Fuel cell system control method and fuel cell system

Abstract

A fuel cell system control method is a control method for controlling a fuel cell system, the fuel cell system comprising: a fuel cell that uses a mixed gas composed of multiple components as fuel; a fuel supply mechanism that has a fuel tank and supplies the mixed gas to the fuel cell; and a burner that generates combustion gas for heating air supplied to the fuel cell at startup, wherein the fuel cell system control method includes the following steps: setting the fuel composition and the fuel flow rate to the burner as unknowns and setting multiple air flow rate conditions to the burner; estimating the composition ratio of the components constituting the mixed gas based on a simultaneous equation consisting of at least one of a first characteristic equation and a second characteristic equation and a composition equation, wherein the first characteristic equation is an equation based on the relationship between the amount of air supplied to the burner and the oxygen concentration in the exhaust gas discharged from the burner, the second characteristic equation is an equation based on the relationship between the amount of air supplied to the burner and the temperature of the exhaust gas discharged from the burner, and the composition equation is an equation representing the sum of the composition ratios of the multiple components of the mixed gas; and adjusting the flow rate of the fuel supplied to the fuel cell based on the estimation result.

Description

Technical Field

[0001] The present invention relates to a control method of a fuel cell system and a fuel cell system. Background Art

[0002] The use of city gas as fuel for fuel cells has long been proposed. City gas (mixed gas) is modified in a reformer or a fuel cell equipped with a reforming function, allowing it to be used as fuel. However, city gas is defined by its calorific value per unit volume, and its composition can vary. Therefore, if the composition of the city gas changes, the amount of hydrogen generated by the modification also changes, making it difficult to supply the amount of hydrogen corresponding to the required output of the fuel cell.

[0003] To solve this problem, JP2005-200260A burns fuel in a combustion unit at startup, calculates the calorific value per unit amount of fuel supplied at that time, and estimates the number of carbon atoms contained in the fuel based on a previously prepared line chart. Summary of the Invention

[0004] However, it is difficult to estimate the amount of hydrogen generated by reforming with high accuracy simply by estimating the number of carbon atoms as described in the above-mentioned literature.

[0005] Therefore, an object of the present invention is to provide a fuel cell system control method and a fuel cell system control device capable of estimating the composition of a mixed gas with high accuracy.

[0006] According to one aspect of the present invention, a method for controlling a fuel cell system is provided. The fuel cell system includes: a fuel cell that uses a mixed gas composed of multiple components (saturated hydrocarbons or hydrogen) as fuel; a fuel supply mechanism including a fuel tank that stores the mixed gas and supplies the mixed gas to the fuel cell; and a burner that generates combustion gas for heating air supplied to the fuel cell during fuel cell startup. In this control method, the fuel composition and the fuel flow rate to the burner are unknown, multiple air flow rate conditions to the burner are set, and the composition ratios of the multiple components of the mixed gas are estimated based on simultaneous equations consisting of at least one of a first characteristic equation and a second characteristic equation, wherein the first characteristic equation is based on the relationship between the amount of air supplied to the burner and the oxygen concentration in the exhaust gas discharged from the burner; the second characteristic equation is based on the relationship between the amount of air supplied to the burner and the temperature of the exhaust gas discharged from the burner; and the composition equation represents the sum of the composition ratios of the multiple components of the mixed gas. The flow rate of the fuel supplied to the fuel cell is then adjusted based on the estimated composition ratios.

[0007] According to another embodiment of the present invention, a fuel cell system is provided, comprising: a fuel cell that uses a mixed gas composed of multiple components (saturated hydrocarbons or hydrogen) as fuel; a fuel supply mechanism that has a fuel tank for storing the mixed gas and supplies the mixed gas to the fuel cell; a burner that generates combustion gas for heating air supplied to the fuel cell when the fuel cell is started; and a control unit that controls the flow rate of air supplied to the burner and the flow rate of the mixed gas supplied to the burner and the fuel cell. The control unit sets the fuel composition and fuel flow rate to the burner as unknowns, sets multiple air flow rate conditions to the burner, and estimates the composition ratios of the multiple components of the mixed gas based on simultaneous equations consisting of at least one of a first characteristic equation and a second characteristic equation, and a composition equation. The first characteristic equation is based on the relationship between the amount of air supplied to the burner and the oxygen concentration in the exhaust gas discharged from the burner, as detected by an oxygen concentration sensor; the second characteristic equation is based on the relationship between the amount of air supplied to the burner and the temperature of the exhaust gas discharged from the burner, as detected by a temperature sensor; and the composition equation represents the sum of the composition ratios of the multiple components of the mixed gas. The control unit then adjusts the flow rate of fuel supplied to the fuel cell based on the estimated composition ratios. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of a fuel cell system to which the control method according to the first embodiment is applied.

[0009] Figure 2 : is a flowchart showing a control routine of warm-up control.

[0010] Figure 3 1 is a diagram showing the relationship between the gas flowing into the combustor 7 and the gas exhausted.

[0011] Figure 4 1 is a flowchart showing a control routine for composition estimation according to the first embodiment.

[0012] Figure 5 This table summarizes the combustion heat, specific heat ratio, and molecular weight of chain saturated hydrocarbon monomers that may be contained in the mixed gas.

