Fuel cell control device and fuel cell control method

Abstract

Provided are a fuel cell control device and a fuel cell control method for controlling power distribution of a fuel cell vehicle in which a hybrid system configured from a fuel cell and a secondary battery is used as a drive source, the fuel cell control device and the fuel cell control method comprising a feedforward control unit or a feedforward control step for determining a power generation command value for the fuel cell with respect to requested power on the basis of a control parameter and performing durability prioritization control or fuel consumption prioritization control of the fuel cell, a deterioration / internal state estimation unit or a deterioration / internal state estimation step for estimating a deterioration state and an internal state of the fuel cell and determining a deterioration / internal state estimation value of the fuel cell, and a control correction unit or a control correction step for correcting the control parameter on the basis of the deterioration / internal state estimation value, and the fuel cell control device and the fuel cell control method also being such that, in the feedforward control unit or the feedforward control step, the durability prioritization control and the fuel consumption prioritization control are switched on the basis of the corrected control parameter.

Description

Fuel cell control device and fuel cell control method

[0001] The present invention relates to a control device and control method for a fuel cell, and more particularly to a control device and control method for a fuel cell for controlling power distribution in a fuel cell vehicle powered by a hybrid system composed of a fuel cell and a secondary battery.

[0002] BACKGROUND ART Conventionally, various control devices and control methods for fuel cells have been studied with the aim of suppressing deterioration of fuel cells and improving their performance in fuel cell vehicles that use a hybrid system composed of a fuel cell and a secondary battery as a drive source.

[0003] For example, Japanese Patent Laid-Open Publication No. 2022-81346 (Patent Document 1) discloses a power generation control device that improves the durability of a fuel cell without worsening the fuel cell's fuel efficiency by controlling the intermittent state of the fuel cell under predetermined conditions in a system equipped with a fuel cell and a secondary battery. Also, Japanese Patent Laid-Open Publication No. 2023-277 (Patent Document 2) discloses an SOC control device that, in a fuel cell system equipped with a fuel cell and a secondary battery, controls the state of charge (SOC) from the secondary battery based on the power required for the fuel cell system, thereby achieving both high fuel efficiency and high power performance while avoiding an increase in the temperature of the fuel cell.

[0004] In addition, Japanese Patent Laid-Open No. 2021-197304 (Patent Document 3) discloses a catalyst degradation suppression device that generates a dynamic filter using a time constant corresponding to the catalyst voltage and corrects the catalyst voltage using this dynamic filter, thereby suppressing catalyst particle degradation in transient states where voltage changes rapidly. Furthermore, Japanese Patent Laid-Open No. 2022-95107 (Patent Document 4) discloses a fuel cell power generation control command device that can control a fuel cell so that power generation efficiency is high and cathode catalyst degradation is suppressed by selecting an estimated value of current and an estimated value of total voltage from which a power command value to the fuel cell is obtained, as well as a combination of control parameters for realizing the estimated value of current and the estimated value of total voltage, so that a comprehensive index including an estimated value of fuel cell loss and an estimated value of fuel cell degradation is minimized. In addition, Japanese Patent Laid-Open No. 2022-166957 (Patent Document 5) discloses a fuel cell potential control device that can minimize cathode catalyst degradation by changing the upper and lower limit potential of the fuel cell based on the total amount of precious metal oxide and precious metal hydroxide contained in the cathode catalyst particles and controlling the output potential based on the upper and lower limit potential of the fuel cell. Furthermore, Japanese Patent Laid-Open No. 2023-126025 (Patent Document 6) discloses a fuel cell performance estimation device that acquires the voltage and current of a polymer electrolyte fuel cell, calculates the cathode catalyst voltage, the effective surface utilization rate of the precious metal catalyst particles contained in the polymer electrolyte fuel cell, the electrode catalyst surface area, and the activity per surface area of ​​the precious metal catalyst, and further uses these to calculate an estimated voltage of the polymer electrolyte fuel cell and calculates an estimated value of the IV characteristic that represents the relationship between this estimated voltage and the current, thereby estimating the net performance of a polymer electrolyte fuel cell that has deteriorated over time.

[0005] JP 2022-81346 A JP 2023-277 A JP 2021-197304 A JP 2022-95107 A JP 2022-166957 A JP 2023-126025 A

[0006] However, conventional fuel cell control devices and control methods control fuel cells using fixed control, making it difficult to achieve multiple improvements. For example, known fuel cell control methods include durability-priority control, which prioritizes durability, and fuel economy-priority control, which prioritizes fuel economy. As shown in Figure 1, durability-priority control improves durability but reduces fuel economy, while fuel economy-priority control improves fuel economy but reduces durability. With conventional fixed control, there is a limit to achieving both fuel economy and durability (as indicated by the Pareto line in Figure 1). This tendency becomes more pronounced as the fuel cell's power generation characteristics (IV characteristics) become more efficient. In other words, achieving both durability and fuel economy becomes more difficult (specifically, durability-priority control further reduces fuel economy, while fuel economy-priority control further reduces durability). The total fuel economy in Figure 1 is calculated by dividing the total fuel cost required for a given durability mileage by the total mileage.

