Power System

Abstract

A power supply system (1) is described, comprising a stack (2) of fuel cells and a device (4) for regulating the voltage at the poles of the stack (2). The device (4) also comprises a resistive load (5) connected across the poles of the stack (2) for creating a voltage drop therebetween, and a control switch (6) inserted in series with the resistive load (5) and operable between an open configuration and a closed configuration.

Description

[Technical field]

[0001] The present invention relates to a power supply system, in particular a power supply system starting from a fuel cell-based power generation system suitable for charging batteries, for example lithium batteries. [Background technology]

[0002] A fuel cell is, in general terms, an electricity generating device that directly chemically combines hydrogen and oxygen. These two reagents are appropriately transported to a fuel cell stack, i.e. a series of plates made of suitable materials separated by a suitable catalytic membrane. The reagents, flowing in suitable flow channels formed in the surfaces of the plates, each on one side of the catalytic membrane, combine to produce water vapor and a flow of electrons, which is an electric current and determines the voltage of the poles of the stack.

[0003] This voltage is not regulated, can be highly variable and depends on the output current absorbed by the stack or fuel cell as a function of the so-called polarization curve of the stack, an example of which is shown in FIG.

[0004] In addition to the stack, the power generation system comprises a so-called balance of plant (BOP), which is formed by additional devices necessary for the correct operation of the fuel cell: the BOP, which absorbs a certain amount of current supplied by the stack, comprises, for example, a ventilation system for pumping air inside the stack and a set of valves for the hydrogen and for a system for cooling the cells.

[0005] The voltages measured at the poles of the stack can vary widely as a function of the current required by the stack, as mentioned above. The output voltage of a fuel cell following a particular polarization curve can, for example, be reduced by half, or even by a factor of three or less, relative to the open circuit voltage, i.e., the voltage when there is no output load.

[0006] As shown in Figure 3, the voltage drop across the poles of the stack does not tend to be perfectly linear as load is applied (i.e., current is absorbed). The same variation in load will cause a larger voltage drop at a given voltage than would be seen at a lower voltage.

[0007] In other words, a given load change applied to a cell when the stack has an open circuit will cause a significantly larger voltage drop than if the previous load was active on the stack.

[0008] A lithium-ion battery pack (hereafter also referred to simply as a battery or lithium battery) typically consists of a series of individual elements, the maximum and minimum rated voltages of which depend on the particular chemistry used in the battery.

[0009] Each element of a battery has a maximum applicable voltage which, when multiplied by the number of elements in a battery pack, yields the maximum voltage that can be applied to the pack itself, for example during recharging.

[0010] Therefore, the voltage applied to the lithium battery must remain within a precise range.

[0011] Overvoltage on the poles of a battery can, for example, damage the battery or lead to having very high currents in a lithium battery, with the resultant risk of overheating and fire or explosion.

[0012] Therefore, at least the connection of the stack to the battery pack requires specific intermediate devices capable of regulating the voltage of the fuel cell poles and handling the associated currents.

[0013] Conventional connection devices use suitable active electronic circuitry, such as a DC / DC power converter, located between the stack and the battery pack to regulate the fuel cell voltage to a voltage acceptable to the lithium battery pack.

[0014] Furthermore, typically a DC / DC converter only makes it possible to connect the stack to a load that requires a regulated voltage, but if a battery pack is also connected then a suitable battery charger is also required, which takes as input the regulated voltage at output from the DC / DC and further regulates the charging of the battery.

[0015] Patent document US2018026463A1 shows a power supply system that uses a so-called boost converter to regulate the voltage of a fuel cell to a voltage acceptable to a lithium battery pack. Despite how simple the above system may be, boost converters have significant complexity and cost.

[0016] Typically, a device interposed between the stack and the battery pack, such as the DC / DC converter referred to herein, i.e., an active device or electronic circuit, converts the output voltage from the fuel cell to provide a substantially stable voltage while accommodating significant variations over time.

[0017] The DC / DC converter must be able to control the overall current and associated power that can be delivered to the battery pack and associated loads connected to it.

