REDOX FLOW BATTERY WITH FLOATING POWER MODULE UNDER IMBALANCED CHARGE CONDITIONS

The present disclosure is directed, in certain embodiments, to a flow cell battery system. A battery management system detects that a first power module and a second power module located adjacent to the first power module are operating at different states of charge. After determining that the second power module is at the lower state of charge than the first power module, a negative-side switch associated with the second power module is adjusted to an open position, thereby preventing flow of electrical current from a negative terminal of the second power module to electrical ground.

TECHNICAL FIELD OF THE DISCLOSED SUBJECT MATTER

The present disclosure generally relates to energy storage devices, and more specifically to a redox flow battery with floating power module under imbalanced charge conditions.

BACKGROUND OF THE DISCLOSED SUBJECT MATTER

A redox flow battery facilitates energy storage using liquid electrolyte solutions. Electrolytes are pumped through redox cells of the flow battery to facilitate conversion between chemical energy and electricity (e.g., for charging and discharging the flow cell battery). There exists a need for improved redox flow batteries and methods of their operation.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

The purpose and advantages of the disclosed subject matter will be set forth in and are apparent from the description that follows, as well as will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the devices particularly pointed out in the written description and claims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes a battery system with an AC/DC inverter, a first power module, a second power module, and a battery management system. The first power module includes a first positive terminal electronically coupled to a positive bus connected to a positive side of the AC/DC inverter and a first negative terminal electronically coupled to a first negative-side switch. When closed, the first negative-side switch is operable to allow flow of electrical current from the first negative terminal of the first power module to electrical ground. When open, the first negative-side switch is operable to prevent flow of electrical current from the first negative terminal of the first power module to electrical ground. The second power module is located adjacent to the first power module (i.e., the second power module shares electrolyte manifold used by the first power module, such that the first and second power modules are fluidically connected). The second power module includes a second positive terminal electronically coupled to the positive bus connected to the positive side of the AC/DC inverter and a second negative terminal electronically coupled to a second negative-side switch. When closed, the second negative-side switch is operable to allow flow of electrical current from the second negative terminal of the first power module to electrical ground. When open, the second negative-side switch is operable to prevent flow of electrical current from the negative terminal of the first power module to electrical ground. The battery management system includes a hardware processor configured to detect that the first and second power modules are operating at a different state of charge. The battery management system determines that the second power module is at a lower state of charge than the first power module. After determining that the second power module is at the lower state of charge than the first power module, the second negative-side switch is adjusted to (e.g., moved or placed in) the open position.

Additionally, after determining that the second power module is at the lower state of charge than the first power module, the first negative-side switch may be in the closed position. Adjusting the second negative-side switch to the open position may cause the second power module to electronically float at a predetermined range of voltages relative to an electronic voltage of the first power module. In some embodiments, the hardware processor is further configured to detect that the first and second power modules are operating at a different state of charge by determining that the first power module is in a charging state and the second power module is in a shutdown state.

Furthermore, the battery system may include one or more pumps and corresponding liquid manifolds operable to control a flow of electrolyte solution through cells of the first and second power modules. The one or more pumps and corresponding liquid manifolds may include a first pump and first liquid manifolds configured to provide the flow of electrolyte solution to the first power module and a second pump and second liquid manifolds configured to provide the flow of electrolyte solution to the second power module. The battery system may include an electrolyzer configured to electrolyze an electrolyte solution provided to the second power module.

Moreover, the first positive terminal of the first power module may be electronically coupled to a first positive-side switch. When closed, the first positive-side switch may be operable to allow flow of electrical current from the first positive terminal of the first power module to a positive side of the AC/DC inverter. When open, the first positive-side switch may be operable to prevent flow of electrical current from the first positive terminal of the first power module to the positive side of the AC/DC inverter. The second positive terminal of the second power module may be electronically coupled to a second positive-side switch. When closed, the second positive-side switch may be operable to allow flow of electrical current from the second positive terminal of the second power module to a positive side of the AC/DC inverter. When open, the second positive-side switch may be operable to prevent flow of electrical current from the second positive terminal of the second power module to the positive side of the AC/DC inverter. When the first power module is in a charging state, the first positive-side switch may be closed, and when the second power module is in a shutdown state, the second positive-side switch may be open.