[0007] The present invention has been made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide a fuel cell control device and control method that can achieve both improved durability and improved fuel efficiency of the fuel cell.

[0008] As a result of extensive research to achieve the above-mentioned objective, the inventors discovered that by switching between durability-priority control and fuel efficiency-priority control of the fuel cell based on estimated values ​​of the fuel cell's deterioration state and internal state, it is possible to achieve both improved fuel cell durability and improved fuel efficiency, and thus completed the present invention.

[0009] That is, the present invention provides the following aspects. [1] A fuel cell control device for controlling power distribution in a fuel cell vehicle powered by a hybrid system composed of a fuel cell and a secondary battery, comprising: a feedforward control unit that determines a power generation command value for the fuel cell relative to required power based on control parameters, and performs durability-priority control or fuel economy-priority control of the fuel cell; a degradation / internal state estimating unit that estimates a degradation state and an internal state of the fuel cell and determines an estimated degradation / internal state value of the fuel cell; and a control correcting unit that corrects the control parameters based on the estimated degradation / internal state value, wherein the feedforward control unit switches between the durability-priority control and the fuel economy-priority control based on the corrected control parameters. [2] The fuel cell control device according to [1], wherein the degradation / internal state estimating unit estimates a particle size distribution of catalyst particles of the fuel cell as the degradation state and internal state of the fuel cell, and determines an estimated value based on the estimated particle size distribution as the degradation / internal state estimated value. [3] The fuel cell control device according to [1], wherein the degradation / internal state estimating unit determines an estimated value of a total surface area of ​​catalyst particles of the fuel cell as the estimated degradation / internal state value. [4] The fuel cell control device according to [1], wherein the degradation / internal state estimation unit determines an estimated value of a rate of change per unit time of a total surface area of ​​catalyst particles of the fuel cell as the degradation / internal state estimated value. [5] A fuel cell control method for controlling power distribution in a fuel cell vehicle powered by a hybrid system composed of a fuel cell and a secondary battery, comprising: a feedforward control step of determining a power generation command value for the fuel cell relative to required power based on control parameters, and performing durability priority control or fuel economy priority control of the fuel cell, a degradation / internal state estimation step of estimating the degradation state and internal state of the fuel cell and determining degradation / internal state estimated values ​​of the fuel cell, and a control modification step of modifying the control parameters based on the degradation / internal state estimated values, wherein in the feedforward control step, switching between the durability priority control and the fuel economy priority control is performed based on the modified control parameters.[6] The fuel cell control method according to [5], wherein in the degradation / internal state estimating step, a particle size distribution of catalyst particles of the fuel cell is estimated as the degradation state and internal state of the fuel cell, and an estimated value based on the estimated particle size distribution is determined as the degradation / internal state estimated value. [7] The fuel cell control method according to [5], wherein in the degradation / internal state estimating step, an estimated value of the total surface area of ​​catalyst particles of the fuel cell is determined as the degradation / internal state estimated value. [8] The fuel cell control method according to [5], wherein in the degradation / internal state estimating step, an estimated value of the rate of change per unit time of the total surface area of ​​catalyst particles of the fuel cell is determined as the degradation / internal state estimated value.

[0010] According to the present invention, it is possible to improve both the durability and fuel economy of a fuel cell.

[0011] 1 is a graph showing the relationship between the endurance distance and total fuel efficiency of a fuel cell vehicle under conventional single control (durability priority control, fuel efficiency priority control). It is a conceptual diagram showing an embodiment of a fuel cell control device of the present invention. It is a conceptual diagram showing an embodiment of a feedforward control unit and a feedforward control process in the fuel cell control device and fuel cell control method of the present invention. It is a graph showing an example of an objective function in the power distribution control unit and the power distribution control process of the feedforward control unit and the feedforward control process. It is a graph showing an example of upper and lower limit constraints on (a) power, (b) voltage, and (c) current in the upper and lower limit constraint control unit and the upper and lower limit constraint control process of the feedforward control unit and the feedforward control process. It is a graph showing an example of current-voltage characteristics. The upper graph shows the relationship between the travel distance of a fuel cell vehicle under durability optimal control and fuel efficiency optimal control and the total surface area (ECSA) maintenance rate of catalyst particles, and the lower graph shows the particle size distribution of catalyst particles at each travel distance under durability optimal control and fuel efficiency optimal control. It is a flowchart showing an embodiment of the present invention in which durability priority control is switched to fuel efficiency priority control using an estimated value of the proportion of small particle diameter catalysts as an estimated value of deterioration / internal state. 1 is a flowchart showing an embodiment of the present invention in which durability priority control is switched to fuel efficiency priority control using an estimated value of the proportion of large particle diameter catalyst as an estimated value of the deterioration / internal state. 2 is a flowchart showing an embodiment of the present invention in which durability priority control is switched to fuel efficiency priority control using an estimated value of the total surface area (ECSA) of catalyst particles as an estimated value of the deterioration / internal state. 3 is a flowchart showing an embodiment of the present invention in which durability priority control is switched to fuel efficiency priority control using an estimated value of the rate of change per unit time of the total surface area (ECSA) of catalyst particles as an estimated value of the deterioration / internal state. 4 is a graph showing the relationship between the driving distance and the total surface area (ECSA) maintenance rate of catalyst particles in durability optimum control, fuel efficiency optimum control, and variable control. 5 is a graph showing the relationship between the endurance distance and total fuel efficiency of a fuel cell vehicle in variable control, and the relationship between the endurance distance and total fuel efficiency of a fuel cell vehicle in conventional single control (durability priority control, fuel efficiency priority control).

