Fuel cell system

Abstract

To provide a fuel cell system which can make a fuel cell stack which has just replaced a previous fuel cell stack easily generate power.SOLUTION: The fuel cell system having a plurality of fuel cell stacks has a control unit. When a part of the fuel cell stacks are replaced, the control unit sets a first output of the replaced fuel cell stacks to be different from a second output of the other fuel cell stacks not having been replaced.SELECTED DRAWING: Figure 3

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). In Patent Document 1, a fuel cell system having a plurality of power generation systems is disclosed. In Patent Document 2, a fuel cell system that determines a combination of a plurality of fuel cell stacks based on the degree of degradation is disclosed.

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 the prior art, component replacement is not mentioned, and the state of the fuel cell after replacement cannot be grasped.

[0005] The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a fuel cell system capable of bringing a fuel cell stack that has just been replaced into a state where it is easy to generate power.

Means for Solving the Problems

[0006] In the present disclosure, a fuel cell system having a plurality of fuel cell stacks, the fuel cell system has a control unit, when a part of the plurality of fuel cell stacks is replaced, The control unit is characterized by setting the first output of the replaced fuel cell stack to be different from the second output of the other fuel cell stacks that have not been replaced, thereby providing a fuel cell system.

[0007] In this disclosure, the first output may be an output that serves as a predetermined refresh operating point to enhance the performance of the replaced fuel cell stack.

[0008] In this disclosure, the first output may be the output that is the optimal operating point of the replaced fuel cell stack.

[0009] In this disclosure, before replacing some of the fuel cell stacks among the plurality of fuel cell stacks, the control unit records the output characteristics of the plurality of fuel cell stacks that are not to be replaced. During or after the replacement of a fuel cell stack that is to be replaced, the control unit may set the outputs of the fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output required by the fuel cell system, such that the third output of the fuel cell stack that is not relatively degraded among the multiple fuel cell stacks that are not to be replaced is higher than the fourth output of the fuel cell stack that is relatively degraded.

[0010] In this disclosure, if a request for power generation is received from the fuel cell system before replacing some of the fuel cell stacks among the plurality of fuel cell stacks, the control unit determines whether it is necessary to replace some of the fuel cell stacks among the plurality of fuel cell stacks. If the control unit determines that some of the fuel cell stacks among the plurality of fuel cell stacks need to be replaced, it may record the output characteristics of the plurality of fuel cell stacks that are not to be replaced before replacing some of the fuel cell stacks.

[0011] In this disclosure, if a request for power generation is received from the fuel cell system after some of the fuel cell stacks have been replaced, the control unit determines whether it can set the output of the remaining fuel cell stacks that were not replaced by unevenly distributing the load based on the output requested by the fuel cell system. If the control unit determines that the load can be distributed unevenly, the control unit will distribute the load unevenly and set the outputs of the fuel cell stacks that are not to be replaced such that the third output of the fuel cell stack that is not relatively degraded among the fuel cell stacks that are not to be replaced is higher than the fourth output of the fuel cell stack that is relatively degraded. If the control unit determines that it is not possible to distribute the load unevenly, the control unit may distribute the load evenly and set the outputs of the multiple fuel cell stacks that are not subject to replacement.

[0012] In this disclosure, when some of the fuel cell stacks among the plurality of fuel cell stacks are replaced, The control unit may be configured such that the first output of the replaced fuel cell stack is given preferential treatment over the second output of the other fuel cell stacks that have not been replaced. [Effects of the Invention]

[0013] The fuel cell system of this disclosure can put a newly replaced fuel cell stack into a state that is conducive to generating electricity. [Brief explanation of the drawing]

[0014] [Figure 1] This flowchart shows an example of the control performed by the fuel cell system of this disclosure before the replacement of some fuel cell stacks. [Figure 2] This flowchart shows an example of the control performed by the fuel cell system of this disclosure during the replacement of a portion of the fuel cell stack. [Figure 3] This flowchart shows an example of the control performed by the fuel cell system of this disclosure after the replacement of some fuel cell stacks.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments according to the present disclosure will be described. In addition, 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 technical knowledge in the relevant field. In this specification, “~” indicating a numerical range is used in the sense of including the numerical values described before and after as the lower limit value and the upper limit value. Also, the upper limit value and the lower limit value in the numerical range can adopt any combination.