[0013] Figure 6 This is a table summarizing the composition ratios, specific heat ratio terms, molecular weight terms, and products of the specific heat ratio terms and molecular weight terms of the first to third mixed gases composed of two types of saturated hydrocarbons.

[0014] Figure 7 1 is a flowchart showing a control routine for composition estimation according to the second embodiment.

[0015] Figure 8: is a flowchart showing a control routine for composition estimation according to the third embodiment. DETAILED DESCRIPTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0017] [First embodiment]

[0018] Figure 1 This is a schematic diagram of a fuel cell system 100 to which the control according to the present embodiment is applied. The fuel cell system 100 includes: a fuel cell (also referred to as a fuel cell stack) 1; a fuel supply mechanism 2 that supplies a mixed gas serving as fuel to the anode of the fuel cell stack 1; a blower 5 that supplies air to the cathode of the fuel cell stack 1; and a control unit 11 that controls the entire system. The fuel cell system 100 also includes: a burner 7 that generates combustion gas for heating the air supplied to the fuel cell stack 1 during startup; and a heat exchanger 8 that performs heat exchange between the combustion gas generated by the burner 7 and the air supplied from the blower 5. A temperature sensor 9 that detects the temperature of the exhaust gas; a pressure sensor 10 that detects the pressure of the exhaust gas; and an oxygen concentration sensor (also referred to as an O2 sensor) 14 that detects the oxygen concentration in the exhaust gas are provided in the gas flow path from the heat exchanger 8.

[0019] The fuel cell stack 1 is a solid oxide fuel cell (SOFC). In this example, a cell is provided with a catalyst on the anode side that reforms the mixed gas. However, the reformer can also be a separate component from the SOFC. The fuel cell stack 1 reforms the mixed gas to produce a reformed gas (anode gas) containing hydrogen. Furthermore, the fuel cell stack 1 generates electricity through an electrochemical reaction between the anode gas (hydrogen) and the cathode gas (oxygen) via an electrolyte.

[0020] The fuel supply mechanism 2 includes a fuel tank 3, a main injector 4 that supplies fuel to the fuel cell stack 1, and a startup injector 6 that supplies fuel to the burner 7. Furthermore, a pressure reducing valve and a pressure sensor (not shown) are installed in the gas flow path between the fuel tank 3 and the main injector 4 and startup injector 6.

[0021] The fuel tank 3 stores a mixed gas at a specified pressure. Here, city gas is used as the mixed gas. City gas may contain a variety of chain saturated hydrocarbons, but there is no regulation about its composition, but it is regulated by the heat per unit volume. Therefore, when the fuel cell system 100 is mounted on a vehicle, there is a concern that the composition of the mixed gas in the fuel tank 3 will change before and after filling due to filling of the mixed gas in different regions. Moreover, the amount of hydrogen generated by the reforming reaction varies depending on the fuel composition. That is, even if the fuel flow rate is fixed, if the fuel composition changes, the amount of hydrogen supplied to the fuel cell stack 1 also changes, resulting in a change in the output of the fuel cell stack 1. Furthermore, if the amount of hydrogen changes in the direction of deficiency, there is a concern that the fuel cell stack 1 will deteriorate.

[0022] Therefore, in order to supply an amount of hydrogen corresponding to the output required for the fuel cell stack 1 , it is necessary to estimate the composition of the mixed gas in the fuel tank 3 with high accuracy.

[0023] The main injector 4 receives a signal from the control unit 11 to adjust the supply amount of the mixed gas.

[0024] The air flow path supplied from the blower 5 includes a flow path that flows through the heat exchanger 8 and into the fuel cell stack 1, and a bypass flow path 13 that bypasses the heat exchanger 8 and flows into the fuel cell stack 1. A bypass valve 12 is installed in the bypass flow path 13 for adjusting the flow rate of air flowing through the bypass flow path.

[0025] The control unit 11 performs warm-up control, normal power generation control, and shutdown control of the fuel cell stack 1. Normal control and shutdown control are conventional technologies, so their description is omitted. In addition, the control unit 11 controls the fuel supply mechanism 2 to control the flow rate of the mixed gas.

[0026] Warm-up control is used to warm up the fuel cell stack 1 when starting the fuel cell system 100. Specifically, a mixed gas and air are supplied to the burner 7 and combusted to generate combustion gas. The combustion gas is then used by the heat exchanger 8 to heat the air supplied from the blower 5. The heated air is then supplied to the fuel cell stack 1. During this warm-up control, the composition of the mixed gas is estimated using the method described below.

[0027] [Warm-up control]

[0028] Figure 2 1 is a flowchart showing a control routine of warm-up control executed by the control unit 11. This warm-up control is executed in response to a start request based on a driver's operation or the like.

[0029] In step S100 , heating by the burner 7 is started by operating a heater (not shown).

[0030] In step S101, it is determined whether the temperature of the burner 7 has reached a first temperature. If the temperature has reached the first temperature, the process of step S102 is executed. If the temperature has not reached the first temperature, this determination is repeated. The first temperature here is a temperature at which combustion in the burner 7 is possible.

