Fuel cell system

Abstract

Provided is a fuel cell system capable of efficiently preheating a plurality of fuel cell stacks. A fuel cell system includes a cooling system, a control unit, and a plurality of fuel cell stacks, the plurality of fuel cell stacks including at least a first fuel cell stack and a second fuel cell stack, and the cooling system includes a first cooling water pipe, a second cooling water pipe, a cooler, a first connection pipe, and a second connection pipe.

Description

Technical Field

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

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

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-102005

[0004] In Patent Document 1, a fuel cell system is disclosed that separately includes a cooler for each of a plurality of fuel cell stacks.

[0005] In the prior art, when starting at sub-zero temperatures and each of a plurality of fuel cell stacks is preheated, the fuel utilization rate may deteriorate. Summary of the Invention

[0006] The present disclosure has been made in view of the above actual situation, and a main object thereof is to provide a fuel cell system capable of efficiently preheating a plurality of fuel cell stacks.

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

[0008] <1>

[0009] A fuel cell system, wherein

[0010] the above fuel cell system has a cooling system, a control unit, and a plurality of fuel cell stacks,

[0011] the above plurality of fuel cell stacks include at least a first fuel cell stack and a second fuel cell stack,

[0012] the above cooling system has a first cooling water pipe, a second cooling water pipe, a cooler, a first connection pipe, and a second connection pipe,

[0013] the above first cooling water pipe connects the cooler to the cooling water inlet of the above first fuel cell stack, and connects the cooling water outlet of the above first fuel cell stack to the cooler,

[0014] the above second cooling water pipe connects the cooler to the cooling water inlet of the above second fuel cell stack, and connects the cooling water outlet of the above second fuel cell stack to the cooler,

[0015] the above first connection pipe has a first connection valve,

[0016] the above first connection pipe connects the above first cooling water pipe and the above second cooling water pipe, and when the above first connection valve is opened, cooling water can be supplied from the above first cooling water pipe to the above second cooling water pipe bypassing the cooler,

[0017] The second connecting pipe described above has a second connecting valve.

[0018] The second connecting pipe described above connects the first cooling water pipe and the second cooling water pipe. When the second connecting valve is opened, cooling water can be supplied from the second cooling water pipe to the first cooling water pipe bypassing the cooler.

[0019] When the fuel cell system starts up below the freezing point, when the cooling water temperature of at least the first fuel cell stack among the plurality of fuel cell stacks is not below the freezing point, the control unit performs normal start-up of the first fuel cell stack, and then opens the first connecting valve.

[0020] When the fuel cell system starts up below the freezing point, when the cooling water temperatures of all the fuel cell stacks among the plurality of fuel cell stacks are below the freezing point, the control unit compares the cooling water temperatures of the plurality of fuel cell stacks.

[0021] When the cooling water temperature of the first fuel cell stack among the plurality of fuel cell stacks is the highest, the control unit performs specified preheating of the first fuel cell stack, and then, when the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connecting valve.

[0022] When there is no temperature difference in the cooling water temperatures of the plurality of fuel cell stacks, the control unit performs specified preheating of the first fuel cell stack determined in advance, and then, when the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connecting valve.

[0023] <2>

[0024] In the fuel cell system described in <1>.

[0025] When the fuel cell system starts up below the freezing point, when the cooling water temperatures of all the fuel cell stacks among the plurality of fuel cell stacks are below the freezing point and above -10°C, the control unit does not compare the cooling water temperatures of the plurality of fuel cell stacks, and

[0026] the control unit performs specified preheating of the first fuel cell stack determined in advance, and then, when the cooling water temperature of the first fuel cell stack reaches 0°C or higher, the control unit opens the first connecting valve.

[0027] <3>

[0028] In the fuel cell system described in <1> or <2>.

[0029] The first connecting pipe branches from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe, and merges with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe.

[0030] <4>

[0031] In the fuel cell system described in any one of <1> to <3>,

[0032] The second connecting pipe branches from the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe, and merges with the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe.

[0033] <5>

[0034] In the fuel cell system described in any one of <1> to <4>,

[0035] The first cooling water pipe has a first bypass pipe,

[0036] The first bypass pipe has a first bypass valve,

[0037] The first bypass pipe branches from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe, and merges with the first cooling water pipe at a position downstream of the cooler in the first cooling water pipe, thereby bypassing the cooler.

