, TB), in particular up to 5 hours long.