Fuel cell system and its control method

Abstract

This technology is suitable for extending the cumulative power generation time of multiple fuel cell units as a whole. [Solution] The fuel cell unit 5 belonging to the first group 5G1 is controlled based on the first operation plan. The fuel cell unit 5 belonging to the second group 5G2 is controlled based on the second operation plan. The first and second operation plans are configured such that the first ratio ξ1 is greater than the second ratio ξ2. The first ratio ξ1 is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell unit 5 belonging to the first group 5G1. The second ratio ξ2 is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell unit 5 belonging to the second group 5G2.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system and a control method thereof.

Background Art

[0002] Patent Document 1 describes a power generation system including a plurality of power generation units including fuel cells. In this power generation system, when a first ratio of the cumulative power generation time or the cumulative power generation amount of the power generation unit to the number of power generation times of the power generation unit is less than a predetermined threshold value, the power generation time or the power generation amount of the power generation unit is controlled so that the first ratio increases.

Prior Art Documents

Patent Documents

[0003] <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The first ratio is the ratio of the cumulative power generation time to the cumulative number of startups of the fuel cell units belonging to the first group, The second ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the second group. We provide fuel cell systems. [Effects of the Invention]

[0006] The technology described herein is suitable for extending the cumulative power generation time of multiple fuel cell units as a whole. [Brief explanation of the drawing]

[0007] [Figure 1] Configuration diagram of a fuel cell system in an embodiment [Figure 2] Diagram illustrating the advantages of having different ratios for the first and second ratios. [Figure 3] Graph showing the system operation plan according to the embodiment [Figure 4] Lifetime graph of fuel cell stacks, discovered by the inventor through experiments. [Modes for carrying out the invention]

[0008] (Knowledge and other information that formed the basis of this disclosure) Consider a fuel cell unit that includes a fuel cell stack (hereinafter referred to as the stack). The degree of stack degradation increases with the cumulative number of starts of the fuel cell unit, and also with the cumulative power generation time of the fuel cell unit. The stack reaches the end of its lifespan due to degradation.

[0009] Figure 4 shows the lifespan graph 500 discovered by the inventors through experiments. The lifespan graph 500 represents the lifespan of a stack of a single fuel cell unit. In Figure 4, the horizontal axis represents the cumulative number of starts for a single fuel cell unit, and the vertical axis represents the cumulative power generation time for a single fuel cell unit. The values ​​of j on the horizontal axis and k on the vertical axis are predetermined numbers (this is also true for Figure 2). The lifespan graph 500 shows the relationship between the cumulative number of starts and the cumulative power generation time of a fuel cell unit when the stack of a single fuel cell unit reaches the end of its lifespan. The lifespan graph 500 is a downward-convex, monotonically decreasing graph, specifically a logarithmic graph.

[0010] The inventors, taking advantage of the finding that the lifespan graph 500 has a downward convex shape, investigated a technology suitable for extending the cumulative power generation time of multiple fuel cell units as a whole.

[0011] Embodiments will be described in detail below with reference to the drawings. However, descriptions that are unnecessarily detailed may be omitted. For example, detailed descriptions of already well-known matters or redundant descriptions of substantially identical configurations may be omitted. The accompanying drawings and the following description are provided for the full understanding of the disclosure by those skilled in the art and are not intended to limit the subject matter described in the claims.

[0012] (Embodiment) [1-1. Structure] Figure 1 is a diagram of the configuration of a fuel cell system 100 in an embodiment. The fuel cell system 100 includes a plurality of fuel cell units 5 and a controller 8. The plurality of fuel cell units 5 are connected to a load 14. The number of fuel cell units 5 is 2 or more, for example, 2 to 1000. Each of the plurality of fuel cell units 5 includes a fuel cell stack (hereinafter referred to as a stack) and auxiliary equipment. The auxiliary equipment includes, for example, a pump, a sensor, etc. The plurality of fuel cell units 5 may have the same configuration as each other.

