Fuel cell power grid system and its control method

Abstract

The present application relates to a fuel cell grid system, which includes: a fuel cell configured to generate electricity through a reaction between a fuel gas and an oxidizing gas; a power storage device configured to charge or discharge using the electricity generated by the fuel cell to supply electricity; a main line configured to electrically connect the fuel cell and the power storage device to each other; a main relay provided on the main line to disconnect or establish an electrical connection between the fuel cell and the power storage device; a bypass line branched from the main line, bypassing the main relay and connected to the power storage device; a bypass relay provided on the bypass line to disconnect or establish an electrical connection of the bypass line; and a controller configured to control the main relay or the bypass relay so that the power charged in the power storage device is supplied to the fuel cell when power generation of the fuel cell is stopped.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell grid system and a control method thereof, and to a technology for removing hydrogen from an air electrode when a fuel cell is restarted or an FC stop mode is released. Background Art

[0002] A fuel cell converts chemical energy into electrical energy by utilizing an oxidation-reduction reaction between hydrogen and oxygen supplied from a hydrogen supplier and an oxygen supplier, respectively. The fuel cell includes a fuel cell stack for generating electrical energy and a cooling system for cooling the fuel cell stack.

[0003] Specifically, hydrogen is supplied to the anode of the fuel cell, where it undergoes an oxidation reaction to produce hydrogen ions (protons) and electrons. The generated hydrogen ions and electrons then travel to the cathode through an electrolyte membrane and external wires. In the cathode, the hydrogen ions and electrons that have migrated from the anode react electrochemically with oxygen in the air to generate electrical energy.

[0004] A phenomenon known as crossover occurs within a fuel cell, where gas crosses the electrolyte membrane due to diffusion caused by differences in gas partial pressures. Specifically, when the fuel cell stops generating electricity, the air supply to the cathode is blocked. Furthermore, when the fuel cell restarts generating electricity and air is supplied to the cathode, hydrogen that crosses from the anode to the cathode can be discharged to the outside through the air handling line.

[0005] Specifically, when high-concentration hydrogen is discharged to the outside, there is a risk of hydrogen combustion if static electricity or sparks occur in nearby locations. In addition, there are problems with regulations governing the hydrogen concentration of the exhaust gas.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and should not be regarded as an admission that this information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0007] The present disclosure is proposed to solve the above-mentioned problems in the prior art, and aspects of the present disclosure provide a fuel cell grid system and a control method thereof, wherein the system enables hydrogen that passes from the anode side to the cathode side to move back to the anode side when power generation of the fuel cell is stopped.

[0008] In order to achieve the above aspects, a fuel cell power grid system according to the present disclosure includes: a fuel cell, configured to generate electricity through a reaction between a fuel gas and an oxidizing gas; a power storage device, configured to charge or discharge using the electricity generated by the fuel cell to supply electricity; a main line, configured to electrically connect the fuel cell and the power storage device to each other; a main relay, arranged on the main line to disconnect or establish an electrical connection between the fuel cell and the power storage device; a bypass line, branched from the main line, bypassing the main relay and connected to the power storage device; a bypass relay, arranged on the bypass line to disconnect or establish an electrical connection of the bypass line; and a controller, configured to control the main relay or the bypass relay so that the power charged in the power storage device is supplied to the fuel cell when power generation of the fuel cell is stopped.

[0009] The main line includes: a main cathode line configured to connect the cathode of the fuel cell to the cathode of the power storage device; and a main anode line configured to connect the anode of the fuel cell to the anode of the power storage device. The main relay includes: a first main relay provided on the main cathode line; and a second main relay provided on the main anode line.

[0010] At least one of the main cathode line and the main anode line is provided with a diode configured to allow current in only one direction. The bypass line branches from the main cathode line or the main anode line provided with the diode and bypasses both the diode and the first main relay or the second main relay.

[0011] The fuel cell grid system may further include: a cathode COD line branched from the main cathode line on the fuel cell side relative to the first main relay; an anode COD line branched from the main anode line on the fuel cell side relative to the second main relay; and a COD resistor connected to each of the cathode COD line and the anode COD line to consume power.

[0012] The fuel cell grid system may further include: a first COD relay provided on the cathode COD line or the anode COD line to disconnect or establish an electrical connection.

[0013] The fuel cell grid system may further include: a second COD relay connected to the cathode COD line or the anode COD line to bypass the first COD relay and configured to disconnect or establish an electrical connection, wherein an allowable current or allowable power of the second COD relay may be relatively smaller than an allowable current or allowable power of the first COD relay.

[0014] The fuel cell grid system may further include: a current limiting resistor provided on the bypass line to form a potential difference between a front end and a rear end of the current limiting resistor when electrical connection of the bypass line is allowed.

[0015] The fuel cell grid system may further include: a COD resistor provided on the bypass line and consuming power, wherein the bypass relay may be located on the power storage device side of the bypass line relative to the COD resistor.

[0016] The fuel cell grid system may further include: a connecting line configured to connect the bypass line between the COD resistor and the bypass relay to the main cathode line or the main anode line between the first main relay or the second main relay and the diode; and a first COD relay and a second COD relay located between the COD resistor and a point where the connecting line branches from the bypass line and connected in parallel to each other to disconnect or establish an electrical connection, wherein an allowable current or allowable power of the second COD relay may be relatively smaller than an allowable current or allowable power of the first COD relay.

[0017] The fuel cell grid system may further include: a current sensor located between the fuel cell and a point where the bypass line branches from the main line to sense current output from or input into the fuel cell.

[0018] The fuel cell grid system may further include: a bidirectional converter connected to the fuel cell via a main line; and a low-voltage converter located between the bidirectional converter and the power storage device to convert the power converted by the bidirectional converter into a relatively low potential, wherein the power storage device is a low-voltage battery connected to the low-voltage converter and charged or discharged at a relatively low potential, the main line includes a first main line and a second main line, the bypass line branches from the first main line and is connected to the first battery line of the low-voltage battery, and the second battery line of the low-voltage battery is connected to the second main line and has a battery relay configured to disconnect or establish an electrical connection of the second battery line.

[0019] To achieve the above aspects, a control method for a fuel cell power grid system includes: stopping the power generation of the fuel cell by shutting down the fuel cell or placing the fuel cell into FC stop mode; supplying power stored in a power storage device to the fuel cell when the power generation of the fuel cell is stopped to move hydrogen on the cathode side to the anode side; and generating power through a reaction between fuel gas and oxidizing gas in the fuel cell.

[0020] Stopping power generation by the fuel cell may further include: executing shutdown control for reducing the voltage of the fuel cell when stopping power generation by the fuel cell. When executing the shutdown control, by closing a first COD relay provided on a COD line branching from the main line, the voltage of the fuel cell is reduced to a preset first voltage by utilizing a COD resistor of the COD line; the voltage of the fuel cell is reduced to a preset second voltage in a state where the first COD relay and a first main relay provided on a main cathode line of the main line are disconnected while a second COD relay is closed, wherein the second COD relay bypasses the first COD relay and an allowable current or allowable power of the second COD relay is relatively smaller than the allowable current or allowable power of the first COD relay; and the second main relay provided on the main anode line of the main line remains in an open state.

[0021] When hydrogen on the cathode side is moved to the anode side, the power stored in the power storage device can be supplied to the fuel cell at preset periodic intervals or when the fuel cell generates power by starting the fuel cell or releasing the FC stop mode.

[0022] When hydrogen on the cathode side is moved to the anode side, the bypass relay is closed, and the bidirectional converter located between the fuel cell and the power storage device can be controlled to discharge the power storage device.

[0023] When hydrogen on the cathode side is moved to the anode side, the voltage of the main line can be maintained within a preset voltage range for a preset time, or the power storage device can be discharged until the integrated value of the current flowing in the main line reaches a predetermined current amount.

