Fuel cell based rechargable power pack system and associated methods for controlling same

A power pack system for charging a set of isolated batteries is provided. In an illustrative embodiment of the invention, a single fuel cell, a single DC-DC converter and a single system controller device comprises the power-generation side of the power pack. A set of switches is used to connect the power-generation side of the Power pack to one of the isolated batteries in the power pack, thereby recharging that particular battery in the battery power pack set. A battery protection and powerpath control device communicates with the system controller to determine which switches are to be closed depending upon which battery requires recharging. During normal operation the switches will follow the direction from the system controller. If a fault is detected by the battery protection circuit, the protection circuit will take priority and turn off the appropriate switch(es).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to fuel cell systems that include fuel cells and rechargeable batteries for various power needs.

2. Background Information

Many electrically powered devices, including commercial and military applications require a reliable battery with high-energy density and long life. There are numerous conventional techniques and components for charging rechargeable batteries such as lithium ion batteries which are widely used in both consumer and military electronic applications. Typically an A/C wall outlet or a 12 volt DC source commonly provided in vehicles can be used for a power source for such recharging. However, such power sources may not be available and a portable recharging device is required.

Use of a fuel cell in the power source for use as a battery recharger for a battery which is powering a portable device has been described in commonly owned U.S. Pat. No. 6,590,370, of Leach, for a SWITCHING DC-DC POWER CONVERTER AND BATTERY CHARGER FOR USE WITH DIRECT OXIDATION FUEL CELL POWER SOURCE, which issued on Jul. 8, 2003, which is currently herein incorporated by reference in its entirety.

Many commonly used battery power packs include two isolated batteries which can be connected in different ways depending on the user's needs. For example, most portable battery poweredelectronic equipment runs on either a 10-15 volt (V) low-voltage rail or a 20-30V high voltage rail. Rather than requiring two different battery types to be carried, a power pack will include two isolated 10-15V batteries with a plus and minus of each battery terminal being available on a multi-pin output connector. The user thus has the option of connecting the batteries in parallel, series, or leaving them independent to meet the power needs of the equipment.

Primary batteries are normally used where continuous, reliable operation is highly desireable because of their higher energy density and longer life as compared to rechargeable batteries. Users would prefer to commence with a fully charged battery because existing primary batteries do not have an indicator showing the amount of charge left. For this reason, many batteries are thrown away with useful life left in them. Rechargeable batteries would thus be encouraged; however, a person can not be assured that they would remain charged and would be ready at all times. A power pack that uses a fuel cell to continuously recharge the batteries so that they act essentially as primary batteries would be desired.

Batteries typically include battery protection circuits, which include switches which are used to protect the battery from under or over voltage conditions or excessive charge or discharge currents. A battery normally is packaged with it's protection circuit attached and two wires coming out of the package. To achieve all of the functionality desired of a fuel cell battery hybrid power pack, such as disconnecting the load while continuing to recharge the battery with the fuel cell power, or bypassing the battery to charge an external battery connected to the load pins, additional switches are required. However, the switches have an on resistance that results in power loss while current is flowing through the switch. It would be advantageous to have a switch network that both protects the battery and minimizes the number of switches, and therefore the total resistance, of all the current paths in the system.

It is thus object of the present invention to provide a power pack that uses one or more fuel cells as a primary energy source to charge one or more isolated rechargeable batteries so that external equipment can draw power from any of the battery(ies).

It is also an object of the invention to provide a fuel cell system that uses one or more fuel cells and one or more rechargeable batteries which can also be used to charge one or more additional external batteries.

It is also noted that a fuel cell system requires power to start (for pumps, fans, etc.), after which the fuel cell output power can be used to maintain operation. Normally this start-up power comes from a battery that is part of the power pack. It is another object of the invention to provide a mechanism by which an external power source can be used to jump-start the system even if all internal batteries are discharged.

It is yet a further object of the invention to provide an improved power pack which minimizes the number of components, such as switches, that are in the powerpath between the fuel cell(s), batteries, and the load(s).

SUMMARY OF THE INVENTION

The disadvantages of prior techniques have been overcome by the present invention which is a fuel cell based power pack system that has functionality that separates the fuel cell charging current path to the battery from the load current path from the battery.

Each embodiment of the power pack system of the present invention includes at least one fuel cell and one or more isolated rechargeable batteries that can be connected externally (series, parallel, isolated) as required to power external equipment. A battery protection circuit monitors the voltage and current of each battery and disconnects the battery if it's voltage or current limits are exceeded.

