Fuel battery system

Abstract

To provide a fuel battery system capable of improving a startability under an ice point.SOLUTION: A fuel battery system comprises: a fuel battery stack; a cooling water pump; a temperature sensor; and a control device. The fuel battery stack includes a plurality of cell to be laminated. The cooling water pump circulates a cooling water for cooling the fuel battery stack. The temperature sensor measures an external temperature at a start of the fuel battery system. The control device determines a deterioration level of the plurality of cells, and the control device determines a time when the cooling water pump is stopped in accordance with the deterioration level of the plurality of cells at a start time under a freezing point of the fuel battery system.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Various technologies have been proposed regarding fuel cells (FCs) as disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a means for improving the startability at sub-zero start of a fuel cell system, there is coolant stop control. If the coolant stop time is too long, the catalyst and the like deteriorate due to abnormal temperature rise of the fuel cell. If the coolant 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 coolant stop time. On the other hand, when the fuel cell is applied commercially, as the total usage time of the fuel cell becomes longer, the catalyst layer deteriorates, and the sub-zero startability of the fuel cell system gradually decreases. Therefore, it is necessary to consider the degree of deterioration of the fuel cell when determining the coolant stop time. In Patent Document 1, a fuel cell system is disclosed that prevents the generated water inside the fuel cell from freezing by stopping the coolant pump for a predetermined time if the temperature sensor value is below a predetermined temperature at sub-zero start. If the stop time of the coolant pump is determined only considering the performance at the time of manufacturing the fuel cell system, it cannot be applied after the durability deterioration of the fuel cell system. Further, 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, there is a possibility of overheating the fuel cell.

[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 improving sub-zero startability.

Means for Solving the Problems

[0006] That is, the present disclosure includes the following aspects. <1> A fuel cell system, The fuel cell system includes a fuel cell stack, a cooling water pump, a temperature sensor, and a control device, The fuel cell stack has a plurality of stacked cells, The cooling water pump circulates cooling water for cooling the fuel cell stack, The temperature sensor measures the outside air temperature at the start of the fuel cell system, The control device determines the degree of degradation of the plurality of cells, When starting the fuel cell system below freezing, the control device determines the time to stop the cooling water pump according to the degree of degradation of the plurality of cells. A fuel cell system.

[0007] <2> The control device estimates the water content of the plurality of cells when the operation of the fuel cell stack stops, When the time determined by the control device to stop the cooling water pump exceeds a predetermined time corresponding to the water content, the control device performs scavenging so that the estimated water content of the plurality of cells is less than a predetermined water content when the operation of the fuel cell stack stops. The predetermined time is the stop time of the cooling water pump at which the fuel cell stack abnormally overheats. The fuel cell system according to <1>.

Advantages of the Invention

[0008] The fuel cell system of the present disclosure can improve sub-zero startability.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments according to the present disclosure will be described. In addition, matters other than those particularly mentioned in this specification and matters necessary for carrying out 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 knowledge in the relevant field. Also, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. 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 mainly a gas containing hydrogen and may be hydrogen. The oxidant gas is a gas containing oxygen and may be oxygen, air, etc.

[0011] In the present disclosure, there is provided a fuel cell system, the fuel cell system includes a fuel cell stack, a cooling water pump, a temperature sensor, and a control device, the fuel cell stack has a plurality of stacked cells, the cooling water pump circulates cooling water for cooling the fuel cell stack, the temperature sensor measures the outside air temperature at the start of the fuel cell system, the control device determines the degree of deterioration of the plurality of cells, When starting the fuel cell system below freezing point, the control device determines the time to stop the cooling water pump according to the degree of degradation of the plurality of cells, and provides a fuel cell system.

[0012] In the present disclosure, according to the degradation of the fuel cell (the number of cells whose voltage has dropped below a predetermined value), the time to stop the cooling water pump (the criterion for integrating the heat generation amount of the fuel cell) is changed. In the present disclosure, after the time to stop the cooling water pump (the criterion for integrating the heat generation amount of the fuel cell) becomes longer than the criterion for overheating of the 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 cells at the start of the fuel cell system. Thereby, since the cooling water is not stopped unnecessarily, while minimizing the degradation of the electrolyte membrane, catalyst, etc. due to abnormal overheating of the fuel cell and the degradation of the separator due to thermal distortion generated when supplying the cooling water from the cooling water stop state, the starting performance below freezing point can be ensured regardless of the degree of degradation of the cells. Even when the fuel cell is applied commercially, the starting performance below freezing point can be ensured even after the durability of the fuel cell while minimizing the durability input due to the cooling water stop. Even in a state where the degradation of the cells progresses and the cooling water stop time reaches the abnormal overheating threshold of the fuel cell, the starting performance below freezing point of the fuel cell system can be ensured without causing abnormal overheating. Even when the fuel cell is applied commercially and the degradation of the cells progresses, the starting performance below freezing point of the fuel cell system can be ensured without causing abnormal overheating of the fuel cell even after the durability of the fuel cell.

