Redox flow battery system and method of operation

Abstract

The invention relates to a redox flow battery system and method for operating it, wherein the method for operating it increases the reliability and availability of the redox flow battery system.

Description

The invention relates to a redox flow battery system and method of operation, the method of operation increasing the reliability and availability of the redox flow battery system.Considerations of the Prior Art:DE10 2020 108068 A1 and DE10 2020 108053 A1 : The documents mentioned show a redox flow battery system (RFBS) 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 are connected to the converter (7), and wherein each battery module (1) comprises a cell arrangement (2) having a plurality of redox flow cells and a tank device (3) for storing electrolyte and for supplying the cell arrangement (2) with electrolyte, and wherein the battery system comprises a DC voltage converter (17) for each battery module (1), wherein one terminal of each DC voltage converter (17) is connected to a respective battery module (1), and a second terminal of each DC-to-DC converter (17) is connected to a common DC bus, and wherein the battery system comprises a further converter (16) which is connected to the DC bus, and wherein the control device (8) is connected to the further converter (16) and to the DC-to-DC converters (17) in such a way that the control device (8) can control the further converter (16) and the DC-to-DC converters (17) (see in particular FIGS. 6 and 7 of the documents mentioned).Disadvantages and limitations of the cited prior art: Redox flow battery systems, which are produced from a series circuit of a plurality of battery modules, are subject to the need for the availability of the RFBS to be defined by the functionality of all battery modules. For this reason, switches are used in many of these systems (see (9) and (10) in the cited prior art), the purpose of which is a bypass of individual battery modules. One of the main causes of defects in individual battery modules is the lifetime and unreliability of the interconnection of the electronic components (e.g. the converters ( 16) and the DC-DC converters ( 17) in the documents cited). In addition, the above-mentioned bypass switches ( 9) and ( 10) are subject to a high load due to short-circuit currents and thus to an increased failure rate. In addition, the embodiment according to the prior art has the disadvantage that, in the event of failure of the converter ( 16) in the connection of the common DC bus, damage patterns arise which cause failures in a plurality of the DC-to-DC converters ( 17) and thus result in failure of the entire RFBS despite an embodiment with bypass switches ( 9) and ( 10). In the RFBS disclosed in the prior art, due to the spatial form in combination with a low voltage level in a spatially very distributed common direct current bus, it can result in additional electrical losses arising in such RFBS, which reduce the efficiency, or the same must be avoided by large cable cross sections, which however results in increased costs for the RFBS thus formed.US 2023126285 A and DE 10 2020 108053 A1: The documents cited disclose the following method for reducing imbalance occurring during charging and discharging of the battery system comprising at least one of the following steps:• During charging of the battery system, the DC-to-DC converters 17 are controlled by the control device 8 in order to reduce the difference between a first and a second battery module with respect to a controlled variable in such a way that a DC-to-DC converter 17 transfers so much electrical energy to the DC bus that one of the two battery modules is thereby charged less quickly than the other battery module.• During the discharging of the battery system, the DC-to-DC converters 17 are controlled by the control device 8 in order to reduce the difference between a first and a second battery module 1 with respect to a controlled variable in such a way that a DC-to-DC converter 17 dissipates so much electrical energy from the DC bus that one of the two battery modules is thereby discharged less quickly than the other battery module.The disclosed arrangement also makes it possible, at least if the converter 16 has a separate mains connection, for it to support the converter 7 during charging or discharging of the battery modules. This is advantageous in particular when the converter 7 meets its power limits. Since this support by the DC-to-DC converters 17 can also be carried out selectively for each battery module, this can of course also be used for balancing. This mechanism for accelerating loading and unloading of the "slow" modules.Disadvantages and Limitations of the Cited Prior Art:The same disadvantages and restrictions as shown above arise, in particular for spatial propagation, susceptibility to errors and losses of the common DC bus. And in addition, in this embodiment, in the case of a problem, individual battery modules can be deactivated only by the bypass switches 9 or 10 at the converters 16 or at the DC-DC converters 17. A further disadvantage of this embodiment is the fact that three advantageous states can be achieved for the compensation logic only if the DC / DC converters 17 are configured bidirectionally.WO 2022033750 A1: This document discloses a method for operating a vanadium redox flow battery