Fast switching back-up power supply system employing rechargeable electrochemical cells

A back-up rechargeable battery supply system comprises communication linkages and a configuration of switches to allow battery back-up power to be provided by cells within a battery unit that are in a ready mode and to by-pass batteries that are in a non-ready mode, or maintenance mode. The unique configuration of switches and communication methods enables the back-up power to be provided very quickly to avoid disruptions in power to a load. Each battery cell has a charge and discharge switch and a power switch. Both the power switch and one of the charge or discharge switches must be closed to allow the battery cell to charge or discharge respectively. The by-pass switch may be controlled by the battery system control or by the cell controller and when closed, the cell may be bypassed from discharging or charging. The battery cells may be electrochemical cells such as metal air batteries.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to fast switching back-up power supply systems employing rechargeable electrochemical cells.

Background

Back-up power supply systems have to respond quickly when a primary power source is interrupted. When a primary power source goes down or has a drop in power supply levels, a loss of power to a load, even for a fraction of a second can be problematic, especially with today's complex computer systems.

In prior art back-up systems using batteries as the source of back-up power with connecting switches operated at the cell level, communication of the drop or loss in power is provided to a central controller, which in turn sends out a signal to the cells to activate their switches for connecting the batteries to the circuit. Because there may be a lag in bringing the batteries on-line to meet the power demands when a power loss occurs, high discharge rate capacitors are often used to avoid interruption. High discharge rate capacitors can discharge power extremely quickly, but typically have low energy density and are expensive.

High rate capacitors are also used for applications where the charging load can spike or saturate quickly before batteries can be brought on-line for charging/storage. For example, clearing of cloud coverage or changes in wind pattern may cause the energy available on a solar cell or wind turbine farm to rapidly increase beyond the needs of the grid it powers, and high charge rate capacitors are used to buffer the battery banks until sufficient capacity comes on line to accept the power delivered.

Rechargeable electrochemical cells have other specific characteristics that make utilizing them in a back-up power supply system challenging. Rechargeable electrochemical cells, such as metal-air cells, lead-acid batteries and lithium batteries, have to undergo maintenance in which the cell is taken off-line to prevent them from being coupled with the primary power source and/or load. Such maintenance may include load balancing, deep discharging, forced resetting, or the like. In addition, rechargeable electrochemical cells may have a reduced state of charge that is not sufficient to enable utilizing the cells in a power supply mode. Because each cell behaves individually, a fast responding back-up power supply utilizing such cells can pose unique problems.

Examples of designs in accordance with prior art techniques are discussed in the detailed description section with reference toFIGS. 1-3. These designs suffer the shortcoming that the transition of the cells to a state where they are ready to discharge or charge is managed by the system controller, which is slow and dedicated to various other functions that create possible delays in the transition.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a back-up power supply system for use in conjunction with a primary electrical power source. The system comprises a primary power sensor configured to detect a characteristic of primary electrical power provided by the primary electrical power source to a load. The primary power sensor is configured to output a threshold signal, indicating a discharge mode or a charge mode based on the characteristic detected. The system also comprises a system controller and a battery system.

The battery system comprises a plurality of rechargeable battery cells arranged in series. Each cell comprises:(i) a cell controller;(ii) at least one ready state sensor coupled to the cell controller for sensing one or more conditions of the cell for determining if the rechargeable battery cell is in a ready charge mode for charging, and if the rechargeable battery cell is in a ready discharge mode for discharging;(iii) a cell bypass switch coupled to the cell controller, the cell bypass switch being switchable between a normal state for enabling said cell to be electrically coupled in said series and a bypass state bypassing the cell within the series; and(iv) a power switch switchable between a closed state electrically coupling the battery cell within the series to communicate power between the battery and the load and an open state electrically decoupling the battery cell from the series.

The primary power sensor is coupled in parallel to the system controller and each cell for transmitting the threshold signal directly thereto. This avoids passing the transmission of the threshold signal to the cells through the system controller. Each cell is configured to switch its power switch to the closed state in response to receiving the threshold signal. Each cell controller is also configured to switch the bypass switch between the bypass state and the normal state in response to the at least one ready state sensor.