[0013] The controller 8 controls each of the plurality of fuel cell units 5. Thereby, the output power of the fuel cell system 100 is controlled. The controller 8 is, for example, a DSP (Digital Signal Processor) including an arithmetic circuit, a memory circuit, etc. The arithmetic circuit includes a CPU (Central Processing Unit). The memory circuit includes a memory.

[0014] [1-2. Operation] The controller 8 divides the plurality of fuel cell units 5 into a plurality of groups 5G. Each group 5G includes two or more fuel cell units 5. The plurality of groups 5G includes a first group 5G1 and a second group 5G2. The group 5G can be referred to as a fuel cell unit group.

[0015] In the control of the plurality of fuel cell units 5, a plurality of operation plans are used. The plurality of operation plans are different from each other. The plurality of operation plans represent the operation contents of the plurality of fuel cell units 5 over a predetermined period. The plurality of groups 5G and the plurality of operation plans are associated with each other one-to-one. The plurality of operation plans includes a first operation plan and a second operation plan. The first group 5G1 is associated with the first operation plan. The second group 5G2 is associated with the second operation plan.

[0016] The controller 8 controls the fuel cell units 5 belonging to each group 5G based on the operation plan associated with that group 5G. The fuel cell units 5 belonging to one group 5G refer to the number of fuel cell units 5 belonging to that group 5G. The controller 8 controls the fuel cell units 5 belonging to the first group 5G1 based on the first operation plan, and controls the fuel cell units 5 belonging to the second group 5G2 based on the second operation plan.

[0017] In the following, the term "specific ratio ξ" will be used. The specific ratio ξ is the ratio of the cumulative power generation time to the cumulative number of starts of a single fuel cell unit 5. Specifically, the cumulative power generation time of fuel cell unit 5 is the cumulative power generation time of fuel cell unit 5 counted from the state in which the stack of fuel cell unit 5 is new. The cumulative number of power generation cycles of fuel cell unit 5 is the cumulative number of starts of fuel cell unit 5 counted from the state in which the stack of fuel cell unit 5 is new. Startup refers to switching from a stopped state to a power generation state.

[0018] Multiple operating plans are configured such that, for any two groups 5G in the multiple groups 5G, the specific ratio ξ of fuel cell units 5 belonging to one of the two groups 5G is greater than the specific ratio ξ of fuel cell units 5 belonging to the other group 5G. The specific ratio ξ of fuel cell units 5 belonging to one group 5G may be the same or may vary.

[0019] The first and second operating plans are configured such that the first ratio ξ1 is greater than the second ratio ξ2. The first ratio ξ1 is a specific ratio ξ relating to the first group 5G1, and the second ratio ξ2 is a specific ratio ξ relating to the second group 5G2. Having different first and second ratios ξ1 and ξ2 is advantageous from the perspective of extending the overall cumulative power generation time of the multiple fuel cell units 5, specifically from the perspective of extending the average value of the cumulative power generation time of the multiple fuel cell units 5. The reasons for this will be explained below with reference to the reference form and Figure 2.

[0020] The controller 8 in the reference configuration controls all of the multiple fuel cell units 5 in the fuel cell system 100 based on a single reference operation plan. The reference operation plan represents the operation content of the multiple fuel cell units 5 over a predetermined period. The reference operation plan is configured so that the specific ratio ξ of all of the multiple fuel cell units 5 in the fuel cell system 100 is the same. Hereinafter, the specific ratio ξ in the reference configuration may be referred to as the reference ratio ξ0.

