JP6642197B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell control method.

  In general, a fuel cell includes a cell stack in which a plurality of single cells are stacked. In a fuel cell mounted on a vehicle as a power source, when the temperature of the cell stack (stack temperature) rises, for example, when the vehicle is traveling under a high load such as uphill traveling or high-speed traveling, the cell stack is dried. Patent Literature 1 describes a control method of a fuel cell that suppresses drying of a cell stack by adjusting a back pressure of a cathode gas of the fuel cell using a stack temperature.

JP 2015-179620 A

  However, when the drying of the cell stack is suppressed, there is a problem that the power consumption for that is increased and the efficiency of the fuel cell is deteriorated.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following embodiments.
A first aspect of the present invention is a fuel cell system,
A fuel cell,
An anode pump provided in an anode gas recirculation pipe for recirculating anode exhaust gas discharged from the fuel cell to the fuel cell,
A pressure regulating valve provided on a cathode gas exhaust pipe for discharging cathode exhaust gas from the fuel cell to adjust a cathode back pressure of the fuel cell;
An impedance sensor for measuring the impedance of the fuel cell or the rate of increase thereof,
A control device that controls the operation of the anode pump and the pressure regulating valve using the measurement value of the impedance sensor,
With
The control device includes:
Under normal operating conditions including a first anode pump rotation speed and a first cathode back pressure, the operations of the anode pump and the pressure regulating valve are controlled, and the impedance of the fuel cell measured by the impedance sensor or the rate of increase thereof is determined in advance. When the threshold value is equal to or greater than a predetermined threshold value, a second anode pump rotation speed for efficiency consideration higher than the first anode pump rotation speed, and a second cathode backpressure for efficiency consideration higher than the first cathode back pressure. A first combination with a pressure, or a second combination different from the first combination, wherein the second anode pump rotation speed for emphasis on efficiency higher than the first anode pump rotation speed; Under the wet operating condition comprising one of the second combination with the second cathode back pressure for efficiency non-emphasis higher than one cathode back pressure, Controls the operation of Doponpu and the pressure regulating valve, when emphasizing the efficiency of power consumption of the fuel cell, of the second combination and the first combination, the first consisting of a lower combination of power And selecting the second combination when the efficiency of power consumption of the fuel cell is not emphasized .
Fuel cell system.
Further, the present invention can be realized as the following modes.

(1) According to one aspect of the present invention, a method for controlling a fuel cell is provided. The fuel cell control method includes controlling the impedance or the impedance of the fuel cell during normal operation under normal operation conditions including the first anode pump speed, the first cathode pump speed, and the first cathode back pressure. Measuring the rate of increase, and when the impedance or the rate of increase is equal to or greater than a predetermined threshold, the second anode pump rotation speed higher than the first anode pump rotation speed; Performing a wet operation under wet operation conditions including a second cathode back pressure higher than the back pressure. As the wet operation condition, a combination having lower power consumption is selected from a first combination and a second combination that can be adopted as a combination of the second anode pump rotation speed and the second cathode back pressure.

  According to the fuel cell control method of this aspect, when the cell stack of the fuel cell is dry, the wet operation is performed under the wet condition of lower power consumption, thereby preventing the power consumption from excessively increasing. And drying of the cell stack can be suppressed.

  The present invention can be realized in various forms other than the above. For example, it can be realized in the form of a fuel cell system, a control method of the fuel cell system, and the like.

FIG. 1 is an explanatory diagram schematically showing a fuel cell system according to a first embodiment of the present invention. 3 is a flowchart illustrating a control method of the fuel cell according to the first embodiment. FIG. 4 is an explanatory diagram showing a relationship between the impedance of the fuel cell, the rotation speed of the anode pump, and the cathode back pressure. FIG. 3 is an explanatory diagram showing the relationship between the number of revolutions of an anode pump, cathode back pressure, and power consumption in a fuel cell. 9 is a flowchart illustrating a control method of a fuel cell according to a second embodiment.

