JP2023104027A - fuel cell system - Google Patents

Abstract

To reduce an energization time to a combustible gas sensor to delay the progress of deterioration thereof while more reliably determining gas leakage.SOLUTION: A fuel cell system includes a control section, a combustible gas sensor, an energization switching section, and a determination section. The control section controls a raw fuel gas supply section such that a raw fuel gas is supplied at a target gas flow rate based on a required power output, and also upwardly corrects the target gas flow rate, as a protection control, based on the status of a fuel cell. The determination section controls, until the protection control is performed, the energization switching section such that energization to the combustible gas sensor is turned off, and, when the protection control is performed, the determination section controls the energization switching section such that energization to the combustible gas sensor is turned on and also determines whether a combustible gas leakage occurs based on the detection signal of the combustible gas sensor.SELECTED DRAWING: Figure 5

Description

The present invention relates to fuel cell systems.

Conventionally, a fuel cell system of this type has been proposed that includes a combustible gas sensor for detecting leaks of combustible gas and a relay for turning on and off the power supply to the combustible gas sensor so that the power supply to the combustible gas sensor is intermittently applied. (See Patent Document 1, for example). In this system, while the fuel cell is generating power, power supply to the combustible gas sensor is stopped. It is determined whether gas leakage occurs between the gas supply valve and the flow sensor. Also, during system start-up, ignition and misfire abnormalities are detected based on the temperature of the combustion section between the flow rate sensor and the raw fuel gas pump in the raw fuel gas supply pipe and between the raw fuel gas pump and the fuel cell stack. During power generation, a drop in stack voltage is determined based on the power output detected by the voltage sensor, and the temperature of the combustion catalyst detected by the temperature sensor is determined. The possibility of gas leakage is detected by determining the high temperature abnormality of the combustion catalyst. Since the combustible gas sensor is likely to deteriorate when it reaches a high temperature due to energization, the deterioration of the combustible gas sensor can be delayed by reducing the energization time of the combustible gas sensor.

JP 2018-147620 A

In the fuel cell system described above, if protective control is executed to prevent the system from becoming abnormal, even if combustible gas leaks, the protective control will work and the system will continue without any abnormalities being detected. There is a risk of continued operation.

In the fuel cell system of the present invention, even when protective control is executed to prevent the system from becoming abnormal, gas leakage can be determined more reliably, and the energization time of the combustible gas sensor can be shortened to prevent its deterioration. The main purpose is to slow progression.

The fuel cell system of the present invention employs the following means in order to achieve the above-described main object.

A first fuel cell system of the present invention comprises:
a fuel cell that generates electricity based on an anode gas and a cathode gas;
a reformer that reforms the raw fuel gas into the anode gas;
a combustion unit for burning off-gas from the fuel cell;
a raw fuel gas supply unit that supplies the raw fuel gas to the reforming unit;
The raw fuel gas supply unit is controlled so that the raw fuel gas is supplied at a target gas flow rate based on the required power generation output required for the fuel cell system, and the target is controlled as protection control based on the state of the fuel cell. a control unit that increases and corrects the gas flow rate;
a combustible gas sensor for detecting leakage of combustible gas;
an energization switching unit that turns on and off energization of the combustible gas sensor;
Until the protection control is executed, the energization switching unit is controlled so that the energization to the combustible gas sensor is turned off, and when the protection control is executed, the energization to the combustible gas sensor is turned on. a determination unit that controls the energization switching unit and determines whether or not the combustible gas is leaking based on the detection signal of the combustible gas sensor;
The gist is to provide

In the first fuel cell system of the present invention, protection control is executed to increase the target gas flow rate based on the state of the fuel cell. In this system, the power to the combustible gas sensor is turned off until the protection control is executed. is occurring. Normally, power to the combustible gas sensor is turned off, and by turning on the power to the combustible gas sensor when the protective control that is triggered by the occurrence of a gas leak is executed, the gas leak can be determined more reliably using the combustible gas sensor. It is also possible to shorten the energization time of the combustible gas sensor while delaying the progress of its deterioration.

In the first fuel cell system of the present invention, a battery temperature detection unit that detects a cell correlated temperature that correlates with the temperature of the fuel cell is provided, and the control unit performs the protection control so that the cell correlated temperature reaches a predetermined temperature. The target gas flow rate may be corrected to increase based on the following. In a fuel cell whose power generation reaction is an exothermic reaction, when the fuel supplied to the fuel cell runs short due to gas leakage, the temperature of the fuel cell drops, and as a result, protective control is activated to increase the amount of raw fuel gas. Therefore, by turning on the energization of the combustible gas sensor by executing the protection control, it is possible to more reliably determine the gas leakage while reducing the energization time of the combustible gas sensor.

Further, in the first fuel cell system of the present invention, a misfire detection section for detecting a misfire in the combustion section is provided, and the control section performs the protection control based on detection of a misfire by the misfire detection section. The target gas flow rate may be corrected by increasing the amount of the target gas flow rate. If the fuel supplied to the fuel cell becomes insufficient due to gas leakage, the off-gas supplied to the combustion section also becomes insufficient, which may lead to misfire, and protective control is activated to increase the amount of raw fuel gas. Therefore, by turning on the energization of the combustible gas sensor by executing the protection control, it is possible to more reliably determine the gas leakage while reducing the energization time of the combustible gas sensor. In this case, the misfire detection section may detect a temperature drop of the combustion section or a temperature rise of a combustion catalyst installed in a path of combustion exhaust gas discharged from the combustion section.

