Redox flow battery systems and methods of operation

Abstract

Redox flow battery system, comprising at least two battery modules (1), a bidirectional converter (7) and a control device (8), wherein the battery modules (1) are connected in series and to the converter (7), and wherein each battery module (1) comprises a cell facility (2) with a plurality of redox flow cell and a tank device (3) for storing and supplying electrolyte to the cell facility (2), and wherein the battery system comprises for each battery module (1) a DC voltage converter (17), wherein each DC voltage converter (17) has one connection each to one battery module (1), and a second connection of each DC voltage converter (17) is connected to a common DC current bus, and wherein the battery system comprises a further converter (16) connected to the DC current bus, and wherein the control device (8) is connected to the further converter (16) and the DC voltage converters (17) such that the control device (8) can control the further converter (16) and the DC voltage converters (17).

Description

Technical Field

[0001] This invention relates to a redox flow battery system and a method for operating such a system. The invention particularly relates to a redox flow battery system having a high output voltage. The method according to the invention relates to a method for reducing or eliminating imbalances occurring between series-connected battery modules during charging and discharging of the battery system. Background Technology

[0002] To achieve high output voltage in redox flow battery systems, multiple individual cells are typically connected in series. This arrangement is called stacking. However, this cannot be continued arbitrarily, as the shunt current caused by the electrolyte would become unacceptably high. However, if multiple stacks are connected in series, with each stack having its own individual can cell, the output voltage can be further increased. A unit consisting of such stacks and their respective individual can cells is called a battery module. However, due to inhomogeneities in the raw materials used and manufacturing variations, the individual battery modules produced are not identical, and therefore such battery systems are susceptible to imbalances in the battery module design, which adversely affects the performance of such battery systems.

[0003] This harmful imbalance can be reduced by battery systems and operating methods known in the prior art. This is commonly referred to as balancing.

[0004] WO 2020 / 030762 A1 addresses the imbalance of the State of Charge (SoC) of a battery module. Here, the SoC of each electrolyte tank is measured and compared. If the difference in SoC exceeds a threshold, the number of cells connected in series in the stack is adjusted so that an electrolyte with a lower charge level discharges through fewer individual cells compared to an electrolyte with a higher charge level, or vice versa.

[0005] WO 2018 / 107097 A1 also addresses the imbalance of the state of charge (SoC) of battery modules. This imbalance is reduced by balancing the SoC of the battery modules with the target SoC after measurement, by transferring a portion of the stored energy in at least one module to the electrical load. Summary of the Invention

[0006] The inventors' objective is to describe a redox flow battery system and an operating method, wherein imbalance can be reduced in an alternative manner.

[0007] According to the invention, this task is accomplished by the battery system and operating method according to the independent claim. Further advantageous embodiments are found in the dependent claims.

[0008] This application discloses two different solutions that can be implemented independently of each other or can be implemented in combination in a particularly advantageous manner. Attached Figure Description

[0009] The solution according to the present invention will now be explained in conjunction with the accompanying drawings. These drawings show in detail:

[0010] Figure 1 Battery module;

[0011] Figure 2 Battery system;

[0012] Figure 3 The battery system according to an embodiment of the present invention (details);

[0013] Figure 4 A battery system according to another embodiment of the present invention;

[0014] Figure 5 A battery system according to another embodiment of the present invention;

[0015] Figure 6 A battery system according to another embodiment of the present invention;

[0016] Figure 7 A battery system according to another embodiment of the present invention. Detailed Implementation

[0017] Figure 1 The battery module is schematically shown on the left. The battery module is labeled 1. The battery module includes a single-cell facility labeled 2, a tank assembly labeled 3, and a measuring device for detecting controlled parameters. The single-cell facility 2 is a facility for multiple redox flow single cells, which can be arranged arbitrarily. For example, it may be a stack of single cells, multiple stacks connected in series, multiple stacks connected in parallel, or a combination of series and parallel connections of multiple stacks. In any case, all the single cells in the single-cell facility 2 are used to store electrical energy when the battery module 1 is charging or to provide electrical energy when the battery module 1 is discharging. The tank assembly 3 is used to store electrolyte and to supply electrolyte to the single-cell facility 2. For this purpose, with a few exceptions, the tank assembly 3 includes at least two tanks, a piping system for connecting the tanks and the single-cell facility 2, and a pump for transporting the electrolyte. Figure 1Two separate pumps are shown here. Equally advantageous, the electrolyte could be transported using a dual-pump system, i.e., two pumps driven by a common motor. The tank assembly 3 is configured such that it can supply electrolyte to all the individual cells of the individual cell facility 2. When the pumps transport electrolyte, the electrolyte flows through all the individual cells of the individual cell facility 2. Therefore, when the battery module 1 is charged or discharged, all the individual cells of the individual cell facility 2 are always used to charge the electrolyte in the tank assembly 3, or all the individual cells of the individual cell facility 3 are always used to discharge the electrolyte in the tank assembly 3.