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the drawings.

[0013] The fuel cell control device of the present invention is a fuel cell control device for controlling the power distribution of a fuel cell vehicle powered by a hybrid (HV) system consisting of a fuel cell and a secondary battery, and as shown in Figure 2, it is equipped with a feedforward control unit, a deterioration / internal state estimation unit, and a control correction unit.

[0014] The fuel cell control method of the present invention is a method for controlling power distribution in a fuel cell vehicle powered by a hybrid (HV) system consisting of a fuel cell and a secondary battery, and includes a feedforward control process, a degradation / internal state estimation process, and a control correction process. Such a fuel cell control method can be implemented using the fuel cell control device of the present invention shown in Figure 2.

[0015] In the fuel cell control device and fuel cell control method of the present invention, there are no particular restrictions on the fuel cell, the secondary battery, and the HV system configured from them, and fuel cells, secondary batteries, and HV systems configured from them used in conventionally known fuel cell vehicles can be used.

[0016] [Feedforward Control Unit and Feedforward Control Process] In the feedforward control unit and the feedforward control process, a power generation command value for the fuel cell relative to the power required for the HV system is determined based on the control parameters, and durability-prioritized control (preferably, durability-optimized control) or fuel-efficiency-prioritized control (preferably, fuel-efficiency-optimized control) of the fuel cell is performed. An example of such a feedforward control unit is one having a structure consisting of three sub-blocks, namely, a power distribution control unit, an upper / lower limit constraint control unit, and an intermittent control unit, as shown in FIG. 3 . An example of the feedforward control process is one including three sub-blocks, namely, a power distribution control step in the power distribution control unit, an upper / lower limit constraint control step in the upper / lower limit constraint control unit, and an intermittent control step in the intermittent control unit, as shown in FIG. 3 . Furthermore, the durability-prioritized control and the fuel-efficiency-prioritized control are not particularly limited, and conventionally known durability-prioritized control (preferably, durability-optimized control) and fuel-efficiency-prioritized control (preferably, fuel-efficiency-optimized control) can be used.

[0017] (Power distribution control unit and power distribution control process) In the power distribution control unit and the power distribution control process, power distribution is controlled using a power generation command value for the fuel cell or a discharge / charge command value for the secondary battery in relation to the power required for the HV system as a control parameter. ｒｅｑ The fuel cell power generation command value (power generation share) p ｆｃ The provisional value (provisional power generation command value) p ｆｃ＿ｔｅｍｐ In order to use the fuel cell at maximum efficiency, it is necessary to generate power at the operating point where the fuel cell system efficiency is at its maximum. However, the power generation at the operating point where the fuel cell system efficiency is at its maximum is uniquely determined, so the required power p ｒｅｑ Furthermore, the required power p ｒｅｑ Therefore, an objective function (for example, a function using a penalty coefficient for the power sharing constraint of the secondary battery and a charge / discharge rate as control parameters, as shown in FIG. 4) is introduced to maximize the system efficiency of the fuel cell under the constraint of the power sharing of the secondary battery, and the provisional power generation command value p ｆｃ＿ｔｅｍｐ It is preferable to optimize the calculation of

