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, and more particularly to a power supply system starting with a fuel cell-based power generation system suitable for charging batteries, such as lithium batteries. [Background technology]

[0002] A fuel cell is, conceptually, a power generation device that chemically bonds hydrogen and oxygen directly. These two reagents are appropriately delivered to the fuel cell stack, which is a series of plates made of appropriate materials separated by an appropriate catalytic membrane. As the reagents flow through appropriate flow channels formed on the surface of each plate on one side of the catalytic membrane, they combine to produce water vapor and a flow of electrons, which is an electric current and determines the voltage at the poles of the stack.

[0003] This voltage is not regulated and can take on a highly variable value, and is determined by the output current absorbed by the stack, as a function of the stack, i.e., the so-called polarization curve of the fuel cell (an example of which is shown in Figure 3).

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

[0005] As mentioned earlier, the voltage measured at the poles of the stack can vary considerably as a function of the current required by the stack. The output voltage of a fuel cell following a specific polarization curve can be reduced to half, or even less than one-third, of the open-circuit voltage, i.e., the voltage when there is no output load.

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

[0007] In other words, when a given load change is applied to a cell while the stack has an open circuit, it generates a significantly larger voltage drop than when the previous load was active in the stack.

[0008] Lithium-ion battery packs (hereinafter also simply called batteries or lithium batteries) typically consist of a series of individual components, and their maximum and minimum nominal voltages depend on the specific chemicals used in the battery.

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

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

[0011] Overvoltage at the battery terminals can, for example, damage the battery or result in extremely high currents within a lithium battery, which can lead to overheating and a risk of fire or explosion.

[0012] Therefore, connecting the stack to the battery pack requires a specific intermediate device capable of adjusting the voltage of the fuel cell electrodes and handling the associated current.

[0013] Conventional connection devices use appropriate active electronic circuits, such as DC / DC power converters, placed between the stack and the battery pack to adjust the fuel cell voltage to a voltage acceptable to the lithium battery pack.

[0014] Furthermore, while a DC / DC converter generally only allows you to connect a stack to a load that requires a regulated voltage, if a battery pack is also connected, a suitable battery charger is also required, which takes the regulated voltage from the DC / DC output as input and further regulates the battery charging.

[0015] Patent document US2018026463A1 describes a power supply system that uses a so-called boost converter to adjust the voltage of a fuel cell to a voltage acceptable to a lithium battery pack. Despite how simple the above system may be, the boost converter is considerably complex and costly.

[0016] Generally, devices inserted between the stack and the battery pack, such as the DC / DC converter mentioned, i.e., active devices or electronic circuits, convert the output voltage from the fuel cell to provide a substantially stable voltage, while accepting considerable fluctuations over time.

[0017] A DC / DC converter needs to be able to control the total current and associated power that can be transmitted to the battery pack and the associated load connected to it.

[0018] For considerable power outputs on the order of thousands or tens of thousands of watts, the complexity of such devices, and the costs associated with them, can each reach very high levels.

[0019] Furthermore, the efficiency of the DC / DC converter is unlikely to reach 85%, and therefore some of the energy is lost in the form of heat, which needs to be dissipated within the converter by a suitable dissipation device or liquid cooling system, which increases the size and weight.

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

[0021] Commercially available DC / DC converters can usually also handle standard battery voltages, i.e., for example, nominal 24 V or 36 V or 48 V or 96 V.

[0022] Considering the fact that each battery pack comprises a plurality of individual elements in series as described above, the user must therefore use a predetermined number of elements that will adversely affect the possibility of selecting the required number of elements unless a dedicated DC / DC converter is developed or customized.

[0023] Furthermore, since a DC / DC power converter can generate sparks during operation, it cannot be used near flammable substances unless appropriate countermeasures are taken (e.g., refer to the ATEX standard).

[0024] An alternative solution to a DC / DC converter specifically designed for environments with an explosion risk, such as in an aircraft where adequate ventilation is not possible, is described and illustrated in the patent document US2016159492A1.

[0025] Specifically, as shown in the drawings of the patent document US2016159492A1 and described in its section 43 - 48, instead of a DC / DC converter, a battery charger 29 arranged between the fuel cell and the battery is used schematically. In practice, by using a contact system, energy is supplied to the battery charger, and the battery charger supplies power to the battery for charging with an appropriate charging curve. Thus, for the reasons above, the fuel cell is never directly connected to the battery.

