Fuel cell system

Abstract

The invention provides a fuel cell system capable of improving startability at a freezing point. The fuel cell system is provided with a fuel cell stack having a plurality of stacked unit cells, a cooling water pump for circulating cooling water for cooling the fuel cell stack, a temperature sensor for measuring the temperature of outside air at the time of startup of the fuel cell system, and a control device for controlling the temperature sensor to measure the temperature of the outside air at the time of startup of the fuel cell system. The control device determines the degree of deterioration of the plurality of unit cells, and when the fuel cell system is started at the freezing point, the control device determines the time for stopping the cooling water pump on the basis of the degree of deterioration of the plurality of unit cells.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system. Background Art

[0002] Regarding fuel cells (FCs) such as those disclosed in Patent Document 1, various techniques have been proposed.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-033975

[0004] As a method for improving startability when starting at the freezing point of a fuel cell system, there is cooling water stop control. If the cooling water stop time is too long, the catalyst and the like deteriorate due to abnormal heating of the fuel cell. If the cooling water stop time is too short, the effect of improving the startability of the fuel cell system cannot be obtained, and there is a possibility that the fuel cell system cannot be started. Therefore, it is necessary to appropriately determine the cooling water stop time. On the other hand, in the case of industrial application of fuel cells, as the total usage time of the fuel cell becomes longer, the catalyst layer deteriorates, and the startability of the fuel cell system at the freezing point gradually decreases. Therefore, when determining the cooling water stop time, it is necessary to consider the degree of deterioration of the fuel cell.

[0005] Patent Document 1 discloses a fuel cell system configured to stop a coolant pump for a predetermined time if a temperature sensor value is below a predetermined temperature when starting at the freezing point, thereby preventing water generated inside the fuel cell from freezing. If the stop time of the coolant pump is determined only considering the performance at the time of manufacturing the fuel cell system, the stop time cannot be applied after the fuel cell system has deteriorated due to durability. In addition, if the stop time is determined considering the durability deterioration of the fuel cell system and the stop time is applied at the initial start after manufacturing the fuel cell system, the fuel cell may overheat. Summary of the Invention

[0006] The present disclosure has been made in view of the above actual situation, and its main object is to provide a fuel cell system capable of improving startability at the freezing point.

[0007] That is, the present disclosure includes the following aspects.

[0008] <1> A fuel cell system, wherein

[0009] the fuel cell system includes a fuel cell stack, a coolant pump, a temperature sensor, and a control device,

[0010] the fuel cell stack has a plurality of stacked single cells,

[0011] the coolant pump circulates cooling water for cooling the fuel cell stack,

[0012] The above temperature sensor measures the external air temperature at the start of the above fuel cell system.

[0013] The above control device determines the degree of deterioration of the above multiple single cells.

[0014] When starting below the freezing point of the above fuel cell system, the above control device determines the time to stop the above cooling water pump according to the degree of deterioration of the above multiple single cells.

[0015] <2> According to the fuel cell system described in <1>, wherein

[0016] The above control device infers the water content of the above multiple single cells when the operation of the above fuel cell stack stops.

[0017] When the time to stop the above cooling water pump determined by the above control device exceeds the specified time corresponding to the above water content, the above control device performs scavenging when the operation of the above fuel cell stack stops, so that the inferred water content of the above multiple single cells is less than the specified water content.

[0018] The above specified time is the stop time of the above cooling water pump when the above fuel cell stack becomes abnormally overheated.

[0019] The fuel cell system of the present disclosure can improve the startability below the freezing point. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a system configuration diagram showing an example of the fuel cell system of the present disclosure.

[0021] Figure 2 It is a graph showing the relationship between the number of single cells deteriorated below a specified voltage and the allowable generated water amount.

[0022] Figure 3 It is a flowchart showing an example of the control of the fuel cell system of the present disclosure.

[0023] DESCRIPTION OF REFERENCE NUMERALS

[0024] 10... fuel cell stack; 50... cooling system; 51... cooling water pump; 52... radiator; 53... rotary valve; 60... control device; 70... oxidant gas system; 71... air compressor; 80... fuel gas system; 81... injector; 82... fuel gas pump; 83... gas-liquid separator; 84... exhaust and drain valve; P... pressure sensor; T... temperature sensor. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present disclosure will be described. In addition, matters required for the implementation of the present disclosure other than those specifically mentioned in this specification (for example, the general structure and manufacturing process of a fuel cell system that do not give features to the present disclosure) can be understood as design matters of those skilled in the art based on the prior art in this field. The present disclosure can be implemented based on the content disclosed in this specification and common general knowledge in this field.