system, wherein the method comprises the following steps: S1: connecting at least one battery module (1) to a converter (6, 7); S2: feeding a current into the at least one battery module (1) which has been connected to the converter (6, 7) in step S1 until at least part of the electrolyte associated with this battery module (1) reaches a state of charge which is at least as high as a predefined threshold value; S3: driving the first and second switches (9, 10) such that all battery modules (1) are in a series circuit which is connected to the bidirectional converter (6); S 4: Feeding a current into the series circuit from step S 3, wherein electrolyte is conveyed in all battery modules ( 1) (see in particular FIGS. 3 and 4 ).Disadvantages and Limitations of the Cited Sand of the Art:The converter 7 cannot be used in a fully flexible manner because the switches 11 and 12 can only be used to connect or disconnect the converter to one or more battery modules 1. However, it is not possible to use the inverter 7 for charging and discharging for the respective battery modules 1 simultaneously.DE 10 2017 222979 A1: This document discloses a balancing unit that balances voltages of a plurality of electric storage cells; and an electricity sending / receiving unit that receives, without turning off or switching an electrical connection between (a) the plurality of electric storage cells and (b-1) a load that uses electric power of the plurality of electric storage cells, or (b-2) a charging device that charges the plurality of electric storage cells, (i) electric power of the plurality of electric storage cells to an external array different from the load and the charging device, or (ii) electric power supplied to the plurality of electric storage cells from the external array.The electricity transmitting / receiving unit shows an isolated bidirectional DC-DC converter.Disadvantages and Limitations of the Cited Prior Art:The cited document discloses, like the above-mentioned documents, embodiments which can lead to a reduction in the availability of the RFBS by a dependence / coupling of the compensation correction unit 220 and / or the protection unit 230 and / or the DC-DC converter 330.The functionality of all battery modules also defines here the availability of the series-connected battery. Here, too, the prior art does not offer any suitable possibility of increasing the availability and of enabling important functions for establishing the operability and maintaining the operability.The object of the invention is to specify redox flow battery systems and methods for operating the same, which have a high reliability and availability.The object of the invention is in particular to eliminate the problems and restrictions from the prior art and to increase the availability of an RFBS. This is achieved according to the invention by a decentralized and improved compensation unit which is capable of permitting maintenance of the operability and restoration of the operability. In addition, the arrangement according to the invention enables individual battery modules to be shut down, which assists the service of the RFBS. In addition, the arrangement according to the invention can be used to restore the performance of a battery mode.The object is achieved according to the invention by an embodiment and a method according to the independent claims. Further advantageous embodiments of the present invention are found in the dependent claims.The invention is explained below with reference to figures. The figures show in detail: FIG. 1 : Battery module FIG. 2 : Redox flow battery system according to the invention FIG. 3 : Compensating unit according to the invention FIG. 4 : Switching device in a first embodiment FIG. 5 : Switching device in a further embodiment FIG. 6 : Switching device in a further embodiment FIG. 7 : Switching device in a further embodimentFIG. 1 shows a battery module which is designated by 1. It comprises a cell arrangement, which is denoted by 2, a tank device for storing electrolyte liquid, which is denoted by 3, an optional measurement device for determining the open circuit voltage, which is denoted by 4, and an optional measurement device for determining the terminal voltage, which is denoted by 5. The battery module generally comprises auxiliary systems which are indicated by the rectangle with the designation 6. The battery module 1 also comprises pumps for supplying the cell arrangement 2 with electrolyte liquid from the tank device 3.FIG. 2 shows a redox flow battery system according to the invention in schematic representation. The battery system comprises at least two battery modules, one of which is denoted by 1, a bidirectional power conversion system (PCS) which is denoted by 7 and a control device which is denoted by 8. For better differentiation with other converters (see below) of the battery system, the bidirectional inverter is referred to below as "main converter". The battery modules 1 are connected in series and connected to the main converter 7. Four battery modules are shown in FIG. 2, the dashed lines in the series circuit being intended to indicate any desired number of further modules. The main converter 7 carries out the connection of the battery system to the grid or to a superordinate electrical system. Optionally, the battery system may comprise a bypass switch for each battery module 1, which is denoted by 9 