[0018] For significant power outputs, on the order of thousands or tens of thousands of watts, the complexity of such devices, and the associated costs at the outset, respectively, can reach prohibitively high values.

[0019] Furthermore, the efficiency of DC / DC converters is unlikely to reach 85%, and therefore part of the energy is lost in the form of heat, which needs to be dissipated within the converter by suitable dissipation devices or liquid cooling systems, which increase the size and weight.

[0020] Another problem associated with power converters is that of electromagnetic emissions caused by the use of active power switching components such as MOSFETs and IGBTs, which generate significant electromagnetic interference during switching and therefore need to be properly protected.

[0021] DC / DC converters available on the market are usually also able to handle standard battery voltages, ie for example 24V or 36V or 48V or 96V nominal.

[0022] As mentioned above, given the fact that each battery pack comprises multiple individual elements in series, the user is therefore required to use a predetermined number of elements which adversely affects the possibility of selecting the required number of elements unless a dedicated DC / DC converter is developed or customized.

[0023] Furthermore, DC / DC power converters can generate sparks during operation and therefore cannot be used near flammable materials unless appropriate countermeasures are taken (see, for example, ATEX standards).

[0024] An alternative solution for DC / DC converters specifically designed for poorly ventilated and potentially explosive environments, such as aircraft, is described and illustrated in patent document US2016159492A1.

[0025] As shown in particular in the drawings of patent document US2016159492A1 and described in sections 43-48 thereof, a battery charger 29 is generally used instead of a DC / DC converter, which is placed between the fuel cell and the battery. In practice, by using a contact system, energy is supplied to the battery charger, which supplies power to the battery with an appropriate charging curve to charge it. Thus, for the reasons mentioned above, the fuel cell is never directly connected to the battery.

[0026] It should be noted that since even a battery charger cannot supply power to an input at an unregulated voltage such as the voltage of a fuel cell, the system according to patent US2016159492A1 comprises a resistor 34 that is always connected in parallel to the battery charger to bring the voltage of the output from the cell to an acceptable value for the battery charger. Summary of the Invention

[0027] In this context, the main object of the present invention is to overcome the above-mentioned drawbacks.

[0028] It is an object of the present invention to provide a fuel cell based power supply system which is simpler than prior art systems.

[0029] It is an object of the present invention to provide a fuel cell based power supply system that can also be used to charge batteries, for example lithium batteries, preferably having any number of elements.

[0030] The object of the present invention is to provide a power supply system also designed for charging lithium batteries, which has a lower operating temperature than conventional solutions.

[0031] It is an object of the present invention to provide a power supply system for charging batteries that has reduced electromagnetic emissions. [Brief description of the drawings]

[0032] Further features and advantages of the present invention will become more apparent in the following non-limiting description of preferred but non-exclusive embodiments of a power supply. [Figure 1] 1 shows a block diagram of a technical system of a first embodiment of a power supply system according to the invention; [Diagram 2] FIG. 2 shows a technical system block diagram of a second embodiment of the power supply system according to the invention. [Diagram 3] 1 shows an example of a polarization curve for a fuel cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] 1 and 2, numeral 100 designates a technical system according to the present invention.

[0034] The technical system 100 comprises a battery pack, indicated generally at block 101 , and an electrical load, indicated generally at block 102 , which is powered by the battery pack 101 .

[0035] The battery pack 101 comprises a plurality of individual rechargeable and suitably connected basic elements, not shown, of a substantially known type. The battery pack 101 has a positive electrode 101a and a negative electrode 101b.

[0036] A number of elements within the lithium battery pack 101 provide the maximum voltage that can be applied to the battery pack, for example, while the battery pack is charging or recharging.

[0037] Preferably, the individual basic elements, and therefore also the battery pack, are of the lithium-ion type.

[0038] The system 100 comprises a power supply system, generally labeled 1, for providing electrical power, i.e., for charging a battery pack 101 and / or for powering an electrical load 102.

[0039] Thus, the electrical loads 102 are preferably powered by the battery pack 101 and / or the power supply system 1.