In a first embodiment of the invention, a fuel cell is used in connection with a DC-DC converter and a system controller which includes a microprocessor programmed in accordance with the invention, as well as various individual components including fans, pumps, valves, pressure transducers, temperature transducers and the like. The controller and additional components are referred to herein as the “system controller and balance of plant.” This power-generation side of the circuit provides power to a battery and or load connected to the battery output terminals through a battery protection and power path control circuit associated with that battery. To achieve two isolated batteries in the power pack, this embodiment includes a second fuel cell and DC-DC converter combination that provides power to a second battery, which has its own battery protection and power path control circuit. The user can connect the batteries to draw on either one or both batteries either together or independently.

In a second embodiment of the invention, one fuel cell is coupled to a first DC-DC converter which provides power to a first battery. A second, isolated DC-DC converter draws power from either the fuel cell or the first battery and is used to provide power to a second isolated battery in the power pack.

In another embodiment of the invention, a single fuel cell powered by an internal battery and a set of isolation switches connect a non-isolated DC-DC converter to either the first battery or the second battery. The control logic for the switches acts to keep the batteries at the same state of charge so that they charge or discharge substantially together. The logic directs charging current to the battery with the lowest state of charge until it is slightly more charged than the other battery and then directs current to the other battery until it is slightly more charged than the first battery and so on. The drivers for the switches in the switch network can be powered from either the fuel-cell side or the battery side of the switches.

In each of the embodiments, a battery protection and power pack control circuit protects the battery from excessive currents and over or under voltage conditions.

In an illustrative embodiment of the invention, a single fuel cell, a single DC-DC converter and a single system controller device comprise the power-generation side of the power pack. A switching side includes a switch network that includes a set of switches that connect the power-generation side of the power pack to one of the isolated batteries in the power pack, thereby recharging that particular battery in the battery power pack set. A battery protection and power path control device communicates with the system controller to determine which switches are to be closed depending on which battery requires recharging. During normal operation the switches will follow the direction from the system controller. If a fault is detected by the battery protection circuit, the protection circuit will take priority and turn off the appropriate switch(es). An isolated communication interface is provided for communicating between the switch drivers associated with each isolated battery and the fuel cell side of the circuit.

The power pack of the present invention can be used with its rechargeable batteries to charge one or more auxiliary batteries. In addition, such auxiliary batteries or another available power source can be used to jump-start the fuel cell power source when the internal batteries contained therein have been fully discharged.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

FIG. 1is a schematic block diagram of a fuel-cell battery power pack with a single battery output that makes use of a battery protection circuit modified to allow the system controller to turn the switches on and off during non-fault conditions in accordance with an illustrative embodiment of the present invention. More specifically,FIG. 1illustrates a power pack100that includes a fuel cell102, a DC-DC converter104and a system controller and balance of plant106, which is powered either by the optional internal battery108or the main battery B1. As noted, the system controller and balance of plant106includes items such as the fans, pumps, valves, and sensors necessary to operate the fuel cell102. A rechargeable battery B1with a battery protection circuit120and a load disconnect switch S2, as well as the DC-DC converter104are controlled in the manner described in the above-cited U.S. Pat. No. 6,590,370.

In operation, the output voltage of a fuel cell102is provided to DC-DC converter104. The direct oxidation fuel cell102serves as a power source for the converter104. The fuel cell102is preferably implemented as a stack of direct methanol fuel cells, but should be understood that other configurations, such as a planar arrangement, or a single fuel cell and/or other types of direct oxidation fuel cells may be used within the scope of the present invention, and thus, as used herein, the word “fuel cell” shall include one or more of the aforementioned configurations. The battery B1may be of any chemistry and comprised of one or more cells in series and/or parallel combinations. The protection circuit120is similar to protection circuits that are readily available from third party manufacturers as will be understood by those skilled in the art, except it has been modified to allow the system controller106to turn the switches on and off during non-fault conditions.

Fuel cell102is connected directly to converter104such that the output voltage of the fuel cell102is the input voltage to the DC-DC converter104. The output voltage of the DC-DC converter104is provided to a battery protection and power path control circuit120which protects battery B1. The power path control circuit120is in turn connected to battery B1, to which a load can be connected in the manner desired by the user. Consequently, the output voltage of the DC-DC converter104equals the battery voltage and the output current will either charge the battery or aid the battery in supplying current.

As noted herein, the fuel cell102and the DC-DC power converter104are controlled by a number of components including a system controller106, which includes a microprocessor programmed in accordance with the invention, as well as various individual components including fans, pumps, valves, pressure transducers and temperature transducers and the like. The controller and additional components are referred to herein as the “system controller and balance of plant block” The system controller and balance of plant block for the battery B1is designated inFIG. 1by reference character106.

The power pack100can be connected to any of the following at it's load terminals Load B1+ and Load B1−: 1) a load that is to be powered by the power pack that can accept the same voltage range as the battery B1; 2) an external rechargeable battery that the power pack can recharge; or 3) a power source that can be used to recharge B1if it is completely discharged and unable to start the fuel cell system.