[0016] In the present disclosure, there is provided a fuel cell system having a plurality of fuel cell stacks, the fuel cell system having a control unit, when a part of the plurality of fuel cell stacks is replaced, the control unit is characterized in that it sets the first output of the replaced fuel cell stack to be different from the second output of the other fuel cell stacks that have not been replaced.

[0017] Stationary power generation systems and the like are assumed to continue generating power with the remaining fuel cell stacks instead of stopping the entire system (the remaining fuel cell stacks) even during the replacement of some fuel cell stacks, and it is assumed that the power generation demand is covered by the remaining fuel cell stacks. In this case, a higher load than normal is required for the remaining fuel cell stacks. If the load corresponding to the reduction in the number of fuel cell stacks during the replacement of some fuel cell stacks is simply equally divided and assigned to the remaining fuel cell stacks, some fuel cell stacks will have a high-temperature history and a high-load history, leading to sudden state changes and a decrease in IV performance. Therefore, in the prior art, when continuously operating the non-replacement fuel cell stacks remaining during the replacement of some fuel cell stacks, the degree of deterioration progress of the non-replacement fuel cell stacks is not considered, so there is a possibility that the optimal state of the non-replacement fuel cell stacks cannot be maintained. As a characteristic of a fuel cell stack, the IV performance tends to improve by initially providing a power generation history, and it reaches a state where its original performance can be exhibited. However, for this, it may be necessary to add a history of a certain load or more. At that time, if load dispersion is continued from the perspective of efficiency, the desired load will not be applied to the replaced fuel cell stack, so the performance of the replaced fuel cell stack cannot be immediately extracted after replacement. Particularly, in a system where fixed power generation such as a stationary power generation system is the main system, it is likely that the desired load cannot be achieved. Therefore, in the prior art, there is a possibility that the maximum performance of the fuel cell stack cannot be immediately extracted after replacement.

[0018] Based on the premise of having a plurality of fuel cell stacks, the fuel cell system of the present disclosure performs load dispersion in view of the characteristics of the fuel cell stacks when replacing some fuel cell stacks. When replacing some fuel cell stacks, load balancing is intentionally performed before the replacement to understand the characteristics of the remaining fuel cell stacks, and the load balancing ratio of the remaining fuel cell stacks during the replacement is determined. After the fuel cell stack replacement, load balancing is prioritized for the newly installed fuel cell stacks to promote their refresh operation. This optimizes the load balancing of the remaining fuel cell stacks during power generation while some fuel cell stacks are being replaced, and also enables the creation of a state where the performance of the newly installed fuel cell stacks can be maximized at an early stage after the replacement. Therefore, according to this disclosure, a newly replaced fuel cell stack can be put into a state that is conducive to generating power. Furthermore, according to this disclosure, the output characteristics of the fuel cell stack that has just been replaced can be determined immediately after the replacement. Furthermore, this disclosure enables efficient power generation by the entire fuel cell system having multiple fuel cell stacks during and after the replacement of fuel cell stacks.

[0019] The fuel cell system of this disclosure comprises a plurality of fuel cell stacks and a control unit. The fuel cell system of this disclosure may include an oxidizer gas system, a fuel gas system, and a cooling system. The fuel cell system described herein is a system that continues to generate electricity even while some of the fuel cell stacks among multiple fuel cell stacks are being replaced. The fuel cell system of this disclosure only needs to have three or more fuel cell stacks, and there is no particular upper limit; it may be 200 or less, or 20 or less. The fuel cell system of this disclosure may be used mounted on a mobile body such as a vehicle. Alternatively, 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 an external source. 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 capable of propelling the vehicle by using both the output of the fuel cell and the power of a secondary battery.

[0020] A fuel cell stack (sometimes referred to as an FC stack, stack, etc.) is a stack made up of multiple single cells stacked on top of each other. In this disclosure, both a single cell and a fuel cell stack may be referred to as a fuel cell. The number of stacked single cells is not particularly limited; for example, it could range from 2 to several hundred.

[0021] A single cell of a fuel cell typically comprises a membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly comprises, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer.

[0022] The cathode (oxidizing electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. The cathode catalyst layer and the anode catalyst layer are collectively referred to as the catalyst layer. The catalyst layer may comprise, for example, a catalytic metal that promotes electrochemical reactions, a proton-conducting electrolyte, and an electronically conductive support. Examples of catalyst metals that can be used include platinum (Pt), and alloys made of Pt and other metals (for example, Pt alloys mixed with cobalt and nickel). The electrolyte may be a fluororesin or the like. For example, a Nafion solution may be used as the fluororesin. The catalyst metal is supported on a support, and in each catalyst layer, the support on which the catalyst metal is supported (catalyst support) and the electrolyte may be mixed. Examples of carriers for supporting the catalytic metal include commercially available carbon materials such as carbon.