[0040] The power supply system 1 comprises a power generation system, shown diagrammatically in block 2, comprising a stack of fuel cells of a substantially known type, the stack of fuel cells having a positive electrode 2a and a negative electrode 2b, also called the "terminals" of the stack, forming a plurality of fuel cells, not shown.

[0041] In general terms, the stack 2 allows the direct combination of hydrogen and oxygen, which flow in suitable flow channels and combine to produce water vapor and a flow of electrons that determine the voltage V at the terminals of the stack, i.e. the voltage V between the positive and negative electrodes 2a and 2b.

[0042] The power generation system also comprises auxiliary components, indicated generally at block 3 , in communication with the stack 2 of fuel cells for operation of the stack 2 .

[0043] These auxiliary components constitute the so-called BOP (balance of plant) of the stack 2 to which reference will be made below.

[0044] The BOP of the stack 2 is substantially known and is formed by further devices necessary for the correct automatic operation of the fuel cells. The BOP, which absorbs a certain amount of current generally provided by the stack 2, i.e. is preferably powered by the stack itself, comprises, for example, a ventilation system for blowing air into the stack 2 and a set of solenoid valves for the hydrogen and for a system for cooling the fuel cells of the stack 2.

[0045] The electrical load 102 comprises both the BOP 3 and a working load, the latter being indicated generally by block 103 , which may be powered by the stack 2 and / or the battery pack 101 .

[0046] The type of operational load depends on the type of technical system.

[0047] In an automotive application, the operational load 103 may be defined, for example, by a motor for transporting the vehicle.

[0048] In a preferred application according to the present invention, the operating load is defined by the traction system of the lift truck and at least in part by the associated actuators.

[0049] The power supply system 1 comprises a device, generally labelled 4, for regulating the voltage between the positive and negative poles 2a, 2b of the stack 2.

[0050] In other words, the regulating device 4 actually regulates the voltage of the poles of the battery pack 101 .

[0051] The regulating device 4 comprises a resistive load, indicated diagrammatically by a block 5, connected to the positive pole 2a and the negative pole 2b of the stack 2 for creating a voltage drop between them.

[0052] The resistive load 5 comprises at least one electrical dissipation resistor designed to absorb and dissipate electrical current.

[0053] The resistive load and / or the size of said resistor is preferably determined according to the number of individual basic elements of the battery pack and / or the number of fuel cells which make up the stack 2.

[0054] For example, referring to the fuel cell polarization curve shown in FIG. 3, as is known, the X-axis represents current density (mA / cm 2 ) and the Y-axis represents cell voltage (V). Note that applying a resistive load to the terminals of a cell will generate a current and create a voltage drop at the terminals of the cell.

[0055] The regulating device 4 comprises at least one control switch, represented diagrammatically as a block 6 inserted in series with a resistive load 5, which can be operated between an open configuration and a closed configuration.

[0056] The resistive load 5 and the control switch 6 form a system defining a branch of a regulating device 4 arranged between the positive pole 2a and the negative pole 2b of the stack 2, which system can be switched between an open configuration in which the resistive load 5 is not powered by the stack 2, and a closed configuration in which the resistive load 5 is powered by the stack 2 and actually causes a drop in the potential of the terminals.

[0057] Thus, the technical system 100 generally comprises a power supply system 1, a battery pack 101 comprising a number of individual elements powered by a stack 2, and an electrical load 102 also powered by the stack 2, the electrical load 102 and the battery pack 101 being connected to the stack 2 in parallel with a system comprising a resistive load 5 and a controlled switch 6.

[0058] Preferably, the control switch 6 is powered by a battery pack 101 .

[0059] The regulating device 4 comprises a control device 7 in communication with the control switch 6 and with the positive pole 2 a and the negative pole 2 b of the stack 2 .

[0060] The control device 7 determines the voltage value V measured between the positive pole 2a and the negative pole 2b at the poles of the stack 2 and a predetermined maximum voltage value V max A comparator, shown diagrammatically as block 8, is provided for calculating a voltage error ΔV as the difference between

[0061] A given maximum voltage value V max is preferably a function of the number of fuel cells that make up the stack 2.