During normal operation a load is powered solely by the main battery B1through a load disconnect switch S2. If the load draws more average power than the fuel cell is providing the external battery will ultimately discharge. Before it is completely discharged the control logic, which is shared between the system controller and the battery protection circuit, will open the load disconnect switch S2so that the fuel cell power can recharge B1. The control logic operates such that protecting the battery from excessive current, overvoltage, or undervoltage takes precedence over other desired functionality.

A fault condition at the load terminals, e.g., a short or power source at higher voltage at the battery, will be detected by the protection circuit which will open switch S1, disconnecting the battery from the remainder of the circuit. This will trigger the control logic in the system controller106to open switch S2as well. Both S1and S2are of a type that can block current in both directions when open to protect against both short circuits and excessive voltages from an external power source. The fault condition is detected by current and voltage monitors that are part of the protection circuit. The current monitor is shown explicitly here as current sense resistor R1, but the current-sense circuit may use the voltage across S1or other methods known in the prior art. It is understood that S1, R1, and B1need only be connected in series for the function described, but these components may be connected in an order that is different than that illustrated while remaining within the scope of the invention. The order shown here is for illustrative purposes only.

Although the load disconnect switch S2is shown for illustrative purposes on the high side in series with the Load B+ terminal it could also be implemented on the low-side in series with the Load B1− terminal and such configuration should be understood as being part of this invention. The protection circuit may contain any of the features typically found in such components, such as battery temperature measurement or cell balancing features for multicell batteries, as will be understood by those skilled in the art.

In the illustrative embodiment, there is an internal battery108connected to the system controller106that can provide power if the battery protection switch S1opens for any reason. The controller106can then communicate with the protection circuit120to reset S1to the closed position—or it can attempt to charge the battery which will typically reset S1. It is noted that the internal battery will have its own protection circuit (not shown).

In accordance with another aspect of the invention, the extra internal battery can be omitted in which case the system controller switches the PWM control of the DC-DC converter from fuel cell control to output voltage control so the controller can use the power from the fuel cell to continue running and reset the battery switches to try again. If the fault persists, the fuel cell system will shutdown and the battery protection logic monitors conditions at the load terminal to determine when the fault condition has been repaired.

In practice, components on the battery side of the circuit, including the battery protection circuit120and load disconnect switch S2, would be packaged together with the battery and installed in the system as a unit so that the battery is protected during handling and assembly.

FIG. 2is a schematic block diagram of a fuel-cell battery power pack of the present invention with a single battery output, and which includes the dual-path battery protection circuit of the present invention.FIG. 2illustrates a power pack200with the same functionality as that ofFIG. 1and thus like components have the same reference characters. However, the power pack200includes an alternative battery protection and powerpath control circuit230. It is a key feature of the invention that two primary paths to get current into and out of the battery are provided. Specifically one path provides current from the fuel cell102through switch S1, and through current sense resistor R1to thus charge the battery B1from the fuel cell. The second path is from the battery B1through the current sense resistor R2through switch S2to the load. The protection circuit230monitors the current in each path separately and if limits are exceeded only the switch which is in the path of the excessive current will be opened.

This power pack200has two advantages over the approach shown inFIG. 1: 1) there is only one switch between the battery and the load; and 2) a fault condition at the load will not disconnect the fuel cell system from the battery. Current flowing from the battery to the load must flow only through switch S2, rather than through two switches as shown inFIG. 1, which reduces the conduction losses in the circuit during high current discharges. The current path through S1is also monitored to protect from fault conditions that might arise within the fuel cell electronics or during handling and assembly.

A third path for current into the battery is shown as the jump-start charger240which is controlled by the protection logic. If the battery has been completely discharged the protection circuit230can wake up when an external power source is attached to the load terminals. The protection circuit230can ascertain the status of the battery and if necessary use the external power source to charge the battery at a safe charging rate. The jump-start charger circuit can be a simple linear charger element that accepts voltages higher than the battery voltage or a complex universal-input charger circuit that can accept a wide range of voltages and power sources such as primary batteries, voltage supplies, or a photovoltaic panel. It accordance with another aspect of this invention the universal-input charger circuit will monitor the voltage and if the power source is of limited power, such as from a solar panel, the circuit will vary the amount of current it draws until it finds the maximum power condition of the power source. Though not shown specifically in every figure herein, this jump-start circuit can be included in each embodiment of this invention.