[0031] In step S102, a mixed gas and air are supplied to the burner 7 to start combustion. The mixed gas is supplied via the start-up injector 6. Air is supplied from the blower 5 via the bypass flow path 13 to the fuel cell stack 1, and the air that has passed through the fuel cell stack 1 is supplied.

[0032] The upper limit of the flow rate (fuel flow rate) of the supplied mixed gas is the fuel flow rate assuming that the chain saturated hydrocarbons constituting the mixed gas are methane and ethane, and that the calorific value per unit volume of the mixed gas is the upper limit of the calorific value of the mixed gas used in the corresponding region. As mentioned above, city gas is specified by the calorific value per unit flow rate. Therefore, the control unit 11 stores calorific value data for each region in its memory, and the upper limit of the calorific value can be obtained by comparing this data with location information acquired through a navigation system, etc. This upper limit is set to prevent excessive temperature increases in the burner 7.

[0033] Here, the reason for determining the upper limit of the fuel flow rate as described above will be described.

[0034] The temperature reached by the burner 7 is determined by the amount of heat supplied. The amount of heat is represented by the product of the amount of heat per unit volume, the fuel flow rate, and time.

[0035] The fuel flow rate passing through the starting injector 6 can be regarded as the flow rate W of the fluid passing through the orifice, and can be expressed by equation (1).

[0036] [Number 1]

[0037]

[0038] In formula (1), K is the flow coefficient [-], A is the cross-sectional area of ​​the orifice [m 2 ], γ is the specific heat ratio [-], ρ is the density [kg / m 3 ], P is pressure [Pa], k byps is the bypass valve opening [-].

[0039] In formula (1), γ is a physical property value of the fluid (mixed gas). Therefore, if the composition of the mixed gas is unknown, the right-hand side 2γ / (γ-1) is unknown, and the flow rate W cannot be calculated.

[0040] That is, if the composition of the mixed gas is unknown, the calorific value per unit volume and the fuel flow rate are unknown, and the calorific value supplied to the burner 7 cannot be calculated.

[0041] Therefore, the calorific value per unit volume is assumed to be the upper limit of the calorific value of the mixed gas used in the region. The flow rate is calculated assuming that the mixed gas consists of methane and ethane. This assumption results in two components, so the composition ratio is also determined based on the calorific value per unit volume. Furthermore, once the composition ratio is determined, γ, a physical property value, is also determined, allowing the flow rate to be calculated.

[0042] Here, the reason why the components constituting the mixed gas are assumed to be two components, methane and ethane, will be described.

[0043] The right side of equation (1) can be expanded as equation (2).

[0044] [Number 2]

[0045]

[0046] In formula (2), M is the molecular weight of the mixed gas, and T is the temperature of the mixed gas.

[0047] In formula (2), the terms 2 / (1-(1 / γ)) related to the specific heat ratio (hereinafter also referred to as the specific heat ratio term) and R / M related to the molecular weight (hereinafter also referred to as the molecular weight term) are related to the physical properties of the mixed gas. The larger the specific heat ratio γ of the mixed gas, the larger the specific heat ratio term. The specific heat ratio γ of the mixed gas is determined by the composition ratio of the components contained. The smaller the molecular weight M of the mixed gas, the larger the molecular weight term. The molecular weight M is also determined by the composition ratio of the components contained.

[0048] Figure 5 This table summarizes the heat of combustion, specific heat ratio, and molecular weight of individual chain saturated hydrocarbons (methane, ethane, propane, and butane) that may be present in a gas mixture. As shown in the chart, the lower the carbon number, the higher the specific heat ratio and the lower the heat of combustion and molecular weight. In other words, the greater the content of low-carbon components, the greater the specific heat ratio and molecular weight of the gas mixture.

[0049] Figure 6 This table summarizes the composition ratios, specific heat ratio terms, molecular weight terms, and the product of the specific heat ratio terms and molecular weight terms for the first to third mixed gases composed of two saturated hydrocarbons. The heat capacity per unit volume of the first to third mixed gases is 46 MJ / m 3 The first mixed gas consists of methane and butane, the second mixed gas consists of methane and propane, and the third mixed gas consists of methane and ethane. As shown in the figure, the third mixed gas, which has the most low-carbon components and is composed of methane and ethane, has the largest specific heat ratio and molecular weight terms.

[0050] The upper limit of the fuel flow rate is set to suppress excessive temperature rise in the burner 7. Therefore, it is desirable to set the upper limit of the fuel flow rate to the maximum value among all possible combinations of components. Therefore, the combination that maximizes the product of the specific heat ratio term and the molecular weight term is set, namely, the combination of methane and ethane.

[0051] Returning to the description of the flowchart, in step S103 , the composition of the mixed gas is estimated by a method described later.

[0052] In step S104, heated air begins to be supplied to the fuel cell stack 1. Specifically, the bypass valve 12 of the bypass flow path 13 is controlled to supply air from the blower 5 to the heat exchanger 8. Heat is then exchanged between the air and the combustion gas generated in the burner 7 in the heat exchanger 8. The air heated in the heat exchanger 8 is then supplied to the fuel cell stack 1.

[0053] In step S105, a determination is made as to whether the temperature of the fuel cell stack 1 has reached a second temperature. If so, the routine ends, i.e., warm-up control ends. If not, the determination is repeated. The second temperature here is the warm-up completion temperature, i.e., the temperature at which the aforementioned electrochemical reaction can proceed.

