Fuel cell system

Abstract

To provide a fuel cell system capable of increasing the efficiency.SOLUTION: The fuel cell system includes a fuel cell, a cooling system, and a control unit. The cooling system includes a cooling water pump and a reserve tank. The control unit is configured so as to, when the temperature of the cooling water is below the low temperature determination threshold, perform temperature rise control so that the temperature of the cooling water is controlled to reach the target temperature. After the temperature rise control, the control unit cools the temperature of the cooling water to a normal operating temperature that is lower than the target temperature. The target temperature is set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Various techniques have been proposed regarding fuel cells (FCs) as disclosed in Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the upper limit flow rate of cooling water is calculated based on the opening degree of a three-way valve, and the target flow rate of cooling water corresponding to the power generation amount of the fuel cell is calculated. A fuel cell system is disclosed that controls within the pressure resistance of the cooling system by driving a cooling water pump (W / P) based on these calculation results. It becomes necessary to control the flow rate of cooling water so as not to exceed the pressure resistance of the cooling system. As a result, due to the inability to flow the cooling water at the desired flow rate, it becomes necessary to suppress the power generation amount of the fuel cell, and there is a possibility that the required power of the fuel cell system cannot be met. Increasing the pressure resistance of the cooling system results in cost increase and size increase, and also narrows the design freedom on the user side. If the pressure resistance of the cooling system is not increased, in order to maintain the desired power generation amount of the fuel cell, it is necessary to increase the pressures of the fuel gas system and the oxidant gas system higher than that of the cooling system, and it is necessary to supply the reaction gas to the fuel cell in excess. As a result, the efficiency of the fuel cell system decreases.

[0005] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a fuel cell system capable of enhancing efficiency.

Means for Solving the Problems

[0006] That is, the present disclosure includes the following aspects. <1> A fuel cell system, wherein the fuel cell system includes a fuel cell, a cooling system, and a control device, the cooling system includes a cooling water pump and a reserve tank, when the temperature of the cooling water is equal to or lower than a low temperature determination threshold, the control device performs a temperature increase control to increase the temperature of the cooling water to a target temperature, after the temperature increase control, the control device cools the temperature of the cooling water to a normal use temperature lower than the target temperature, the target temperature is set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank, a fuel cell system.

[0007] <2> The control device monitors the temperature history of the cooling water, when the temperature history becomes equal to or lower than the low temperature determination threshold, the control device performs the temperature increase control, the fuel cell system according to <1>.

Advantages of the Invention

[0008] The fuel cell system of the present disclosure can enhance efficiency.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments according to the present disclosure will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present disclosure (for example, general configurations and manufacturing processes of fuel cell systems that do not characterize the present disclosure) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and common general technical knowledge in the relevant field. Also, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. 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 mainly a gas containing hydrogen and may be hydrogen. The oxidant gas is a gas containing oxygen and may be oxygen, air (air), etc.

[0011] In the present disclosure, there is provided a fuel cell system, The fuel cell system includes a fuel cell, a cooling system, and a control device. The cooling system includes a cooling water pump and a reserve tank. When the temperature of the cooling water is equal to or lower than a low-temperature determination threshold, the control device performs a temperature increase control to increase the temperature of the cooling water to a target temperature. After the temperature increase control, the control device cools the temperature of the cooling water to a normal operating temperature lower than the target temperature. The target temperature is set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank, providing a fuel cell system.