[0021] Figure 2 is an explanatory diagram of the advantages of ξ1≠ξ2. In the example in Figure 2, There are two groups of 5G: Group 1 5G1 and Group 2 5G2. The number of fuel cell units 5 belonging to group 1, 5G1, is α units. The number of fuel cell units 5 belonging to group 2, 5G2, is β units. • When the fuel cell units 5 belonging to group 1, 5G1 reach the end of their lifespan, the cumulative number of starts for those fuel cell units 5 is the same. • When the fuel cell units 5 belonging to the first group 5G1 reach the end of their lifespan, the cumulative power generation time of those fuel cell units 5 is the same. • When the fuel cell units 5 belonging to group 2, 5G2 reach the end of their lifespan, the cumulative number of starts for those fuel cell units 5 is the same. • When the fuel cell units 5 belonging to group 2, 5G2 reach the end of their lifespan, the cumulative power generation time of those fuel cell units 5 is the same.

[0022] The lifespan graph 300 in Figure 2 represents the lifespan of a stack of one fuel cell unit 5. The lifespan graph 300 is an application of the lifespan graph 500 in Figure 4 to the fuel cell unit 5 of the embodiment. That is, the lifespan graph 300 shows the relationship between the cumulative number of starts and the cumulative power generation time of a fuel cell unit 5 when the stack of one fuel cell unit 5 reaches the end of its lifespan. The lifespan graph 300 is a downward-convex, monotonically decreasing graph, specifically a logarithmic graph.

[0023] In Figure 2, • In the reference configuration, the reference life point P represents the cumulative number of starts and cumulative power generation time of each fuel cell unit 5 when the stack of that fuel cell unit 5 reaches the end of its life. • In this embodiment, the first life point A represents the cumulative number of starts and cumulative power generation time of each fuel cell unit 5 belonging to the first group 5G1 when that stack reaches the end of its life. • The second life point B, in this embodiment, represents the cumulative number of starts and cumulative power generation time of each fuel cell unit 5 belonging to the second group 5G2 when that stack reaches the end of its life. The solid line 310 is a straight line that passes through the origin and the reference life point P. The dotted line 330 is a straight line passing through the first lifetime point A and the second lifetime point B. The dashed line 351 is a straight line that passes through the origin and the first lifetime point A. The dashed line 352 is a straight line that passes through the origin and the second lifetime point B. The apportioned life point Q is the point where the first life point A and the second life point B are apportioned by α and β units, and is located on the solid line 310 and the dotted line 330.

[0024] At this time, The slope of the solid line 310 is the reference ratio ξ0. The slope of the dashed line 351 is the first ratio ξ1. The slope of the dashed line 352 is the second ratio ξ².

[0025] Also, in Figure 2, The cumulative number of activations at the reference life point P is denoted as x0. The cumulative power generation time at the reference life point P is denoted as y0. The cumulative number of activations at the first life point A is denoted as x1. The cumulative power generation time at the first lifetime point A is denoted as y1. The cumulative number of activations at the second life point B is denoted as x2. The cumulative power generation time at the second lifetime point B is denoted as y2. · The cumulative number of activations at the proportional lifetime point Q is x d It is written as, · The cumulative power generation time at the proportional lifetime point Q is y d It is written as, The coordinates of the reference life point P are denoted as [x0, y0], The coordinates of the first lifetime point A are denoted as [x1, y1], The coordinates of the second lifetime point B are denoted as [x2, y2], · The coordinates of the proportional lifetime point Q are [x d , y d It is written as ].

[0026] At this time, the following equations 1 and 2 hold true.

number

number

[0027] In Figure 2, because the life graph 300 has a downward convex shape, the apportioned life point Q is located above the life graph 300. From this, it can be understood that by configuring the first and second operation plans so that ξ1 ≠ ξ2, it is possible to extend the total cumulative power generation time of the multiple fuel cell units 5, specifically extending the average value of the cumulative power generation time of the multiple fuel cell units 5. This is advantageous from the standpoint of increasing the total cumulative power generation amount of the multiple fuel cell units 5.

