Fuel cell system

Abstract

To provide a fuel cell system capable of maintaining the output of the fuel cell system.SOLUTION: A fuel cell system includes a fuel cell stack, a cooling flow path, a radiator, a bypass flow path, a switching valve for switching whether cooling water flows to the radiator or the bypass flow path, a power source for supplying power to the switching valve, a voltmeter for measuring the voltage of the power source, and a secondary battery. When the voltage of the power source measured by the voltmeter is equal to or more than a predetermined voltage, an upper limit of the output from the secondary battery is set to a first output, and when the voltage of the power source is less than the predetermined voltage, the upper limit of the output from the secondary battery is set to a second output larger than the first output.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to fuel cell systems. [Background technology]

[0002] Various technologies have been proposed regarding fuel cells (FCs), such as those disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-170378 A [Patent Document 2] JP 2008-130424 A Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional technology, the fuel cell water temperature is controlled by a circuit using a water pump and a switching valve to control the fuel cell cooling water temperature. In a fuel cell system, the motor torque of the cooling water switching valve fluctuates depending on the power supply voltage, so when the power supply voltage drops, the motor torque is not sufficient and the response of the switching valve decreases. The decrease in response of the switching valve reduces the output of the fuel cell and the output of the fuel cell system.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main object to provide a fuel cell system capable of maintaining the output of the fuel cell system. [Means for solving the problem]

[0006] In a first embodiment of the present disclosure, there is provided a fuel cell system, The fuel cell system includes a fuel cell stack and a cooling flow path for circulating cooling water for cooling the fuel cell stack inside and outside the fuel cell stack; a radiator disposed on the cooling passage; a bypass flow path that branches off from the cooling flow path upstream of the radiator, bypasses the radiator, and merges with the cooling flow path downstream of the radiator; a switching valve that is disposed at a branch point of the cooling flow path with the bypass flow path and switches whether the cooling water discharged from the fuel cell stack flows to the radiator or to the bypass flow path; A power source for supplying power to the switching valve; a voltmeter for measuring the voltage of the power supply; A secondary battery, A fuel cell system is provided in which, when the voltage of the power source measured by the voltmeter is equal to or higher than a predetermined voltage, the upper limit of the output from the secondary battery is set to a first output, and, when the voltage of the power source is less than the predetermined voltage, the upper limit of the output from the secondary battery is set to a second output greater than the first output.

[0007] In a second embodiment of the present disclosure, in the first embodiment, a response time of the switching valve is estimated based on the voltage of the power source measured by the voltmeter, estimating a temperature of the cooling water flowing into the fuel cell stack based on the response time; When the estimated temperature of the coolant is equal to or lower than a predetermined temperature, an upper limit of the output from the secondary battery may be set as the second output. Effect of the Invention

[0008] The fuel cell system of the present disclosure can maintain the output of the fuel cell system. [Brief description of the drawings]

[0009] [Figure 1] 4 is a graph showing an example of the relationship between a pulse rate, a driving torque, and a power supply voltage. [Diagram 2]1 is a diagram showing an example of the ratio of the fuel cell output to the secondary battery output when the power supply voltage is high, and the ratio of the fuel cell output to the secondary battery output when the power supply voltage is low; [Diagram 3] 1 is a system configuration diagram showing an example of a fuel cell system according to the present disclosure. [Figure 4] 4 is a flowchart showing an example of control of the fuel cell system of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described. Note that matters other than those specifically mentioned in this specification and necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a fuel cell system that does not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the field. Furthermore, 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 a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, etc.

[0011] The present disclosure provides a fuel cell system, comprising: The fuel cell system includes a fuel cell stack and a cooling flow path for circulating cooling water for cooling the fuel cell stack inside and outside the fuel cell stack; a radiator disposed on the cooling passage; a bypass flow path that branches off from the cooling flow path upstream of the radiator, bypasses the radiator, and merges with the cooling flow path downstream of the radiator; a switching valve that is disposed at a branch point of the cooling flow path with the bypass flow path and switches whether the cooling water discharged from the fuel cell stack flows to the radiator or to the bypass flow path; A power source for supplying power to the switching valve; a voltmeter for measuring the voltage of the power supply; A secondary battery, A fuel cell system is provided in which, when the voltage of the power source measured by the voltmeter is equal to or higher than a predetermined voltage, the upper limit of the output from the secondary battery is set to a first output, and, when the voltage of the power source is less than the predetermined voltage, the upper limit of the output from the secondary battery is set to a second output greater than the first output.