[0024] During power generation, the oxidizing gas may be supplied to the fuel cell, the bypass relay may be opened, and the first main relay provided on the main cathode line of the main line may be closed.

[0025] The fuel cell grid system and control method disclosed herein can re-move hydrogen that has passed through the cathode side to the anode side, thereby reducing hydrogen emissions to the air. This reduces the risk of combustion caused by hydrogen emissions and improves fuel efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other aspects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0027] Figure 1 shows a configuration of a fuel cell grid system according to one embodiment of the present disclosure;

[0028] Figure 2 and Figure 3 shows power generation and hydrogen movement reactions of a fuel cell according to one embodiment of the present disclosure;

[0029] Figure 4 shows states of an air electrode and a hydrogen electrode according to a hydrogen transfer reaction of a fuel cell according to one embodiment of the present disclosure;

[0030] Figure 5 is a flow chart of a control method for a fuel cell power grid system according to one embodiment of the present disclosure;

[0031] Figure 6 shows a configuration of a fuel cell grid system according to another embodiment of the present disclosure; and

[0032] Figure 7 The configuration of a fuel cell grid system according to yet another embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0033] The description of the specific structure or function of the embodiments of the present disclosure disclosed in the specification or application is given only for the purpose of describing the embodiments according to the present disclosure. Therefore, the embodiments according to the present disclosure can be implemented in various forms, and the present disclosure should not be interpreted as being limited to the embodiments described in the specification or application.

[0034] Various changes and modifications may be made to the embodiments according to the present disclosure, and therefore specific embodiments will be shown in the drawings and described in the specification or application. However, it should be understood that the embodiments according to the concepts of the present disclosure are not limited to the specific embodiments disclosed, but that the present disclosure includes all modifications, equivalents, and alternatives that fall within the spirit and scope of the present disclosure.

[0035] Although terms such as "first," "second," and the like may be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another, and thus, without departing from the scope of protection of the concepts of the present disclosure, a first element may be named a second element, and a second element may be similarly named a first element.

[0036] When an element is referred to as being "connected" to or "accessing" another element, it should be understood that this not only means that the element is directly connected to or accessing the other element, but also that another element may exist between the element and the other element. Conversely, when a component is referred to as being "directly connected" to or "directly accessing" another component, it should be understood that no component exists between the component and the other component. Other expressions describing the relationship between elements, namely, "between" and "only between" or "adjacent" and "directly adjacent", should be interpreted similarly to the above description.

[0037] In this specification, terms are used only to describe specific embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, as used herein, the singular form is also intended to include the plural form. In the specification, it should be understood that the term "comprising" or "having" represents the presence of a feature, number, step, operation, element, component or a combination thereof, and does not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components or a combination thereof.

[0038] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. It should be understood that terms that are the same as those defined in general dictionaries have the same meaning as in the context of the relevant technology. Unless explicitly defined in the specification, terms should not be ideally or excessively interpreted as having a formal meaning.

[0039] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, wherein the same reference numerals in the accompanying drawings represent the same elements.

[0040] Figure 1 The configuration of a fuel cell 10 grid system according to one embodiment of the present disclosure is shown.

[0041] Reference Figure 1 According to an embodiment of the present disclosure, a fuel cell 10 power grid system includes: a fuel cell 10, configured to generate electricity by a reaction between a fuel gas and an oxidizing gas; power storage devices 21 and 22, configured to charge or discharge using the electricity generated by the fuel cell 10 to supply electricity; a main line 40, configured to electrically connect the fuel cell 10 to the power storage devices 21 and 22; main relays 43 and 44, provided on the main line 40 to disconnect or establish an electrical connection between the fuel cell 10 and the power storage devices 21 and 22; a bypass line 50, branched from the main line 40, bypassing the main relays 43 and 44 and connected to the power storage devices 21 and 22; a bypass relay 51, provided on the bypass line 50 to disconnect or establish an electrical connection of the bypass line 50; and a controller 60, configured to control the main relays 43 and 44 or the bypass relay 51 so that the power charged in the power storage devices 21 and 22 is supplied to the fuel cell 10 when power generation of the fuel cell 10 is stopped.

[0042] The fuel cell 10 generates electricity through a chemical reaction between hydrogen and oxygen. Specifically, the polymer electrolyte fuel cell (PEFC) 10 is used as driving energy for a fuel cell vehicle (fuel cell electric vehicle (FCEV)) driven by a motor.

[0043] The polymer electrolyte fuel cell 10 is used in the form of a fuel cell stack 10 obtained by assembling a structure having tens to hundreds of unit cells repeatedly stacked on each other and a clamping device for maintaining an appropriate clamping pressure, wherein each unit cell includes a membrane electrode assembly (MEA) in which electrodes mainly composed of catalyst layers, where electrochemical reactions occur, are attached to hydrogen ions (protons, H + ) moves through each of the opposite sides of the polymer electrolyte membrane; a separator (bipolar plate (BP)) including a gas diffusion layer (GDL) for uniformly distributing the reaction gas and a channel for movement of the reaction gas and coolant; and a gasket for ensuring airtightness of the reaction gas and coolant.

[0044] In particular, in a membrane electrode assembly (MEA) where a direct electrochemical reaction occurs, a polymer electrolyte membrane is provided between a pair of electrodes. Hydrogen, serving as fuel gas, is supplied to a hydrogen electrode (anode) occupying a predetermined volume in the fuel cell stack 10, and air containing oxygen, serving as an oxidizing gas, is supplied to an air electrode (cathode).

[0045] The hydrogen supplied to the hydrogen electrode is separated into hydrogen ions (protons, H + ) and electrons (e - Only hydrogen ions selectively pass through the polymer electrolyte membrane, which serves as a cation exchange membrane, and move to the air electrode attached to the other surface of the polymer electrolyte membrane. Electrons are then transferred to the air electrode via an external lead. The chemical reaction in the fuel cell 10 is represented by the following reaction formula.

[0046] [Reaction at the hydrogen electrode] H2→2H + +2e -

[0047] [Reaction in the air electrode] 1 / 2*O2(g)+2H + +2e - →H2O(l)

[0048] [Overall reaction] H2(g) + 1 / 2*O2(g) → H2O(l) + electrical energy + thermal energy

[0049] The fuel cell 10 can be connected to a drive system 70 such as a motor, a high-voltage battery (HV battery) 21, and high-voltage auxiliary systems (balance-of-plants (BOPs)) through a main line 40. When the main line 40 is connected to the fuel cell 10, the main line 40 can maintain the same voltage as the output voltage of the fuel cell 10.

[0050] Main relays 43 and 44 may be provided on the main line 40 to disconnect or establish electrical connections between the fuel cell 10 and the power storage devices 21 and 22. Specifically, the main relays 43 and 44 may be located between the fuel cell 10 and the drive system 70, the high-voltage battery 21, and the high-voltage BOPs connected to the main line 40, so that the fuel cell 10 is disconnected from the main line 40 when the electrical connections are disconnected.

[0051] Furthermore, the fuel cell 10 is connected to power storage devices 21 and 22 that can be charged and discharged, and the power storage devices 21 and 22 can be charged with the power generated by the fuel cell 10, or can supply the power to the outside when discharging the charged power. Here, the power storage devices 21 and 22 can be batteries or supercapacitors, and in particular, can be a high-voltage battery (HV battery) 21 or a low-voltage battery (LV battery) 22.

[0052] Specifically, a bidirectional converter 31 (bidirectional high-voltage DC-DC converter (BHDC)) is further provided between the high-voltage battery 21 that can be charged and discharged and the stack of the fuel cell 10 .

[0053] In addition, the fuel cell 10 grid system includes: a fuel processing pipeline (FPL) for supplying and discharging hydrogen used as fuel to the fuel cell 10 stack; an air processing pipeline (APL) for supplying and discharging air including oxygen used as oxidant to the fuel cell 10 stack; a thermal management pipeline (TML) for removing heat as a by-product of the fuel cell 10 reaction of the fuel cell 10 stack from the fuel cell 10 grid system and managing water in the polymer electrolyte fuel cell 10; and auxiliary systems (BOPs) constituting the fuel processing pipeline, the air processing pipeline and the thermal management pipeline.