[0028] Each specific ratio ξ can be determined, for example, by the controller 8 based on various constraints that multiple fuel cell units 5 must satisfy, output power patterns 400, etc. The constraints include, for example, at least one selected from the group consisting of an upper limit on the cumulative number of starts of the fuel cell unit 5, an upper limit on the cumulative number of power generations of the fuel cell unit 5, and an upper limit on the continuous operating time per start of the fuel cell unit 5. The first ratio ξ1 may be the same as the upper limit on the continuous operating time per start of the fuel cell unit 5, or it may be a value smaller than that upper limit. The second ratio ξ2 may be the minimum value derived based on the upper limit on the cumulative number of power generations of the fuel cell unit 5, or it may be a value larger than that minimum value. For the output power patterns 400, please refer to the explanation using Figure 3 described later.

[0029] In this embodiment, multiple operating plans are configured such that a specific ratio ξ of the fuel cell units 5 belonging to each group 5G converges to a target value that differs for each group 5G. The first operating plan is configured such that the first ratio ξ1 converges to a first target value. The second operating plan is configured such that the second ratio ξ2 converges to a second target value. The first target value is greater than the second target value.

[0030] For example, the first ratio ξ1 is between 2 and 80 times the second ratio ξ2, and the first target value is between 2 and 80 times the second target value. In one specific example, the first ratio ξ1 is between 4 and 40 times the second ratio ξ2. The first target value is between 4 and 40 times the second target value.

[0031] In this embodiment, the first operation plan is configured such that the first ratio ξ1 is greater than the overall ratio. The second operation plan is configured such that the second ratio ξ2 is less than the overall ratio. The overall ratio is the ratio of the total cumulative power generation time to the total cumulative number of starts of the multiple fuel cell units 5.

[0032] Figure 3 is a graph showing a system operation plan according to an embodiment. The system operation plan represents the time progression (hereinafter referred to as the output power pattern) 400 of the total output power of multiple fuel cell units 5. In this embodiment, the total output power is supplied to a load 14. The output power pattern 400 corresponds to an estimated value of the time progression (hereinafter referred to as the load pattern) of the power consumption of the load 14. The explanation of Figure 3 is for the case where there are two groups 5G, the first group 5G1 and the second group 5G2. Although Figure 3 shows the output power pattern 400 for 24 hours, the actual system operation plan may show the output power pattern 400 for a period longer than one day.

[0033] The output power pattern 400 includes a steady-state component 410 and a variable component 420. The steady-state component 410 is the steady-state component of the total output power of multiple fuel cell units 5 and remains constant over time. The variable component 420 is the variable component of the total output power and fluctuates over time. In Figure 3, the steady-state component 410 is represented by dot hatching, and the variable component 420 is represented by diagonal hatching.

[0034] In Figure 3, the amount of energy shown in the region of the output power pattern 400 below the pattern dividing line 450 is supplied by the first group 5G1. The amount of energy shown in the region of the output power pattern 400 above the pattern dividing line 450 is supplied by the second group 5G2. In Figure 3, the pattern dividing line 450 is positioned higher as the number of fuel cell units 5 belonging to the first group 5G1 (α) increases and the number of fuel cell units 5 belonging to the second group 5G2 (β) decreases. The number of units (α) and (β) can be determined, for example, by the controller 8 based on various constraints that multiple fuel cell units 5 must satisfy, the output power pattern 400, etc. The constraints include, for example, at least one selected from the group consisting of an upper limit on the cumulative number of starts of the fuel cell unit 5, an upper limit on the cumulative number of power generations of the fuel cell unit 5, and an upper limit on the continuous operating time per start of the fuel cell unit 5. In general, the more stable the output power pattern 400 is over time, the more the number of units α increases and the number of units β decreases when setting the number of units α and β. Conversely, the more pronounced the fluctuations in the output power pattern 400 over time, the more the number of units α decreases and the number of units β increases when setting the number of units α and β.

