Fuel cell system

Abstract

During the operation of a fuel cell, it is appropriate to determine whether there are energy-saving advantages based on the power generation of the fuel cell. The fuel cell system includes: a fuel cell, a power conversion device that converts the DC power generated by the fuel cell into AC power that can be connected to the power grid and outputs it, a waste heat output device that recovers the waste heat generated during the power generation of the fuel cell and outputs the waste heat to the outside for waste heat utilization, and a control unit. The control unit makes the following determination using a specified threshold during the operation of the fuel cell: compared with the power generation by the power generation equipment of the power system supplier using the energy contributed to power generation after removing the energy used for waste heat utilization from the input energy of the fuel, whether there are energy-saving advantages in generating power using the input energy by the fuel cell and outputting it from the power conversion device, and the control unit performs a specified process for stopping the operation of the fuel cell based on the determination that there are no advantages.

Description

Technical Field

[0001] The present invention relates to a fuel cell system. Background Art

[0002] Conventionally, as such a fuel cell system, there is known a fuel cell system that diagnoses the state of a fuel cell included in the system. For example, Patent Document 1 discloses that a dedicated diagnostic device is connected to a fuel cell, and when the fuel cell is operated in a diagnostic dedicated operation mode, a generated current, a generated voltage, etc. are detected, and by comparing these detected values with reference values during normal operation, mechanical defects of the fuel cell, deterioration due to long-term use, etc. are determined.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 4352688

[0006] Problems to be Solved by the Invention

[0007] In the system of Patent Document 1 described above, in order to diagnose the fuel cell, the fuel cell is operated in a diagnostic dedicated operation mode, and during this period, normal operation of the fuel cell cannot be performed. Therefore, there is a concern that the advantage of energy saving by operating the fuel cell is reduced. In addition, in a fuel cell system, waste heat generated during power generation can be recovered and utilized. Therefore, even if the fuel cell deteriorates, depending on the degree of deterioration, an energy saving advantage may be obtained. Therefore, if waste heat utilization is not considered, an inappropriate determination result may be obtained. Summary of the Invention

[0008] A main object of the fuel cell system of the present invention is to appropriately determine the presence or absence of an energy saving advantage based on power generation during operation of the fuel cell.

[0009] Technical Means for Solving the Problems

[0010] The fuel cell system of the present invention adopts the following means in order to achieve the above main object.

[0011] The fuel cell system of the present invention includes:

[0012] A fuel cell that receives fuel input and generates power;

[0013] A power conversion device that converts DC power generated by the fuel cell into AC power that can be connected to the power system and outputs it,

[0014] A waste heat output device that recovers waste heat generated during the power generation of the fuel cell and outputs the waste heat to the outside for waste heat utilization; and

[0015] A control unit that controls the fuel cell, the power conversion device, and the waste heat output device,

[0016] In this fuel cell system,

[0017] During the operation of the fuel cell, the control unit makes the following determination using a specified threshold value: Compared with the power generation by the power generation equipment of the power system supplier using the energy contributed to power generation after removing the energy for waste heat utilization from the input energy of the fuel, whether there is an energy-saving advantage in generating power through the fuel cell using the input energy and outputting from the power conversion device. And, based on the situation where it is determined that there is no such advantage, the control unit performs a specified process for stopping the operation of the fuel cell.

[0018] In the fuel cell system of the present invention, during the operation of the fuel cell, a determination is made using a specified threshold value as to whether there is an energy-saving advantage in generating power through the fuel cell and outputting from the power conversion device compared with the power generation by the power generation equipment of the power system supplier. In addition, based on the determination that there is no advantage, a specified process for stopping the operation of the fuel cell is performed. Thus, even without operating the fuel cell in a diagnostic dedicated operation mode, it is possible to determine whether there is an energy-saving advantage. In addition, by using the energy contributed to power generation after removing the energy for waste heat utilization from the input energy of the fuel in the power generation of the supplier's power generation equipment, the power generation of the fuel cell system can reflect the advantage of the energy for waste heat utilization. Therefore, it is possible to more appropriately determine the energy-saving advantage. Therefore, it is possible to appropriately determine whether there is an energy-saving advantage based on power generation during the operation of the fuel cell.

[0019] In the fuel cell system of the present invention, it may also be provided with a storage unit that stores a determination mapping diagram establishing the following relationship: using the output current or the input energy of the fuel cell as an input value, using the power generation power of the fuel cell system or the output voltage of the fuel cell as an output value, and using the output value corresponding to the input value as the threshold value. During the operation of the fuel cell, the control unit acquires the input value and the output value, and derives the threshold value corresponding to the acquired input value from the determination mapping diagram to make the determination, and determines that there is no such advantage when the acquired output value is less than the threshold value. In this way, it is possible to quickly derive the threshold value from the determination mapping diagram for determination, suppressing an increase in the processing burden, and thus being able to more appropriately determine whether there is an energy-saving advantage.

[0020] In the fuel cell system of the present invention, the determination map may have an advantage boundary line indicating a correspondence between the input value and the threshold value, and an assumed degradation line indicating a correspondence between the output value and the input value, assumed to be degraded based on the power generation characteristics of the fuel cell system, with the input value on the horizontal axis and the output value on the vertical axis. Furthermore, a range in which the assumed degradation line is below the advantage boundary line is determined. When the input value acquired during operation of the fuel cell is outside this range, the control unit derives the threshold value corresponding to the input value from the advantage boundary line and performs the determination. When the input value acquired during operation of the fuel cell is within this range, the control unit derives the output value corresponding to the input value from the assumed degradation line and performs the determination using the derived output value as the threshold value. Thus, outside the range in which the assumed degradation line is below the advantage boundary line, even if the output value corresponding to the input value falls below the assumed degradation line due to degradation of the fuel cell system, as long as the output value is greater than the threshold value derived from the advantage boundary line, it is determined that there is an energy-saving advantage and the fuel cell is operated. Therefore, even if further degradation occurs, the energy-saving advantage can be achieved. On the other hand, within the range where the degradation assumption line falls below the advantage threshold, degradation of the fuel cell system progresses, and power generation output tends to become unstable. It is believed that fuel cell operation within this range is rare under normal usage conditions. Within this range, using a threshold based on the degradation assumption line for determination can prevent fuel cell operation in a state where degradation progresses without benefiting from energy savings.