[0018] (Upper and lower limit constraint control section and upper and lower limit constraint control step) In the upper and lower limit constraint control section and the upper and lower limit constraint control step, the upper and lower limits of parameters such as power, voltage, and current are used as control parameters to control the power generation command value of the fuel cell. Therefore, in such an upper and lower limit constraint control section and the upper and lower limit constraint control step, for example, as shown in Figures 5(a) to 5(c), ｆｃ＿ｍａｘ , p ｆｃ＿ｍｉｎ ), upper and lower voltage limits (V ｍａｘ , V ｍｉｎ ), upper and lower limits of current (I ｍａｘ , I ｍｉｎ), the range of the provisional power generation command value pfc_temp_ltd constrained by the upper and lower limits of each of the power, voltage, and current is determined, and the range of the provisional power generation command value pfc_temp_ltd that satisfies all of the ranges of the provisional power generation command value pfc_temp_ltd constrained by the upper and lower limits of each of the power, voltage, and current (thick arrow in FIG. 5(a)) is determined, and the provisional power generation command value pfc_temp_ltd (the provisional power generation command value after upper and lower limit constraints) constrained by all of the upper and lower limits of the power, voltage, and current is determined (FIG. 3). Therefore, in the power, voltage, and current upper and lower limit constraint control section and the upper and lower limit constraint control process, the upper and lower limits of the power (p ｆｃ＿ｍａｘ , p ｆｃ＿ｍｉｎ ), upper and lower voltage limits (V ｍａｘ , V ｍｉｎ ), upper and lower limits of current (I ｍａｘ , I ｍｉｎ ) are control parameters. The voltage-power curve shown in FIG. 5(b) and the current-power curve shown in FIG. 5(c) depend on the current-voltage characteristics shown in FIG.

[0019] (Intermittent control unit and intermittent control process) In the intermittent control unit and the intermittent control process, the intermittent state (ON / OFF) of power generation by the fuel cell is controlled. Therefore, in such an intermittent control unit and the intermittent control process, the temporary power generation command value pfc_temp_ltd after the upper and lower limit constraints, the required power pfc_temp_ltd to the HV system, ｒｅｑ Based on the intermittent state at the current time, it is determined whether the fuel cell is in a state where power is not being generated (intermittent) or a state where power is being generated (non-intermittent). Therefore, in the intermittent control unit and intermittent control process, a threshold value for determining the start of intermittent power generation (intermittent ON threshold) and a threshold value for determining the end of intermittent power generation (intermittent OFF threshold) are control parameters. As a method for such intermittent control, for example, the method described in Japanese Patent Laid-Open No. 2022-81346 can be adopted.

[0020] In the feedforward control unit and the feedforward control step, a power generation command value (power generation share) pfc_temp_ltd for the fuel cell is calculated by multiplying the temporary power generation command value pfc_temp_ltd after the upper and lower limit constraints determined in the upper and lower limit constraint control unit and the upper and lower limit constraint control step by the intermittent control unit and the intermittent control step. ｆｃ Further, a combination of the control parameters in the power distribution control unit and the power distribution control process, the control parameters in the upper and lower limit constraint control unit and the upper and lower limit constraint control process, and the control parameters in the intermittent control unit and the intermittent control process is set as the control parameters of the feedforward control unit and the entire feedforward control process.

[0021] [Deterioration / Internal State Estimation Unit and Deterioration / Internal State Estimation Step] The deterioration / internal state estimation unit and the deterioration / internal state estimation step estimate the deterioration / internal state of the fuel cell and determine the estimated deterioration / internal state of the fuel cell. The deterioration / internal state of the fuel cell can be determined, for example, by changes in the particle size distribution of the catalyst particles, since the current-voltage characteristics of the fuel cell deteriorate as the particle size of the catalyst particles increases (e.g., Ferreira, P.J. et al., Journal of the Electrochemical Society, 2005, Vol. 152, No. 11, A2256-A2271). Furthermore, the current-voltage characteristics of the fuel cell deteriorate as the total surface area of ​​the catalyst particles decreases, so the deterioration / internal state of the fuel cell can also be determined by changes in the total surface area of ​​the catalyst particles. Therefore, it is believed that the deterioration / internal state of the fuel cell can be estimated by estimating the particle size distribution of the catalyst particles and the total surface area of ​​the catalyst particles.

[0022] Furthermore, as shown in the upper graph of FIG. 7 , even if the mileage is the same, the total surface area (ECSA) of the catalyst particles is smaller under fuel efficiency priority control (fixed control) than under durability priority control (fixed control). This is presumably because, as shown in the lower graph of FIG. 7 , the number of small particles is smaller and the number of large particles is larger under fuel efficiency priority control (fixed control) than under durability priority control (fixed control). Also, as shown in the upper graph of FIG. 7 , even if the ECSA is the same, the mileage is shorter under fuel efficiency priority control (fixed control) than under durability priority control (fixed control). This is presumably because, as shown in the lower graph of FIG. 7 , the number of small particles is rapidly reduced and the number of large particles is rapidly increased in the initial stage (short mileage range) under fuel efficiency priority control (fixed control) compared to durability priority control (fixed control). Therefore, it is believed that the deterioration state and internal state of the fuel cell can also be estimated by estimating the rate of change per unit time of the total surface area of ​​the catalyst particles. In the upper graph of FIG. 7, "ECSA maintenance rate = 1" indicates the initial state of the ECSA.