[0035] As can be understood from the explanation with reference to Figure 3, in the embodiment, the first operating plan is configured such that at least a portion of the steady-state component of the total output power of the multiple fuel cell units 5 is supplied by the first group 5G1. The second operating plan is configured such that at least a portion of the fluctuating component of the total output power is supplied by the second group 5G2.

[0036] The first operating plan may be configured such that the entire steady-state component is covered by the first group 5G1, and the second operating plan may be configured such that the entire fluctuating component is covered by the second group 5G2. This example corresponds to the case in Figure 3 where the pattern dividing line 450 is located at the boundary between the steady-state component 410 and the fluctuating component 420.

[0037] A first operation plan may be configured such that the entire steady-state component and a portion of the fluctuating component are covered by the first group 5G1, and a second operation plan may be configured such that the remaining portion of the fluctuating component is covered by the second group 5G2. This example corresponds to the case in Figure 3 where the pattern division line 450 intersects with the fluctuating component 420.

[0038] The first operation plan may be configured such that a portion of the steady-state component is covered by the first group 5G1, and the second operation plan may be configured such that a portion of the steady-state component and the entirety of the fluctuating component are covered by the second group 5G2. This example corresponds to the case in Figure 3 where the pattern division line 450 intersects with the steady-state component 410.

[0039] In this embodiment, the controller 8 determines the number of fuel cell units 5 belonging to the first group 5G1 and the number of fuel cell units 5 belonging to the second group 5G2 based on information representing the time progression of the total output power of multiple fuel cell units 5. For example, information representing an estimated time progression of the power consumption of load 14 is provided to the controller 8 in advance as information representing the time progression of the total output power.

[0040] As described above, of the first ratio ξ1 and the second ratio ξ2, the first ratio ξ1 is relatively large. Therefore, of the first group 5G1 and the second group 5G2, the first group 5G1 can be assigned the role of extending the cumulative power generation time of the multiple fuel cell units 5 as a whole (hereinafter referred to as power generation time extension). In contrast, the second ratio ξ2 is relatively small. Therefore, the second group 5G2 can be assigned the role of making the total output power of the multiple fuel cell units 5 follow the planned output power pattern 400 (hereinafter referred to as pattern tracking). Thus, according to this embodiment, the controller 8 can perform role-based control in which the first group 5G1 is assigned the role of power generation time extension and the second group 5G2 is assigned the role of pattern tracking.

[0041] (Technologies applicable to the embodiments) The stack of the fuel cell unit 5 may be a polymer electrolyte fuel cell (PEFC) or a solid oxide fuel cell (SOFC). The raw material supplied to the stack of the fuel cell unit 5 may be pure hydrogen gas or a gas obtained by steam reforming. The fuel cell unit 5 may or may not be capable of partial load operation. Partial load operation is operation in which the output power is greater than zero but less than the rated power.

[0042] The controller 8 and the multiple fuel cell units 5 may be connected via a public network or not. The public network is, for example, the internet. The controller 8 may be an on-premise device or a cloud device.

[0043] The number of groups 5G may be 2 or 3 or more. Unless otherwise inconsistent, the description of the embodiments is also applicable when the number of groups 5G is 3 or more.

[0044] (Note) This disclosure provides for the following technologies:

[0045] (Technology 1) Multiple fuel cell units, Equipped with a controller, The controller is, The fuel cell units belonging to the first group among the plurality of fuel cell units are controlled based on the first operation plan. The fuel cell units belonging to the second group among the plurality of fuel cell units are controlled based on the second operating plan. The first and second operation plans are configured such that the first ratio is greater than the second ratio. The first ratio is the ratio of the cumulative power generation time to the cumulative number of startups of the fuel cell units belonging to the first group, The second ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the second group. Fuel cell system.

[0046] (Technology 2) The first operation plan is configured such that the first ratio converges to a first target value. The second operating plan is configured such that the second ratio converges to the second target value. The first target value is greater than the second target value. The fuel cell system described in Technology 1.

