WO2025108979A1 - Redox flow battery system and method for operating same - Google Patents

Abstract

The invention relates to a redox flow battery system and to a method for operating same, the operating method increasing the reliability and availability of the redox flow battery system.

Description

Redox flow battery system and method of operation

The invention relates to a redox flow battery system (RFBS) and method for operation, wherein the method for operation increases the reliability and availability of the redox flow battery system.

Considerations on the state of the art:

DE 10 2020 108 068 A1 and DE 10 2020 108 053 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 to the converter (7), and wherein each battery module (1) comprises a cell arrangement (2) with 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-DC converter (17) for each battery module (1), wherein one connection of each DC-DC converter (17) is connected to a respective battery module (1), and a second connection of each DC-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 thus connected to the further converter (16) and to the DC-DC converters (17) are connected so that the control device (8) can control the further converter (16) and the DC-DC converters (17) (see in particular Figures 6 and 7 of the documents mentioned).

Disadvantages and limitations of the cited prior art:

Redox flow battery systems, which are constructed from a series connection of a large number of battery modules, are subject to the requirement that the availability of the RFBS be defined by the functionality of all battery modules. For this reason, many of these systems use switches (see (9) and (10) in the cited prior art) whose purpose is to bypass 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 converter (16) and the DC-DC converters (17) in the cited documents). In addition, the above-mentioned bypass switches (9) and (10) are subject to high loads from short-circuit currents and thus an increased failure rate. In addition, the prior art design has the disadvantage that failure of the converter (16) can cause damage to the common DC bus, which can lead to failures in several of the DC-DC converters (17) and thus result in a failure of the entire RFBS despite a design with bypass switches (9) and (10). In the RFBS disclosed in the prior art, the spatial characteristics in combination with a low voltage level in a spatially very distributed common DC bus can lead to additional electrical losses occurring in such RFBS, which reduce efficiency, or these losses must be avoided by using large cable cross-sections, which, however, results in increased costs for the RFBS designed in this way.

US 2023126285 A and DE 10 2020 108 053 A1 :

The cited documents disclose the following method for reducing imbalances occurring during charging and discharging of the battery system, comprising at least one of the following steps:

• When charging the battery system, the DC-DC converters 17 are controlled by the control device 8 to reduce the difference between a first and second battery module with regard to a controlled variable in such a way that a DC-DC converter 17 transfers so much electrical energy to the DC bus that one of the two battery modules is charged less quickly than the other battery module.

• When discharging the battery system, the DC-DC converters 17 are controlled by the control device 8 to reduce the difference between a first and second battery module 1 with regard to a controlled variable in such a way that a DC-DC converter 17 dissipates so much electrical energy from the DC bus that one of the two battery modules is discharged less quickly than the other battery module.

The disclosed arrangement also allows, at least when the converter 16 has a separate grid connection, for the converter 7 to support the charging or discharging of the battery modules. This is particularly advantageous when the converter 7 reaches its performance limits. Since this support can also be provided selectively for each battery module by the DC-DC converters 17, it can of course also be used for balancing. This mechanism leads to accelerated charging or discharging of the "slow" modules.

Disadvantages and limitations of the cited prior art:

The same disadvantages and limitations as shown above arise, in particular regarding spatial spread, susceptibility to errors and losses of the common DC bus. In addition, in this embodiment, individual battery modules can only be replaced by the bypass switches 9 or 10 are deactivated. A further disadvantage of this design is the fact that three advantageous states for the balancing logic can only be achieved if the DC/DC converters 17 are bidirectional.

WO 2022033750 A1 :

This document discloses a method for operating a vanadium redox flow battery system, the method comprising 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) that was connected to the converter (6, 7) in step S1, until at least a portion of the electrolyte belonging to this battery module (1) reaches a state of charge that is at least as high as a predefined threshold value; S3: controlling the first and second switches (9, 10) such that all battery modules (1) are in a series circuit that is connected to the bidirectional converter (6); S4: feeding a current into the series circuit from step S3, wherein electrolyte is pumped into all battery modules (1) (see in particular Figures 3 and 4).

Disadvantages and limitations of the cited prior art:

The converter 7 cannot be used with complete flexibility because 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 converter 7 to charge and discharge different battery modules 1 simultaneously.

DE 10 2017 222 979 A1 :

This document discloses an equalization unit that equalizes voltages of a plurality of electric storage cells; and an electricity transmission/reception unit that, 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 from the plurality of electric storage cells or (b-2) a charging device that charges the plurality of electric storage cells, (i) transmits electric power from the plurality of electric storage cells to an external device different from the load and the charging device, or (ii) receives electric power supplied to the plurality of electric storage cells from the external device.

The electricity transmitting/receiving unit shows an isolated bidirectional DC-DC converter.

Disadvantages and limitations of the cited prior art: The cited document, like the above-mentioned documents, discloses embodiments that can lead to a reduction in the availability of the RFBS due to a dependency/coupling of the compensation correction unit 220 and/or the protection unit 230 and/or the DC-DC converter 330.

