KR20250028801A - Fuel cell system and controlling method thereof - Google Patents

Abstract

According to various embodiments of the present disclosure, a fuel cell system may include a cell module in which a plurality of unit cells are stacked and arranged between a fuel electrode and an air electrode, a fuel cell stack including the cell module, a cell load including a plurality of unit cell loads and disposed on a surface of the fuel cell stack, the unit cell loads being connected to each of the plurality of unit cells to receive electric energy, a stack load connected to the fuel cell stack to receive electric energy, a power conversion device connected to the fuel cell stack and the stack load to convert electric energy produced in the fuel cell stack into electric power required by a load end, and a fuel cell control unit that controls an operation of the cell load or the stack load based on at least one of a voltage of the unit cell, a voltage of the cell module, a temperature of the fuel cell stack, and a surface temperature of the fuel cell stack.

Description

FUEL CELL SYSTEM AND CONTROLLING METHOD THEREOF

Various embodiments of the present disclosure relate to a fuel cell system and a control method thereof, which prevents damage to cells and stacks due to deterioration or the like by connecting cell modules in a fuel cell stack and a cell load arranged on a surface of the fuel cell stack in series and connecting the fuel cell stack and the stack load in parallel.

A fuel cell is a device that electrochemically generates electricity using fuel (hydrogen or reformed gas) and an oxidizer (oxygen or air). It is a device that directly converts fuel and oxidizer continuously supplied from the outside into electrical energy through an electrochemical reaction.

Pure oxygen or air containing a large amount of oxygen is used as the oxidizer of the fuel cell, and pure hydrogen or reformed gas containing a large amount of hydrogen produced by reforming hydrocarbon fuel (LNG, LPG, CH3OH) is used as the fuel.

Fuel cells generate electricity and heat simultaneously, and are gaining attention as high-efficiency energy production devices with a total efficiency of over 80%, which is the sum of power generation efficiency and heat efficiency. In addition, fuel cells can be installed in actual buildings or residential houses to directly produce and use the electricity and heat that users need, which not only improves user convenience but also drastically reduces energy usage costs.

Recently, fuel cell systems that produce high-efficiency energy by integrating multiple fuel cells have been built and operated.

These fuel cells can be broadly classified into phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), polymer electrolyte membrane fuel cells (PEMFC), and direct methanol fuel cells (DMFC).

에 이른다.The solid oxide fuel cell (SOFC) is a low-carbon, high-efficiency new renewable energy power generation facility that produces electricity through an electrochemical reaction between oxygen and hydrocarbons made by oxidizing liquefied natural gas (LNG), etc. Its operating temperature is the highest among fuel cells, at 600 to 1000

It reaches .

Because solid oxide fuel cells (SOFCs) operate at high temperatures, they do not require expensive precious metal electrode catalysts such as platinum, do not require electrolyte loss or replenishment, have no cell corrosion problems, and have high power generation efficiency.

In addition, because it emits high-temperature gas, it can also be used for combined heat and power generation using waste heat.

Additionally, polymer electrolyte membrane fuel cells (PEMFCs) operate at relatively low temperatures compared to other types of fuel cells, have short startup times, and have fast response characteristics to load changes.

In addition, polymer electrolyte fuel cells have high efficiency and high current density and power density. They are also less sensitive to pressure changes in the reaction gases (hydrogen and oxygen in the air) and can produce a wide range of outputs. For this reason, they can be applied to various fields such as power sources for zero-emission vehicles, self-generation, mobile and military power sources.

A polymer electrolyte membrane fuel cell is a device that generates electricity by electrochemically reacting hydrogen and oxygen to produce water. The supplied hydrogen is separated into hydrogen ions and electrons by the catalyst of the anode, and the separated hydrogen ions pass through the electrolyte membrane to the cathode. At this time, the oxygen in the air supplied to the cathode combines with the electrons that enter the cathode through an external conductor to produce water and generate electrical energy.

In order to obtain the required potential in actual buildings, industrial sites, vehicles, drones, etc., unit cells must be stacked as much as the required potential, and the stacked unit cells are called a stack (or fuel cell stack). The potential generated from one unit cell is approximately 1.2 V, and multiple cells are stacked in series to supply the power required for the load. Each unit cell includes a membrane electrode assembly (MEA), and an anode electrode to which hydrogen is supplied on both sides and a cathode electrode to which air (oxygen) is supplied are provided, with a polymer electrolyte membrane between which hydrogen ions are transferred from the membrane electrode assembly. In addition, a gas diffusion layer is arranged on the outside of the anode electrode and the cathode electrode, which include a catalyst layer, and a fuel cell stack is formed by sequentially stacking such a membrane electrode assembly and a separator in which a reaction gas and coolant path are formed.

Meanwhile, the fuel cell stack has a long structural characteristic due to the large area of the separator and the stacking of multiple cells. Due to the structural characteristic of the stack, a voltage imbalance may occur between the cells, such as the formation of a high potential in some cells. In addition, a temperature imbalance may occur between the cells. In particular, the surface of the fuel cell stack in the external environment has a large temperature difference from the inside of the fuel cell stack, which can greatly increase the temperature imbalance of the fuel cell stack.

Accordingly, various embodiments of the present disclosure aim to solve the above-described problems by connecting a cell module in a fuel cell stack and a cell load arranged on the surface of the fuel cell stack in series, and connecting the fuel cell stack and the stack load in parallel, thereby preventing the cells and the stack from being damaged due to deterioration or the like.

In addition, it aims to operate the fuel cell system stably, prevent deterioration of the fuel cell stack, provide a heat source necessary for preheating during startup, and provide a heat source necessary in extreme cold weather.

The technical problems to be achieved in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

According to one embodiment of the present invention, a fuel cell system may include a cell module in which a plurality of unit cells are stacked and arranged between a fuel electrode and an air electrode, a fuel cell stack including the cell module, a cell load including a plurality of unit cell loads and arranged on a surface of the fuel cell stack, the unit cell loads being connected to each of the plurality of unit cells to receive electric energy, a stack load connected to the fuel cell stack to receive electric energy, a power conversion device connected to the fuel cell stack and the stack load to convert electric energy produced in the fuel cell stack into electric power required by a load end, and a fuel cell control unit that controls an operation of the cell load or the stack load based on at least one of a voltage of the unit cell, a voltage of the cell module, a temperature of the fuel cell stack, and a surface temperature of the fuel cell stack.

The above cell load can transfer electric energy to the unit cell load when the unit cell and the unit cell load are each connected in series and the voltage of the unit cell exceeds a preset voltage.

The above stack load includes a plurality of different resistors and is connected in parallel with the fuel cell stack, and can vary the electric energy transmitted from the fuel cell stack depending on the resistance connected in parallel.

The fuel cell control unit can control to supply or block fuel to the fuel electrode and to supply or block air to the air electrode based on at least one of the voltage of the unit cell, the voltage of the cell module, the temperature of the fuel cell stack, and the surface temperature of the fuel cell stack.

The above fuel cell control unit can control the operation of the cell load or stack load so that the electric energy produced in the cell module by the supply of the fuel and air is transmitted to the cell load or stack load.

The fuel cell control unit can control the operation of the cell load or the stack load based on at least one of the voltage of the unit cell, the voltage of the cell module, the temperature of the fuel cell stack, and the surface temperature of the fuel cell stack in at least one of the startup purge phase, the startup preheating phase, the stop purge phase, the cold damage prevention phase, and the heat supply amount increase phase.

The above-described purge step may include a fuel electrode purge step and an air electrode purge step.