in FIG. 2. The bypass switches 9 are arranged in parallel with the associated battery modules 1 and can be used for balancing, among other things (see e.g. DE 10 2022 109 193 B3). However, they can also be used to permanently disconnect a battery module 1 which has a fault from the series circuit of the battery system and thus ensure the availability of the battery system as a whole even in the event of failure of a battery module 1 (or of a few battery modules 1).The redox flow battery system further comprises a compensation unit, which is designated 60. The compensation unit 60 can be assigned to a single battery module ( 1). For reasons of clarity, only one compensation unit 60 is shown in FIG. 2, which compensation unit is assigned to the battery module 1 shown on the far left. In a redox flow battery system according to the invention, each battery module 1 is preferably assigned a separate compensation unit 60. However, it is also conceivable that a separate compensation unit 60 is not assigned to each battery module 1. In general, at least two battery modules 1 are each assigned a separate compensation unit 60.The compensation unit 60 is fed by an energy supply unit 30, which in a preferred variant of the invention is designed as an AC voltage network. In further embodiments, the energy supply unit 30 can be designed as an uninterrupted supply, which temporarily compensates errors and temporary faults in the AC voltage network and thus further increases the availability. The advantageous use of the uninterrupted power supplies, which can be used as an electrical source for the auxiliary systems 6 in the battery modules 1, for the auxiliary systems of the main converter 7 and for the control device 8, is the enabling of the RFBS for grid-independent operation. This is particularly advantageous if the redox flow battery system is to be used for the purpose of network stabilization, for operation of an island network or for restoration of the public network (black start).One way to enable seamless power supply is to use back-up systems such as diesel generators, batteries or capacitors. These systems can supply the necessary energy in the event of undervoltages or power failures in order to put the energy supply unit 30 and thus the battery power plant back into operation. This ensures that the power supply remains stable even in the event of unpredictable events. These backup systems have different voltage forms as alternating voltage or direct voltage depending on the embodiment. In an advantageous embodiment, the converter 20 is implemented in the same voltage form that is provided by the uninterrupted power supply by the power supply unit 30. In the case of an alternating voltage, the converter 20 is designed as AC-DC, and in the case of a direct voltage, the converter 20 is designed as DC-DC.A further advantage of an embodiment of the energy supply unit 30 as an uninterrupted power supply is the possibility, by a comparatively small energy input, of raising the voltage level in the cell arrangement 2, when the flow from the tank device 3 is deactivated, to a level at which the main converter 7 can be activated and actively participate in the grid stabilization.The balancing unit 60 further comprises a protection and insulation unit, which is designated 40, an inverter, which is designated 20, and a unit for increasing availability, which is designated 50. The protection and insulation unit is to be considered optional. The power supply unit 30 can be separated from the potential of the battery module 1 by the protection and insulation unit 40.The control device 8 is designed such that it can control the compensation units 60, the pumps in the battery modules 1, the main converter 7 and any bypass switches 9 present.The availability increasing unit 50 serves the purpose of increasing the availability of the battery module 1. This will be explained in more detail in connection with FIGS. 3 to 7.FIG. 3 shows a compensation unit 60 according to the invention. In order for the protection and insulation unit 40 to be able to disconnect the energy supply unit 30 from the potential of the battery module 1, the protection and insulation unit 40 comprises a protection unit which is denoted by 41 and which can disconnect the energy supply unit 30 from the converter 20, for example by means of suitable switches. Additionally, the protection unit 41 may include a ballast circuit for relieving the power supply unit 30 from temporarily high inrush currents that may be caused by the balancing unit 60. Optionally, the protection and isolation unit 40 may comprise an isolation unit, indicated at 42. This can be used when the battery system 1 is operated in the network form of an IT system (Isolé Terre), in which there is no galvanic connection between active conductors and grounded parts of the battery system 1. In this case, within the protection and isolation unit 40, the isolation unit 42 is used to isolate the potential of the battery module 1 and the power supply unit 30 from each other.In a preferred embodiment of the invention, the protection unit 41 is realized by an all-pole relay and / or by a passive circuit which attenuates high inrush currents when the compensation unit 60 is activated and deactivated.In a preferred embodiment of the invention, the isolation unit 42 is implemented by an isolation transformer, e.g., in the embodiment of a