Here, too, the functionality of all battery modules determines the availability of the series-connected battery. Here, too, the current state of the art does not offer a suitable way to increase availability and enable important functions for establishing and maintaining operational capability.

The object of the invention is to provide a redox flow battery system and a method for operating the same, which have a high level of reliability and availability.

The object of the invention is, in particular, to improve the problems and limitations of the prior art and to increase the availability of an RFBS. This is achieved according to the invention by a decentralized and improved balancing unit capable of maintaining and restoring operational capability. Furthermore, the arrangement according to the invention enables the decommissioning of individual battery modules, which supports the servicing 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 can be found in the subclaims.

Description of the Revelation

The invention is explained below with reference to the figures. The figures show in detail:

Fig. 1 : Battery module

Fig. 2: Redox flow battery system according to the invention

Fig. 3: Compensation 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 embodiment

Figure 1 shows a battery module, designated 1. It comprises a cell arrangement, designated 2, a tank device for storing electrolyte fluid, which is designated 3, an optional measuring device for determining the open-circuit voltage, which is designated 4, and an optional measuring device for determining the terminal voltage, which is designated 5. The battery module generally includes auxiliary systems, which are indicated by the rectangle designated 6. Furthermore, the battery module 1 includes pumps for supplying the cell arrangement 2 with electrolyte fluid from the tank device 3.

Figure 2 shows a schematic representation of a redox flow battery system according to the invention. The battery system comprises at least two battery modules, one of which is designated 1, a bidirectional power conversion system (PCS), designated 7, and a control device, designated 8. To better distinguish it from other converters (see below) of the battery system, the bidirectional inverter is referred to below as the "main converter." The battery modules

1 are connected in series and to the main converter 7. Figure 2 shows four battery modules, with the dashed lines in the series connection indicating any number of additional modules. The main converter 7 connects the battery system to the grid or to a higher-level electrical system. Optionally, the battery system can include a bypass switch for each battery module 1, designated 9 in Figure 2. The bypass switches 9 are arranged parallel to the associated battery modules 1 and can be used, among other things, for balancing (see, for example, DE 10 2022 109 193 B3). However, they can also be used to permanently bypass a battery module 1 that has a fault, thereby de facto removing it from the series connection of the battery system and thus ensuring the availability of the battery system as a whole even in the event of a battery module 1 (or a few battery modules 1) failing.

The redox flow battery system further comprises a balancing unit, designated 60. The balancing unit 60 can be assigned to a single battery module (1). The balancing unit 60 can be a decentralized balancing unit. In the figure

2 shows three separate, decentralized balancing units 60, each of which is assigned to one of the battery modules 1 shown. In a redox flow battery system according to the invention, preferably each battery module 1 is assigned a separate balancing unit 60. However, it is also conceivable that not each battery module 1 is assigned a separate balancing unit 60. In general, at least two battery modules 1 can each be assigned a separate balancing unit 60. In general, a) all or a) all other battery modules 1 except for one battery module 1 can each be assigned a separate balancing unit 60. In other words, the redox flow battery system can comprise n battery modules 1 and a) n or b) n-1 separate balancing units 60. With In other words, the redox flow battery system can comprise n battery modules 1 and at least n-1 separate balancing units 60. The redox flow battery system can, for example, have at least two battery modules 1 and at least one separate balancing unit 60, wherein the at least one separate balancing unit 60 is assigned to one of the at least two battery modules 1.

The balancing unit 60 is powered by a power supply unit 30, which in a preferred variant of the invention is designed as an AC voltage network. In further embodiments, the power supply unit 30 can be designed as an uninterruptible power supply that temporarily compensates for faults and temporary disturbances in the AC voltage network and thus further increases availability. The advantageous use of the uninterruptible 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 upgrading 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 grid stabilization, for operating an island grid, or for restoring the public grid (black start).

One way to enable an uninterruptible power supply is to use backup systems, such as diesel generators, batteries, or capacitors. In the event of undervoltages or power outages, these systems can supply the necessary energy to restart the power supply unit 30 and thus the battery power plant. This ensures that the power supply remains stable even in the event of unforeseen events. Depending on their design, these backup systems have different voltage waveforms, such as alternating voltage or direct voltage. In an advantageous embodiment, the converter 20 is implemented with the same voltage waveform that is provided by the uninterruptible power supply via the power supply unit 30. In the case of alternating voltage, the converter 20 is implemented as an AC-DC voltage; in the case of direct voltage, the converter 20 is implemented as a DC-DC voltage.

A further advantage of designing the energy supply unit 30 as an uninterruptible power supply is the possibility of using a comparatively small amount of energy to maintain the voltage level in the cell arrangement 2, with the flow from the tank device 3 deactivated, at a level at which the main converter 7 is activated and can actively participate in the grid stabilization.