[0054] The high-voltage BOPs of the fuel cell 10 grid system include a coolant stack pump (CSP), an air compressor (ACP), and a coolant heater (CHT) 63, which are operated by the fuel cell 10 stack connected to the main line 40 as a high-voltage power source or the high-voltage battery 21 connected to the main line 40 via a bidirectional converter 31.

[0055] In addition, a low-voltage electronic device (LV electronic device) operated by a low-voltage power supply can be connected to a low-voltage line (LV line), which connects a low-voltage battery (LV battery) 22 used for normal operation of the LV electronic device and operation of the controller 60 to a low-voltage converter (low-voltage DC-DC converter (LDC)) 32, which is arranged between the low-voltage battery 22 and the bidirectional converter 31 and is connected to the low-voltage battery 22.

[0056] The hydrogen as the fuel supplied from the hydrogen storage device is mixed with the post-reaction gas and supplied to the hydrogen electrode of the fuel cell 10 stack, wherein the post-reaction gas includes unreacted hydrogen except for hydrogen consumed by participating in the fuel cell 10 reaction in the hydrogen electrode of the fuel cell 10 stack via a fuel recycling device such as an injector in the fuel processing line, moisture generated in the air electrode of the stack by the fuel cell 10 reaction, which diffuses to the hydrogen electrode through the polymer electrolyte membrane, and nitrogen in the air supplied to the air electrode by the air compressor and mainly comprising oxygen and nitrogen, which does not participate in the fuel cell 10 reaction but remains in the air electrode and diffuses from the air electrode to the hydrogen electrode through the polymer electrolyte membrane.

[0057] When moisture in the fuel gas in the fuel processing line condenses into liquid droplets as the fuel gas circulates through a fuel recirculation device such as an injector, it is collected as liquid water by a water trap (FWT). When the liquid water level reaches or exceeds a predetermined level, a drain valve (FDV) connected to the water trap switches from a closed state to an open state for a predetermined period of time, thereby draining the liquid water into the air processing line and removing it from the fuel processing line.

[0058] When the fuel cell 10 is operating in a normal state, the purge valve (FPV) is in a closed state. In this case, as the amount of hydrogen consumed by the fuel cell 10 reaction increases, the hydrogen concentration present in the hydrogen electrode gradually decreases. Compared to when the hydrogen concentration present in the hydrogen electrode is equal to or higher than the predetermined level under the same load conditions, when the hydrogen concentration present in the hydrogen electrode is equal to or lower than the predetermined level, the voltage of the output terminal of the fuel cell 10 stack becomes lower. Therefore, in order to maintain the hydrogen concentration present in the hydrogen electrode at a predetermined level or higher, new hydrogen needs to be introduced into the hydrogen electrode of the fuel cell 10 stack.

[0059] To this end, the purge valve (FPV) is switched from a closed state to an open state for a predetermined time, a portion of the reacted fuel gas in the hydrogen electrodes of the fuel cell 10 stack is discharged into the air processing pipeline and removed from the fuel processing pipeline, and new hydrogen in an amount equal to the volume of the discharged reacted fuel gas is introduced into the hydrogen electrodes of the fuel cell 10 stack.

[0060] A portion of the reacted fuel gas discharged into the air handling line is mixed with reacted air and then discharged to the outside, wherein the reacted air includes nitrogen in the air supplied to the air electrodes of the fuel cell 10 stack through the air compressor for the fuel cell 10 reaction and reacted oxygen other than the oxygen participating in the fuel cell 10 reaction, as well as moisture as a by-product of the fuel cell 10 reaction.

[0061] The air supplied by the air compressor is oversupplied to prevent the hydrogen concentration in the gas discharged to the outside from reaching a dangerous level. Furthermore, the time the purge valve (FPV) remains open is reduced in proportion to the amount of air supplied by the air compressor. This prevents the hydrogen concentration in the gas discharged to the outside from reaching a dangerous level even if the amount of gas corresponding to a portion of the reacted fuel gas discharged to the air processing line increases.

[0062] In particular, regulations specify a hydrogen concentration corresponding to a level that becomes dangerous, and the hydrogen concentration specified by the regulations may be limited to, for example, a maximum of 8% and an average of 4% or less over three seconds.

[0063] When the fuel cell 10 enters a stop mode, marking the end of normal operation for power generation, the air compressor ceases operation, thereby ceasing the introduction of air. Furthermore, with the air shutoff valve (ACV), drain valve (FDV), and purge valve (FPV) closed, the stack voltage drops to ground, leaving a small amount of unreacted oxygen, nitrogen, and water in the air electrode. Furthermore, after the air shutoff valve (ACV) is closed, the hydrogen supply valve (FSV), which supplies hydrogen to the hydrogen processing line, may also be closed.

[0064] In the storage state of the maintained stop mode, the hydrogen electrode and the air electrode of the stack are stored while being electrically connected to each other through the COD resistor embedded in the coolant heater (CHT) 63, and the small amount of oxygen remaining in the air electrode is completely removed, while the hydrogen in the reaction gas remaining in the hydrogen electrode diffuses to the air electrode by passing through the polymer electrolyte membrane and becomes closer to the equilibrium state as the storage time becomes longer.

[0065] During the restart process, which causes the fuel cell 10 to enter a normal operating state and generate electricity again, the air shutoff valve (ACV) opens and the air compressor operates to begin supplying air to the air electrodes of the fuel cell stack 10. The restart process includes a period of time during which a small amount of hydrogen remaining in the air electrodes within the stack coexists with oxygen in the air supplied by the air compressor, as hydrogen that has passed through the polymer electrolyte membrane from a stored state and diffused into the air electrodes is discharged to the outside while the stack voltage rises. The greater the amount of air supplied to the air electrodes in the stack by the air compressor, the shorter the duration of this period.

[0066] FC stop mode is an idle state in which the fuel cell 10 temporarily stops power generation while in a startup state. In this mode, the air compressor stops operating until the stopped vehicle receives an accelerator signal and restarts. However, when the vehicle resumes driving, the air shutoff valve (ACV) remains open and a predetermined stack voltage is maintained to ensure rapid response of the fuel cell 10 power grid.

[0067] Specifically, the FC stop mode can be entered when the vehicle's driving speed is equal to or less than a preset speed, or when the power required by the fuel cell 10 is equal to or less than a preset power and the state of charge (SOC) of the high-voltage battery 21 is equal to or greater than a preset SOC.

[0068] Even in FC shutdown mode, hydrogen concentration in the air electrode increases due to hydrogen crossover, where hydrogen from the hydrogen electrode diffuses through the polymer electrolyte membrane to the air electrode. To discharge hydrogen from the air electrode to the outside to avoid safety concerns, the air compressor is operated periodically and repeatedly over a predetermined period of time to remove hydrogen from the air electrode from the stack.

[0069] By opening and closing the air cutoff valve (ACV), the drain valve (FDV), and the purge valve (FPV), reaction gases of the hydrogen electrode and the air electrode occupying a predetermined volume in the stack of the fuel cell 10 of the vehicle are exhausted.

[0070] In a normal state of the fuel cell 10, when the fuel cell 10 is generating electricity or restarting after stopping the fuel cell 10, the hydrogen concentration of the gas discharged to the outside can meet a normal range. However, if a portion of the polymer electrolyte membrane included in the fuel cell 10 is ruptured or degraded due to long-term use of the fuel cell 10, the amount of hydrogen passing through the air electrode increases significantly. Therefore, the hydrogen concentration of the gas discharged to the outside may increase to a dangerous level when restarting or releasing the FC stop mode.

[0071] To solve the above problem, the controller 60 may control the main relays 43 and 44 or the bypass relay 51 so that the power stored in the power storage devices 21 and 22 is supplied to the fuel cell 10 when power generation of the fuel cell 10 is stopped.