The fuel cell control unit controls hydrogen to be supplied and circulated through a hydrogen line to the fuel electrode of the fuel cell stack in the fuel electrode purge step, controls a hydrogen purge valve to be turned on so that inert gas in the fuel electrode is discharged, compares and determines a first reference voltage for initiating operation of the plurality of unit cells with the voltage of the cell load, and controls the operation of the cell load to transfer electric energy to the unit cell load connected to the unit cell when the voltage of any one unit cell among the plurality of unit cells exceeds the first reference voltage, compares and determines a second reference voltage for terminating the operation of the cell load, and controls the operation of the cell load to block the transfer of electric energy to the unit cell load connected to the unit cell when the voltage of any one unit cell among the plurality of unit cells is lower than the second reference voltage, and compares and determines a voltage of the cell module with a third reference voltage for terminating the operation of the cell load, and controls the cell load so that the operation of the cell load is terminated when the voltage of the cell module does not exceed the third reference voltage, and opens the hydrogen purge valve. It can be turned off to control fuel from leaking out of the fuel line.

The fuel cell control unit controls air to be supplied to the cathode of the fuel cell stack through an air line during the cathode purge step, controls inert gas in the cathode to be discharged through an air discharge blocking valve, compares and determines a fourth reference voltage for initiating operation of the plurality of unit cells with the voltage of the cell load, and controls the operation of the cell load to transfer electric energy to the unit cell load connected to the unit cell when the voltage of any one of the plurality of unit cells exceeds the fourth reference voltage, compares and determines a fifth reference voltage for initiating operation of the cell module with the voltage of the stack load, and controls the operation of the stack load to transfer electric energy from the fuel cell stack to the stack load when the voltage of the cell module exceeds the fifth reference voltage, and further, compares and determines a current flowing in the stack load due to the electric energy being transferred to the stack load with a preset maximum current of the stack load, and controls to terminate the start-up purge step when the current flowing in the stack load is greater than or equal to the maximum current.

The above fuel cell control unit can repeatedly compare and determine the voltages of the plurality of unit cells with the first reference voltage and the second reference voltage during a preset fuel purge time.

The fuel cell control unit can control the stack load so that, when the current flowing through the stack load is less than the maximum current, electric energy is transferred from the fuel cell stack and the current flows more than the maximum current.

The fuel cell control unit may determine by comparing the difference between the temperature of the fuel cell stack and the surface temperature of the fuel cell stack in the startup preheating step with a preset allowable temperature difference, and if the temperature difference exceeds the preset allowable temperature difference, may control to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preset allowable temperature difference, and may control the operation of the cell load such that the electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the cell load.

The above cell load can convert the transmitted electrical energy into thermal energy to increase the surface temperature of the fuel cell stack.

The fuel cell control unit can control the operation of the cell load so that electric energy is not transmitted to the cell load when the temperature difference is less than or equal to the preset allowable temperature difference, and can control to block the supply of fuel to the fuel electrode and block the supply of air to the air electrode.

The fuel cell control unit compares and determines the temperature of the fuel cell stack with a preset preheating completion determination temperature, and if the temperature of the fuel cell stack exceeds the preheating completion determination temperature, controls the operation of the stack load so that electric energy is not transmitted from the fuel cell stack to the stack load.

The fuel cell control unit may control, when the temperature of the fuel cell stack is lower than or equal to the preheating completion determination temperature, to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preheating completion determination temperature, and control the operation of the stack load so that electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the stack load.

The above cell module can increase the temperature of the fuel cell stack by using heat energy produced by the electrochemical reaction of the additionally supplied fuel and air.

The fuel cell control unit may control a hydrogen purge valve and an air discharge cutoff valve to discharge water into the fuel electrode and the air electrode after power generation is terminated in the stop purge step, compare the voltage of the fuel cell stack with a preset purge completion determination voltage to make a determination, and control the operation of the stack load to block electric energy transmitted from the fuel cell stack to the stack load when the voltage of the fuel cell stack is lower than the purge completion determination voltage, and control an air line to block the supply of air into the air electrode.

The fuel cell control unit compares and determines the voltage of a unit cell having the lowest voltage among the voltages of the plurality of unit cells with a sixth reference voltage for cutting off a preset fuel, and controls to cut off the fuel supply to the fuel electrode if the voltage of the unit cell having the lowest voltage is less than the sixth reference voltage, compares and determines the voltages of the plurality of unit cells with a seventh reference voltage for determining the termination of the cell load, and controls the operation of the cell load so that the transmission of electric energy to the unit cell load connected to the unit cell is cut off if the voltage of any one unit cell among the plurality of unit cells is less than the seventh reference voltage, and compares and determines the voltage of the cell module with an eighth reference voltage for terminating the operation of the cell load, and controls to terminate the operation of the cell load if the voltage of the cell module is less than the eighth reference voltage, and turns on a hydrogen purge valve to control so that hydrogen of the fuel electrode is discharged.

The fuel cell control unit may compare and determine an external temperature with a preset cold damage protection determination temperature in the cold damage prevention step, and if the external temperature is lower than the cold damage protection determination temperature, compare and determine a difference between a temperature of the fuel cell stack and a surface temperature of the fuel cell stack with the preset allowable temperature difference, and if the temperature difference exceeds the preset allowable temperature difference, control to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preset allowable temperature difference, and control the operation of the cell load so that electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the cell load.

The above cell load can convert the transmitted electrical energy into thermal energy to increase the surface temperature of the fuel cell stack.

The fuel cell control unit can control the operation of the cell load so that electric energy is not transmitted to the cell load when the temperature difference is less than or equal to the preset allowable temperature difference, and can control to block the supply of fuel to the fuel electrode and block the supply of air to the air electrode.

The fuel cell control unit may compare and determine the amount of heat generation produced by the fuel cell stack and the amount of heat demand in the heat supply increase stage, and control the operation of the stack load so that electric energy is not transmitted from the fuel cell stack to the stack load when the amount of heat generation exceeds the amount of heat demand, and control to block the supply of fuel to the fuel electrode and block the supply of air to the air electrode.

The fuel cell control unit may control, when the amount of generated heat production is less than or equal to the amount of heat demand, to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the amount of heat demand, control the operation of the stack load so that electrical energy produced in the cell module by the additionally supplied fuel and air is transferred to the stack load, and control the fuel cell stack so that thermal energy produced in the cell module by the additionally supplied fuel and air is transferred to an operating device of the fuel cell system requiring a heat demand.

According to various embodiments of the present disclosure, a cell module in a fuel cell stack and a cell load disposed on a surface of a fuel cell stack are connected in series, and the fuel cell stack and the stack load are connected in parallel, so as to prevent the cells and the stack from being damaged due to deterioration or the like.

In addition, it can operate the fuel cell system stably, prevent deterioration of the fuel cell stack, provide a heat source required for preheating during startup, and provide a heat source required in extreme cold weather.

The effects obtainable from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

FIG. 1 is a drawing showing the configuration of a fuel cell system according to one embodiment of the present invention.
FIG. 2 is a drawing showing a partial configuration of a fuel cell system according to one embodiment of the present invention.
FIGS. 3A and 3B are flowcharts showing a start-up purge step according to one embodiment of the present invention.
FIG. 4 is a diagram showing a flow chart of a preheating step according to one embodiment of the present invention.
FIG. 5 is a flow diagram showing a stop purge step according to one embodiment of the present invention.
FIG. 6 is a diagram showing a flow chart of a cold damage prevention step according to one embodiment of the present invention.
FIG. 7 is a diagram showing a flow chart of a heat supply increase step according to one embodiment of the present invention.

The advantages and features of the present disclosure, and the methods for achieving them, will become apparent by referring to the embodiments described in detail below together with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below, but may be implemented in various different forms, and the embodiments are provided only to make the disclosure of the present disclosure complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

When a component is referred to as being "connected to" or "coupled to" another component, it includes both the case where it is directly connected or coupled to the other component, or where there are other intervening components. On the other hand, when a component is referred to as being "directly connected to" or "directly coupled to" another component, it indicates that there are no other intervening components. "And/or" includes each and every combination of one or more of the mentioned items.