[0062] Considering the technical system 100 according to an aspect of the present invention, a predetermined maximum voltage value V max is preferably a function of the number of individual base elements of the battery pack 101, i.e., the maximum voltage that can be applied to the battery pack 101 while charging or recharging the battery pack.

[0063] According to a preferred embodiment, a predetermined maximum voltage value V max corresponds to the maximum voltage value that can be applied to the battery pack 101 while the battery pack is being charged or recharged.

[0064] The control device 7 is configured to actuate the control switch 6 from an open configuration to a closed configuration and from a closed configuration to an open configuration as a function of a voltage error ΔV calculated by a comparator 8 .

[0065] According to one embodiment, the comparator 8 may comprise a voltage sensor.

[0066] According to one embodiment, the comparator 8 may comprise a current sensor in combination with or as an alternative to a voltage sensor.

[0067] According to the invention, the regulating device 4 basically comprises a resistive load 5 connected to the positive pole 2a and the negative pole 2b, which generates a voltage drop between them by means of a control switch 6 inserted in series with the resistive load 5 by means of a device 7 for controlling the control switch 6.

[0068] With reference to FIG. 1, according to the embodiment shown by way of example, the controlled switch 6 is preferably defined by a voltage controlled relay.

[0069] The relay 6 is in communication with a comparator 8 and is actuated directly between an open and a closed configuration by a voltage error ΔV, which is precisely an analog voltage signal.

[0070] With reference to FIG. 2, according to the embodiment shown as an example, the control device 7 comprises a computerized command and control unit, represented diagrammatically as block 9, in communication with a comparator 8 receiving the voltage error ΔV as input.

[0071] The computerized unit 9 is arranged to generate a digital control signal S as a function of the voltage error ΔV and to actuate the control switch 6 by means of the signal S.

[0072] Advantageously, the regulating device 4 may comprise a number of voltage sensors in communication with a computerized unit 9 in order to determine the signal S for actuating the control switch 6 .

[0073] According to this embodiment, the controlled switch 6 may be a digitally controlled switch.

[0074] Preferably, the computerized unit 9 is configured to generate the control signal S as a function of the number of individual elements of the battery pack 101 .

[0075] Preferably, the computerized unit 9 is arranged to generate the control signal S as a function of the number of fuel cells in the stack 2 .

[0076] A preferred application for the technology system 100 as described is a lift truck.

[0077] A lift truck of substantially known type is typically equipped with a technical system 100 as described.

[0078] Indeed, lift trucks are typically equipped with an electric traction system and a number of electric actuators.

[0079] The electric traction system and the plurality of electric actuators define the operating load of the technical system 100 .

[0080] The lift truck is equipped with a battery pack that matches the battery pack 101 of the technical system 100 .

[0081] The lift truck includes a stack of fuel cells corresponding to stack 2 and a BOP corresponding to auxiliary component 3 .

[0082] Thus, the lift truck's BOP, traction system and actuators define an electrical load on the lift truck's stack and battery pack.

[0083] For example, a method for controlling a technical system 100 aimed at supplying power to an electrical load 102 and maintaining a charge on a battery pack 101 comprises: - measuring a voltage value V between the positive electrode 2a and the negative electrode 2b of the stack 2 of fuel cells; - a measured voltage value V and a predetermined maximum voltage value V, which preferably corresponds to a maximum allowable voltage value of the battery pack 101; max calculating a voltage error ΔV between - actuating the controlled switch 6 to the closed configuration if the voltage error ΔV is positive; - actuating the controlled switch 6 to the open configuration if the voltage error ΔV is negative.

[0084] The output voltage from the stack 2 is fed directly to the input to the battery pack 101 suitably modulated by resistor 5 .