[0021] In the fuel cell system of the present invention, it is also possible that in the determination map, with the input value as the horizontal axis and the output value as the vertical axis, a merit boundary line indicating the correspondence between the input value and the threshold value and a degradation assumption line indicating the correspondence between the output value and the input value at the time of degradation assumed based on the power generation characteristics of the fuel cell system are determined, and the range where the degradation assumption line is lower than the merit boundary line is determined. When the input value obtained during the operation of the fuel cell is outside the range, the control unit derives the threshold value corresponding to the input value from the merit boundary line for the determination. When the input value obtained during the operation of the fuel cell is within the range, the control unit omits the determination. In this way, outside the range where the degradation assumption line is lower than the merit boundary line, even if the output value corresponding to the input value is lower than the degradation assumption line due to the degradation of the fuel cell system, as long as the output value is greater than the threshold value derived from the merit boundary line, it is determined that there is a merit of energy saving and the fuel cell is operated. Therefore, even if the degradation progresses, the merit of energy saving can be achieved. On the other hand, within the range where the degradation assumption line is lower than the merit boundary line, as the degradation of the fuel cell system progresses, the power generation output is likely to become unstable, and it can be considered that the fuel cell operates within this range less frequently under normal use conditions. Within this range, by omitting the determination, it is possible to prevent misjudgment of the presence or absence of merits, etc.

[0022] In the fuel cell system of the present invention, it is also possible that the waste heat output device includes: a hot water storage tank that recovers and stores waste heat as hot water; a supply water temperature sensor that detects the temperature of the water supplied to the hot water storage tank; a hot water discharge temperature sensor that detects the temperature of the hot water discharged from the hot water storage tank; and a hot water discharge amount sensor that detects the amount of the hot water discharged from the hot water storage tank. The control unit uses the energy derived based on the following heat as the energy for waste heat utilization: the heat is based on the temperature difference between the temperature of the hot water detected by the hot water discharge temperature sensor and the temperature of the water detected by the supply water temperature sensor and the amount of the hot water detected by the hot water discharge amount sensor. In this way, the actual energy for waste heat utilization during the operation of the fuel cell can be derived, and therefore, it is possible to more appropriately determine the presence or absence of the merit of energy saving.

[0023] In the fuel cell system of the present invention, it is also possible that when the condition of determining that there is no such merit continues for a specified time, the control unit performs the specified process. In this way, in addition to the case where the merit is temporarily reduced due to load fluctuations, output fluctuations, etc., it is possible to more appropriately determine the presence or absence of the merit of energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram showing an outline of the structure of the fuel cell system 10.

[0025] Figure 2 It is a flowchart showing an example of the production order of the determination mapping diagram.

[0026] Figure 3 It is an explanatory diagram showing an example of the determination mapping diagram 93a.

[0027] Figure 4 It is an explanatory diagram showing an example of a voltage line and a power line.

[0028] Figure 5 It is an explanatory diagram showing an example of the relationship between the generated power W and the generation efficiency ks.

[0029] Figure 6 It is a flowchart showing an example of the abnormality determination process.

[0030] Figure 7 It is an explanatory diagram showing the determination mapping diagram 193a of the modified example.

[0031] Figure 8 It is a flowchart showing the abnormality determination process of the modified example.

[0032] Symbol Explanation

[0033] 2 Commercial power system, 4 Electric wire, 10 Fuel cell system, 20 Fuel cell unit, 25 Hot water supply unit, 26 Gas burner, 30 Power generation module, 31 Module housing, 32 Vaporizer, 34 Reformer, 36 Fuel cell stack, 38 Combustion section, 40 Primary fuel gas supply device, 41 Primary fuel gas supply pipe, 42 Gas supply valve, 43 Gas pump, 44 Flow sensor, 45 Air supply device, 46 Air supply pipe, 47 Filter, 48 Blower, 50 Reforming water supply device, 51 Reforming water supply pipe, 52 Reforming water pump, 53 Reforming water tank, 60 Waste heat recovery device, 61 Circulation pipe, 62 Circulation pump, 63 Heat exchanger, 64 Condensate supply pipe, 65 Exhaust gas discharge pipe, 70 Hot water storage tank, 71 Water supply pipe, 72 Hot water discharge pipe, 73 Mixing valve, 74 Water supply temperature sensor, 75 Hot water discharge temperature sensor, 76 Hot water discharge amount sensor, 80 Power conditioner, 81 Stack current sensor, 82 Stack voltage sensor, 83 Output current sensor, 84 Output voltage sensor, 90 Control device, 91 Control section, 92 Communication section, 93 Storage section, 93a, 193a Determination mapping diagram, 95 Operation panel. Detailed Embodiment

[0034] The mode for carrying out the present invention will be described.

[0035] Figure 1 This is a structural diagram showing an overview of the structure of the fuel cell system 10. As shown in the figure, the fuel cell system 10 includes: a fuel cell unit 20, a hot water supply unit 25, a control device 90, and an operation panel 95. This fuel cell system 10 can supply the electric power generated by the fuel cell unit 20 to electrical equipment in a house (not shown), etc., and can supply hot water from the hot water supply unit 25 to hot water equipment in the house, etc.

[0036] The fuel cell unit 20 includes: a power generation assembly 30, a raw fuel gas supply device 40, an air supply device 45, a reforming water supply device 50, a waste heat recovery device 60, a hot water storage tank 70, and a power conditioner 80.

[0037] The power generation assembly 30 has: a vaporizer 32 that vaporizes reforming water to generate water vapor, a reformer 34 that reforms a raw fuel gas such as natural gas or LP gas by steam reforming to generate a reformed gas, a fuel cell stack 36 that receives the supply of the reformed gas and an oxidant gas and generates electricity, an ignition heater (not shown), etc. The vaporizer 32, the reformer 34, and the fuel cell stack 36 are housed in a box-shaped assembly housing 31 formed of a heat-insulating material. In order to supply the heat required for the start-up of the fuel cell stack 36, the generation of water vapor in the vaporizer 32, and the steam reforming reaction in the reformer 34, a combustion part 38 is provided in the assembly housing 31, and the combustion part 38 burns the fuel exhaust gas (anode exhaust gas) and the oxidant exhaust gas (cathode exhaust gas) after passing through the fuel cell stack 36.