The balancing unit 60 further comprises a protection and isolation unit, designated by 40, and a converter, designated by 20. The balancing unit 60 may further comprise a unit for increasing availability, designated by 50. The protection and isolation unit is considered optional. The power supply unit 30 can be isolated from the potential of the battery module 1 by the protection and isolation unit 40.

The control device 8 can be configured to control the balancing units 60, the pumps in the battery modules 1, the main converter 7, and any bypass switches 9 that may be present. Alternatively, the control device 8 can be configured to control the balancing units 60 but not the main converter 7. A higher-level controller (not shown) can assume control of the main converter 7. Both controllers can communicate with each other.

The availability enhancement unit 50 serves the purpose of increasing the availability of the battery module 1, particularly in the event that negative module voltages may occur intentionally or unintentionally. This is explained in more detail in connection with Figures 3 to 7.

Figure 3 shows a balancing unit 60 according to the invention. So that the protection and isolation unit 40 can separate the power supply unit 30 from the potential of the battery module 1, the protection and isolation unit 40 comprises a protection unit, designated 41, which can, for example, separate the power supply unit 30 from the converter 20 using suitable switches. Furthermore, the protection unit 41 can comprise a pre-circuit to relieve the power supply unit 30 from temporarily high inrush currents that can be caused by the balancing unit 60. Optionally, the protection and isolation unit 40 can comprise an isolation unit, designated 42. In this case, the isolation unit 42 is used within the protection and isolation unit 40 to isolate the potential of the battery module 1 and the power supply unit 30 from one another.

In a preferred embodiment of the invention, the protection unit 41 is implemented as an omnipolar relay and/or a passive circuit that dampens high inrush currents when activating and deactivating the balancing unit 60. It can thus serve as an inrush current limiter. By connecting an AC relay upstream of the protection unit 41, no-load losses can be avoided when the balancing unit is not in use.

In a preferred embodiment of the invention, the isolation unit 42 is implemented by an isolation transformer, e.g., in the form of a toroidal transformer. Further embodiments are possible and may be advantageous, for example, for different voltages or network configurations. In a further embodiment, the protection and isolation unit 40 can be completely omitted if the converter 20 already has galvanic isolation.

The converter 20 enables a method for reducing imbalances occurring during charging and discharging of the battery system. The converter can be unidirectional or bidirectional. The converter 20 can be used to accelerate or delay, or not influence, a voltage buildup in the battery module 1. In a preferred embodiment, individual or all components of the protection and insulation unit 40 can be integrated into the converter 20 on the input or output side. The converter 20 is capable of exerting this influence in addition to an external charging or discharging of the battery system (and thus the battery modules 1) by the main converter 7.

The design of the converter 20 as a unidirectional or bidirectional converter allows for restoration of operational capability during initial commissioning or after discharge for service purposes. In this case, the voltage buildup in the battery modules 1 is provided by the respective equalization unit 60 and the power supply unit 30.

The bidirectional design of the converter 20 allows the respective battery module 1 to be configured to a state that supports decommissioning, e.g., for servicing or maintenance work, without the need for more complex protective measures for working under voltage. In this case, the voltage reduction in the respective battery module 1 is achieved by the equalization unit 60 and the power supply unit 30.

The design of the converter 20 as a bidirectional converter further allows the restoration of the performance of a battery module 1 by the equalization unit (60) and the energy supply unit 30 by using the voltage reduction exclusively by the equalization unit 60 or in conjunction with the external discharge via the bidirectional main converter 7 to reverse the voltage polarity in a battery module 1.

As mentioned, the availability-enhancing unit 50 serves the purpose of increasing the availability of the battery module 1. For this purpose, the availability-enhancing unit 50 can comprise an integrated switching device, designated 52. With the aid of the integrated switching device 52, the respective battery module 1 can be decoupled from influences by the balancing 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. Figure 4 shows a first embodiment of the integrated switching device 52. The integrated switching device 52 shown comprises a switch, designated 53. With the switch 53, one of the two DC connections to the battery module 1 can be interrupted.

Figure 5 shows a further embodiment of the integrated switching device 52. The illustrated integrated switching device 52 comprises two switches, designated 54 and 55. Both DC connections to the battery module 1 can be disconnected using switches 54 and 55.

Figures 6 and 7 show two further particularly advantageous embodiments of the integrated switching device 52. In addition to the separation of the balancing unit 60 from the respective battery module 1, the two embodiments enable a change in the polarity of the balancing unit 60 with respect to the respective battery module 1.

For this purpose, the embodiment shown in Figure 6 comprises two coupled switches, designated 54a and 55b, each having three switching states. In the switching state shown in Figure 6, a first polarity results (the lines are simply fed through). In the second switching state, the two switches 54a and 55b are switched to the middle contact (neutral position), thereby disconnecting the balancing unit 60 from the respective battery module 1. In the third switching state, the switches 54a and 55b are switched to the lower contact, thereby reversing the polarity compared to the switching state shown in Figure 6.