The terminology used herein is for the purpose of describing embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular includes the plural unless the context clearly dictates otherwise. The terms "comprises" and/or "comprising," as used herein, do not exclude the presence or addition of one or more other components, steps, operations, and/or elements.

Although the terms first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another.

Therefore, it should be understood that the first component mentioned below may also be the second component within the technical concept of the present disclosure. Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with a meaning that can be commonly understood by a person having ordinary knowledge in the technical field to which the present disclosure belongs. In addition, terms defined in a commonly used dictionary shall not be ideally or excessively interpreted unless explicitly specifically defined.

The term 'part' or 'module' used in this embodiment means a software or hardware component such as an FPGA or ASIC, and the 'part' or 'module' performs certain roles. However, the 'part' or 'module' is not limited to software or hardware. The 'part' or 'module' may be configured to be on an addressable storage medium and may be configured to play one or more processors. Thus, as an example, the 'part' or 'module' may include components such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functionality provided in the components and 'parts' or 'modules' may be combined into a smaller number of components and 'parts' or 'modules', or may be further separated into additional components and 'parts' or 'modules'.

The steps of a method or algorithm described in connection with some embodiments of the present disclosure may be implemented directly in hardware, a software module, or a combination of the two, executed by a processor. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an application specific integrated circuit (ASIC). The ASIC may reside in a user terminal.

FIG. 1 is a drawing schematically showing the configuration of a fuel cell system according to another embodiment of the present invention.

Referring to FIG. 1, the fuel cell system may include a cell module (103), a cell load (102), a stack module (101) including a fuel cell stack (104), a hydrogen supply cut-off valve (201), a hydrogen purge valve (202), a hydrogen circulation blower (203), an air supply blower (301), an air supply cut-off valve (302), an air exhaust cut-off valve (303), a stack load (401), a coolant circulation pump (402), a coolant heat exchanger (403), and a fuel cell control unit (not shown).

Fuel cell systems can generate electrical energy by electrochemically reacting hydrogen and oxygen.

The fuel cell stack (104) can receive fuel and air from a fuel supply unit (not shown) and an air supply unit (not shown). The fuel cell stack (104) can generate electrical energy and thermal energy by electrochemically reacting hydrogen contained in the fuel and oxygen contained in the air.

The fuel cell stack (104) can be supplied with pure hydrogen or reformed gas containing a large amount of hydrogen from a fuel supply unit (not shown). Here, the reformed gas can be generated by the reforming unit (not shown) causing a hydrocarbon fuel in a liquid or gaseous state, such as methanol, ethanol, natural gas, or LPG, to undergo an oxidation reaction with a catalyst layer.

Hydrogen or reformed gas supplied from a fuel supply unit can be supplied to a fuel cell stack (104) through a fuel line. Hydrogen or reformed gas delivered through the fuel line can be supplied, blocked, and circulated to a fuel electrode of a fuel cell stack (104) by a hydrogen supply cutoff valve (201), a hydrogen purge valve (202), a hydrogen circulation blower (203), etc.

The hydrogen supply cutoff valve (201) can selectively open and close according to a control signal from the fuel cell control unit to cut off the supply of hydrogen delivered to the fuel cell stack (104). The hydrogen supply cutoff valve (201) can control the amount of fuel delivered from the fuel supply unit and deliver it to the fuel cell stack (104).

The hydrogen purge valve (202) can be selectively opened and closed under the control of the fuel cell control unit to discharge inert gas or water that has not reacted with the fuel electrode.

The hydrogen circulation blower (203) can circulate hydrogen or reformed gas that has not reacted at the fuel electrode and supply it back to the fuel electrode. The hydrogen circulation blower (203) can circulate hydrogen or reformed gas that has not been converted to hydrogen ions through an oxidation reaction at the fuel electrode and supply it back to the fuel electrode in order to increase the efficiency of fuel use.

An air supply unit (not shown) can supply atmospheric air containing oxygen to the fuel cell stack (104) through an air line.

The air supply blower (301) can control the flow rate of air delivered through the air line and supply it to the fuel cell stack (104).

The air supply blower (301) may be equipment such as an air pump. The air supply blower (301) can apply pressure to air supplied from the air supply unit and transmit it to the fuel cell stack (104).

The air supply cutoff valve (302) can be selectively opened and closed by a control signal from the fuel cell control unit to cut off the supply of air to the fuel cell stack (104).

The air discharge blocking valve (303) can be selectively opened and closed by a control signal from the fuel cell control unit to block the discharge of air while oxygen in the air electrode reacts.

The coolant circulation pump (402) can circulate the coolant so that the coolant can exchange heat with the heat energy generated from the stack load (401) or the fuel cell stack (104). The coolant can be supplied to the stack load (401) by the coolant circulation pump (402).

The coolant can exchange heat with the heat generated from the stack load (401) so that the temperature around the stack load (401) is maintained within a predetermined temperature range. The coolant that has undergone heat exchange primarily in the stack load (401) can be supplied to the fuel cell stack (104). The coolant can undergo heat exchange secondarily in the fuel cell stack (104). The coolant that has undergone heat exchange secondarily can be delivered to the coolant heat exchanger.

The cooling water heat exchanger can adjust the temperature of the cooling water, which has been increased or decreased by heat exchange, back to within a preset temperature range. In order to maintain the cooling water within a preset constant temperature range, the cooling water heat exchanger can adjust the temperature of the heat-exchanged cooling water to within a preset temperature range and deliver it to the cooling water circulation pump (402).

That is, the coolant can primarily recover or release heat from the stack load (401), and secondarily recover or release heat from the fuel cell stack (104). As a result, the coolant temperature can be increased or decreased, and the coolant temperature can be lowered or increased so that the coolant temperature in the coolant heat exchanger is maintained within a preset temperature range.

FIG. 2 is a drawing schematically showing the configuration of a fuel cell stack (104) according to one embodiment of the present invention.

Referring to FIG. 2, the stack module (101) may include a cell module (103), a cell load (102), and a fuel cell stack (104).

The cell module (103) may be arranged such that a plurality of unit cells are stacked between the fuel electrode and the air electrode. The unit cell may generate electric energy through an electrochemical reaction using hydrogen and oxygen. Since the electric energy generated from the unit cell is approximately 1.2 [V] or less, the unit cells may be stacked in series to supply the power required for the load. The flow rates of hydrogen and oxygen supplied to each unit cell, and the reaction rates and sizes of hydrogen and oxygen may be different. Therefore, the potential value of the electric energy generated from each unit cell may be different.

The unit cell load may be connected in series to each of the plurality of unit cells. The electric energy generated from each unit cell may be transferred to the unit cell load connected in series. The potential value of the electric energy produced by each unit cell may be different, and the greater the potential value of the electric energy, the greater the electric energy transferred to the unit cell load.

A voltage sensor may be connected to each of the plurality of unit cells so that the potential value of the electric energy produced in each unit cell can be measured as a voltage. In addition, a voltage sensor for measuring the potential value of the total electric energy produced in the cell module (103) may be connected to the cell module (103). The higher the potential value of the electric energy, the higher the voltage can be measured.

Information about the voltage of each unit cell measured by the voltage sensor and the voltage of the cell module (103) can be transmitted to the fuel cell control unit. The fuel cell control unit can control the cell load (102) so that electrical energy can be transmitted between the unit cell and the unit cell load connected to each unit cell based on the information about the voltage of each unit cell and the voltage of the cell module (103). For example, a switch can be arranged between the unit cell and the unit cell load, and the fuel cell control unit can control the connection between the unit cell and the unit cell load by turning the switch on or off.