[0012] FIG. 1 is a graph showing an example of the relationship between the pulse rate, the driving torque, and the power supply voltage. In a fuel cell system, the motor torque (driving torque) of the coolant switching valve varies with the power supply voltage as shown in Fig. 1, so when the power supply voltage drops, the motor torque is insufficient, the pulse rate of the coolant switching valve drops, and the responsiveness drops. When the responsiveness of the switching valve drops, the switching of the coolant from the radiator side to the bypass flow path that bypasses the radiator becomes slower, and compared to before the responsiveness decreased, the temperature of the coolant increases more slowly, causing a drop in the temperature of the coolant flowing into the fuel cell, lowering the inlet and outlet water temperatures of the fuel cell, and lowering the output of the fuel cell when a moving object such as a vehicle accelerates. FIG. 2 is a diagram showing an example of the ratio of the fuel cell output to the secondary battery output when the power supply voltage is high, and the ratio of the fuel cell output to the secondary battery output when the power supply voltage is low. In the present disclosure, when the voltage of the power source supplying power to the switching valve is below a predetermined voltage, a greater than normal output is supplied from the secondary battery (Bat), thereby compensating for the reduced output of the fuel cell, maintaining the output of the entire system and obtaining a predetermined system output, and under normal circumstances, the output from the secondary battery is kept low to suppress deterioration of the secondary battery.

[0013] The fuel cell system of the present disclosure may be mounted on a moving object such as a vehicle, etc. Also, the fuel cell system of the present disclosure may be mounted on a stationary power generation system such as a generator that supplies electric power to the outside of the fuel cell system. The vehicle may be a fuel cell vehicle, etc. Examples of moving bodies other than vehicles include trains, ships, and aircraft. Furthermore, the fuel cell system of the present disclosure may be mounted on and used in a mobile object such as a vehicle that can also run on power from a secondary battery. A mobile object and a stationary power generation system may include the fuel cell system of the present disclosure. The mobile object may have a drive unit such as a motor, an inverter, a hybrid control system, and the like. The hybrid control system may be capable of running a mobile object using both the output of the fuel cell and the power of the secondary battery.

[0014] The fuel cell system includes a fuel cell that generates electricity by reacting hydrogen and oxygen, a fuel gas system that supplies the fuel cell with fuel gas containing the hydrogen necessary for the fuel cell to generate electricity, an oxidant gas system that supplies the fuel cell with oxidant gas containing oxygen, and a cooling system that supplies the fuel cell with cooling water to cool the heat generated by power generation.

[0015] The fuel cell may have only one unit cell (cell) of the fuel cell, or may be a fuel cell stack (stack) which is a laminate of a plurality of cells. In this disclosure, both cells and fuel cell stacks may be referred to as fuel cells. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, from 2 to several hundred. The fuel cell stack may have current collector plates, pressure plates, etc. at the ends in the stacking direction.

[0016] The cell may have a power generation portion. The power generating section may have a rectangular shape in a plan view. The power generating section 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 a fluorine-based electrolyte membrane such as a thin film of perfluorosulfonic acid containing water, and a hydrocarbon-based electrolyte membrane. 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 (oxidizer electrode). The electrodes include a catalyst layer and may include a gas diffusion layer as necessary, and the power generating portion may be a membrane electrode gas diffusion layer assembly (MEGA). The catalyst layer includes a catalyst, and the catalyst may include a catalytic metal that promotes an electrochemical reaction, an electrolyte having proton conductivity, and a carrier having electron conductivity. Examples of the catalytic metal that can be used include platinum (Pt) and alloys of Pt with other metals (e.g., Pt alloys mixed with cobalt and nickel, etc.) The catalytic metal used as the cathode catalyst and the catalytic metal used as the anode catalyst may be the same or different. The electrolyte may be a fluorine-based resin, etc. As the fluorine-based resin, for example, a Nafion solution, etc. may be used. The catalytic metal is supported on a carrier, and in each catalyst layer, the carrier supporting the catalytic metal (catalyst-supporting carrier) and the electrolyte may be mixed. The support for supporting the catalytic metal may be, for example, a carbon material such as carbon that is generally available commercially. The gas diffusion layer may be a conductive member having air holes. Examples of the conductive member include porous carbon materials such as carbon cloth and carbon paper, and porous metal members such as metal mesh and foamed metal. The fuel cell may include a separator. The separators collect the electric current generated by power generation and function as partition walls. In a fuel cell, the separators are usually arranged on both sides of the power generation section in the stacking direction so that the power generation section is sandwiched between a pair of separators. One of the pair of separators is an anode separator and the other is a cathode separator. The anode separator may have grooves that serve as fuel gas flow paths on the surface facing the power generation section. The cathode separator may have grooves that serve as oxidant gas flow paths on the surface facing the power generation section. The separator may have holes forming manifolds such as supply holes and discharge holes for circulating a fluid in the stacking direction of the cells. The separator may be made of, for example, dense carbon obtained by compressing carbon to make it gas impermeable, or a press-molded metal (for example, iron, titanium, stainless steel, etc.). The cell may include an insulating resin frame disposed on the outer side (periphery) of the membrane electrode assembly in the planar direction between the anode separator and the cathode separator. The resin frame is molded into a plate-like and frame-like shape using a thermoplastic resin, and seals the gap between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. For the resin frame, for example, a resin such as PE, PP, PET, or 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.