The embodiment shown in Figure 7 has the same functionality. The integrated switching device 52 shown comprises four switches, designated 56, 57, 58, and 59. Two switches are coupled to each other. If both pairs of switches are opened, the balancing unit 60 is disconnected from the respective battery module 1. The polarity can be influenced by alternately opening and closing the two pairs of switches.

These particularly advantageous embodiments with the possibility of changing the polarity of the balancing unit 60 allow the use of a unidirectional converter for the converter 20. As a result, the converter 20 can be used to imprint a state on the battery module 1 that allows it to be taken out of service, for example, during servicing. In this case, the voltage reduction in the respective battery module 1 is provided by the balancing unit 60 and the energy supply unit 30. Furthermore, the converter 20 can be used to restore the performance of the respective battery module 1 by the balancing unit 60 and the energy supply unit 30 by using the voltage reduction exclusively by the compensation unit 60 or in conjunction with the external voltage reduction by the main converter 7 to reverse the voltage in the relevant battery module 1.

Furthermore, the native function of the balancing unit 60 can also be used to accelerate or delay, or not influence, a voltage build-up in the respective battery module 1. The three aforementioned states 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 balancing unit 60 depending on the desired state (accelerating or delaying the voltage build-up of the respective battery module 1) and the current operating state of the RFBS (charging or discharging) in order to implement the desired function with a unidirectional converter 20. Without the switching device 52 with polarity reversal, a bidirectional converter 20 would always be necessary, which entails lower availability, a higher probability of failure, and higher costs.

The above-mentioned embodiments of the switching device 52 could lead to malfunctions of the balancing unit 60 and/or the relevant battery module 1 in the event of faulty control or faults in the switches. To avoid the problems mentioned, the availability-enhancing unit 50 can be expanded to include a protective device, designated 51 in Figure 3, which uses active or passive electronic components to prevent protection against polarity reversal or a forced current reversal at the output of the converter 20.

In order for a redox flow battery system to be able to automatically carry out the method steps briefly outlined above and explained in detail below, it comprises a computer system. The term computer system refers to all devices that are suitable for automatically carrying out the described method steps, in particular also specially developed programmable logic controllers, ICs or microcontrollers, as well as 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 that includes instructions that cause the battery system to carry out the method steps described above. Furthermore, the present application is directed to a computer-readable medium on which such a computer program is stored. Description of the processes possible with the battery system according to the invention:

Increase availability:

A fault in at least one of the balancing units 60 may negatively affect the associated battery module 1. To prevent this and thus increase the availability of the battery system as a whole, the respective balancing unit is electrically disconnected from the associated battery module 1 in the event of a fault.

The separation of the battery modules 1 or the cell assemblies 2 from the unidirectional or bidirectional converter 20 can be accomplished with the aid of the switching device 52 by performing one of the following steps:

- Opening switch 53 in a one-switch configuration as shown in Figure 4.

- Opening at least one switch 54 or 55 in a two-switch configuration, as shown in Figure 5

- Moving at least one switch 54a or 55b to a neutral position in a two-switch configuration (with neutral positions), as shown in Figure 6.

- Opening all switches 56, 57, 58 and 59 in a four-switch configuration as shown in Figure 7.

Alternatively or additionally, the availability enhancement unit 50 can protect the balancing unit, in particular the associated converter 20, from negative polarity and corresponding damage caused by a negative voltage of the battery module (for example, by applying the method described in DE 10 2022 113 939 B3). To prevent the negative voltage at the converter 20, the availability enhancement unit can comprise a switching device 52 with which the converter 20 can be disconnected from the module 1, or a reverse polarity protection device 51.

Initialization or restoration of operational capability after initial commissioning or after discharge:

The initialization of the battery modules 1 with a unidirectional or bidirectional converter 20 can be carried out with a switching device 52 by performing one of the following steps:

- Closing the switch 53 in a one-switch configuration, as shown in Figure 4, and applying a charging power to the battery module 1 (in particular to the cell assembly 2) with pumps running to carry out the initial charge of battery module 1 and without pumps running to carry out the initial charge of cell assembly 2.

- Closing the two switches 54 and 55 in a two-switch configuration as shown in Figure 5 and applying a charging power to the battery module 1 (in particular to the cell assembly 2) with the pumps running to perform an initial charge of the battery module 1 and without the pumps running to perform an initial charge of the cell assembly 2.

- Switching the two switches 54a and 55b to the first position in a two-switch configuration, as shown in Figure 6, and applying a charging power to the battery module 1 (in particular to the cell assembly 2) with the pumps running to perform an initial charge of the battery module 1 and without the pumps running to perform an initial charge of the cell assembly 2.

- Closing the two switches 57 and 58 in a four-switch configuration as shown in Figure 7 and applying a charging power to the battery module 1 (in particular to the cell assembly 2) with the pumps running to perform an initial charge of the battery module 1 and without the pumps running to perform an initial charge of the cell assembly 2.