[0026] Note that the system according to patent US2016159492A1 comprises a resistor 34 that is always connected in parallel to the battery charger in order to make the voltage of the output from the cell within the tolerance of the battery charger, since even a battery charger cannot supply power to the input with an unregulated voltage such as that of a fuel cell. Summary of the Invention

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

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

[0029] Another object of the present invention is to provide a fuel cell-based power supply system that can also be used to charge a battery, such as, preferably, a lithium battery having any number of elements.

[0030] A further object of the present invention is to provide a power supply system designed to charge a lithium battery and having a lower operating temperature than conventional solutions.

[0031] Yet another object of the present invention is to provide a power supply system for charging a battery with reduced electromagnetic radiation.

Brief Description of the Drawings

[0032] Further features and advantages of the present invention will become clearer in the following non-limiting description of preferred but non-exclusive embodiments of the power supply. [Figure 1] A block diagram of the technical system of a first embodiment of the power supply system according to the present invention is shown. [Figure 2] A block diagram of the technical system of a second embodiment of the power supply system according to the present invention is shown. [Figure 3] An example of the polarization curve of a fuel cell is shown.

Best Mode for Carrying Out the Invention

[0033] Referring particularly to FIGS. 1 and 2, the numeral 100 denotes a technical system according to the present invention.

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

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

[0036] The number of elements within the lithium battery pack 101 provides, for example, the maximum voltage applicable to the battery pack during charging or recharging.

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

[0038] System 100 comprises a power supply system collectively labeled 1 for supplying power, i.e., for charging the battery pack 101 and / or supplying power to the electrical load 102.

[0039] Therefore, the electrical load 102 is preferably powered by a battery pack 101 and / or a power supply system 1.

[0040] Power system 1 comprises a power generation system schematically shown in block 2, which includes a stack of substantially known types of fuel cells, the fuel cell stack having a positive electrode 2a and a negative electrode 2b, also called the “terminals” of the stack, and forming a plurality of fuel cells not shown.

[0041] In general terms, stack 2 allows for the direct bonding of hydrogen and oxygen, which then flow through appropriate flow channels and bond 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 electrode 2a and the negative electrode 2b.

[0042] The power generation system also includes auxiliary components, schematically shown in block 3, that communicate with stack 2 of the fuel cells for the operation of stack 2.

[0043] These auxiliary components constitute the so-called BOP (Balance of Plant) of Stack 2, which will be mentioned below.

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

[0045] The electrical load 102 comprises both a BOP3 and a working load, the working load being schematically shown in block 103 and potentially powered by stack 2 and / or battery pack 101.

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

[0047] In automotive applications, the operating load 103 may be defined, for example, by a motor used for vehicle transport.

[0048] In a preferred application of the present invention, the operating load is defined by the towing system of the lift truck and at least a portion of the associated actuators.

[0049] The power supply system 1 includes a device for adjusting the voltage between the positive electrode 2a and the negative electrode 2b of the stack 2, collectively labeled 4.

[0050] In other words, the adjustment device 4 actually adjusts the voltage of the terminals of the battery pack 101.

[0051] The adjustment device 4 is a resistive load schematically shown in block 5, connected to the positive electrode 2a and negative electrode 2b of stack 2, and comprises a resistive load for generating a voltage drop between them.

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

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

[0054] For example, referring to the polarization curve of a fuel cell shown in Figure 3, as is well known, the X-axis represents the current density (mA / cm²). 2 The diagram shows the voltage (V) on the Y axis, and it should be noted that when a resistive load is applied to the cell terminals, current is generated and a voltage drop occurs at the cell terminals.

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

[0056] The resistive load 5 and the control switch 6 form a system that defines the branching of the adjustment device 4, which is positioned between the positive electrode 2a and the negative electrode 2b of the stack 2. This system can switch 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 decrease in the terminal potential.

[0057] Therefore, the technical system 100 comprises, in general terms, a power supply system 1, a battery pack 101 containing multiple 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 in parallel to the stack 2 with a system comprising a resistive load 5 and a control switch 6.

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

[0059] The adjustment device 4 includes a control device 7 that communicates with the control switch 6 and also with the positive electrode 2a and negative electrode 2b of the stack 2.

[0060] The control device 7 measures the voltage value V measured between the positive electrode 2a and the negative electrode 2b at the poles of the stack 2 and a predetermined maximum voltage value V max It includes a comparator, schematically shown as block 8, for calculating the voltage error ΔV as the difference between and .

[0061] A predetermined maximum voltage value V max Preferably, this is a function of the number of fuel cells constituting stack 2.

[0062] Considering the technical system 100 according to one aspect of the present invention, a predetermined maximum voltage value V max Preferably, this is a function of the number of individual basic elements of the battery pack 101, i.e., the maximum voltage applicable to the battery pack 101 during charging or recharging of the battery pack.