[0072] The controller 60 according to an exemplary embodiment of the present disclosure can be implemented by a non-volatile memory (not shown) and a processor (not shown), wherein the non-volatile memory is configured to store an algorithm configured to control the operation of various components of the vehicle or data about software instructions for reproducing the algorithm, and the processor is configured to perform the operations described below by using the data stored in the memory. Here, the memory and the processor can be implemented as separate chips. Alternatively, the memory and the processor can be implemented as a single chip in which the memory and the processor are integrated with each other. The processor can take the form of one or more processors.

[0073] In particular, the bypass line 50 branches from the main line 40 and is connected to the power storage devices 21 and 22, wherein since the bypass line 50 bypasses the main relays 43 and 44, the bypass line 50 can electrically connect the fuel cell 10 to the power storage devices 21 and 22 even if the main relays 43 and 44 are disconnected.

[0074] A bypass relay 51 may be provided on the bypass line 50 to establish or disconnect the connection between the fuel cell 10 and the power storage devices 21 and 22 through the bypass line 50 .

[0075] Figure 2 and Figure 3 The power generation and hydrogen movement reactions of the fuel cell 10 according to one embodiment of the present disclosure are shown.

[0076] Reference Figure 2 and Figure 3 , when a voltage difference is generated by energy supplied from the outside to the fuel cell 10, a potential is generated in the fuel cell 10. Therefore, hydrogen ions (protons, H + ) moves through the polymer electrolyte membrane and then recombines into new molecular hydrogen. This reaction is called the electrochemical hydrogen pump (EHP) reaction.

[0077] Specifically, the fuel cell 10 is a galvanic cell in which a voltage difference is generated by a spontaneous redox reaction to flow electrons. Therefore, the hydrogen electrode and the air electrode can be electrically represented as a positive electrode (+ electrode) or a negative electrode (- electrode) alternately.

[0078] The electrical polarity of the hydrogen electrode and the air electrode of the polymer electrolyte fuel cell 10 is not only Figure 2 In the fuel cell 10 shown for power generation, Figure 3 The power consumption of the EHP reaction is shown to be unchanged.

[0079] That is, since the polarity of the power components connected to the fuel cell 10 is not changed in both the fuel cell 10 reaction and the EHP reaction, the components of the fuel cell 10 grid system can be used as they are.

[0080] The current flows between the fuel cell stack 10 and the bidirectional converter 31, and between the fuel cell stack 10 and the inverter 71. Because the current flows in opposite directions during the power generation process (generating electricity) and the EHP process (consuming electricity), the current flows in opposite directions in the fuel cell stack 10. Specifically, during power generation, the fuel cell stack 10 functions as a power source, while during EHP, the fuel cell stack 10 functions as a resistor using a separate power source. In this regard, even when the current flows in opposite directions, the polarity does not change.

[0081] In addition, hydrogen ions (protons, H + ) is affected by the amount and distribution of water in the electrolyte membrane. When water is not supplied from outside the fuel cell stack 10, the amount of current flow reaches a maximum and then decreases.

[0082] Figure 4 States of an air electrode and a hydrogen electrode according to a hydrogen transfer reaction of the fuel cell 10 according to one embodiment of the present disclosure are shown.

[0083] like Figure 4 As shown, EHP control was performed while the fuel cell 10 was stopped, resulting in a significant reduction in the hydrogen concentration at the air electrode. Specifically, the experimental conditions involved applying a voltage of 370V to the fuel cell 10 via the high-voltage battery 21. Even when EHP control was maintained for only three seconds, the effect of reducing the hydrogen concentration at the air electrode by more than half was confirmed.

[0084] Furthermore, it was confirmed that the pressure of the hydrogen electrode after EHP control became higher than before. Therefore, it was confirmed that hydrogen from the air electrode migrated to the hydrogen electrode. In particular, fuel efficiency can be improved by collecting the hydrogen that would otherwise be exhausted.

[0085] Specifically, refer to Figure 1 The main line 40 may include: a main cathode line 41 configured to connect the cathode of the fuel cell 10 to the cathodes of the power storage devices 21 and 22; and a main anode line 42 configured to connect the anode of the fuel cell 10 to the anodes of the power storage devices 21 and 22. The main relays 43 and 44 may include: a first main relay 43 provided on the main cathode line 41; and a second main relay 44 provided on the main anode line 42.

[0086] The main cathode line 41 can connect the cathode of the fuel cell 10 to the cathode of the storage device 21 and 22 (especially the positive electrode of the bidirectional converter 31), and the main anode line 42 can connect the anode of the fuel cell 10 to the anode of the storage device 21 and 22 (especially the negative electrode of the bidirectional converter 31).

[0087] The first main relay 43 is provided on the main cathode line 41, and the second main relay 44 is provided on the main anode line 42. The first main relay 43 and the second main relay 44 can respectively establish or disconnect the connection between the main cathode line 41 and the main anode line 42.

[0088] At least one of the main cathode line 41 and the main anode line 42 is provided with a diode 45 configured to allow current in only one direction. The bypass line 50 can branch from the main cathode line 41 or the main anode line 42 provided with the diode and can bypass the diode 45 and the first main relay 43 or the second main relay 44.

[0089] The diode 45 is provided on the main cathode line 41, and can allow only the current output from the fuel cell 10 to the main cathode line 41. Therefore, it is possible to prevent a reverse current from being input to the fuel cell 10.

[0090] The bypass line 50 may branch from the main cathode line 41 on the fuel cell 10 side relative to the diode 45. Therefore, the bypass line 50 may bypass both the first main relay 43 and the diode 45, and current may flow from the high voltage battery 21 to the fuel cell 10 through the bypass line 50.

[0091] The fuel cell 10 power grid system may further include: a cathode COD line 61, branched from the main cathode line 41 on the fuel cell 10 side relative to the first main relay 43; an anode COD line 62, branched from the main anode line 42 on the fuel cell 10 side relative to the second main relay 44; and a COD resistor, embedded in the coolant heater (CHT) 63 but not specifically shown, connected to each of the cathode COD line 61 and the anode COD line 62 to consume electricity.

[0092] The COD resistor may be connected to a coolant heater (CHT) 63 and may be immersed in cooling water for the fuel cell 10. The COD resistor may consume power to generate heat and may be cooled by the circulation or flow of cooling water. The COD resistor is configured to consume power from the fuel cell 10 to quickly reduce the voltage of the fuel cell 10.

[0093] A COD resistor may be connected to the main cathode line 41 via a cathode COD line 61. Specifically, the COD resistor may be connected to the main cathode line 41 at a position between the diode 45 and the first main relay 43. Furthermore, the COD resistor may be connected to the main anode line 42 via an anode COD line 62. Specifically, the anode COD line 62 may be connected to the main anode line 42 on the fuel cell 10 side rather than on the second main relay 44 side.

[0094] Therefore, even if both the first main relay 43 and the second main relay 44 are turned off, the COD resistor can quickly lower the voltage of the fuel cell 10 by consuming the power of the fuel cell 10 .

[0095] The fuel cell 10 grid system may further include a first COD relay 64 provided on the cathode COD line 61 or the anode COD line 62 to disconnect or establish an electrical connection.

[0096] The first COD relay 64 may be provided on the cathode COD line 61 to establish or disconnect the connection between the COD resistor and the main cathode line 41. The first COD relay 64 is a normally open type that usually maintains an open state and may be controlled to be closed to establish an electrical connection.

[0097] The fuel cell 10 grid system may further include a second COD relay 65, which is connected to the cathode COD line 61 or the anode COD line 62 to bypass the first COD relay 64 and is configured to disconnect or establish an electrical connection, wherein the allowable current or allowable power of the second COD relay 65 may be relatively smaller than the allowable current or allowable power of the first COD relay 64.