[0023] The cathode-side gas diffusion layer and the anode-side gas diffusion layer are collectively referred to as the gas diffusion layer. The gas diffusion layer may be a conductive material or the like that has gas permeability. Examples of conductive materials include carbon porous materials such as carbon cloth and carbon paper, and metal porous materials such as metal mesh and foamed metal.

[0024] The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as a thin film of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. The electrolyte membrane may also be, for example, a Nafion membrane (manufactured by DuPont).

[0025] A single cell may optionally include two separators that sandwich both sides of the membrane electrode gas diffusion layer assembly. One of the two separators is the anode-side separator, and the other is the cathode-side separator. In this disclosure, the anode-side separator and the cathode-side separator are collectively referred to as the separator. The separator may have holes that constitute a manifold, such as supply holes and discharge holes, for circulating fluids such as reaction gases and cooling media in the stacking direction of the single cells. As a cooling medium, cooling water such as a mixed solution of ethylene glycol and water can be used to prevent freezing at low temperatures. Alternatively, cooling air can be used as a cooling medium. Examples of supply ports include fuel gas supply ports, oxidizer gas supply ports, and cooling medium supply ports. Examples of exhaust ports include fuel gas exhaust ports, oxidizer gas exhaust ports, and cooling medium exhaust ports. The separator may have a reaction gas channel on the side in contact with the gas diffusion layer. Alternatively, the separator may have a cooling medium channel on the side opposite to the side in contact with the gas diffusion layer to maintain a constant temperature in the fuel cell. The separator may be a gas-impermeable conductive material. Examples of conductive materials include dense carbon, which is compressed to be gas-impermeable, and press-formed metal plates (e.g., iron, aluminum, and stainless steel). The separator may also have a current-collecting function.

[0026] The fuel cell stack may have manifolds such as an inlet manifold through which each supply port is connected, and an outlet manifold through which each discharge port is connected. Inlet manifolds include anode inlet manifolds, cathode inlet manifolds, and cooling medium inlet manifolds. Outlet manifolds include anode outlet manifolds, cathode outlet manifolds, and cooling medium outlet manifolds.

[0027] In this disclosure, the fuel gas and the oxidizer gas are collectively referred to as the reaction gas. The reaction gas supplied to the anode is the fuel gas (sometimes referred to as the anode gas), and the reaction gas supplied to the cathode is the oxidizer gas (sometimes referred to as the cathode gas). The fuel gas is mainly a gas containing hydrogen, but may also be hydrogen. The oxidizer gas is a gas containing oxygen, and may also be oxygen, air, dry air, etc.

[0028] The fuel cell system may also include an oxidizer gas system. The oxidizer gas system supplies oxidizer gas to the fuel cell. The oxidizer gas system may include an oxidizer gas supply unit, oxidizer gas supply piping, oxidizer off-gas discharge piping, bypass piping, etc.

[0029] The oxidizer gas supply unit may be an air compressor or the like. The air compressor is electrically connected to the control unit, and the rotational speed of its rotor is controlled according to a control signal from the control unit. The air compressor may be located in the oxidizer gas supply piping.

[0030] The oxidizer gas supply piping connects the outside of the fuel cell system to the cathode inlet of the fuel cell. The oxidizer gas supply piping enables the supply of oxidizer gas from the oxidizer gas supply section to the cathode of the fuel cell. The cathode inlet may be an oxidizer gas supply port, a cathode inlet manifold, or the like. An oxidizer gas inlet sealing valve may be located downstream of the oxidizer gas supply section in the oxidizer gas supply piping. The oxidizer gas inlet sealing valve is electrically connected to the control unit, and the control unit opens the oxidizer gas inlet sealing valve to supply oxidizer gas to the cathode of the fuel cell. The flow rate of oxidizer gas supplied to the cathode may also be adjusted by adjusting the opening degree of the oxidizer gas inlet sealing valve.