[0038] The fuel cell stack 36 is formed by laminating solid oxide fuel cell components. The solid oxide fuel cell component includes: a solid electrolyte composed of an oxygen ion conductor, an anode provided on one surface of the solid electrolyte, and a cathode provided on the other surface of the solid electrolyte. The fuel cell stack 36 generates electricity through the electrochemical reaction between hydrogen in the fuel gas supplied to the anode and oxygen in the air supplied to the cathode.

[0039] The raw fuel gas supply device 40 has a raw fuel gas supply pipe 41 that connects the supply source of the fuel gas to the vaporizer 32. In the raw fuel gas supply pipe 41, a gas supply valve 42, a gas pump 43, a desulfurizer (not shown), a flow sensor 44, etc. are provided in sequence from the supply source side of the fuel gas. By driving the gas pump 43 with the gas supply valve 42 in the open state, the raw fuel gas is desulfurized by the desulfurizer and supplied to the vaporizer 32.

[0040] The air supply device 45 has an air supply pipe 46 that connects a filter 47 communicating with outside air to the fuel cell stack 36. A blower 48 is provided in the air supply pipe 46, and the air inhaled through the filter 47 is supplied to the fuel cell stack 36 by driving the blower 48. Further, a flow rate sensor (not shown) and the like are provided in the air supply pipe 46.

[0041] The reformed water supply device 50 has a reformed water supply pipe 51 that connects a reformed water tank 53 storing reformed water to the vaporizer 32. A reformed water pump 52 is provided in the reformed water tank 53. By driving the reformed water pump 52, the reformed water in the reformed water tank 53 is sucked up and supplied to the vaporizer 32 via the reformed water supply pipe 51. Further, a flow rate sensor (not shown) and the like are provided in the reformed water supply pipe 51.

[0042] The waste heat recovery device 60 includes: a circulation pump 62, a circulation pipe 61 that circulates the stored hot water in the hot water storage tank 70 by driving the circulation pump 62, and a heat exchanger 63 that exchanges heat between the stored hot water in the circulation pipe 61 and the combustion exhaust gas from the combustion unit 38. The water vapor component of the combustion exhaust gas from the combustion unit 38 is condensed by the heat exchange, and the condensed water (condensate) is recovered by the reformed water tank 53 via the condensate supply pipe 64. A water purifier (not shown) is provided in the condensate supply pipe 64, and the water purified (purified) by the water purifier is recovered by the reformed water tank 53. In addition, the remaining exhaust gas (gas component) is discharged to the outside air via the exhaust gas discharge pipe 65.

[0043] The hot water storage tank 70 stores warm water (stored hot water) heated by the waste heat recovery of the waste heat recovery device 60. Water from a water supply source (water supply pipe) flows into the hot water storage tank 70 via a water supply pipe 71. In addition, the hot water stored in the hot water storage tank 70 is discharged to the hot water supply unit 25 via a hot water discharge pipe 72. A mixing valve 73 is provided in the hot water discharge pipe 72 and is connected to a branch pipe of the water supply pipe 71. After mixing with the water flowing in from the branch pipe according to the required temperature of the discharged hot water and the upper limit temperature set for the discharged hot water, the hot water is discharged to the hot water supply unit 25. Further, a water supply temperature sensor 74 is provided in the water supply pipe 71, and the water supply temperature Ti of the water supplied to the hot water storage tank 70 through the water supply pipe 71 is detected by the water supply temperature sensor 74. In addition, a hot water discharge temperature sensor 75 that detects the hot water discharge temperature To of the hot water discharged to the hot water supply unit 25 through the hot water discharge pipe 72 and a hot water discharge amount sensor 76 that detects the flow rate of the hot water through the hot water discharge pipe 72 are provided in the hot water discharge pipe 72.

[0044] Although the illustration is omitted, the power conditioner 80 includes a DC / DC converter that boosts the DC voltage output from the fuel cell stack 36 to a specified voltage and an inverter that converts the boosted DC voltage into an AC voltage capable of being interconnected with the commercial power system 2, converting the DC power generated by the fuel cell stack 36 into AC power and supplying power to electrical appliances in the house and the like from the electric wire 4 connected to the commercial power system 2. In addition, provided in the electric wire connected to the fuel cell stack 36 are a current sensor 81 that detects the stack current Is output from the fuel cell stack 36 and a voltage sensor 82 that detects the stack voltage Vs. Further, provided in the electric wire connected to the commercial power system 2 are a current sensor 83 that detects the output current Io output from the power conditioner 80 and a voltage sensor 84 that detects the output voltage Vo.

[0045] The hot water supply unit 25 includes a gas burner 26 that burns the fuel gas supplied from the fuel gas supply source and the like. The hot water supply unit 25 heats the hot water discharged from the hot water storage tank 70 via the hot water discharge pipe 72 in the gas burner 26 to adjust it to a desired water temperature, and thus supplies hot water to the warm water equipment in the house and the like.

[0046] The control device 90 includes a control unit 91 that controls the entire fuel cell system 10, a communication unit 92 that communicates with the operation panel 95 via a wireless or wired communication line, and a storage unit 93 that stores various processing programs and various information. In addition, the control unit 91 includes a timer T for measuring time and the like. Input to the control unit 91 via the input port are detection signals from various sensors such as the gas flow rate Qg from the flow sensor 44, the supply water temperature Ti from the supply water temperature sensor 74, the hot water discharge temperature To from the hot water discharge temperature sensor 75, the flow rate F of the hot water from the hot water discharge amount sensor 76, the stack current Is from the current sensor 81, the stack voltage Vs from the voltage sensor 82, the output current Io from the current sensor 83, and the output voltage Vo from the voltage sensor 84. Further, output from the control unit 91 via the output port are drive signals to various auxiliary devices such as the gas supply valve 42, the gas pump 43, the blower 48, the reforming water pump 52, the circulation pump 62, the mixing valve 73, and the gas burner 26, and a control signal to the power conditioner 80. Further, via the control unit 91, the communication unit 92 receives an operation signal from the operation panel 95, performs various controls based on the operation signal, sends a display signal to the operation panel 95 via the communication unit 92, and displays various information based on the display signal. In addition, the operation panel 95 is provided inside the house, and various operations of the fuel cell system 10 are performed by the user (the resident of the house), and various information about the fuel cell system 10 is displayed.