[0018] Figure 1 The battery module 1 shown includes two measuring devices for providing controlled parameters. The measuring device labeled 4 is used to provide the so-called open circuit voltage (OCV). The OCV value is a measure of the state of charge (SoC) of the battery module. The measuring device labeled 5 is used to provide the terminal voltage of the individual cell facility 2, and thus the battery module 1. During charging or discharging of the battery module 1, the terminal voltage differs from the open circuit voltage by a voltage drop across the internal resistance of the individual cell facility 3. An alternative for determining the OCV value is the so-called coulomb counting method, which also represents a measure of the state of charge of the battery module. For this, a measuring device is needed to provide the current flowing through the series-connected modules. Therefore, this measuring device for coulomb counting can also be implemented outside the battery module 1, thus allowing the battery module 1 to optionally include a measuring device for providing controlled parameters. In any case, the battery system (see below) includes at least one measuring device for providing controlled parameters for each battery module 1 of the battery system.

[0019] Battery module 1 also includes auxiliary systems, which are indicated by rectangles marked with 6. Auxiliary systems 6 are supplied with current from outside battery module 1 via two terminals. Specifically, auxiliary systems 6 are used to feed power to pumps, any available ventilation devices, and similar devices.

[0020] exist Figure 1 The right side shows a symbolic graphic representation of battery module 1. Here, the above representation shows the terminals of the individual battery cells and the terminals of the auxiliary system, which are missing from the graphic representation below. These symbolic graphic representations will be used below. When the graphic representation below is used here, it does not mean that the battery module shown does not include the auxiliary system, but simply that the auxiliary system is not functional within its respective scope.

[0021] Figure 2A schematic diagram of a battery system according to a first embodiment is shown. The battery system includes at least two battery modules (one labeled 1), a bidirectional power conversion system (PCS) labeled 7, and a control device labeled 8. Battery module 1 is connected in series and connected to the converter 7. Figure 2 Four battery modules are shown, with dashed lines in the series circuit intended to indicate any number of additional modules. Converter 7 is responsible for connecting the battery system to the grid or an upstream electrical system. The battery system also includes a first switch (one labeled 9) and a second switch (one labeled 10) for each battery module 1. The first switch 9 is arranged in series with each battery module 1, wherein, of course, the location of the corresponding switch 9 on which side of the respective battery module is irrelevant. The second switch 10 is arranged in a bypass line (bypass) that bypasses both the battery module 1 and its corresponding first switch 9. Figure 2 In the diagram, all switches 9 and 10 are shown in the open state. In fact, in almost all operating methods according to the invention (described in detail in the following sections), the switches are driven by the control device 8 such that in each switch pair consisting of the first and second switches, exactly one switch is closed and one switch is open (alternating between open and closed). That is, here, the switch pair has exactly two switch positions, where in the first switch position (first switch 9 closed, second switch 10 open), the corresponding battery module 1 is in the series circuit of the battery system, and in the second switch position (first switch 9 open, second switch 10 closed), the corresponding battery module 1 is separated from the series circuit of the battery system via a bypass line. With switch 10 closed, the opening of the first switch 9 here prevents the module from discharging via the bypass line. The control device 8 is connected to each battery module so that it can acquire the measurement values ​​of the measuring device 4 or 5. If the battery system includes one or more measuring devices that are not part of the battery module 1, then the control device is of course also connected to these measuring devices in order to acquire their measurement values. For example, a measuring device for coulomb counting may also be part of the control device 8. Furthermore, the control device 8 is connected to each of the switches 9 and 10, enabling the control device to determine the respective switch position in order to connect or disconnect the battery module 1 from the series circuit. These connections can also be made wirelessly.

