Fuel cell system

Abstract

To provide a fuel cell system that can suppress the decrease in power generation efficiency of fuel cells. [Solution] A fuel cell system comprising a fuel cell and a control unit, wherein the control unit calculates a current deviation between the initial current value of the fuel cell and the current value of the fuel cell when the fuel cell is generating power, the control unit calculates the amount of pressure control for the oxygen electrode of the fuel cell necessary to reduce the current deviation from the calculated current deviation, and controls the pressure of the oxygen electrode based on the amount of pressure control.

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] In Patent Document 1, a protection control device during battery performance deterioration is disclosed, which adjusts the output by increasing or decreasing the current value according to an output command based on the result of periodically measuring the voltage V and current I of the fuel cell. In order to maintain the same power generation output after battery performance deterioration, it is necessary to instruct the fuel cell to generate electricity at a high current. However, the heat loss of the fuel cell increases and the power generation efficiency of the fuel cell decreases compared to before the battery performance deterioration.

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

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 and a control unit, During power generation of the fuel cell, the control unit calculates a current deviation between a current value in an initial state and a current value in a current state of the fuel cell. The fuel cell system is characterized in that the control unit calculates the amount of pressure control for the oxygen electrode of the fuel cell necessary to reduce the current deviation from the calculated current deviation, and controls the pressure of the oxygen electrode based on the pressure control amount. [Effects of the Invention]

[0007] The fuel cell system of this disclosure can suppress the decrease in the power generation efficiency of the fuel cell. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a system configuration diagram showing an example of the fuel cell system of this disclosure. [Figure 2] Figure 2 is a flowchart showing an example of oxygen polar pressure control. [Figure 3] Figure 3 shows (1) a graph illustrating an example of data used to determine IV characteristic degradation due to current deviation, and (2) an example of oxygen electrode pressure control logic. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure are described below. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (e.g., general configurations and manufacturing processes of fuel cell systems not characterizing this disclosure) can be understood as design matters for those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed herein and common technical knowledge in the art. Furthermore, the dimensions (length, width, thickness, etc.) shown in the diagram do not necessarily reflect the actual dimensions. In this disclosure, the reaction gas supplied to the anode of the fuel cell is the fuel gas (anode gas), and the reaction gas supplied to the cathode of the fuel cell is the oxidizing gas (cathode gas). The fuel gas is mainly a gas containing hydrogen, but may also be hydrogen. The oxidizing gas is a gas containing oxygen, but may also be oxygen, air, etc.

[0010] In this disclosure, a fuel cell system, The fuel cell system comprises a fuel cell and a control unit. The control unit calculates the current difference between the current value of the fuel cell in its initial state and the current value of the fuel cell in its current state when the fuel cell is generating power. The control unit calculates the amount of pressure control for the oxygen electrode of the fuel cell necessary to reduce the current deviation from the calculated current deviation, and controls the pressure of the oxygen electrode based on the pressure control amount, thereby providing a fuel cell system.

[0011] According to this disclosure, even if the current-voltage characteristics of a fuel cell deteriorate over time, the deterioration of the current-voltage characteristics can be determined from the current deviation between the target current value calculated based on the target power generation value and the current value measured by the sensor. The oxygen electrode pressure required to reduce the current deviation can be calculated, and the current deviation can be reduced by controlling the oxygen electrode pressure (pressurizing the oxygen electrode), thereby restoring the current-voltage characteristics of the fuel cell and bringing it closer to the state at the beginning of fuel cell power generation. This suppresses the increase in heat loss of the fuel cell due to deterioration over time, and as a result, it is possible to suppress the decrease in power generation efficiency of the fuel cell due to deterioration over time.

[0012] The fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle, or it may be used mounted on a vehicle. Furthermore, the fuel cell system of this disclosure may be used mounted on a stationary power generation system such as a generator that supplies power to the outside of the fuel cell system. The vehicle may be a fuel cell vehicle or the like. Other means of transport include, for example, trains, ships, and aircraft. Furthermore, the fuel cell system of this disclosure may be used mounted on a mobile device such as a vehicle that can also run on the power of a secondary battery. The mobile unit and the stationary power generation system may include the fuel cell system of this disclosure. The mobile unit may have drive units such as a motor, inverter, and hybrid control system. The hybrid control system may be able to run a moving body by using the output of a fuel cell and the power of a secondary battery together.