[0023] Furthermore, there are no particular limitations on the catalyst particles for the fuel cell used in the present invention, and catalyst particles for conventionally known fuel cells can be used.

[0024] (Estimation of particle size distribution of catalyst particles) First, as the degradation state and internal state of the fuel cell, the particle size distribution of catalyst particles of the fuel cell is estimated according to the method described in Schneider, P. et al., Journal of the Electrochemical Society, 2019, Vol. 166, No. 4, F322-F333. Next, a degradation / internal state estimate is determined based on the estimated particle size distribution of the catalyst particles. Examples of the degradation / internal state estimate based on the estimated particle size distribution of the catalyst particles include an estimate of the proportion of small particle size catalysts having particle sizes equal to or smaller than a predetermined particle size in the estimated particle size distribution of the catalyst particles, and an estimate of the proportion of large particle size catalysts having particle sizes equal to or larger than a predetermined particle size.

[0025] (Estimation of the total surface area of ​​catalyst particles and its rate of change per unit time) As an estimated value of the deterioration and internal state of the fuel cell, an estimated value of the total surface area of ​​the catalyst particles is determined according to the method described in Schneider, P. et al., Journal of the Electrochemical Society, 2019, Vol. 166, No. 4, F322-F333. In addition, an estimated value of the absolute value of the rate of change per unit time of the total surface area of ​​the catalyst particles determined from the change over time of the total surface area of ​​the catalyst particles can also be used as an estimated value of the deterioration and internal state of the fuel cell.

[0026] [Control Modification Unit and Control Modification Step] The control modification unit and control modification step modify the control parameters of the feedforward control unit and the entire feedforward control step based on the degradation / internal state estimated value. In the fuel cell control device and fuel cell control method of the present invention, the durability-priority control and the fuel economy-priority control are switched between based on the control parameters modified in this manner. This makes it possible to improve both the durability and fuel economy of the fuel cell. Specifically, the control parameters are modified as follows based on the estimated value of the proportion of small particle diameter catalyst, the estimated value of the proportion of large particle diameter catalyst, the estimated value of the total surface area of ​​the catalyst particles, or the estimated value of the rate of change per unit time of the total surface area of ​​the catalyst particles, which are determined in the degradation / internal state estimation unit and the degradation / internal state estimation step, and the durability-priority control and the fuel economy-priority control are switched between based on the modified control parameters.

[0027] (Modification Based on Estimated Value of Small Particle Size Catalyst Proportion) When the estimated value of the small particle size catalyst proportion becomes smaller than a threshold, the control parameters are modified so as to switch from durability-priority control to fuel-efficiency-priority control. For example, as shown in FIG. 8 , in the initial stage, the fuel cell is first controlled using durability-priority control (S101). Specifically, durability-priority control is achieved by setting the upper limit potential to a relatively low value (e.g., around 0.8 V) to limit power generation at high potential and low current density and thereby suppress fuel cell degradation, or by setting the minimum power generation amount to a high value to lower the upper limit potential. Furthermore, when the power generation command value for the fuel cell is determined via a filter, setting the filter's time constant to a large value suppresses fluctuations in the power generation command value and thus suppresses potential fluctuations, thereby achieving durability-priority control.

[0028] However, when the fuel cell is controlled by durability-priority control in this manner, power generation at the high-efficiency operating point at a high potential is limited, resulting in a sacrifice of fuel economy. Therefore, with the fuel cell controlled by durability-priority control, the deterioration / internal state estimation unit and the deterioration / internal state estimation step determine an estimated value of the proportion of the small particle diameter catalyst, and determine whether this estimated value of the proportion of the small particle diameter catalyst is smaller than a preset threshold value (S102).

[0029] If the estimated value of the proportion of small particle diameter catalyst is smaller than a preset threshold, the system switches to fuel efficiency priority control (S103) described below, and if the estimated value is equal to or greater than the threshold, the durability priority control (S101) continues. Specifically, the fuel efficiency priority control may involve setting the upper limit potential to a value higher than the upper limit potential in the durability priority control (for example, around 0.9 V), or setting the minimum power generation amount to a low value in order to increase the upper limit potential. Furthermore, if the power generation command value for the fuel cell is determined via a filter, the fuel efficiency priority control can be realized by setting the time constant of the filter to a small value.

[0030] In this way, by switching from durability priority control to fuel economy priority control based on the estimated value of the proportion of small particle diameter catalyst, it is possible to improve both the durability and fuel economy of the fuel cell.