Other means at the system level regulates the current and/or voltage output from or input to the cell, and the operation of the power switch (and possibly other switches) enables rapid transition of the available cells to a condition to charge or discharge, as may be applicable. For any cell not ready, the bypass switch function can be used to bypass that cell while maintaining the series.

In some embodiments, the primary power sensor may be coupled in parallel to the cell controller of each cell for transmitting the threshold signal directly thereto. In other embodiments, the primary power sensor may be coupled in parallel to dedicated circuits for managing the relevant switches at the cell level.

Other objects, features and advantages of the present invention will become appreciated from the following detailed description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control.

“Directly,” as used herein in reference to communication or signal transmission, means that a communication is transferred from one element, such as a sensor or controller, directly to another element of the system, such as a controller, charge control circuit, discharge control circuit or inverter gate without passing through any additional controller or microprocessor responsible for other functions. Directly may include passing from the first element through a communication transceiver and the signal may be a wireless signal. The notion of direct communication is intended to exclude the signal passing through a component that can delay the transmission because of dedication to other processes. For example, the microprocessor or microcontroller of the system controller is generally responsible for a number of high level functions, and routing the threshold signal through that microcontroller may create an unacceptable delay.

FIGS. 1-3are provided as a reference to illustrate a control topology using a more conventional technique. As shown inFIGS. 1 and 2, an exemplary back-up power supply system10is coupled to a load12and configured to detect, such as by measuring a power level of a primary power supply14by a primary power source sensor22. The primary power source sensor22is coupled to a controller70in the form of a microprocessor that communicates with each cell80to80″, each comprising a rechargeable battery81. That controller70is at the system level, and is responsible for a wide variety of functions at the system level and collecting/sending data and commands to and from the individual cells. This controller70can also manage the power electronics for connection to the load/power source and DC-DC or DC-AC conversion. The primary power sensor detects a characteristic of the primary electrical power provided by the primary electrical power source to a load.

InFIG. 1, the primary power source sensor22is a voltage sensor24detecting voltage as the characteristic, and inFIG. 2the primary power source sensor22is a current sensor26detecting current as the characteristic. Otherwise, these embodiments are generally the same.

A set of power lines78,78′ electrically couple the battery cells to a BUS40which couples the battery cells to the primary power source14and the load12. Where an AC power source is used, the AC signal may be converted to DC, such as by rectifier44. When the primary power source sensor22detects a reduction in the primary electrical power below a threshold, for example a lower threshold level, the system controller70will send a command to cause the cell controllers to close their power switches75(for those cells that are ready to discharge and not bypassed in the manner discussed below) to couple the batteries in series to the load to supply battery power to the load. The same happens for charging, except that power is delivered to the series of connected cells. A power regulator77may control the electrical power produced by the battery system for supply to the load. For example, the load may be configured to receive power at 44-54 volts, and the power regulator may be used to control the amount of power delivered to the load. As an example, if the bus voltage drops to 30 volts, the power regulator may limit the voltage produced to 14-24 additional volts to maintain the bus voltage at an acceptable range to support the load. Likewise, if the power available to the load is higher, the regulator77may divert excess voltage to the cells for recharging purposes. This power regulator is conventional and well-known, and may be embodied in separate components, such as one regulator dedicated to charging and one dedicated to discharging. The operation of the power regulator(s)77is handled by the system controller70.

The power regulator77may also include a power conditioner, such as a DC-DC or DC-AC converter, depending on the application. Alternatively, the power regulation (e.g., the ability to limit voltage or current output from or input into the cell series) and the power conditioning (e.g., signal conversion or matching) may be performed by separate components.