[0022] According to Figure 2In a battery system with identical battery modules 1, harmful imbalances may not occur. However, real battery modules 1 differ due to manufacturing variations and aging processes. Furthermore, different operating conditions for individual modules, such as temperature differences, can lead to variations in their characteristics. For these reasons, real battery modules have different efficiency values ​​and different internal resistances. Higher efficiency results in reaching the relevant battery module's final state more quickly given a charging or discharging current. Because in accordance with... Figure 2 In a series circuit, all battery modules 1 are circulated by the same current, so the more efficient modules reach their final state faster than the less efficient modules. To avoid damage, the charging or discharging process must be immediately interrupted when a module reaches its final state. Without compensation for this effect, the usable storage capacity of such a battery system decreases with each cycle (“capacity decay”). Different internal resistances of the modules have a similar effect. There are upper and lower boundary values ​​that must not be exceeded or fallen below for the terminal voltage. Even with the same efficiency, modules with higher internal resistance reach their respective terminal voltage boundary values ​​faster during charging or discharging than modules with lower internal resistance. When the first module reaches its boundary value, its process must be interrupted, thus similarly leading to a reduction in the usable capacity of the battery system. Alternatively, the system power may also decrease. In any case, these effects lead to damage to the system. Balancing should reduce or completely eliminate these effects so that the usable capacity of the battery system is maintained at a high level for a sustained period, or eliminates the aforementioned damage. On the other hand, a successful balance enables the use of batteries with relatively high dispersion in terms of efficiency and / or internal resistance, which is reflected in the reduction of production costs.

[0023] The following describes a method according to the invention for reducing Figure 2 The imbalance that occurs in the battery system shown during charging and discharging, wherein all the steps mentioned are of course performed during the charging or discharging of the battery system, that is, the charging or discharging is not interrupted as a result.

[0024] The method for reducing imbalances occurring during charging and discharging of a battery system according to the present invention, in a first embodiment, includes the following steps:

[0025] • The measurement values ​​of the measuring device used to provide controlled parameters for each battery module 1 are acquired by the control device 8;

[0026] • If at the first time point, at least one measurement value of the first battery module 1 differs from the measurement value of the second battery module 1:

[0027] The control device 8 regulates the number of battery modules 1 in the series circuit in order to reduce the difference in the measured values ​​of the first and second battery modules 1 at a subsequent second time point, wherein, during the time period between the first and second time points during the charging or discharging of the battery system, one of the two battery modules 1 is in the series circuit for a shorter time than the other battery module 1.

[0028] When a battery system with multiple battery modules operates for a sufficiently long period without balancing (i.e., charging or discharging), a situation typically arises where the measured values ​​of the controlled parameters for each battery module exhibit a statistical distribution. In any case, this satisfies the condition that at least one measured value of the first battery module 1 differs from that of the second battery module 1. Of course, in such a system with many battery modules, the purpose of balancing is to minimize the bandwidth of the measured value distribution at later time points, or ideally, to make all the measured values ​​completely equal to each other. This automatically leads to the measured values ​​of the first and second battery modules also converging at subsequent time points. According to the invention, this is achieved by temporarily disconnecting at least a portion of the battery modules from the series circuit of the battery system, wherein the disconnected modules do not participate in the charging or discharging of the system during this time, while the modules remaining in series do participate.

[0029] It is important to note that removing too many battery modules from the series circuit at the same time point is not advisable. For example, this could cause the voltage applied to PCS 7 to drop below a critical boundary value, as this voltage is derived from the sum of the terminal voltages of all battery modules in the series circuit. Therefore, the control device 8 also regulates the number of battery modules 1 in the series circuit in this regard, that is, to ensure that the battery system operates fault-free at any point in time. In addition to the lower boundary voltage of converter 7, other parameters and boundary conditions, such as the upper boundary voltage of converter 7, may also be considered here.

[0030] To this end, the control unit 8 can, for example, monitor the voltage applied to the PCS 7 and ensure the corresponding switching behavior. Alternatively, it may be possible to directly limit the maximum number of modules that can be removed from the series circuit simultaneously. It is also conceivable that such a maximum number could be related to other parameters, such as the charging state of the system or any module. Thus, for example, in a first charging state, it may be possible to simultaneously disconnect up to n modules, while in a second charging state, it may be possible to simultaneously disconnect up to m modules, where n is not equal to m. Other conceivable parameters are the charging or discharging current or the power of the PCS 7.

[0031] The method according to the invention can be further explained if we consider that during the charging or discharging of the battery system, the measured values ​​of the battery modules and the corresponding controlled parameters monotonically tend towards a final value. However, this pursued "speed" is different for the battery modules, so some modules "run ahead" while others "fall behind." Therefore, the aim of balancing is to keep the "moving group" of modules together despite each module moving at a different speed. The control device achieves this goal by forcing the faster modules to "force a stop" (temporarily remove them from the series circuit) from time to time, while the slowest modules continue to move forward. Here, the control unit ensures that not too many modules are stopped at any given time. The control device here has two controlled parameters: the length of the stop and the frequency of the stop.