[0038] The second cooling water pipe has a second bypass pipe,

[0039] The second bypass pipe has a second bypass valve,

[0040] The second bypass pipe branches from the second cooling water pipe at a position upstream of the cooler in the second cooling water pipe, and merges with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe, thereby bypassing the cooler.

[0041] The fuel cell system of the present disclosure can efficiently perform preheating of multiple fuel cell stacks. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a system structure diagram showing an example of the fuel cell system of the present disclosure during normal operation.

[0043] Figure 2 It is a system structure diagram showing an example of the fuel cell system of the present disclosure when starting at freezing point.

[0044] Figure 3 This is a system structure diagram showing another example when the fuel cell system of the present disclosure starts at the freezing point.

[0045] Figure 4 This is a flowchart showing an example of the control of the fuel cell system of the present disclosure.

[0046] Figure 5 This is a flowchart showing another example of the control of the fuel cell system of the present disclosure.

[0047] Explanation of reference numerals:

[0048] 10... First fuel cell stack; 11... First cooling water pipe; 12... First connecting pipe; 13... First bypass pipe; 14... First connecting valve; 15... First bypass valve; 16... First cooling water pump; 17... First cooling water inlet valve; 20... Second fuel cell stack; 21... Second cooling water pipe; 22... Second connecting pipe; 23... Second bypass pipe; 24... Second connecting valve; 25... Second bypass valve; 26... Second cooling water pump; 27... Second cooling water inlet valve; 30... Cooler; 31... First cooler; 32... Second cooler. Detailed Description of the Invention

[0049] Hereinafter, embodiments of the present disclosure will be described. In addition, cases required for implementing the present disclosure in cases other than those specifically mentioned in this specification (for example, normal structures and manufacturing processes that do not characterize the fuel cell system of the present disclosure) can be grasped 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 the common general knowledge in this field.

[0050] In addition, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships.

[0051] In the present disclosure, the reaction gas supplied to the anode of the fuel cell is a fuel gas (anode gas), and the reaction 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 gas. The oxidant gas is a gas containing oxygen and may also be oxygen, air (atmosphere), etc.

[0052] In the present disclosure, a fuel cell system is provided, wherein

[0053] the above fuel cell system has a cooling system, a control unit, and a plurality of fuel cell stacks,

[0054] the above plurality of fuel cell stacks at least include a first fuel cell stack and a second fuel cell stack,

[0055] The above cooling system includes a first cooling water pipe, a second cooling water pipe, a cooler, a first connection pipe, and a second connection pipe.

[0056] The above first cooling water pipe connects the cooler to the cooling water inlet of the above first fuel cell stack, and connects the cooling water outlet of the above first fuel cell stack to the cooler.

[0057] The above second cooling water pipe connects the cooler to the cooling water inlet of the above second fuel cell stack, and connects the cooling water outlet of the above second fuel cell stack to the cooler.

[0058] The above first connection pipe has a first connection valve.

[0059] The above first connection pipe connects the above first cooling water pipe and the above second cooling water pipe. When the above first connection valve is opened, cooling water can be supplied from the above first cooling water pipe to the above second cooling water pipe bypassing the cooler.

[0060] The above second connection pipe has a second connection valve.

[0061] The above second connection pipe connects the above first cooling water pipe and the above second cooling water pipe. When the above second connection valve is opened, cooling water can be supplied from the above second cooling water pipe to the above first cooling water pipe bypassing the cooler.

[0062] When the above fuel cell system starts up below the freezing point, when the cooling water temperature of at least the above first fuel cell stack among the above multiple fuel cell stacks is not below the freezing point, the above control unit performs the normal start-up of the above first fuel cell stack, and then opens the above first connection valve.

[0063] When the above fuel cell system starts up below the freezing point, when the cooling water temperatures of all the fuel cell stacks among the above multiple fuel cell stacks are below the freezing point, the above control unit compares the cooling water temperatures of the above multiple fuel cell stacks.

[0064] When the cooling water temperature of the above first fuel cell stack among the above multiple fuel cell stacks is the highest, the above control unit performs the specified preheating of the above first fuel cell stack, and then, when the cooling water temperature of the above first fuel cell stack reaches or exceeds the specified temperature, the above control unit opens the above first connection valve.

[0065] When there is no temperature difference in the cooling water temperatures of the above multiple fuel cell stacks, the above control unit performs the specified preheating of the above first fuel cell stack determined in advance, and then, when the cooling water temperature of the above first fuel cell stack reaches or exceeds the specified temperature, the above control unit opens the above first connection valve.