The cell load (102) includes a unit cell load and may be placed on the surface of the fuel cell stack (104). The unit cell load may be connected to each unit cell to receive electrical energy. Specifically, the unit cell load may be connected in series to each unit cell.

The unit cell load can receive electric energy from the unit cell or have the electric energy transmission blocked depending on the potential value of the electric energy produced in the unit cell. As described above, the fuel cell control unit can control the operation of the cell load (102) so that electric energy is transmitted to the unit cell load connected to the unit cell based on the voltage information of each unit cell, or control the operation of the cell load (102) so that the electric energy is blocked.

For example, as described below, the voltage of electrical energy produced in one unit cell among a plurality of unit cells may be measured, and if the measured voltage exceeds a first reference voltage for preventing high potential exposure, the electrical energy may be transferred to a unit cell load connected to the unit cell.

More specifically, for example, the reaction of hydrogen and oxygen may be greater in the first unit cell than in the second unit cell, so that the first unit cell may produce electrical energy having a higher potential than the second unit cell. The first voltage measured in the first unit cell may exceed a first reference voltage for preventing high potential exposure, and the electrical energy may be transferred to the first unit cell load connected to the first unit cell. On the other hand, the second voltage measured in the second unit cell may not exceed the first reference voltage, and the electrical energy may not be transferred to the second unit cell load connected to the second unit cell.

The cell load (102) is arranged on the surface of the fuel cell stack (104) to convert electric energy received from the unit cell into thermal energy and increase the temperature of the surface of the fuel cell stack (104). The cell load (102) can preheat during the startup phase or, when the external temperature is lower than a preset cold damage judgment temperature, such as in a cold season, to convert electric energy into thermal energy and increase the surface temperature of the fuel cell stack (104).

A fuel cell stack (104) includes a cell module (103) and can transmit electrical energy generated by electrochemical reaction of hydrogen and oxygen in the cell module (103) to a stack load (401) or a power conversion device (501).

The fuel cell stack (104) may include a fuel electrode that receives fuel from a fuel supply unit and an air electrode that receives air from an air supply unit.

The fuel cell stack (104) may have a wide structural feature in which multiple unit cells are stacked between the fuel electrode and the air electrode. Due to this structural feature of the fuel cell stack (104), a voltage imbalance may occur between the cells, such as high potential being formed in some cells. In addition, a temperature imbalance may occur between the cells. In particular, the surface of the fuel cell stack (104) in the external environment has a large temperature difference with the inside of the fuel cell stack (104), which may greatly increase the temperature imbalance of the fuel cell stack (104).

The fuel cell stack (104) includes a voltage sensor, and the voltage sensor can measure a voltage produced by the fuel cell stack (104). Information about the voltage of the fuel cell stack (104) measured by the voltage sensor can be transmitted to a fuel cell control unit. The fuel cell control unit can control the operation of the fuel cell stack (104) and the stack load (401) to transmit electric energy to the stack load (401) when the voltage of the fuel cell stack (104) exceeds a reference voltage for initiating operation of the stack load (401) based on the voltage information of the fuel cell stack (104).

The fuel cell stack (104) may include temperature sensors inside and on the surface, and the temperature sensors may measure the temperature of the fuel cell stack (104) and the surface temperature. The surface temperature of the fuel cell stack (104) and the temperature of the stack measured by the temperature sensors may be transmitted to the fuel cell control unit. The fuel cell control unit may control to additionally supply fuel and air to the fuel cell stack (104) based on the information about the surface temperature of the fuel cell stack (104) and the temperature of the stack. Fuel and air are additionally supplied to the fuel cell stack (104), so that more electrochemical reactions may occur in the cell module (103), and more electrical energy and thermal energy may be produced. The electrical energy additionally produced in the cell module (103) may be transmitted to the cell load (102), and the cell load (102) may convert the received electrical energy into thermal energy to increase the temperature of the surface of the fuel cell stack (104). In addition, the heat energy additionally produced in the cell module (103) can increase the temperature of the fuel cell stack (104). In addition, the fuel cell stack (104) can produce electric energy exceeding the limit of the electric energy that the cell load (102) can receive, and the produced electric energy can be transmitted to the stack load (401). At the same time, more heat energy can be produced, and the produced heat energy can increase the temperature of the fuel cell stack (104) more. Through this, the fuel cell stack (104) can be stably preheated in an environment such as a startup phase or a cold season, or the temperature imbalance of the fuel cell stack (104) can be reduced.

The stack load (401) can be connected to the fuel cell stack (104) and receive electric energy. The stack load (401) can include a plurality of different resistors and can be connected in parallel with the fuel cell stack (104). Depending on the resistance connected in parallel, the electric energy received from the fuel cell stack (104) can be changed. For example, by reducing or increasing the resistance of the stack load (401), the proportion of the electric energy transmitted to the stack load (401) can be increased or decreased with respect to the electric energy distributed and transmitted from the fuel cell stack (104) to the stack load (401) and the power conversion device (501).

The stack load (401) can place a switch between the fuel cell stack (104) and the resistor, and the fuel cell control unit can turn the switch on or off to transmit or block electric energy. As described above, the fuel cell control unit can control the fuel cell stack (104) and the stack load (401) to be electrically connected based on voltage information of the fuel cell stack so that electric energy can be transmitted.

The power conversion device (501) is connected to the fuel cell stack and the stack load (401) and can convert electric energy produced by the fuel cell stack (104) into electric power required by the load.

The power conversion device (501) can convert the voltage, frequency, etc. of the direct current generated from the fuel cell stack (104) so that it can be used in an electric load (motor, system, etc.).

Based on the electrical energy delivered to the power conversion device (501), the electrical energy delivered to the cell load (102) or the stack load (401) can be determined, and the flow rates of fuel and air supplied to the fuel cell stack (104) can be determined.

The fuel cell control unit can control the operation of the cell load (102) or the stack load (401) based on at least one of the voltage of the unit cell, the voltage of the cell module (103), the temperature of the fuel cell stack (104), and the surface temperature of the fuel cell stack (104).

The fuel cell control unit can control to supply or block fuel to the fuel electrode and to supply or block air to the air electrode based on the voltage of the unit cell, the voltage of the cell module (103), the temperature of the fuel cell stack (104), and the surface temperature of the fuel cell stack (104).

As described above, the fuel cell control unit can control the fuel line and the air line so that a large amount of fuel and air is supplied to the fuel cell stack (104) when the voltage of the unit cell or the voltage of the cell module (103) is low. In addition, the fuel line and the air line can be controlled so that a large amount of fuel and air is supplied to the fuel cell stack (104) when the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) are low.

On the other hand, the fuel cell control unit can control the fuel line and the air line so that the fuel and air are blocked to the fuel cell stack (104) when the voltage of the unit cell or the voltage of the cell module (103) is high. In addition, the fuel line and the air line can be controlled so that the fuel and air are blocked to the fuel cell stack (104) when the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) are high.

The fuel cell control unit can control the operation of the cell load (102) or the stack load (401) so that the electric energy produced in the cell module (103) by the supply of fuel and air is transferred to the cell load (102) or the stack load (401).

As described above, the fuel cell control unit can control the operation of the cell load so as to transfer electrical energy to the unit cell load connected to the unit cell when the voltage measured from the unit cell exceeds a preset voltage.

Additionally, the fuel cell control unit can control the operation of the cell load (102) so that electrical energy is not transferred to the unit cell load connected to the unit cell when the voltage measured from the unit cell is lower than a preset voltage.

The fuel cell control unit can control the operation of the cell load (102) or the stack load (401) based on at least one of the voltage of the unit cell, the voltage of the cell module (103), the temperature of the fuel cell stack (104), and the surface temperature of the fuel cell stack (104) in at least one of the start-up purge phase, the start-up preheat phase, the stop purge phase, the cold damage prevention phase, and the heat supply increase phase.