[0047] The control unit 91 of the control device 90 controls the raw fuel gas supply device 40, the air supply device 45, and the reformed water supply device 55 to generate electricity according to the required power demanded by the fuel cell system 10. In addition, operation control is performed to stably operate at the rated output according to the required power. Specifically, the control unit 91 first sets the current command Is* as the output current required to be output by the fuel cell stack 36 through feedback control based on the deviation between the above-mentioned required power and the generated power of the fuel cell stack 36. In addition, the generated power of the fuel cell stack 36 can be calculated as the DC output Wdc, which is the product of the stack current Is detected by the current sensor 81 and the stack voltage Vs detected by the voltage sensor 82. Next, based on the set current command Is*, the target gas flow rate, the target air flow rate, and the target water volume are set. Next, the control device 90 controls the gas pump 43 through feedback control based on the deviation between the target gas flow rate and the gas flow rate measured by the flow sensor 44 to supply the fuel gas (raw fuel gas supply control) from the raw fuel gas supply device 40 at the target gas flow rate. In addition, the blower 48 is controlled through feedback control based on the deviation between the target air flow rate and the air flow rate measured by the flow sensor to supply air (air supply control) from the air supply device 45 at the target air flow rate. In addition, the reformed water pump 52 is controlled through feedback control based on the deviation between the target water volume and the reformed water volume measured by the flow sensor to supply the reformed water from the reformed water supply device 50 at the target water volume (reformed water supply control).

[0048] Here, a determination map 93a is stored in the storage unit 93 of the control device 90, and this determination map 93a is used to determine whether there is an advantage in energy saving by generating electricity with the fuel cell system 10. The production sequence of this determination map 93a will be described. Figure 2 is a flowchart showing an example of the production sequence of the determination map, Figure 3 is an explanatory diagram showing an example of the determination map 93a. The determination map 93a is made by, for example, the designer of the fuel cell system 10 and stored in the storage unit 93 at the time of factory shipment. Alternatively, the map made through the production process of the control unit 91 can also be stored in the storage unit 93 when the fuel cell system 10 is installed in a house or the like, during the trial operation after installation, or when normal operation starts.

[0049] At Figure 2In the order of creating the judgment map, first, the generated power W (AC output) of the fuel cell system 10 (fuel cell unit 20) relative to the stack current Is is calculated based on the characteristics (IV characteristics) of the stack current Is [A] and the stack voltage Vs [V] of the fuel cell stack 36 (S100). Here, first, the product of the stack current Is and the stack voltage Vs based on the IV characteristics (Is×Vs) is calculated as the DC power (DC output Wdc) of the fuel cell stack 36 relative to the stack current Is. Then, based on the DC output Wdc [W], the auxiliary equipment loss AL [W], and the power conditioner conversion efficiency kp [%], the generated power W [W] as the AC output of the fuel cell system 10 is calculated by the following formula (1). In formula (1), the generated power W is calculated by multiplying the value obtained by subtracting the auxiliary equipment loss AL, which is the power consumed by the auxiliary equipment, from the DC output Wdc by the power conditioner conversion efficiency kp, which is the AC / DC conversion efficiency of the power conditioner 80. Therefore, the generated power W reflects the increase in auxiliary equipment loss AL associated with degradation and the decrease in power conditioner conversion efficiency kp. In addition, the power consumption of the degraded auxiliary equipment is determined as auxiliary equipment loss AL based on the characteristics of each auxiliary equipment, and the power conditioner conversion efficiency kp is determined based on the characteristics of the power conditioner 80.

[0050] W=(Wdc-AL)×kp···(1)

[0051] here, Figure 4 This is an explanatory diagram showing an example of voltage lines and power lines. Figure 4 In the figure, as a voltage line representing the stack voltage Vs (right vertical axis) relative to the stack current Is on the horizontal axis, an initial voltage line (dotted line) at the initial stage of use (before degradation) of the fuel cell system 10 and a final voltage line (single-dotted dashed line) assumed to be degraded based on the power generation characteristics of the fuel cell system 10 are shown. In addition, as a power line representing the generated power W (left vertical axis) relative to the stack current Is, an initial power line (dashed line) derived from the initial voltage line and a final power line (double-dotted dashed line) derived from the final voltage line are shown. In the fuel cell system 10, as degradation progresses, the operating point representing the stack voltage Vs relative to the stack current Is and the operating point representing the generated power W relative to the stack current Is are not on the initial voltage line or the initial power line, but shift to the final voltage line and the final power line. In addition, when the operating point is lower than the final voltage line or the final power line, it is preferable to stop the operation from the perspective of degradation of the fuel cell system 10, but it is not impossible to continue the operation.

[0052] Next, the input energy Et of the fuel gas with respect to the stack current Is is calculated (S110). Here, first, the fuel utilization rate Uf [%] with respect to the stack current Is is obtained. The fuel utilization rate Uf is the ratio of the fuel gas used for power generation among the fuel gas input (supplied) to the fuel cell stack 36 by the original fuel gas supply device 40. The fuel utilization rate Uf is determined by the characteristics of the fuel cell unit 20 and is represented by, for example, a cubic function of the stack current Is. Based on the fuel utilization rate Uf, the stack current Is, and the constant α, the gas flow rate Qg [L / min] of the fuel gas is calculated by the following formula (2). The constant α [L / min·A], which is the gas flow rate of hydrogen required for power generation for supplying 1 A of the stack current Is, is determined by the composition of the fuel gas and the characteristics of the fuel cell unit 20. Then, based on the gas flow rate Qg and the calorific value Hg [MJ / m 3 , the input energy Et [W] of the fuel gas is calculated by the following formula (3). In addition, the value 60 is a conversion coefficient for converting the unit of time from minutes to seconds.

[0053] Qg = Is × α / Uf ··· (2)

[0054] Et = Qg × Hg / 60 ··· (3)

[0055] Next, based on the waste heat utilization amount Ho of the fuel cell system 10, the energy Eh for waste heat utilization is calculated (S120). The waste heat utilization amount Ho, as the heat of the hot water discharged to the hot water supply unit 25 recovered by the hot water storage tank 70 in the fuel cell system 10, for example, can be calculated by the following formula (4). In formula (4), the waste heat utilization amount Ho is calculated by multiplying the temperature difference (To - Ti) obtained by subtracting the water supply temperature Ti [°C] of the water supplied to the hot water storage tank 70 from the hot water discharge temperature To [°C] of the hot water discharged from the hot water storage tank 70 by the tank capacity TC [L] of the hot water storage tank 70, the specific heat Cw [kJ / (kg·°C)] of water, the density ρ (kg / L) of water, and the number of hot water discharges N [times / day]. In addition, the number of hot water discharges N is, for example, a value of 2 [times / day], etc., and the value 24 is a conversion coefficient converted to [times / hour]. And, based on the waste heat utilization amount Ho, the energy Eh for waste heat utilization is calculated by the following formula (5). In addition, the hot water supply efficiency kh [%] is determined based on the waste heat loss of the hot water discharge pipe 72, etc., and the value 3600 is a conversion coefficient for converting the unit of time from hours to seconds. The energy Eh for waste heat utilization is the energy in the input energy Et utilized by the discharged hot water.