-1st Embodiment:
FIG. 1 is an explanatory diagram schematically showing a fuel cell system 10 mounted on a vehicle. The fuel cell system 10 includes a fuel cell FC, an oxidant gas supply / discharge system 100, a fuel gas supply system 200, a cooling system 500, an impedance sensor 600, and a control device 700. In the present embodiment, a fuel cell system applied to a fuel cell vehicle will be described as an example. The fuel cell vehicle runs by driving a motor with electricity generated by the fuel cell FC. However, the fuel cell system of the present embodiment is not limited to fuel cell vehicle applications, but can be applied to other applications.

The fuel cell FC is a solid polymer electrolyte fuel cell, and includes a cell stack in which a plurality of single cells are stacked. Each single cell has a membrane electrode assembly (MEA: Membrane Electrode Assembly) formed by sandwiching a polymer electrolyte membrane between a pair of electrodes, and a pair of separators sandwiching the membrane electrode assembly from both sides. The fuel cell generates power by an oxidation-reduction reaction between oxygen gas (cathode gas) in air supplied through a cathode-side separator and hydrogen gas (anode gas) supplied through an anode-side separator. Specifically, an oxidation reaction of the formula (1) occurs at the anode electrode, and a reduction reaction of the formula (2) occurs at the cathode electrode. Then, the chemical reaction of the formula (3) occurs in the entire fuel cell FC.
_{^{H 2 → 2H + + 2e -}} ··· (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (１ ／) O ₂ → H ₂ O (3)

  The oxidizing gas supply / discharge system 100 includes an oxidizing gas supply pipe 110 and an oxidizing gas discharge pipe 120. The oxidizing gas supply pipe 110 is a pipe for supplying oxygen gas in the air, which is an oxidizing gas (cathode gas), to the fuel cell. On the oxidant gas supply pipe 110, an air compressor (cathode pump) ACP and a gas flow sensor 150 are provided. The air compressor ACP drives air taken in from outside the system and sends it to the fuel cell FC. The gas flow sensor 150 measures the flow rate of the oxidizing gas. The oxidizing gas discharge pipe 120 is a pipe for discharging the oxidizing gas after the reaction from the fuel cell FC. On the oxidizing gas discharge pipe 120, a pressure sensor 130 and a pressure regulating valve 140 are provided. Pressure regulating valve 140 regulates the cathode back pressure in fuel cell FC. The pressure sensor 130 is provided between the oxidizing gas discharge port of the fuel cell FC and the pressure regulating valve 140, and measures the cathode back pressure.

Here, the oxidant gas after the reaction discharged from the fuel cell FC contains generated water as shown in the equation (2). Since the generated water is present as water vapor in the oxidizing gas discharge pipe 120, when the cathode back pressure increases, the partial pressure of the water vapor decreases, and the discharge amount of the water vapor decreases. That is, if the cathode back pressure is increased by adjusting the pressure regulating valve 140, drying of the cell stack of the fuel cell FC can be suppressed. In addition, when increasing the cathode back pressure, it is preferable to increase the rotation speed of the air compressor ACP in order to keep the flow rate of the oxidizing gas constant.

  The fuel gas supply system 200 includes a fuel gas tank 210, a fuel gas supply pipe 220, a fuel gas recirculation pipe 230, a main stop valve 250, a pressure regulating valve 260, a pressure sensor 270, and an anode pump HP. I have. The fuel gas tank 210 stores a high-pressure hydrogen gas, for example, a fuel gas (anode gas). The fuel gas tank 210 and the fuel cell FC are connected by a fuel gas supply pipe 220. On the fuel gas supply pipe 220, a main stop valve 250 and a pressure regulating valve 260 are provided from the fuel gas tank 210 side. The main stop valve 250 turns on / off the supply of the fuel gas from the fuel gas tank 210. Pressure regulating valve 260 regulates the pressure of the fuel gas supplied to fuel cell FC. Pressure sensor 270 measures the pressure of the fuel gas supplied to fuel cell FC. The fuel gas recirculation pipe 230 is a pipe for returning the fuel gas not consumed by the fuel cell FC to the fuel gas supply pipe 220. The anode pump HP provided on the fuel gas recirculation pipe 230 drives the fuel gas discharged from the fuel cell FC and sends it to the fuel gas supply pipe 220. As the anode pump HP, for example, various pumps such as a variable ejector and a rotary pump can be used.