toroidal core transformer. Further embodiments are possible here and can be advantageous, for example, in the case of different voltages or grid shapes.In a further embodiment, the protection and insulation unit 40 can be completely omitted.The inverter 20 enables a method for reducing imbalance occurring during charging and discharging of the battery system. The converter can be configured uni- or bi-directional. The converter 20 can be used to speed up or delay or not influence a voltage build-up in the battery module 1. In a preferred embodiment, individual or all components of the protection and insulation unit 40 can be integrated in the converter 20 on the input or output side. The converter 20 is capable of performing this influence in addition to an external charge or discharge of the battery system (and thus of the battery modules 1) by the main converter 7.The embodiment of the converter 20 as a unidirectional or bidirectional converter allows the operability to be restored during initial startup or after discharge for service purposes. In this case, the voltage build-up in the battery module 1 is provided by the respective compensation unit 60 and the power supply unit 30.The embodiment of the converter 20 as a bidirectional converter allows the relevant battery module 1 to be impressed with a state which assists deactivation, for example during service. In this case, the voltage reduction in the relevant battery module 1 is effected by the compensation unit 60 and the energy supply unit 30.The embodiment of the converter 20 as a bidirectional converter furthermore makes it possible to restore the performance of a battery module 1 by the compensation unit ( 60) and the energy supply unit 30, by the voltage reduction being used exclusively by the compensation unit 60 or in cooperation with the external discharge via the bidirectional main converter 7 to reverse the voltage in a battery module 1.The availability increasing unit 50 serves, as stated, the purpose of increasing the availability of the battery module 1. For this purpose, the availability increasing unit 50 comprises an integrated switching device, which is designated 52. With the aid of the integrated switching device 52, the relevant battery module 1 can be decoupled from influences by the compensation unit 60. For this purpose, an integrated switching device 52 comprises at least one switch, by means of which any of the two DC connections to the battery module 1 can be disconnected.FIG. 4 shows a first embodiment of the integrated switching device 52. With the switch 53, one of the two DC connections to the battery module 1 can be interrupted.FIG. 5 shows a further embodiment of the integrated switching device 52 The integrated switching device 52 shown comprises two switches for this purpose, which are designated by 54 and 55. The switches 54 and 55 can be used to disconnect both DC connections to the battery module 1.FIGS. 6 and 7 show two further particularly advantageous embodiments of the integrated switching device 52. In addition to the disconnection of the compensation unit 60 from the relevant battery module 1, the two embodiments make it possible to change the polarity of the compensation unit 60 with respect to the relevant battery module 1.For this purpose, the embodiment shown in FIG. 6 comprises two coupled switches, which are designated by 54 aand 55 band which each have three switching states. In the switching state shown in FIG. 6, a first polarity results (the lines are simply carried out). In the second switching state, the two switches 54 aand 55 bare switched to the middle contact (neutral position), as a result of which the compensation unit 60 is disconnected from the relevant battery module 1. In the third switching state, the switches 54a and 55b are switched to the lower contact, whereby the polarity is reversed from the switching state shown in FIG. 6.The same functionality is provided by the embodiment shown in FIG. 7. For this purpose, the integrated switching device 52 shown comprises four switches, which are designated 56, 57, 58 and 59. Two switches are coupled to one another. If both pairs of switches are opened, the compensation unit 60 is separated from the relevant battery module 1. By alternately opening and closing the two pairs of switches, the polarity can be influenced.These particularly advantageous embodiments with the possibility of changing the polarity of the compensation unit 60 allow a unidirectional converter to be used for the converter 20. As a result, the converter 20 can be used to impose a state to the battery module 1 which enables deactivation, for example during service. In this case, the voltage reduction in the relevant battery module 1 is provided by the compensation unit 60 and the energy supply unit 30. In addition, the converter 20 can be used to restore the performance of the battery module 1 in question by the compensation unit 60 and the energy supply unit 30 by using the voltage reduction exclusively by the compensation unit 60 or in cooperation with the external reduction of the voltage by the main converter 7 to reverse the voltage in the battery module 1 in question.Furthermore, the native function of the compensation unit 60 can also be used to accelerate or delay or not influence a voltage build-up in the relevant battery module 1. The three states mentioned can be implemented by using a unidirectional