[0026] In addition, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0027] In the present disclosure, the gas supplied to the anode of the fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas mainly containing hydrogen, and may also be hydrogen. The oxidant gas is a gas containing oxygen, and may also be oxygen, air, etc.

[0028] In the present disclosure, a fuel cell system is provided, wherein

[0029] The above fuel cell system includes a fuel cell stack, a cooling water pump, a temperature sensor, and a control device.

[0030] The above fuel cell stack has a plurality of stacked single cells.

[0031] The above cooling water pump circulates the cooling water for cooling the fuel cell stack.

[0032] The above temperature sensor measures the external air temperature when the fuel cell system is started.

[0033] The above control device determines the degree of deterioration of the above plurality of single cells.

[0034] When starting below the freezing point of the above fuel cell system, the above control device determines the time to stop the above cooling water pump according to the degree of deterioration of the above plurality of single cells.

[0035] In the present disclosure, according to the deterioration of the fuel cell (the number of single cells whose voltage drops below a specified value), the time to stop the cooling water pump (the standard of the cumulative heat generation amount of the fuel cell) is changed.

[0036] In the present disclosure, when the time to stop the cooling water pump (the standard of the cumulative heat generation amount of the fuel cell) is long enough to reach the standard of overheating of the single cell, the scavenging (drainage to the outside of the fuel cell system) level at the stop of the operation of the fuel cell stack is strengthened to reduce the water content of the plurality of single cells at the start of the fuel cell system.

[0037] Thus, since the cooling water is not stopped unnecessarily, deterioration of the electrolyte membrane, catalyst, etc. caused by abnormal overheating of the fuel cell and deterioration of the separator caused by thermal strain generated when supplying cooling water from a state where the cooling water is stopped can be suppressed to a minimum, and starting performance below the freezing point can be ensured regardless of the degree of deterioration of the single cell. In the case of an industrially applied fuel cell, the durability input based on the stop of the cooling water can also be suppressed to a minimum, and starting performance below the freezing point can also be ensured after the durability of the fuel cell.

[0038] Even in a state where the deterioration of the single cell has progressed and the cooling water stop time has reached the abnormal overheating threshold of the fuel cell, abnormal overheating will not occur, and starting performance below the freezing point of the fuel cell system can be ensured.

[0039] Even in a state where the deterioration of the single cell has progressed in an industrially applied fuel cell, the fuel cell will not overheat abnormally, and starting performance below the freezing point of the fuel cell system can also be ensured after the durability of the fuel cell.

[0040] Figure 1 It is a system configuration diagram showing an example of the fuel cell system of the present disclosure.

[0041] Figure 1 The shown fuel cell system includes a fuel cell stack 10, a cooling system 50, a temperature sensor T, a control device 60, an oxidant gas system 70, and a fuel gas system 80. The cooling system 50 includes a cooling water pump 51, a radiator 52, a rotary valve 53, etc. The oxidant gas system 70 includes an air compressor 71, a pressure sensor P, a temperature sensor T, etc. The fuel gas system 80 includes an injector 81, a fuel gas pump 82, a gas-liquid separator 83, an exhaust drain valve 84, a pressure sensor P, etc.

[0042] The fuel cell system of the present disclosure can also be used by being mounted on a moving body such as a vehicle. In addition, the fuel cell system of the present disclosure can also be used by being mounted on a stationary power generation system such as a generator that supplies power to the outside of the fuel cell system.

[0043] The vehicle can also be a fuel cell vehicle or the like. As a moving body other than a vehicle, for example, a train, a ship, an airplane, etc. can be cited.

[0044] In addition, the fuel cell system of the present disclosure can also be used by being mounted on a moving body such as a vehicle that can also travel by the power of a secondary battery.

[0045] The moving body and the stationary power generation system can also include the fuel cell system of the present disclosure.

[0046] The moving body can also have drive units such as a motor, an inverter, and a hybrid control system.

[0047] A system for hybrid control can also use the output of a fuel cell and the power of a secondary battery together to drive a moving body.