A second fuel cell system of the present invention comprises:
a fuel cell that generates electricity based on an anode gas and a cathode gas;
a reformer that reforms the raw fuel gas into the anode gas;
a combustion unit for burning off-gas from the fuel cell;
a raw fuel gas supply unit that supplies the raw fuel gas to the reforming unit;
The sweep current of the fuel cell is controlled so that the power generation output of the fuel cell becomes the required power generation output required by the fuel cell system, and the output voltage is reduced as protective control when the output voltage of the fuel cell drops. a control unit that limits the sweep current so that it does not fall below a predetermined voltage;
a combustible gas sensor for detecting leakage of combustible gas;
an energization switching unit that turns on and off energization of the combustible gas sensor;
Until the protection control is executed, the energization switching unit is controlled so that the energization to the combustible gas sensor is turned off, and when the protection control is executed, the energization to the combustible gas sensor is turned on. a determination unit that controls the energization switching unit and determines whether or not the combustible gas is leaking based on the detection signal of the combustible gas sensor;
The gist is to provide

The second fuel cell system of the present invention controls the sweep current of the fuel cell so that the power output of the fuel cell becomes the required power output required of the fuel cell system, and when the output voltage of the fuel cell drops, Secondly, as protection control, the sweep current is limited so that the output voltage does not fall below a predetermined voltage. In this system, the power to the combustible gas sensor is turned off until the protection control is executed. is occurring. When the fuel supplied to the fuel cell runs short due to gas leakage, the output voltage drops, so protective control is activated to limit the sweep current so that the voltage does not fall below a predetermined voltage. Therefore, by turning on the power supply to the combustible gas sensor with the execution of the protection control that is triggered by the occurrence of gas leakage, the combustible gas sensor can be used to determine the gas leak more reliably, while the power supply time to the combustible gas sensor is reduced. can be shortened to delay the progress of its deterioration.

Further, in the first or second fuel cell system of the present invention, the determination unit determines that the combustible gas is not leaking, and determines whether the execution of the protection control is canceled or the combustible gas sensor When a predetermined time elapses after turning on the energization of the combustible gas sensor, the energization of the combustible gas sensor may be turned off. In this way, it is possible to minimize the energizing time of the combustible gas sensor while determining gas leakage more reliably.

1 is a schematic configuration diagram of a fuel cell system according to an embodiment; FIG. 1 is a schematic configuration diagram of a power supply system including a power supply substrate; FIG. 4 is a flow chart showing an example of a power generation control routine; 4 is a flowchart showing an example of gas leak determination processing; It is a state transition diagram of a combustible gas sensor.

A mode for carrying out the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a fuel cell system 10 of this embodiment, and FIG. 2 is a schematic configuration diagram of a power supply system including a power supply substrate 91. As shown in FIG. As shown in FIG. 1, the fuel cell system 10 of this embodiment includes a power generation module 20 including a fuel cell stack 21 that generates power through an electrochemical reaction between hydrogen in the anode gas and oxygen in the cathode gas; A raw fuel gas supply device 30 that supplies a raw fuel gas (for example, natural gas or LP gas) as a raw material of anode gas to the power generation module 20 via a supply pipe 31, and a raw fuel gas to the anode gas to the power generation module 20. A reformed water supply device 40 that supplies reformed water necessary for reforming (steam reforming), an air supply device 50 that supplies air as a cathode gas to the power generation module 20 (fuel cell stack 21), and a power generation module. An exhaust heat recovery device 60 for recovering the exhaust heat generated in the fuel cell stack 20, and a reflux device for refluxing part of the unused fuel that has not been used for the electrochemical reaction (power generation) in the fuel cell stack 21 to the raw fuel gas supply pipe 31. 80, a combustible gas sensor 116 for detecting gas leakage of combustible gas, and a controller 100 for controlling the entire system.

The power generation module 20 includes a fuel cell stack 21, a vaporizer 22, a reformer 23, a combustor 24, and two heat exchangers 26 and 27, which are housed in a heat insulating module case 29. .

The fuel cell stack 21 has an electrolyte such as zirconium oxide and an anode electrode and a cathode electrode sandwiching the electrolyte, and includes a plurality of solid oxide single cells arranged in the left-right direction (horizontal direction). An anode gas passage (not shown) is formed in the anode electrode of each single cell. A cathode gas passage (not shown) is formed in the cathode electrode of each single cell. Furthermore, a temperature sensor 112 is installed near the fuel cell stack 21 . The temperature sensor 112 detects a temperature correlated with the temperature of the fuel cell stack 21 (stack correlated temperature Tst).

The vaporizer 22 and the reformer 23 of the power generation module 20 are arranged above the fuel cell stack 21 in the module case 29 with a space therebetween. Between the fuel cell stack 21 and the vaporizer 22 and the reformer 23 is a combustor 24 that generates heat necessary for the operation of the fuel cell stack 21 and the reaction in the vaporizer 22 and the reformer 23. is arranged. An ignition heater 25 is installed in the combustor 24 .

The vaporizer 22 heats the raw fuel gas from the raw fuel gas supply device 30 and the reformed water from the reformed water supply device 40 with the heat from the combustor 24, preheats the raw fuel gas, and heats the reformed water. evaporate to form water vapor. The raw fuel gas preheated by the vaporizer 22 is mixed with steam, and the mixed gas flows from the vaporizer 22 into the reformer 23 . A temperature sensor 111 is installed near the inlet of the reformer 23 to detect the temperature of the mixed gas flowing into the reformer 23 (vaporizer temperature).