If a fault condition occurs at the load terminals which causes too much current to flow in or out of the battery, the protection circuit will open switches S2and S3, but leave S1closed so that the fuel cell can continue charging the battery while the fault condition is fixed by the user. Thus, no internal battery or extra circuitry is needed to recover from the fault condition or safely shut down the fuel cell if it is not addressed by the user. If it is desired that the fuel cell charge an external rechargeable battery attached to the Load pins while being unconnected from the battery B1then switch S3is closed while switches S1and S2are open. Switches S1, S2, and S3are all of a type that can block current in both directions when open.

It is understood that an alternative embodiment of this invention uses the resistances across the switches S1and S2as the current sense resistors to reduce conduction losses at the expense of accuracy of the current measurements. Another embodiment is to place all of the switches on the low side (in series with the Load B1− terminal).

FIG. 3depicts an illustrative modular embodiment of the system ofFIG. 1with an internal battery in the fuel-cell module to allow safe shutdown if the battery module is disconnected from the fuel cell while in use. More specifically,FIG. 3illustrates a power pack300which is a modular version of the system inFIG. 1in which the fuel-cell and the main battery are separated into two modules, a fuel cell module301and a battery module351. The fuel cell module301includes a fuel cell302, DC-DC converter304and a system controller and balance of plant306, which is powered either by an internal battery308or the external battery Bi when it is connected. With the modules301and351connected, the power pack300has the same functionality as the system ofFIG. 1. If the battery module351is disconnected from the fuel-cell module301, the internal battery308of the fuel cell module provides power for a safe and orderly shutdown of the fuel cell system.

The communication link310is shown as a two-wire communication link (CLK312and DAT314) but could use a single wire or have more wires. The communication link310not only allows the system controller306to control the switches S1and S2on and off during non-fault conditions, but it also allows the charging algorithms in the system controller to be modified if different types of batteries are attached, making it a smart battery and smart charger system.

The fuel cell module301is coupled to the battery module351at FC_out+ terminal320which is connected to Battery In+ terminal360, and at FC_Out− terminal322being connected to Battery In− terminal362. The battery module includes a battery protection circuit320which has its own current sense and resistor R1and internal protection switch S1.

FIG. 4depicts an illustrative modular embodiment of the system ofFIG. 2, with an internal battery in the fuel cell module similar toFIG. 3. Specifically,FIG. 4illustrates a modular power pack400which is a modular version of the system inFIG. 2in which the fuel cell and the main battery are separated into two modules, which are fuel cell module401and battery module451. With the modules connected, it has the same functionality as the system ofFIG. 2. The fuel-cell module401is the same as that inFIG. 3, and thus like components have the same reference characters as inFIG. 3. The fuel cell module401has an internal battery308to provide for a safe and orderly shutdown of the fuel cell system if the battery module451is disconnected while running.

The battery module451includes the main battery B1which is protected by the dual path battery protection circuit430of the present invention. Thus, there are two primary paths to get current into and out of the battery. One path provides current from the fuel cell302through switch S1, and through current sense resistor R1to thus charge the battery B1from the fuel cell. The second path is from the battery B1through the current sense resistor R2through switch S2to the load. The protection circuit430monitors the current in each path separately and if limits are exceeded only the switch which is in the path of the excessive current will be opened. Bypass switch S3can be used when the fuel cell302is providing power directly to the load or to charge an additional external rechargeable battery.

FIGS. 5-10illustrate several embodiments of the invention to provide two isolated battery outputs from one unit that are kept charged by one or more fuel cells. Because the two battery outputs are isolated, they can be connected externally by the user as needed, e.g., in series, parallel, or kept isolated.

FIG. 5is a schematic block diagram of a fuel-cell battery power pack in accordance with the present invention with two isolated battery outputs comprised of two independent single battery systems of the type shown inFIGS. 1 & 2. The first embodiment500of the invention for two isolated battery outputs is illustrated inFIG. 5and is comprised of two independent single battery systems501,551of the type shown inFIGS. 1 and 2. Each battery system includes its own respective fuel cell502,552, and its own DC-DC converter504,554, as well as a system controller and balance of plant block506,556. It is noted that the battery protection and powerpath control blocks510,560can be that ofFIG. 1or that ofFIG. 2. This embodiment500is has an extra overhead of two system controllers and balance of plant blocks506,556which consume additional volume that could be used for fuel, and because the two fuel cells would be half the size of a single fuel cell and if the user draws power from only one of the two batteries only half of the available fuel cell power can be used to recharge it. However, there may be practical applications in which the embodiment ofFIG. 5is desirable.

FIGS. 6-10illustrate embodiments of this invention in which a single fuel cell is used to charge two isolated batteries. There are two general approaches described with respect to this aspect of the invention: 1) use of an isolated DC-DC converter to charge the second battery as illustrated inFIGS. 6 & 7; and 2) use of a switch network to switch the output of the single fuel cell to one of the two batteries as illustrated inFIGS. 8-10. The control logic in all embodiments operates to keep the state of charge of the two batteries equal to each other at all times. For example, if the load draws more average power than the fuel cell can make, by keeping the batteries at the same state of charge they will be discharged together rather than one battery being discharged before the other which will maximize the time the system can be run in such a mode. If all of the current is being drawn from a single battery, it will be the battery that gets all of the fuel cell power to recharge it.