[0066] In a fuel cell system in which two or more fuel cells are connected in parallel, when the fuel cell system is started below the freezing point, if each fuel cell performs inefficient preheating, the fuel utilization rate at low temperatures deteriorates.

[0067] In the prior art, there is a bypass pipe for a cooler in the cooling system of each fuel cell, but there is no connecting pipe for the cooling system between fuel cells. As a whole cooling system, it is connected via the cooler.

[0068] If heat generated in one fuel cell is to be transferred to another fuel cell through the cooling pipes of the entire cooling system, the heat capacity becomes large, so the efficiency is low.

[0069] The present disclosure relates to a piping structure of a cooling system corresponding to starting below the freezing point and a starting method of a fuel cell system in a fuel cell system connected with two or more fuel cells.

[0070] In the present disclosure, one fuel cell is heated by power generation, and the heat generated in one fuel cell is transferred to another fuel cell.

[0071] If the cooling water temperature of one fuel cell exceeds a specified temperature (for example, 30 °C), the rotational speed of the water pump increases, and at the same time, the connection valve between fuel cells is opened.

[0072] It is also possible to confirm the cooling water temperature of each fuel cell at the start of the fuel cell system and start from the fuel cell with the higher cooling water temperature.

[0073] 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 fixed power generation system such as a generator that supplies power to the outside of the fuel cell system.

[0074] The vehicle can also be a fuel cell vehicle or the like. As moving bodies other than vehicles, for example, railways, ships, aircraft, etc. can be cited.

[0075] 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 travel using the power of a secondary battery.

[0076] The moving body and the fixed power generation system can also be equipped with the fuel cell system of the present disclosure.

[0077] The moving body can also have drive units such as a motor, an inverter, and a hybrid control system.

[0078] The hybrid control system can also use the output of the fuel cell and the power of the secondary battery in combination to make the moving body travel.

[0079] A fuel cell system has a cooling system, a control unit, and a plurality of fuel cell stacks. The fuel cell system may also include a fuel gas system, an oxidant gas system, etc.

[0080] A fuel cell stack (stack) is a laminate formed by laminating a plurality of single cells (unit cells) of fuel cells.

[0081] In the present disclosure, sometimes both the single cell and the fuel cell stack are referred to as fuel cells.

[0082] The number of single cells laminated in the fuel cell stack is not particularly limited, and for example, it may be 2 to several hundred.

[0083] The fuel cell stack may also have a current collector plate, a pressure plate, etc. at the ends in the lamination direction.

[0084] The fuel cell system includes at least a first fuel cell stack and a second fuel cell stack as the plurality of fuel cell stacks, and may also include three or more fuel cell stacks. The fuel cell system may also include a number of fuel cell stacks such that the total output of the plurality of fuel cell stacks becomes about 1 MW.

[0085] The single cell may also have a power generation unit.

[0086] In a plan view, the shape of the power generation unit may be rectangular.

[0087] The power generation unit may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes sandwiching the electrolyte membrane.

[0088] The electrolyte membrane may 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, hydrocarbon-based electrolyte membranes, etc. may be mentioned. As the electrolyte membrane, for example, a proton exchange membrane (Nafion membrane, manufactured by DuPont) etc. may also be used.

[0089] Among the two electrodes, one is an anode (fuel electrode) and the other is a cathode (oxidant electrode).

[0090] The electrode includes a catalyst layer, and may also include a gas diffusion layer as needed. The power generation unit may be a membrane electrode gas diffusion layer assembly (MEGA). In this case, the single cell may also include a cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator.

[0091] The membrane electrode gas diffusion layer assembly sequentially has an anode-side gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode-side gas diffusion layer.

[0092] The anode catalyst layer and the cathode catalyst layer are collectively referred to as the catalyst layer.

[0093] The anode-side gas diffusion layer and the cathode-side gas diffusion layer are collectively referred to as the gas diffusion layer.

[0094] The catalyst layer contains a catalyst, and the catalyst may also include a catalyst metal that promotes an electrochemical reaction, an electrolyte with proton conductivity, and a carrier with electron conductivity, etc.

[0095] As the catalyst metal, for example, platinum (Pt) and alloys composed of Pt and other metals (such as Pt alloys mixed with cobalt and 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.