[0056] Ho = (To - Ti) × Tc × Cw × ρ × N / 24 ··· (4)

[0057] Eh = Ho / (kh × 3600) ··· (5)

[0058] When the energy Eh for waste heat utilization is obtained, the power generation efficiency ks of the fuel cell unit 20 that provides energy savings is calculated using the following equation (6) based on the energy contributed to power generation after deducting the energy Eh for waste heat utilization and the power generation efficiency kc of the commercial power system supplier's power generation equipment. On the left side of equation (6), the energy Eh for waste heat utilization is subtracted from the energy (equivalent to the input energy) obtained by dividing the generated power W by the power generation efficiency ks of the fuel cell unit 20. This yields the energy contributed to power generation actually used to generate the generated power W in the fuel cell system 10. Furthermore, the right side of equation (6) is the energy obtained by dividing the generated power W by the power generation efficiency kc of the supplier's power generation equipment. The power generation efficiency kc is a value determined by the supplier. The power generation efficiency ks relative to the generated power W is calculated by varying the generated power W so that equation (6) holds true. Thus, using the energy contributed to power generation, the minimum power generation efficiency ks that provides energy savings when the fuel cell system 10 generates power compared to power generation by the commercial power system supplier's power generation equipment is derived. Based on the generated power W and the generated power efficiency ks thus obtained, an approximate expression (ks=f(W)) expressing the relationship between the two is set (S140). Figure 5 This diagram illustrates an example of the relationship between generated power W and power generation efficiency ks. For example, multiple plot points are taken for power generation efficiency ks relative to generated power W, and an approximate equation for an approximate line passing through each plot point is set as an approximate equation, such as a quintic equation for generated power W.

[0059] W / ks-Eh=W / kc···(6)

[0060] Next, the lower limit power Wmin[W] (S150) that produces an energy-saving advantage relative to the stack current Is is calculated by the following formula (7). Here, as the generated power W relative to the stack current Is, the generated power efficiency ks is obtained by using the generated power W calculated by formula (1) of S100 and the approximate formula (ks=f(W)), and the generated power efficiency ks is multiplied by the input energy Et calculated by formula (3) of S110, thereby calculating the lower limit power Wmin (ks×Et). In formulas (1) and (3), after calculating the values relative to the stack current Is as the generated power W and the input energy Et, the stack current Is is changed, and the lower limit power Wmin relative to multiple stack currents Is can be calculated separately. In addition, as described above, the generated power efficiency ks is the minimum generated power efficiency for producing an energy-saving advantage. Therefore, the lower limit power Wmin obtained by multiplying the generated power efficiency ks by the input energy Et is calculated as the minimum generated power that produces an energy-saving advantage in each of the multiple stack currents Is. In Figure 4In it, the illustration of the plotted points is omitted, but multiple plotted points are taken for the relationship between the lower limit power Wmin and the stack current Is, and an approximate line passing through each plotted point is shown as the lower limit power line. The lower limit power line is determined to be a line where the lower limit power Wmin decreases as the stack current Is decreases due to deterioration. Additionally, the lower limit power line intersects the end - stage power line, and in a small range where the stack current Is is less than the intersection current Isp at the intersection point, the end - stage power line is below the lower limit power line, and in a large range where the stack current Is is equal to or greater than the intersection current Isp, the lower limit power line is above the end - stage power line. Furthermore, the stack current Is has a tendency to decrease as the deterioration of the fuel cell system 10 (fuel cell stack 36) progresses. Therefore, the range less than the intersection current Isp can be referred to as the range where the deterioration of the fuel cell system 10 has progressed. Also, when the stack current Is becomes significantly small like this, it may be difficult to obtain an appropriate output or the output may become unstable. Moreover, in the normal use of the fuel cell system 10 installed in a residence, it takes a long period to reach the range less than the intersection current Isp, and the fuel cell stack 36 hardly operates in the range less than the intersection current Isp.

[0061] Wmin = ks × Et ···(7)

[0062] When the lower limit power Wmin (lower limit power line) corresponding to the stack current Is is obtained in this way, a determination map 93a is created based on the lower limit power Wmin. As Figure 4 shown, the determination map 93a is created as a map with the stack current Is as the input value on the horizontal axis and the power generation power W as the output value on the vertical axis. In the determination map 93a of the present embodiment, in a large range where the stack current Is is equal to or greater than the intersection current Isp, the power generation power (lower limit power Wmin) on the lower limit power line is derived as the determination threshold, and in a small range where the stack current Is is less than the intersection current Isp, the power generation power on the end - stage power line is derived as the determination threshold. Additionally, the area indicated by diagonal lines in the figure is the area without the advantage of energy conservation. The determination map 93a created in this way is stored in the storage unit 93.

[0063] Next, the abnormal determination process executed during the operation of the fuel cell system 10 will be described. Figure 6It is a flowchart showing an example of abnormal determination processing. In this abnormal determination processing, first, the control unit 91 of the control device 90 acquires the reactor current Is from the current sensor 81, the output current Io from the current sensor 83, and the output voltage Vo from the voltage sensor 84 (S200), and determines whether the acquired reactor current Is is equal to or greater than the intersection current Isp (S210). When it is determined that the reactor current Is is equal to or greater than the intersection current Isp, the control unit 91 derives the generated power W corresponding to the current reactor current Is as a threshold value from the lower limit power line of the determination map 93a (S220), and compares this threshold value with the current generated power W (S240). That is, the generated power W derived from the lower limit power line of the determination map 93a using the current reactor current Is acquired in S200 is compared with the current generated power W, and this current generated power W is calculated as the product of the current output current Io and the output voltage V acquired in S200.