[0054] [Estimation of the composition of mixed gas]

[0055] Here, the estimation of the composition of the mixed gas executed in step S103 will be described.

[0056] In this embodiment, the fuel composition and the fuel flow rate to the burner 7 are first assumed to be unknown. Then, multiple conditions for the air flow rate to the burner 7 are set, and simultaneous equations are established consisting of a first characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the oxygen concentration in the exhaust gas discharged from the burner, and a composition equation representing the sum of the composition ratios of the various components of the mixed gas. The composition ratios of the various components are calculated by solving these simultaneous equations.

[0057] The first characteristic equation is an equation expressing the relationship that the amount of oxygen in the air supplied to the burner 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the burner 7 (that is, the law of conservation of mass).

[0058] Here, refer to Figure 3 Let's explain the composition equation and the first characteristic equation.

[0059] Figure 3This is a diagram showing the relationship between the gas flowing into the burner 7 and the gas discharged. As shown in the figure, a mixed gas of air and fuel flows into the burner 7. The air flow rate is Q an , let the fuel flow rate be Q f The composition of air is considered to be 79% nitrogen (N2) and 21% oxygen (O2). The mixed gas may contain various chain saturated carbons, specifically, methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H 10 ) etc., and set their respective composition ratios to x%, y%, z%, ...

[0060] Regarding the composition ratio, the relationship of formula (3) holds true.

[0061] [Number 3]

[0062] x+y+z+…=100…(3)

[0063] This formula (3) is also called a composition equation.

[0064] When the components contained in the mixed gas are methane, ethane, and propane, if the combustion in the burner 7 is complete combustion, the components react as follows.

[0065] CH4+2O2→CO2+2H2O

[0066] C2H6+3.5O2→2CO2+3H2O

[0067] C3H8+5O2→3CO2+4H2O

[0068] Furthermore, the flow rate Q of the exhaust gas discharged from the burner 7 is out It is expressed by formula (4).

[0069] [Number 4]

[0070]

[0071] In the first term on the right side of formula (4), x+2y+3z is the CO2 component, 2x+3y+4z is the H2O component, the second term on the right side is the N2 component, and the third term on the right side is the O2 component.

[0072] Furthermore, according to the above-mentioned law of conservation of mass related to oxygen, the relationship of formula (5) holds. This formula (5) is referred to as the first characteristic equation.

[0073] [Number 5]

[0074]

[0075] The left side of equation (5) is the amount of oxygen flowing into the burner 7, the first term on the right side is the amount of oxygen in the exhaust gas detected by the O2 sensor 14, and the second term on the right side is the amount of oxygen consumed by combustion.

[0076] The fuel flow rate Q is the unknown f Set it as a fixed value and set the air flow rate Q a Changed to Q a1 , Q a2 ...and detect the oxygen concentration in the exhaust gas to derive multiple equations (5). Then, by solving the simultaneous equations consisting of the composition equation and multiple equations (5), the composition ratios x%, y%, and z% are calculated. Figure 4 The specific estimation method is explained below.

[0077] Figure 4 The control routine for the composition estimation described above is shown in FIG. Figure 3 Flowchart of the control routine executed by the control unit 11 in step S103.

[0078] In step S200 , the oxygen concentration in the exhaust gas is detected.

[0079] In step S201, the first characteristic equation (5) is derived. In the initial calculation, the equation (5) is derived assuming that the chain saturated hydrocarbons in the mixed gas are only methane. The air flow rate Q in equation (5) is an The initial value (Q a1 ) is set to a flow rate that allows complete combustion when the fuel flow rate is at the above-mentioned upper limit.

[0080] In step S202, the simultaneous equations consisting of the component equations and equation (5) are solved.

[0081] In step S203, it is determined whether the composition ratio of any component in the composition ratio of each component is 0%. If there is a component that has become 0%, this routine is terminated and the execution is performed. Figure 1 If the component does not reach 0% in the process of step S104, the process returns to step S200.

[0082] In the second and subsequent calculations, the air flow condition, that is, the air flow rate Q an Increase to Q a2 , Q a3 ..., and the types of components are added until any component reaches 0% in step S203. That is, by increasing the conditions of the air flow rate, the number of equations (5) required to obtain the solution of the unknown number is derived without increasing the number of unknowns. At this time, the components are added in order from the component with the smallest number of carbon atoms. In addition, the air flow rate Q an Taking Q as the initial value a1When the air flow rate condition is increased, that is, when the air flow rate is changed, the resolution of the O2 sensor 14 is changed by an amount greater than the lower limit.

[0083] This routine is terminated when any component reaches 0% because 0% of any component means that no other component exists.

[0084] The estimation of the composition ratio of the mixed gas described above can be performed when the fuel tank 3 is newly filled with the mixed gas. When the fuel cell system 100 is mounted on a vehicle, it is moved to a gas station that supplies the mixed gas for filling, the key is locked, the cover of the fuel tank 3 is opened and the mixed gas is filled, and after filling, the cover is closed, the key is unlocked (that is, the fuel cell system 100 is started), and the vehicle is moved from the gas station. However, the pressure (temperature) of the mixed gas in the fuel tank 3 changes not only due to the decrease in the temperature of the mixed gas after the fuel cell system 100 stops, but also due to changes in the external temperature. Therefore, the control unit 11 can determine that the mixed gas has been overfilled when the ratio of the pressure of the fuel tank 3 during the above-mentioned unlocking action to the pressure of the fuel tank 3 during the above-mentioned locking action exceeds a specified value that is higher than the ratio caused by changes in the external temperature.