[0012] In general control, the cooling water is set to a uniform target temperature to operate the fuel cell. On the other hand, in the present disclosure, the target temperature of the cooling water is made variable. FIG. 1 is a graph showing the relationship between the temperature of the cooling water and the pressure in the cooling system. As the fuel cell generates heat during operation, the temperature of the cooling water rises. And the outlet pressure of the cooling water pump increases according to the flow rate of the cooling water driven by the pump. For example, when the temperature of the cooling water is A°C which is below the low temperature determination threshold, if the fuel cell is operated as it is, before the temperature of the cooling water reaches the normal operating temperature T°C, the pressure in the cooling system will reach the operating pressure of the reserve tank. When the fuel cell is operated when the temperature of the cooling water is B°C or C°C, even if the temperature of the cooling water reaches the normal operating temperature T°C, the pressure in the cooling system will not reach the operating pressure of the reserve tank, but there may be a case where the output of the cooling water pump has to be restricted. Therefore, without operating the fuel cell and without changing the pressure in the cooling system, the temperature of the cooling water is intentionally raised to the target temperature D°C. The target temperature is higher than the normal operating temperature T°C of the cooling water and is a temperature considering at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank. Then, the temperature of the cooling water is cooled to the normal operating temperature T°C and the fuel cell is operated. As a result, even when the cooling water pump is driven, the pressure in the cooling system will not exceed the pressure resistance of the cooling system. Therefore, according to the present disclosure, it is possible to maintain the cooling system so that the pressure resistance of the cooling system is not exceeded without restricting the operating range of the cooling water pump. In addition, due to the temperature increase control of the present disclosure, it is not necessary to perform a pressure resistance design assuming the worst case, the cost of the cooling system can be reduced, and since cooling water with a desired flow rate can be supplied to the fuel cell, power generation restriction of the fuel cell can also be avoided.

[0013] In the present disclosure, it is possible to maintain the cooling system so that the pressure resistance of the cooling system is not exceeded without restricting the operating range of the cooling water pump. In the present disclosure, it is possible to avoid unnecessary temperature increase control of the cooling water.

[0014] The fuel cell system of the present disclosure may be mounted on a moving body such as a vehicle and used. Also, the fuel cell system of the present disclosure may be mounted on a stationary power generation system such as a generator that supplies power to the outside of the fuel cell system and used. The vehicle may be a fuel cell vehicle or the like. Examples of moving bodies other than vehicles include railways, ships, aircraft, and the like. Further, the fuel cell system of the present disclosure may be mounted on a moving body such as a vehicle that can also run on the power of a secondary battery and used. The moving body and the stationary power generation system may include the fuel cell system of the present disclosure. The moving body may have a drive unit such as a motor, an inverter, and a hybrid control system. The hybrid control system may be capable of running the moving body by using the output of the fuel cell and the power of the secondary battery in combination.

[0015] The fuel cell system includes a fuel cell that generates electricity by the reaction of hydrogen and oxygen, a control device, and a cooling system that supplies cooling water for cooling the heat generated by the fuel cell during power generation. The fuel cell system may include a fuel gas system that supplies a fuel gas containing hydrogen necessary for the power generation of the fuel cell to the fuel cell, and an oxidant gas system that supplies an oxidant gas containing oxygen to the fuel cell.

[0016] The fuel cell system includes a fuel cell. The fuel cell may be a fuel cell stack in which a plurality of single cells (cells) of the fuel cell are stacked. In the present disclosure, both the cell and the fuel cell stack may be referred to as a fuel cell in some cases. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, 2 to several hundred. The fuel cell stack may have a current collector plate, a pressure plate, etc. at the ends in the stacking direction.