[0031] The oxidizer off-gas exhaust piping connects the cathode outlet of the fuel cell to the outside of the fuel cell system. The oxidizer off-gas exhaust piping allows the oxidizer off-gas, which is the oxidizer gas emitted from the cathode of the fuel cell, to be discharged to the outside of the fuel cell system. The cathode outlet may be an oxidizer gas discharge port, a cathode outlet manifold, or the like. A pressure regulating valve may be installed in the oxidizer off-gas exhaust piping. The pressure regulating valve is electrically connected to the control unit, and when the control unit opens the pressure regulating valve, the reacted oxidant gas, or oxidant off-gas, is discharged to the outside of the fuel cell system through the oxidant off-gas discharge pipe. The pressure of the oxidant gas supplied to the cathode (cathode pressure) may also be adjusted by adjusting the opening degree of the pressure regulating valve. The oxidant off-gas may have the same components as the oxidant gas, or it may be oxygen, air, dry air, etc., or it may contain water vapor, etc.

[0032] The bypass piping connects the oxidizer gas supply piping and the oxidizer off-gas discharge piping, bypassing the fuel cell. The bypass piping branches off from the oxidizer gas supply piping at a branching point downstream of the oxidizer gas supply section, bypasses the fuel cell, and merges with the oxidizer off-gas discharge piping at a confluence point downstream of the pressure regulating valve of the oxidizer off-gas discharge piping. Bypass valves may be installed in the bypass piping. The bypass valve may be a valve with an adjustable opening degree, or it may be a three-way valve for oxidizer gas. In the case of a three-way valve for oxidizer gas, it may be installed at the branching point, which is the uppermost point of the bypass piping, and it also serves as an oxidizer gas inlet sealing valve. The bypass valve is electrically connected to the control unit, and when the control unit opens the bypass valve, at least a portion of the oxidizer gas can be supplied to the oxidizer off-gas discharge pipe, bypassing the fuel cell. If the bypass valve is a three-way valve for oxidizer gas, when it is not necessary to supply oxidizer gas to the fuel cell, the control unit can close the valve on the downstream side of the bypass valve to the oxidizer gas supply pipe and open the valve on the bypass pipe side, so that the flow of oxidizer gas goes from the oxidizer gas supply pipe to the bypass pipe, thereby supplying the entire amount of oxidizer gas to the oxidizer off-gas discharge pipe.

[0033] The oxidizer gas system may include a cooler (intercooler) downstream of the oxidizer gas supply section of the oxidizer gas supply piping. The cooler may be located downstream of the oxidizer gas supply section of the oxidizer gas supply piping and upstream of the branching point with the bypass piping. A cooler may perform its cooling function by circulating the cooling medium of the cooling system inside and outside the cooler.

[0034] The oxidizing gas system may include a humidifier downstream of the oxidizing gas supply section of the oxidizing gas supply piping. The humidifier may be located downstream of the oxidizing gas supply section of the oxidizing gas supply piping and downstream of the branching point with the bypass piping. The humidifier may be positioned across the oxidizer gas supply piping and the oxidizer off-gas discharge piping.

[0035] A fuel cell system may also be equipped with a fuel gas system. The fuel gas system supplies fuel gas to the fuel cell. The fuel gas system may include a fuel gas supply unit, fuel gas supply piping, fuel off-gas discharge piping, circulation piping, ejectors, etc. Examples of fuel gas supply units include fuel tanks, specifically liquid hydrogen tanks and compressed hydrogen tanks. The fuel gas supply piping connects the fuel gas supply unit to the anode inlet of the fuel cell. The fuel gas supply piping enables the supply of hydrogen-containing fuel gas to the anode of the fuel cell. The anode inlet may be a fuel gas supply port, an anode inlet manifold, or the like. The fuel off-gas exhaust piping connects the anode outlet of the fuel cell to the outside of the fuel cell system. The anode outlet may be a fuel gas exhaust port, an anode outlet manifold, or the like. The fuel off-gas may include fuel gas that has passed through the anode unreacted, and water generated at the cathode that has reached the anode. The fuel off-gas may also include corrosive substances generated in the catalyst layer and electrolyte membrane, and oxidizing gas that may be supplied to the anode during scavenging. The circulation piping branches off from the fuel off-gas discharge piping at its branching point and merges with the fuel gas supply piping at its junction point, circulating the fuel off-gas as a circulating gas within the fuel gas system. The circulation piping may include a circulation pump that circulates the circulating gas within the fuel gas system. The ejector may be placed at the junction of the fuel gas supply piping. A fuel gas inlet sealing valve may be placed upstream of the ejector in the fuel gas supply piping. The fuel gas inlet sealing valve is electrically connected to the control unit, and the control unit opens the fuel gas inlet sealing valve to supply fuel gas to the anode of the fuel cell. The flow rate of fuel gas supplied to the anode may also be adjusted by adjusting the opening degree of the fuel gas inlet sealing valve. The fuel gas inlet sealing valve may also be a linear solenoid valve or the like. An anode gas-liquid separator and an exhaust drain valve may be located at the branching point of the fuel off-gas exhaust piping. The exhaust drain valve is electrically connected to the control unit, and its opening and closing are controlled by the control unit. Downstream of the fuel gas supply section of the fuel gas supply piping, a fuel gas inlet sealing valve, regulator, injector, ejector, etc., may be arranged in this order.