For example, during initial commissioning or recommissioning (with the pumps turned off), battery modules can be charged using an associated converter 20 to a minimum voltage required for the main converter 7 to start operation and continue and complete the initialization process. For this purpose, the converter 20 should have a minimum DC-side voltage of 0 V, while the main converter 7 can have a minimum voltage much greater than 0 V.

De-initialization or provision of a state that supports decommissioning, e.g. during service:

The de-initialization of the respective battery module 1 or cell assembly 2 using a bidirectional converter 20 can be achieved with a switching device 52 by performing one of the following steps:

- Closing the switch 53 in a one-switch configuration, as shown in Figure 4, and applying a discharge power to the battery module 1 (in particular to the cell array 2) with the pumps running to perform the deinitialization of the battery module 1 and without the pumps running to perform the deinitialization of the cell array 2. - Closing both switches 54 and 55 in a two-switch configuration as shown in Figure 5 and applying a discharge power to the battery module 1 (in particular to the cell array 2) with the pumps running to de-initialise the battery module 1 and without the pumps running to de-initialise the cell array 2.

- Switching the two switches 54a and 55b to a first position in a two-switch configuration as shown in Figure 6 and applying a discharge power to the battery module 1 (in particular to the cell assembly 2) with the pumps running to de-initialize the battery module 1 and without the pumps running to de-initialize the cell assembly (2).

- Closing the two switches 57 and 58 in a four-switch configuration as shown in Figure 7 and applying a discharge power to the battery module 1 (in particular to the cell array 2) with the pumps running in order to de-initialise the battery module 1 and without the pumps running in order to de-initialise the cell array 2.

The de-initialization of the respective battery module 1 or cell arrangement 2 with a unidirectional or bidirectional (only supporting the charging function) converter 20 can be achieved with a switching device 52 by performing one of the following steps:

- Switching the two switches 54a and 55b to a third position in a two-switch configuration, as shown in Figure 6, and applying a charging power to the battery module 1 (in particular to the cell array 2) with the pumps running to de-initialize the battery module 1, and without the pumps running to de-initialize the cell array 2. In this case, a reverse polarity protection circuit 51 is required.

- Closing the two switches 56 and 59 in a four-switch configuration, as shown in Figure 7, and applying a charging voltage to the battery module 1 (in particular to the cell array 2), with the pumps for performing the deinitialization of the battery module 1 running and the pumps for performing the deinitialization of the cell array 2 not running. In this case, a reverse polarity protection circuit 51 is required.

For example, for service purposes, the battery modules with their respective converters 20 can be discharged below a voltage threshold that supports decommissioning or service. For service technicians, working under Voltage is only possible with specific protective equipment and training. It is significantly less complex below a certain voltage threshold. However, this cannot be achieved by simply discharging using the main converter 7, as it does not function below a certain minimum voltage. Using converter 20, voltages close to 0 volts can be achieved.

Reducing imbalances occurring during charging and discharging of a redox flow battery system:

The redox flow battery system and/or the method can be used for balancing the battery modules, i.e. charging or discharging individual battery modules by the converter 20 in order to compensate for a difference in the charge states between the battery modules.

Balancing the state of charge (SOC) of a group of modules connected in a string configuration can be achieved by using a bidirectional inverter 20 together with a switching device 52 by performing one of the following steps:

- Closing switch 53 in a one-switch configuration as shown in Figure 4 and applying a charge or discharge power to battery module 1.

- Closing the two switches 54 and 55 in a two-switch configuration as shown in Figure 5 and applying a charge or discharge power to Battery Module 1.

- Switching the two switches 54a and 55b to a first position in a two-switch configuration, as shown in Figure 6, and applying a charging or discharging power to the battery module 1.

- Closing the two switches 57 and 58 in a four-switch configuration as shown in Figure 7 and applying a charge or discharge power to Battery Module 1.

In addition, balancing the state of charge (SOC) of a group of modules connected in a string configuration can be achieved by using a unidirectional or bidirectional (supporting only the charging function) inverter 20 together with a switching device 52 by performing one of the following steps:

- Switching both switches 54a and 55b to a third position in a two-switch configuration, as shown in Figure 6, and applying a charging power to the battery module 1. In this case, a reverse polarity protection circuit 51 is required. - In a four-switch configuration, as shown in Figure 7, close both switches 56 and 59 and apply a charging voltage to battery module 1. In this case, a reverse polarity protection circuit 51 is required.

Restoring the performance of a battery module 1 :

Reversing the polarity of the cell array 2 can be beneficial for cell aging recovery by charging the cell array 2 with a negative voltage. This can be achieved by using a unidirectional or bidirectional (supporting only the charging function) inverter 20 together with the switching device 52 and a battery module 1 by performing one of the following steps:

- Switching both switches 54a and 55b to position 3 in a two-switch configuration as shown in Figure 6, adjusting the speed of the pumps to set a reduced or no flow through the cell array 2, and applying a charging power to the battery module 1. In this case, a reverse polarity protection circuit 51 is required.