[0096] As the electrolyte, a fluorine-based resin, etc. can also be used. As the fluorine-based resin, for example, a perfluorinated resin solution (Nafion solution) can also be used.

[0097] The above-mentioned catalyst metal can also be supported on a carrier, and in each catalyst layer, the carrier supporting the catalyst metal (catalyst-supported carrier) and the electrolyte can coexist in a mixed state.

[0098] For the carrier used to support the catalyst metal, for example, carbon materials such as commonly sold carbon can be cited.

[0099] The gas diffusion layer can also be a conductive component with pores, etc.

[0100] As the conductive component, for example, carbon porous bodies such as carbon cloth and carbon paper, and metal porous components such as metal meshes and foamed metals can be cited.

[0101] The single cell can also include a separator.

[0102] The separator collects the current generated by power generation and functions as a partition wall. In the single cell, the separator is usually arranged on both sides in the stacking direction of the power generation part in such a way that a pair of separators sandwich the power generation part. In a pair of separators, one is the anode separator and the other is the cathode separator.

[0103] The anode separator can also have grooves on the surface on the power generation part side that form a fuel gas flow path.

[0104] The cathode separator can also have grooves on the surface on the power generation part side that form an oxidant gas flow path.

[0105] The separator can also have holes such as supply holes and discharge holes for allowing fluids to flow in the stacking direction of the single cell, which constitute the manifold holes.

[0106] As the separator, for example, it can also be dense carbon obtained by compressing carbon to make it airtight, and metals (such as iron, titanium, and stainless steel, etc.) obtained by stamping and forming.

[0107] The single cell can also include a resin frame for insulation disposed on the outer side (outer 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-like and frame-like shape by using a thermoplastic resin, and seals the space 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 can also be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0108] In order to seal each gas, the fuel cell stack can also have gaskets, resin sheets, etc. between the single cells.

[0109] The cooling system supplies cooling water as a cooling medium to the fuel cell.

[0110] Examples of the cooling water include water and ethylene glycol, and it can also be a mixture thereof, etc.

[0111] The cooling system has a first cooling water pipe, a second cooling water pipe, a cooler, a first connection pipe, and a second connection pipe, and can also include a cooling water pump, a storage tank, an ion exchanger, an intercooler, etc. as needed.

[0112] The first cooling water pipe and the second cooling water pipe are collectively referred to as the cooling water pipe.

[0113] The first connection pipe and the second connection pipe are collectively referred to as the connection pipe.

[0114] The first cooling water pipe connects the cooler to the cooling water inlet of the first fuel cell stack, and also connects the cooling water outlet of the first fuel cell stack to the cooler.

[0115] The first cooling water pipe can also have a first bypass pipe.

[0116] The first bypass pipe can also have a first bypass valve.

[0117] The first bypass pipe can branch from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe, and merge with the first cooling water pipe at a position downstream of the cooler in the first cooling water pipe, thereby bypassing the cooler.

[0118] The first bypass valve performs a flow path switching of switching the cooling water discharged from the first fuel cell stack to flow either to the cooler or to the first bypass pipe. The first bypass valve can also include an electric motor such as an electric actuator for performing the flow path switching.

[0119] The first cooling water pipe may also have a first cooling water inlet valve. The first cooling water inlet valve is arranged at a position downstream of the cooler, may also be arranged at a position upstream of the confluence part of the first cooling water pipe and the first bypass pipe, and may also be arranged at a position upstream of the branch part of the first cooling water pipe to the first connecting pipe.

[0120] The second cooling water pipe connects the cooler to the cooling water inlet of the second fuel cell stack and connects the cooling water outlet of the second fuel cell stack to the cooler.

[0121] The second cooling water pipe may also have a second bypass pipe.

[0122] The second bypass pipe may also have a second bypass valve.

[0123] The second bypass pipe may branch from the second cooling water pipe at a position upstream of the cooler in the second cooling water pipe and merge with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe, so as to bypass the cooler.

[0124] The second bypass valve performs a flow path switching of switching the cooling water discharged from the second fuel cell stack to flow to the cooler or to flow to the second bypass pipe. The second bypass valve may also be equipped with an electric motor such as an electric actuator for performing the flow path switching.

[0125] The second cooling water pipe may also have a second cooling water inlet valve. The second cooling water inlet valve is arranged at a position downstream of the cooler, may also be arranged at a position upstream of the confluence part of the second cooling water pipe and the second bypass pipe, and may also be arranged at a position upstream of the branch part of the second cooling water pipe to the second connecting pipe.