[0098] In contrast to the first COD relay 64, the second COD relay 65 is a normally closed type that is usually kept closed and can be controlled to be opened to disconnect the electrical connection. That is, when there is no control in the shutdown state of the fuel cell 10, the second COD relay 65 can be closed to establish the electrical connection.

[0099] In other words, the second COD relay 65 and the first COD relay 64 may be connected in parallel to each other on the cathode COD line 61. Even if only one of the first and second COD relays 64 and 65 is closed, the COD resistor is connected to the main cathode line 41 to allow current to flow.

[0100] In particular, the allowable current or allowable power of the second COD relay 65 can be relatively smaller than the allowable current or allowable power of the first COD relay 64. Therefore, the rate of power consumption or voltage drop of the fuel cell 10 when only the first COD relay 64 is closed can be higher than the rate of power consumption or voltage drop of the fuel cell 10 when only the second COD relay 65 is closed.

[0101] The fuel cell 10 grid system may further include a current limiting resistor 52 provided on the bypass line 50 to form a potential difference between a front end and a rear end of the current limiting resistor 52 when electrical connection of the bypass line 50 is allowed.

[0102] The current limiting resistor 52 is configured to limit an inrush current, which is a current that rapidly increases through the bypass line 50 when the bypass relay 51 is closed. The current limiting resistor 52 may be a resistor, an NTC thermistor, or the like.

[0103] Since the resistance of the current limiting resistor 52 may be proportional to the time required to maintain the EHP reaction, the current limiting resistor 52 is configured to have an appropriate resistance in consideration of the time required to start the fuel cell 10. For example, the current limiting resistor 52 may be an 18.5 ohm (Ω) resistor and may be a metal-clad resistor to which a heat sink is attached for removing resistance heat.

[0104] The current limiting resistor 52 may form a potential difference between the front end and the rear end thereof to reduce the voltage applied to the fuel cell 10 through the high voltage battery 21 , thereby preventing a surge current from being generated in the fuel cell 10 .

[0105] The fuel cell 10 grid system may further include a current sensor 46 located between the fuel cell 10 and a point where the bypass line 50 branches from the main line 40 to sense current output from or input into the fuel cell 10 .

[0106] Specifically, the current sensor 46 can sense the current output from the fuel cell 10 when the fuel cell 10 is in a power generation state. In addition, the current sensor 46 can sense the current input into the fuel cell 10 when the fuel cell 10 is in an EHP reaction state.

[0107] Figure 5 FIG. 1 is a flow chart of a method for controlling a fuel cell 10 power grid system according to an embodiment of the present disclosure.

[0108] Reference Figure 5 According to an embodiment of the present disclosure, a control method of a fuel cell 10 power grid system includes: stopping power generation of the fuel cell 10 by shutting down the fuel cell 10 or putting the fuel cell 10 into an FC stop mode (S200); in a state where power generation of the fuel cell 10 is stopped, supplying power stored in the power storage devices 21 and 22 to the fuel cell 10 to move hydrogen on the cathode side to the anode side (S300); and generating power through a reaction between the fuel gas and the oxidizing gas in the fuel cell 10 (S400).

[0109] The method may further include: before stopping (S200) power generation of the fuel cell 10, normally generating power in the fuel cell 10 (S100). When the fuel cell 10 normally generates power (S100), the fuel gas and the oxidizing gas may be supplied to the fuel cell 10, and power may be generated by a chemical reaction between the fuel gas and the oxidizing gas in the fuel cell 10.

[0110] When stopping power generation of the fuel cell 10 (S200), power generation can be stopped by inputting a shutdown signal (S210) of the fuel cell 10. When power generation is stopped by shutdown, shutdown control for reducing the voltage of the fuel cell 10 and removing oxygen from the fuel cell 10 can be executed (S230).

[0111] When stopping power generation of the fuel cell 10 ( S200 ), the fuel cell 10 may enter an FC stop mode ( S220 ) for temporarily stopping power generation while the fuel cell 10 is started.

[0112] Stopping power generation of the fuel cell 10 ( S200 ) may further include performing shutdown control for reducing the voltage of the fuel cell 10 ( S230 ) when power generation of the fuel cell 10 is stopped by shutting down the fuel cell 10 ( S210 ).

[0113] When executing shutdown control (S230), by closing the first COD relay 64 set on the COD line branched from the main line 40, the voltage of the fuel cell 10 can be reduced to a preset first voltage by utilizing the COD resistor of the COD line, and when the first COD relay 64 and the first main relay 43 set on the main cathode line 41 are disconnected and the second COD relay 65 is closed, the voltage of the fuel cell 10 can be reduced to a preset second voltage, wherein the second COD relay 65 bypasses the first COD relay 64 and the allowable current or allowable power of the second COD relay 65 is relatively smaller than the allowable current or allowable power of the first COD relay 64, and the second main relay 44 set on the main anode line 42 of the main line 40 can remain in a disconnected state.

[0114] When hydrogen on the cathode side is moved to the anode side (S300), the electricity stored in the power storage devices 21 and 22 can be supplied to the fuel cell 10 at preset periodic intervals (S260) or when the fuel cell 10 is caused to generate electricity by starting the fuel cell 10 (S240) or releasing the FC stop mode (S250).

[0115] When the power generation of the fuel cell 10 is stopped, the fuel cell 10 can be controlled to move hydrogen from the cathode side to the anode side at preset periodic intervals, or to move hydrogen from the cathode side to the anode side when the power generation of the fuel cell 10 is restarted by starting the fuel cell 10 or releasing the FC stop mode.

[0116] Specifically, when power generation stops in the shutdown state of the fuel cell 10 , when the fuel cell 10 is restarted by inputting a start signal ( S240 ) to the fuel cell 10 , the fuel cell 10 may be controlled to move hydrogen on the cathode side to the anode side.

[0117] When power generation is stopped in the fuel cell 10's FC stop mode, the fuel cell 10 can be controlled to move hydrogen from the cathode side to the anode side when power generation is restarted by releasing the FC stop mode. Alternatively, the fuel cell 10 can be controlled to move hydrogen from the cathode side to the anode side at preset periodic intervals during the FC stop mode. This allows hydrogen to be removed from the cathode side in preparation for releasing the FC stop mode. This reduces energy consumption of the entire fuel cell system by reducing the amount of hydrogen that does not participate in the fuel cell reaction and is emitted to the outside when the FC stop mode is released.

[0118] The above-mentioned EHP reaction can be induced by moving hydrogen from the cathode side to the anode side ( S300 ).

[0119] Specifically, when hydrogen on the cathode side is moved to the anode side ( S300 ), the bypass relay 51 may be closed, and the power storage devices 21 and 22 may be discharged by controlling the bidirectional converter 31 located between the fuel cell 10 and the power storage devices 21 and 22 .

[0120] When hydrogen on the cathode side is moved to the anode side (S300), the voltage of the main line 40 can be maintained within a preset voltage range for a preset time, or the storage devices 21 and 22 can be discharged until the integrated value of the current flowing in the main line 40 reaches a predetermined current amount.

[0121] The preset voltage range can be preset based on the control voltage (D) obtained by adding a preset offset (α) to the operating minimum voltage (G) of the high-voltage BOPs or inverter 71 connected to the motor. Specifically, the preset voltage range can be preset to a range obtained by adding a preset error range (β) to the control voltage (D) or subtracting the preset error range (β) from the control voltage (D) (G-β<=>G+β). That is, the bidirectional converter 31 can be controlled to have a constant voltage so that the voltage of the main line 40 connected to the power storage devices 21 and 22 is uniformly maintained at the control voltage (D).

[0122] The preset time may be set according to a preset voltage range or a control voltage (D). In addition, the preset time may be appropriately adjusted in consideration of the resistance of the current limiting resistor 52 and the time required for the fuel cell 10 to resume operation.

[0123] The current flowing along the main line 40 may be the current input to the fuel cell 10 and may be represented using a value sensed by the current sensor 46 .