Each of the battery cells80-80″ has a ready state sensor82-82″ that measures one or more parameters of the battery that are used to determine if the battery is in a ready state for discharge mode or charge mode. The ready state sensor may determine if the battery cell is defective, and provide a signal to the cell controller and/or system controller to place the cell in a defect mode. The ready state sensor may also measure a state of charge of the battery and if the state of charge is too low, then the bypass switch85(and optionally power switch75and/or discharge switch90) may be opened to prevent the battery being coupled with the load in a discharge mode. When the state of charge of the cell is above an upper threshold limit, the bypass switch85(and optionally power switch75and/or charge switch92) may be opened to prevent the cell from going into charge mode, whereby overcharging can have detrimental effects on the battery cell. The ready state sensor provides input for determining if the cell is in a ready mode for charging or discharging and the primary power supply sensor22also provides input to the system for switching cells to a charge or discharge mode. The two sensors work in tandem to allow only cells that are in a proper ready mode to be coupled with the load or primary power supply.

The primary power source sensor22communicates with the battery system controller70and the battery system controller70communicates with each of the cells through a communication line79. A communication transceiver72, comprising a signal transmitter and in some case a signal receiver, communicates with the battery system controller70and with each of the cells. The communication line79couples the battery system controller70with the cell controllers87. Each of the cells80-80″ has a cell controller87that receives communication signals from the battery system controller70and controls switches75,85,90,92of the cells.

Each cell has a discharge switch90. Each discharge switch90is switchable between a closed position for coupling the cell80,80′,80″ to the series by the cathode thereof for discharging the cell, and an open position for decoupling the cathode from the series. In the example of a metal-air cell, the cathode is the air cathode.

Each cell also has a charge switch92. Each charge switch92is switchable between a closed position for coupling the cell to the series by the charging electrode for charging, and an open position for decoupling the charging electrode from the series. In the example of a metal-air cell, the charging electrode may be an oxygen evolving electrode, such as a nickel based one.

Each cell also has a power switch75. Each power switch75is switchable between a closed state electrically coupling the battery cell within the series to communicate power between the battery and the load, and an open state electrically decoupling the battery cell from the series. As can be seen in the drawings, the power switch75couples the cell to the series by the negative electrode, such as the metal (e.g., zinc) fuel electrode in a metal-air cell.

Each cell has a cell bypass switch85that is used to disengage or bypass the cell from charging or discharging, as described herein. The cell bypass switch85is coupled to the cell controller87. The cell bypass switch85is switchable between a normal state for enabling the cell80,80′,80″ to be electrically coupled in the series and a bypass state bypassing the cell within the series.

As shown inFIG. 3, the communication line79is coupled with the cell controller87and the cell controller87controls the opening and closing of one or more of the cell switches, i.e., the cell bypass switch85, the power switch75, the discharge switch90and/or the charge switch92. The cell controller87may close the bypass switch85to put the cell in bypass mode when the cell is in a maintenance mode, service mode, non-ready mode or a fault mode. The use of such bypassed modes is known, for purposes of keeping a cell off-line for certain activities, such as deep discharging, replacement, resetting, etc., while allowing the remaining cells to remain connected in series.

The shortcoming of this prior approach, as mentioned above in the background section, is that the system controller70is responsible for sending the signal to trigger the cells to close their respective power switches, and to close the discharge or charge switch of each cell based on whether discharge or charge mode is being entered. Because the system controller70also has a number of other responsibilities, there can be a delay in supplying power or making capacity available for charging.

The following embodiments address that problem by using a more direct technique for switching the cells to a state for charge or discharge. Similarities between the topology inFIGS. 1-3will not be repeated in detail.