[0013] FIG. 1 is a system configuration diagram showing an example of the fuel cell system of the present disclosure. The fuel cell system includes a fuel cell 1, a control unit 2, a current sensor 3, a voltage sensor 4, a fuel gas system 10, and an oxygen system 20. The fuel gas system 10 and the oxygen system 20 are controlled by the control unit 2. In FIG. 1, the cooling system is omitted for convenience. The fuel gas system 10 includes a regulator 13, controls the hydrogen stored in the hydrogen tank 11 to an appropriate supply pressure, and supplies it to the fuel cell stack 1. The fuel gas system 10 includes a shut-off valve 12, an ejector 14, a hydrogen electrode pressure sensor 15, a gas-liquid separator 17, a drain valve 18, and a muffler 19. The oxygen system 20 includes a regulator 23, controls the oxygen stored in the oxygen tank 21 to an appropriate supply pressure, and supplies it to the fuel cell stack 1. The oxygen system 20 includes a shut-off valve 22, an ejector 24, a cathode outlet pressure sensor 25, a gas-liquid separator 27, and a drain valve 28. In FIG. 1, an oxygen circulation system using an ejector that utilizes the pressure of the high-pressure oxygen tank 21 as oxygen electrode pressure control means is assumed. Different from a system using an air compressor, since oxygen electrode pressure control such as pressurization can be performed using the tank pressure, the auxiliary loss is extremely small, and an improvement in the FC system efficiency can be expected together with the effect of improving the FC power generation efficiency.

[0014] The fuel cell system of the present disclosure includes a fuel cell and a control unit. The fuel cell system may include a fuel gas system, an oxygen system, a cooling system, etc.

[0015] The fuel cell may be a fuel cell stack (stack) that 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 for example, it may be 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.

[0016] 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) etc. may be used. One of the two electrodes is an anode (hydrogen electrode), and the other is a cathode (oxygen 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, etc. 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 etc. may be used. As the fluorine-based resin, for example, a Nafion solution etc. 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 etc. Examples of conductive materials include carbon porous materials such as carbon cloth and carbon paper, as well as metal porous materials such as metal mesh and foamed metal. A cell may include a separator. Separators collect the current generated by power generation and function as partitions. In a cell, separators are usually placed on both sides of the power generation section in the stacking direction, with a pair of separators sandwiching the power generation section. One of the separators is the anode separator and the other is the cathode separator. The anode separator may have a groove on the side facing the power generation section that serves as a fuel gas passage, or a groove on the side opposite to the side facing the power generation section that serves as a cooling medium passage. The cathode separator may have grooves on the side facing the power generation section that serve as oxidizing agent gas channels, and may have grooves on the side opposite to the side facing the power generation section that serve as cooling medium channels. The separator may have holes that constitute a manifold, such as supply holes and discharge holes, for circulating fluid in the stacking direction of the cells. The separator may be, for example, dense carbon that has been compressed to be gas-impermeable, or press-formed metal (for example, iron, titanium, and stainless steel). The cell may include an insulating resin frame positioned on the outer (circumferential) side in the planar direction of the membrane electrode assembly between the anode separator and the cathode separator. The resin frame is molded from a thermoplastic resin to form a plate-like or frame-like structure, and seals the space between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. For example, resins such as PE, PP, PET, and PEN can be used for the resin frame. The resin frame may also be a three-layer sheet composed of three layers with an adhesive layer on the surface.

[0017] Figure 2 is a flowchart showing an example of oxygen polar pressure control. In S101, after power generation starts, the current deviation between the initial current value of the fuel cell and the current value of the fuel cell is calculated and the current deviation is detected. In S102, it is determined whether the detected current deviation is 0A. In S103, if the current deviation detected in S102 is 0A, the oxygen pole pressure is maintained and the control is terminated. In S104, the required oxygen pole pressure is calculated if the current deviation detected in S102 is not 0A. In S105, the oxygen polar pressure is controlled based on the calculated required oxygen polar pressure, and the process either returns to S102 or terminates.

[0018] The control unit calculates the current deviation between the current value of the fuel cell in its initial state and the current value of the fuel cell in its current state when the fuel cell is generating power. The current value of the fuel cell in its initial state may be prepared in advance as data. The current value of the fuel cell in its current state may be measured by a current sensor.

[0019] Figure 3(1) is a graph showing an example of data used to determine IV characteristic degradation due to current deviation. The control unit may calculate a target current value (corresponding to the initial current value of the fuel cell) and a target voltage value based on the target power generation value required for the fuel cell system, and may also calculate the current deviation between the target current value at the target voltage value and the current value of the current state measured by the current sensor. The control unit may prepare data in advance, as shown in Figure 3(1), and determine whether or not the current-voltage characteristics of the fuel cell have deteriorated over time based on the current deviation.

[0020] The control unit calculates the amount of pressure control for the oxygen electrode of the fuel cell necessary to reduce the current deviation from the calculated current deviation, and controls the pressure of the oxygen electrode based on the pressure control amount. The pressure of the oxygen electrode may be measured by an oxygen electrode pressure sensor. The control unit calculates the amount of oxygen electrode pressure control required to reduce the current deviation calculated by the current deviation calculation unit, and controls the oxygen electrode pressure to reduce the current deviation and restore the current-voltage characteristics of the fuel cell. The control unit controls the pressure of the oxygen electrode to increase when the current deviation is positive, and controls the pressure of the oxygen electrode to decrease when the current deviation is negative.