[0047] (Technology 3) The first operating plan is configured such that at least a portion of the steady-state component of the total output power of the multiple fuel cell units is supplied by the first group, The second operating plan is configured such that at least a portion of the fluctuating component of the total output power is covered by the second group. A fuel cell system as described in Technology 1 or 2.

[0048] (Technology 4) The controller determines the number of fuel cell units belonging to the first group and the number of fuel cell units belonging to the second group based on information representing the time progression of the total output power of the plurality of fuel cell units. A fuel cell system as described in any one of the three technical specifications.

[0049] (Technology 5) The first ratio is between 2 and 80 times the second ratio. A fuel cell system as described in any one of the technical items 1 to 4.

[0050] (Technology 6) The first operational plan is configured such that the first ratio is greater than the overall ratio. The second operation plan is configured such that the second ratio is smaller than the overall ratio. The aforementioned overall ratio is the ratio of the total cumulative power generation time to the total cumulative number of times the multiple fuel cell units have been started. A fuel cell system as described in any one of the technical items 1 to 5.

[0051] (Technology 7) A control method for a fuel cell system comprising multiple fuel cell units, Controlling the fuel cell units belonging to the first group among the plurality of fuel cell units based on the first operation plan, The system includes controlling the fuel cell units belonging to the second group among the plurality of fuel cell units based on the second operating plan, The first and second operation plans are configured such that there is a difference between the first ratio and the second ratio. The first ratio is the ratio of the cumulative power generation time to the cumulative number of startups of the fuel cell units belonging to the first group, The second ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the second group. Control method. [Industrial applicability]

[0052] The role-based control described herein makes it possible to extend the overall lifespan of multiple fuel cell units while ensuring that the total output power of the multiple fuel cell units follows a planned output power pattern. [Explanation of symbols]

[0053] 5. Fuel cell unit 5G, 5G1, 5G2 group 8. Controller 14 load 100 Fuel Cell Systems

Claims

1. Multiple fuel cell units, Equipped with a controller, The controller is, The fuel cell units belonging to the first group among the plurality of fuel cell units are controlled based on the first operation plan. The fuel cell units belonging to the second group among the plurality of fuel cell units are controlled based on the second operating plan. The first and second operation plans are configured such that the first ratio is greater than the second ratio. The first ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the first group, The second ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the second group. Fuel cell system.

2. The first operation plan is configured such that the first ratio converges to a first target value. The second operating plan is configured such that the second ratio converges to the second target value. The first target value is greater than the second target value. The fuel cell system according to claim 1.

3. The first operating plan is configured such that at least a portion of the steady-state component of the total output power of the plurality of fuel cell units is supplied by the first group, The second operating plan is configured such that at least a portion of the fluctuating component of the total output power is covered by the second group. The fuel cell system according to claim 1.

4. The controller determines the number of fuel cell units belonging to the first group and the number of fuel cell units belonging to the second group based on information representing the time progression of the total output power of the plurality of fuel cell units. The fuel cell system according to claim 1.

5. The first ratio is between 2 and 80 times the second ratio. The fuel cell system according to claim 1.

6. The first operation plan is configured such that the first ratio is greater than the overall ratio. The second operation plan is configured such that the second ratio is smaller than the overall ratio. The aforementioned overall ratio is the ratio of the total cumulative power generation time to the total cumulative number of times the multiple fuel cell units have been started. The fuel cell system according to claim 1.

7. A control method for a fuel cell system comprising multiple fuel cell units, Controlling the fuel cell units belonging to the first group among the plurality of fuel cell units based on the first operation plan, The system includes controlling the fuel cell units belonging to the second group among the plurality of fuel cell units based on a second operating plan, The first and second operation plans are configured such that there is a difference between the first ratio and the second ratio. The first ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the first group, The second ratio is the ratio of the cumulative power generation time to the cumulative number of starts of the fuel cell units belonging to the second group. Control method.

Images