[0032] It is meaningful to use a threshold for the deviation of the measured values ​​in the method according to the invention. A first threshold can be defined for the initiation of the method according to the invention, i.e., a threshold that the difference between the measured values ​​of the first battery module and the second battery module must exceed at a first time point in order to trigger the balancing mechanism. A second threshold can be defined for the cessation of the balancing mechanism, i.e., a threshold that the difference between the measured values ​​of the first battery module and the second battery module must be lower than at a subsequent second time point, causing the balancing mechanism to stop at that second time point. Obviously, the second threshold must be chosen to be smaller than the first threshold. In particular, the second threshold is useful for eliminating the negative impact of measurement inaccuracies. Alternatively, the measured values ​​can, of course, also be filtered to remove noise.

[0033] However, the method according to the invention can also be implemented just as well without a threshold. For example, empirical values ​​can be determined for the duration after which a given battery system loses balance during a given charge or discharge cycle, necessitating compensatory intervention. This also applies to the duration for which the balancing mechanism according to the invention must be implemented to restore balance to the given battery system during a given charge or discharge cycle. Advantageously, the control unit of the given battery system can learn these empirical values ​​through self-learning over several charge / discharge cycles using appropriate algorithms. If the battery system should change in this regard over a longer operating period, for example due to aging effects, the empirical values ​​can also be adjusted. Similarly, the characteristics of each battery module 1 can be determined, i.e., which battery modules operate at high efficiency or have high internal resistance, so as to determine which battery modules need to be stopped more frequently and / or for longer periods according to the invention in order to keep the "moving group" together (see also below). Therefore, when using such empirical values, it is not necessary to continuously acquire or evaluate the measured values ​​of the controlled parameters. This is similarly applicable to model-based processing methods, where the behavior of the battery modules can be predicted by means of a model. Here, the model can match the respective battery systems with measured parameters and appropriate parameters.

[0034] It is also conceivable that the balancing mechanism according to the invention, at least for a certain period of time, without the need for additional acquisition or evaluation of measurements, is performed by continuously subjecting the faster module to correspondingly long or frequent pauses. Therefore, the uninterrupted imbalance is effectively corrected immediately, while the differences in the controlled parameters are not persistently acquired or evaluated. Of course, this does not preclude the implementation of such uninterrupted balancing while continuously acquiring and evaluating measurements.

[0035] In embodiments of the method according to the invention that do not require persistent acquisition or evaluation of the measured values ​​of the controlled parameters, the necessary pause length and frequency for each battery module are determined once or at a later time point. Self-learning algorithms or model-assisted methods can also be used here. This process, along with the determination of empirical values ​​for the aforementioned time periods, can be referred to as a calibration of the balancing mechanism. Such calibration may have already been performed at the factory, i.e., before delivery to the customer, or it may have been performed during the initial initialization. At least during this calibration, the method according to the invention needs to be implemented in the aforementioned manner (i.e., acquiring and evaluating the measured values). In cases where the balancing mechanism is implemented without acquiring or evaluating the measured values, it is recommended to check the success of the balancing at least periodically based on the measured values. In cases of insufficient balancing, recalibration can be performed.

[0036] Therefore, the most general form of the method according to the invention (i.e., the execution balancing mechanism - BM) can be defined as follows:

[0037] The steps (BM) included in the method for reducing imbalances that occur during the charging and discharging of a battery system are:

[0038] • The control device 8 regulates the number of battery modules 1 in the series circuit in order to reduce the difference between the first and second battery modules 1 in terms of controlled parameters, wherein, during the time period of charging or discharging of the battery system, one of the two battery modules 1 is in the series circuit for a shorter time than the other battery module 1.

[0039] However, it is necessary to monitor the measured values ​​of the controlled parameters at least periodically in order to obtain the termination criteria for the charging or discharging process of the battery system. However, if balancing is successfully achieved, monitoring the measured values ​​of a single, arbitrary module is sufficient.

[0040] It is important to note in this respect that WO 2020 / 030762 A1 is... Figure 4 The information disclosed in this application is related to the present application. Figure 2 The arrangement is similar to that of the first and second switches (9, 10) of this application, wherein switches 1221 and 1222, referred to as "outer circuit switches", correspond to the first and second switches (9, 10). However, WO 2020 / 030762 A1 states that the purpose of the outer circuit switches 1221 and 1222 is that these switches are used in very rare, infrequent situations, such as in the event of electrolyte leakage or electrolyte replacement (see the last sentence of the specification, "The latter switching is likely to be infrequent and foreventualities such as electrolyte leakage or replacement"). Therefore, WO 2020 / 030762A1 neither discloses nor suggests the method of the present invention described above.