FIG. 6is an illustrative embodiment of the present invention of a fuel-cell battery power pack with two isolated battery outputs in which power from a single fuel cell is used to charge the two isolated batteries, and in which one of the batteries is charged through a DC-DC converter similar to that ofFIGS. 1 and 2, and the second battery is charged through a second isolated DC-DC converter that is powered directly from the fuel cell.FIG. 6illustrates an embodiment of a power pack600in which power from a single fuel cell602is used to charge the two batteries B1and B2. The portion of the system that charges B1is identical to that shown inFIGS. 1or2with DC-DC converter604used to charge B1, and a battery protection circuit and powerpath control circuit626may be either circuit for protecting the battery B1as inFIGS. 1 and 2The output voltage of the fuel cell602is also provided to a second DC-DC converter, which in this embodiment is an isolated DC-DC converter620(e.g., a transformer-based DC-DC converter), which in turn provides its output voltage to a second battery protection and power path control circuit624which protects battery B2as it is being charged. The battery protection and powerpath control circuit for battery B2can be like that ofFIG. 1or2.

A system controller and balance of plant assembly block610is used to control the power pack600. More specifically, the system controller monitors the state of charge of each battery, e.g. the voltage or information from a coulomb counting circuit (battery gas gauging), and sends more current to the battery (B1or B2) which is at the lowest state of charge. The system controller can either run both DC-DC converters simultaneously, with DC-DC converter604operated under fuel-cell control and DC-DC converter620operated under current control (or vice versa) or it can select that only one of the converters should be operated at a time in which case the converter that is operating will operate under fuel cell control.

In this embodiment of the invention, the system controller610communicates with the battery protection and powerpath control circuit624through an isolated communication interface630. The digital isolation circuit may use any of the common isolations methods, such as optical, magnetic, or capacitive, that are known to those skilled in the art. Notably, in this embodiment of the power pack600, just one fuel cell is needed to provide the power to charge the batteries B1and B2.

FIG. 7is an illustrative embodiment of the present invention with two isolated battery outputs similar toFIG. 6in which the second isolated DC-DC converter charging the second battery is powered by the first battery which is also connected to the output of the first DC-DC converter704. Specifically power pack700includes a single fuel cell702which is used to charge batteries B1and B2. A first stage of the power pack700is used to recharge battery B1. In that portion of the power pack700, the output of the fuel cell702is provided to DC-DC converter704and in turn to a first battery protection and power path control circuit726. This is used to recharge battery B1similar to the systems shown inFIGS. 1 & 2. A system controller and balance of plant block710is used to control the charging of the batteries and to maintain appropriate operation of fuel cell702. With respect to the second stage, an isolated DC-DC converter720is coupled to battery B2to provide its current, but this isolated DC-DC converter720is itself powered by the battery B1, in this embodiment instead of by the fuel cell702. The DC-DC converter720should have a slightly higher efficiency in this embodiment than in the embodiment ofFIG. 6, however, the power from the fuel cell has already been reduced due to the <100% efficiency of DC-DC converter704, prior to going through DC-DC converter720so the power pack700may overall be somewhat less efficient than the embodiment ofFIG. 6, but may be desirable in a particular application of the invention.

FIG. 8illustrates another embodiment of the invention with two isolated battery outputs which is a power pack having a single fuel cell, a single DC-DC converter and a switch network to connect the output of the single DC-DC converter to either of the isolated batteries and isolated communication links between the system controller and the battery protection logic to control the switches, in which the switch drivers for S1-S4are powered from the fuel cell side.

As shown inFIG. 8, power pack800has fuel cell802and a single DC-DC converter804, and system controller and balance of plant block806, powered by internal battery808. The single DC-DC converter804is coupled with a switch network810. The switch network810connects the fuel-cell-powered charger to either battery B1or battery B2. More specifically, when switches S1and S2are closed the fuel cell power is directed to battery B1. When switches S3and S4are closed the fuel cell power is directed to battery B2. The control logic, which is shared between the system controller806and the protection circuits826,828, ensures that only one battery is connected at a time. A further part of the invention is an isolated communication link830,832between the system. controller806and the two protection circuits826,828, respectively, which allow the system controller806to turn the switches S1-S4of the battery protection and powerpath control circuits on and off during non-fault conditions.