[0085] The operation of the power supply system 1 can therefore be summarised with reference also to the polarization curves of Figure 3. During a transient step, when setting up the system for power generation comprising the stack 2 and the auxiliary components 3, the output voltage V of the fuel cell measured by the comparator 8 will be at its maximum possible value, close to the open circuit voltage value of the stack 2, typically the volts per cell of the stack being V, until the operational load 103 becomes active and the consumption of the BOP 3 is at a minimum sufficient to operate the stack 2. max will be significantly larger than

[0086] In these conditions, the comparator 8 detects the maximum V max To easily accommodate this, for example, the output voltage of stack 2 can be calculated based on an algorithm to a given maximum value V max Measure the positive voltage error ΔV between

[0087] The comparator 8 transmits this information to the control device 7 , which requests the control switch 6 to close, thus diverting the current flow on the resistive load 5 .

[0088] The regulating device 4 thus allows to instantaneously absorb a given amount of current, which results in an instantaneous drop in the voltage V at the terminals of the stack 2, and therefore at the terminals of the battery pack 101.

[0089] The battery pack 101 is recharged directly by transfer from the stack 2 without any other connecting devices or electronic circuits or intervening converters or battery chargers.

[0090] With reference to the prior art described in the above mentioned patent document US2016159492A1, the solution according to the invention makes the battery charger 29 and the contactors 40 and 36 unnecessary, and even the basic diodes of the described system unnecessary.

[0091] As soon as the current starts to increase in the operational load 103 and the BOP3 moves to a steady state, the voltage at the terminals of the stack 2 drops further, which can be measured again by the comparator 8.

[0092] The total electrical load 102 reduces the voltage V at the terminals of the stack 2 to the maximum value V that the lithium battery 2 can tolerate. max As soon as the input current is reduced below 0 V, the control device 7 disconnects the resistive load 5 using the controlled switch 6.

[0093] As shown in FIGS. 1 and 2, the control switch 6 can be operated by a computerized unit 9 or directly by a comparator 8 .

[0094] The power supply system 1 has important advantages.

[0095] The absence of active switching components avoids electromagnetic noise generation, improves system efficiency, and significantly reduces costs.

[0096] The regulating device actually only intervenes during momentary switch-on and in the rare cases when the operating load tends towards zero.

[0097] These events are virtually insignificant in almost all applications, especially lift truck applications, whereas current systems are constantly active between the stack and battery pack, continually impacting efficiency.

[0098] Cooling of the additional resistive load is much easier or even unnecessary.

[0099] The power supply system described above may be used to power any battery pack formed by any desired number of individual elements.

[0100] Appropriate selection of resistive loads and comparators allows for any combination of number of fuel cells in the stack and number of battery pack elements.

[0101] The cost of the regulation device is substantially reduced to only the cost of the resistive load and the associated command and voltage comparators, since no other devices are required.

[0102] The current that needs to be managed by the control switch is a small fraction of the nominal current of the stack.

[0103] Another advantage is that the components are simplified, and are sized for the starting transient instead of the entire plant.

[0104] Furthermore, volume and weight savings are also evident, since only a few components are actually needed, versus the tens or hundreds of components that make up other devices such as DC / DC power converters or battery chargers.

[0105] The above advantages are achieved during operation with any type of battery as well. [Prior art documents] [Patent documents]

[0106] [Patent Document 1] US2018026463A1 [Patent Document 2] US2016159492A1

Claims

1. 1. A power supply system, comprising: A power generation system (2, 3) including a fuel cell stack (2) having a plurality of fuel cells and having a positive electrode (2a) and a negative electrode (2b); and a regulating device (4) for regulating the voltage between the positive electrode (2a) and the negative electrode (2b), the regulating device (4) comprising: a resistive load (5) connected to the positive electrode (2a) and the negative electrode (2b) to generate a voltage drop between the positive electrode (2a) and the negative electrode (2b); a control switch (6) interposed in series with the resistive load (5) between the positive pole (2a) and the negative pole (2b) and operable between an open configuration and a closed configuration; a control device (7) in communication with said controlled switch (6), comprising a comparator (8) for calculating a voltage error (ΔV) as the difference between a voltage value measured between said positive pole (2a) and said negative pole (2b) of the terminals of said stack and a predetermined maximum voltage value, said control device (7) being configured to operate said controlled switch (6) from said open configuration to said closed configuration and from said closed configuration to said open configuration as a function of said voltage error (ΔV).