[0048] A fuel cell system includes a fuel cell in which hydrogen and oxygen react to generate electricity, a fuel gas system that supplies a fuel gas containing hydrogen required for the power generation of the fuel cell to the fuel cell, an oxidant gas system that supplies an oxidant gas containing oxygen to the fuel cell, and a cooling system that supplies cooling water for cooling the heat generated by power generation to the fuel cell, etc.

[0049] The fuel cell system includes a fuel cell stack.

[0050] A fuel cell stack (battery stack) is a laminate formed by laminating a plurality of single fuel cells (monolithic cells).

[0051] In the present disclosure, there are cases where both a single cell and a fuel cell stack are referred to as a fuel cell.

[0052] The number of single cells laminated in the fuel cell stack is not particularly limited. For example, it can be 2 to several hundreds.

[0053] The fuel cell stack may also have a current collector plate, a pressure plate, etc. at the ends in the lamination direction.

[0054] The single cell may also have a power generation part.

[0055] The shape of the power generation part may be rectangular in a top view.

[0056] The power generation part may also be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes.

[0057] The electrolyte membrane may also be a solid polymer electrolyte membrane. As the solid polymer electrolyte membrane, for example, fluorine-based electrolyte membranes such as thin films containing perfluorosulfonic acid with water, and hydrocarbon-based electrolyte membranes, etc. can be cited. As the electrolyte membrane, for example, Nafion membrane (manufactured by DuPont) etc. can also be used.

[0058] One of the two electrodes is an anode (fuel electrode), and the other is a cathode (oxidant electrode).

[0059] The electrode includes a catalyst layer, and may also include a gas diffusion layer as needed. The power generation part may also be a membrane electrode gas diffusion layer assembly (MEGA).

[0060] It can also be configured such that the catalyst layer contains a catalyst, and the catalyst includes a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity, etc.

[0061] As the catalyst metal, for example, platinum (Pt), an alloy composed of Pt and other metals (for example, a Pt alloy mixed with cobalt, nickel, etc.) can be used. The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst can be the same or different.

[0062] As the electrolyte, a fluororesin or the like can also be used. As the fluororesin, for example, a Nafion solution or the like can be used.

[0063] The above-mentioned catalyst metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supported carrier) and the electrolyte may be mixed and present.

[0064] Examples of the carrier for supporting the catalyst metal include carbon materials such as carbon commercially available on the market.

[0065] The gas diffusion layer can also be a conductive member having pores.

[0066] Examples of the conductive member include carbon porous bodies such as carbon cloth and carbon paper, and metal porous members such as metal mesh and foamed metal.

[0067] The single cell of the fuel cell includes a separator.

[0068] The separator collects the current generated by power generation and functions as a partition wall. The separator is usually disposed on both sides in the stacking direction of the power generation unit in such a manner that a pair of separators sandwich the power generation unit. One of the pair of separators is the anode separator, and the other is the cathode separator.

[0069] The anode separator may have a groove serving as a fuel gas flow path on the surface facing the power generation unit.

[0070] The cathode separator may have a groove serving as an oxidant gas flow path on the surface facing the power generation unit.

[0071] The separator may also have holes such as supply holes and discharge holes for allowing a fluid to flow in the stacking direction of the single cell to form a manifold.

[0072] As the separator, for example, it can also be dense carbon obtained by compressing carbon to be airtight, and stamped metals (for example, iron, titanium, stainless steel, etc.).

[0073] The single cell may also include an insulating resin frame disposed on the outer side (periphery) in the plane direction of the membrane electrode assembly between the anode separator and the cathode separator. The resin frame is formed into a plate shape and a frame shape using a thermoplastic resin, and seals between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. As the resin frame, for example, resins such as PE, PP, PET, and PEN can be used. The resin frame may also be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0074] The cooling system supplies cooling water as a cooling medium to the fuel cell stack.

[0075] The cooling water can be water, ethylene glycol, etc., and can also be a mixture thereof, etc.

[0076] The cooling system includes a cooling water pump, and may also include, as needed, a cooling flow path, a radiator, a bypass flow path, a rotary valve, a storage tank, an ion exchanger, an intercooler, a temperature sensor, etc.

[0077] The cooling water pump circulates the cooling water that cools the fuel cell stack and adjusts the flow rate of the cooling water supplied to the fuel cell stack.

[0078] The cooling flow path is a flow path that circulates the cooling water that cools the fuel cell stack inside and outside the fuel cell stack.