[0031] (Modification Based on Estimated Value of Proportion of Large Particle Size Catalyst) When the estimated value of the proportion of large particle size catalyst becomes greater than a threshold, the control parameters are modified so as to switch from durability-priority control to fuel-efficiency-priority control. For example, as shown in FIG. 9 , in the initial stage, the fuel cell is first controlled using durability-priority control (S201). Specifically, durability-priority control is achieved by setting the upper limit potential to a relatively low value (e.g., near 0.8 V) to limit power generation at high potential and low current density and thereby suppress fuel cell degradation, or by setting the minimum power generation amount to a high value to lower the upper limit potential. Furthermore, when the power generation command value for the fuel cell is determined via a filter, setting the filter's time constant to a large value suppresses fluctuations in the power generation command value and thus suppresses potential fluctuations, thereby achieving durability-priority control.

[0032] However, when the fuel cell is controlled by durability-priority control in this manner, power generation at the high-efficiency operating point at a high potential is limited, resulting in a sacrifice of fuel economy. Therefore, with the fuel cell controlled by durability-priority control, the deterioration / internal state estimation unit and the deterioration / internal state estimation step determine an estimated value of the proportion of the large particle diameter catalyst, and determine whether this estimated value of the proportion of the large particle diameter catalyst is greater than a preset threshold value (S202).

[0033] If the estimated value of the proportion of large particle diameter catalyst is greater than a preset threshold, the system switches to fuel efficiency priority control (S203) described below, and if the estimated value is equal to or less than the threshold, the durability priority control (S201) continues. Specifically, the fuel efficiency priority control may involve setting the upper limit potential to a value higher than the upper limit potential in the durability priority control (for example, around 0.9 V), or setting the minimum power generation amount to a low value in order to increase the upper limit potential. Furthermore, if the power generation command value for the fuel cell is determined via a filter, the fuel efficiency priority control can be realized by setting the time constant of the filter to a small value.

[0034] In this way, by switching from durability priority control to fuel economy priority control based on the estimated value of the proportion of large particle diameter catalyst, it is possible to improve both the durability and fuel economy of the fuel cell.

[0035] (Modification Based on Estimated Total Surface Area of ​​Catalyst Particles) When the estimated total surface area of ​​catalyst particles becomes smaller than a threshold, the control parameters are modified so as to switch from durability-priority control to fuel-efficiency-priority control. For example, as shown in FIG. 10 , in the initial stage, the fuel cell is first controlled using durability-priority control (S301). Specifically, durability-priority control is achieved by setting the upper limit potential to a relatively low value (e.g., around 0.8 V) to limit power generation at high potential and low current density and thereby suppress fuel cell degradation, or by setting the minimum power generation amount to a high value to lower the upper limit potential. Furthermore, when the power generation command value for the fuel cell is determined via a filter, setting the filter's time constant to a large value suppresses fluctuations in the power generation command value and thus suppresses potential fluctuations, thereby achieving durability-priority control.

[0036] However, when the fuel cell is controlled by durability-priority control in this manner, power generation at a high-efficiency operating point at a high potential is limited, resulting in a sacrifice of fuel efficiency. Therefore, with the fuel cell controlled by durability-priority control, the deterioration / internal state estimation unit and the deterioration / internal state estimation step determine an estimated value of the total surface area (ECSA) of the catalyst particles, and determine whether the estimated value of ECSA is smaller than a preset threshold value (S302).

[0037] If the estimated ECSA value is smaller than a preset threshold, the system switches to fuel economy priority control (S303), which will be described later, and if the estimated ECSA value is equal to or greater than the threshold, the system continues the durability priority control (S301). Specifically, the fuel economy priority control may involve setting the upper limit potential to a value (e.g., around 0.9 V) higher than the upper limit potential in the durability priority control, or setting the minimum power generation amount to a low value in order to increase the upper limit potential. Furthermore, if the power generation command value for the fuel cell is determined via a filter, the fuel economy priority control can be realized by setting the time constant of the filter to a small value.

[0038] In this way, by switching from durability priority control to fuel economy priority control based on the estimated value of the total surface area of ​​the catalyst particles, it is possible to improve both the durability and fuel economy of the fuel cell.

[0039] (Modification Based on Estimated Rate of Change Per Unit Time of Total Surface Area of ​​Catalyst Particles) When the estimated absolute value of the rate of change per unit time of the total surface area of ​​catalyst particles becomes smaller than a threshold value, the control parameters are modified so as to switch from durability-priority control to fuel-efficiency-priority control. For example, as shown in FIG. 11 , in the initial stage, the fuel cell is first controlled using durability-priority control (S401). Specifically, durability-priority control is achieved by setting the upper limit potential to a relatively low value (e.g., around 0.8 V) to limit power generation at high potential and low current density and thereby suppress fuel cell degradation, or by setting the minimum power generation amount to a high value to lower the upper limit potential. Furthermore, when the power generation command value for the fuel cell is determined via a filter, setting the filter's time constant to a large value suppresses fluctuations in the power generation command value and potential fluctuations, thereby achieving durability-priority control.