The reformer 23 has, for example, a Ru-based or Ni-based reforming catalyst filled therein, and in the presence of heat from the combustor 24, the mixed gas from the vaporizer 22 reacts with the reforming catalyst. A (steam reforming reaction) produces hydrogen gas and carbon monoxide. Furthermore, the reformer 23 produces hydrogen gas and carbon dioxide through a reaction (carbon monoxide shift reaction) between carbon monoxide produced in the steam reforming reaction and steam. As a result, the reformer 23 generates anode gas containing hydrogen, carbon monoxide, carbon dioxide, water vapor, unreformed raw fuel gas, and the like. The anode gas generated by the reformer 23 flows through the anode gas pipe 71 into the anode gas passage of each single cell and is supplied to the anode electrode.

Air as the cathode gas flows into the cathode gas passage of each unit cell through the cathode gas pipe 72 and is supplied to the cathode electrode. Oxide ions (O ₂ ⁻ ) are generated at the cathode electrode of each single cell, and the oxide ions permeate the electrolyte and react with hydrogen and carbon monoxide at the anode electrode to obtain electrical energy.

The anode gas not used for the electrochemical reaction (power generation) in each single cell (hereinafter referred to as "anode off-gas") is supplied to the condenser 62 through the anode off-gas pipe 73 and cooled by the condenser 62. After water vapor contained in the anode offgas is removed, the anode offgas is supplied to the combustor 24 through the anode offgas pipe 74 . A heat exchanger 26 is installed in the anode offgas pipes 73 and 74 , and the anode offgas (the anode offgas after passing through the condenser 62 ) flowing through the anode offgas pipe 74 is transferred from the fuel cell stack 21 to the anode offgas in the heat exchanger 26 . The temperature is raised by heat exchange with the high-temperature anode off-gas flowing through the pipe 73 (the anode off-gas before passing through the condenser 62). Also, the cathode gas not used for the electrochemical reaction (power generation) in each unit cell (hereinafter referred to as “cathode off-gas”) is supplied to the combustor 24 through the cathode off-gas pipe 75 .

The anode off-gas that has flowed into the combustor 24 is combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the oxygen-containing cathode off-gas that has flowed into the combustor 24 . Then, when the mixture gas (hereinafter referred to as "off gas") is ignited in the combustor 24 by being ignited by the ignition heater 25, the combustion of the off gas causes the operation of the fuel cell stack 21 and the raw fuel gas in the vaporizer 22. Heat necessary for preheating of the gas, generation of steam, steam reforming reaction in the reformer 23, and the like is generated. Further, in the combustor 24, combustion exhaust gas containing unburned fuel is generated, and the combustion exhaust gas passes through the combustion exhaust gas pipe 76, the heat exchanger 27 and the combustion catalyst 28, and is discharged to the outside air. The combustion catalyst 28 is an oxidation catalyst for reburning unburned fuel in the combustion exhaust gas. The combustion catalyst 28 is provided with a temperature sensor 113 for detecting its temperature (catalyst temperature Tca).

The raw fuel gas supply device 30 includes a raw fuel gas supply pipe 31 that connects a raw fuel gas supply source 1 that supplies the raw fuel gas and a vaporizer 22, and an on-off valve (2) installed in the raw fuel gas supply pipe 31. connected valves) 32, 33, an orifice 34, a zero governor (pressure equalizing valve) 35, a gas pump 36 and a desulfurizer 38. The raw fuel gas is pumped (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 38 by operating the gas pump 36 . Between the orifice 34 of the raw fuel gas supply pipe 31 and the zero governor 35, a flow rate sensor 39 for detecting the flow rate (gas flow rate Qg) of the raw fuel gas flowing through the raw fuel gas supply pipe 31 per unit time is installed. It is

The reforming water supply device 40 is installed in a reforming water tank 42 that stores reforming water, a reforming water supply pipe 41 that connects the reforming water tank 42 and the vaporizer 22 , and the reforming water supply pipe 41 . and a modified water pump 43 . The reformed water in the reformed water tank 42 is pumped (supplied) to the vaporizer 22 by the reformed water pump 43 by operating the reformed water pump 43 .

The air supply device 50 includes an air supply pipe 51 connected to the cathode gas pipe 72 installed in the module case 29 , an air filter 52 provided at the inlet of the air supply pipe 51 , and an air filter 52 installed in the air supply pipe 51 . and an air pump 53 . By operating the air pump 53, air as the cathode gas is sucked into the air supply pipe 51 through the air filter 52 and pressure-fed (supplied) through the cathode gas pipe 72 to the fuel cell stack 21 (cathode electrode). be done. The air flowing through the cathode gas pipe 72 is heat-exchanged with the high-temperature flue gas flowing through the flue gas pipe 76 in the heat exchanger 27 to raise the temperature thereof.

The exhaust heat recovery device 60 includes a hot water storage tank 61 that stores hot water, and a condenser 62 that exchanges heat between the hot water and the anode off-gas flowing through the anode off-gas pipe 73 from the fuel cell stack 21 to condense water vapor contained in the anode off-gas. , a circulation pipe 63 connected to the hot water storage tank 61 and the condenser 62 , and a circulation pump 64 incorporated in the circulation pipe 63 . The hot water stored in the hot water storage tank 61 is introduced into the condenser 62 by operating the circulation pump 64, and heated by the condenser 62 by heat exchange with the anode off-gas. sent back to.