[0036] A fuel cell system may be equipped with a cooling system. The cooling system regulates the temperature of the fuel cell. The cooling system may include piping for the cooling medium. The cooling medium piping allows the cooling medium to circulate inside and outside the fuel cell. The cooling medium piping communicates with the cooling medium supply port and cooling medium discharge port provided in the fuel cell, enabling the cooling medium to circulate inside and outside the fuel cell. A cooling medium supply unit may be provided in the cooling medium piping. The cooling medium supply unit is electrically connected to the control unit. The cooling medium supply unit is driven according to a control signal from the control unit. The control unit controls the flow rate of the cooling medium supplied from the cooling medium supply unit to the fuel cell. This controls the temperature of the fuel cell. The cooling medium supply unit may be, for example, a cooling water pump. The cooling medium piping may be equipped with a radiator to dissipate the heat from the cooling medium. The cooling medium piping may be equipped with a reserve tank for storing the cooling medium.

[0037] A fuel cell system may also be equipped with a battery. The battery (secondary battery) can be any type that is capable of charging and discharging, such as conventionally known secondary batteries like nickel-metal hydride secondary batteries and lithium-ion secondary batteries. The secondary battery may also include an energy storage element such as an electric double-layer capacitor. Multiple secondary batteries may be 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 in the vehicle, such as a household power supply. The secondary battery may also be charged by the output of a fuel cell. The charging and discharging of the secondary battery may be controlled by a control unit.

[0038] Physically, the control unit comprises, 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) primarily used as various work areas for control processing, and an input / output interface. Alternatively, the control unit may also be a control device such as a Power Control Unit (PCU) or an Electronic Control Unit (ECU). The control unit may be electrically connected to an ignition switch, which may be mounted on the vehicle. The control unit may also be able to operate using an external power source even when the ignition switch is turned off.

[0039] When some of the fuel cell stacks among multiple fuel cell stacks are replaced, the control unit sets the first output of the replaced fuel cell stack to be different from the second output of the other fuel cell stacks that were not replaced. Here, "some" means at least one, and may be just one. The control unit may set the first output of the replaced fuel cell stack to be lower than the second output of the other fuel cell stacks that have not been replaced, or to be set to be higher than the second output of the other fuel cell stacks that have not been replaced. For example, when two fuel cell stacks are replaced in sequence, the power generation performance of the first replaced fuel cell stack and the second replaced fuel cell stack may differ. If the power generation performance of the second replaced fuel cell stack is lower than that of the first replaced fuel cell stack, the control unit may set the output of the second replaced fuel cell stack to be lower than the output of the other fuel cell stacks, including the first replaced fuel cell stack. The first output may be an output that serves as a predetermined refresh operating point to enhance the performance of the replaced fuel cell stack. The first output may be the output that represents the optimal operating point of the replaced fuel cell stack. The operating point is the product of the operating voltage and operating current on the IV curve. The optimal operating point (maximum output operating point) is the point on the IV curve where the product of the operating voltage and operating current is largest. The operating point for refresh operation (refresh operating point) may be predetermined according to the characteristics of the fuel cell stack, as the required pattern varies depending on the characteristics of the fuel cell stack. Refresh operation may also be an operation that fluctuates the voltage, such as reducing the current of the fuel cell stack by reducing the amount of oxidant gas supplied. This can remove the coating on the catalyst surface and improve the power generation performance of the fuel cell stack. In operation at the optimal operating point, waste materials constituting the MEGA during manufacturing can be washed away by the generated water produced by power generation, thereby improving the power generation performance of the fuel cell stack. By considering the overall condition of the fuel cell system, it becomes possible to quickly bring the replaced fuel cell stack to an optimal state.