2. 2. The power supply system of claim 1, wherein the predetermined maximum voltage value is a function of the number of fuel cells comprising the stack (2).

3. 3. The power supply system of claim 1, wherein the predetermined maximum voltage value is a function of the number of elements of a battery pack (101) that are rechargeable by the power supply system.

4. 4. The power supply system of claim 1, wherein the comparator (8) comprises a voltage sensor.

5. 5. The power supply system according to claim 1, wherein the comparator (8) comprises a current sensor.

6. 6. The power supply system according to claim 1, wherein the control device (7) comprises a computerized command and control unit (9) in communication with the comparator (8), the computerized command and control unit (9) being configured to generate a control signal (S) as a function of the voltage error (ΔV) and to operate the controlled switch (6) by means of the control signal (S).

7. 7. The power supply system of claim 1, wherein the controlled switch (6) is defined by a voltage controlled relay in communication with the comparator (8), the voltage controlled relay being actuated between the open and closed configurations depending on the voltage error (ΔV).

8. A technical system comprising a power supply system according to any one of claims 1 to 7, a battery pack (101) comprising a plurality of individual elements powered by the stack of fuel cells (2), and an electrical load (102) powered by the stack of fuel cells (2) and / or the battery pack (101), the electrical load (102) and the battery pack (101) being connected to the stack of fuel cells (2) in parallel with a system including the resistive load (5) and the controlled switch (6).

9. The technical system according to claim 8, wherein the predetermined maximum voltage value corresponds to a maximum voltage value allowed by the battery pack (101).

10. The technical system according to claim 8 or 9 when dependent on claim 6, wherein the computerized command and control unit (9) is configured to generate the control signals (S) as a function of the number of individual elements of the battery pack (101).

11. The technical system according to any one of claims 8 to 10 when dependent on claim 6, wherein the computerized command and control unit (9) is configured to generate the control signal (S) as a function of the number of fuel cells in the stack (2) of fuel cells.

12. The technical system according to any one of claims 8 to 11, wherein the electrical load (102) comprises an operational load (103) powered by the stack (2) of fuel cells.

13. The technical system according to any one of claims 8 to 12, wherein the electrical load (102) comprises auxiliary components (3) in communication with the stack (2) of fuel cells for the operation of the stack (2) of fuel cells.

14. The technical system according to any one of claims 8 to 13, wherein the battery pack (101) is a lithium battery pack.

15. A method for controlling a technical system according to any one of claims 8 to 14, comprising: measuring a voltage value between the positive and negative electrodes of the stack of fuel cells; calculating the voltage error between the voltage value measured between the positive and negative electrodes of the stack of fuel cells and the predetermined maximum voltage value, preferably corresponding to the maximum voltage value allowed by the battery pack; and if the voltage error is positive, actuating the controlled switch to transition it to the closed configuration.

16. 16. The method of claim 15, comprising activating the control switch to transition it to the open configuration if the voltage error is negative.

17. 1. A recharging method for recharging a battery pack from a stack of fuel cells, comprising: providing power directly from the stack of fuel cells to the battery pack; and a regulating step of regulating the voltage between the positive electrode (2a) and the negative electrode (2b) of said stack of fuel cells, said regulating step being exclusively carried out by a regulating device (4) consisting of a resistive load (5) connected to said positive pole (2a) and said negative pole (2b) for generating a voltage drop between said positive pole (2a) and said negative pole (2b), a control switch (6) inserted in series with said resistive load (5) between said positive pole (2a) and said negative pole (2b) and operable between an open configuration and a closed configuration, and a control device (7); The recharging method comprises the step of controlling, by the control device (7), the control switch as a function of a voltage error (ΔV) calculated as the difference between a voltage value measured between the positive pole (2a) and the negative pole (2b) of the terminals of the stack of fuel cells and a predetermined maximum voltage value.

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