[0017] The fuel cell system may include a control device that controls the oxidant gas system, the fuel gas system, the cooling system, etc., and may control the entire fuel cell system. The control device physically has, for example, a processing device such as a CPU (central processing unit), a ROM (read-only memory) that stores control programs and control data processed by the CPU, a storage device such as a RAM (random access memory) that is mainly used as various working areas for control processing, and an input / output interface, and may be an ECU (electronic control unit), etc.

[0018] The cooling system supplies cooling water as a cooling medium to the fuel cell. The cooling water may be water, ethylene glycol, or a mixture thereof. The cooling system includes a cooling passage, a radiator, a bypass passage, and a switching valve, and may also include a reserve tank, a cooling water pump, an ion exchanger, an intercooler, a temperature sensor, and the like, as necessary. The cooling flow passage is a flow passage through which cooling water for cooling the fuel cell stack is circulated inside and outside the fuel cell stack. The radiator is disposed on the cooling passage. The bypass flow passage branches off from the cooling flow passage upstream of the radiator of the cooling flow passage, bypasses the radiator, and merges with the cooling flow passage downstream of the radiator of the cooling flow passage. The switching valve is disposed at a branch point of the cooling flow path with the bypass flow path, and switches the flow path so that the cooling water discharged from the fuel cell stack flows either to the radiator or to the bypass flow path. The switching valve may include an electric motor such as an electric actuator for switching the flow path. The cooling water pump adjusts the flow rate of the cooling water supplied to the fuel cell.

[0019] The fuel cell system includes a power source that supplies power to the switching valve. The fuel cell system includes a voltmeter that measures the voltage of the power source. The fuel cell system includes a secondary battery. The secondary battery may be any battery capable of being charged and discharged, and examples of such batteries include conventionally known secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries. The secondary battery may also include a storage element such as an electric double layer capacitor. The secondary battery may be configured with a plurality of batteries connected in series. The secondary battery supplies power to a power source, an air compressor, etc. The secondary battery may be capable of being charged from a power source external to the fuel cell system, such as a household power source. 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.

[0020] The fuel cell system sets the upper limit of the output from the secondary battery to a first output when the voltage of the power source measured by the voltmeter is equal to or higher than a predetermined voltage. On the other hand, the fuel cell system sets the upper limit of the output from the secondary battery to a second output that is higher than the first output when the voltage of the power source measured by the voltmeter is lower than the predetermined voltage. The first output and the second output are not particularly limited as long as the second output is higher than the first output, and can be set appropriately taking into consideration the maximum output of the secondary battery, the maximum output of the fuel cell, etc.