[0126] The first connecting pipe has a first connecting valve.

[0127] The first connecting pipe connects the first cooling water pipe and the second cooling water pipe. When the first connecting valve is opened, the first connecting pipe can supply the cooling water from the first cooling water pipe to the second cooling water pipe bypassing the cooler. When the first connecting valve is closed, the first connecting pipe does not supply the cooling water from the first cooling water pipe to the second cooling water pipe.

[0128] The connection part of the first connecting pipe to the first cooling water pipe and the second cooling water pipe is not particularly limited. From the viewpoint of efficiently preheating a plurality of fuel cell stacks, it is also possible to branch from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe and merge with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe. The branch part of the first connecting pipe from the first cooling water pipe may also be located at a position upstream of the branch part of the first bypass pipe from the first cooling water pipe. The merging part of the first connecting pipe to the second cooling water pipe may also be located at a position downstream of the merging part of the second bypass pipe to the second cooling water pipe. The merging part of the first connecting pipe to the second cooling water pipe may also be located at a position downstream of the branch part of the second connecting pipe from the second cooling water pipe.

[0129] The first connecting valve performs a flow path switching for switching the cooling water discharged from the first fuel cell stack to flow to the cooler or the first fuel cell stack or to flow to the second cooling water pipe. The first connecting valve may also include an electric motor such as an electric actuator for performing the flow path switching.

[0130] The second connecting pipe has a second connecting valve.

[0131] The second connecting pipe connects the first cooling water pipe and the second cooling water pipe. When the second connecting valve is open, the second connecting pipe can supply the cooling water from the second cooling water pipe to the first cooling water pipe bypassing the cooler. When the second connecting valve is closed, the second connecting pipe does not supply the cooling water from the second cooling water pipe to the first cooling water pipe.

[0132] The connection part of the second connecting pipe to the first cooling water pipe and the second cooling water pipe is not particularly limited. From the viewpoint of efficiently preheating a plurality of fuel cell stacks, it is also possible to branch from the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe and merge with the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe. The branch part of the second connecting pipe from the second cooling water pipe may also be located at a position downstream of the merging part of the second bypass pipe to the second cooling water pipe. The merging part of the second connecting pipe to the first cooling water pipe may also be located at a position upstream of the branch part of the first bypass pipe from the first cooling water pipe. The merging part of the second connecting pipe to the first cooling water pipe may also be located at a position downstream of the branch part of the first connecting pipe from the first cooling water pipe.

[0133] The second connecting valve performs a flow path switching for switching the cooling water discharged from the second fuel cell stack to flow to the cooler or the second fuel cell stack or to flow to the first cooling water pipe. The second connecting valve may also include an electric motor such as an electric actuator for performing the flow path switching.

[0134] The cooling water pump circulates the cooling water for cooling the fuel cell and adjusts the flow rate of the cooling water supplied to the fuel cell.

[0135] The reserve tank is a tank that temporarily stores the cooling water that overflows from the cooling water pipe whose internal pressure increases due to the temperature rise of the cooling water.

[0136] The cooler is arranged on the cooling water pipe to cool the cooling water. Examples of the cooler include a radiator and the like. The cooler can also be shared by the first cooling water pipe and the second cooling water pipe. The cooler can also be independently provided for the first cooling water pipe and the second cooling water pipe respectively. That is, it can also be configured such that the first cooling water pipe is connected to the first cooler and the second cooling water pipe is connected to the second cooler.

[0137] The oxidant gas system supplies an oxidant gas containing oxygen to the fuel cell and adjusts the flow rate of the oxidant gas. The oxidant gas system can 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, and the like.

[0138] The oxidant gas supply unit can also be an air compressor or the like.

[0139] The fuel gas system supplies a fuel gas containing hydrogen required for the power generation of the fuel cell to the fuel cell and adjusts the flow rate of the fuel gas. The fuel gas system can also include a fuel gas tank, a fuel gas inlet valve, an injector, a gas-liquid separator, an exhaust and drain valve, an ejector for fuel gas circulation, a fuel gas pump for fuel gas circulation, and a fuel gas pipe.

[0140] The fuel cell system can also be equipped with a secondary battery.