Further, a condensed water pipe 44 and an anode offgas pipe 74 are connected to a passage outlet on the anode offgas side of the condenser 62 , and water vapor in the anode offgas is condensed by heat exchange with hot water from the hot water storage tank 61 . The condensed water thus obtained is introduced into the reforming water tank 42 through the condensed water pipe 44 . The reformed water tank 42 is provided with a water purifier (not shown) for purifying the condensed water that has passed through the condensed water pipe 44 . Further, as described above, the anode off-gas from which water vapor has been removed in the condenser 62 is supplied to the combustor 24 through the anode off-gas pipe 74 .

Furthermore, the exhaust heat recovery device 60 includes a radiator 65 incorporated in the circulation pipe 63 , a radiator fan (electric fan) 66 that sends air to the radiator 65 , and the electric power generated by the power generation module 20 to consume the power generated in the circulation pipe 63 . and an electric heater 67 for heating hot water. The radiator 65 is installed so as to be positioned between the circulation pump 64 of the circulation pipe 63 and the condenser 62 . The electric heater 67 is installed so as to be positioned between the radiator 65 of the circulation pipe 63 and the circulation pump 64 .

The reflux device 80 includes a reflux pipe 81 branched from the anode offgas pipe 74 and connected between the zero governor 35 and the gas pump 36 in the raw fuel gas supply pipe 31; and an orifice 83 formed in the pipe 81 . The solenoid valve 82 is a normally closed on-off valve, and the anode offgas recirculation line from the anode offgas pipe 74 to the raw fuel gas supply pipe 31 is cut off when the solenoid valve 82 is closed. It is released by opening the valve.

The output terminal of the fuel cell stack 21 is connected to the input terminal of a power conditioner 90, and the output terminal of the power conditioner 90 is connected to the power line 3 from the power system 2 to the load 4 via a relay. there is A current sensor 114 for detecting a current (output current I) output from the fuel cell stack 21 is installed at the output terminal of the fuel cell stack 21 . A voltage sensor 115 for detecting the voltage (output voltage V) output from the fuel cell stack 21 is installed between the output terminals of the fuel cell stack 21 .

The power conditioner 90 is a DC/DC converter that converts the DC power output from the fuel cell stack 21 into DC power of a predetermined voltage (for example, DC 250 V to 300 V), and the converted DC power can be interconnected with the power system. It has an inverter that converts it into AC power with a reasonable voltage (for example, AC 200V). As a result, the DC power from the fuel cell stack 21 can be converted into AC power and supplied to the load 4 such as a home appliance.

A power substrate 91 is connected to the power conditioner 90 . The power supply board 91 converts the DC power from the fuel cell stack 21 and the AC power from the power system 2 into low-voltage DC power, and supplies auxiliary equipment such as the gas pump 36, the reformed water pump 43, the air pump 53, and the circulation pump 64. Sensors such as the flow rate sensor 39 , the temperature sensors 111 , 112 , 113 , the current sensor 114 and the voltage sensor 115 are supplied to the controller 100 . Also, as shown in FIG. 2, the power supply board 91 is connected to the combustible gas sensor 116 via a relay 92, and by turning on and off the relay 92, the power supply board 91 can be operated independently of other auxiliary equipment. The combustible gas sensor 116 can be supplied with DC power and the supply can be stopped. In addition, a cooling fan and a ventilation fan (not shown) for cooling the power conditioner 90 and the power supply board 91 are arranged in the auxiliary machine room where the power conditioner 90 and the power supply board 91 are arranged. The cooling fan sends air to the heat generating portions of the power conditioner 90 and the power supply board 91 . The air heated by cooling the heat-generating part is discharged into the atmosphere by a ventilation fan.

The combustible gas sensor 116 is configured as a catalytic combustion gas sensor in this embodiment. Here, the catalytic combustion gas sensor consists of a detection element in which an oxidation catalyst (combustion catalyst) such as a platinum catalyst (combustion catalyst) supported on a carrier such as alumina is fixed on a platinum wire coil, and a compensating element that does not have an oxidation catalyst. It constitutes a bridge circuit. The catalytic combustion gas sensor is used with current applied to the bridge circuit, and the sensing element is heated by the current application and held at a temperature (for example, 200 to 500° C.) at which the catalytic reaction is likely to occur. When the sensing element comes into contact with combustible gas, it generates heat due to a catalytic combustion reaction and changes its resistance value. Since there is a proportional relationship between the imbalance voltage and the gas concentration, the gas concentration can be detected by measuring the imbalance voltage. For example, by setting a sensor output (imbalance voltage) corresponding to a gas concentration near the lower explosion limit concentration as a threshold, it is possible to determine that a gas leak has occurred when the sensor output is equal to or higher than the threshold. It is known that the catalyst of such a catalytic combustion type gas sensor is poisoned by organic silicon compounds, etc., and the catalyst is thermally deteriorated when used above the heat-resistant temperature. , which is likely to cause performance degradation.

The control device 100 is configured as a microprocessor centered around a CPU 101, and in addition to the CPU 101, includes a ROM 102 for storing processing programs, a RAM 103 for temporarily storing data, and an input/output port (not shown). Various detection signals from the flow rate sensor 39, the temperature sensors 111, 112, 113, the current sensor 114, the voltage sensor 115, the combustible gas sensor 116, etc. are input to the control device 100 via input ports. Also, from the control device 100, the solenoids of the on-off valves 32 and 33, the pump motor of the gas pump 36, the pump motor of the reforming water pump 43, the pump motor of the air pump 53, the pump motor of the circulation pump 64, the ignition heater 25, the electromagnetic Various control signals to the solenoid of the valve 82 and the like are output through the output port. A remote controller (not shown) is connected to the control device 100 via a wireless or wired communication line. The control device 100 executes various controls based on signals from the remote controller operated by the user of the fuel cell system 10 .