In accordance with another aspect of the disclosed subject matter, a battery management system for a flow cell battery includes an input/output interface and a hardware processor communicatively coupled to the input/output interface. The input/output interface is communicatively coupled to a first negative-side switch associated with a first power module of the flow cell battery and a second negative-side switch associated with a second power module of the flow cell battery. The second power module is located adjacent to the first power module. When closed, the first negative-side switch is operable to allow flow of electrical current from the first negative terminal of the first power module to electrical ground. When open, the first negative-side switch is operable to prevent flow of electrical current from the first negative terminal of the first power module to electrical ground. When closed, the second negative-side switch is operable to allow flow of electrical current from the second negative terminal of the second power module to electrical ground. When open, the second negative-side switch is operable to prevent flow of electrical current from the second negative terminal of the second power module to electrical ground. The hardware processor is communicatively coupled to the input/output interface and configured to detect that the first and second power modules are operating at a different state of charge. The hardware processor determines that the second power module is at a lower state of charge than the first power module. After determining that the second power module is at the lower state of charge than the first power module, the second negative-side switch is adjusted to (e.g., moved or placed in) the open position.

Moreover, after determining that the second power module is at the lower state of charge than the first power module, the first negative-side switch may be in the closed position. Adjusting the second negative-side switch to the open position may cause the second power module to electronically float at a predetermined range of voltages relative to an electronic voltage of the first power module. In some embodiments, the hardware processor is further configured to detect that the first and second power modules are operating at a different state of charge by determining that the first power module is in a charging state and the second power module is in a shutdown state.

Additionally, the battery system may include one or more pumps and corresponding liquid manifolds operable to control a flow of electrolyte solution through cells of the first and second power modules. The one or more pumps and corresponding liquid manifolds may include a first pump and first liquid manifolds configured to provide the flow of electrolyte solution to the first power module and a second pump and second liquid manifolds configured to provide the flow of electrolyte solution to the second power module. The battery system may include an electrolyzer configured to electrolyze an electrolyte solution provided to the second power module.

Furthermore, the input/output interface may be further communicatively coupled to a first positive-side switch associated with the first power module and operable to, when closed, allow flow of electrical current from the first positive terminal of the first power module to a positive side of the AC/DC inverter, and, when open, prevent flow of electrical current from the first positive terminal of the first power module to the positive side of the AC/DC inverter. The input/output interface may be further communicatively coupled to a second positive-side switch associated with the second power module and operable to, when closed, allow flow of electrical current from the second positive terminal of the second power module to the positive side of the AC/DC inverter, and, when open, prevent flow of electrical current from the second positive terminal of the second power module to the positive side of the AC/DC inverter. When the first power module is in a charging state, the first positive-side switch may be closed, and when the second power module is in a shutdown state, the second positive-side switch may be open.

In accordance with another aspect of the disclosed subject matter, a method of operating a flow cell battery includes (1) detecting that a first power module and a second power module located adjacent to the first power module are operating at different states of charge; (2) determining that the second power module is at a lower state of charge than the first power module; and (3) after determining that the second power module is at the lower state of charge than the first power module, adjusting a negative-side switch associated with the second power module to an open position, thereby preventing flow of electrical current from a negative terminal of the second power module to electrical ground.

Additionally, after determining that the second power module is at the lower state of charge than the first power module, a negative-side switch associated with the first power module may be in the closed position, thereby allowing flow of electrical current from a negative terminal of the first power module to electrical ground. Adjusting the second negative-side switch to the open position may cause the second power module to electronically float at a predetermined range of voltages relative to an electronic voltage of the first power module. Detecting that the first and second power modules are operating at a different state of charge may be performed by determining that the first power module is in a charging state and the second power module is in a shutdown state.

Moreover, the method may further include, after determining that the second power module is at the lower state of charge than the first power module, placing a first positive-side switch associated with the first power module in a closed position, such that flow of electrical current from a first positive terminal of the first power module to a positive side of an AC/DC inverter is allowed and placing a second positive-side switch associated with the second power module in an open position, such that flow of electrical current from a second positive terminal of the second power module to the positive side of the AC/DC inverter is prevented.

Technical advantages of certain embodiments of this disclosure may include one or more of the following. For example, this disclosure facilitates flow cell batteries with improved efficiency and with less chance of unwanted electrolyte side reactions. For example, an improved battery management system may actuate negative-side switches, or electronic relays, that electronically float power modules that are at a lower charge state than neighboring or adjacent power module(s), thereby removing a shunt current path that can lead to decreased battery performance.