Below, the method by which the fuel cell control unit controls the fuel cell system according to each control step is specifically described.

1) First, the mobile purge step is explained in detail below.

FIGS. 3A and 3B are flowcharts showing a start-up purge step according to one embodiment of the present invention.

Referring to FIGS. 3a and 3b, the start-up purge step may include a fuel electrode purge step and an air electrode purge step.

In the fuel electrode purge step during the start-up purge step, first, in step S301, the fuel cell control unit controls hydrogen to be supplied and circulated through a hydrogen line to the fuel electrode of the fuel cell stack (104), and turns on the hydrogen purge valve (202) to control inert gas within the fuel electrode to be discharged.

In step S302, the fuel cell control unit can compare and determine the voltage of the plurality of unit cells with the first reference voltage that initiates the operation of the cell load (102). Specifically, residual oxygen may exist on the air electrode during the fuel purge step. Hydrogen supplied from some unit cells may react with residual oxygen to produce electric energy having a high potential. Deterioration may occur due to a potential difference with adjacent unit cells, and the unit cell may be damaged. In order to prevent such high potential exposure, when electric energy is generated above a preset reference potential, the unit cell may be protected by transmitting electric energy to the unit cell load connected to the unit cell. Therefore, the fuel cell control unit can set the first reference voltage that initiates the operation of the cell load (102) in order to prevent high potential exposure, and can compare the measured voltage of each unit cell with the preset first reference voltage to make a determination.

And, if the voltage of the plurality of unit cells is lower than or equal to the first reference voltage during the preset purge time, the fuel cell control unit can compare and determine the voltage of the plurality of unit cells with the first reference voltage by repeating step S302.

In step S303, the fuel cell control unit can control the operation of the cell load (102) to transfer electric energy to the unit cell load connected to the unit cell when the voltage of any one unit cell among the plurality of unit cells exceeds the first reference voltage. By transferring the electric energy of the unit cell exceeding the first reference voltage to the cell load (102), the potential value of the electric energy of the unit cell can be lowered and exposure to a high potential can be prevented.

In step S304, the fuel cell control unit can compare and determine the voltages of the plurality of unit cells and the second reference voltage that terminates the operation of the cell load (102). As described above, hydrogen and oxygen may react in the unit cell and oxygen may be consumed in the air electrode. In addition, the unit cell may reduce the risk of being exposed to a high potential by transmitting electrical energy to the connected unit cell load, thereby lowering the potential value. Accordingly, there is no need to transmit electrical energy from the unit cell to the unit cell load, and the operation of the cell load (102) may be controlled to cut off the electrical connection between the unit cell and the unit cell load. Accordingly, the fuel cell control unit can set the second reference voltage that terminates the operation of the cell load (102) when oxygen in the air electrode is consumed, and can determine whether the operation of the cell load (102) is terminated by comparing the measured unit cell voltage with the second reference voltage.

And, if the voltage of the plurality of unit cells is higher than the second reference voltage during the preset purge time, the fuel cell control unit can compare and determine the voltage of the plurality of unit cells with the second reference voltage by repeating step S304.

In step S305, the fuel cell control unit may control the operation of the cell load (102) so that the transmission of electric energy to the unit cell load connected to the unit cell is blocked when the voltage of any one of the plurality of unit cells is less than the second reference voltage. As described above, the fuel cell control unit may control the operation of the cell load (102) so that the transmission of electric energy to the unit cell load connected to the unit cell is blocked when the measured unit cell voltage is less than the preset second reference voltage.

In step S306, the fuel cell control unit can compare and determine the voltage of the cell module (103) and the third reference voltage that terminates the operation of the cell load (102). The fuel cell control unit can control the cell load (102) so that the operation of the cell load (102) is terminated when the voltage of the cell module (103) does not exceed the third reference voltage after the preset purge time has elapsed. Here, the third reference voltage means a reference voltage that controls the operation of the cell load (102) so that most of the oxygen in the cathode is consumed, so that no reaction of hydrogen and oxygen occurs in all the unit cells included in the cell module (103), hardly any electric energy is generated, and thus the transmission of electric energy to all the unit loads connected to all the unit cells is blocked.

If the voltage of the cell module (103) exceeds the third reference voltage, step S303 can be repeated to lower the potential value of the electric energy generated in the cell module (103).

And the fuel cell control unit can terminate the fuel electrode purge step and proceed with the air electrode purge step.

Next, in the air electrode purge step among the driving purge steps, first, in step S307, the fuel cell control unit can control air to be supplied to the air electrode of the fuel cell stack (104) through an air line. Then, the fuel cell control unit can control inert gas in the air electrode to be discharged through the air discharge blocking valve (303).

In step S308, the fuel cell control unit can compare and determine the voltage of the plurality of unit cells and the fourth reference voltage that initiates the operation of the cell load (102). In the initial stage of the air electrode purge, the air delivered through the air electrode can react quickly with hydrogen in the unit cell adjacent to the air electrode due to the structure of the cell module (103), but can react slowly with hydrogen in the unit cell located in the opposite direction to the air electrode. In addition, the density of air in the unit cell adjacent to the air electrode can be higher than the density of air in the unit cell located in the opposite direction to the air electrode. Therefore, among the plurality of unit cells of the cell module (103), hydrogen and oxygen can react first in the unit cell adjacent to the air electrode and produce electric energy having a high potential. In order to prevent exposure to such a high potential, electric energy can be transmitted to the unit cell load (102) connected to the unit cell. Therefore, the fuel cell control unit can set the fourth reference voltage to prevent exposure to the high potential, and can determine by comparing the measured voltage of each unit cell with the preset fourth reference voltage. Here, the fourth reference voltage may have the same value as the first reference voltage described above or may have a different value.

In step S309, the fuel cell control unit can control the operation of the cell load (102) to transfer electric energy to the unit cell load connected to the unit cell when the voltage of any one of the plurality of unit cells exceeds the fourth reference voltage. As described above, by transferring electric energy to the unit cell load connected to the unit cell adjacent to the air electrode, the potential value can be lowered and the risk of exposure to a high potential can be reduced.

And, the fuel cell control unit can compare and determine the voltage of a plurality of unit cells and the fourth reference voltage that initiates the operation of the cell load (102) by repeating step S308 while sufficient air is supplied to the unit cells located in the opposite direction to the air electrode.

In step S310, the fuel cell control unit can compare and determine the voltage of the cell module (103) with the fifth reference voltage that initiates the operation of the stack load (401). In step S309, when the cell load (102) is operated by receiving electric energy from all unit cells of the cell module (103) to all unit cell loads, the fuel cell control unit can set the fifth reference voltage that initiates the operation of the stack load (401) so that the electric energy produced in the cell module (103) can be transmitted to the stack load (401). The fuel cell control unit can compare the measured voltage of the cell module (103) with the preset fifth reference voltage.

In step S311, the fuel cell control unit can control the operation of the stack load (401) so that electric energy is transferred from the fuel cell stack (104) to the stack load (401) when the voltage of the cell module (103) exceeds the fifth reference voltage.

In step S312, the fuel cell control unit can compare the current flowing in the stack load (401) with the preset maximum current of the stack load (401) by transferring electric energy to the stack load (401). If the current flowing in the stack load (401) is less than the maximum current, the fuel cell control unit can control the stack load (401) to receive electric energy from the fuel cell stack (104) and to flow current greater than the maximum current. If the current flowing in the stack load (401) is greater than the maximum current, the fuel cell control unit can control to end the air electrode purge phase. In other words, the entire start-up purge phase can be ended.

2) Next, the start-up warm-up phase is described in detail below.

FIG. 4 is a diagram showing a flow chart of a preheating step according to one embodiment of the present invention.

Referring to FIG. 4, first, in step S401, the fuel cell control unit can compare the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) with a preset allowable temperature difference.