[0040] However, when the fuel cell is controlled by durability-priority control in this manner, power generation at a high-efficiency operating point at a high potential is limited, resulting in a sacrifice of fuel economy. Therefore, with the fuel cell controlled by durability-priority control, the deterioration / internal state estimation unit and the deterioration / internal state estimation step determine an estimate of the absolute value of the rate of change per unit time of the total surface area (ECSA) of the catalyst particles, and determine whether or not this estimate of the absolute value of the rate of change per unit time of the ECSA is smaller than a preset threshold value (S402).

[0041] If the estimated absolute value of the rate of change of the ECSA per unit time is smaller than a preset threshold, the system switches to fuel efficiency priority control (S403), which will be described later. If the estimated absolute value is equal to or greater than the threshold, the system continues the durability priority control (S401). Specifically, the fuel efficiency priority control may involve setting the upper limit potential to a value higher than the upper limit potential in the durability priority control (for example, around 0.9 V), or setting the minimum power generation amount to a low value in order to increase the upper limit potential. Furthermore, if the power generation command value for the fuel cell is determined via a filter, the fuel efficiency priority control can be realized by setting the time constant of the filter to a small value.

[0042] In this way, by switching from durability-priority control to fuel economy-priority control based on an estimated value of the rate of change per unit time of the total surface area of ​​the catalyst particles, it is possible to achieve both improved durability and improved fuel economy of the fuel cell.

[0043] Furthermore, in the fuel cell control device and fuel cell control method of the present invention, the durability priority control may be switched to the fuel efficiency priority control in one stage as described above, but it is also possible to set multiple thresholds and switch from the durability priority control to the fuel efficiency priority control in stages.

[0044] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0045] (Example 1) When a fuel cell vehicle using a hybrid system consisting of a fuel cell and a secondary battery as a drive source was operated under the following conditions, the relationship between the driving distance and the total surface area (ECSA) of the catalyst particles of the fuel cell, the endurance distance, and the relationship between the endurance distance and the total fuel consumption were calculated by simulation.

[0046] <Operating Conditions> First, the fuel cell was subjected to durability optimal control using durability optimal control parameters such that the relationship between mileage and ECSA maintenance rate (the ratio of ECSA during operation to the initial ECSA) was as shown in Figure 12, and the fuel cell vehicle was then started to operate. The ECSA during operation was estimated, and when the estimated ECSA maintenance rate reached 0.525 (corresponding to a mileage of 1 million km under durability optimal control), the control parameters were modified to fuel efficiency optimal control parameters such that the relationship between mileage and ECSA maintenance rate was as shown in Figure 12. The control mode of the fuel cell was switched from durability optimal control to fuel efficiency optimal control (variable control), and the fuel cell vehicle was continued to operate for a predetermined mileage (2 million km). Note that in Figure 12, "ECSA maintenance rate = 1" indicates the initial state of the ECSA.

[0047] <Relationship between Travel Distance and ECSA> The relationship between the travel distance of the fuel cell vehicle under variable control and the ECSA maintenance rate was calculated using a previously determined relational expression between the travel distance and the ECSA maintenance rate (the relational expression for durability optimum control up to a travel distance of 1 million km, and the relational expression for fuel economy optimum control for a travel distance of 1 million km or more). The results are shown in Figure 12.

[0048] <Relationship between Endurance Distance and Total Fuel Economy> Based on the results shown in Figure 12, the endurance distance was determined as the mileage under the variable control (1.45 million km) at which the ECSA maintenance rate (0.450) was the same as when the mileage under the durability optimum control reached a predetermined mileage (2 million km). The total fuel economy was calculated by dividing the fuel cost required up to the predetermined mileage (2 million km) by the mileage. For the variable control, the relationship between mileage and fuel economy was calculated using a previously determined relationship (the relationship under the durability optimum control up to a mileage of 1 million km, and the relationship under the fuel economy optimum control for mileages of 1 million km or more). Figure 13 shows the results of plotting the calculated total fuel economy against the endurance distance (1.45 million km).

[0049] Comparative Example 1 The durability distance and the relationship between the durability distance and the total fuel consumption were calculated by simulation in the same manner as in Example 1, except that the driving conditions were changed as follows.

[0050] <Operating Conditions> The fuel cell vehicle was started and operated under durability optimum control (fixed control) using durability optimum control parameters that provided the relationship between the mileage and the ECSA maintenance rate (the ratio of the ECSA during operation to the initial ECSA) shown in FIG. 12 , and this was continued until the predetermined mileage (2 million km) was reached.

[0051] <Relationship Between Endurance Distance and Total Fuel Economy> In the durability optimum control (fixed control), the predetermined mileage (2 million km) at which the ECSA maintenance rate reached 0.450 was defined as the endurance distance. The total fuel economy (the fuel cost required to reach the predetermined mileage (2 million km) divided by the mileage) was calculated using the relationship between the mileage and fuel economy under durability optimum control that was previously determined. Figure 13 shows the results of plotting the calculated total fuel economy against the endurance distance (2 million km).