[0041] The inventors recognize that if the above combination Figure 2 The first and second switches of the described battery system are implemented using semiconductor transistors, so the method according to the invention described above can be implemented particularly advantageously. Figure 3 A particularly advantageous embodiment of the switch with a semiconductor transistor according to the invention is shown, wherein, Figure 3 Only one battery module and its associated switch are shown. All other battery modules and their associated switches in the battery system according to the invention are implemented accordingly in this embodiment.

[0042] The first switch 9 includes two normally off MOSFETs connected in series, such that one of the reverse diodes is always off in either current direction. For clarity, Figure 3 The reverse diode is not shown. The second switch 10 includes a normally off MOSFET. The battery system includes at least one switching unit that... Figure 3 The MOSFET is labeled 11. The gate terminals of the MOSFETs are connected to the switching unit 11, wherein the gate terminals of the two MOSFETs of the first switch 9 are also connected to each other, so that the driving of these gates is always simultaneous. If the switching unit 11 internally ensures simultaneous driving of the relevant gates, the aforementioned gate connections can be omitted. A switching unit 11 can be provided for each switch pair (9, 10), or the switching unit 11 can be used for multiple switch pairs (9, 10) or all switch pairs. In the latter two cases, the switching unit 11 must of course have a corresponding number of independent terminals, so that the connected switch pairs can be switched independently of each other. One or more switching units 11 can be an integrated component of the control device 8.

[0043] Using MOSFETs enables wear-free and rapid implementation of the switching processes required for the method described above according to the invention, which is particularly advantageous for frequent but brief pauses used for balancing. Here, the arrangement of the MOSFETs according to the invention prevents the battery module from unintentionally discharging during periods when it is not in a series circuit, and therefore does not participate in the charging or discharging of the battery system. Optionally, each switch 9 and 10 may additionally include a relay arranged in parallel with the MOSFET. Thus, the respective switches can also be operated losslessly with the relays, which is advantageous when the associated switches should be operated only minimally.

[0044] It should be mentioned that, in Figure 3 The MOSFET is shown as an n-channel MOSFET. However, the arrangement according to the invention is not limited to this MOSFET. P-channel MOSFETs can also be used effectively.

[0045] Figure 4A battery system according to another embodiment of the invention is shown. This battery system additionally includes third and fourth switches, labeled 12 and 13, and wiring for each battery module, wherein the additional switches and wiring are connected to each other and to the battery modules, such that when all the additional switches are closed, all battery modules are connected in parallel. Of course, for this purpose, all the first and second switches must be open. The parallel circuit of the battery modules results in equalization of the terminal voltages of the modules, wherein a compensating current flows between the battery modules. Therefore, the parallel circuit shown can be used for balancing. Here, all modules or only a few modules, i.e., at least two modules, for example, the fastest and slowest modules respectively, can be connected in parallel for a limited time period. The additional switches are also operated by a control device, which, due to space constraints, is located in... Figure 4 It is not shown in the document.

[0046] In principle, battery modules can also be charged or discharged in a parallel circuit via PCS 7. However, for this reason, PCS 7 is typically not designed in high-voltage battery systems of this type, thus preventing balancing through parallel connection during charging or discharging.

[0047] Figure 4 Two additional switches are also shown, which can be used to isolate PCS 7 from the interconnected battery module. This can be advantageous. If necessary, only one isolation switch can be used. One or more such switches can also be used in all other implementations.

[0048] Figure 5 A battery system according to another embodiment of the invention is shown. For each battery module 1, the battery system additionally includes a fifth switch, one of which is labeled 14. It should be noted that the designation "fifth" switch is for clarity only and does not imply that if the battery system includes a fifth switch, then it must automatically also include the third and fourth switches. Furthermore, the battery system includes a resistor for each battery module 1, one of which is labeled 15. The fifth switch 14 and resistor 15 are respectively arranged in additional bypass lines bypassing each battery module 1, such that when the corresponding fifth switch 14 is closed, each battery module 1 is short-circuited via resistor 15. The fifth switch 14 is also operated by a control device 8. Figure 5The arrangement allows each battery module to be selectively discharged via a fifth resistor. If one or more fifth switches 14 are closed during charging or discharging of the battery system, a portion of the charging or discharging current flows past the respective battery module 1. This can be used for balancing. However, this type of balancing involves a loss of electrical power and is therefore only an additional balancing measure to other measures, thereby allowing for further flexibility and improvement in balancing through this additional possibility. Since heat is released in the resistor in this manner, it is advantageous that the switching of the fifth switches can be performed in a pulsed manner to avoid overheating.