[0064] On the other hand, when it is determined in S210 that the reactor current Is is less than the intersection current Isp, the control unit 91 derives the generated power W corresponding to the current reactor current Is as a threshold value from the end-stage power line of the determination map 93a (S230), and compares this threshold value with the current generated power W (S240). That is, the generated power W derived from the end-stage power line of the determination map 93a using the current reactor current Is acquired in S200 is compared with the current generated power W, and this current generated power W is calculated as the product of the current output current Io and the output voltage Vo acquired in S200.

[0065] Next, the control unit 91 determines the result of the comparison in S240, whether the current generated power W is less than the threshold value (S250). When it is determined that the current generated power W is less than the threshold value, it is determined whether the timer T provided in the control unit 91 is measuring time (S260). When it is determined that the measurement is not in progress, the measurement of time by the timer T is started (S270), and when it is determined that the measurement is in progress, S270 is skipped. Then, it is determined whether the measurement time of the timer T is equal to or greater than the specified time Tref (S300). When it is determined that the measurement time is less than the specified time Tref, the process returns to S200. The specified time Tref can be set to a time of several hundred minutes such as 500 minutes or 600 minutes. In addition, in order to determine an abnormality at an early stage, the specified time Tref can also be set to a time of several tens of minutes or one hundred and several tens of minutes.

[0066] Further, when it is determined in S250 that the threshold is smaller than the current power generation power W, that is, when the current power generation power W is larger than the threshold, the control unit 91 determines whether the timer T is measuring time (S280). When it is determined that the measurement is not in progress, the process returns to S200. When it is determined that the measurement is in progress, the time measurement by the timer T is ended (S290), and the process returns to S200. In S290, the timer T whose timing has ended is reset. Further, in order to prevent frequent fluctuations in the start and end of the time measurement by the timer T, a threshold obtained by adding a certain margin to the power generation power of the lower limit power line and the end period power line of the determination mapping 93a may also be used during the time measurement by the timer T to end the time measurement by the timer T.

[0067] Also, when the time measurement by the timer T is not ended and the state where the power generation power W is smaller than the threshold continues for the entire specified time Tref, the control unit 91 determines in S300 that the measurement time of the timer T is equal to or longer than the specified time Tref. In this case, the control unit 91 determines that there is no advantage (the advantage is reduced) in power generation by the fuel cell system 10 compared to power generation by the power generation equipment of the supplier, and notifies the user by displaying a warning prompting the stop of the operation of the fuel cell stack 36 on the operation panel 95 (S310), and then ends the abnormality determination process. That is, since it is advantageous for the user to purchase the power generated by the power generation equipment of the supplier compared to power generation by the fuel cell system 10, the operation of the fuel cell stack 36 is prompted to stop.

[0068] The fuel cell system 10 described above uses a threshold determined as a point of divergence as to whether there is an energy-saving advantage in power generation by the fuel cell system 10 compared to power generation by the power generation equipment of the supplier, and determines whether there is an advantage during the operation of the fuel cell stack 36. Further, when it is determined that there is no advantage, a warning for stopping the operation of the fuel cell stack 36 is notified. Thereby, it is possible to determine whether there is an energy-saving advantage even when not operating in a diagnosis dedicated operation mode. Further, as the threshold, in the order of creating the determination mapping, the lower limit power Wmin is used, and the lower limit power Wmin is determined based on the energy contributed to power generation after removing the energy Eh used for waste heat utilization from the input energy, the power generation efficiency kc of the supplier, and the relationship between the power generation efficiency ks having an energy-saving advantage and the power generation power W. Therefore, the energy Eh used for waste heat utilization can be reflected, and the energy-saving advantage can be determined more appropriately.

[0069] Furthermore, a determination map 93a defining a threshold value (lower limit power Wmin) for stack current Is is stored in storage unit 93. Determination is performed by deriving a threshold value corresponding to stack current Is during operation from determination map 93a. This allows for rapid deriving of the threshold value for determination, thereby minimizing any increase in processing load.

[0070] Furthermore, in the judgment map 93a, a range is determined in which the final power line (degradation assumption line), which represents the relationship between generated power W and stack current Is when assumed to be degraded, is lower than the lower power line (advantage boundary line), which represents the relationship between stack current Is and lower power limit Wmin. The intersection current Isp of the two lines is also determined. When the stack current Is is above the intersection current Isp, the lower power limit Wmin is used as the threshold for judgment. When the stack current Is is less than the intersection current Isp, the generated power W derived from the final power line is used as the threshold for judgment. Therefore, within the range where the lower power limit line is lower than the final power line, even if the generated power W is lower than the final power line, as long as it is determined that the generated power W is greater than the threshold based on the lower power line, and an energy-saving advantage exists, the fuel cell stack 36 can be operated. In other words, by using the lower power line, which takes into account the energy used for waste heat utilization, rather than the final power line, judgment is made. This allows the user to enjoy the energy-saving advantage of including the energy used for waste heat utilization, even as degradation of the fuel cell system 10 progresses. On the other hand, even in the range where the final power line is lower than the lower limit power line, by making a determination using a threshold value based on the final power line, the operation of the fuel cell stack 36 can be stopped in a state where degradation has progressed, which is not advantageous.

[0071] In addition, when the state in which the generated power W is less than the threshold value continues for more than the prescribed time Tref, a warning (prescribed processing) is issued to prompt the operation to be stopped. Therefore, except for the state in which the generated power W is temporarily lower than the threshold value due to changes in the load of the residential electrical equipment and the changes in the generated power W, it is possible to appropriately determine the state in which there is no energy-saving advantage.

[0072] In the above embodiment, when the stack current Is is less than the intersection current Isp in the determination map 93a, the threshold value is derived from the final power line, but the present invention is not limited to this. For example, when the stack current Is is less than the intersection current Isp, the determination of whether there is an advantage or not can be omitted. In this case, the threshold value can be omitted. Figure 6If the stack current Is is determined to be less than the intersection current Isp in S210, the process returns to S200. Furthermore, if the stack current Is is determined to be less than the intersection current Isp in S210, the process may proceed to S260, indicating that the degradation is severe. Alternatively, regardless of whether the stack current Is is less than the intersection current Isp, the process may always derive a threshold value from the lower limit power line of the determination map 93a to determine whether an advantage exists.