- In a four-switch configuration, as shown in Figure 7, closing both switches 56 and 59, adjusting the pump speed to achieve reduced or no flow through cell array 2, and supplying charging power to battery module 1. In this case, a reverse polarity protection circuit 51 is required.

Degradation of a battery module can be at least partially reversed by operating it with reversed polarity for a certain period of time. Such polarity reversal (i.e., discharging the module and charging it in the opposite direction) can be achieved via the balancing unit. For this purpose, the battery string can be stopped and the pumps can be deactivated.

For this purpose, for example, the relevant battery modules can be discharged to ~0 V (below the minimum voltage of the converter's diodes). The switching device shown in Fig. 6 or Fig. 7 can then be switched over. The modules can then be charged for a certain period of time (with reversed polarity). They can then be discharged again to ~0 V, whereupon the switching device is switched over again, and the pumps are switched back on.

Disconnecting the relevant battery module 1 from the balancing unit 60:

The separation of the respective battery module 1 or the associated cell arrangement (2) from the unidirectional or bidirectional converter 20 by means of the switching devices (52) is achieved by carrying out one of the following steps: - Opening switch 53 in a one-switch configuration as shown in Figure 4.

- Opening at least one switch 54 or 55 in a two-switch configuration, as shown in Figure 5

- Moving at least one switch 54a or 55b to a neutral position in a two-switch configuration (with neutral positions), as shown in Figure 6.

- Opening all switches 56, 57, 58 and 59 in a four-switch configuration as shown in Figure 7.

Examples

In one embodiment, a redox flow battery system can comprise at least two battery modules 1, a main converter 7, a power supply unit 30 and a control device 8, wherein the battery modules 1 are connected in series and to the main converter 7, and wherein each battery module 1 comprises a cell arrangement 2 with a plurality of redox flow cells and a tank device 3 for storing electrolyte fluid and pumps for supplying the cell arrangement 2 with electrolyte fluid, wherein the battery system for at least two battery modules 1 each comprises a balancing unit 60, and wherein one connection of each balancing unit 60 is connected to the associated battery module 1, and a second connection of each balancing unit 60 is connected to the power supply unit 30, and wherein each balancing unit 60 comprises a converter 20 and a unit for increasing the availability 50, and wherein the unit for increasing the availability 50 is connected on a first side to the converter 20 and on a second side is connected to the associated battery module 1, and wherein the control device 8 is designed such that it can control the balancing units 60, the pumps in the battery modules 1 and the main converter 7.

In one embodiment, the converters 20 can be bidirectional or unidirectional and connected to the power supply unit 30 via DC or AC voltage, and wherein the units 50 can each comprise a switching device 52 to increase availability, and wherein each switching device can comprise at least one switch 53, 54, 55, 54a, 55b, 56, 57, 58, 59.

In one embodiment, the power supply unit 30 can be designed as an uninterruptible supply, 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 power supply unit 30. In one embodiment, the power supply unit 30 can provide an alternating voltage, wherein the converters 20 are designed as AC-DC converters.

In one embodiment, the power supply unit 30 can provide a DC voltage, wherein the converters 20 are designed as DC-DC converters.

In one embodiment, each balancing unit 60 may comprise a protection and isolation unit 40, which is designed to galvanically isolate the potential of the energy supply unit 30 from the potential of the associated battery module 1.

In one embodiment, each switching device 52 can comprise at least two switches (54, 55, 54a, 55b, 56, 57, 58, 59), wherein optionally the converters 20 are designed to be unidirectional and are connected to the energy supply unit 30 via direct or alternating voltage, wherein optionally each switching device 52 is designed such that it can change the polarity of the balancing unit 60 with respect to the associated battery module 1, and wherein each unit 50 comprises a protective device 51 to increase availability, which is designed such that it can protect the associated converter 20 from inadmissible polarity states.

In one embodiment, the battery system can comprise a bypass switch 9 for each battery module 1, wherein the first switch 9 is 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 or out of the series circuit.

In one embodiment, a method for increasing the availability of the battery modules in a redox flow battery system of the type described can be provided, in which the control device 8, in the event of at least one error in at least one of the balancing units 60, controls at least one switch 53, 54, 55, 54a, 55b, 56, 57, 58, 59 of the switching device 52 belonging to the affected battery module 1 in order to prevent further influencing of the affected battery module 1 by separating the connection between the associated balancing unit 60 and the affected battery module 1.

In one embodiment, a method may be provided for reducing imbalances occurring during charging and discharging of a redox flow battery system according to the type described, in which the control device 8 controls the balancing units 60 and optionally the main converter 7, the method comprising at least one of the following steps: - When charging the battery system, a compensation unit 60 is controlled by the control device 8 to reduce the difference between a first and second battery module 1 with regard to a controlled variable such that at least one converter 20 transmits so much electrical energy to a battery module 1 that one of the two battery modules 1 is charged less quickly than the other battery module 1;

- When discharging the battery system, a compensation unit 60 is controlled by the control device 8 to reduce the difference between a first and second battery module 1 with regard to a controlled variable in such a way that at least one converter 20 dissipates so much electrical energy from a battery module 1 that one of the two battery modules 1 is discharged less quickly than the other battery module.