As shown inFIGS. 4 and 5, an exemplary back-up power supply system10is coupled to a load12and configured to detect, such as by measuring, a characteristic of a power level of a primary power supply14by a primary power source sensor22(e.g., voltage or current). For example, in a grid application supplying power to a bank of computers as the load, the primary power source may detect a characteristic indicative of the power available on that grid to make an informed decision as to whether there is sufficient power to operate the computers, insufficient power requiring backup power from the batteries, or more than sufficient power such that there is excess that can used for charging the batteries. In a solar farm application, the electrical power source may be the amount of power output by the solar farm to an area wide grid as the load, and the sensor can detect a characteristic of the power generated by the solar farm to make the same informed decision. In different applications, differing priorities may be given to charging and discharging, or they may be of equal priority. In the computer example, keeping a level supply of power without interruption is critical, and thus such a system may be designed to react more quickly for discharge purposes. For a solar farm application, because spikes in output may occur that needs to be stored by the batteries, the system may be designed to react more quickly for charge purposes. In some systems both charge and discharge functions may be prioritized equally. Context for these differences will be mentioned below in reference to the bypass functionality.

The primary power source sensor24/26is directly communicated inFIGS. 4 and 5, such as by hard wiring, to each of the cell controllers87for cells80′-80″. Specifically, as shown inFIG. 4, the primary power source sensor is a voltage sensor24and as shown inFIG. 5, the primary power source sensor is a current sensor26. The primary power source sensor is also directly communicated to the battery system controller70. Thus, the primary power sensor24/26is coupled in parallel to the controller87of each cell and the system controller70. Direct signals are transferred by a direct line95to each of the cells80-80″. In this embodiment, the cell controllers87are configured to (a) switch the power switch75and the discharge switch90to the closed states thereof in response to a threshold signal (discussed below) indicating the discharge mode and (b) switch the power switch75and the charge switch92to the closed states thereof in response to the threshold signal indicating the charge mode. Because the primary power source sensor24/26is connected directly to each of the cell controllers87, the battery system controller70is bypassed. This provides higher speeds for switching to a battery power supply.

Either sensor24/26is configured to output a threshold signal that indicates a discharge mode or a charge mode for the system. The threshold signal is a signal emitted when the sensor24/26detects the relevant characteristic as passing an applicable threshold. Using voltage as an example, the sensor24may have a single threshold and output a threshold signal indicating a charge mode when the voltage is above the threshold, and a threshold signal indicating a discharge mode when the voltage is below the threshold. Multiple thresholds may be used, such as a higher threshold that triggers sending the threshold signal indicating the charge mode when the voltage exceeds it and a lower threshold that triggers sending the threshold signal indicating the discharge mode when the voltage drops below it. The threshold signal is thus a signal that indicates breaking of a threshold and whether that breaking indicates charge or discharge for the system. The threshold signal is a global or unitary command or data signal to which all the cells respond, in contrast to addressed signals that indicate the address for a specific cell and are intended for a specific cell. A global or unitary command allows one command to be sent in parallel to all cells, and to the system controller70also. The threshold signal may be as simple as a high/low data bit or a hardware type signal. At the system controller70, the system will make decisions about how much power is required for a discharge event and operate the regulator77responsible for controlling and managing power output (or for a charge event it will do the inverse and decide how much power is available for charging).

When the primary power source sensor24/26detects a reduction in the primary electrical power below a threshold, or lower threshold level, it sends out a threshold signal indicating a discharge mode. The cell controller87in turn receives that signal and reacts accordingly. Preferably, primary power source sensor is connected to an interrupt input (also called an interrupt pin) of the cell controller87, which triggers the responsive action as high priority and makes the process faster without waiting for the cell controller87to perform other processes that may delay the response. The cell controller's reaction to a threshold signal indicating the discharge mode is to close (i.e., switch it to its closed state) the power switch75and the discharge switch90to provide a flow of electrical power from the cell80to the load12.

If the cell is in maintenance or a non-ready mode, including not being ready for discharge, the bypass switch85will be closed causing the cell to be bypassed wherein no power is provide from the cell to the load. In that case, the controller need not close the power switch75and the discharge switch90. In fact, it is preferred (but optional) that it not do that, as such connections may permit some connectivity between the cell and the series.

As a result of that threshold signal indicating the discharge mode, this enables each cell available for discharge to make the appropriate switching connections rapidly and in parallel simultaneously.