[0085] Here, if the prescribed value related to the above ratio is taken into consideration, the mixed gas does not escape from the fuel tank 3 during the period from the locking operation to the unlocking operation, and there is no change in the volume of the fuel tank 3. Therefore, the pressure p of the mixed gas in the fuel tank 3 during the locking operation is off and the pressure p of the mixed gas in the fuel tank 3 during the unlocking operation on The temperature T of the mixed gas in the fuel tank 3 during the locking operation can be determined. off and the temperature T of the mixed gas in the fuel tank 3 during the unlocking operation. on And transform it into P on / P off =T on / T off =(T off + daily range) / T off =1+daily range / T off Considering the situation in Japan, the maximum daily temperature difference (the difference between the highest and lowest temperatures) is 31.5°C (Nagano), and the lowest temperature is -41°C (Asahikawa). Therefore, when we calculate 1 + daily temperature difference / T off 1+ day difference / T off =1+31.5 / (273-41)=1.14. Therefore, the control unit 11 can control the pressure ratio P on / P offIf the value exceeds 1.14, it is determined that the fuel tank 3 has just been filled with the mixed gas.

[0086] Furthermore, since the lid is opened and closed as described above when filling the fuel tank 3 with the mixed gas, the control unit 11 may also determine whether the ratio of the pressure in the fuel tank 3 during the unlocking operation to the pressure in the fuel tank 3 during the locking operation exceeds a predetermined value even if the lid has been opened and closed. Furthermore, the control unit 11 may also perform the above determination if, based on navigation information or the like, it is determined that the gas supplier is different from the gas supplier of the gas station where the fuel tank was previously filled.

[0087] The composition of the mixed gas is estimated as described above, and after the warm-up of the fuel cell stack 1 is completed (that is, after Figure 2 After the control routine is completed, the control unit 11 adjusts the flow rate of the fuel supplied to the fuel cell stack 1. Specifically, the fuel flow rate is calculated using equation (1) based on the physical properties of the mixed gas based on the estimated composition (e.g., specific heat ratio γ), the flow index of the flow control unit of the fuel supply mechanism 2 (e.g., the orifice diameter A in equation (1)), and an index representing the state of the mixed gas (e.g., pressure and temperature). The pressure reducing valve (not shown) is adjusted based on this fuel flow rate.

[0088] As described above, this embodiment provides a control method for a fuel cell system 100 comprising: a fuel cell stack (fuel cell) 1 that uses a mixed gas composed of multiple components as fuel; a fuel supply mechanism 2 that includes a fuel tank 3 for storing the mixed gas and supplies the mixed gas to the fuel cell stack 1; and a burner 7 that generates combustion gas for heating air supplied to the fuel cell stack 1 during startup of the fuel cell stack 1. In this control method, the fuel composition and the fuel flow rate to the burner 7 are assumed to be unknowns, multiple air flow rate conditions to the burner 7 are set, and the composition ratios of the multiple components of the mixed gas are estimated based on simultaneous equations consisting of a first characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the oxygen concentration in the exhaust gas discharged from the burner 7, and a composition equation representing the sum of the composition ratios of the multiple components of the mixed gas. The flow rate of fuel supplied to the fuel cell stack 1 is then adjusted based on the estimated composition ratios. The first characteristic equation is an equation that represents the relationship that the amount of oxygen in the air supplied to the burner 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the burner 7. When estimating the composition ratio of multiple components of the mixed gas based on the simultaneous equations consisting of the first characteristic equation and the composition equation, the number of first characteristic equations required to obtain the solution of the unknown number is derived by changing the conditions of the air flow rate to the burner 7.

[0089] According to this embodiment, the composition ratio can be estimated simply by adding the air flow rate condition while maintaining the fuel flow rate as an unknown quantity. This allows estimation of not only the number of carbon atoms but also the specific composition ratio, thereby improving the accuracy of the estimated amount of hydrogen after modification. Furthermore, since the fuel flow rate can be maintained as an unknown quantity, a device for detecting the fuel flow rate is no longer necessary.

[0090] In this embodiment, the initial setting is that the mixed gas contains only methane. From this initial setting, additional air flow rate conditions and component types are added. The composition ratios of multiple components are estimated based on simultaneous equations. This estimation is repeated while changing the air flow rate conditions until any of the multiple components reaches 0%. This allows accurate estimation of the composition and composition ratio of the components in the mixed gas without unnecessary calculations.

[0091] In this embodiment, the components are methane and ethane, and the upper limit of the fuel flow rate is set to the fuel flow rate when the calorific value of the mixed gas is the upper limit calorific value of the mixed gas used in the corresponding region. This can suppress excessive temperature rise of the burner 7.