[0021] When the oxygen electrode pressure is changed, the control unit may control the hydrogen electrode pressure in accordance with the oxygen electrode pressure, maintaining the relationship oxygen electrode pressure < hydrogen electrode pressure. This prevents back pressure from the oxygen electrode to the hydrogen electrode in fuel cell cells, which are normally designed so that oxygen electrode pressure < hydrogen electrode pressure, and prevents excessive differential pressure between the cell electrodes. Specifically, the target hydrogen electrode pressure can be calculated by adding the pressure deviation in the form of oxygen electrode pressure sensor value + 10 kPa. Alternatively, back pressure can be prevented by setting the upper limit of the target oxygen electrode pressure to the hydrogen electrode pressure. The hydrogen electrode pressure may also be measured by a hydrogen electrode pressure sensor. The control unit may control the oxygen electrode pressure to a level above the lower limit of the oxygen electrode pressure. However, if the oxygen electrode pressure is lowered too drastically, there is a risk of power generation becoming impossible due to oxygen deficiency. Therefore, the minimum required oxygen pressure is set to the lower limit to prevent oxygen deficiency.

[0022] The control unit may control the oxygen system, fuel gas system, cooling system, etc., and control the entire fuel cell system. Physically, the control unit includes, for example, a processing unit such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) for storing control programs and control data processed by the CPU, a storage device such as a RAM (Random Access Memory) used primarily as various work areas for control processing, and an input / output interface. It may also be an ECU (Electronic Control Unit).

[0023] The cooling system supplies cooling water to the fuel cell as a cooling medium. Cooling water may include water and ethylene glycol, or a mixture thereof. The cooling system may include a coolant pump, reserve tank, cooling passages, radiator, bypass passages, rotary valve, ion exchanger, intercooler, etc.

[0024] Figure 3(2) shows an example of oxygen pole pressure control logic. Figure 3(2) shows the process for determining the secondary outlet pressure reading of the oxygen system regulator, which is an actuator that controls the oxygen pole pressure. Based on the operating status of the fuel cell (e.g., FC current), the oxygen consumption is calculated, and the regulator secondary pressure F / F value that can secure an oxygen flow rate to compensate for it is calculated using a predetermined formula. On the other hand, the oxygen electrode pressure target value and the oxygen electrode pressure sensor value are compared as described later, and if there is a deviation, a regulator secondary pressure F / B correction value is calculated from that deviation. The oxygen system regulator secondary pressure indication value is determined by adding the regulator secondary pressure F / F value and the regulator secondary pressure F / B correction value. The target oxygen electrode pressure is calculated by adding the feedforward term (F / F term) and the feedback term (F / B term). Oxygen electrode pressure target value F / F term: The F / F term is estimated from a map that derives the oxygen electrode pressure target value under predetermined conditions based on the operating state of the fuel cell (e.g., FC current, FC voltage). Oxygen electrode pressure target value F / B term: First, the current deviation ΔI between the FC current target value and the FC current sensor value is calculated. Next, based on the current improvement map corresponding to the oxygen electrode pressure, the current improvement due to pressurization (ΔI / ΔP) [A / kPa] at the current oxygen electrode pressure sensor value is calculated. Then, by dividing the current deviation ΔI by ΔI / ΔP, the amount of oxygen electrode pressurization ΔP required to restore the IV characteristics is calculated, and the oxygen electrode pressure target value F / B term is calculated based on that ΔP. [Explanation of symbols]

[0025] 1: Fuel cell stack, 2: Control unit, 3: Current sensor, 4: Voltage sensor, 10: Fuel gas system, 11: Hydrogen tank, 12: Shut-off valve, 13: Regulator, 14: Ejector, 15: Hydrogen electrode pressure sensor, 17: Gas-liquid separator, 18: Drain valve, 19: Muffler, 20: Oxygen system, 21: Oxygen tank, 22: Shut-off valve, 23: Regulator, 24: Ejector, 25: Cathode outlet pressure sensor (oxygen electrode pressure sensor), 27: Gas-liquid separator, 28: Drain valve

Claims

[Claim 1] A fuel cell system, The fuel cell system comprises a fuel cell and a control unit. The control unit calculates the current difference between the current value of the fuel cell in its initial state and the current value of the fuel cell in its current state when the fuel cell is generating power. The fuel cell system is characterized in that the control unit calculates the amount of pressure control for the oxygen electrode of the fuel cell necessary to reduce the current deviation from the calculated current deviation, and controls the pressure of the oxygen electrode based on the pressure control amount.

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