Likewise, when the primary power source sensor24/26detects an increase in the primary electrical power above a threshold, such as an upper threshold level, it sends out a threshold signal indicating a charge mode. The cell controller87in turn receives that signal and reacts accordingly. The cell controller's reaction to a threshold signal indicating the charge mode is to close (i.e., switch it to its closed state) the power switch75and the charge switch92to provide a flow of electrical power from the cell80to the load12.

If the cell is in maintenance or a non-ready mode, including not being ready for charging, the bypass switch85will be closed causing the cell to be bypassed wherein no power is provide to the cell. In that case, the controller need not close the power switch75and the charge switch92. Again, it is preferred (but optional) that it not do that, as such connections may permit some connectivity between the cell and the series.

As a result of that threshold signal indicating the charge mode, this enables each cell available for charge to make the appropriate switching connections rapidly and in parallel simultaneously.

The bypass switching decision may be made by the cell controller87independently of the threshold signal reaction. Thus, the decision to place a given cell in bypass mode could have happened in advance, and reference to that decision is not intended to mean that the bypass switch action necessarily happens at the same time as the signaling to close the power and discharge/charge power switches75,90/92happens. Some systems may have a configuration bias toward discharge or charge depending on the application. For example, as mentioned above, a system for backing up power to sensitive electronics, such as computers, may have an emphasis on rapid discharge, while a system for backing up a solar or wind farm may have an emphasis on rapid charging.

In systems where rapid discharge is a priority, the system may have a configuration bias towards keeping those cells not ready for discharge in a bypass state with the bypass switch85closed, and those that are ready for discharge in a normal state with the bypass switch85open. This is particularly useful where the cell ready state sensor(s) are used to identify cells that are ready for discharge but not ready for charge (e.g., a full cell that requires no further charging) and vice versa. Where discharging is more of a priority, the cell controllers87can be configured to set the bypass switches85in anticipation that discharge will be requested. This allows the system to react more rapidly when the threshold signal indicating a discharge mode is sent because the bypassing switches85have already been set in the correct positions, and the only action needed is closure of the power and discharge switches75,90.

Likewise, in systems where rapid charge is a priority, the system may have a configuration bias towards keeping those cells not ready for charging in a bypass state with the bypass switch85closed, and those that are ready for charging in a normal state with the bypass switch85open. This is particularly useful where the cell ready state sensor(s) are used to identify cells that are ready for charging but not ready for discharge (e.g., a depleted cell that cannot discharge further and needs to be charged) and vice versa. Where charging is more of a priority, the cell controllers87can be configured to set the bypass switches in anticipation that charging will be requested. This allows the system to react more rapidly when the threshold signal indicating a charge mode is sent because the bypassing switches have already been set in the correct positions, and the only action needed is closure of the power and charge switches75,92.

Other system may have no configuration bias towards charge or discharge.

Referring now toFIGS. 6 to 8, an additional back-up power supply system10is coupled to a load12and configured to measure a power level of a primary power supply14by a primary power source sensor22. InFIG. 6, the primary power source sensor22is a voltage sensor24, and inFIG. 7the primary power source sensor22is a current sensor26. The system design is the same as inFIGS. 4 and 5, except that the sensor24/26is coupled in parallel to a discharge control circuit96and a charge control circuit98of each cell for transmitting the threshold signal directly thereto. These circuits96,98control the discharge and charge switches90,92, respectively, and the direct connection enables extremely rapid response to close the appropriate switch.

The discharge control circuit96may be designed as an AND gate. The AND gate has a first input connected to the primary power source sensor24/26for receipt of the appropriate threshold signal. That is, the primary power source sensor24/26is coupled in parallel to the discharge control circuit96of each cell, and particularly to the first input of the AND gate in the illustrated embodiment, for transmitting the threshold signal directly thereto. The AND gate of the discharge control circuit96also has a second input connected to the cell controller87to receive a signal indicating whether the cell is in a ready discharge state. The discharge control circuit96is configured to switch the discharge switch90to the closed state in response to two conditions being met: receiving the threshold signal indicating a discharge mode at the first input and a ready discharge signal from the cell controller87at the second input indicating the cell is in a ready discharge state. If both conditions are met the discharge control circuit96will close the discharge switch90.