Switch network810is shown as powered on the control side. The switches S1through S4may be for example, optically-isolated solid-state relays, electromagnetic (EM) relays or MOSFETs with transformer-coupled gate drives. A lower power latching relay may be used in particular applications of the invention. The embodiment ofFIG. 8has greater efficiency than the power packs600and700ofFIGS. 6 and 7, respectively because the isolated DC-DC converters using transformers are not as efficient as the inductor-based non-isolated DC-DC converter used here. However, there may be applications in which the transformer based DC-DC converters are desirable despite the cost in efficiency. The system controller and balance of plant components are illustrated as a box806for the sake of clarity of illustration. In this embodiment, the system controller and balance of plant block806is powered by its own internal battery808in order to have power to drive the switches.

FIG. 9illustrates an embodiment of the power pack with two isolated battery outputs with a switch network and isolated communications similar to that ofFIG. 8but with the switch drivers powered from each of the batteries, B1and B2, respectively. More specifically,FIG. 9illustrates an embodiment of the power pack900of the present invention in which like components have the same reference numerals as inFIG. 8. The switch network910includes switch drivers912and914which are powered from each of the batteries, B1and B2, respectively. In this embodiment the switches S1-S4may be back to back MOSFETs (that block current flow in both directions) and are used with the switch drivers912and914in such manner that substantially no power is required as compared to the types of switches that are described with respect to the embodiment ofFIG. 8. An isolated communication link922allows the system controller and the circuitry on the battery side to communicate so that the system controller gets battery status information and it can also control the switches during non-fault conditions.

In one embodiment there is an internal battery808on the fuel cell side of the switch network910that ensures that the system controller has power and can control which set of switches, if any, are to be closed. In a preferred embodiment this internal battery can be eliminated by designating one of the switch drivers912,914upon initial configuration as the MASTER that communicates with the other switch driver to ensure that only one set of switches is closed. The fuel cell is used to recharge only one battery at a time. It is noted, however, that one battery can be supplying power to a load while the other battery is being recharged.

It is noted that switches S1and S3of power pack900may be included in the battery protection and powerpath control circuit as shown in detail inFIGS. 11 & 12. They are shown separately here for illustration purposes.

The power pack1000ofFIG. 10uses a single fuel cell1002and a single DC-DC converter1004with the switch network1010and is a variation on the embodiments shown inFIGS. 8 & 9in which the system controller and balance of plant block1006is disposed on the battery side of the switch network1010and specifically connected to the battery B2. Battery B1has Vsense and switch driver1012and battery protection and powerpath control circuit1026, and battery B2has battery protection and powerpath control circuit1028. The system controller and balance of plant block1006communicates through isolation communications interface1030with the Vsense and switch driver1012.

The common features of the embodiments ofFIGS. 8-10are a single fuel cell, a single DC-DC converter, a switch network, two isolated batteries with battery protection and powerpath control circuits, and isolated communication links between the system controller and the battery protection circuits and associated switch drivers. It is understood that any combination of these elements that achieve the same functionality is envisioned as within the scope of the present invention.

FIG. 11illustrates in greater detail the embodiment ofFIG. 9where the battery protection and powerpath control circuit makes use of a battery protection circuit modified to allow the system controller to turn the switches on and off during non-fault conditions. More specifically, the power pack1100ofFIG. 11includes a fuel cell1102, a DC-DC converter1104, a system controller and balance of plant block1106, powered by either an optional internal battery1108or one of the batteries B1or B2. The first battery B1is protected by a battery protection circuit1120, as modified in accordance with the invention such that the system controller can control the switches in non-fault situations and retrieve battery status information; the protection circuit has its own current sense resistor R1and switch S9. Battery B2has its own battery protection circuit1140which includes the current sense resistor R2and the switch S9. The battery can be recharged and the current delivered to the load by setting the switches in the manner described with reference toFIG. 9.

As noted,FIG. 11illustrates the embodiment ofFIG. 9in greater detail, specifically showing one embodiment of the battery protection and powerpath control circuit integrated with the switch network. The protection circuits for B1and B2are similar to the protection circuit ofFIG. 1described above except that the switches that are part of the switch network that corrects to the fuel cell (S1-S4) are now incorporated with the drivers of all switches powered by their respective batteries. An alternative embodiment of this invention would have switches S7(S5) and S8(S6) moved to the low side with S8(S6) in line with the Load B2− (Load B1−) terminal.