[0079] The radiator is disposed on the cooling flow path.

[0080] The bypass flow path branches from the cooling flow path at a position upstream of the radiator in the cooling flow path, bypasses the radiator, and merges with the above cooling flow path at a position downstream of the radiator in the cooling flow path.

[0081] The rotary valve is disposed at the branch point of the cooling flow path and the bypass flow path, and performs a flow path switching that allows the cooling water discharged from the fuel cell stack to flow to the radiator or to the bypass flow path. The rotary valve may also include an electric motor such as an electric actuator for performing the flow path switching.

[0082] The temperature sensor of the cooling system measures the temperature of the cooling water.

[0083] The oxidant gas system supplies an oxidant gas to the fuel cell and adjusts the flow rate of the above oxidant gas. The oxidant gas system may also include an oxidant gas supply unit, an oxidant gas pipe, an inlet side seal valve located at the oxidant gas inlet of the fuel cell, an outlet side seal valve located at the oxidant gas outlet of the fuel cell, etc.

[0084] The oxidant gas supply unit may also be an air compressor, etc.

[0085] The fuel gas system supplies a fuel gas to the fuel cell and adjusts the flow rate of the above fuel gas.

[0086] The fuel gas system may also include a fuel gas tank, a fuel gas inlet valve, an injector, a gas-liquid separator, an exhaust drain valve, an ejector for fuel gas circulation, a fuel gas pump for fuel gas circulation, and piping for fuel gas, etc.

[0087] The fuel cell system is provided with a temperature sensor.

[0088] The temperature sensor measures the external air temperature at the start-up of the fuel cell system.

[0089] The fuel cell system may also be provided with a secondary battery.

[0090] The secondary battery only needs to be able to charge and discharge. For example, well-known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries can be cited. In addition, the secondary battery may also include energy storage elements such as electric double layer capacitors. The secondary battery may also be a structure in which a plurality of them are connected in series. The secondary battery supplies power to an air compressor, etc. The secondary battery can also be charged from an external power source such as a household power supply for example. The secondary battery can also be charged by the output of the fuel cell. The charge and discharge of the secondary battery can also be controlled by a control device.

[0091] The fuel cell system may also be provided with a converter.

[0092] The fuel cell system is provided with a control device. The control device may control the oxidant gas system, the fuel gas system, the cooling system, etc., and control the entire fuel cell system.

[0093] Physically, the control device has, for example, an arithmetic processing device such as a CPU (Central Processing Unit), a storage device such as a ROM (Read Only Memory) that stores control programs and control data processed by the CPU, and a RAM (Random Access Memory) that is mainly used as various working areas for control processing, and an input / output interface, and may also be an ECU (Electronic Control Unit), etc.

[0094] The control device determines the degree of deterioration of a plurality of single cells.

[0095] When the fuel cell system starts up below the freezing point, the control device determines the time to stop the cooling water pump (required cooling water stop time) according to the degree of deterioration of a plurality of single cells.

[0096] The degree of deterioration of a plurality of single cells may also be determined based on the voltage of each single cell or the voltage of the fuel cell stack, and the average value or the maximum air stoichiometry during preheating, etc.

[0097] The fuel cell system may also be provided with a voltage sensor.

[0098] The voltage of each single cell or the voltage of the fuel cell stack can also be measured by a voltage sensor.

[0099] The control device may also have a single cell monitor for monitoring the voltage of each single cell.

[0100] The control device determines whether the voltage of each single cell measured by the voltage sensor is below a specified voltage.

[0101] When the voltage of the single cell measured by the voltage sensor is below the specified voltage, the control device determines that the single cell is deteriorated.

[0102] The required cooling water stop time determined by the control device may also be the required cooling water stop time at the next startup below the freezing point.

[0103] The control device may also infer the water content of a plurality of single cells when the fuel cell stack stops operating.

[0104] When the time for stopping the above-mentioned cooling water pump determined by the control device exceeds a specified time (permissible cooling water stop time) corresponding to the above-mentioned water content, when the fuel cell stack stops operating, the control device may also perform scavenging in such a way that the inferred water content of the plurality of single cells is less than a specified water content (permissible generated water amount). For example, the scavenging time may be longer than the normal scavenging time.

[0105] The specified time (permissible cooling water stop time) may also be the stop time of the cooling water pump when the fuel cell stack becomes abnormally overheated.