The charge control circuit98may also be designed as an AND gate. The AND gate also has a first input connected to the primary power source sensor24/26for receipt of the appropriate threshold signal. That is, the primary power source sensor24/26is coupled in parallel to the charge control circuit98of each cell, and particularly to the first input of the AND gate in the illustrated embodiment, for transmitting the threshold signal directly thereto. The AND gate of the charge control circuit98also has a second input connected to the cell controller87to receive a signal indicating whether the cell is in a ready charge state. The charge control circuit98is configured to switch the charge switch92to the closed state in response to two conditions being met: receiving the threshold signal indicating a charge mode at the first input and a ready charge signal from the cell controller87at the second input indicating the cell is in a ready discharge state. If both conditions are met the charge control circuit98will close the charge switch92.

An inverter gate99prevents both switches90,92from being activated at the same time wherein only one of the discharge and charge switch can be closed at a time.

Similarly, the power switch75may also have a power switch control circuit93for controlling the power switch75. The power source sensor24/26may be communicated directly to the power source control circuit93in parallel to the other elements. The power switch control circuit93may also be designed as an AND gate. The AND gate also has a first input connected to the primary power source sensor24/26for receipt of the appropriate threshold signal. That is, the primary power source sensor24/26is coupled in parallel to the power switch control circuit93of each cell, and particularly to the first input of the AND gate in the illustrated embodiment, for transmitting the threshold signal directly thereto. The AND gate of the power switch control circuit93also has a second input connected to the cell controller87to receive a signal indicating whether the cell is in a ready state. The power switch control circuit93is configured to switch the charge switch92to the closed state in response to two conditions being met: receiving any threshold signal indicating a discharge or charge mode at the first input and a ready signal from the cell controller87at the second input indicating the cell is in a ready state, i.e. not in bypass. If both conditions are met the power switch control circuit93will close the power switch75.

In some embodiments, the signal applied to the second input of the power switch control circuit AND gate may be a generic ready signal, i.e., a signal output for by the cell controller that indicates to the power switch control circuit93that the cell is ready for the power switch75to be closed (but does not differentiate between ready for charge and ready for discharge). In some embodiments, the signal applied to the second input control circuit AND gate may differentiate between the two states, i.e, be a ready discharge signal or a ready charge signal. The power switch control circuit93may be configured to react to either of those signals (assuming a threshold signal is also received). It is also possible to use multiple components, such as an AND gate that closes the power switch75when both a ready discharge signal from the cell controller87and a threshold signal indicating discharge mode is received, and an AND gate that closes the power switch75when both a ready charge signal from the cell controller and a threshold signal indicating charge mode is received. Thus, the use of a singular AND gate is not limiting, and other fast acting circuits may be used as well.

This direct communication and circuit driven switching inFIGS. 6-8provides very fast responsiveness to a primary power source dropping below a threshold level.

In an embodiment, the back-up power supply system10may be coupled to a load12configured to receive AC power. An inverter is used to convert DC power from the primary power source14, e.g., a solar panel, to AC power. The same inverter (or a different one) will convert DC power produced by the back-up power supply system to AC power for application to the load when the primary power supply drops below a threshold power level.

In some embodiments, the cell may not have charge/discharge switches that couple separate electrodes to the circuit for discharging and charging functions. For example, some battery cells (e.g., lithium ion and lead acid batteries) only have an anode and a cathode and can be discharged and charged using the same electrodes by simply reversing the polarity. However, because it may be desirable to take such cells off-line for maintenance/defect purposes without interrupting the entire series, those cells can have the same power switch75and by-pass switch85as the previously discussed embodiments, with no need for multiple switches to toggle between different electrodes for charge and discharge purposes. It is also possible to have two power switches, one for the anode and one for the cathode of such a cell to ensure the cell is completely isolated from the series. The connection, configuration, and responsiveness of such switches on cells having only an anode and a cathode are the same as those discussed above,

As shown in the control diagram ofFIG. 9, an exemplary back-up power supply system10connects cells that are in a ready discharge mode to the load to supply battery power to the load when the sensor detects that the primary power source is below a threshold level. The primary power source sensor22communicates with a battery system controller which then communicates with each of the cells.