[0141] The secondary battery only needs to be able to charge and discharge. For example, known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries can be cited. In addition, the secondary battery can also include energy storage elements such as electric double layer capacitors. The secondary battery can also be structured such that a plurality of them are connected in series. The secondary battery supplies power to an air compressor or the like. For example, the secondary battery can also be configured to be rechargeable from an external power source such as a household power supply of the fuel cell system. The secondary battery can also be charged by the output of the fuel cell. The charging and discharging of the secondary battery can also be controlled by the control unit.

[0142] The fuel cell system is equipped with a control unit. The control unit can also control the oxidant gas system, the fuel gas system, the cooling system, etc., and control the entire fuel cell system.

[0143] The control unit physically includes 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, control data, etc. processed by the CPU, and a RAM (Random Access Memory) mainly used as various working areas for control processing, and an input / output interface, and it can also be an ECU (Electronic Control Unit), etc.

[0144] When the fuel cell system starts up below the freezing point, when the cooling water temperature of at least the first fuel cell stack among the multiple fuel cell stacks is not below the freezing point, the control unit performs a normal start of the first fuel cell stack, and then opens the first connection valve. At this time, the control unit can also open the second connection valve together.

[0145] In the present disclosure, opening the first connection valve means that the cooling water flows from the first cooling water pipe through the first connection pipe to the second cooling water pipe.

[0146] In the present disclosure, opening the second connection valve means that the cooling water flows from the second cooling water pipe through the second connection pipe to the first cooling water pipe.

[0147] When the fuel cell system starts up below the freezing point, when the cooling water temperatures of all the fuel cell stacks among the multiple fuel cell stacks are below the freezing point, the control unit compares the cooling water temperatures of the multiple fuel cell stacks.

[0148] When the cooling water temperature of the first fuel cell stack among the multiple fuel cell stacks is the highest, the control unit performs a specified preheating of the first fuel cell stack. After the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connection valve.

[0149] At this time, the control unit can also open the second connection valve together.

[0150] When there is no temperature difference in the cooling water temperatures of the multiple fuel cell stacks, the control unit performs a specified preheating of the first fuel cell stack determined in advance. After the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connection valve. At this time, the control unit can also open the second connection valve together.

[0151] The specified temperature is not particularly limited, but it can also be 0°C or higher.

[0152] When the fuel cell system starts up below the freezing point, when the cooling water temperatures of all the fuel cell stacks among the multiple fuel cell stacks are below the freezing point and above -10°C, the control unit may not compare the cooling water temperatures of the multiple fuel cell stacks.

[0153] In the above case, the control unit can perform the specified preheating of the first fuel cell stack. After that, when the cooling water temperature of the first fuel cell stack becomes 0 °C or higher, the control unit opens the first connection valve. At this time, the control unit can also open the second connection valve together.

[0154] When the fuel cell system starts up below the freezing point, when the cooling water temperatures of multiple fuel cell stacks are all higher than -10 °C, there is almost no difference in the startability of the fuel cell stacks. Therefore, it is also possible not to perform the determination of the starting fuel cell stack and to perform the specified preheating of the first fuel cell stack determined in advance.

[0155] The first fuel cell stack determined in advance may also be the fuel cell stack that is not the most deteriorated among multiple fuel cell stacks. The degree of deterioration of the fuel cell stack can also be judged based on the total operating time of the fuel cell stack, the voltage of the fuel cell stack, etc.

[0156] The fuel cell stack with the shortest total operating time may not be the most deteriorated fuel cell stack.

[0157] The fuel cell stack with the highest voltage may not be the most deteriorated fuel cell stack.

[0158] In the case of a cooling system combined with cooling water pipes of different lengths, it is also possible to make the fuel cell stack of the cooling system with less cooling water capacity the first fuel cell stack determined in advance.

[0159] The fuel cell system may also be equipped with a temperature sensor.

[0160] It is also possible to measure the temperature of the cooling water through the temperature sensor. The temperature of the cooling water can be the temperature of the cooling water on the inlet side of the fuel cell stack or the temperature of the cooling water on the outlet side of the fuel cell stack.

[0161] The control unit can also determine whether the temperature of the cooling water measured by the temperature sensor is below the freezing point at the start of the fuel cell system or at all times.

[0162] Figure 1 It is a system structure diagram showing an example of the fuel cell system of the present disclosure during normal operation.