In one embodiment, a method may be provided for reducing imbalances occurring during charging and discharging of a redox flow battery system according to the type described, in which the control device 8 can control the balancing unit 60 and bidirectional main converter 7, and wherein the method comprises at least one of the following steps:

- When charging the battery system, a compensation unit 60 is controlled by the control device 8 to reduce the difference between a first and second battery module 1 with regard to a controlled variable such that at least one converter 20 supplies so much electrical energy to a battery module 1 that one of the two battery modules 1 is charged faster than the other battery module 1;

- When discharging the battery system, a compensation unit 60 is controlled by the control device 8 to reduce the difference between a first and second battery module 1 with regard to a controlled variable such that at least one converter 20 transmits so much electrical energy to at least one interface to the battery module 1 that one of the two battery modules 1 is discharged faster than the other battery module 1.

In one embodiment, the control device 8 can control the balancing unit 60 and the bidirectional converter 7 such that the control device 8 controls at least one unit for increasing the availability 50 with the switching device 52, so that by changing the polarity of the balancing unit 60, the energy is not discharged to the energy supply unit 30, but remains in the battery module 1.

In one embodiment, the control device 8 can control the balancing 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, wherein in each battery module 1 the cell arrangement 2 is discharged by the balancing unit 60 alone or in cooperation with the main converter 7 can, wherein an electrolyte transfer or no electrolyte transfer to the cell arrangement 2 can be present and the discharge of the cell arrangement 2 results in a voltage level at the relevant cell arrangement in at least one battery module 1 which falls below a certain threshold value and thus supports decommissioning or service work without more complex protective measures for working under voltage.

In one embodiment, the control device 8 can control the equalization 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, wherein in each battery module 1, in a state in which the voltage potential of the cell arrangement 2 in question is too low for activation of the main converter 7, the cell arrangement 2 in question is charged by the associated equalization unit 60 alone, wherein there may or may not be an electrolyte transfer to the cell arrangement 2 and until at least a voltage level is reached that allows activation of the main converter 7.

In one embodiment, a method for restoring the performance of a battery module 1 of a redox flow battery system according to the type described can be provided, wherein the control device 8 can control the main converter 7, the battery modules 1 and/or the balancing units 60 such that a reversal of the voltage takes place in at least one battery module 1 during the discharge process of the redox flow battery system.

In one embodiment, the control device 8 can control the balancing units 60 and the main converter 7 such that the control device 8 controls at least one unit for increasing availability 50 with the associated switching device 52 such that by changing the polarity of the balancing unit 60 in the balancing units 60, a unidirectional converter 20 can be used for the voltage build-up and/or reduction of the associated battery modules 1.