  Here, the fuel gas discharged from the fuel cell FC contains steam generated by water generated by power generation of the fuel cell FC. This water vapor or liquid water is returned to the fuel gas supply pipe 220 by the anode pump HP together with the fuel gas, and is again supplied to the fuel cell FC. Therefore, when the rotation speed of the anode pump HP increases, the water supplied to the fuel cell increases, and it is possible to suppress the drying of the cell stack of the fuel cell FC.

  The cooling system 500 includes a cooling water supply pipe 510, a cooling water discharge pipe 515, a radiator pipe 520, a cooling water pump 525, a bypass pipe 540, a three-way valve 545, and a radiator 530. The cooling water supply pipe 510 is a pipe for supplying cooling water to the fuel cell FC, and the cooling water is driven by a cooling water pump 525 provided on the cooling water supply pipe 510. The cooling water discharge pipe 515 is a pipe for discharging cooling water from the fuel cell FC. The downstream portion of the cooling water discharge pipe 515 is connected to a radiator pipe 520 and a bypass pipe 540 via a three-way valve 545. The radiator tube 520 is provided with a radiator 530. The radiator 530 is provided with a radiator fan 535. The radiator fan 535 sends air to the radiator 530 to promote heat radiation from the radiator 530. The downstream part of the radiator pipe 520 and the downstream part of the bypass pipe 540 are connected to a cooling water supply pipe 510.

  The impedance sensor 600 is attached to the fuel cell FC, and measures the impedance of the fuel cell FC using, for example, an AC impedance method. For example, according to Japanese Patent Application Laid-Open No. 2009-252706, when the frequency of the applied current is large (ω = 膜), the electrolyte membrane resistance can be obtained as the impedance, and when the frequency of the applied current is small (ω = 0), the electrolyte is set as the impedance. The sum of the membrane resistance and the reaction resistance due to the electrochemical reaction can be obtained. As shown in JP-A-2009-252706, the impedance of the fuel cell FC depends on the amount of water (wet state) of an electrolyte membrane (not shown) of the fuel cell FC. That is, when the impedance is small, the electrolyte membrane is sufficiently wet, and when the impedance is equal to or higher than a certain threshold, the electrolyte membrane may be dry. Further, the impedance sensor 600 can also measure the rate of increase in the impedance of the fuel cell FC. If the rate of increase in the impedance is equal to or higher than a certain threshold, the degree of dryness of the electrolyte membrane may increase. .

  The control device 700 is configured by a microcomputer including a central processing unit and a main storage device, and controls operations of various devices in the fuel cell system 10. Control device 700 determines the impedance of fuel cell FC measured by impedance sensor 600 or the rate of increase thereof, and controls the operations of anode pump HP, air compressor ACP, and pressure regulating valve 140 as described below.

  FIG. 2 is a flowchart illustrating a control method of the fuel cell system 10 according to the first embodiment. At the start, the fuel cell FC is operating normally. “Normal operation” means a state in which the fuel cell FC is not dry and the operation is good. Here, the normal operation conditions at the time of the start are that the rotation speed of the anode pump HP is 1000 rpm (first anode pump rotation speed), the cathode back pressure is 100 kpa (first cathode back pressure), and the rotation of the air compressor ACP is performed. It is assumed that the number is a value (first cathode pump rotation speed) corresponding to the first cathode back pressure in order to keep the cathode gas flow rate constant. At this time, the impedance sensor 600 measures the impedance of the fuel cell FC or the rate of increase thereof.