[0106] The inference of the water content of a plurality of single cells can also be performed by measuring the resistance of each single cell. A data set representing the relationship between the resistance and the water content of each single cell may be prepared in advance, and the resistance of each single cell may be compared with the data set to infer the water content of each single cell.

[0107] The determination of the required cooling water stop time at the startup below the freezing point of the fuel cell system can also be performed by the following method.

[0108] In the relationship between the permissible generated water amount (g / cell) and the permissible cooling water stop time (sec) or the permissible cumulative heat generation amount (kJ), as long as the strength (permissible generated water amount) is greater than the stress (permissible cooling water stop time or permissible cumulative heat generation amount), the fuel cell system can be started below the freezing point.

[0109] Figure 2 It is a graph showing the relationship between the number of single cells deteriorated below a specified voltage and the permissible generated water amount (g / cell).

[0110] Prepare a second data set representing the relationship between the allowable water generation amount (g / cell) and the allowable cooling water stop time (sec) or the allowable cumulative heat generation amount (kJ), and a third data set representing Figure 2 the relationship between the number of single cells below the specified voltage shown and the allowable water generation amount.

[0111] Then, compare with the second data set and the third data set to determine the required cooling water stop time corresponding to the number of single cells below the specified voltage, and prepare a fourth data set representing the relationship between the number of single cells below the specified voltage and the required cooling water stop time. According to the fourth data set, determine the required cooling water stop time corresponding to the number of single cells below the specified voltage at startup under freezing point.

[0112] Then, when the required cooling water stop time determined according to the number of single cells below the specified voltage reaches the threshold value ΔT (sec) of the allowable cooling water stop time as the single cell overheat standard, strengthen the scavenging level at the stop of the fuel cell operation to increase the allowable water generation amount (intensity).

[0113] Figure 3 It is a flowchart showing an example of the control of the fuel cell system of the present disclosure.

[0114] Start the operation of the fuel cell system. When the external air temperature measured by the temperature sensor is below the freezing point, as a startup under freezing point, the control device preheats the fuel cell stack.

[0115] During the preheating, the control device judges the degree of deterioration of a plurality of single cells. Specifically, count the number of single cells below the specified voltage.

[0116] If the temperature of the cooling water of the fuel cell stack (FC water temperature) exceeds the specified temperature β, end the preheating.

[0117] During the preheating or after the preheating ends, the control device determines the time of the cooling water pump at the next stop of startup under freezing point (required cooling water stop time) according to the degree of deterioration of a plurality of single cells (the number of single cells below the specified voltage).

[0118] The control device infers the water content of a plurality of single cells at the stop of the operation of the fuel cell stack.

[0119] When the required cooling water stop time determined by the control device exceeds the specified time (permissible cooling water stop time) γ corresponding to the water content of the plurality of individual cells inferred, at the time of stopping the operation of the fuel cell stack, the control device sets the scavenging time longer than the normal scavenging time so that the water content of the plurality of individual cells inferred is less than the specified water content (permissible generated water amount), performs scavenging, and ends the control.

[0120] On the other hand, when the required cooling water stop time determined by the control device is within the specified time (permissible cooling water stop time) corresponding to the water content of the plurality of individual cells inferred, at the time of stopping the operation of the fuel cell stack, the control device sets the scavenging time to the normal scavenging time, performs scavenging, and ends the control.

Claims

1. A fuel cell system, wherein: The fuel cell system comprises a fuel cell stack, a cooling water pump, a temperature sensor and a control device. The fuel cell stack comprises a plurality of stacked single cells. The cooling water pump circulates cooling water for cooling the fuel cell stack. The temperature sensor measures the outside air temperature when the fuel cell system is started. The control device determines the degree of degradation of the plurality of single cells. When the fuel cell system is started up below freezing point, the control device determines a time to stop the cooling water pump according to a degree of degradation of the plurality of single cells.

2. The fuel cell system according to claim 1, wherein: The control device estimates the water content of the plurality of cells when the operation of the fuel cell stack is stopped, When the time for stopping the cooling water pump determined by the control device exceeds a prescribed time corresponding to the water content, the control device performs scavenging in such a manner that the estimated water content of the plurality of single cells is less than a prescribed water content when the operation of the fuel cell stack is stopped. The predetermined time is a stop time of the cooling water pump when the fuel cell unit becomes abnormally overheated.

Images