converter 20 and a switching device 52 with polarity reversal functionality. In this case, the control unit 8 can adjust the polarity of the compensation unit 60 depending on the desired state (voltage build-up of the relevant battery module 1 accelerating or delaying) and on the current operating state of the RFBS (charging or discharging) in order to implement the desired function using a unidirectional converter 20. Without the switching device 52 with polarity changer, a bidirectional converter 20 would always be necessary for this purpose, which entails lower availability, a higher probability of failure and higher costs.The above-mentioned embodiments of the switching device 52 could lead to faults in the compensation unit 60 and / or the relevant battery module 1 in the event of incorrect actuation or faults in the switches. The availability increasing unit 50 can be extended, in order to avoid the aforementioned problems, by a protection device which is denoted by 51 in FIG. 3 and which, by means of active or passive electronic components, prevents the protection against polarity reversal or a forced current reversal at the output of the converter 20.In order that a redox flow battery system, which is briefly indicated above and is explained in detail below, can be carried out in an automated manner, it comprises a computer system. The term computer system denotes all devices which are suitable for carrying out the described method steps in an automated manner, in particular also programmable logic controllers, ICs or microcontrollers which are specially designed for this purpose, and ASICs (ASIC: application-specific integrated circuit). The control device 8 itself can comprise a suitable computer system. Alternatively, the computer system can also represent a separate device or be part of a separate device. The present application is also directed to a computer program comprising instructions for causing the battery system to perform the method steps described above. Moreover, the present application is directed to a computer readable medium on which such a computer program is stored.Description of the Methods Possible with the Battery System According to the Invention:Increase in Availability:In the event of a fault in at least one of the compensation units 60, the associated battery module 1 may be adversely affected. In order to prevent this and thus to increase the availability of the battery system overall, the relevant compensation unit is electrically disconnected from the associated battery module 1 in the event of a fault.The disconnection of the battery modules 1 or the cell arrangements 2 from the unidirectional or bidirectional converter 20 can be accomplished with the aid of the switching device 52 by carrying out one of the following steps:opening the switch 53 in a one-switch configuration as shown in FIG. 4.opening at least one switch 54 or 55 in a two-switch configuration as shown in FIG. 5shifting at least one switch 54a or 55b to a neutral position in a configuration having two switches (neutral positions) as shown in FIG. 6.opening all switches 56, 57, 58 and 59 in a four switch configuration as shown in Fig. 7.Initialization or Restoration of Operability after Initial Startup or After Discharge:The battery modules 1 can be initialized using a unidirectional or bidirectional converter 20 using a switching device 52 by carrying out one of the following steps:closing the switch 53 in a one-switch configuration, as shown in FIG. 4, and applying a charging power to the battery module 1 (in particular to the cell arrangement 2) with running pumps for carrying out the initial charging of the battery module 1 and without running pumps for carrying out the initial charging of the cell arrangement 2.closing the two switches 54 and 55 in a configuration with two switches as illustrated in FIG. 5, and applying charging power to the battery module 1 (in particular to the cell arrangement 2) with running pumps to perform initial charging of the battery module 1 and without running pumps to perform initial charging of the cell arrangement 2.switching the two switches 54 aand 55 bto the first position in a two-switch configuration as illustrated in FIG. 6 and applying charging power to the battery module 1 (in particular to the cell arrangement 2), wherein the pumps run to perform initial charging of the battery module 1 and without the pumps running to perform initial charging of the cell arrangement 2.closing the two switches 57 and 58 in a configuration with four switches, as shown in FIG. 7, and applying a charging power to the battery module 1 (in particular to the cell arrangement 2) with running pumps in order to perform an initial charging of the battery module 1 and without running pumps in order to perform an initial charging of the cell arrangement 2.De-initialization or provision of a state supporting out of service, for example:The de-initialization of the relevant battery module 1 or the cell arrangement 2 using a bidirectional converter 20 can be achieved with a switching device 52 by carrying out one of the following steps:closing the switch 53 in a one-switch configuration as illustrated in FIG. 4, and applying a discharge power to the battery module 1 (in particular to the cell array 2) with pumps running to perform the de-initialization of the battery module 1 and without pumps running to perform the