[0163] The fuel cell system of the present disclosure has a first fuel cell stack 10, a second fuel cell stack 20, and a cooling system. Although not shown, the fuel cell system may also be equipped with a control unit, a fuel gas system, an oxidant gas system, etc.

[0164] The cooling system includes a first cooling water pipe 11, a second cooling water pipe 21, a cooler 30, a first connecting pipe 12, a second connecting pipe 22, a first bypass pipe 13, a first connecting valve 14, a first bypass valve 15, a second bypass pipe 23, a second connecting valve 24, a second bypass valve 25, a first cooling water pump 16, a second cooling water pump 26, a first cooling water inlet valve 17, and a second cooling water inlet valve 27.

[0165] During normal operation of the fuel cell system, the first cooling water inlet valve 17 and the second cooling water inlet valve 27 are opened. The side of the first connecting pipe 12 of the first connecting valve 14 is closed, and the upstream and downstream sides of the first cooling water pipe 11 are opened. The side of the first bypass pipe 13 of the first bypass valve 15 is closed, and the upstream and downstream sides of the first cooling water pipe 11 are opened. The side of the second connecting pipe 22 of the second connecting valve 24 is closed, and the upstream and downstream sides of the second cooling water pipe 21 are opened. The side of the second bypass pipe 23 of the second bypass valve 25 is closed, and the upstream and downstream sides of the second cooling water pipe 21 are opened.

[0166] Figure 2 It is a system structure diagram showing an example when the fuel cell system of the present disclosure starts at sub-zero temperature. In Figure 2 , the same reference numerals are attached to the same structures as Figure 1 and their descriptions are omitted.

[0167] When the fuel cell system starts at sub-zero temperature, the first cooling water inlet valve 17 and the second cooling water inlet valve 27 are closed. The downstream side of the first cooling water pipe 11 of the first connecting valve 14 is closed, and the upstream side of the first cooling water pipe 11 and the side of the first connecting pipe 12 are opened. The downstream side of the first cooling water pipe 11 of the first bypass valve 15 is closed, and the upstream side of the first cooling water pipe 11 and the side of the first bypass pipe 13 are opened. The downstream side of the second cooling water pipe 21 of the second connecting valve 24 is closed, and the upstream side of the second cooling water pipe 21 and the side of the second connecting pipe 22 are opened. The downstream side of the second cooling water pipe 21 of the second bypass valve 25 is closed, and the upstream side of the second cooling water pipe 21 and the side of the second bypass pipe 23 are opened.

[0168] Figure 3 It is a system structure diagram showing another example when the fuel cell system of the present disclosure starts at sub-zero temperature. In Figure 3 , the same reference numerals are attached to the same structures as Figure 1 and their descriptions are omitted.

[0169] Figure 3 The fuel cell system shown has a first cooler 31 and a second cooler 32 instead of the cooler 30.

[0170] Figure 4It is a flowchart showing an example of the control of the fuel cell system of the present disclosure.

[0171] The control unit determines whether the cooling water temperature of the two fuel cell stacks is below the freezing point.

[0172] When the cooling water temperature of any of the two fuel cell stacks is not below the freezing point, the control unit performs a normal start-up of the two fuel cell stacks.

[0173] When the cooling water temperature of the first fuel cell stack of one of the two fuel cells is not below the freezing point, the control unit performs a normal start-up of the first fuel cell stack, and then opens the first connection valve of the first connection pipe of the first fuel cell stack to supply cooling water to the second cooling water pipe. At this time, the control unit may also open the second connection valve together.

[0174] When the cooling water temperatures of both of the two fuel cell stacks are below the freezing point, the control unit determines whether there is a temperature difference in the cooling water temperatures of the two fuel cell stacks.

[0175] When there is no temperature difference in the cooling water temperatures of the two fuel cell stacks, the control unit performs a predetermined preheating of the first fuel cell stack. After the cooling water temperature of the first fuel cell stack reaches a predetermined temperature or higher, the control unit opens the first connection valve to supply cooling water to the second cooling water pipe. At this time, the control unit may also open the second connection valve together.

[0176] When there is a temperature difference in the cooling water temperatures of the two fuel cell stacks, and the cooling water temperature of the first fuel cell stack is higher than the cooling water temperature of the second fuel cell stack, the control unit performs a predetermined preheating of the first fuel cell stack. After the cooling water temperature of the first fuel cell stack reaches a predetermined temperature or higher, the control unit opens the first connection valve to supply cooling water to the second cooling water pipe. At this time, the control unit may also open the second connection valve together.