List of reference symbols

1 battery module

2 Cell arrangement

3 Tank facility

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 converters

30 power supply unit

40 Protection and insulation unit

41 Protection Unit

42 Isolation Unit

50 units to increase availability

51 Reverse polarity protection circuit

52 Switching device

53 switches

54 switches

54a switch

55 switches

55b switch

56 switches

57 switches

58 switches

59 switches

60 balancing units

Claims

Patent claims 1. A redox flow battery system comprising at least two battery modules (1), a main converter (7), a power supply unit (30), and a control device (8), wherein the battery modules (1) are connected in series and to the main converter (7), and wherein each battery module (1) comprises a cell arrangement (2) with a plurality of redox flow cells and a tank device (3) for storing electrolyte fluid and pumps for supplying the cell arrangement (2) with electrolyte fluid, characterized in that the battery system comprises a separate balancing unit (60) for each of at least two battery modules (1), and wherein one connection of each balancing unit (60) is connected to the associated battery module (1), and a second connection of each balancing unit (60) is connected to the power supply unit (30), and wherein each balancing unit (60) comprises a converter (20). 2. Redox flow battery system according to claim 1, wherein the converters (20) are bidirectional or unidirectional and are connected to the power supply unit (30) via direct or alternating voltage. 3. Redox flow battery system according to claim 1 or 2, wherein each balancing unit (60) comprises an availability enhancement unit (50) connected on a first side to the associated converter (20) and on a second side to the associated battery module (1). 4. Redox flow battery system according to claim 3, wherein the units for increasing availability (50) each comprise a switching device (52) to decouple the associated battery module (1) from influences by the balancing unit (60), and wherein each switching device comprises at least one, preferably at least two, switches (53, 54, 55, 54a, 55b, 56, 57, 58, 59); and/or wherein the units for increasing availability (50) each comprise a protective device (51) which is designed such that it can protect the associated converter (20) from impermissible polarity states. 5. Redox flow battery system according to one of the preceding claims, wherein the energy supply unit (30) is designed as an uninterruptible supply, and wherein preferably each battery module (1) comprises auxiliary systems (6), and preferably 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 power supply unit (30). 6. Redox flow battery system according to one of the preceding claims, wherein the energy supply unit (30) provides an alternating voltage, and wherein the converters (20) are designed as AC-DC converters. 7. Redox flow battery system according to one of the preceding claims, wherein the energy supply unit (30) provides a direct voltage, and wherein the converters (20) are designed as DC-DC converters. 8. Redox flow battery system according to one of the preceding claims, wherein each balancing 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). 9. Redox flow battery system according to one of the preceding claims, at least dependent on claim 4, wherein each switching device (52) comprises at least two switches (54, 55, 54a, 55b, 56, 57, 58, 59), wherein preferably the converters (20) are unidirectional and are connected to the energy supply unit (30) via DC or AC voltage. 10. Redox flow battery system according to claim 8, wherein each switching device (52) is designed such that it can change the polarity of the balancing unit (60) with respect to the associated battery module (1). 11. 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 bypass switch (9) is 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 or out of the series circuit. 12. Redox flow battery system according to one of the preceding claims, wherein the control device (8) is designed such that it can control the balancing units (60), the pumps in the battery modules (1) and the main converter (7). 13. Redox flow battery system according to one of the preceding claims, wherein the redox flow battery system comprises n battery modules (1) and at least n-1 separate balancing units (60). 14. Method for increasing the availability of the battery modules (1) in a redox flow battery system according to one of the preceding claims, at least dependent on claim 4, in which the control device (8) in the event of at least one fault in at least one of the compensation units (60) controls at least one switch (53, 54, 55, 54a, 55b, 56, 57, 58, 59) of the switching device (52) belonging to the affected battery module (1) in order to prevent further influencing of the affected battery module (1) by separating the connection between the associated compensation unit (60) and the affected battery module (1). 15. A method for reducing imbalances occurring during charging and discharging of a redox flow battery system according to one of claims 1 to 13, wherein the control device (8) can control the balancing units (60) and the main converter (7), and wherein the method comprises at least one of the following steps: - When charging the battery system, a compensation unit (60) is controlled by the control device (8) to reduce the difference between a first and second battery module (1) with regard to a controlled variable in such a way that at least one converter (20) transmits so much electrical energy to a battery module (1) that one of the two battery modules (1) is charged less quickly than the other battery module (1); - When discharging the battery system, a compensation unit (60) is controlled by the control device (8) to reduce the difference between a first and second battery module (1) with regard to a controlled variable in such a way that at least one converter (20) dissipates so much electrical energy from a battery module (1) that one of the two battery modules (1) is discharged less quickly than the other battery module. 16. A method for reducing imbalances occurring during charging and discharging of a redox flow battery system according to one of claims 1 to 13, wherein the control device (8) can control the balancing unit (60) and the bidirectional main converter (7), and wherein the method comprises at least one of the following steps: - When charging the battery system, a compensation unit (60) is controlled by the control device (8) to reduce the difference between a first and second battery module (1) with regard to a controlled variable in such a way that at least one converter (20) dissipates so much electrical energy to a battery module (1) that one of the two battery modules (1) is charged faster than the other battery module (1); - When discharging the battery system, a balancing unit (60) is switched on by the Control device (8) for reducing the difference between a first and second battery module (1) with regard to a controlled variable, controlled in such a way that at least one converter (20) transmits so much electrical energy to at least one interface to the battery module (1) that one of the two battery modules (1) is discharged faster than the other battery module (1). 17. The method according to one of claims 15 or 16, wherein the control device (8) can control the balancing unit (60) and the bidirectional converter (7) in such a way that the control device (8) controls at least one unit for increasing the availability (50) with the switching device (52), so that by changing the polarity of the balancing unit (60), the energy is not dissipated to the energy supply unit (30) but remains in the battery module (1). 18. The method according to any one of claims 14 to 17, wherein the control device (8) can control the equalization 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 equalization unit (60) alone or in cooperation with the main converter (7), wherein there can be an electrolyte transfer to the cell arrangement (2) or no electrolyte transfer, and the discharge of the cell arrangement (2) results in a voltage level at the relevant cell arrangement in at least one battery module (1) which falls below a threshold value and thus supports decommissioning or servicing. 19. The method according to any one of claims 14 to 18, wherein the control device (8) can control the equalization 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 cell arrangement (2) in question is too low for activation of the main converter (7), the cell arrangement (2) in question is charged by the associated equalization unit (60) alone, wherein there may or may not be an electrolyte transfer to the cell arrangement (2) and until at least one voltage level is reached which allows activation of the main converter (7). 20. A method for restoring the performance of a battery module (1) of a redox flow battery system according to one of claims 1 to 13, wherein the control device (8) can control the main converter (7), the battery modules (1) and/or the balancing units (60) such that a reversal of the voltage occurs in at least one battery module (1) during the discharging process of the redox flow battery system.