DETAILED DESCRIPTION

This disclosure recognizes that previous flow battery systems suffer from certain drawbacks and disadvantages. For example, in previous flow battery systems a shunt current path may exist between adjacent power modules (i.e., power modules that are fluidically connected) that are operating at different states of charge, resulting in inefficiency and/or unwanted side reactions during operation. This disclosure provides technical solutions to these and other problems of previous technology by electronically floating a power module with a lower charge state than that of one or more adj acent module(s). For example, when two adj acent power modules are at different charge states (e.g., one charging and the other shutdown), the lower charge state (e.g., the shutdown) power module may be electronically disconnected from a shared electrical ground. This removes a shunt current path from the charging power module through the electrolyte solution in the shutdown power module and to electrical ground, which may lead to battery inefficiency and/or unwanted side-reactions.

Reference will now be made in detail to embodiments of the disclosed subject matter, an example of which is illustrated in the accompanying drawings.FIG.1illustrates an example flow cell battery system.FIGS.2and3illustrate exemplary configurations of power module subsystems of improved flow cell battery systems that prevent development of a shunt current path between adj acent power modules, in accordance with embodiments of this disclosure.FIG.4illustrates an example manifold and pump configuration of a portion of an improved flow cell battery system, in accordance with embodiments of this disclosure.FIG.5is a flowchart of an exemplary method of operating a flow cell battery system. While these figures often depict or refer to a flow cell battery system with two adjacent power modules, it is to be understood that the present disclosure is not necessarily limited to such a configuration, and the principles disclosed herein may have applicability to various types or forms of flow cell battery systems, as understood by one of skill in the art.

FIG.1illustrates an example flow cell battery system100of this disclosure. The flow cell battery system100includes one or more power sources102, an AC/DC inverter104, a power module subsystem106, a power management system114, and electrolyte tanks126. The power source(s)102may be any source of electricity, such as one or more solar panels, wind turbines, or the like. In typical applications, the power sources102may employ a renewable energy source for which power storage is desirable during off time (e.g., when there is no sunlight or wind). The AC/DC inverter104is generally an electronic device that converts typically alternating current (AC) voltage (or current) of the power source(s) to a direct current (DC) voltage (or current) for storage in the power module subsystem106. The reverse process occurs during discharge of the power module subsystem106. The AC/DC inverter104may include any appropriate electronic circuitry known in the art. Further details of electronic connections between the AC/DC inverter104and components of the power module subsystem106are illustrated and described with respect toFIGS.2and3below.

The power module subsystem106includes multiple direct current (DC) power modules108a,b; fluid pumps110a,b; and corresponding fluid manifolds112a,b. While the drawings show two adjacent modules108a,b(e.g., or202a,binFIGS.2and3) for simplicity, a multiplicity of modules108a,b(e.g., or202a,binFIGS.2and3) greater than two may be employed. The power modules108a,bare connected to a common AC/DC inverter104and common liquid electrolyte manifolds112a,b. Example power modules108a,bare illustrated in greater detail inFIGS.2and3and described in greater detail below. Briefly, a power module108a,bmay include a set of battery cells (e.g., connected electrically in series). The battery cells include positive and negative cells with corresponding electrodes. The cells are separated by an ion-selective membrane. When charging or discharging of the power modules108a,band pumps110a,bprovide flow of electrolyte solution (also referred to as “electrolyte”) from electrolyte tanks126through the cells of the battery cells of the power modules108a,b. The electrolyte facilitates charge transfer between the cells. Generally, any number of power modules108a,bmay be connected to a common inverter104and/or electrolyte manifolds112a,b. The fluid pumps110a,band electrolyte manifolds112a,bmay be any appropriate fluid pumps and fluid conduit, respectively, for allowing transport of electrolyte solution from the electrolyte tanks126.

This disclosure recognizes that each power module108a,bof the power module subsystem106may need to be able to operate independently from the other power modules108a,bon the same inverter104and/or electrolyte manifolds112a,b. It is also desirable for each power module108a,bto be able to enter and remain in any operating state (e.g., OFF, STANDBY, IDLE, or ACTIVE) while adj acent power modules108a,bare in a different state. Examples of improved power module subsystems106in accordance with embodiments of this disclosure are illustrated inFIGS.2and3and described below.