[0124] When generating electricity ( S400 ), the oxidizing gas may be supplied to the fuel cell 10 , the bypass relay 51 may be opened, and the first main relay 43 provided on the main cathode line 41 of the main line 40 may be closed.

[0125] When the movement of hydrogen from the cathode side to the anode side ( S300 ) is completed, power generation of the fuel cell 10 may be restarted by supplying an oxidizing gas to the fuel cell 10 ( S400 ).

[0126] Specifically, a control method of the fuel cell 10 power grid system during shutdown and restart of the fuel cell 10 according to one embodiment of the present disclosure can be shown in Table 1 below.

[0127] [Table 1]

[0128]

[0129] During normal operation, both the first main relay 43 and the second main relay 44 may be closed, and the bypass relay 51 , the first COD relay 64 , and the second COD relay 65 may all be open.

[0130] When the fuel cell 10 is shut down, the controller 60 starts executing a stop process of the fuel cell 10 by cutting off the power supplied from the inverter 71 to the motor and stopping the air compressor to prevent air from being supplied to the stack.

[0131] The controller 60 may adjust the voltage of the bidirectional converter 31 to reduce the output voltage of the fuel cell stack 10 , and when the output voltage of the stack is lower than a preset output voltage, the controller 60 may disconnect the first main relay 43 .

[0132] Here, the preset output voltage is a value used to determine whether the high-voltage battery 21 can be charged, and may have various values according to the specifications of the stack or the high-voltage battery 21 .

[0133] Furthermore, the controller that reduces the output voltage of the fuel cell stack 10 to charge the high voltage battery 21 may control the output voltage at a preset rate of change so that the output voltage does not exceed the charge allowable current value of the high voltage battery 21 .

[0134] Furthermore, the controller 60 can quickly reduce the output voltage of the fuel cell stack 10 to minimize stack degradation caused by the fuel cell 10 being exposed to high voltage during the initial shutdown phase. To this end, the controller 60 closes the first COD relay 64 to consume the power generated by the fuel cell 10 via the COD resistor-embedded coolant heater (CHT) 63.

[0135] The coolant stack pump (CSP) may be operated at a minimum idle RPM in order to reduce the resistive heat generated in the coolant heater (CHT) 63. When the output voltage of the fuel cell 10 stack decreases and, as a result, the resistive heat generated in the coolant heater (CHT) 63 becomes equal to or lower than a predetermined level, the controller 60 may stop the operation of the coolant stack pump (CSP).

[0136] When the voltage value at the output terminal of the fuel cell stack 10 falls below a preset charging voltage, the controller 60 opens the first main relay 43 and continues to close the first COD relay 64, thereby reducing the output voltage of the fuel cell stack 10. When the output voltage drops to a predetermined degradation prevention voltage to prevent degradation of the fuel cell stack 10, the controller 60 opens the first COD relay 64. Furthermore, the controller 60 can maintain the output voltage of the fuel cell stack 10 at ground by opening the first COD relay 64 and closing the second COD relay 65.

[0137] During the end of the stop step, the controller 60 closes the hydrogen supply valve (FSV), disconnects the second main relay 44, and enters a storage state in which the fuel cell stack 10 and the coolant heater (CHT) 63 are electrically connected to each other via the second COD relay 65. In the storage state in which the stop mode is maintained, the hydrogen electrode and the air electrode of the stack are stored in a state in which the hydrogen electrode and the air electrode are electrically connected to each other via the resistance unit of the coolant heater (CHT) 63. Therefore, a small amount of unreacted oxygen present in the air electrode is completely removed, and at the same time, hydrogen in the reaction gas present in the hydrogen electrode diffuses to the air electrode by passing through the polymer electrolyte membrane, so that the hydrogen concentration of the air electrode increases according to the storage time and gradually approaches an equilibrium state.

[0138] When the start signal of the fuel cell 10 is input, the controller 60 uses the power of the low-voltage battery 22 to disconnect the second COD relay 65, thereby disconnecting the electrical connection between the fuel cell 10 stack and the coolant heater (CHT) 63, and closes the second main relay 44 to first connect the fuel cell 10 stack to the main anode line 42 of the bidirectional converter 31 (BHDC), thereby synchronizing the references of the two high-voltage power supplies (the fuel cell 10 stack and the high-voltage battery 21).

[0139] When the voltage on the fuel cell 10 side of the bidirectional converter 31 is controlled to a predetermined voltage range (G-β<=>G+β) obtained by adding a preset error range (β) to the control voltage (D) or subtracting the preset error range (β) from the control voltage (D), the controller 60 closes the bypass relay 51 to bypass the diode 45 through the bypass line 50 while allowing the high-voltage battery 21 to be electrically connected to the fuel cell 10 stack.

[0140] In this case, the power supplied from the bidirectional converter 31 (BHDC) to the fuel cell 10 stack causes an EHP reaction, thereby moving hydrogen at the air electrode to the hydrogen electrode and preventing hydrogen at the hydrogen electrode from passing through to the air electrode.

[0141] The speed at which hydrogen moves from the air electrode to the hydrogen electrode through the EHP reaction is expressed as a current proportional to the magnitude of the voltage applied to the stack and is measured by the current sensor 46. The current of the power supplied to the stack through the bypass line 50 for the EHP reaction is affected by the hydration (moisture) state of the polymer electrolyte membrane in the fuel cell 10 stack during the storage state. When the fuel cell 10 stops normal operation, the polymer electrolyte membrane can be stored in a fully hydrated state.

[0142] The controller 60 moves hydrogen from the air electrode to the hydrogen electrode through the EHP reaction within a predetermined time, and then disconnects the bypass relay 51 to cut off the power of the bypass line 50. In particular, the controller can reconfirm the end of the EHP reaction by confirming the current value sensed by the current sensor 46.

[0143] Thereafter, the controller 60 opens the fuel supply valve (FSV) for supplying hydrogen used as fuel to the fuel cell stack 10 and the air shutoff valve (ACV) for supplying air used as an oxidant, while closing the first main relay 43 to connect to the main cathode line 41. In addition, the controller 60 operates the air compressor (ACP) and the coolant stack pump (CSP) to supply the electricity generated in the fuel cell stack 10 to the inverter 71 and the bidirectional converter 31.

[0144] Furthermore, a method for controlling the power grid system of the fuel cell 10 when entering and releasing the FC stop mode according to an embodiment of the present disclosure may be as shown in Table 2 below.

[0145] [Table 2]

[0146]

[0147] Specifically, in the case of entering the FC stop mode, only the supply of air to the fuel cell 10 stack is cut off, and the output voltage of the fuel cell 10 stack alone is not reduced.

[0148] That is, at the initial stage of entering the FC stop mode, the output voltage of the fuel cell 10 stack is in a high voltage state that is the same as the open circuit voltage (OCV) due to the hydrogen remaining in the stack and the oxygen in the air, the bidirectional converter 31 is also maintained in a high voltage state to operate the high voltage BOPs, and in this case, the bypass relay 51 is disconnected.

[0149] The power generated by the fuel cell stack 10 passes through the main cathode line 41 via the diode 45 and then charges the high-voltage battery 21 via the bidirectional converter 31. Optionally, the power is provided to high-voltage BOPs such as the coolant stack pump (CSP). As a result, the output voltage of the fuel cell stack 10 gradually decreases.

[0150] When the output voltage of the fuel cell stack 10 gradually decreases and reaches a level similar to the output voltage of the bidirectional converter 31 (preferably, stack output voltage ≤ bidirectional converter 31 output voltage ± δ (voltage deviation)), the bypass relay 51 can be closed to allow the power output from the bidirectional converter 31 to bypass the diode 45 via the bypass line 50 and then be applied to the fuel cell stack 10. As a result, an EHP reaction can occur in the fuel cell stack 10. Here, when the voltage deviation (δ) is too large, the surge current caused by the voltage difference between the two high-voltage power supplies becomes larger. Therefore, the voltage deviation (δ) can be preset to an appropriate level through experimentation.