de-initialization of the cell array 2.closing both switches 54 and 55 in a configuration with two switches as shown in FIG. 5, and applying a discharge power to the battery module 1 (in particular to the cell arrangement 2) with running pumps to perform de-initialization of the battery module 1 and without running pumps to perform de-initialization of the cell arrangement 2.switching the two switches 54 aand 55 bto a first position in a two-switch configuration as illustrated in FIG. 6, and applying discharge power to the battery module 1 (specifically, to the cell array 2), the pumps running to perform de-initialization of the battery module 1, and without the pumps running to perform de-initialization of the cell array (2).closing the two switches 57 and 58 in a configuration with four switches, as shown in FIG. 7, and applying a discharge power to the battery module 1 (in particular to the cell arrangement 2) during running pumps in order to perform a de-initialization of the battery module 1 and without running pumps in order to perform a de-initialization of the cell arrangement 2.The de-initialization of the relevant battery module 1 or of the cell arrangement 2 with a unidirectional or bidirectional converter 20 (supporting only the charging function) can be achieved with a switching device 52 by carrying out one of the following steps:switching the two switches 54 aand 55 bto a third position in a two-switch configuration as illustrated in FIG. 6, and applying charging power to the battery module 1 (specifically, to the cell array 2) with pumps running to perform the de-initialization of the battery module 1 and without pumps running to perform the de-initialization of the cell array 2. In this case, a polarity reversal protection circuit 51 is required.closing the two switches 56 and 59 in a configuration with four switches, as shown in FIG. 7, and applying a charging voltage to the battery module 1 (in particular to the cell arrangement 2), wherein the pumps run for carrying out the de-initialization of the battery module 1 and the pumps do not run for carrying out the de-initialization of the cell arrangement 2. In this case, a polarity reversal protection circuit 51 is required.Reduction of Imbalance Occurring During Charging and Discharging of a Redox Flow Battery System:State of charge (SOC) balancing of a group of modules connected in a string configuration may be accomplished through the use of a bidirectional inverter 20 along with a switching device 52 by performing one of the following steps:closing the switch 53 in a on-switch configuration as illustrated in FIG. 4 and applying charging or discharging power to the battery module 1.closing the two switches 54 and 55 in a two-switch configuration as illustrated in FIG. 5, and applying charging or discharging power to the battery module 1.switching the two switches 54 aand 55 bto a first position in a two-switch configuration as illustrated in FIG. 6, and applying charging or discharging power to the battery module 1.closing the two switches 57 and 58 in a four switch configuration as shown in FIG. 7 and applying charging or discharging power to the battery module 1.In addition, the balancing of state of charge (SOC) of a group of modules connected in a string configuration may be accomplished by using a unidirectional or bidirectional (only charging function supporting) inverter 20 along with a switching device 52 by performing one of the following steps:Switching both switches 54 aand 55 bto a third position in a two-switch configuration as illustrated in FIG. 6 and applying charging power to the battery module 1.In a configuration with four switches, as shown in FIG. 7, closing both switches 56 and 59 and applying a charging voltage to the battery module 1.Restoration of Performance of Battery Module 1:The reversal of the polarity of the cell arrangement 2 may be advantageous for the recovery of cell aging by charging the cell arrangement 2 with a negative voltage. This can be achieved by using a unidirectional or bidirectional (only supporting the charging function) converter 20 together with the switching devices 52 and a battery module 1 by carrying out one of the following steps:Switch both switches 54a and 55b to position 3 in a two-switch configuration as shown in Figure 6, adjust the speed of the pumps to adjust reduced or no flow through the cell array 2, and apply charging power to the battery module 1.In a configuration with four switches, as shown in FIG. 7, closing the two switches 56 and 59, adjusting the rotational speed of the pumps in order to set a reduced or no flow through the cell arrangement 2, and supplying the battery module 1 with a charging power. In this case, a polarity reversal protection circuit 51 is required.separating the battery module 1 in question from the compensation unit 60:The disconnection of the relevant battery module 1 or the associated cell arrangement ( 2) from the unidirectional or bidirectional converter 20 with the aid of the switching devices ( 52) is achieved by carrying out one of the following steps:opening the switch 53 in a one-switch configuration as shown in FIG. 4.opening at least one switch 54 or 55 in a two-switch configuration as shown in FIG. 5shifting at least one switch 54a or 55b to a neutral position in a configuration having two switches (neutral positions) as shown in FIG. 6.opening all switches 56, 57, 58 and 59 in a four switch configuration as shown in Fig. 7.List of reference characters1 Battery module 2 Cell arrangement 3 Tank device 4 Measuring device for determining the open circuit voltage 5 Measuring device for determining the terminal voltage 6 Auxiliary systems in the battery module 7 Bidirectional inverter / main converter 8 Control unit 9 Bypass switch 20 AC-DC converter 30 Energy supply unit 40 Protection and insulation unit 41 Protection unit 42 Insulation unit 50 Unit for increasing the availability 51 Polarity reversal protection circuit 52 Switching device 53 Switch 54 Switch 54 aSwitch 55Switch 55 bSwitch 56Switch 57Switch 58Switch 59Switch 60 Compensation unitReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 108068 A1