[0049] When implemented according to Figure 3 When the first and second switches 9 and 10 are closed, the possibility of alternatives to achieve the effects just described is obtained. Since the MOSFET has a limited channel resistance, the battery module can also be selectively short-circuited via the channel resistance of these switches by simultaneously closing the first and second switches 9 and 10. Therefore, in this embodiment of the method according to the invention, the switches mentioned do not alternately open and close in all cases as described above. Here, the two switches 9 and 10 effectively represent the fifth switch 14. The simultaneous closure of switches 9 and 10 can also be interpreted as the battery module being "partially" removed from the series circuit, because only a portion of the charging or discharging current flows through the module, while the other portion flows around it. Therefore, the statement "the control device 8 regulates the number of battery modules 1 in the series circuit" should also be understood as the modules being partially located in the series circuit. In this case, the above-mentioned content regarding heat generation also applies.

[0050] The following implementation scheme relates to a second solution. As mentioned, these two solutions and all associated implementation schemes can be advantageously combined with each other.

[0051] Figure 6 A battery system according to another embodiment of the present invention is shown. The battery system includes at least two battery modules, a bidirectional inverter 7, a control device 8, and a DC-DC voltage converter for each battery module, one of which is designated 17. The battery modules are connected in series and to the inverter 7. One connector of the DC-DC voltage converter 17 is connected to each battery module, and a second connector of the DC-DC voltage converter 17 is connected to a common DC current bus.

[0052] The DC-DC voltage converter can be implemented unidirectionally or bidirectionally. Depending on the implementation type and orientation, the DC-DC voltage converter 17 can draw power from or supply power to the DC current bus in a controlled manner, or both.

[0053] The battery system also includes an additional converter, designated 16. Converter 16 is connected to a DC current bus. A control unit 8 is connected to converter 16 and a DC-DC voltage converter 17, enabling control of both converter 16 and the DC-DC voltage converter 17. Converter 7 is connected to the power grid or another upstream electrical system. The additional converter 16 may also be connected to the power grid or another upstream electrical system, or optionally configured as a DC / DC regulator and connected to converter 7. In the latter case, converter 16 receives power from or supplies power to converter 7. The additional converter 16 can be implemented unidirectionally or bidirectionally.

[0054] As described above, the inverter 7 ensures that charging or discharging current can flow through the series-connected battery modules, allowing them to be charged or discharged. Now, the DC-DC converter 17 connected in parallel with each battery module enables at least a portion of the current supplied by the inverter 7 to be directed and controlled to bypass the battery modules during charging. In this case, the associated DC-DC converter 17 transfers electrical energy to the DC current bus. Thus, during the period when the associated DC-DC converter 17 operates in this manner, the associated battery module will charge more slowly or not at all. During discharging, one or more DC-DC converters 17 can be driven to transfer electrical energy from the DC current bus to their respective battery modules. Here, the associated DC-DC converters 17 are each driven so that during the period when the associated DC-DC converter 17 operates in this manner, the associated battery module will discharge more slowly or not at all.

[0055] It is evident here that a unidirectional DC-DC converter, depending on its orientation, can function either only during charging or only during discharging, as described above. A bidirectional DC-DC converter, of course, can function during both charging and discharging.

[0056] Here, the additional converter 16 supplies power to the DC current bus or draws excess energy away from the DC current bus. Of course, in the case of the additional converter 16 being implemented in one direction, not all of the energy flows mentioned are possible.

[0057] according to Figure 6 The arrangement enables a method for reducing imbalances occurring during the charging and discharging of a battery system, the method comprising at least one of the following steps:

[0058] • During the charging of the battery system, the control device 8 drives the DC voltage converter 17 to reduce the difference in controlled parameters between the first and second battery modules, so that the DC voltage converter 17 transmits to the DC current bus the amount of electrical energy that makes one of the two battery modules charge more slowly than the other.

[0059] • During the discharge of the battery system, the control device 8 drives the DC voltage converter 17 to reduce the difference in controlled parameters between the first and second battery modules 1, so that the DC voltage converter 17 draws away from the DC current bus the amount of electrical energy that makes one of the two battery modules discharge more slowly than the other.

[0060] according to Figure 6 This arrangement also enables, at least when inverter 16 has a separate grid connection, for inverter 7 to support the battery modules during charging or discharging. This is particularly advantageous when inverter 7 reaches its performance limits. Since this support via DC-DC voltage converter 17 can also occur selectively for each battery module, it can certainly also be used for balancing. Compared to the balancing measures described so far, this mechanism results in accelerated charging or discharging of “slow” modules.

[0061] In another embodiment, the method according to the invention for reducing imbalances occurring during charging and discharging of a battery system further includes one of the following steps:

[0062] • When the battery system is charging, the control device 8 drives the DC voltage converter 17 to reduce the difference in controlled parameters between the first and second battery modules, so that the DC voltage converter 17 draws away from the DC current bus the amount of electrical energy that makes one of the two battery modules charge faster than the other.