Next, the operation of the fuel cell system 10 configured in this way will be described. FIG. 3 is a flow chart showing an example of a power generation control routine executed by the CPU 101 of the control device 100. As shown in FIG. This routine is repeatedly executed at predetermined time intervals (for example, every several milliseconds or several tens of milliseconds) when the system is started.

When the power generation control routine is executed, the CPU 101 of the control device 100 first determines the required output (required power) Preq required by the load 4, the output current I from the current sensor 114, the output voltage V from the voltage sensor 115, Data such as the stack correlation temperature Tst from the temperature sensor 112 and the catalyst temperature Tca from the temperature sensor 113 are input (step S100). Next, the CPU 101 determines whether or not the input output voltage V is greater than the threshold α (step S110). Here, the threshold value α is set to a voltage slightly higher than the lower limit value of the output voltage that is allowed for proper operation of the fuel cell stack 21 .

When the CPU 101 determines that the output voltage V is greater than the threshold value α, the CPU 101 calculates the output power P based on the input output current I and the output voltage V (step S120). Based on Preq, the required current Ireq to be output from the fuel cell stack 21 is set so that the output power P approaches the required output Preq (step S130). Subsequently, the CPU 101 sets the smaller one of the requested current Ireq and the input output current I plus a predetermined amount ΔI as the target output current Itag (step S140). Here, the predetermined amount ΔI is an allowable increase in the output current I per unit time, and is set so that the rate of decrease in the output voltage V accompanying the increase in the output current I does not exceed a predetermined specification upper limit. It is defined. Then, the CPU 101 sets the target gas flow rate Qgtag, which is the target flow rate of the raw fuel gas supplied by the raw fuel gas supply device 30, based on the set target output current Itag (step S150), and sets the first protection control flag F1. A value of 0 is set to indicate that the first protection control is not being executed (step S160).

On the other hand, when the CPU 101 determines that the output voltage V is equal to or lower than the threshold value α, the power conditioner 90 (DC/DC converter) is controlled so that the output voltage V is maintained at the threshold value α (near the voltage lower limit value). The sweep current of the fuel cell stack 21 (current taken out from the fuel cell stack 21) is adjusted (step S170), and the raw fuel gas is supplied from the raw fuel gas supply device 30 according to the magnitude of the sweep current. A gas flow rate Qtag is set (step S175). The adjustment of the sweep current is performed as first protection control for protecting the fuel cell stack 21. In this embodiment, the sweep current is feedback-controlled based on the deviation between the output voltage V and the threshold value α. can do. As a result, the output current I decreases, and the output voltage V is maintained at the threshold value α (near the voltage lower limit value). Then, the CPU 101 sets the value 1 indicating that the first protection control is being executed to the first protection control flag F1 (step S180).

After setting the target output current Itag, the CPU 101 sets the target gas flow rate Qgtag, which is the target flow rate of the raw fuel gas supplied by the raw fuel gas supply device 30, based on the target output current Itag set in step S140 or S160 ( step S180).

Next, CPU 101 determines whether or not stack correlation temperature Tst input in step S100 is greater than threshold value β (step S190). Here, the threshold β is set to a temperature slightly higher than the lower limit temperature in the proper operating temperature range of the fuel cell stack 21 . When the CPU 101 determines that the stack correlation temperature Tst is higher than the threshold value β, the CPU 101 determines that the fuel cell stack 21 is within the proper temperature range, and indicates in the second protection control flag F2 that the second protection control is not being executed. A value of 0 is set (step S200).

On the other hand, when the CPU 101 determines that the stack correlation temperature Tst is equal to or lower than the threshold β, it determines that the fuel cell stack 21 is near the lower limit temperature within the appropriate temperature range, and raises the fuel cell stack 21 as second protection control. In order to increase the temperature, an increase correction is performed to increase the target gas flow rate Qgtag (step S210). The increase correction can be performed, for example, by adding a larger flow rate as the stack correlation temperature Tst is lower to the target gas flow rate Qgtag set in step S180. Then, the CPU 101 sets the value 1 indicating that the second protection control is being executed to the second protection control flag F2 (step S220).

Next, the CPU 101 determines whether or not the catalyst temperature Tca input in step S100 is less than the threshold value γ (step S230). Here, the threshold γ is a threshold for determining misfire (partial misfire) of the combustor 24 . The greater the amount of unburned fuel contained in the combustion exhaust gas that has passed through the combustor 24, the higher the catalyst temperature Tca due to combustion of the unburned fuel. Therefore, by estimating the amount of unburned fuel left unburned in the combustor 24 based on the catalyst temperature Tca, it is possible to determine the combustion state in the combustor 24, that is, misfire (partial misfire). When the CPU 101 determines that the catalyst temperature Tca is less than the threshold value γ, it determines that a misfire (partial misfire) has not occurred in the combustor 24, and sets the third protection control flag F3 to indicate that the third protection control is not being executed. 0 is set (step S240).

On the other hand, when the CPU 101 determines that the catalyst temperature Tca is equal to or higher than the threshold value γ, it determines that a misfire (partial misfire) has occurred in the combustor 24, and performs third protection control to return to a normal combustion state. , increase correction is performed to increase the target gas flow rate Qgtag (step S250). The increase correction is performed by adding an addition amount that differs depending on the misfire pattern to the target gas flow rate Qgtag. For example, for a single misfire, a fixed flow rate is added to the target gas flow rate Qgtag, and for continuous misfires, the addition amount of the target gas flow rate Qgtag is further increased. Then, the CPU 101 sets the third protective control flag F3 to a value of 1 indicating that the third protective control is being executed (step S260).