[0013] FIG. 1 is a system configuration diagram showing an example of the fuel cell system of the present disclosure. The fuel cell system shown in Fig. 1 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 and drain valve 84, a pressure sensor P, etc.

[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, airplanes, etc. Also, the fuel cell system of the present disclosure may be mounted on a moving body such as a vehicle that can 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, a hybrid control system, etc. 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 fuel gas system that supplies a fuel gas containing hydrogen necessary 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 the power generation to the fuel cell, etc.

[0016] The fuel cell system includes a fuel cell stack. The fuel cell stack (stack) is a laminate in which a plurality of single cells (cells) of the fuel cell are laminated. 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 hundreds. The fuel cell stack may have a current collector plate, a pressure plate, etc. at the end 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. The electrolyte membrane may be, for example, a Nafion membrane (manufactured by DuPont). 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 includes 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. The electrolyte may be a fluorine-based resin. As the fluorine-based resin, for example, a Nafion solution 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 of the fuel cell may include a separator. The separator collects the current generated by power generation and functions as a partition. In the cell of the fuel 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 part side. The cathode separator may have grooves serving as oxidant gas flow paths on the surface on the power generation part side. The separator may have holes constituting a manifold such as supply holes and discharge holes for allowing a fluid to flow in the stacking direction of the cell. Examples of the separator 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 arranged 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 using a thermoplastic resin into a plate-like and frame-like shape, and seals the space between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. Examples of the resin that can be used for the resin frame include resins such as PE, PP, PET, and PEN. The resin frame may be a three-layer sheet composed of three layers with an adhesive layer arranged on the surface layer.

[0018] The cooling system supplies cooling water as a cooling medium to the fuel cell stack. 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 may include, as necessary, a cooling flow path, a radiator, a bypass flow path, a rotary valve, a reserve tank, an ion exchanger, an intercooler, a temperature sensor, etc. 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. 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. The radiator is arranged on the cooling flow path. The bypass flow path branches off from the cooling flow path upstream of the radiator in the cooling flow path, bypasses the radiator, and merges with the cooling flow path downstream of the radiator in the cooling flow path. The rotary valve is arranged at the branch point between the bypass flow path and the cooling flow path in the cooling flow path, and performs flow path switching to switch whether the cooling water discharged from the fuel cell stack flows to the radiator or the bypass flow path. The rotary valve may be provided with an electric motor such as an electric actuator for performing flow path switching. The temperature sensor of the cooling system measures the temperature of the cooling water.

[0019] The oxidant gas system supplies 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, etc. The oxidant gas supply means may be an air compressor or the like.

[0020] The fuel gas system supplies 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 and drainage valve, an ejector for fuel gas circulation, a fuel gas pump for fuel gas circulation, and a fuel gas pipe, etc.

[0021] The fuel cell system includes a temperature sensor. The temperature sensor measures the outside air temperature when the fuel cell system starts up.

[0022] 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 cells 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 supply, 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. The fuel cell system may include a converter.

[0023] 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 storage device such as a RAM (Random Access Memory) mainly used as various work areas for control processing, and an input / output interface, and may be an ECU (Electronic Control Unit) or the like.

[0024] The control device determines the degree of deterioration of a plurality of cells. When starting the fuel cell system below the freezing point, the control device determines the time (required cooling water stop time) to stop the cooling water pump according to the degree of deterioration of a plurality of cells. The degree of deterioration of a plurality of cells may be determined from the voltage of each cell or the voltage of the fuel cell stack, and the average or maximum air stoichiometry during warm-up. The fuel cell system may include a voltage sensor. The voltage of each cell or the voltage of the fuel cell stack may be measured by the voltage sensor. The control device may have a cell monitor that monitors the voltage of each cell. The control device may determine whether the voltage of each cell measured by the voltage sensor is equal to or lower than a predetermined voltage. When the voltage of the cell measured by the voltage sensor is equal to or lower than a predetermined voltage, the control device may determine that the cell is deteriorated. The required cooling water stop time determined by the control device may be the required cooling water stop time at the next sub-zero start.