[0092] In this embodiment, the air flow rate at the initial setting is set to a flow rate that allows complete combustion at the upper limit of the fuel flow rate. Furthermore, when changing the air flow conditions, the air flow rate at the initial setting is set as the lower limit, and the air flow rate is increased from this lower limit. This can suppress the generation of carbon monoxide during the reaction in the burner 7.

[0093] In this embodiment, when the fuel cell system 100 is mounted on a vehicle and the vehicle key is locked and then unlocked, if the ratio of the fuel tank pressure at the time of unlocking to the fuel tank pressure at the time of locking is greater than a predetermined value, it is determined that the vehicle has just been filled with a mixed gas. Furthermore, if the lid of the vehicle's fuel tank 3 is opened between the unlocking and locking operations, it is determined whether the pressure in the fuel tank 3 has risen by a predetermined value. This makes it possible to determine whether the vehicle has just been filled with a mixed gas without adding any special configuration.

[0094] In this embodiment, the flow rate of fuel supplied to the fuel cell stack 1 is adjusted based on the fuel physical properties based on the estimated fuel composition, the flow index of the flow control unit of the fuel supply mechanism, and the temperature and pressure of the fuel. This improves the control accuracy of the fuel flow rate supplied to the fuel cell stack 1.

[0095] [Second embodiment]

[0096] This embodiment differs from the first embodiment in that Figure 2 The contents of the estimation of the composition of the mixed gas executed in step S103 of the control routine of the warm-up control are shown. The other controls are the same as those of the first embodiment. The following description will focus on the method of estimating the composition of the mixed gas according to this embodiment.

[0097] In this embodiment, the fuel composition and the fuel flow rate to the burner 7 are first assumed to be unknown. Then, multiple conditions for the air flow rate to the burner 7 are set, and simultaneous equations are established consisting of a second characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the temperature of the exhaust gas discharged from the burner 7, and a composition equation representing the sum of the composition ratios of the various components of the mixed gas. The composition ratios of the various components are calculated by solving these simultaneous equations.

[0098] The second characteristic equation is an equation that represents the relationship (that is, the law of conservation of energy) that the thermal energy of the gas (air and mixed gas) flowing into the burner 7 at startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed due to combustion in the burner 7.

[0099] That is, in the first embodiment, the composition of the mixed gas is estimated by solving a simultaneous equation consisting of a composition equation (Equation (3)) and multiple first characteristic equations (Equation (5)), but in this embodiment, the composition of the mixed gas is estimated by solving a simultaneous equation consisting of a composition equation and multiple second characteristic equations.

[0100] When the components of the mixed gas are methane, ethane, and propane, the composition equation is as described in the first embodiment. Under steady-state conditions, the heat of combustion manifests entirely as a change in the temperature of the mixed gas, so the relationship of equation (6) holds. This equation (6) is referred to as the second characteristic equation.

[0101] [Number 6]

[0102] Inflow energy = outflow energy... (6)

[0103] Here, if the enthalpy of methane, ethane, and propane is respectively H me 、H et 、H pr , then the inflow energy is expressed by formula (7) and the outflow energy is expressed by formula (8).

[0104] [Number 7]

[0105]

[0106] [Number 8]

[0107]

[0108] In formula (7) and formula (8), C is the specific heat, T in is the temperature at the burner inlet, T out is the temperature at the burner outlet. in A temperature sensor (not shown) detects the pressure of the air at the burner inlet, a pressure sensor (not shown) detects the pressure of the mixed gas at the burner inlet, and a pressure sensor (not shown) detects the pressure of the mixed gas at the burner inlet. The pressure terms of the above enthalpies are set as the detection values ​​of these two pressure sensors.

[0109] Figure 7 This is a control routine showing the composition estimation involved in this embodiment, that is, Figure 3 Flowchart of the control routine executed by the control unit 11 in step S103.

[0110] In step S300 , the temperature of the exhaust gas discharged from the combustor 7 is detected.

[0111] In step S301, the second characteristic equation, that is, equation (6), is derived. In the initial calculation, equation (6) is derived assuming that the component contained in the mixed gas is only methane.

[0112] In step S302, the simultaneous equations consisting of the constituent equations (Equation (3)) and Equation (6) are solved.

[0113] In step S303, it is determined whether any of the composition ratios of the components is 0%. If any of the components has become 0%, this routine is terminated and the execution is performed. Figure 1 If the component does not reach 0% in the process of step S104, the process returns to step S300.

[0114] In the second and subsequent calculations, the air flow condition, that is, the air flow rate Q an Increase to Q a2 , Q a3 ..., and the types of components are added until any component reaches 0% in step S303. That is, by increasing the conditions of the air flow rate, the number of equations (6) required to obtain the solution of the unknown number is derived without increasing the number of unknowns. At this time, the components are added in order from the component with the smallest number of carbon atoms. In addition, the air flow rate Q an Taking Q as the initial value a1 is the lower limit, and changes in an increasing direction from this lower limit.

[0115] This routine is terminated when any component reaches 0% because 0% of any component means that no other component exists.