The battery management system114generally monitors operation of various components of the battery system100, including the power module subsystem106and determines control instructions122for effectively operating the battery system100. For example, the battery management system114may be in communication with and control operations of the fluid pumps110a,band circuitry of the power modules108a,bin order to improve their efficiency and reduce or remove opportunities for unwanted side reactions in power modules108a,boperating at a low state of charge. As an example, which is described in greater detail below with respect toFIGS.2,3, and5, the improved battery management system114of this disclosure may detect that adjacent power modules108a,bare operating at a different state of charge and determine which power module108a,bis operating at the lower state of charge. The power module108a,bat the lower state of charge is then electronically floated relative to a common electrical ground of the power modules108a,b. This removes a possible shunt current path through the power module108a,bwith the lower state of charge, thereby improving overall efficiency and reducing or eliminating unwanted side reactions.

The battery management system114may include a processor116, input/output interface118, memory120, and/or one or more sensors124. The processor116includes one or more processors. The processor116is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g. a multi-core processor), field-programmable gate array (FPGAs), application specific integrated circuits (ASICs), or digital signal processors (DSPs). The processor116may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor116is communicatively coupled to and in signal communication with the input/output interface118and memory120. The processor116may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor116may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory120and executes them by directing the coordinated operations of the ALU, registers, and other components.

The memory120is operable to store any data, instructions, logic, rules, or code operable to execute the functions of the battery management system114. For example, the memory may store control instructions122, which may include instructions for operating switches206a,band218a,bofFIGS.2and3based on the relative state of charge of adjacent power modules202a,b, as described in greater detail below. The memory120includes one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory120may be volatile or non-volatile and may comprise read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM).

The interface118is configured to enable wired and/or wireless communications. The interface118is configured to communicate data between the battery management system114and other components of the system100, such as the power module subsystem106. The interface118is an electronic circuit that is configured to enable communications between devices. For example, the interface118may include one or more serial ports (e.g., USB ports or the like) and/or parallel ports (e.g., any type of multi-pin port) for facilitating this communication. As a further example, the interface118may include a WIFI interface, a local area network (LAN) interface, a wide area network (WAN) interface, a modem, a switch, or a router. The processor116is configured to send and receive data using the interface118. The interface118may be configured to receive data and/or signals from sensors124. The interface118may be configured to use any suitable type of communication protocol as would be appreciated by one of ordinary skill in the art.

Sensors124may include any appropriate sensors (e.g., voltage, current, and/or state of charge sensors) for monitoring operations of the battery system100. For example, a sensor124may measure voltages and/or currents at different points along circuitry of the power modules108a,b. As another example, sensors124may measure temperature, pressure, and/or flow rate of electrolyte solution through electrolyte manifolds112a,bor at another location in the battery system100. In some embodiments, sensors124may help facilitate a determination that adjacent power modules108a,bare operating at different charge states, such that the power module108a,bwith the lower charge state should be electronically floated, as described in greater detail below with respect toFIGS.2,3, and5.

The electrolyte tanks126generally include a first fluid-storing tank128afor storing a first electrolyte and a second fluid-storing tank128bfor storing a second electrolyte. For example, the first electrolyte stored in fluid-storing tank128amay be a positive electrolyte (or “posolyte”). Meanwhile, the second electrolyte stored in fluid-storing tank128bmay be a negative electrolyte (or “negolyte”). The positive and negative electrolytes include electroactive species that facilitate charge transfer in the positive and negative cells, respectively of the power modules108a,b. The electrolytes may be any appropriate electrolytes for a given power module108a,btype or electrode material. Pumps110a,bfacilitate flow of electrolyte into and out of electrolyte tanks126when appropriate (e.g., when a power module108a,bis charging or discharging, having its electrolyte removed/recycled, undergoing electrolyzation of electrolyte, or undergoing balancing or rebalancing).

Previous Power Module Configuration

FIGS.2and3show improved power module subsystems200and300that may be used as the power module subsystem106in the battery system100ofFIG.1.FIG.3shows the same configuration asFIG.2with an electrolyzer302in-line with the portion of the electrolyte manifold208leading to/from the first power module202a, as described further below. Power module subsystem200,300includes a first power module202athat is located adjacent to a second power module202b. Each power module202a,bincludes a set of battery cells204a,b. WhileFIGS.2and3show four cells204a,bin each power module202a,bfor simplicity, any number of cells204a,bless than or greater than four may be employed. The battery cells204a,binclude half-cells (marked positive (+) and negative (-)) and electrodes (shown in black). The positive and negative half-cells are separated by an ion-exchange membrane. An electrolyte manifold208, which may be a portion of electrolyte manifold112a,bofFIG.1returns/delivers electrolyte from/to the cells of battery cells204a,bto the corresponding electrolyte tanks126illustrated inFIG.1.