  In step S100, control device 700 determines whether or not the impedance of fuel cell FC or the rate of increase thereof is equal to or greater than a predetermined threshold. The “threshold” here is a threshold immediately before the fuel cell FC becomes in an excessively dry state. If the threshold is exceeded, the “threshold” is set in advance as a value at which the cell stack of the fuel cell FC is excessively dried. If the impedance of the fuel cell FC or the rate of increase thereof is not equal to or greater than a predetermined threshold, the fuel cell FC continues normal operation. On the other hand, when the impedance of the fuel cell FC or the rate of increase thereof exceeds a predetermined threshold, it is necessary to execute the wet operation of the fuel cell FC. At this time, first, in step S110, control device 700 determines whether or not the efficiency of fuel cell FC is to be emphasized.

  When importance is placed on efficiency, in step S120, the control device 700 selects the second anode pump rotation speed for efficiency consideration (for example, 4500 rpm) as the rotation speed of the anode pump HP, and the second cathode pump pressure corresponding thereto is set as the cathode back pressure. Select back pressure (eg, 130 kpa). On the other hand, when efficiency is not emphasized, in step S130, a second anode pump rotation speed (for example, 2000 rpm) for efficiency non-importance is selected as the rotation speed of the anode pump HP, and the second cathode back pressure corresponding thereto is selected as the cathode back pressure. Select a pressure (for example, 144 kpa). In the case where efficiency is emphasized, the rotation speed of the anode pump HP is extremely high. Therefore, considering the life of the anode pump HP, it is not preferable to always emphasize efficiency. In this sense, it is preferable to select efficiency-oriented and efficiency-insensitive at a predetermined ratio. Here, the second anode pump rotation speed and the second cathode back pressure selected in step S120 or S130 are both higher values than the first anode pump rotation speed and the first cathode back pressure at the start time. In step S140, control device 700 sets the rotation speed of air compressor ACP and the opening of pressure regulating valve 140 so as to maintain the cathode gas flow rate during normal operation according to the increase in the cathode back pressure.

  In step S150, the anode pump HP, the air compressor ACP, and the pressure regulating valve 140 are driven using the set values selected in steps S120 to S140. When the fuel cell FC performs this wet operation, the impedance of the fuel cell FC decreases. In step S160, control device 700 determines whether or not a predetermined time has elapsed since the impedance became equal to or less than a predetermined threshold. If the predetermined time has not elapsed after the impedance has become equal to or less than the predetermined threshold, the control device 700 maintains the driving of each of the anode pump HP, the air compressor ACP, and the pressure regulating valve 140, and the fuel cell FC performs the wet operation. Continue. On the other hand, when a predetermined time has elapsed since the impedance became equal to or less than the predetermined threshold, control device 700 ends the control of the wet operation, and fuel cell FC returns to the normal operation.

  FIG. 3 is an explanatory diagram showing the relationship between the impedance of the fuel cell FC, the rotation speed of the anode pump HP, and the cathode back pressure during the wet operation. Here, it is assumed that the fuel cell FC generates power at a temperature of 80 ° C. and a current of 50 A, and performs a wet operation. As the wet operating conditions, the first combination is an anode pump rotation speed of 4500 rpm and a cathode back pressure of 130 kpa, and the second combination is an anode pump rotation speed of 2000 rpm and a cathode back pressure of 144 kpa. The solid line shows the change in impedance when the anode pump speed is fixed at 4500 rpm and the cathode back pressure is changed. As shown in FIG. 3, the impedance of the fuel cell FC decreases as the cathode back pressure increases. However, in the first combination (4500 rpm, 130 kpa) and the second combination (2000 rpm, 144 kpa), the impedance of the fuel cell FC is The same is true, and the fuel cell FC can be brought into a similar wet state.