In step S402, if the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) exceeds a preset allowable temperature difference, the fuel cell control unit can control to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preset allowable temperature difference.

In order to increase the reactivity of hydrogen and oxygen in the power generation stage, sufficient preheating of the fuel cell stack (104) may be required in the starting stage prior to the power generation stage. As described below, additionally supplied fuel and air can promote hydrogen and oxygen reactions in the fuel cell stack (104) to produce electrical energy and thermal energy, and the electrical energy and thermal energy can increase the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104), thereby increasing the reactivity of hydrogen and oxygen in the power generation stage.

In step S403, the fuel cell control unit can control the operation of the cell load (102) so that the electric energy produced in the cell module (103) by the additionally supplied fuel and air is transferred to the cell load (102).

The cell load (102) can convert the received electric energy into heat energy to increase the surface temperature of the fuel cell stack (104). Specifically, the cell load (102) can be located on the surface of the stack. The cell load (102) can receive electric energy from the cell and generate heat. The heat generated from the cell load (102) can be transferred to the stack surface, and the temperature of the stack surface can be increased by the heat transferred from the cell load (102). That is, the temperature of the stack surface can be increased through the arrangement structure of the cell load (102), and this can reduce the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) to within a preset allowable temperature difference.

In step S404, the fuel cell control unit can control the operation of the cell load (102) so that electric energy is not transmitted to the cell load (102) if the temperature difference is less than or equal to a preset allowable temperature difference.

In step S405, the fuel cell control unit can control to block the supply of fuel to the fuel electrode and block the supply of air to the air electrode.

In step S406, the fuel cell control unit can compare and determine the temperature of the fuel cell stack (104) with a preset preheating completion determination temperature.

In step S407, the fuel cell control unit can control the operation of the stack load (401) so that electric energy is not transferred from the fuel cell stack (104) to the stack load (401) when the temperature of the fuel cell stack (104) exceeds the preheating completion determination temperature.

In step S408, if the temperature of the fuel cell stack (104) is lower than or equal to the preheating completion determination temperature, the fuel cell control unit can control to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preheating completion determination temperature.

In step S409, the fuel cell control unit can control the operation of the stack load (401) so that the electric energy produced in the cell module (103) by the additionally supplied fuel and air is transferred to the stack load (401). The cell module (103) can increase the temperature of the fuel cell stack (104) by using the thermal energy produced by the electrochemical reaction of the additionally supplied fuel and air.

The stack load (401) is electrically connected to the fuel cell stack (104) and can receive electric energy produced by the fuel cell stack (104). The fuel cell stack (104) may generate heat energy in the process of producing electric energy and supplying the produced electric energy to the stack load (401), thereby increasing the temperature of the stack. The more electric energy the stack load (401) receives, that is, the more electric energy the stack produces, the more heat energy is generated in the fuel cell stack (104). Accordingly, the more electric energy the stack load (401) receives from the fuel cell stack (104), the more the temperature of the fuel cell stack (104) may increase.

The stack load (401) is arranged between the fuel cell stack (104) and the load stage and can consume the electric energy produced in the stack and delivered to the load stage. Since the stack load (401) consumes the electric energy required for the load stage in the middle, the fuel cell stack (104) needs to additionally produce the electric energy consumed by the stack load (401). Therefore, the fuel cell control unit controls to additionally supply fuel and air to the fuel cell stack (104), and the fuel cell stack (104) can produce electric energy and thermal energy by the additionally supplied fuel and air. The thermal energy produced in the fuel cell stack (104) can increase the temperature of the fuel cell stack (104).

The fuel cell control unit can prepare for the power generation stage by controlling the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) to sufficiently increase during the start-up preheating stage.

3) Next, the stop purge step is described in detail below.

FIG. 5 is a flow diagram showing a stop purge step according to one embodiment of the present invention.

Referring to FIG. 5, in the stop purge step, first, in step S501, the fuel cell control unit can control the operation of the cell load (102) and the stack load (401) so that electric energy is transferred to the cell load (102) and the stack load (401) before the end of power generation.

In step S502, power generation of the fuel cell system can be terminated.

In step S503, the fuel cell control unit may control the hydrogen purge valve (202) and the air discharge cutoff valve (303) to discharge water inside the fuel electrode and the air electrode after power generation is terminated. Water inside the fuel electrode and the air electrode may cause corrosion of the cell module (103) and deterioration of the fuel cell stack (104) in the next power generation stage. Therefore, purge is performed to discharge water inside the fuel electrode and the air electrode after power generation is terminated. Purge of the fuel electrode and the air electrode may be performed with reference to the startup purge step described above in step S503.

In step S504, the fuel cell control unit can compare the voltage of the fuel cell stack (104) with a preset purge completion determination voltage to make a determination. In the process of purging the fuel electrode and the air electrode, electric energy can be produced in the fuel cell stack (104), and the fuel cell control unit can set the purge completion determination voltage to a voltage low enough that the fuel cell stack (104) is not damaged even if the electric energy is consumed inside the fuel cell stack (104) without transmitting it to the stack load (401).

In step S505, the fuel cell control unit can control the operation of the stack load (401) to block the electric energy transmitted from the fuel cell stack (104) to the stack load (401) when the voltage of the fuel cell stack (104) is lower than the purge completion judgment voltage. In addition, the fuel cell control unit can control the air line to block the supply of air to the cathode. In a state where the supply of air to the cathode is blocked, the oxygen in the air remaining in the cathode can be consumed by the reaction of hydrogen and oxygen in the cell module (103).

In step S506, the fuel cell control unit can compare the voltage of a unit cell having the lowest voltage among the voltages of a plurality of unit cells with a sixth reference voltage for cutting off a preset fuel.

As described above, when the air supply is cut off and the oxygen in the air electrode is consumed, the reaction rate of hydrogen and oxygen in the plurality of unit cells decreases, and electric energy with a low potential can be produced. When most of the oxygen in the air electrode is consumed, the fuel cell control unit can measure the voltage of the unit cell producing electric energy with the lowest potential value among the plurality of unit cells and compare it with a sixth reference voltage for cutting off the fuel supply to the preset fuel electrode.

In step S507, the fuel cell control unit can control to cut off the fuel supply to the fuel electrode when the voltage of the unit cell having the lowest voltage is lower than the sixth reference voltage. In a state where the fuel supply to the fuel electrode is cut off, the hydrogen remaining in the fuel electrode can be consumed by the reaction of hydrogen and oxygen in the cell module (103).

In step S508, the fuel cell control unit can compare and determine the voltage of the plurality of unit cells with the seventh reference voltage for determining the end of the cell load (102).

In step S509, the fuel cell control unit can control the operation of the cell load (102) so that the transmission of electric energy to the unit cell load connected to the unit cell is blocked when the voltage of any one unit cell among the plurality of unit cells is lower than the seventh reference voltage.

As described above, when the hydrogen in the fuel electrode is consumed while the fuel supply is cut off, the reaction rate of hydrogen and oxygen in the plurality of unit cells decreases, and electric energy having a low potential may be produced. The fuel cell control unit may control the operation of the cell load (102) so that the electric energy is cut off to the unit cell load sequentially connected to the unit cell when the voltage of the plurality of measured unit cells is lower than the seventh reference voltage for determining the end of the preset cell load (102).

In step S510, the fuel cell control unit can compare and determine the voltage of the cell module (103) and the eighth reference voltage that terminates the operation of the cell load (102). Here, the eighth reference voltage means a reference voltage that controls the operation of the cell load (102) so that most of the fuel electrode hydrogen is consumed, so that no reaction of hydrogen and oxygen occurs in all the unit cells included in the cell module (103), hardly any electrical energy is generated, and thus the transmission of electrical energy to all the unit loads connected to all the unit cells is blocked.