A positive-side terminal220a,bof each power module202a,bis connected to a positive bus212leading to the positive side or terminal of the AC/DC inverter104. A relay, or switch,206a,bmay be positioned to control the flow of electrical current from each positive-side terminal220a,bto the positive side of the AC/DC inverter104. In the open position shown for switch206a, electric current does not flow from the positive-side terminal220ato the AC/DC inverter104. In the closed position shown for switch206b, electric current flows from the positive-side terminal220bto the AC/DC inverter104. In other words, electric current flows when a switch206a,bis closed and does not flow when the switch206a,bis open.

A negative-side terminal222a,bof each power module202a,bis connected to a negative bus214leading to the negative side of the AC/DC inverter104and to electrical ground210. Both power modules202a,bshare a common electrical ground210. The common electrical ground210is a common reference point for voltages of the power modules202a,b. For example, the electrical ground210may be a shared connection to the earth or some other common return path for electrical current. The negative-side terminal222a,bmay be at a lower voltage relative to the positive-side terminal220a,b(e.g., with respect to the shared electrical ground210). This disclosure recognizes that problems may be encountered in previous technology when the adjacent power modules202a,benter dissimilar operating states that would cause a large state of charge gradient and a corresponding large electrical voltage gradient between the adjacent power modules202a,b. In such scenarios, the conductive electrolyte being pumped to/from each power module202a,bcan create a shunt current path216between the adjacent power modules216. The shunt current path216can allow current from the charging second module202bto be directed to electrical ground210via the illustrated shunt current path216. This shunt current path216can result in system inefficiency and drive unwanted and potentially harmful side-reactions in the first power module202athat is operating at the lower state of charge.

The improved power module subsystems200and300overcome the problems associated with the shunt current path216, using negative-side switches218a,bthat are connected to the negative-side terminals222a,bof the power modules202a,b. As described further below and with respect toFIG.5, these switches218a,bare operated to prevent the connection to electrical ground210for the power module202a,bthat is operating at a lower state of charge than its adjacent power module(s)202a,b. In the examples ofFIGS.2and3, the first power module202ais in a shutdown state (or in the process of shutting down) and therefore at a lower state of charge than the second power module202bthat is in a charging state. To break the shunt current path216, switch218ais opened, causing the first power module202ato electronically float at or near the electrical voltage of the second power module202b. For example, the first power module202amay float at a predetermined range of voltages relative to (e.g., within a predetermined number of Volts above or below) the electronic voltage of the second power module202b. This prevents development of the shunt current path216and associated problems of inefficiency and unwanted side reactions.

Switches218a,bmay be any appropriate electronic switch or relay. For example, the switches218a,bmay be the same as or similar to switches206a,bdescribed above. When the switch218a,bassociated with a given power module202a,bis open (as for switch218ainFIGS.2and3), flow of electrical current is prevented from the negative terminal222a,bof the power module202a,bto electrical ground210. Meanwhile, when the switch218a,bassociated with a given power module202a,bis closed (as for switch218binFIGS.2and3), flow of electrical current is allowed from the negative terminal222a,bof the power module202a,bto electrical ground210.