[0025] The control device may estimate the water content of a plurality of cells when the operation of the fuel cell stack stops. When the time for stopping the cooling water pump determined by the control device exceeds a predetermined time (permissible cooling water stop time) corresponding to the water content, the control device may perform scavenging so that the estimated water content of the plurality of cells becomes smaller than a predetermined water content (permissible generated water amount) when the operation of the fuel cell stack stops. For example, the scavenging time may be longer than the normal scavenging time. The predetermined time (permissible cooling water stop time) may be the stop time of the cooling water pump at which the fuel cell stack abnormally overheats. The estimation of the water content of the plurality of cells may be performed by measuring the impedance of each cell. A data group showing the relationship between the impedance and the water content of each cell may be prepared in advance, and the water content of each cell may be estimated by comparing the impedance of each cell with the data group.

[0026] The determination of the required cooling water stop time at the sub-zero start of the fuel cell system may be performed by the following method. In the relationship between the permissible generated water amount (g / cell) and the permissible cooling water stop time (sec) or the permissible integrated heat generation amount (kJ), if the strength (permissible generated water amount) is greater than the stress (permissible cooling water stop time or permissible integrated heat generation amount), the sub-zero start of the fuel cell system is possible. FIG. 2 is a graph showing the relationship between the number of cells deteriorated to below a predetermined voltage and the permissible generated water amount (g / cell). Prepare a second data group indicating the relationship between the allowable generated water volume (g / cell) and the allowable cooling water stop time (sec) or the allowable integrated heat generation amount (kJ), and a third data group indicating the relationship between the number of cells below a predetermined voltage shown in FIG. 2 and the allowable generated water volume. Then, determine the necessary cooling water stop time corresponding to the number of cells below a predetermined voltage in comparison with the second data group and the third data group, and prepare a fourth data group indicating the relationship between the number of cells below a predetermined voltage and the necessary cooling water stop time. Determine the necessary cooling water stop time corresponding to the number of cells below a predetermined voltage at the time of starting below freezing based on the fourth data group. When the necessary cooling water stop time determined from the number of cells below a predetermined voltage reaches the threshold value ΔT (sec) of the allowable cooling water stop time, which is the cell overheat criterion, strengthen the scavenging level at the time of stopping the operation of the fuel cell and increase the allowable generated water volume (strength).

[0027] FIG. 3 is a flowchart showing an example of the control of the fuel cell system of the present disclosure. Start the operation of the fuel cell system. When the outside air temperature measured by the temperature sensor is below freezing, the control device warms up the fuel cell stack as a start below freezing. During warm-up, the control device determines the degree of degradation of a plurality of cells. Specifically, count the number of cells below a predetermined voltage. When the temperature of the cooling water of the fuel cell stack (FC water temperature) exceeds a predetermined temperature β, end the warm-up. During warm-up or after warm-up, the control device determines the time (necessary cooling water stop time) to stop the cooling water pump at the next start below freezing according to the degree of degradation of a plurality of cells (the number of cells below a predetermined voltage). The control device estimates the water content of a plurality of cells at the time of stopping the operation of the fuel cell stack. When the necessary cooling water stop time determined by the control device exceeds a predetermined time (allowable cooling water stop time) γ corresponding to the estimated water content of a plurality of cells, the control device sets the scavenging time longer than the normal scavenging time so that the estimated water content of a plurality of cells becomes smaller than a predetermined water content (allowable generated water volume) at the time of stopping the operation of the fuel cell stack, performs scavenging, and ends the control. On the other hand, when the determined required cooling water stop time of the control device is within a predetermined time (permissible cooling water stop time) corresponding to the water content of the plurality of estimated cells, the control device performs scavenging by setting the scavenging time to the normal scavenging time when stopping the operation of the fuel cell stack and ends the control.

Explanation of Signs

[0028] 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

Claims

1. A fuel cell system comprising: a fuel cell stack, a cooling water pump, a temperature sensor, and a control device; the fuel cell stack having a plurality of stacked cells; the cooling water pump circulating cooling water for cooling the fuel cell stack; the temperature sensor measuring the outside air temperature at the start of operation of the fuel cell system; the control device determining the degree of degradation of the plurality of cells; a fuel cell system, wherein, when starting the fuel cell system below the freezing point, the control device determines the time to stop the cooling water pump according to the degree of degradation of the plurality of cells.

2. the control device estimating the water content of the plurality of cells at the stop of operation of the fuel cell stack; when the time to stop the cooling water pump determined by the control device exceeds a predetermined time corresponding to the water content, the control device performs scavenging at the stop of operation of the fuel cell stack so that the estimated water content of the plurality of cells becomes less than a predetermined water content; the fuel cell system according to claim 1, wherein the predetermined time is the stop time of the cooling water pump at which abnormal overheating of the fuel cell stack occurs.

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