[0040] [Recording the status of the fuel cell stack] In this disclosure, the control unit may record the output characteristics (state) of the fuel cell stacks that are not to be replaced before replacing some of the fuel cell stacks among the multiple fuel cell stacks. Furthermore, the control unit may record the output characteristics of the fuel cell stacks that are not to be replaced during or after the replacement of some of the fuel cell stacks among the multiple fuel cell stacks. The control unit may intentionally adjust the load distribution and store the state of the fuel cell stacks that are not to be replaced (e.g., IV characteristics) before replacing some of the fuel cell stacks. This may allow the control unit to define a minimum and maximum power generation limit for each fuel cell stack. To understand the state (output characteristics) of a fuel cell stack, accurate assessment can be performed by using at least one piece of information selected from the following: the IV characteristics of the fuel cell stack, the cooling water temperature of the fuel cell stack, the ambient temperature, the water content of the fuel cell stack, the impedance of the fuel cell stack, the tilt angle of the fuel cell stack, and the mounting position of the fuel cell stack (end of the moving body, center, etc.). Furthermore, using at least one piece of information selected from the IV characteristics of the fuel cell stack, the cooling water temperature of the fuel cell stack, the ambient temperature, the water content of the fuel cell stack, and the impedance of the fuel cell stack can be performed with even greater accuracy. Understanding the condition of the fuel cell stack provides information to determine whether the entire fuel cell system is in a state where it can tolerate the refresh operation of the replaced fuel cell stack.

[0041] The fuel cell system may include temperature sensors for measuring the temperature of the fuel cell stack's cooling water and ambient temperature, current sensors and voltage sensors for measuring the IV characteristics of the fuel cell stack, resistance sensors for measuring the water content and impedance of the fuel cell stack, angle sensors for measuring the tilt angle of the fuel cell stack, and position information sensors for measuring the mounting position of the fuel cell stack. Each sensor is electrically connected to the control unit. The control unit detects the information measured by each sensor.

[0042] [Determining whether the fuel cell stack needs to be replaced] In this disclosure, if a request for power generation is received from the fuel cell system before replacing some of the fuel cell stacks among the multiple fuel cell stacks, the control unit may determine whether or not it is necessary to replace some of the fuel cell stacks among the multiple fuel cell stacks. If the control unit determines that some of the fuel cell stacks among the multiple fuel cell stacks need to be replaced, before replacing some of the fuel cell stacks, the control unit may intentionally change the load on the remaining fuel cell stacks to be replaced, issue power generation commands to the remaining fuel cell stacks, and record the output characteristics (state) of the remaining fuel cell stacks.

[0043] [Uneven distribution of load] The control unit may, during or after the replacement of some fuel cell stacks, load balancing of fuel cell stacks that are not to be replaced based on information about the status of those stacks. The control unit may also issue pre-adjusted power generation commands to avoid excessive power generation requests to any particular fuel cell stack. During or after the replacement of a fuel cell stack that is to be replaced, the control unit may set the outputs of the fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output required by the fuel cell system, so that the third output of the fuel cell stack that is not relatively degraded among the multiple fuel cell stacks that are not to be replaced is higher than the fourth output of the fuel cell stack that is relatively degraded.

[0044] [Determining whether uneven distribution of the fuel cell stack load is permissible] In this disclosure, if a request for power generation is received from the fuel cell system during or after the replacement of some of the fuel cell stacks among a plurality of fuel cell stacks, the control unit may determine whether it can set the output of the remaining fuel cell stacks that are not being replaced by unevenly distributing the load based on the output requested by the fuel cell system. The control unit may store the state of the fuel cell stacks that are not to be replaced during or after the replacement of some fuel cell stacks, and determine whether load balancing (shifting to the lower load side) is possible. If the control unit determines that the load can be distributed unevenly, it may distribute the load unevenly and set the outputs of the fuel cell stacks that are not to be replaced such that the third output of the fuel cell stack that is not relatively degraded is higher than the fourth output of the fuel cell stack that is relatively degraded. If the control unit determines that it is not possible to distribute the load unevenly, the control unit may distribute the load evenly and set the outputs of multiple fuel cell stacks that are not to be replaced. If load balancing is possible, the control unit may prioritize determining the load so that the replaced fuel cell stack reaches an operating point or optimal operating point where it can be refreshed, and then decide to distribute the load to the remaining fuel cell stacks that are not to be replaced. By incorporating a check to determine whether uneven load distribution is permissible, the system can avoid simply prioritizing the replaced fuel cell stack and instead consider the entire fuel cell system to determine the appropriate timing for implementing uneven load distribution. If the water content of fuel cell stacks that have not been replaced and are not subject to replacement is high, it may be deemed unacceptable if load balancing occurs that results in a power generation level below the minimum required to avoid water clogging. If the water temperature of an unreplaced fuel cell stack that is not subject to replacement is low, it may be deemed unacceptable if load balancing occurs that results in a power output below the minimum required to maintain the appropriate temperature.