[0073] In the embodiment, if the state of generated power W being less than a threshold value continues for the entire predetermined time Tref, a warning prompting the operation to be stopped is issued. However, the present invention is not limited to this. A predetermined process for stopping the operation of the fuel cell stack 36, such as forcibly stopping the operation of the fuel cell stack 36, may also be performed. Furthermore, if it is determined that the generated power W is less than the threshold value, a predetermined process such as immediately issuing a warning may also be performed. In this case, the operation may also be forcibly stopped if the generated power W is less than the threshold value for the entire predetermined time Tref.

[0074] In the embodiment, the threshold value is derived using the determination map 93a, but the present invention is not limited thereto. Instead of using the determination map, the threshold value may be calculated and derived based on values (input values) acquired during the operation of the fuel cell stack 36. In this case, the determination map 93a may not be stored in the storage unit 93.

[0075] In the embodiment, the determination map 93 a has the stack current Is on the horizontal axis and the generated power W on the vertical axis. However, the present invention is not limited thereto and may have the input energy Et on the horizontal axis and the stack voltage Vs on the vertical axis. Figure 7 This is an explanatory diagram showing a modified example of a determination map 193a. In the modified example of a determination map 193a, the stack current Is, which is an input value, is plotted on the horizontal axis, and the stack voltage Vs, which is a determination value, is plotted on the vertical axis. Figure 2 The determination map shown is created as part of the process for creating the map. For example, the lower limit power Wmin calculated in S150 is converted into a lower limit voltage Vsmin, which is the lower limit voltage of the stack voltage Vs, based on the following equation (8). In equation (8), the lower limit voltage Vsmin is calculated by dividing the lower limit power Wmin by the power conditioner conversion efficiency kp and adding the auxiliary equipment loss AL, and then dividing the value by the stack current Is. Therefore, the lower limit voltage Vsmin reflects the increase in the auxiliary equipment loss AL and the decrease in the power conditioner conversion efficiency kp.

[0076] Vsmin=(Wmin / kp+AL) / Is···(8)

[0077] In addition, as described above, the lower limit power Wmin is calculated as a value corresponding to a plurality of stack currents Is. Therefore, the lower limit voltage Vsmin can also be calculated as a value corresponding to a plurality of stack currents Is. In Figure 7 the illustration of the plotted points is omitted, but for the relationship between the lower limit voltage Vsmin and the stack current Is, a plurality of plotted points are taken, and the lower limit voltage line is represented as an approximate line passing through each plotted point. The lower limit voltage line intersects the end-stage voltage line, and has the following relationship: in a small range where the stack current Is is less than the intersection current Isp’, the end-stage voltage line is lower than the lower limit voltage line; in a large range where the stack current Is is greater than or equal to the intersection current Isp’, the lower limit voltage line is higher than the end-stage voltage line. Therefore, similarly to the embodiment, when the stack current Is is less than the intersection current Isp’, the stack voltage Vs derived from the end-stage voltage line is used as the threshold; when the stack current Is is greater than the intersection current Isp’, the stack voltage Vs (lower limit voltage Vsmin) derived from the lower limit voltage line is used as the threshold. Therefore, the slanted portion is the region determined to have no advantage.

[0078] Figure 8 is a flowchart showing the abnormality determination process of the modified example. In the modified example, the same step numbers are assigned to the same processes as in the embodiment and the description thereof is omitted. In this abnormality determination process, the control unit 91 first acquires the stack current Is from the current sensor 81 and the stack voltage Vs from the voltage sensor 82 (S200b), and determines whether the stack current Is is greater than or equal to the intersection current Isp’ (S210b). When it is determined that the stack current Is is greater than or equal to the intersection current Isp’, the stack voltage Vs corresponding to the current stack current Is is derived as the threshold from the lower limit voltage line of the determination map 193a (S220b), and this threshold is compared with the current stack voltage Vs (S240b). On the other hand, when it is determined in S210b that the stack current Is is less than the intersection current Isp’, the control unit 91 derives the stack voltage Vs corresponding to the current stack current Is as the threshold from the end-stage voltage line of the determination map 193a (S230b), and this threshold is compared with the current stack voltage Vs (S240b). Then, when the control unit 91 determines in S250b that the current stack voltage Vs is less than the threshold, it proceeds to S260; when it is determined that the current stack voltage Vs is not less than the threshold, it proceeds to S280. Therefore, even in the modified example where the stack voltage Vs is used as the threshold, it is possible to appropriately determine the presence or absence of an advantage in the same manner as in the embodiment.

[0079] In the embodiment, the generated power W (mainly the lower limit power Wmin) is used as the threshold value, the generated power W relative to the stack current Is is used as the judgment value, and the threshold value is compared with the judgment value to determine whether there is an advantage. In addition, in a modified example, the stack voltage Vs (mainly the lower limit voltage Vsmin) is used as the threshold value, the stack voltage Vs relative to the stack current Is is used as the judgment value, and the threshold value is compared with the judgment value to determine whether there is an advantage. However, it is not limited to this, and the judgment value related to the power generation of the fuel cell stack 36 in operation and the threshold value can be compared to determine whether there is an advantage. For example, the power generation efficiency that will become the divergence point of whether there is an energy-saving advantage can be used as the threshold value, and compared with the power generation efficiency derived during operation to determine whether there is an advantage. In addition, it is not limited to the judgment value (output value) and threshold value relative to the stack current Is (input value), and it can also be the judgment value (output value) and threshold value relative to the input energy Et (input value). Since these currents, voltages, generated power, energy, etc. can be converted into each other, they can be appropriately selected.

[0080] In the embodiment, the waste heat utilization amount Ho is calculated using Equation (4), for example, as the amount of heat in the hot water recovered by the hot water storage tank 70 in the fuel cell system 10 and discharged to the hot water supply unit 25. However, the present invention is not limited to this. For example, during operation, the supply water temperature Ti from the supply water temperature sensor 74, the hot water discharge temperature To from the hot water discharge temperature sensor 75, and the hot water flow rate F from the hot water discharge flow rate sensor 76 are obtained. Based on the temperature difference between the hot water discharge temperature To and the supply water temperature Ti and the hot water flow rate F, the waste heat utilization amount Ho is calculated using Equation (9) below. By calculating the waste heat utilization amount Ho based on actual measured values during operation in this manner, it is possible to derive the energy Eh for waste heat utilization corresponding to the waste heat utilization status. Therefore, since the threshold reflects the actual waste heat utilization status, it is possible to more appropriately determine whether the energy saving advantage has been reduced. In addition, instead of the hot water discharge flow rate sensor 76, the flow rate detected by the flow rate sensor provided in the hot water supply unit 25 can also be obtained and used. In addition to the waste heat utilization amount Ho, the gas flow rate Qg may be a value detected by the flow rate sensor 44, and the input energy Et calculated based on the gas flow rate Qg may be used.