In step S511, the fuel cell control unit can control the operation of the cell load (102) to be terminated when the voltage of the cell module (103) is lower than the eighth reference voltage.

In step S512, the fuel cell control unit can control the hydrogen purge valve (202) to turn on so that hydrogen in the fuel electrode is discharged.

4) Next, the cold damage prevention step is explained in detail below.

FIG. 6 is a diagram showing a flow chart of a cold damage prevention step according to one embodiment of the present invention.

Referring to FIG. 6, in the cold damage prevention step, first, in step S601, the fuel cell control unit can compare and determine the external temperature and the preset cold damage protection judgment temperature. If the fuel cell system generates power in a state where the external temperature is very low, such as in a very cold season, it may be difficult to produce the electric energy required by the load, and the fuel cell stack (104) may be damaged during the power generation process. Therefore, the fuel cell control unit can set the judgment temperature that can protect the fuel cell stack (104) from cold damage.

In step S602, the fuel cell control unit can compare the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) with a preset allowable temperature difference when the external temperature is lower than the cold damage protection judgment temperature.

In step S603, if the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) exceeds a preset allowable temperature difference, the fuel cell control unit can control to supply fuel to the fuel electrode and additionally supply air to the air electrode based on the preset allowable temperature difference.

The temperature of the surface of the fuel cell stack (104) may be lowered due to the external temperature. The fuel cell stack (104) may be damaged due to the temperature difference between the inside and the outside of the fuel cell stack (104). Therefore, there is a need to reduce the temperature difference between the inside and the outside of the fuel cell stack (104). As described below, additionally supplied fuel and air can promote hydrogen and oxygen reactions in the fuel cell stack (104) to produce electrical energy and thermal energy, and the electrical energy and thermal energy can increase the surface temperature of the fuel cell stack (104).

In step S604, the fuel cell control unit can control the operation of the cell load (102) so that the electric energy produced in the cell module (103) by the additionally supplied fuel and air is transferred to the cell load (102).

The cell load (102) can convert the transferred electric energy into heat energy to increase the surface temperature of the fuel cell stack (104). As described above, the cell load (102) can be located on the surface of the stack. The cell load (102) can receive electric energy from the cell and generate heat. The heat generated from the cell load (102) can be transferred to the stack surface, and the stack surface can have a high temperature due to the heat transferred from the cell load (102). That is, the temperature of the stack surface can be increased through the arrangement structure of the cell load (102), and this can reduce the difference between the temperature of the fuel cell stack (104) and the surface temperature of the fuel cell stack (104) to within a preset allowable temperature difference.

In step S605, the fuel cell control unit can control the operation of the cell load (102) so that electric energy is not transmitted to the cell load (102) if the temperature difference is less than or equal to a preset allowable temperature difference.

In step S606, the fuel cell control unit can control to block the supply of fuel to the fuel electrode and block the supply of air to the air electrode.

The fuel cell control unit can compare and determine the external temperature with the preset cold damage protection judgment temperature by repeating step S601 after transmitting electric energy to the cell load (102) or cutting off the fuel and air supply.

5) Next, the step of increasing the heat supply is described in detail below.

FIG. 7 is a diagram showing a flow chart of a heat supply increase step according to one embodiment of the present invention.

Referring to FIG. 7, in the step of increasing the heat supply, first, in step S701, the fuel cell control unit can compare and determine the amount of heat generation produced by the fuel cell stack (104) with the amount of heat demand.

A large amount of heat may be required in the process of producing electrical energy in a fuel cell system. For example, heat demand may be required in an endothermic reaction, such as producing hydrogen reforming gas from fuel, producing a catalyst material, or increasing the temperature of a coolant. Hydrogen and oxygen react within the fuel cell stack (104) to produce electrical energy and thermal energy, and the thermal energy produced may be used to supply the aforementioned heat demand.

The fuel cell control unit can compare and determine the amount of heat generated by the fuel cell stack (104) with the amount of heat demand required by the balance of plant (BOP) of the fuel cell system. Here, the balance of plant (BOP) means all devices included in the fuel cell system.

In step S702, the fuel cell control unit can control the operation of the stack load (401) so that electrical energy is not transferred from the fuel cell stack (104) to the stack load (401) when the amount of generated heat production exceeds the amount of heat demand. When electrical energy is transferred to the stack load (401), the positive reaction of hydrogen and oxygen in the fuel cell stack (104) increases, so that electrical energy can be produced as much as is transferred to the stack load (401). Since thermal energy is produced together with electrical energy, the fuel cell control unit controls the operation of the stack load (401) so that additional thermal energy is not produced.

In step S703, the fuel cell control unit can control to cut off the fuel supply to the fuel electrode and to cut off the air supply to the air electrode. This is to prevent the fuel cell control unit from producing additional heat energy.

In step S704, the fuel cell control unit can control to supply additional fuel to the fuel electrode and additionally supply air to the air electrode based on the heat demand.

In step S705, the fuel cell control unit can control the operation of the stack load (401) so that the electric energy produced in the cell module (103) by the additionally supplied fuel and air is transferred to the stack load (401).

The fuel cell control unit can control the fuel cell stack (104) so that the heat energy produced in the cell module (103) by the additionally supplied fuel and air is transferred to the driving device of the fuel cell system requiring heat demand.

The fuel cell system and its control method according to one embodiment of the present invention described above can stably operate the fuel cell system by using the cell load (102) and the stack load (401). In addition, it can provide a heat source necessary for preventing deterioration of the fuel cell stack (104), preheating during startup, and a heat source necessary in extremely cold weather.

It should be understood that the various embodiments of this posting and the terminology used herein are not intended to limit the technical features described in this posting to specific embodiments, but rather to encompass various modifications, equivalents, or substitutes of the embodiments.

Claims (18)