[0017] The cell may have a power generation part. The shape of the power generation part may be rectangular in plan view. The power generation part may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of the solid polymer electrolyte membrane include fluorine-based electrolyte membranes such as thin films of perfluorosulfonic acid containing moisture, and hydrocarbon-based electrolyte membranes. As the electrolyte membrane, for example, a Nafion membrane (manufactured by DuPont) may be used. One of the two electrodes is an anode (fuel electrode), and the other is a cathode (oxidant electrode). The electrode includes a catalyst layer and may optionally include a gas diffusion layer. The power generation part may be a membrane electrode gas diffusion layer assembly (MEGA). The catalyst layer contains a catalyst, and the catalyst may include a catalyst metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity. As the catalyst metal, for example, platinum (Pt) and alloys composed of Pt and other metals (for example, Pt alloys 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 may be the same or different. As the electrolyte, a fluorine-based resin or the like may be used. As the fluorine-based resin, for example, a Nafion solution or the like may be used. The above 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. Examples of the carrier for supporting the catalyst metal include carbon materials such as generally commercially available carbon. The gas diffusion layer may be a conductive member having pores. 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. The cell may include a separator. The separator collects the current generated by power generation and functions as a partition. In the cell, usually, a pair of separators are arranged on both sides in the stacking direction of the power generation part so as to sandwich the power generation part. One of the pair of separators is an anode separator, and the other is a cathode separator. The anode separator may have grooves serving as fuel gas flow paths on the surface on the power generation unit side. The cathode separator may have grooves serving as oxidant gas flow paths on the surface on the power generation unit side. The separator may have holes forming a manifold such as supply holes and discharge holes for allowing a fluid to flow in the stacking direction of the cells. Examples of the separator may include dense carbon obtained by compressing carbon to make it gas-impermeable, and press-molded metals (for example, iron, titanium, stainless steel, etc.). The cell may include an insulating resin frame disposed outside (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 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 be a three-layer sheet composed of three layers with an adhesive layer disposed on the surface layer.

[0018] The cooling system supplies cooling water as a cooling medium to the fuel cell. Examples of the cooling water include water and ethylene glycol, and a mixture thereof may also be used. The cooling system includes a cooling water pump and a reserve tank, and may include a cooling flow path, a radiator, a bypass flow path, a rotary valve, an ion exchanger, an intercooler, etc. as necessary. 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. The reserve tank is a tank that temporarily stores the cooling water overflowing from the cooling flow path whose internal pressure has increased due to the temperature rise of the cooling water. The cooling flow path is a flow path that circulates the cooling water for cooling the fuel cell inside and outside the fuel cell. The radiator is disposed on the cooling flow path and cools the cooling water. The bypass flow path branches off from the cooling flow path upstream of the radiator of the cooling flow path, bypasses the radiator, and merges with the cooling flow path downstream of the radiator of the cooling flow path. The rotary valve is disposed at the branch point from the cooling flow path to the bypass flow path. The rotary valve performs a flow path switching to switch whether to flow the cooling water discharged from the fuel cell to the radiator or to the bypass flow path. The rotary valve may include an electric motor such as an electric actuator for performing the flow path switching.

[0019] The oxidant gas system supplies an oxidant gas to the fuel cell and adjusts the flow rate of the oxidant gas. The oxidant gas system may include an oxidant gas supply means, an oxidant gas pipe, an inlet side sealing valve at the oxidant gas inlet of the fuel cell, an outlet side sealing valve at the oxidant gas outlet of the fuel cell, and the like. The oxidant gas supply means may be an air compressor or the like.

[0020] The fuel gas system supplies a fuel gas to the fuel cell and adjusts the flow rate of the fuel gas. The fuel gas system may 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 a fuel gas pipe and the like.

[0021] The fuel cell system may include a secondary battery. The secondary battery may be any rechargeable battery, and examples include conventionally known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. Further, the secondary battery may include a power storage element such as an electric double layer capacitor. The secondary battery may be configured with a plurality of them connected in series. The secondary battery supplies power to an air compressor or the like. The secondary battery may be rechargeable from an external power source of the fuel cell system such as a household power source, for example. The secondary battery may be charged by the output of the fuel cell. The charging and discharging of the secondary battery may be controlled by a control device.

[0022] The fuel cell system includes 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. Physically, the control device may include, for example, an arithmetic processing device such as a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a control program and control data processed by the CPU, and a RAM (Random Access Memory) that is mainly used as various work areas for control processing. It may also be an ECU (Electronic Control Unit) or the like.