FIG. 12illustrates in greater detail the embodiment ofFIG. 9where the battery protection and powerpath control circuit is the dual-path battery protection circuit of the present invention, and in which a charging circuit is provided that can charge each battery from the load terminals if the internal battery is discharged and an external power source is connected to the load terminals;

FIG. 12illustrates power pack1200, which is similar to the embodiment ofFIG. 9and, in detail similar toFIG. 11, having fuel cell1202, DC-DC converter1204and system controller and balance of plant block1206. However, in the power pack1200the alternative dual-path protection scheme of the present invention is shown. The protection circuits1230,1232, for B1and B2, respectively are similar to the protection circuit ofFIG. 2described above except that the switches that are part of the switch network that connects to the fuel cell (S1-S4) are now incorporated with the drivers of all switches powered by their respective batteries. An alternative embodiment of this invention would have switches S7(S5) and S8(S6) moved to the low side with S8(S6) in line with the Load B2− (Load B1−) terminal. This embodiment has advantages over the embodiment ofFIG. 11because there is only one switch in the current path between the battery and the load, and because a fault on the load terminals will cause switches S7and S8to open to protect the battery but leave S3and S4closed to allow the fuel cell to continue charging while the fault is rectified by the user.

In the various embodiments of the invention, a number of different types of switches can be used in the protection circuits and switch networks of the present invention, depending upon the particular application of the invention. For example, back to back MOSFETs that can block current in both directions when off can be used. N-channel devices have better characteristics and can be driven simply on the low side. MOSFETs on the high side can be P-channel or N-channel with drivers that make a higher voltage than the battery. An example is a switched capacitor charge pump converter known to those skilled in the art.

As mentioned earlier, it is possible for the fuel cell power pack of this invention to charge an external rechargeable battery connected to the load terminals. It is envisioned that rechargeable batteries of any chemistry, different numbers of cells, and varying ampacity can be charged by making use of an external communication interface to batteries equipped with the same interface. This communication interface is illustrated as the CLK and DAT lines onFIGS. 11-14. Thus information such as battery type, charge termination voltage, max charging current, charge termination current, etc, can be communicated to the charging logic of the power pack to ensure that the proper charging protocols are used. Such smart battery/charger systems are known in the prior art.

FIG. 13illustrates a modular embodiment of the system ofFIG. 11with an internal battery in the fuel-cell module to allow safe shutdown if the battery module is disconnected from the fuel cell while in use. Specifically, the fuel cell module1301provides power to recharge the batteries B1and B2in the battery module1350. The fuel cell module1301includes a fuel cell1302, which provides power to a DC-DC converter1304. The module1301also includes a system controller and balance of plant block1306which operates in a manner similar to that described herein. Battery1308is large enough to provide start up power from a frozen state if the batteries in module1350are dead.

The fuel cell module1301is also provided with a communication interface1312which has a clock line1314and a data line1316. Alternative communication protocols using a single wire or more wires may also be used. The fuel cell module1301is coupled to the battery module1350at FC_out+ terminal1310which is coupled to battery In+ terminal1374, and at FC_Out_terminal1311coupled to battery In− terminal1376.

The battery module1350contains batteries B1and B2each with its own battery protection circuit1356and1386, respectively. With respect to battery B1, the battery protection circuit1356, which includes is own internal protection switch S9located on the high side of the battery and its own internal current sense resistor R1, which is coupled on the low side of the battery B1, but which has been modified in accordance with the invention so that the system controller1306can control its switches in non-fault conditions. The battery protection circuit monitors the voltage and current of the battery and disconnects the battery if the current exceeds the charge or discharge limits for that particular battery, or if the battery is overvoltaged.

Multicell protection circuits can be used to monitor the voltage on each individual cell of a multicell battery and may have the ability to perform charge balancing among the cells. Protection circuits, such as the circuit1356, may also have one or more components for measuring battery temperature, which disconnects the battery if the temperature is outside of a predetermined range. The switch S9and the current sense resistor R1may be located in any manner in series with the battery string to provide the same functionality. In addition, the switch S9may itself act as the current sense resistance which reduces the conduction losses at the expense of accuracy in the current measurement. The configuration illustrated inFIG. 13is one illustrative embodiment, but the components shown may be configured differently and additional components may be included while remaining within the scope of the present invention.

To achieve the functionality and methods as described herein in accordance with the present invention, several switches external to the battery are provided. More specifically, S1and S2are placed on the high and low terminals of the load in parallel with the DC-DC converter. Switch S5is an optional bypass switch and switch S6controls current from the battery to the load. As noted, switch S9is already included in the battery protection circuit.

In operation, to power a load with B1, both switch S9and switch S6must be closed. To charge B1with the fuel cell power both S1and S2must be closed. When charging B1and having B1power the load an extra switch S5can be used to reduce the conduction losses for charging current going directly to the load (which happens when the load current is larger than the charging current). If an external battery is attached to the load it can be charged directly by closing bypass switch S5and S2, with S9being opened. Or, S1and S6could be opened in that case of charging the external battery.