A cell module in which a plurality of unit cells are stacked and arranged between a fuel electrode and an air electrode;
A fuel cell stack comprising the above cell modules;
A cell load including a plurality of unit cell loads and arranged on the surface of the fuel cell stack, the unit cell load being connected to each of the plurality of unit cells to transmit electric energy;
A stack load connected to the above fuel cell stack and receiving electric energy;
A power conversion device connected to the fuel cell stack and the stack load and converting electric energy produced by the fuel cell stack into electric power required by the load; and
A fuel cell control unit that controls the operation of the cell load or the stack load based on at least one of the voltage of the unit cell, the voltage of the cell module, the temperature of the fuel cell stack, and the surface temperature of the fuel cell stack;
Fuel cell system.
In the first paragraph,
The above cell load is,
When the above unit cell and the above unit cell load are each connected in series and the voltage of the unit cell exceeds a preset voltage, electric energy is transferred to the unit cell load, and
The above stack load is,
A fuel cell stack is connected in parallel with a plurality of different resistors, and the electric energy transmitted from the fuel cell stack is changed according to the resistance connected in parallel.
Fuel cell system.
In the first paragraph,
The above fuel cell control unit,
Controlling to supply or cut off fuel to the fuel electrode and to supply or cut off air to the air electrode based on at least one of the voltage of the unit cell, the voltage of the cell module, the temperature of the fuel cell stack, and the surface temperature of the fuel cell stack, and
Controlling the operation of the cell load or stack load so that the electric energy produced in the cell module by the supply of the fuel and air is transmitted to the cell load or stack load.
Fuel cell system.
In the first paragraph,
The above fuel cell control unit,
Controlling the operation of the cell load or the stack load based on at least one of the voltage of the unit cell, the voltage of the cell module, the temperature of the fuel cell stack, and the surface temperature of the fuel cell stack in at least one of the startup purge step, the startup warm-up step, the stop purge step, the cold damage prevention step, and the heat supply amount increase step.
Fuel cell system.
In the fourth paragraph,
The above-mentioned purge step includes a fuel electrode purge step and an air electrode purge step,
In the above fuel electrode purge step, the fuel cell control unit,
Controlling the supply and circulation of hydrogen through a hydrogen line to the fuel electrode of the fuel cell stack, and controlling the discharge of inert gas within the fuel electrode by turning on the hydrogen purge valve,
Comparing and judging the voltage of the plurality of unit cells and the first reference voltage that initiates the operation of the cell load, and controlling the operation of the cell load to transfer electric energy to the unit cell load connected to the unit cell when the voltage of any one unit cell among the plurality of unit cells exceeds the first reference voltage,
Comparing and judging the voltage of the plurality of unit cells and the second reference voltage that terminates the operation of the cell load, and controlling the operation of the cell load so that the transmission of electric energy to the unit cell load connected to the unit cell is blocked when the voltage of any one unit cell among the plurality of unit cells is less than the second reference voltage, and
By comparing and judging the voltage of the cell module and the third reference voltage that terminates the operation of the cell load, the cell load is controlled so that the operation of the cell load is terminated when the voltage of the cell module does not exceed the third reference voltage, and the start-up purge step is controlled to be terminated.
Fuel cell system.
In clause 5,
In the above air electrode purge step, the fuel cell control unit,
Controlling so that air is supplied to the air electrode of the above fuel cell stack through an air line, and controlling so that inert gas within the air electrode is discharged through an air discharge blocking valve,
By comparing and judging the voltage of the plurality of unit cells and the fourth reference voltage that initiates the operation of the cell load, if the voltage of any one unit cell among the plurality of unit cells exceeds the fourth reference voltage, the operation of the cell load is controlled to transfer electric energy to the unit cell load connected to the unit cell.
By comparing and judging the voltage of the cell module and the fifth reference voltage that initiates the operation of the stack load, if the voltage of the cell module exceeds the fifth reference voltage, the operation of the stack load is controlled so that electric energy is transferred from the fuel cell stack to the stack load, and,
The electrical energy is transferred to the stack load, and the current flowing through the stack load is compared with the maximum current of the preset stack load, and the air electrode purge step is controlled to be terminated when the current flowing through the stack load is greater than the maximum current.
Fuel cell system.
In clause 5,
The above fuel cell control unit,
Comparing and determining the voltage of the plurality of unit cells with the first reference voltage and the second reference voltage repeatedly for a preset fuel purge time.
Fuel cell system.
In Article 6,
The above fuel cell control unit,
When the current flowing through the stack load is less than the maximum current, the stack load is controlled so that electric energy is transferred from the fuel cell stack and the current flows more than the maximum current.
Fuel cell system.
In the fourth paragraph,
In the above mentioned preheating step, the fuel cell control unit,
The difference between the temperature of the fuel cell stack and the surface temperature of the fuel cell stack is compared with the preset allowable temperature difference, and
If the temperature difference exceeds the preset allowable temperature difference, the fuel is supplied to the fuel electrode and additional air is supplied to the air electrode based on the preset allowable temperature difference, and the operation of the cell load is controlled so that the electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the cell load, and
The above cell load is,
Converting the transmitted electrical energy into thermal energy to increase the surface temperature of the fuel cell stack.
Fuel cell system.
In Article 9,
The above fuel cell control unit,
If the above temperature difference is less than or equal to the preset allowable temperature difference, the operation of the cell load is controlled so that electric energy is not transmitted to the cell load, and
Controlling to block the supply of fuel to the above fuel electrode and to block the supply of air to the above air electrode,
Fuel cell system.
In Article 9,
The above fuel cell control unit,
Compare and determine the temperature of the above fuel cell stack with the preset preheating completion judgment temperature,
If the temperature of the fuel cell stack exceeds the preheating completion determination temperature, the operation of the stack load is controlled so that electric energy is not transmitted from the fuel cell stack to the stack load.
Fuel cell system.
In Article 11,
The above fuel cell control unit,
If the temperature of the fuel cell stack is lower than or equal to the preheating completion judgment temperature,
Based on the above preheating completion determination temperature, control is provided to supply fuel to the fuel electrode and additionally supply air to the air electrode, and the operation of the stack load is controlled so that the electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the stack load.
The above cell module,
The temperature of the fuel cell stack is increased by using the heat energy produced by the electrochemical reaction of the additionally supplied fuel and air.
Fuel cell system.
In the fourth paragraph,
In the above stop purge step, the fuel cell control unit,
After the power generation is completed, the hydrogen purge valve and the air discharge cutoff valve are controlled to discharge water inside the fuel electrode and air electrode.
Comparing the voltage of the fuel cell stack with a preset purge completion judgment voltage and determining, and controlling the operation of the stack load to block electric energy transmitted from the fuel cell stack to the stack load when the voltage of the fuel cell stack is lower than the purge completion judgment voltage, and
Controlling the air line to block the supply of air into the above air electrode,
Fuel cell system.
In Article 13,
The fuel cell control unit is
By comparing the voltage of the unit cell having the lowest voltage among the voltages of the plurality of unit cells with the sixth reference voltage for blocking the preset fuel, if the voltage of the unit cell having the lowest voltage is lower than the sixth reference voltage, the fuel supply to the fuel electrode is controlled to be blocked.
By comparing the voltages of the plurality of unit cells with the seventh reference voltage for determining the end of the cell load, if the voltage of any one unit cell among the plurality of unit cells is lower than the seventh reference voltage, the operation of the cell load is controlled so that the transmission of electric energy to the unit cell load connected to the unit cell is blocked, and
By comparing the voltage of the cell module with the eighth reference voltage that terminates the operation of the cell load, if the voltage of the cell module is lower than the eighth reference voltage, the operation of the cell load is terminated, and the hydrogen purge valve is turned on to control the hydrogen of the fuel electrode to be discharged.
Fuel cell system.
In the fourth paragraph,
In the above cold damage prevention step, the fuel cell control unit,
By comparing the external temperature with the preset cold damage protection judgment temperature, if the external temperature is lower than the cold damage protection judgment temperature, the difference between the temperature of the fuel cell stack and the surface temperature of the fuel cell stack is compared with the preset allowable temperature difference.
If the above temperature difference exceeds the preset allowable temperature difference, the fuel is supplied to the fuel electrode and additional air is supplied to the air electrode based on the preset allowable temperature difference, and the operation of the cell load is controlled so that the electric energy produced in the cell module by the additionally supplied fuel and air is transmitted to the cell load, and
The above cell load is,
Converting the transmitted electrical energy into thermal energy to increase the surface temperature of the fuel cell stack.
Fuel cell system.
In Article 15,
The above fuel cell control unit,
If the above temperature difference is less than or equal to the preset allowable temperature difference, the operation of the cell load is controlled so that electrical energy is not transmitted to the cell load, and
Controlling to block the supply of fuel to the above fuel electrode and to block the supply of air to the above air electrode,
Fuel cell system.
In the fourth paragraph,
In the step of increasing the heat supply, the fuel cell control unit,
Compare and judge the amount of power generation heat produced by the fuel cell stack and the amount of heat demand,
Controlling the operation of the stack load so that electrical energy is not transferred from the fuel cell stack to the stack load when the generated heat production exceeds the heat demand;
Controlling to cut off the fuel supply to the above fuel electrode and to cut off the air supply to the air electrode,
Fuel cell system.
In Article 17,
The above fuel cell control unit,
When the heat production is less than the heat demand,
Based on the above heat demand, control is provided to supply fuel to the fuel electrode and additionally supply air to the air electrode,
Controlling the operation of the stack load so that the electrical energy produced in the cell module by the additionally supplied fuel and air is transmitted to the stack load, and,
Controlling the fuel cell stack so that the heat energy produced in the cell module by the additionally supplied fuel and air is transmitted to the driving device of the fuel cell system requiring heat demand.
Fuel cell system.