[0177] Figure 5 It is a flowchart showing another example of the control of the fuel cell system of the present disclosure.

[0178] The control unit determines whether the cooling water temperature of the two fuel cell stacks is below the freezing point.

[0179] When the cooling water temperatures of both of the two fuel cell stacks are below the freezing point, the control unit determines whether the cooling water temperatures of the two fuel cell stacks are below the freezing point and above -10°C among the two fuel cell stacks.

[0180] When both of the two fuel cell stacks have a cooling water temperature below the freezing point and above -10°C, the control unit does not compare the cooling water temperatures of the two fuel cell stacks, and the control unit implements the specified preheating of the first fuel cell stack as determined in advance. After the cooling water temperature of the first fuel cell stack reaches 0°C or higher, the control unit opens the first connection valve and supplies the cooling water to the second cooling water pipe. At this time, the control unit may also open the second connection valve together.

Claims

1. A fuel cell system, wherein, the fuel cell system has a cooling system, a control unit, and a plurality of fuel cell stacks, the plurality of fuel cell stacks includes at least a first fuel cell stack and a second fuel cell stack, the cooling system has a first cooling water pipe, a second cooling water pipe, a cooler, a first connection pipe, and a second connection pipe, the first cooling water pipe connects the cooler to the cooling water inlet of the first fuel cell stack and connects the cooling water outlet of the first fuel cell stack to the cooler, the second cooling water pipe connects the cooler to the cooling water inlet of the second fuel cell stack and connects the cooling water outlet of the second fuel cell stack to the cooler, the first connection pipe has a first connection valve, the first connection pipe connects the first cooling water pipe and the second cooling water pipe, and when the first connection valve is opened, cooling water can be supplied from the first cooling water pipe to the second cooling water pipe bypassing the cooler, the second connection pipe has a second connection valve, the second connection pipe connects the first cooling water pipe and the second cooling water pipe, and when the second connection valve is opened, cooling water can be supplied from the second cooling water pipe to the first cooling water pipe bypassing the cooler, when the fuel cell system starts up below the freezing point, if the cooling water temperature of at least the first fuel cell stack among the plurality of fuel cell stacks is not below the freezing point, the control unit performs normal start-up of the first fuel cell stack and then opens the first connection valve, when the fuel cell system starts up below the freezing point, if the cooling water temperatures of all the fuel cell stacks among the plurality of fuel cell stacks are below the freezing point, the control unit compares the cooling water temperatures of the plurality of fuel cell stacks, if the cooling water temperature of the first fuel cell stack among the plurality of fuel cell stacks is the highest, the control unit performs specified preheating of the first fuel cell stack, and then, when the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connection valve, if there is no temperature difference in the cooling water temperatures of the plurality of fuel cell stacks, the control unit performs specified preheating of the first fuel cell stack determined in advance, and then, when the cooling water temperature of the first fuel cell stack reaches a specified temperature or higher, the control unit opens the first connection valve.

2. The fuel cell system according to claim 1, wherein, when the fuel cell system starts up below the freezing point, if the cooling water temperatures of all the fuel cell stacks among the plurality of fuel cell stacks are below the freezing point and above -10°C, the control unit does not compare the cooling water temperatures of the plurality of fuel cell stacks, and the control unit performs specified preheating of the first fuel cell stack determined in advance, and then, when the cooling water temperature of the first fuel cell stack reaches 0°C or higher, the control unit opens the first connection valve.

3. The fuel cell system according to claim 1, wherein, The first connecting pipe branches from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe, and merges with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe.

4. The fuel cell system according to claim 1, wherein The second connecting pipe branches from the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe, and merges with the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe.

5. The fuel cell system according to claim 1, wherein The first cooling water pipe has a first bypass pipe, The first bypass pipe has a first bypass valve, The first bypass pipe branches from the first cooling water pipe at a position upstream of the cooler in the first cooling water pipe, and merges with the first cooling water pipe at a position downstream of the cooler in the first cooling water pipe, thereby bypassing the cooler. The second cooling water pipe has a second bypass pipe, The second bypass pipe has a second bypass valve, The second bypass pipe branches from the second cooling water pipe at a position upstream of the cooler in the second cooling water pipe, and merges with the second cooling water pipe at a position downstream of the cooler in the second cooling water pipe, thereby bypassing the cooler.

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