[0023] When the temperature of the cooling water is equal to or lower than the low temperature determination threshold value, the control device performs a temperature increase control to raise the temperature of the cooling water to the target temperature. In order to control the reference pressure of the cooling system, the control device temporarily raises the temperature of the cooling water to the target temperature. For the temperature increase control, a heater may be provided at an arbitrary position in the cooling system, and the temperature of the cooling water may be raised by the heater. After the temperature increase control, the control device cools the cooling water to the normal use temperature lower than the target temperature. The target temperature may be higher than the normal use temperature. The target temperature is set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank. The low temperature determination threshold value may be set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank, and may be below the freezing point. For the pressure resistance of the cooling system, a data group related to the pressure resistance may be prepared in advance, and the pressure resistance may be set by referring to the data group related to the pressure resistance. For the operating pressure of the reserve tank, a data group showing the relationship between the pressure resistance of the cooling system and the operating pressure of the reserve tank may be prepared in advance, and the operating pressure may be set based on the pressure resistance of the cooling system.

[0024] The fuel cell system may include a temperature sensor. The temperature of the cooling water may be measured by the temperature sensor. The control device may determine whether or not the temperature of the cooling water measured by the temperature sensor is equal to or lower than the low temperature determination threshold value. When the temperature of the cooling water measured by the temperature sensor is equal to or lower than the low temperature determination threshold value, the control device may perform the temperature increase control. The control device may determine whether or not the temperature of the cooling water measured by the temperature sensor is equal to or lower than the low temperature determination threshold value at the time of starting the fuel cell system or constantly.

[0025] The control device may monitor the temperature history of the cooling water. When the temperature history becomes equal to or lower than the low temperature determination threshold value, the control device may perform the temperature increase control. The control device may have a temperature monitor that monitors the temperature of the cooling water.

[0026] FIG. 2 is a flowchart showing an example of the control of the fuel cell system of the present disclosure. The control device performs temperature increase control and intentionally raises the temperature of the cooling water to the target temperature (target water temperature). The control device determines whether or not the temperature of the cooling water has reached the target temperature. After determining that the temperature of the cooling water has reached the target temperature, the control device cools the temperature of the cooling water to the normal use temperature and shifts to the normal operation of the fuel cell.

[0027] FIG. 3 is a flowchart showing another example of the control of the fuel cell system of the present disclosure. The control device monitors (checks the water temperature) the temperature history of the cooling water. The control device determines whether or not the temperature of the cooling water measured by the temperature sensor is equal to or lower than the low temperature determination threshold value. When it is determined that the temperature history exceeds the low temperature determination threshold value, the control device does not perform the temperature increase control and sets the temperature of the cooling water to the normal use temperature. On the other hand, when it is determined that the temperature history is equal to or lower than the low temperature determination threshold value, the control device performs the temperature increase control and raises the temperature of the cooling water to the target temperature. The control device determines whether or not the temperature of the cooling water has reached the target temperature. After determining that the temperature of the cooling water has reached the target temperature, the control device cools the temperature of the cooling water to the normal operating temperature, shifts to the normal operation of the fuel cell, and ends the control. After the control ends, the low-temperature determination may be repeatedly performed. Thereby, it is possible to avoid performing unnecessary temperature increase control, which is excellent from the viewpoints of the efficiency of the fuel cell system and the durability of the fuel cell.

Claims

Claim 1 A fuel cell system comprising: a fuel cell, a cooling system, and a control device; the cooling system comprising a cooling water pump and a reserve tank; the control device performing a temperature increase control to increase the temperature of the cooling water to a target temperature when the temperature of the cooling water is equal to or lower than a low temperature determination threshold; the control device cooling the temperature of the cooling water to a normal operating temperature lower than the target temperature after the temperature increase control; the target temperature being set based on at least one of the pressure resistance of the cooling system and the operating pressure of the reserve tank, a fuel cell system. Claim 2 the control device monitoring a temperature history of the cooling water; the control device performing the temperature increase control when the temperature history becomes equal to or lower than the low temperature determination threshold, the fuel cell system according to claim 1.

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