[0002] DE 10 2020 108053 A1 [0002, 0004]US 2023126285 A

[0004] WO 2022033750 A1

[0007] DE 10 2017 222979 A1

[0009] DE 10 2022 109 193 B3

[0018]

Claims

Redox flow battery system comprising at least two battery modules (1), a main converter (7), an energy supply unit (30) and a control device (8), wherein the battery modules (1) are connected in series and are connected to the main converter (7), and wherein each battery module (1) comprises a cell arrangement (2) having a plurality of redox flow cells and a tank device (3) for storing electrolyte liquid and pumps for supplying the cell arrangement (2) with electrolyte liquid, characterized in that the battery system comprises a compensation unit (60) each for at least two battery modules (1), and wherein one connection of each compensation unit (60) is connected to the associated battery module (1) each, and a second connection of each compensation unit (60) is connected to the energy supply unit (30), and wherein each compensation unit (60) comprises an inverter (20) and an availability increasing unit (50), and wherein the availability increasing unit (50) is connected on a first side to the inverter (20) and on a second side to the associated battery module (1), and wherein the control device (8) is designed such that it can control the compensation units (60), the pumps in the battery modules (1) and the main inverter (7).Redox flow battery system according to Claim 1, wherein the converters (20) are of bidirectional or unidirectional design and are connected to the energy supply unit (30) via direct or alternating voltage, and wherein the units for increasing availability (50) each comprise a switching device (52), and wherein each switching device comprises at least one switch (53, 54, 55, 54a, 55b, 56, 57, 58, 59).Redox flow battery system according to Claim 1 or 2, wherein the energy supply unit (30) is designed as an uninterrupted supply, and wherein each battery module (1) comprises auxiliary systems (6), and wherein the main converter (7) comprises auxiliary systems, and wherein the auxiliary systems (6) of the battery modules (1) and the auxiliary systems of the main converter (7) and the control device (8) are supplied with electrical energy by the energy supply unit (30).Redox flow battery system according to one of Claims 1 to 3, wherein the energy supply unit (30) provides an alternating voltage, and wherein the converters (20) are designed as AC-DC converters.Redox flow battery system according to one of Claims 1 to 3, wherein the energy supply unit (30) provides a direct voltage, and wherein the converters (20) are designed as DC-DC converters.Redox flow battery system according to one of the preceding claims, wherein each compensation unit (60) comprises a protection and insulation unit (40) which is designed such that it galvanically separates the potential of the energy supply unit (30) from the potential of the associated battery module (1).The redox flow battery system according to any one of claims 2 to 6, wherein each switching device (52) comprises at least two switches (54, 55, 54a, 55b, 56, 57, 58, 59).Redox flow battery system according to Claim 7, wherein the converters (20) are of unidirectional design and are connected to the energy supply unit (30) via direct voltage or alternating voltage.Redox flow battery system according to Claim 8, wherein each switching device (52) is designed such that it can change the polarity of the compensation unit (60) with respect to the associated battery module (1), and wherein each availability-increasing unit (50) comprises a protection device (51) which is designed such that it can protect the associated converter (20) from impermissible polarity states.Redox flow battery system according to one of the preceding claims, wherein the battery system comprises a bypass switch (9) for each battery module (1), wherein the first switch (9) is in each case arranged in parallel with the associated battery module (1), and wherein the control device (8) is connected to each of the bypass switches (9) in such a way that it can determine the respective switch position of the bypass switches (9) in order to switch the battery modules (1) into the series circuit or out of the series circuit.Method for increasing the availability of the battery modules (1) in a redox flow battery system according to one of Claims 2 to 8, which actuates at least one switch (53, 54, 55, 54a, 55b, 56, 57, 58, 59) of the switching device (52) associated with the battery module (1) concerned in the event of at least one fault in at least one of the compensation units (60), in order to prevent further influencing of