[0063] According to a preferred embodiment, a predetermined maximum voltage value V max This corresponds to the maximum voltage value applicable to the battery pack 101 during charging or recharging.

[0064] The control device 7 is configured to activate 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 the voltage error ΔV calculated by the comparator 8.

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

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

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

[0068] Referring to Figure 1, according to the embodiment shown as an example, the control switch 6 is preferably defined by a voltage-controlled relay.

[0069] Relay 6 communicates with comparator 8 and operates directly between open and closed configurations by a voltage error ΔV, which is precisely an analog voltage signal.

[0070] Referring to Figure 2, according to an example embodiment, the control device 7 comprises a computerized command and control unit schematically represented as block 9, which communicates with a comparator 8 to receive a voltage error ΔV as input.

[0071] The computerized unit 9 is configured to generate a digital control signal S as a function of the voltage error ΔV, and to activate the control switch 6 with the signal S.

[0072] Advantageously, the adjustment device 4 may include multiple voltage sensors that communicate with a computerized unit 9 to determine a signal S for activating the control switch 6.

[0073] According to this embodiment, the control switch 6 may be a digital control switch.

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

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

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

[0077] A known type of lift truck generally includes the technical system 100 described above.

[0078] In fact, lift trucks typically feature an electric towing system and multiple electric actuators.

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

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

[0081] The lift truck comprises a fuel cell stack corresponding to stack 2 and a BOP corresponding to auxiliary component 3.

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

[0083] For example, a method for controlling a technical system 100, which is intended to supply power to an electrical load 102 and maintain the charge of a battery pack 101, is: - A step of measuring the voltage value V between the positive electrode 2a and the negative electrode 2b of the fuel cell stack 2, - The measured voltage value V and a predetermined maximum voltage value V which preferably corresponds to the maximum allowable voltage value of the battery pack 101. max The steps include calculating the voltage error ΔV between and -If the voltage error ΔV is positive, the control switch 6 is activated to switch to the closed configuration. - The step of activating the control switch 6 to switch to the open configuration if the voltage error ΔV is negative.

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

[0085] Therefore, the operation of power system 1 can be summarized with reference also to the polarization curve of FIG. 3. When setting up a system for power generation with stack 2 and auxiliary components 3, during a temporary step, the output voltage V of the fuel cell measured by comparator 8 reaches the maximum value it can take until the operating load 103 becomes active and the consumption of BOP 3 reaches the minimum value sufficient to operate stack 2, approaching the open circuit voltage value of stack 2. Usually, the voltage per cell of the stack is much larger than V max by a large margin.

[0086] In these states, comparator 8 measures the positive voltage error ΔV between the output voltage of stack 2 and a predetermined maximum value V max in order to easily cope with it, for example, based on an algorithm. max

[0087] Comparator 8 transmits this information to control device 7, and control device 7 requests closing of control switch 6, thus diverting the flow of current on resistor load 5.

[0088] Therefore, adjustment device 4 enables instantaneously absorbing a predetermined amount of current, as a result of which the voltage V at the terminals of stack 2, and thus at the terminals of battery pack 101, immediately drops.

[0089] Battery pack 101 is directly recharged by transfer from stack 2 without any intervening other connection devices or electronic circuits, nor converters or battery chargers.

[0090] Referring to the prior art described in the above patent document US2016159492A1, the solution according to the present invention eliminates the need for battery charger 29 and contactors 40 and 36, and also eliminates even the basic diodes of the described system. ​

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

[0092] The total electrical load 102 is the maximum voltage V that the lithium battery 2 can tolerate at the terminals of stack 2. max As soon as the level is reduced to below a certain point, the control device 7 uses the control switch 6 to disconnect the resistive load 5.

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

[0094] Power supply system 1 has significant advantages.

[0095] Because there are no active switching components, electromagnetic noise generation is avoided, system efficiency is improved, and costs are significantly reduced.

[0096] The adjustment device actually intervenes only during temporary switch-on periods and in rare cases when the operating load tends to shift towards zero.

[0097] These events are virtually negligible in almost all applications, especially in lift truck applications. On the other hand, the current system is constantly active between the stack and the battery pack, continuously negatively impacting efficiency.

[0098] Cooling additional resistive loads is much simpler, or even unnecessary.

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

[0100] The appropriate selection of resistive loads and comparators allows for arbitrary combinations of the number of fuel cells in the stack and the number of elements in the battery pack.

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

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

[0103] Another advantage is that the components are simplified, and these components are sized during the starting transient rather than for the entire plant.

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

[0105] The advantages mentioned above are similarly achieved when operating with any type of battery. [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 poles 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.

Images