[0151] When an FC stop mode release signal (e.g., an accelerator signal or a transmission position signal) is input, the controller 60 can disconnect the bypass relay 51 to disconnect from the main cathode line 41, and can drive the air compressor to supply air to the fuel cell 10 stack, thereby controlling the fuel cell 10 to perform normal operation to restart power generation of the fuel cell 10.

[0152] Figure 6 1 shows a configuration of a fuel cell 10 grid system according to another embodiment of the present disclosure.

[0153] Reference Figure 6 The fuel cell 10 grid system according to another embodiment of the present disclosure may not include the current limiting resistor 52 , and the inrush current may be prevented by using a COD resistor instead of the current limiting resistor 52 .

[0154] Specifically, the fuel cell 10 grid system may further include a COD resistor provided on the bypass line 50 and consuming power, wherein the bypass relay 51 may be located on the power storage devices 21 and 22 side of the bypass line 50 relative to the COD resistor.

[0155] The negative electrode of the COD resistor can be moved from the main anode line 42 to the main cathode line 41 to be connected to the main cathode line 41. Both the negative electrode and the positive electrode of the COD resistor can be connected to the bypass line 50, which bypasses the diode 45 and the first main relay 43 on the main cathode line 41 and is connected to the bidirectional converter 31. That is, both the negative electrode and the positive electrode of the COD resistor can be connected to the bypass line 50 to function as a resistor that limits the current on the bypass line 50.

[0156] In this case, the COD control cannot quickly reduce the voltage of the fuel cell 10 stack. Therefore, the system may further include a circuit including a separate relay or a separate line for connecting the negative electrode of the COD resistor to the main anode line 42.

[0157] The fuel cell 10 grid system may further include: a connecting line 53 configured to connect the bypass line 50 between the COD resistor and the bypass relay 51 to the main cathode line 41 or the main anode line 42 between the first main relay 43 or the second main relay 44 and the diode 45; and a first COD relay 64 and a second COD relay 65, which are located between the COD resistor and the point where the connecting line 53 branches off from the bypass line 50 and are connected in parallel to each other to disconnect or establish an electrical connection, wherein the allowable current or allowable power of the second COD relay 65 may be relatively smaller than the allowable current or allowable power of the first COD relay 64.

[0158] The connecting line 53 may be connected from the bypass line 50 to the main cathode line 41 between the diode 45 and the main relay 43 or 44. The first COD relay 64 and the second COD relay 65 connected in parallel to each other are located on the bypass line 50, in particular, on the bypass line 50 connected to the positive electrode of the COD resistor, and the connecting line 53 may be branched between the first COD relay 64 or the second COD relay 65 and the bypass relay 51 and connected between the diode 45 and the main relay 43 or 44.

[0159] Specifically, a control method of the fuel cell 10 power grid system during shutdown and restart of the fuel cell 10 according to another embodiment of the present disclosure may be as shown in Table 3 below.

[0160] [Table 3]

[0161]

[0162] The description of the control method is mostly the same as the description of the control method of the fuel cell 10 power grid system according to one embodiment of the present disclosure as shown in Table 1. Therefore, only the differences will be described below.

[0163] When the fuel cell 10 starts, the controller 60 closes the second main relay 44 to electrically connect the negative electrode of the fuel cell 10 stack output to the negative electrode of the output terminal of the bidirectional converter 31 , thereby synchronizing the references of the two high voltage power supplies.

[0164] The second COD relay 65 remains in an open state, so the fuel cell stack 10, the bidirectional converter 31, and the coolant heater (CHT) 63 are electrically connected. In addition, closing the first COD relay 64 can strengthen the electrical connection between the fuel cell stack 10 and the coolant heater (CHT) 63. Depending on the amount of power or current that can pass through the first COD relay 64 and the second COD relay 65, this control can be selectively applied to the first COD relay 64 and the second COD relay 65.

[0165] Thereafter, the controller 60 closes the bypass relay 51 to connect the fuel cell 10 and the bidirectional converter 31 to each other through the bypass line 50. When the output voltage of the bidirectional converter 31 is higher than the stack output voltage, power for the EHP reaction can be immediately supplied to the fuel cell 10 stack.

[0166] When the output voltage of the bidirectional converter 31 increases as the controller 60 starts to control the bidirectional converter 31, the power of the bidirectional converter 31 bypasses the diode 45 via the bypass line 50 and is then supplied to the fuel cell 10 stack, and the stack supplied with power causes an EHP reaction to consume the supplied power, thereby reducing the hydrogen concentration of the air electrode.

[0167] That is, the controller 60 can form a path that bypasses the diode 45 and is used to transmit power of the bypass line 50, and then can start controlling the bidirectional converter 31 and gradually increase the output voltage of the bidirectional converter 31 so that the bypass relay 51, the first COD relay 64 and the second COD relay 65 are not damaged by high current or high power.

[0168] The controller 60 starts controlling the bidirectional converter 31 by adding a preset offset (α) to the minimum operating voltage (G) of the inverter 71 for supplying electric power to the motor, thereby obtaining a control voltage (D). When the output voltage of the bidirectional converter 31 is equal to or higher than the minimum operating voltage (G) of the inverter 71, the controller 60 performs constant voltage control to maintain the output voltage of the bidirectional converter 31 constant within a range of ±β (error) of the preset voltage of the bidirectional converter 31 for the EHP reaction.

[0169] Furthermore, the current value of the power for the EHP reaction supplied from the bidirectional converter 31 to the stack varies depending on the output voltage of each of the stack and the bidirectional converter 31, the resistance value of the COD resistor included in the coolant heater (CHT) 63, and the change in the resistance value of the stack due to the EHP reaction. Therefore, the controller 60 can set and control the control change speed of the control voltage (D) of the bidirectional converter 31 in one or more steps through feedback control using the current value measured by the current sensor 46. Therefore, the controller can select the most appropriate current amount range to minimize the additional time required for starting the fuel cell 10 power grid system including the EHP reaction.

[0170] When the voltage at the output terminal of the bidirectional converter 31 increases to a voltage capable of operating the coolant stack pump, the controller 60 can operate the coolant stack pump to remove the resistive heat generated in the coolant heater 63 including the COD resistor. In addition, when the first main relay 43 located on the main cathode line 41 is closed and the fuel cell 10 switches to normal operation after the startup process including the EHP reaction is completed, the operating power of the high-voltage BOPs is controlled to be maintained without being cut off.

[0171] When the control voltage (D) of the bidirectional converter 31 reaches a level capable of performing constant voltage control in which the control voltage (D) is kept constant within the set voltage ±β (error), the controller 60 determines whether to continue the EHP reaction which can be confirmed by the current value of the current sensor 46 or whether a predetermined time measured by an internal timer has been reached, and then opens the bypass relay 51 to complete the EHP reaction.

[0172] Thereafter, the controller 60 may disconnect the first COD relay 64 and the second COD relay 65 to disconnect the electrical connection between the stack and the coolant heater 63 , and may supply hydrogen and air to the stack upon completing the startup process to control normal operation of the fuel cell 10 grid system.

[0173] A method for controlling the power grid system of the fuel cell 10 when entering and releasing the FC stop mode according to another embodiment of the present disclosure may be as shown in Table 4 below.

[0174] [Table 4]

[0175]

[0176] Figure 7 FIG. 2 shows a configuration of a fuel cell 10 power grid system according to yet another embodiment of the present disclosure.

[0177] Reference Figure 7 , the fuel cell 10 grid system according to yet another embodiment of the present disclosure supplies power to the fuel cell 10 stack while the low-voltage battery 22 in the power storage devices 21 and 22 is discharged.