the battery module (1) concerned by disconnecting the connection between the associated compensation unit (60) and the battery module (1) concerned.Method for reducing imbalance occurring during charging and discharging of a redox flow battery system according to one of Claims 1 to 8, wherein the control device (8) can control the compensation units (60) and the main converter (7), and wherein the method comprises at least one of the following steps: - during charging of the battery system, a compensation unit (60) is controlled by the control device (8) in order to reduce the difference between a first and second battery module (1) with respect to a controlled variable such that at least one converter (20) transfers so much electrical energy to a battery module (1) that as a result one of the two battery modules (1) is charged less quickly than the other battery module (1); During the discharging of the battery system, a compensation unit (60) is controlled by the control device (8) in order to reduce the difference between a first and second battery module (1) with respect to a controlled variable in such a way that at least one converter (20)) discharges so much electrical energy from one battery module (1) that as a result one of the two battery modules (1) is discharged less quickly than the other battery module.Method for reducing imbalance occurring during charging and discharging of a redox flow battery system according to one of Claims 1 to 8, in that the control device (8) can control the compensation unit (60) and bidirectional main converter (7), and wherein the method comprises at least one of the following steps: - during charging of the battery system, a compensation unit (60) is controlled by the control device (8) in order to reduce the difference between a first and second battery module (1) with respect to a controlled variable such that at least one converter (20) discharges so much electrical energy to a battery module (1) that as a result one of the two battery modules (1) is charged more quickly than the other battery module (1); During the discharging of the battery system, a compensation unit (60) is controlled by the control device (8) in order to reduce the difference between a first and second battery module (1) with respect to a controlled variable in such a way that at least one converter (20) transfers so much electrical energy to at least one interface to the battery module (1) that as a result one of the two battery modules (1) is discharged more quickly than the other battery module (1).Method according to 12 and 13, wherein the control device (8) can control the compensation unit (60) and the bidirectional converter (7) in such a way that the control device (8) actuates at least one unit for increasing the availability (50) with the switching device (52), that the energy is not discharged to the energy supply unit (30) but remains in the battery module (1) as a result of the change in polarity of the compensation unit (60).Method according to one of the 11 to 14 claims, wherein the control device (8) can control the compensation units (60), the main converter (7) and the electrolyte transfer in the battery modules (1) from the tank device (3) to the cell arrangement (2), and wherein in each battery module (1) the cell arrangement (2) can be discharged by the compensation unit (60) alone or in cooperation with the main converter (7), wherein an electrolyte transfer or no electrolyte transfer to the cell arrangement (2) can be present and voltage levels on the respective cell arrangement resulting from the discharge of the cell arrangement (2) support an out-of-operation or a service in at least one battery module (1).Method according to one of the preceding claims, wherein the control device (8) can control the compensation units (60), the main converter (7) and the electrolyte transfer in the battery modules (1) from the tank device (3) to the cell arrangement (2), and wherein in each battery module (1), in a state in which the voltage potential of the relevant cell arrangement (2) is too low for an activation of the main converter (7), the relevant cell arrangement (2) is charged by the associated compensation unit (60) alone, wherein an electrolyte transfer or no electrolyte transfer to the cell arrangement (2) can be present and until at least one voltage level is established which allows the activation of the main converter (7).Method for restoring the performance of a battery module (1) of a redox flow battery system according to one of Claims 1 to 10, wherein the control device (8) can control the main converter (7), the battery modules (1) and / or the compensation units (60) in such a way that the voltage is reversed in at least one battery module (1) during the discharging process of the redox flow battery system.Method according to one of Claims 11 to 17, wherein the control device (8) can control the compensation units (60) and the main converter (7) in such a way that the control device (8) actuates at least one unit for increasing the availability (50) with that of the associated switching device (52) in such a way that, by changing the polarity of the compensation unit (60) in the compensation units (60), a unidirectional converter (20) can be used in each case for the voltage build-up and dissipation of the associated battery modules (1).

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