  FIG. 4 is an explanatory diagram showing the relationship between the rotational speed of the anode pump HP and the cathode back pressure in the fuel cell FC and power consumption. As shown in FIG. 4, as the wet operation conditions of the fuel cell FC, the first combination (4500 rpm, 130 kpa) consumes 16% lower power than the second combination (2000 rpm, 144 kpa), and the efficiency of the fuel cell FC Is good. For this reason, in this embodiment, when performing the wet operation of the fuel cell FC, it is preferable to select the first combination rather than the second combination of the wet operation conditions.

  As described above, when the cell stack of the fuel cell FC is dry, the power consumption increases excessively by increasing the rotation speed of the anode pump HP to 4500 rpm and increasing the cathode back pressure to 130 kpa. , And drying of the cell stack can be suppressed.

  The numerical values of the two combinations of the wet operation conditions are examples, and various other numerical values may be adopted. Further, the wet operation condition may be changed according to the normal operation condition in the immediately preceding normal operation.

-2nd Embodiment:
FIG. 5 is a flowchart illustrating a control method of the fuel cell system 10 according to the second embodiment. The difference from the first embodiment shown in FIG. 2 is that steps S170 to S210 are added after step S160, and the other configuration is the same as that of the first embodiment. Steps S100 to S160 are the same as those in the first embodiment, so that the illustration is simplified.

  In the second embodiment, when a predetermined time (first predetermined time) has elapsed since the impedance became equal to or less than the predetermined threshold value in step S160, the control device 700 ends the control of the wet operation, and the fuel cell FC returns to normal operation. On the other hand, if the predetermined time has not elapsed since the impedance became equal to or less than the predetermined threshold, in step 170, control device 700 sets a predetermined time (second predetermined time) from the start of the wet operation in step S150. It is determined whether or not it has elapsed. Note that the predetermined time used in step S170 may be the same as or different from the predetermined time used in step S160.

  If the predetermined time has not elapsed from step S150 in step S170, control device 700 maintains the driving of anode pump HP, air compressor ACP, and pressure regulating valve 140, respectively. On the other hand, if the predetermined time has elapsed from step S150, in step S180, control device 700 selects an anode pump rotation speed (for example, 4500 rpm) and a cathode back pressure (for example, 144 kpa) as operating conditions with a higher wettability. (High wet conditions). Here, when a predetermined time has elapsed from step S150, even if the predetermined time has elapsed after the start of the wet operation in step S150, the impedance of the fuel cell FC does not fall below a predetermined threshold value, and the fuel cell FC Has not reached a sufficiently wet state. In this case, by selecting the anode pump rotation speed and the cathode back pressure as operating conditions with higher wettability, the impedance can be quickly reduced to the threshold value or less, and the fuel cell FC can be quickly brought into the wet state. .

  Step S180 is performed when the wet condition has not been reached even after the operation for a predetermined time (second predetermined time) according to the operation conditions selected in step S120 or step S130 in FIG. Then, an operating condition having a higher degree of wetness than the operating condition selected in step S120 or step S130 before that is selected. That is, one of the anode pump rotation speed and the cathode back pressure selected in step S180 is higher than the value selected in step S120 or step S130, and the other is higher than the value selected in step S120 or step S130. Set to value. For example, if step S120 has been executed before step S180, in step S180, the anode pump speed is set to a value (for example, 4600 rpm) higher than the second anode pump speed (4500 rpm) in step S120. , The cathode back pressure may be set to the same value as the second cathode back pressure (130 kpa) in step S120. Alternatively, in step S180, the anode pump rotation speed is set to the same value as the second anode pump rotation speed (4500 rpm) in step S120, and the cathode back pressure is set to a value higher than the second cathode back pressure (130 kpa) in step S120 (130 kpa). For example, it may be set to 140 kpa). The same applies when step S130 has been executed before step S180. Note that the anode pump rotation speed and the cathode back pressure selected in step S180 are equal to or higher than the maximum value (4500 rpm) of the second anode pump rotation speed in steps S120 and S130, and the maximum value of the second cathode back pressure (4500 rpm). More preferably, it is set to a value of 144 kpa) or more.