[0116] As described above, according to this embodiment, a control method for controlling a fuel cell system 100 is provided. The fuel cell system 100 includes: a fuel cell stack 1 that uses a mixed gas composed of multiple components as fuel; a fuel supply mechanism 2 that includes a fuel tank 3 for storing the mixed gas and supplies the mixed gas to the fuel cell stack 1; and a burner 7 that generates combustion gas for heating air supplied to the fuel cell stack 1 during startup of the fuel cell stack 1. In this control method, the fuel composition and the fuel flow rate to the burner 7 are assumed to be unknowns, multiple conditions for the air flow rate to the burner 7 are set, and the composition ratios of the multiple components of the mixed gas are estimated based on simultaneous equations consisting of a second characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the temperature of the exhaust gas discharged from the burner 7, and a composition equation representing the sum of the composition ratios of the multiple components of the mixed gas. The flow rate of the fuel supplied to the fuel cell stack 1 is then adjusted based on the estimated composition ratios. The second characteristic equation expresses the relationship that the thermal energy of the gas flowing into the burner 7 during startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed by combustion in the burner 7. When estimating the composition ratios of the various components of the mixed gas based on the simultaneous equations consisting of the second characteristic equation and the composition equation, the number of second characteristic equations required to find solutions to the unknowns is derived by varying the conditions for the air flow rate to the burner 7. This achieves the same effects as the first embodiment.

[0117] [Third embodiment]

[0118] The difference between this embodiment and the first and second embodiments is that Figure 2 The contents of the mixed gas composition estimation executed in step S103 of the control routine of the warm-up control shown in FIG. The other controls are the same as those of the first and second embodiments. The following description focuses on the mixed gas composition estimation method of this embodiment.

[0119] In this embodiment, the composition of the mixed gas is estimated by solving simultaneous equations consisting of the composition equation, the first characteristic equation, and the second characteristic equation.

[0120] Figure 8 This is a control routine showing the composition estimation involved in this embodiment, that is, Figure 3 Flowchart of the control routine executed by the control unit 11 in step S103.

[0121] Steps S400 and S401 are the same as those described in the first embodiment. Figure 4The same processing as steps S200 to S201 is performed, and steps S402 to S403 are performed as described in the second embodiment. Figure 7 The same processing is performed from step S300 to step S301.

[0122] Steps S404 to S405 are Figure 4 Steps S202 to S203, Figure 7 The same processing is performed from step S302 to step S303.

[0123] As described above, this embodiment provides a method for controlling a fuel cell system 100 comprising: a fuel cell stack 1 that uses a mixed gas composed of multiple components as fuel; a fuel supply mechanism 2 including a fuel tank 3 that stores the mixed gas and supplies the mixed gas to the fuel cell stack 1; and a burner 7 that generates combustion gas for heating air supplied to the fuel cell stack 1 during startup of the fuel cell stack 1. In this control method, the fuel composition and the fuel flow rate to the burner 7 are assumed to be unknowns, multiple air flow rate conditions to the burner 7 are set, and the composition ratios of the multiple components of the mixed gas are estimated based on simultaneous equations consisting of a first characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the oxygen concentration in the exhaust gas exhausted from the burner 7; a second characteristic equation based on the relationship between the amount of air supplied to the burner 7 and the temperature of the exhaust gas exhausted from the burner 7; and a composition equation representing the sum of the composition ratios of the multiple components of the mixed gas. Furthermore, based on the estimated composition ratio, the flow rate of the fuel supplied to the fuel cell stack 1 is adjusted. The first characteristic equation is an equation that expresses the relationship that the amount of oxygen in the air supplied to the burner 7 at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the burner 7. The second characteristic equation is an equation that expresses the relationship that the thermal energy of the gas flowing into the burner 7 at startup is equal to the sum of the thermal energy of the exhaust gas and the thermal energy consumed by combustion in the burner 7. When estimating the composition ratio of multiple components of the mixed gas based on the simultaneous equations consisting of the first characteristic equation, the second characteristic equation, and the composition equation, the number of first characteristic equations and second characteristic equations required to obtain the solution of the unknown number is derived by changing the conditions of the air flow rate to the burner 7. In this way, the same effects as those of the first and second embodiments can be obtained.

[0124] The embodiments of the present invention have been described above. However, the above embodiments are only a part of application examples of the present invention and are not intended to limit the scope of protection of the present invention to the specific structures of the above embodiments.

Claims

1. A fuel cell system control method, comprising: Fuel cells that use a mixed gas composed of multiple components as fuel; a fuel supply mechanism including a fuel tank storing the mixed gas and supplying the mixed gas to the fuel cell; and a burner that generates combustion gas for heating air supplied to the fuel cell when the fuel cell is started up, in, The fuel cell system control method comprises the following steps: The fuel composition and the fuel flow rate to the burner are set as unknowns, and a plurality of conditions for the air flow rate to the burner are set; detecting at least one of an oxygen concentration and a temperature of the exhaust gas discharged from the burner according to a condition for setting and changing the air flow rate; deriving a first characteristic equation based on a relationship between an amount of air supplied to the burner and a detected oxygen concentration in the exhaust gas; deriving a second characteristic equation based on a relationship between an amount of air supplied to the burner and a detected temperature of the exhaust gas; estimating a composition ratio of the components constituting the mixed gas based on simultaneous equations consisting of at least one of the first characteristic equation and the second characteristic equation and a composition equation, wherein the composition equation is an equation representing the sum of the composition ratios of the plurality of components of the mixed gas; and Based on the estimated composition ratio, the flow rate of the fuel supplied to the fuel cell is adjusted.