[0045] [Method for calculating load balancing of fuel cell stacks] To understand the state of a fuel cell stack, the load on each fuel cell stack may be intentionally changed. In particular, in systems that continuously generate a fixed amount of power, it may be necessary to intentionally change the load to obtain accurate information. When monitoring the state, the operating point can be a pre-set load (fixed point), or a current sweep such as a sweep, which can ensure accuracy. The control unit distributes the load to the remaining fuel cell stacks that are not being replaced, based on state information stored before some fuel cell stacks are replaced. Basically, while some fuel cell stacks are being replaced, the number of fuel cell stacks capable of generating power decreases, increasing the load required by the remaining stacks. Because the load can be distributed to the remaining stacks based on pre-stored information, a stable output can be ensured throughout the system even during replacement. This eliminates downtime caused by fuel cell stack replacement and suppresses the degradation of the remaining stacks during the replacement process. Furthermore, the following requirements can be avoided: requirements that result in poor power generation efficiency, such as excessive requirements for fuel cell stacks with high water content and unstable power generation status; air requirements for air blowing; requirements that introduce high-temperature history; excessive requirements for stacks that are already hot; requirements that cause excessive cooling, such as under-requirements that lead to refreezing or water temperatures that result in poor power generation efficiency; requirements that cause large potential fluctuations (degradation), such as large load fluctuations on stacks that are already hot; and requirements that cause water clogging, such as under-requirements that fall below the lower limit air flow rate.

[0046] Figure 1 is a flowchart showing an example of the control performed by the fuel cell system of this disclosure before the replacement of some fuel cell stacks. First, the fuel cell system requests power generation. The control unit determines whether it is necessary to replace some of the fuel cell stacks among the multiple fuel cell stacks. If it determines that replacement is not necessary, the control unit issues a normal operation power generation command to all fuel cell stacks and terminates control. After the control ends, it may be repeated from the beginning. If the control unit determines that a fuel cell stack needs replacing, it intentionally fluctuates the load on multiple fuel cell stacks that are not subject to replacement. The control unit then issues power generation commands to each fuel cell stack. Subsequently, the control unit records the output characteristics (IV characteristics) of multiple fuel cell stacks that are not to be replaced, and then terminates control. After the control is terminated, it may be repeated from the beginning. By recording the output characteristics (state) of multiple fuel cell stacks that are not to be replaced before replacement, when a power generation request is made from the fuel cell system at at least one of the following points in time (during or after replacement), the record can be referenced to smoothly determine whether uneven load distribution is possible and to calculate the load distribution ratio.

[0047] Figure 2 is a flowchart showing an example of the control performed by the fuel cell system of this disclosure during the replacement of some fuel cell stacks. First, the fuel cell system requests power generation while some fuel cell stacks are being replaced. The control unit records the output characteristics (state) of multiple fuel cell stacks that are not to be replaced. Based on the recorded output characteristics information of the fuel cell stacks, the control unit determines whether it is possible to set the output of multiple fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output required from the fuel cell system. If the control unit determines that uneven distribution is possible, it calculates the load distribution ratio for the multiple fuel cell stacks that are not to be replaced. The control unit sets the output of the multiple fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output requested from the fuel cell system. The control unit issues a power generation command to each fuel cell stack with the output set by unevenly distributing the load, and then terminates the control. After the control is terminated, it may be repeated from the beginning. If the control unit determines that uneven distribution is not possible, it evenly distributes the load based on the output requested by the fuel cell system and sets the output of multiple fuel cell stacks that are not to be replaced. The control unit issues a power generation command to each fuel cell stack with the output set by the even distribution of the load, and terminates the control. After the control is terminated, it may be repeated from the beginning.