  In step S190, control device 700 sets the rotation speed of air compressor ACP and the opening degree of pressure regulating valve 140 according to the operating conditions set in step S180 so as to maintain the cathode gas flow rate during normal operation. . In step S200, the anode pump HP, the air compressor ACP, and the pressure regulating valve 140 are driven using the set values selected in steps S180 and S190. Subsequent step S210 is the same as step S160 in the first embodiment. In step S180, instead of setting the final target value of the high-humidity operation condition at one time, steps S180 to S200 are repeatedly performed a plurality of times, and the wetness of the operation condition is gradually increased every time step S180 is performed. You may make it do. For example, when the anode pump rotation speed and the cathode back pressure under the final high wet operating conditions are 4500 rpm and the cathode back pressure is 144 kpa, if 4500 rpm and 130 kpa were selected in step S120 before step S180, the cathode back in step S180 Steps S190 and S200 may be executed by increasing the pressure by a fixed width (for example, 2 kpa). Then, after step S200, the process returns to step S180, and every time step S180 is executed, the cathode back pressure may be gradually increased to the target pressure (144 kpa).

  The present invention is not limited to the above-described embodiment, and can be implemented with various configurations without departing from the spirit of the invention. For example, the technical features in the embodiments corresponding to the technical features in each embodiment described in the summary of the invention may be used to solve some or all of the above-described problems, or to provide one of the above-described effects. In order to achieve a part or all, replacement or combination can be appropriately performed. Unless the technical features are described as essential in the present specification, they can be deleted as appropriate.

Reference Signs List 10 fuel cell system 100 oxidant gas supply / discharge system 110 oxidant gas supply pipe 120 oxidant gas discharge pipe 130 pressure sensor 140 pressure regulator 150 gas flow sensor 200 fuel gas supply system 210 fuel gas tank 220: fuel gas supply pipe 230 ... fuel gas recirculation pipe 250 ... main stop valve 260 ... pressure regulating valve 270 ... pressure sensor 500 ... cooling system 510 ... cooling water supply pipe 515 ... cooling water discharge pipe 520 ... radiator pipe 525 ... cooling water pump 530 radiator 535 radiator fan 540 bypass line 545 three-way valve 600 impedance sensor 700 control device ACP air compressor FC fuel cell HP anode pump

Claims (1)

A fuel cell system,
A fuel cell,
An anode pump provided in an anode gas recirculation pipe for recirculating anode exhaust gas discharged from the fuel cell to the fuel cell,
A pressure regulating valve provided on a cathode gas exhaust pipe for discharging cathode exhaust gas from the fuel cell to adjust a cathode back pressure of the fuel cell;
An impedance sensor for measuring the impedance of the fuel cell or the rate of increase thereof,
A control device that controls the operation of the anode pump and the pressure regulating valve using the measurement value of the impedance sensor,
With
The control device includes:
Under normal operating conditions including a first anode pump rotation speed and a first cathode back pressure, the operations of the anode pump and the pressure regulating valve are controlled, and the impedance of the fuel cell measured by the impedance sensor or the rate of increase thereof is determined in advance. When the threshold value is equal to or greater than a predetermined threshold value, a second anode pump rotation speed for efficiency consideration higher than the first anode pump rotation speed, and a second cathode backpressure for efficiency consideration higher than the first cathode back pressure. A first combination with a pressure, or a second combination different from the first combination, wherein the second anode pump rotation speed for emphasis on efficiency higher than the first anode pump rotation speed; Under the wet operating condition comprising one of the second combination with the second cathode back pressure for efficiency non-emphasis higher than one cathode back pressure, Controls the operation of Doponpu and the pressure regulating valve, when emphasizing the efficiency of power consumption of the fuel cell, of the second combination and the first combination, the first consisting of a lower combination of power And selecting the second combination when the efficiency of power consumption of the fuel cell is not emphasized .
Fuel cell system.

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