Next, the CPU 101 adjusts the steam carbon ratio SC (molar ratio between carbon contained in hydrocarbons in the raw fuel gas and steam added for steam reforming) in the reformer 23 to the target ratio SCtag. Then, the target reforming water flow rate Qwtag, which is the target flow rate of the reforming water supplied by the reforming water supply device 40, is set based on the target gas flow rate Qgtag (step S270). Furthermore, the CPU 101 sets the target air flow rate Qatag, which is the target flow rate of the air supplied by the air supply device 50, so that the air utilization rate Ua becomes the target utilization rate Uatag (step S280).

After setting the target gas flow rate Qgtag, the target reforming water flow rate Qwtag, and the target air flow rate Qtag, the CPU 101 controls the gas pump 36 so that the raw fuel gas is supplied at the target gas flow rate Qgtag (step S290). The reforming water pump 43 is controlled to supply reforming water at the target reforming water flow rate Qwtag (step S300), and the air pump 53 is controlled to supply air at the target air flow rate Qtag (step S310 ), ending the power generation control routine. In this embodiment, a flow rate sensor 39 is installed in the raw fuel gas supply pipe 31 . Therefore, the gas pump 36 is controlled by setting the duty of the gas pump 36 (gas pump duty) by feedback calculation (for example, proportional integral calculation) based on the deviation between the target gas flow rate Qgtag and the gas flow rate Qg from the flow rate sensor 39. This is done by driving and controlling the pump motor of the gas pump 36 with the gas pump duty set. Further, the reforming water pump 43 is controlled by setting the duty of the reforming water pump 43 (reforming water pump duty) based on the target reforming water flow rate Qwtag. This is done by driving and controlling the pump motor of 43. The control of the air pump 53 is performed by setting the duty of the air pump 53 (air pump duty) to the target air flow rate Qatag, and driving and controlling the pump motor of the air pump 53 with the set air pump duty.

Here, the above-described first protection control, second protection control, and third protection control may work due to other factors, but in the route from the flow rate sensor 39 in the raw fuel gas supply pipe 31 to the fuel cell stack 21 It also works in the event of a gas leak. That is, when a gas leak occurs, the fuel (anode gas) required for power generation in the fuel cell stack 21 runs short, so the output voltage V drops. Then, when the output voltage V reaches the threshold value α (near the voltage lower limit value), the first protection control works, and the sweep current of the fuel cell stack 21 is adjusted (reduced) so that the output voltage V is maintained at the threshold value α. be. Further, since the power generation reaction of the fuel cell stack 21 is an exothermic reaction, the temperature of the fuel cell stack 21 (stack correlation temperature Tst) decreases when the fuel required for power generation is insufficient. Then, when the stack correlation temperature Tst drops to the threshold value β, the second protection control works and the target gas flow rate Qgtag is increased. Furthermore, since the off-gas supplied to the combustor 24 is also insufficient, a misfire (partial misfire) may occur in the combustor 24 . In this case, since the amount of unburned fuel that burns in the combustion catalyst 28 increases, the catalyst temperature Tca rises. Then, when the catalyst temperature Tca rises to the threshold value γ, the third protection control works and the target gas flow rate Qgtag is increased. Therefore, execution of any one of the first protection control, the second protection control, and the third protection control allows recognition of the possibility that gas leakage has occurred.

Next, the operation of detecting leakage of combustible gas using combustible gas sensor 116 will be described. FIG. 4 is a flowchart showing an example of gas leak determination processing executed by the CPU 101 of the control device 100. As shown in FIG. This process is repeatedly executed at predetermined time intervals (for example, every several milliseconds or several tens of milliseconds).

In the gas leak determination process, the CPU 101 first determines whether any one of the first protection control flag F1, the second protection control flag F2, and the third protection control flag F3 is 1 (step S400). Determination of whether the first protection control flag F1 is value 1 is determination of whether the first protection control is being executed, and determination of whether the second protection control flag F2 is value 1. determines whether or not the second protection control is being executed. Determination whether or not the third protection control flag F3 is 1 is determination of whether or not the third protection control is being executed. becomes. When the CPU 101 determines that any one of the first protection control flag F1, the second protection control flag F2, and the third protection control flag F3 is 1, it determines that there is a possibility that gas leakage has occurred. It is determined whether or not the executed flag F is 0 (step S410). Here, the execution completion flag F determines whether or not the gas leak determination described later has been executed. show.

When the CPU 101 determines that the execution completion flag F is 0 and the gas leakage determination has not been executed, it determines whether the combustible gas sensor 116 is in the off state (step S420). When the CPU 101 determines that the power is off, it turns on the power to the combustible gas sensor 116 by turning on the relay 92 (step S430), and proceeds to step S440. On the other hand, when the CPU 101 determines that the power supply is on, the CPU 101 skips step S430 and proceeds to step S440.

Next, the CPU 101 inputs a detection signal from the combustible gas sensor 116 (step S440), and determines whether gas leakage occurs based on the input detection signal (step S450). When the CPU 101 determines that gas leakage has occurred, the CPU 101 immediately stops the fuel cell system 10 to ensure safety (step S460), and terminates the gas leakage determination process.