[0052] Comparative Example 2 The durability distance was calculated by simulation in the same manner as in Example 1, except that the operating conditions were changed as follows.

[0053] <Operating Conditions> The fuel cell vehicle was started and operated under fuel efficiency optimum control (fixed control) using fuel efficiency optimum control parameters that provided the relationship between the travel distance and the ECSA maintenance rate (the ratio of the ECSA during operation to the initial ECSA) shown in FIG. 12 , and this was continued until a predetermined travel distance (2 million km) was reached.

[0054] <Durability Distance> Based on the graph shown in FIG. 12 , the durability distance under the fuel economy optimization control was calculated as the mileage under the fuel economy optimization control that resulted in the same ECSA maintenance rate (0.450) as when the mileage under the durability optimization control reached a predetermined mileage (2,000,000 km). This was approximately 350,000 km.

[0055] As shown in Fig. 13, it was confirmed that by controlling the fuel cell using the variable control, it is possible to achieve both improved durability and improved fuel economy performance, exceeding the conventional relationship between endurance distance and total fuel economy (Pareto line). In particular, when compared at the same ECSA maintenance rate, it was confirmed that the variable control (Example 1) provided significantly higher fuel economy performance than the durability optimum control (fixed control) (Comparative Example 1).

[0056] Furthermore, as described above, the endurance distance was 1,450,000 km for the variable control of Example 1, and approximately 350,000 km for the fuel economy optimization control (fixed control). When compared at the same ECSA maintenance rate, it was confirmed that the durability was extremely higher in the case of the variable control than in the case of the fuel economy optimization control (fixed control).

[0057] As described above, according to the present invention, it is possible to improve both the durability and fuel economy of a fuel cell. Therefore, the fuel cell control device and fuel cell control method of the present invention are useful as a fuel cell control device and control method for controlling the power distribution of a fuel cell vehicle powered by a hybrid system consisting of a fuel cell and a secondary battery.

Claims

1. A fuel cell control device for controlling the power distribution of a fuel cell vehicle powered by a hybrid system consisting of a fuel cell and a secondary battery, comprising: a feedforward control unit that determines a power generation command value for the fuel cell relative to the required power based on control parameters, and performs durability-priority control or fuel efficiency-priority control of the fuel cell; a degradation / internal state estimation unit that estimates the degradation state and internal state of the fuel cell and determines degradation / internal state estimate values ​​for the fuel cell; and a control correction unit that corrects the control parameters based on the degradation / internal state estimate values, and the feedforward control unit switches between the durability-priority control and the fuel efficiency-priority control based on the corrected control parameters.

2. A fuel cell control device as described in claim 1, wherein the deterioration / internal state estimation unit estimates the particle size distribution of catalyst particles of the fuel cell as the deterioration state and internal state of the fuel cell, and determines an estimated value based on the estimated particle size distribution as the deterioration / internal state estimated value.

3. The fuel cell control device according to claim 1, wherein the deterioration / internal state estimation unit determines an estimated value of the total surface area of ​​catalyst particles of the fuel cell as the deterioration / internal state estimated value.

4. A fuel cell control device according to claim 1, wherein the deterioration / internal state estimation unit determines an estimated value of the rate of change per unit time of the total surface area of ​​catalyst particles of the fuel cell as the deterioration / internal state estimated value.

5. A fuel cell control method for controlling power distribution in a fuel cell vehicle powered by a hybrid system consisting of a fuel cell and a secondary battery, comprising: a feedforward control process for determining a power generation command value for the fuel cell relative to the required power based on control parameters, and performing durability-priority control or fuel economy-priority control of the fuel cell; a degradation / internal state estimation process for estimating the degradation state and internal state of the fuel cell, and determining estimated values ​​for the degradation / internal state of the fuel cell; and a control modification process for modifying the control parameters based on the estimated values ​​for the degradation / internal state, wherein in the feedforward control process, switching between the durability-priority control and the fuel economy-priority control is performed based on the modified control parameters.

6. A fuel cell control method as described in claim 5, wherein in the degradation / internal state estimation process, the particle size distribution of catalyst particles of the fuel cell is estimated as the degradation state and internal state of the fuel cell, and an estimated value based on the estimated particle size distribution is determined as the degradation / internal state estimated value.

7. The fuel cell control method according to claim 5, wherein in the degradation / internal state estimation step, an estimated value of the total surface area of ​​catalyst particles of the fuel cell is determined as the degradation / internal state estimated value.

8. A fuel cell control method according to claim 5, wherein in the degradation / internal state estimation step, an estimated value of the rate of change per unit time of the total surface area of ​​catalyst particles of the fuel cell is determined as the degradation / internal state estimated value.

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