[0178] Specifically, the power grid system may further include: a bidirectional converter 31, connected to the fuel cell 10 via a main line 40; and a low-voltage converter 32, located between the bidirectional converter 31 and the power storage devices 21 and 22 to convert the power converted by the bidirectional converter 31 into a relatively low potential, wherein the power storage device is a low-voltage battery 22 connected to the low-voltage converter 32 and charged or discharged at a relatively low potential, the main line 40 includes a first main line and a second main line, the bypass line 50 branches from the first main line and is connected to the first battery line 33 of the low-voltage battery 22, the second battery line 34 of the low-voltage battery 22 can be connected to the second main line, and may be provided with a battery relay 36 configured to disconnect or establish an electrical connection of the second battery line 34.

[0179] The bidirectional converter 31 is connected to the low-voltage converter 32 separately from the high-voltage battery 21, and the low-voltage battery 22 is charged with the voltage converted to a low potential by the low-voltage converter 32. Here, the low potential of the low-voltage battery 22 may be, for example, 12 volts (V), and may be a relatively high potential voltage lower than the 300 to 400 volts (V) region of the high-voltage battery 21.

[0180] The first and second battery lines 33 and 34 may be connected to the cathode and anode of the low-voltage battery 22, respectively, and to the low-voltage converter 32. Low-voltage BOPs may be electrically connected to the first and second battery lines 33 and 34.

[0181] Furthermore, a bypass line 50 may be connected to the first battery line 33 , a third battery line 35 may be connected between the second battery line 34 and the second main line, and a battery relay 36 may be provided on the third battery line 35 .

[0182] The controller 60 may control the battery relay 36 to be closed or opened to enable the power of the low-voltage battery 22 to be supplied to the fuel cell stack 10 or to prevent the power of the low-voltage battery 22 from being supplied to the fuel cell stack 10 .

[0183] While the present disclosure has been described and illustrated with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various improvements and modifications may be made thereto without departing from the technical concept of the disclosure as provided by the appended claims.

Claims

1. A fuel cell power grid system comprising: Fuel cells, which generate electricity through the reaction between a fuel gas and an oxidizing gas; a power storage device that is charged or discharged using the power generated by the fuel cell to supply power; a main line electrically connecting the fuel cell and the power storage device to each other; a main relay provided on the main line to disconnect or establish an electrical connection between the fuel cell and the power storage device; a bypass line branching from the main line, bypassing the main relay and connected to the power storage device; a bypass relay, provided on the bypass line to disconnect or establish an electrical connection of the bypass line; as well as a controller that controls the main relay or the bypass relay so that the power charged in the power storage device is supplied to the fuel cell in a state where power generation of the fuel cell is stopped, The power storage device includes a high-voltage battery and a low-voltage battery with different voltages. The bypass line is connected to both the high-voltage battery and the low-voltage battery, The system further includes a bidirectional converter connected between the fuel cell and the high-voltage battery via the main line. The main line includes a first main line and a second main line, The bypass line branches from the first main line and is connected to the first battery line of the low-voltage battery and the bidirectional converter, The second main line is connected to a second battery line of the low-voltage battery, the second battery line having a battery relay that disconnects or establishes an electrical connection of the second battery line and is connected to the bidirectional converter, The controller further controls the main relay, the bypass relay, and the battery relay so that the power stored in the high-voltage battery or the low-voltage battery is supplied to the fuel cell in a state where power generation of the fuel cell is stopped.

2. The fuel cell power grid system according to claim 1, wherein: The main line includes: a main cathode line connecting the cathode of the fuel cell to the cathode of the power storage device; and a main anode line connecting the anode of the fuel cell to the anode of the power storage device, The main relay comprises: a first main relay, disposed on the main cathode line; and The second main relay is provided on the main anode line.

3. The fuel cell grid system according to claim 2, wherein: At least one of the main cathode line and the main anode line is provided with a diode that allows current in only one direction, and The bypass line branches from the main cathode line or the main anode line provided with the diode, and bypasses both the diode and the first main relay or the second main relay.

4. The fuel cell grid system according to claim 2, further comprising: a cathode COD line branching from the main cathode line on the fuel cell side relative to the first main relay; an anode COD line branching from the main anode line on the fuel cell side relative to the second main relay; as well as A COD resistor is connected to each of the cathode COD line and the anode COD line to consume power.

5. The fuel cell grid system according to claim 4, further comprising: A first COD relay is provided on the cathode COD line or the anode COD line to disconnect or establish an electrical connection.

6. The fuel cell grid system according to claim 5, further comprising: a second COD relay connected to the cathode COD line or the anode COD line to bypass the first COD relay and disconnect or establish electrical connection, wherein an allowable current or allowable power of the second COD relay is relatively smaller than an allowable current or allowable power of the first COD relay.

7. The fuel cell grid system according to claim 1, further comprising: A current limiting resistor is provided on the bypass line to form a potential difference between a front end and a rear end of the current limiting resistor when electrical connection of the bypass line is allowed.

8. The fuel cell grid system according to claim 3, further comprising: A COD resistor, provided on the bypass line and consuming power, The bypass relay is located on the power storage device side of the bypass line relative to the COD resistor.

9. The fuel cell grid system according to claim 8, further comprising: a connecting line connecting the bypass line between the COD resistor and the bypass relay to the main cathode line or the main anode line between the first main relay or the second main relay and the diode; as well as a first COD relay and a second COD relay, located between the COD resistor and a point where the connection line branches from the bypass line, and connected in parallel to each other to disconnect or establish electrical connection, The allowable current or allowable power of the second COD relay is relatively smaller than the allowable current or allowable power of the first COD relay.

10. The fuel cell grid system according to claim 1, further comprising: A current sensor is located between the fuel cell and a point where the bypass line branches from the main line to sense current output from or input into the fuel cell.

11. The fuel cell grid system according to claim 1 , further comprising: A low-voltage converter is located between the bidirectional converter and the low-voltage battery to convert the electric power converted by the bidirectional converter into a relatively low electric potential.

12. A method for controlling a fuel cell power grid system according to claim 1, the method comprising: stopping power generation by the fuel cell by shutting down the fuel cell or placing the fuel cell into an FC stop mode; supplying the power stored in the power storage device to the fuel cell in a state where power generation of the fuel cell is stopped, so that hydrogen on the cathode side moves to the anode side; and Electricity is generated by a reaction between a fuel gas and an oxidizing gas in the fuel cell.

13. The method according to claim 12, wherein: Stopping power generation of the fuel cell further comprises: When the power generation of the fuel cell is stopped by shutting down the fuel cell, a shutdown control for reducing the voltage of the fuel cell is executed. When the shutdown control is performed, by closing a first COD relay provided on a COD line branched from a main line, the voltage of the fuel cell is reduced to a preset first voltage by using a COD resistor of the COD line. In a state where the first COD relay and the first main relay provided on the main cathode line of the main line are disconnected and the second COD relay is closed, the voltage of the fuel cell decreases to a preset second voltage, the second COD relay bypasses the first COD relay, and the allowable current or allowable power of the second COD relay is relatively smaller than the allowable current or allowable power of the first COD relay, and The second main relay provided on the main anode line of the main line remains in an off state.

14. The method according to claim 12, wherein: The power stored in the power storage device is supplied to the fuel cell at preset periodic intervals when hydrogen on the cathode side is moved to the anode side or when the fuel cell generates power by starting the fuel cell or releasing the FC stop mode.

15. The method according to claim 12, wherein: When hydrogen on the cathode side is moved to the anode side, a bypass relay is closed, and a bidirectional converter located between the fuel cell and the power storage device is controlled to discharge the power storage device.

16. The method according to claim 15, wherein When hydrogen on the cathode side is moved to the anode side, the voltage of the main line is maintained within a preset voltage range for a preset time, or the power storage device is discharged until the integrated value of the current flowing in the main line reaches a predetermined current amount.

17. The method according to claim 12, wherein: During power generation, the oxidizing gas is supplied to the fuel cell, the bypass relay is opened, and the first main relay provided on the main cathode line of the main line is closed.

Images