On the other hand, when CPU 101 determines that gas leakage has not occurred, CPU 101 determines whether or not a predetermined determination time has elapsed since power supply to combustible gas sensor 116 was turned on (step S470). Here, the determination time is the time required for gas leakage determination, and is set to several seconds or tens of seconds, for example. When the CPU 101 determines that the predetermined determination time has not elapsed, the CPU 101 temporarily terminates the gas leak determination process. On the other hand, when the CPU 101 determines that the predetermined determination time has elapsed, it turns off the power to the combustible gas sensor 116 by turning off the relay 92 (step S480), and sets the executed flag F to a value of 1 (step S490). , the gas leakage determination process ends. Since the gas leakage determination process is repeatedly executed at predetermined time intervals, if any one of the first protection control, the second protection control, and the third protection control is being executed, the CPU 101 determines in step S450 that gas leakage has occurred. The combustible gas sensor 116 continues to be energized and the gas leakage determination using the combustible gas sensor 116 is continued until it is determined in step S470 that the predetermined determination time has elapsed. Then, when the determination time has passed and the gas leakage determination is completed, the value 1 is set in the execution completion flag F, so even if any protection control is being executed, a negative determination is made in step S410. , the gas leakage determination is not executed until the executed flag is reset to the value 0.

In step S400, the CPU 101 determines that all of the first protection control flag F1, the second protection control flag F2, and the third protection control flag F3 are 0, that is, the first protection control, the second protection control, and the third protection control. When it is determined that none of the controls are being executed, it is determined whether or not the combustible gas sensor 116 is in the energized ON state (step S500). When the CPU 101 determines that the combustible gas sensor 116 is in the energized ON state, it turns off the energization of the combustible gas sensor 116 by turning off the relay 92 (step S480), and sets the executed flag F to the value 1 (step S490), the gas leakage determination process is terminated. That is, when the protection control (first protection control, second protection control, or third protection control) being executed ends during the execution of the gas leakage determination, the CPU 101 determines that the predetermined determination time has elapsed, that is, the gas leakage determination is performed. Without waiting for the determination of the result, the gas leakage determination is terminated and the power supply to the combustible gas sensor 116 is turned off. This makes it possible to avoid wasteful energization of the combustible gas sensor 116 and reduce the energization time of the combustible gas sensor 116 .

On the other hand, when the CPU 101 determines that the combustible gas sensor 116 is in the de-energized state, the CPU 101 sets the executed flag F to 0 (step S510), and terminates the gas leakage determination process. Accordingly, when any one of the first protection control, the second protection control and the third protection control is executed, the combustible gas sensor 116 is energized and the gas leakage determination is executed.

FIG. 5 is a state transition diagram of the combustible gas sensor 116. As shown in FIG. As illustrated, the combustible gas sensor 116 is energized when protection control (either of the first protection control, the second protection control, and the third protection control) is executed, and after the energization is turned on, a predetermined When the judgment time has elapsed or the protection control being executed is completed, the power supply is turned off. As noted above, protective controls are activated due to the occurrence of a gas leak. For this reason, the power supply to the combustible gas sensor 116 is normally turned off, and when the protection control is executed, the power supply to the combustible gas sensor 116 is turned on to perform the gas leak determination, thereby shortening the power supply time to the combustible gas sensor 116. It is possible to quickly detect gas leaks while slowing down the progress of deterioration by using the system, thereby ensuring safety.

In this embodiment, the control of the gas pump 36 is performed by setting the gas pump duty by feedback control based on the deviation between the target gas flow rate Qgtag and the gas flow rate Qg detected by the flow rate sensor 39 . In this case, if a gas leak occurs in the path upstream of the flow rate sensor 39 in the raw fuel gas supply pipe 13, the gas flow rate Qg will decrease from the normal state, so the gas pump duty will rise due to the action of feedback control. Therefore, by monitoring the gas pump duty and energizing the combustible gas sensor 116 as the gas pump duty rises to determine gas leakage, gas leakage upstream of the flow sensor 39 can be detected.

In the fuel cell system 10 of the present embodiment described above, until the protective control (first protective control, second protective control, and third protective control) that works due to gas leakage is executed, the combustible gas sensor 116 is When the energization is turned off and the protection control is executed, the energization to the combustible gas sensor 116 is turned on, and gas leakage determination is performed based on the detection signal of the combustible gas sensor 116 . As a result, it is possible to use the combustible gas sensor 116 to more reliably determine gas leakage, and to shorten the energization time of the combustible gas sensor 116 to delay the progress of its deterioration.

In the embodiment described above, the CPU 101 determines the presence or absence of misfire (partial misfire) based on the catalyst temperature Tca from the temperature sensor 113 installed in the combustion catalyst 28 . However, a temperature sensor may be installed in the combustor 24, and the CPU 101 may determine the presence or absence of a misfire (partial misfire) based on the temperature inside the combustor 24 from the temperature sensor.

In the embodiment described above, the CPU 101 executes the first protection control, the second protection control, and the third protection control as protection controls that work due to gas leakage. However, execution of some of the protection controls may be omitted, or other protection controls may be additionally executed. Then, gas leak determination may be performed by turning on the power supply to the combustible gas sensor 116 by executing the other protection control.

The correspondence relationship between the main elements of the embodiments and the main elements of the invention described in the column of Means for Solving the Problems will be described. In the embodiment, the fuel cell stack 21 corresponds to the "fuel cell" of the present invention, the reformer 23 corresponds to the "reforming section", the combustor 24 corresponds to the "combustion section", and the raw fuel gas is supplied. The device 30 corresponds to the "raw fuel gas supply section", the CPU 101 of the control device 100 that executes the power generation control routine corresponds to the "control section", the combustible gas sensor 116 corresponds to the "combustible gas sensor", and the relay 92 corresponds to the " energization switching section", and the CPU 101 of the control device 100 that executes the gas leakage determination process corresponds to the "determination section". Also, the temperature sensor 112 corresponds to the "battery temperature detection unit". Also, the temperature sensor 113 corresponds to the "misfire detector".