[0063] • When the battery system is discharging, the control device 8 drives the DC voltage converter 17 to reduce the difference in controlled parameters between the first and second battery modules, so that the DC voltage converter 17 transmits the same amount of electrical energy to the DC current bus, causing one of the battery modules to discharge faster than the other.

[0064] If multiple battery systems according to the invention operate close to each other, then the multiple systems can of course share the additional converter 16 and the connected DC current bus. Since a DC voltage converter must exist for each battery module, there is no possibility of saving on DC voltage converters when multiple battery systems are operated in parallel.

[0065] Figure 7 A battery system according to another embodiment of the present invention is shown. (Compared to...) Figure 6The only difference in the battery system shown is that the auxiliary system is connected to and powered by the DC-DC bus. This provides the additional benefit of cost savings elsewhere for the DC-DC bus. It is also advantageous and feasible to use a shared DC-DC bus and additional converters to power the auxiliary systems of multiple battery systems operating in parallel.

[0066] The second solution is implemented in a manner similar to the detailed description of the first solution above. However, all measures in the second solution naturally involve different rates of charging or discharging of the individual modules, and the duration of application of these different rates. This also applies to statements regarding the execution of the method, including but not limited to acquiring and evaluating measurements related to the controlled parameters.

[0067] To enable the redox flow battery system to automate the aforementioned method steps, it includes a computer system. The term "computer system" refers to any means suitable for automating the method steps, particularly ICs or microcontrollers specifically developed for this purpose, and ASICs (application-specific integrated circuits). Here, the control device 8 itself may include a suitable computer system. Alternatively, the computer system may be a separate device or part of a separate device. This application also relates to a computer program comprising instructions for causing the battery system to perform the aforementioned method steps. Furthermore, this application relates to a computer-readable medium on which such a computer program is stored.

[0068] List of reference numerals

[0069] 1 Battery Module

[0070] 2. Single cell facility

[0071] 3-tank unit

[0072] 4. Measuring apparatus for determining OCV

[0073] 5. Measuring device for determining terminal voltage

[0074] 6. Auxiliary Systems

[0075] 7. Bidirectional converter (PCS)

[0076] 8. Control device

[0077] 9 First Switch

[0078] 10 Second Switch

[0079] 11 Switching Unit

[0080] 12 Third Switch

[0081] 13 Fourth Switch

[0082] 14. Fifth Switch

[0083] 15 Resistors

[0084] 16. Additional bidirectional converter

[0085] 17 DC-DC voltage converter

Claims

1. A method for reducing imbalances occurring during charging and discharging in a redox flow battery system, wherein, The battery system includes at least two battery modules (1), a bidirectional converter (7), and a control device (8), wherein the battery modules (1) are connected in series and connected to the converter (7), and wherein each battery module (1) includes a single-cell facility (2) having multiple redox flow cells and a tank device (3) for storing electrolyte and supplying electrolyte to the single-cell facility (2), characterized in that the battery system includes a DC voltage converter (17) for each battery module (1), wherein each DC voltage converter (17) has one A connector is connected to each of the battery modules (1), and a second connector of each of the DC voltage converters (17) is connected to a common DC current bus, wherein the battery system includes an additional converter (16) connected to the DC current bus, and wherein the control device (8) is connected to the additional converter (16) and the DC voltage converter (17) such that the control device (8) can control the additional converter (16) and the DC voltage converter (17), and wherein the method includes at least one of the following steps: - When the battery system is being charged, the DC voltage converter (17) is driven by the control device (8) to reduce the difference in controlled parameters between the first battery module (1) and the second battery module (1), so that the DC voltage converter (17) transmits to the DC current bus the amount of electrical energy that makes one of the two battery modules (1) charge more slowly than the other battery module (1); - When the battery system is discharged, the DC voltage converter (17) is driven by the control device (8) to reduce the difference in the controlled parameters between the first battery module (1) and the second battery module (1), so that the DC voltage converter (17) draws away from the DC current bus so that one of the two battery modules (1) is discharged as much energy as the other battery module (1) is discharged slowly; wherein each battery module (1) includes an auxiliary system (6) which can be supplied with current from outside the corresponding battery module (1) through a terminal, wherein the terminal of the auxiliary system (6) is connected to the DC current bus and can be fed through the DC current bus.

2. The method according to claim 1, wherein, The DC voltage converter (17) is implemented bidirectionally or unidirectionally.