As shown in the control diagram ofFIG. 10, an exemplary back-up power supply system10connects the primary power supply to the cells that are in a ready charge mode to supply primary power to the cells when the sensor detects that the primary power source is above a threshold level. The primary power source sensor22communicates with a battery system controller which then communicates with each of the cells.

As shown in the control diagram ofFIG. 11, an exemplary back-up power supply system10connects cells that are in a ready discharge mode to the load, to supply battery power to the load when the sensor detects that the primary power source is below a threshold level. The primary power source sensor22communicates directly with the cells.

As shown in the control diagram ofFIG. 12, an exemplary back-up power supply system10connects the primary power supply to the cells that are in a ready charge mode to supply primary power to the cells when the sensor detects that the primary power source is above a threshold level. The primary power source sensor22communicates directly with the cells, such as to control circuits or directly with the cell controllers.

Referring now toFIGS. 13 and 14, various portions of the electrochemical cell100may be of any suitable structure or composition, including but not limited to being formed from plastic, metal, resin, or combinations thereof. Accordingly, the cell100may be assembled in any manner, including being formed from a plurality of elements, being integrally molded, or so on. In various embodiments the cell100and/or the housing110may include elements or arrangements from one or more of U.S. Pat. Nos. 8,168,337, 8,309,259, 8,491,763, 8,492,052, 8,659,268, 8,877,391, 8,895,197, 8,906,563, 8,911,910, 9,269,996, 9,269,998 and U.S. Patent Application Publication Nos. 20100316935, 20110070506, 20110250512, 20120015264, 20120068667, 20120202127, 20120321969, 20130095393, 20130115523, and 20130115525, each of which are incorporated herein in their entireties by reference.

FIG. 13illustrates a schematic cross sectional view of an electrochemical cell100. As shown, the components of the electrochemical cell100may be contained at least partially in an associated housing110. The cell100utilizes a liquid ionically conductive medium124, such as an electrolyte126that is contained within the housing110, and is configured to circulate therein to conduct ions within the cell100. While at times the ionically conductive medium may be generally stationary within the housing110, such as in a stagnant zone, it may be appreciated that the cell100may be configured to create a convective flow of the ionically conductive medium. In some embodiments, the flow of the ionically conductive medium may be a convective flow generated by bubbles of evolved gas in the cell100, such as is described in U.S. patent application Ser. No. 13/532,374 incorporated above in its entirety by reference

Although in the illustrated embodiment ofFIG. 13the cell housing is configured such that the oxidant reduction electrode150is immersed with the oxidant reduction electrode module160into the cell chamber120, it may be appreciated that in various embodiments, other configurations or arrangements of the cell100are also possible. For example, inFIG. 14, another embodiment of the cell100(specifically, cell100*) is presented, whereby an oxidant reduction electrode150* defines a boundary wall for the cell chamber120, and is sealed to a portion of a housing110* so as to prevent seepage of ionically conductive medium therebetween. Such a configuration is generally not preferred, however, due to concerns that a failure of the oxidant reduction electrode150* would result in leakage of the ionically conductive medium out of the cell100*. Regardless, in some such embodiments the convective flow of the ionically conductive medium in the cell chamber120, described in greater detail below, may be in a direction upwards and away from the oxidant reduction electrode150*, across the top of the fuel electrode130.

Preferably, systems in accordance with embodiments of the invention may complete switching within 10 ms or less of the power source sensor22detecting an applicable threshold being passed. More preferably, the time period is 5 ms or less, or even 2 ms or less.