[0081] Ho=(To-Ti)×F×Cw×ρ···(9)

[0082] In the embodiment, the generated power W is used as a threshold to determine whether there is an energy-saving advantage, but the present invention is not limited to this. For example, the cost can be derived by multiplying the power consumption by the unit price of the electricity bill, or by multiplying the gas supply (input) flow rate by the unit price of the gas fee, and the presence of an energy-saving advantage can be determined based on the cost. In other words, the cost, which is the branch point between the presence and absence of an advantage, is used as a threshold, and by comparing it with the current cost derived during operation, it is determined whether there is an economic advantage through energy saving. In addition, the unit price of the electricity bill and the unit price of the gas fee can use the value stored in the storage unit 93, the value input by the user through the operation panel 95, or the value obtained by the control device 90 from the power supply company or gas supply company via the network connected by the communication unit 92.

[0083] The following describes the correspondence between the main elements of the embodiment and the main elements of the invention described in the section on solving the problems. In the embodiment, the fuel cell stack 36 corresponds to the "fuel cell," the power conditioner 80 corresponds to the "power conversion device," the waste heat recovery device 60 and the hot water storage tank 70 (including the water supply pipe 71, the hot water discharge pipe 72, and the mixing valve 73) correspond to the "waste heat output device," and the control unit 91 of the control device 90 corresponds to the "control unit." Furthermore, the storage unit 93 corresponds to the "storage unit." Furthermore, the hot water storage tank 70 corresponds to the "hot water storage tank," the supply water temperature sensor 74 corresponds to the "supply water temperature sensor," the hot water discharge temperature sensor 75 corresponds to the "hot water discharge temperature sensor," and the hot water discharge amount sensor 76 corresponds to the "hot water discharge amount sensor."

[0084] Furthermore, the correspondence between the main elements of the embodiment and the main elements of the invention described in the means for solving the problem section is an example for specifically describing how the embodiment implements the invention described in the means for solving the problem section and is therefore not limited to the elements of the invention described in the means for solving the problem section. In other words, the invention described in the means for solving the problem section should be interpreted based on the description in this column, and the embodiment is merely a specific example of the invention described in the means for solving the problem section.

[0085] While the modes for carrying out the present invention have been described above using the embodiments, the present invention is not limited to these embodiments and can of course be carried out in various forms without departing from the gist of the present invention.

[0086] Industrial Application Possibilities

[0087] The present invention can be utilized in the fuel cell system manufacturing industry and the like.

Claims

1. A fuel cell system, comprising: A fuel cell that generates electricity upon receiving an input of fuel; A power conversion device that converts the DC power generated by the fuel cell into AC power capable of being connected to a power grid and outputs the AC power; A waste heat output device that recovers waste heat generated during the power generation of the fuel cell and outputs the waste heat to the outside for waste heat utilization; and A control unit that controls the fuel cell, the power conversion device, and the waste heat output device. In this fuel cell system, During the operation of the fuel cell, the control unit makes the following determination using a specified threshold value: Compared with the power generation by the power generation equipment of the power system supplier using the energy contributed to power generation after removing the energy used for waste heat utilization from the input energy of the fuel, whether there is an energy-saving advantage in generating electricity by the fuel cell using the input energy and outputting it from the power conversion device. And, based on the situation where it is determined that there is no such advantage, the control unit performs a specified process for stopping the operation of the fuel cell. The fuel cell system includes a storage unit that stores a determination mapping diagram establishing the following relationship: taking the output current or the input energy of the fuel cell as an input value, taking the power generation power or the output voltage of the fuel cell system as an output value, and using the output value corresponding to the input value as the threshold value. During the operation of the fuel cell, the control unit acquires the input value and the output value, and derives the threshold value corresponding to the acquired input value from the determination mapping diagram to make the determination. When the acquired output value is less than the threshold value, it is determined that there is no such advantage.

2. The fuel cell system according to claim 1, wherein In the determination mapping diagram, with the input value as the horizontal axis and the output value as the vertical axis, a merit demarcation line representing the correspondence between the input value and the threshold value and a degradation assumption line representing the correspondence between the output value and the input value during assumed degradation based on the power generation characteristics of the fuel cell system are determined, and a range where the degradation assumption line is lower than the merit demarcation line is determined. When the input value acquired during the operation of the fuel cell is outside the range, the control unit derives the threshold value corresponding to the input value from the merit demarcation line to make the determination. When the input value acquired during the operation of the fuel cell is within the range, the control unit derives the output value corresponding to the input value from the degradation assumption line and uses the derived output value as the threshold value to make the determination.

3. The fuel cell system according to claim 1, wherein In the determination mapping diagram, with the input value as the horizontal axis and the output value as the vertical axis, a merit boundary line representing the correspondence between the input value and the threshold value and a degradation assumption line representing the correspondence between the output value and the input value during assumed degradation based on the power generation characteristics of the fuel cell system are determined, and a range where the degradation assumption line is lower than the merit boundary line is determined. When the input value obtained during the operation of the fuel cell is outside the range, the control unit derives the threshold value corresponding to the input value from the merit boundary line for the determination. When the input value obtained during the operation of the fuel cell is within the range, the control unit omits the determination.

4. The fuel cell system according to any one of claims 1 to 3, wherein the waste heat output device includes: a hot water storage tank that recovers and stores waste heat as hot water; a supply water temperature sensor that detects the temperature of water supplied to the hot water storage tank; a hot water discharge temperature sensor that detects the temperature of hot water discharged from the hot water storage tank; and a hot water discharge amount sensor that detects the amount of hot water discharged from the hot water storage tank. The control unit uses the energy derived from the following heat as the energy for waste heat utilization: the heat based on the temperature difference between the temperature of the hot water detected by the hot water discharge temperature sensor and the temperature of the water detected by the supply water temperature sensor and the amount of hot water detected by the hot water discharge amount sensor.

5. The fuel cell system according to claim 1, wherein when a state where it is determined that there is no such merit continues for a predetermined time, the control unit performs the predetermined process.

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