Note that the correspondence relationship between the main elements of the embodiment and the main elements of the invention described in the column of Means for Solving the Problem indicates that the embodiment implements the invention described in the column of Means to Solve the Problem. Since it is an example for specifically explaining the mode for solving the problem, it does not limit the elements of the invention described in the column of the means for solving the problem. That is, the interpretation of the invention described in the column of Means to Solve the Problem should be made based on the description in that column, and the embodiment should be based on the description of the invention described in the column of Means to Solve the Problem. This is only a specific example.

As described above, the mode for carrying out the present invention has been described using the embodiment, but the present invention is not limited to such an embodiment at all, and various forms can be used without departing from the scope of the present invention. Of course, it can be implemented.

INDUSTRIAL APPLICABILITY The present invention is applicable to the manufacturing industry of fuel cell systems.

1 raw fuel supply source 2 power system 3 power line 4 load 10 fuel cell system 13 raw fuel gas supply pipe 20 power generation module 21 fuel cell stack 22 vaporizer 23 reformer 24 combustor , 25 ignition heater, 26, 27 heat exchanger, 28 combustion catalyst, 29 module case, 30 raw fuel gas supply unit, 31 raw fuel gas supply pipe, 32, 33 on-off valve, 34 orifice, 35 zero governor, 36 gas pump, 38 Desulfurizer 39 Flow rate sensor 40 Reformed water supply device 41 Reformed water supply pipe 42 Reformed water tank 43 Reformed water pump 44 Condensed water pipe 50 Air supply device 51 Air supply pipe 52 Air Filter, 53 Air pump, 60 Exhaust heat recovery device, 61 Hot water storage tank, 62 Condenser, 63 Circulation pipe, 64 Circulation pump, 65 Radiator, 67 Electric heater, 71 Anode gas pipe, 72 Cathode gas pipe, 73, 74 Anode off gas pipe , 75 cathode offgas pipe, 76 combustion exhaust gas pipe, 80 reflux device, 81 reflux pipe, 82 solenoid valve, 83 orifice, 90 power conditioner, 91 power supply board, 92 relay, 100 control device, 101 CPU, 102 ROM, 103 RAM , 111, 112, 113 temperature sensor, 114 current sensor, 115 voltage sensor, 116 combustible gas sensor.

Claims (6)

a fuel cell that generates electricity based on an anode gas and a cathode gas;
a reformer that reforms the raw fuel gas into the anode gas;
a combustion unit for burning off-gas from the fuel cell;
a raw fuel gas supply unit that supplies the raw fuel gas to the reforming unit;
The raw fuel gas supply unit is controlled so that the raw fuel gas is supplied at a target gas flow rate based on the required power generation output required for the fuel cell system, and the target is controlled as protection control based on the state of the fuel cell. a control unit that increases and corrects the gas flow rate;
a combustible gas sensor for detecting leakage of combustible gas;
an energization switching unit that turns on and off energization of the combustible gas sensor;
Until the protection control is executed, the energization switching unit is controlled so that the energization to the combustible gas sensor is turned off, and when the protection control is executed, the energization to the combustible gas sensor is turned on. a determination unit that controls the energization switching unit and determines whether or not the combustible gas is leaking based on the detection signal of the combustible gas sensor;
a fuel cell system. A fuel cell system according to claim 1,
A battery temperature detection unit that detects a battery correlation temperature that correlates with the temperature of the fuel cell,
As the protection control, the control unit increases and corrects the target gas flow rate based on the battery correlation temperature becoming equal to or lower than a predetermined temperature.
fuel cell system. 3. The fuel cell system according to claim 1 or 2,
A misfire detection unit that detects a misfire in the combustion unit,
As the protective control, the control unit increases and corrects the target gas flow rate based on detection of a misfire by the misfire detection unit.
fuel cell system. The fuel cell system according to claim 3,
The misfire detection unit detects a decrease in temperature of the combustion unit or an increase in temperature of a combustion catalyst installed in a path of combustion exhaust gas discharged from the combustion unit.
fuel cell system. a fuel cell that generates electricity based on an anode gas and a cathode gas;
a reformer that reforms the raw fuel gas into the anode gas;
a combustion unit for burning off-gas from the fuel cell;
a raw fuel gas supply unit that supplies the raw fuel gas to the reforming unit;
controlling the sweep current from the fuel cell so that the power generation output of the fuel cell becomes the required power generation output required by the fuel cell system, and controlling the output voltage as protective control when the output voltage of the fuel cell drops a control unit that limits the sweep current so that does not fall below a predetermined voltage;
a combustible gas sensor for detecting leakage of combustible gas;
an energization switching unit that turns on and off energization of the combustible gas sensor;
Until the protection control is executed, the energization switching unit is controlled so that the energization to the combustible gas sensor is turned off, and when the protection control is executed, the energization to the combustible gas sensor is turned on. a determination unit that controls the energization switching unit and determines whether or not the combustible gas is leaking based on the detection signal of the combustible gas sensor;
a fuel cell system. The fuel cell system according to any one of claims 1 to 5,
The determination unit determines that no leakage of the combustible gas has occurred, and when a predetermined time has elapsed since execution of the protection control was canceled or power supply to the combustible gas sensor was turned on, the combustible gas sensor turn off the power to
fuel cell system.

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