[0021] The fuel cell system may estimate the response time of the switching valve based on the voltage of the power source measured by a voltmeter. Because the response time of the switching valve increases as the voltage of the power source decreases, the fuel cell system may prepare in advance a data set showing the relationship between the voltage of the power source and the response time of the switching valve, and may estimate the response time of the switching valve by comparing the voltage of the power source measured by the voltmeter with the data set. The fuel cell system may estimate the temperature of the cooling water flowing into the fuel cell stack based on the estimated response time of the switching valve. When the response time of the switching valve becomes longer, the switching of the cooling water from the radiator side to the bypass flow path side that bypasses the radiator becomes slower, and the temperature rise of the cooling water becomes slower compared to before the response time became longer (response becomes lower), so the temperature of the cooling water flowing into the fuel cell stack decreases, the inlet water temperature and outlet water temperature of the fuel cell stack become lower, and the output of the fuel cell stack decreases. Therefore, the fuel cell system may prepare in advance a group of data showing the relationship between the response time of the switching valve and the temperature of the cooling water flowing into the fuel cell stack, and estimate the temperature of the cooling water flowing into the fuel cell stack by comparing the estimated response time of the switching valve with the group of data. When the estimated temperature of the cooling water is equal to or lower than a predetermined temperature, the fuel cell system may determine that the output of the fuel cell stack is decreasing, and set the upper limit of the output from the secondary battery to the second output. In the present disclosure, by basing the determination of whether or not output assistance is required in the secondary battery on the estimated coolant temperature, output assistance in the secondary battery can be performed more accurately without adding an additional temperature sensor.

[0022] The oxidant gas system supplies an oxidant gas to the fuel cell and adjusts the flow rate of the oxidant gas, and may include an oxidant gas supply means, an oxidant gas pipe, an inlet-side sealing valve at an oxidant gas inlet of the fuel cell, and an outlet-side sealing valve at an oxidant gas outlet of the fuel cell. The oxidant gas supplying means may be an air compressor or the like.

[0023] The fuel gas system supplies fuel gas to the fuel cell and adjusts the flow rate of the fuel gas, and may include a fuel gas tank, a fuel gas inlet valve, an injector, a gas-liquid separator, a fuel gas purge valve, an ejector for circulating the fuel gas, a fuel gas pump for circulating the fuel gas, and a fuel gas pipe.

[0024] FIG. 3 is a system configuration diagram showing an example of a fuel cell system according to the present disclosure. 3 includes a fuel cell stack 10, a cooling system 50, and a temperature sensor T, and although not shown, the fuel cell system also includes a power source, a voltmeter, a secondary battery, an oxidizer gas system, and a fuel gas system. The cooling system 50 includes a cooling passage 51, a radiator 52, a bypass passage 53, a switching valve 54, a reserve tank 55, a cooling water pump 56, an ion exchanger 57, and an intercooler 58.

[0025] FIG. 4 is a flowchart showing an example of control of the fuel cell system of the present disclosure. The operation of the fuel cell system is started, and it is determined whether or not the supply voltage V from the power source is equal to or higher than a predetermined voltage threshold Vc. When the supply voltage from the power source is equal to or higher than Vc, the output Wout from the secondary battery is set to the output upper limit Wlow. On the other hand, when the voltage supplied from the power source is less than Vc, the output Wout from the secondary battery is set to an output upper limit Wup which is higher than the output upper limit Wlow, and when the voltage supplied from the power source is low, the output from the secondary battery is increased. The fuel cell system may continue to check the power supply voltage V in a predetermined cycle until operation is stopped, and may end the control when operation is stopped. [Explanation of symbols]

[0026] 10. Fuel Cell Stack 50. Cooling system 51. Cooling channel 52. Radiator 53.Bypass flow path 54. Switching valve 55.Reserve tank 56. Cooling water pump 57. Ion exchanger 58. Intercooler T. Temperature sensor

Claims

1. 1. A fuel cell system comprising: The fuel cell system includes a fuel cell stack and a cooling flow path for circulating cooling water for cooling the fuel cell stack inside and outside the fuel cell stack; a radiator disposed on the cooling passage; a bypass flow path that 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; a switching valve that is disposed at a branch point of the cooling flow path with the bypass flow path and switches whether the cooling water discharged from the fuel cell stack flows to the radiator or to the bypass flow path; A power source for supplying power to the switching valve; a voltmeter for measuring the voltage of the power supply; A secondary battery, a first output that is an upper limit of the output from the secondary battery when the voltage of the power source measured by the voltmeter is equal to or higher than a predetermined voltage, and a second output that is greater than the first output that is higher than the predetermined voltage when the voltage of the power source is less than the predetermined voltage.

2. A response time of the switching valve is estimated based on the voltage of the power source measured by the voltmeter; estimating a temperature of the cooling water flowing into the fuel cell stack based on the response time; 2. The fuel cell system according to claim 1, wherein when the estimated temperature of the cooling water is equal to or lower than a predetermined temperature, an upper limit of the output from the secondary battery is set to the second output.

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