2. The fuel cell system control method according to claim 1, wherein: The first characteristic equation is an equation expressing the relationship that the amount of oxygen in the air supplied to the burner at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the burner. When estimating the composition ratio of the plurality of components of the mixed gas based on the simultaneous equations consisting of the first characteristic equation and the composition equation, the first characteristic equations are derived as many as are necessary to obtain solutions to the unknowns by changing the conditions of the air flow rate to the burner.

3. The fuel cell system control method according to claim 1, wherein: The second characteristic equation is an equation expressing the relationship that the heat energy of the gas flowing into the burner at startup is equal to the sum of the heat energy of the exhaust gas and the heat energy consumed by combustion in the burner. When estimating the composition ratio of the plurality of components of the mixed gas based on the simultaneous equations consisting of the second characteristic equation and the composition equation, the second characteristic equations are derived as many as are necessary to obtain solutions to the unknowns by changing the conditions of the air flow rate to the burner.

4. The fuel cell system control method according to claim 1, wherein: The first characteristic equation is an equation expressing the relationship that the amount of oxygen in the air supplied to the burner at startup is equal to the sum of the amount of oxygen in the exhaust gas and the amount of oxygen consumed by combustion in the burner. The second characteristic equation is an equation expressing the relationship that the heat energy of the gas flowing into the burner at startup is equal to the sum of the heat energy of the exhaust gas and the heat energy consumed by combustion in the burner. When estimating the composition ratio of the multiple components of the mixed gas based on the simultaneous equations consisting of the first characteristic equation, the second characteristic equation and the composition equation, the number of the first characteristic equation and the second characteristic equation required to obtain the solution of the unknown number is derived by changing the conditions of the air flow rate to the burner.

5. The fuel cell system control method according to any one of claims 1 to 4, wherein: The initial setting is that the component contained in the mixed gas is only methane. From this initial setting, the conditions of the air flow rate and the types of the components are added, and the composition ratios of the multiple components are estimated based on the simultaneous equations until any one of the multiple components becomes 0%. The estimation is repeated by changing the conditions of the air flow rate.

6. The fuel cell system control method according to any one of claims 1 to 4, wherein: The components are methane and ethane, and the fuel flow rate when the calorific value of the mixed gas is the upper limit calorific value of the mixed gas used in the corresponding region is set as the upper limit of the fuel flow rate.

7. The fuel cell system control method according to claim 5, wherein: The components are methane and ethane, and the fuel flow rate when the calorific value of the mixed gas is the upper limit calorific value of the mixed gas used in the corresponding region is set as the upper limit of the fuel flow rate.

8. The fuel cell system control method according to claim 7, wherein: The air flow rate in the initial setting is set to a flow rate that allows complete combustion at the set upper limit fuel flow rate.

9. The fuel cell system control method according to claim 8, wherein: When the condition of the air flow rate is changed, the air flow rate under the initial setting is set as a lower limit, and the air flow rate is increased from the lower limit.

10. The fuel cell system control method according to any one of claims 1 to 4, wherein: When the fuel cell system is mounted on a vehicle and the vehicle is locked and then unlocked using a key, When the ratio of the pressure of the fuel tank when the unlocking operation is performed to the pressure of the fuel tank when the locking operation is performed is equal to or greater than a predetermined value, it is determined that the fuel tank has just been filled with the mixed gas.

11. The fuel cell system control method according to claim 10, wherein: When the lid of the fuel tank of the vehicle is opened between the unlocking operation and the locking operation, it is determined whether the ratio of the pressure of the fuel tank becomes equal to or greater than the predetermined value.

12. The fuel cell system control method according to any one of claims 1 to 4, wherein: The flow rate of the fuel supplied to the fuel cell is adjusted based on the physical property values ​​of the fuel based on the estimated fuel composition, the flow index of the flow rate adjustment unit of the fuel supply mechanism, and the temperature and pressure of the fuel.

13. A fuel cell system comprising: Fuel cells that use a mixed gas composed of multiple components as fuel; a fuel supply mechanism including a fuel tank storing the mixed gas and supplying the mixed gas to the fuel cell; a burner that generates combustion gas for heating air supplied to the fuel cell when the fuel cell is started; and a control unit that controls the flow rate of air supplied to the burner and the flow rate of the mixed gas supplied to the burner and the fuel cell, in, The control unit performs the following processing: The fuel composition and the fuel flow rate to the burner are set as unknowns, and a plurality of conditions for the air flow rate to the burner are set; detecting at least one of an oxygen concentration and a temperature of the exhaust gas discharged from the burner according to a condition for setting and changing the air flow rate; deriving a first characteristic equation based on a relationship between an amount of air supplied to the burner and a detected oxygen concentration in the exhaust gas; deriving a second characteristic equation based on a relationship between an amount of air supplied to the burner and a detected temperature of the exhaust gas; estimating a composition ratio of the components constituting the mixed gas based on simultaneous equations consisting of at least one of the first characteristic equation and the second characteristic equation and a composition equation, wherein the composition equation is an equation representing the sum of the composition ratios of the plurality of components of the mixed gas; as well as The flow rate of the fuel supplied to the fuel cell is adjusted based on the estimated composition ratio.

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