It is noted that a short circuit on the load connection (or other fault on the load connections happens), the protection circuit will open S9(and S6and S5) automatically, which disconnects power from the system controller and balance of plant1306, as well as not providing a repository for fuel cell power. In this case, the system controller1304will get its power from the internal battery1308and it can reconnect appropriate switches in an orderly many to determine if the fault persists.

FIG. 14illustrates a modular embodiment of the system inFIG. 12with an internal battery in the fuel cell module similar toFIG. 3. Specifically, the fuel cell module1401provides power to recharge the batteries B1and B2in the battery module1450. The fuel cell module1401includes a fuel cell1402, which provides power to a DC-DC converter1404. The module1401also includes a system controller and balance of plant block1406which operates in a manner similar to that described herein. An optional internal battery1408is large enough to provide start up power from a frozen state if the batteries in module1450are dead.

The fuel cell module1401is also provided with a communication interface1412which has a clock line1414and a data line1416. The fuel cell module1401is coupled to the battery module1450at FC_out+ terminal1410which is coupled to battery In+ terminal1474, and at FC_Out_terminal1411coupled to battery In− terminal1476.

The battery module1450includes batteries and B2. The battery B1stage includes a battery charging path such that when the switches S1and S2are closed, current flows through current sense resistor R1and into the battery B1to charge it. The dual path battery protection circuit, switch drivers and SMBus communications interface are shown illustratively as block1456. This circuit1456protects the battery B1from overcurrent and/or overvoltage states, as well as low voltage states and drives the switches accordingly. It also communicates with the system controller and balance of plant block1406, through an isolation barrier1458, which may be any suitable component as described herein. If the system controller and balance of plant block1406is signaling the battery protection circuit1456to recharge the battery B1, and yet the battery B1itself is not in the appropriate state for recharging, e.g., because it is already charged, then the battery protection block1456overrides the system controller1406and force switches S1and S2to remain open. If both batteries are charged the fuel cell system will shut down and wait for the batteries to be partially discharged before turning on again to recharge the batteries.

Turning now to the load current path, the switch S6, when closed, allows current to flow from battery B1through the current sense resistor R2, and through the switch S6to the load. A bypass switch S5allows current to flow directly from the fuel cell to the load for certain applications of the invention such and charging an external rechargeable battery. An optional jump start charger1460is provided for the case in which either or both of the batteries B1and B2are shut down or discharged. The 2-battery module1350may have a similar jump start charger.

Similarly, the B2stage of the battery module contains a battery charging path such that when the switches S3and S4are closed, current flows through current sense resistor R3and into the battery B2to charge it. The dual path battery protection circuit, switch drivers and communications interface are shown illustratively as block1486. This circuit1486protects the battery from overcurrent and/or overvoltage states, as well as low voltage states and drives the switches accordingly. It also controls the communications from the system controller and balance of plant block1406, through an isolation barrier1488, which may be any suitable component as described herein, from the other dual path battery protection circuit, switch drivers and isolated communications interface1456. If the system controller and balance of plant block1406is signaling the battery protection circuit1486to recharge the battery B2, and yet the battery B2itself is not in the appropriate state for recharging, then the battery protection block1486overrides the system controller1406and force switches S3and S4to remain open. If the battery B2is to provide current to the load, then switch S8is closed. Bypass switch S7can be used to close the circuit between the fuel cell and the load if desired in particular applications of the invention. An optional jump start trickle charger1490can be provided in this module as well in a manner similar to that described with reference to the B1stage.

By way of further description, the system controller1406uses the fuel cell1402to keep the internal battery1408fully charged substantially at all times so that if the external battery module1450is disconnected, the internal battery1408will have maximum shelf life so that the powerpack1400can be restarted even a dead external battery module1450is attached. If the external battery module1450has charge, the powerpack1400can start from the external battery even if the internal battery1408is dead.

The 2-battery powerpack1400illustrated inFIG. 14has switch networks and isolated communications so that the fuel cell module1401can charge either B1or B2, independent of how B1and B2may be connected at the load terminals. The battery module1450contains the novel dual current paths as described herein for each battery so as to minimize the number of switches in the path of the load current and to allow the fuel cell module1401to continue charging even if a problem on the load connection triggers the output protection switches S5and S6to open.

Power for jump starting the power pack when its batteries are dead can be connected to the available load terminals as described above in the preferred embodiment, or can be connected to a different connector.

The systems described above with two isolated batteries could easily be extended to systems with more than two isolated batteries and are included in this invention. In addition, the batteries in multibattery systems may be permanently connected in series for some applications in which case the switch networks and isolated communication links ofFIGS. 8-10may be simplified because of the known voltage ranges, e.g., the switches may no longer need to block current in both directions when off because the polarity can no longer be reversed, thus enabling the use of single MOSFETs rather than back-to-back MOSFETs.