In certain embodiments, the power management system114ofFIG.1may coordinate, or otherwise control, the opening and closing of switches218a,band206a,b. For example, the control instructions122ofFIG.1may be executed by the processor116of the power management system114in order to perform functions to prevent the development of the shunt current path216. For example, the power management system114may detect that the adjacent first and second power modules202a,bare operating at different states of charge. For example, the power management system114may detect that the adjacent power modules202a,bare operating at different states of charge by determining that the first power module202ais in a shutdown (or shutting down) state and the second power module202bis in a charging state. The shutdown (or shutting down) state may correspond to the state in which the positive side of the inverter104is no longer coupled to the positive terminal220aof the power module202a(e.g., with positive-side switch206aopen as shown inFIGS.2and3). In the charging state, the positive side of the inverter104is connected to the positive terminal220bof the power module202b(e.g., with positive-side switch206bclosed as shown inFIGS.2and3). In some cases, one or more voltage or current measuring sensors (e.g., a voltmeter, ammeter, or the like) may be positioned and configured to detect a difference in the state of charge, voltage, health, resistance, or impedance between the adjacent power modules202a,b. Such a sensor may correspond to sensor124ofFIG.1, described above. These metrics may be used to determine that adjacent power modulus202a,bare at different states of charge. As used herein, a state of charge may refer to whether a given power module202a,bis charging or in some other state (e.g., discharging, shut down, etc.). In some cases, a different state of charge may refer to power modules202a,bbeing at different relative or reference voltages. For example, in some cases, adjacent power modules202a,bmay both be charging but may have different relative voltages, such that action may need to be taken to prevent shunt current path216.

The power management system114then determines which of the adjacent power modules202a,bis at the lower state of charge. In the examples ofFIGS.2and3, the first power module202ais at the lower state of charge. After determining that the first power module202ais at the lower state of charge than the adjacent second power module202b, the negative-side switch218athat is connected to the negative terminal222aof the first power module202ais moved to the open position, as shown inFIGS.2and3. Switch218bremains in the closed position (or is changed to the closed position if needed). Opening switch218acauses the first power module202ato electronically float at or near the electronic voltage of the second power module202b. This is illustrated inFIGS.2and3, which show both power modules202a,bat a voltage of 1000 V. In some cases, to prevent a shunt current path216, the switch218a,bmay be opened when the associated power module202a,benters a non-operational (e.g., OFF, STANDBY, IDLE) state (e.g., irrespective of a relative state of charge of the adjacent power modules202a,b).

In the exemplary embodiment ofFIG.3, the power module subsystem300includes an electrolyzer302, which includes at least one battery cell304and an inverter306. The electrolyzer302may be used to electrolyze negative electrolyte supplied to the first power module202awhen appropriate. As shown inFIG.3, when negative-side switch218ais open to protect power module202ain a lower charge state, the electrolyzer302shares a common ground via ground path308with its associated power module202a. As such, the presence of electrolyzer302does not prevent the electrical floating of power module202adescribed in this disclosure.

Example Electrolyte Manifold Configuration

Example Operation of Flow Cell Battery System

FIG.5illustrates an example method500of operating the battery system100ofFIG.1with the power module subsystems200or300ofFIGS.2and3used as the power modules106ofFIG.1. The method500may be implemented, at least in part, using the processor116, interface118, memory120, and/or sensors124of the battery management system114. The method500may begin at step502where the battery management system114determines whether adjacent power modules202a,bare at different states of charge. For example, the power modules202a,bmay be determined to be operating at different states of charge (seeFIGS.2and3) because the first power module202ais in a shutdown (or shutting down) state and the second power module202bis in a charging state. If adjacent power modules202a,bare found to be at a different state of charge, the power management system proceeds to step504.

At step504, the power management system114opens the switch218a,bthat connects the negative terminal222a,bof the power module202a,bwith the lower state of charge to the negative bus214. This breaks the power module’s connection to electrical ground210, causing the power module202a,bwith the lower state of charge to electronically float at or near the voltage of the adjacent power module202a,bwith the higher state of charge. At step506, the battery management system114may optionally prevent or reduce charge transfer in the electrolyte path between the power modules202a,bwith different states of charge, for example, by closing fluid valve406in the manifold configuration400ofFIG.4.

In sum, the systems and operations described herein may facilitate improved operation of flow cell batteries without development of a shunt current path between power modules at different states of charge. As a result, flow cell batteries can be operated more reliably and for longer periods of time. Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. The term “approximate” or “near” refers to being within about 30%, 20%, 10%, 5%, or less of a given value or another measurable characteristic. For example, an electronic voltage that is electronically floating near the electronic voltage of an adj acent power module may be within 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, or less of the voltage of the adjacent power module.

While the disclosed subject matter is described herein in terms of certain embodiments, those skilled in the art will recognize that various modifications and improvements can be made to the disclosed subject matter without departing from the scope thereof. Additional features known in the art likewise can be incorporated. Moreover, although individual features of one embodiment of the disclosed subject matter can be discussed herein or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment can be combined with one or more features of another embodiment or features from a plurality of embodiments.

In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having any other possible combination of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.