3. The method according to claim 1, wherein the method comprises one of the following steps: - When the battery system is being charged, the DC voltage converter (17) is driven by the control device (8) to reduce the difference between the first battery module (1) and the second battery module (1) in terms of the controlled parameters, so that the DC voltage converter (17) draws away from the DC current bus the amount of electrical energy that makes one of the two battery modules (1) charge faster than the other battery module (1); - When the battery system is discharged, the DC voltage converter (17) is driven by the control device (8) to reduce the difference between the first battery module (1) and the second battery module (1) in the controlled parameters, so that the DC voltage converter (17) transmits to the DC current bus the same amount of electrical energy that makes one of the two battery modules (1) discharge faster than the other battery module (1).

4. The method according to claim 1, wherein, In the calibration step, the characteristics of each of the battery modules (1) are determined in order to determine different charging or discharging rates for each of the battery modules (1) and to determine the duration for which these different rates are applied.

5. The method according to claim 1, wherein, The battery system includes at least one measuring device (4, 5) for providing the controlled parameter for each of the battery modules (1), and wherein the control device (8) is connected to the measuring device such that the control device can acquire the measured value of the measuring device (4, 5), and wherein the method includes the following steps: - The measurement values ​​of the measuring devices (4, 5) are obtained through the control device (8); - If at a first time point, at least one of the measured values ​​of the first battery module (1) differs from the measured value of the second battery module (1): - Perform at least one of the steps of claim 1 or 3 to reduce the difference in the measured values ​​of the first battery module (1) and the second battery module (1) at a subsequent second time point, wherein the step is performed during a time period between the first time point and the second time point.

6. The method according to any one of the preceding claims, wherein, The battery system includes a first switch (9) and a second switch (10) for each battery module (1), wherein the first switch (9) is arranged in series with the corresponding battery module (1), and the second switch (10) is arranged in a bypass line that bypasses the corresponding battery module (1) and the corresponding first switch (9), and wherein the control device (8) is connected to each of the switches (9, 10) so that the control device can determine the respective switch position in order to connect the battery module (1) to or disconnect it from the series circuit, wherein the method includes the following steps: - The control device (8) regulates the number of battery modules (1) in the series circuit in order to reduce the difference between the first battery module (1) and the second battery module (1) in terms of the controlled parameters, wherein, during the time period of charging or discharging of the battery system, one of the two battery modules (1) is in the series circuit for a shorter time than the other battery module (1).

7. A redox flow battery system, the redox flow battery system comprising at least two battery modules (1), a bidirectional converter (7), and a control device (8), wherein, The battery modules (1) are connected in series with the converter (7), and each battery module (1) includes a single cell facility (2) having a plurality of redox flow cells and a tank device (3) for storing electrolyte and supplying electrolyte to the single cell facility (2). The redox flow battery system includes a DC voltage converter (17) for each battery module (1), wherein each DC voltage converter (17) has a connector connected to one of the battery modules (1), and a second connector of each DC voltage converter (17) is connected to a common DC current bus. The redox flow battery system includes an additional converter (16) connected to the DC current bus. A control device (8) is connected to the additional converter (16) and the DC voltage converter (17) such that the control device (8) can control the additional converter (16) and the DC voltage converter (17). The redox flow battery system is configured to automatically execute the method steps according to any one of claims 1 to 6.

8. The redox flow battery system according to claim 7, wherein, The DC voltage converter (17) is implemented bidirectionally or unidirectionally.

9. The redox flow battery system according to any one of claims 7 or 8, wherein, Each of the battery modules (1) includes an auxiliary system (6) that can be supplied with current from outside the respective battery module (1) via a terminal, wherein the terminal of the auxiliary system (6) is connected to and can be fed through the DC current bus.

10. The redox flow battery system according to claim 9, wherein, The redox flow battery system includes a first switch (9) and a second switch (10) for each of the battery modules (1), wherein the first switch (9) is arranged in series with the corresponding battery module (1), and the second switch (10) is arranged in a bypass line that bypasses the corresponding battery module (1) and the corresponding first switch (9), and wherein the control device (8) is connected to each of the switches (9, 10) so that the control device can determine the respective switch position in order to connect the battery module (1) into or disconnect it from the series circuit.

11. The redox flow battery system according to claim 10, wherein, The first switch (9) includes two normally off MOSFETs, the channels of which are connected in series, such that one of the reverse diodes is always off in both current directions, and the second switch (10) includes two normally off MOSFETs.

12. The redox flow battery system according to any one of claims 10 or 11, wherein the redox flow battery system is configured to automatically perform the method steps according to any one of claims 1 to 6.

13. A computer-readable storage medium, characterized in that, The device stores instructions that, when executed by a processor of the control device of any one of claims 7-12, cause the redox flow battery system to perform the method of any one of claims 1-6.

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