[0048] Figure 3 is a flowchart showing an example of the control performed by the fuel cell system of this disclosure after the replacement of some fuel cell stacks. First, after some fuel cell stacks are replaced, the fuel cell system will request power generation. The control unit records the output characteristics (state) of multiple unreplaced fuel cell stacks that are not subject to replacement. Based on the recorded output characteristics information of multiple unreplaced fuel cell stacks that are not to be replaced, the control unit determines whether it is possible to set the output of multiple unreplaced fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output required from the fuel cell system. If the control unit determines that uneven distribution is possible, it controls the system as follows: The control unit calculates the first load distribution ratio between the replaced fuel cell stack and the multiple unreplaced fuel cell stacks, and sets the first output of the replaced fuel cell stack to be different from the second output of the other fuel cell stacks that have not been replaced (the multiple unreplaced fuel cell stacks that are not subject to replacement). The control unit calculates the second load distribution ratio for the multiple unreplaced fuel cell stacks that are not subject to replacement. The control unit sets the outputs of the multiple unreplaced fuel cell stacks that are not subject to replacement by unevenly distributing the load so that the third output of the fuel cell stack that is relatively not degraded is higher than the fourth output of the fuel cell stack that is relatively degraded. The control unit issues a power generation command for the output set for each fuel cell stack, i.e., the first output for the replaced stack and the output set by unevenly distributing the load for the unreplaced stacks, and then terminates the control. After the control is terminated, it may be repeated from the beginning. If it is determined that uneven distribution is not possible, the control unit controls as follows: The control unit calculates the first load distribution ratio between the replaced fuel cell stack and the multiple unreplaced fuel cell stacks that have not been replaced, and sets the first output of the replaced fuel cell stack to be different from the second output of the other fuel cell stacks that have not been replaced (multiple unreplaced fuel cell stacks that are not subject to replacement). The control unit evenly distributes the load of the multiple unreplaced fuel cell stacks that are not subject to replacement and sets the output of the multiple unreplaced fuel cell stacks that are not subject to replacement. The control unit issues a power generation command for the output set for each fuel cell stack, i.e., the first output for the replaced stack and the output set by evenly distributing the load for the unreplaced stacks, and terminates control. After the control is terminated, it may be repeated from the beginning.

Claims

1. A fuel cell system having multiple fuel cell stacks, The fuel cell system has a control unit, When some of the fuel cell stacks among the aforementioned multiple fuel cell stacks are replaced, The control unit sets the first output of the replaced fuel cell stack to be higher than the second output of the other fuel cell stacks that have not been replaced, Before replacing some of the fuel cell stacks among the plurality of fuel cell stacks, the control unit records the output characteristics of the plurality of fuel cell stacks that are not to be replaced. A fuel cell system characterized in that, during or after the replacement of a fuel cell stack to be replaced, the control unit sets the outputs of the multiple fuel cell stacks that are not to be replaced by unevenly distributing the load based on the output required by the fuel cell system, such that the third output of the fuel cell stack that is not relatively degraded among the multiple fuel cell stacks that are not to be replaced is higher than the fourth output of the fuel cell stack that is relatively degraded.

2. The fuel cell system according to claim 1, wherein the first output is an output that serves as a predetermined refresh operating point to enhance the performance of the replaced fuel cell stack.

3. The fuel cell system according to claim 1, wherein the first output is the output that results in the optimal operating point of the replaced fuel cell stack.

4. If a request for power generation is received from the fuel cell system before replacing some of the fuel cell stacks among the plurality of fuel cell stacks, the control unit determines whether it is necessary to replace some of the fuel cell stacks among the plurality of fuel cell stacks. The fuel cell system according to claim 1, wherein if the control unit determines that it is necessary to replace some of the fuel cell stacks among the plurality of fuel cell stacks, the control unit records the output characteristics of the plurality of fuel cell stacks that are not to be replaced before replacing some of the fuel cell stacks among the plurality of fuel cell stacks.

5. If, after replacing some of the fuel cell stacks among the plurality of fuel cell stacks, the fuel cell system requests power generation, the control unit determines whether it can set the output of the remaining fuel cell stacks that were not replaced by unevenly distributing the load based on the output requested by the fuel cell system. If the control unit determines that the load can be distributed unevenly, the control unit will distribute the load unevenly and set the outputs of the fuel cell stacks that are not to be replaced such that the third output of the fuel cell stack that is not relatively degraded among the fuel cell stacks that are not to be replaced is higher than the fourth output of the fuel cell stack that is relatively degraded. If the control unit determines that it is not possible to distribute the load unevenly, the control unit distributes the load evenly and sets the output of the multiple fuel cell stacks that are not subject to replacement, according to claim 1.

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