JP4876368B2 - Operation control of fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to operation control of a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen.
[0002]
[Prior art]
In recent years, fuel cells that generate electricity by electrochemical reaction between hydrogen and oxygen have attracted attention as energy sources. The fuel cell has a configuration in which a hydrogen electrode and an oxygen electrode are arranged with an electrolyte in between. When a hydrogen-rich fuel gas is supplied to the hydrogen electrode and a gas such as air is supplied to the oxygen electrode, hydrogen and oxygen in these gases react to generate water and power generation is performed. This reaction occurs mainly at the oxygen electrode.
[0003]
In order to perform an efficient reaction, it is preferable to supply hydrogen and oxygen at an appropriate ratio. The number of hydrogen molecules and oxygen molecules contained in the gas per unit volume varies depending on the pressure. Therefore, in order to ensure an appropriate supply amount of gas, in the fuel cell system, pressure sensors are provided at various locations on the piping for supplying these gases (Patent Document 1, etc.).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-237322
[Problems to be solved by the invention]
The supply pressure of gas in the fuel cell system varies within a very wide range. The atmospheric pressure is about 100 Kpa when the operation is stopped, and reaches about 600 Kpa during the operation. The pressure sensor provided in the fuel cell system needs to have a wide range capable of detecting such a wide range of pressure.
[0006]
However, since a wide range sensor generally has a low resolution, a pressure fluctuation of about several tens of Kpa may not be detected with sufficient accuracy. For this reason, fluctuations in atmospheric pressure caused by weather conditions and altitudes are not sufficiently detected and may not be reflected in the control of the gas supply amount. In addition, the detection value of the pressure sensor may include an error due to aging and other factors.
[0007]
As described above, if the gas supply is controlled based on the detection value of the pressure sensor in a state including an error due to various factors, an excess or shortage of the gas supply amount to the fuel cell system is caused, and efficient power generation is performed. May interfere. The present invention has been made in view of the above problems, and an object of the present invention is to improve detection accuracy of a pressure sensor and improve accuracy of control of a gas supply amount in a fuel cell system.
[0008]
[Means for solving the problems and their functions and effects]
The fuel cell system of the present invention includes a fuel cell that generates electric power upon receiving a predetermined gas supply. The predetermined gas includes, for example, hydrogen and an oxidizing gas. Various types of fuel cells can be applied, but from the viewpoint of energy efficiency, it is preferable to apply a solid polymer type using a solid polymer membrane such as Nafion (registered trademark) as an electrolyte. The fuel cell system further includes a gas supply / discharge mechanism for supplying and discharging gas to the fuel cell, and a pressure sensor for detecting the pressure of the gas in the gas supply / discharge mechanism. During operation of the fuel cell system, a correction amount for correcting the detection value of the pressure sensor is set with reference to the atmospheric pressure in a state where the gas supply mechanism is released to the atmospheric pressure. Then, the gas supply amount is controlled based on the correction pressure value obtained by reflecting this correction amount on the detection value of the pressure sensor. When hydrogen and oxygen are supplied to the fuel cell, the correction of the detection value may be applied to both the hydrogen electrode and the oxygen electrode, or may be applied to only one of them. In the former case, the correction value may be an individual value for each of the hydrogen electrode and the oxygen electrode, or may be a common value.
[0009]
According to the present invention, by correcting the detection value of the pressure sensor with reference to the atmospheric pressure, it is possible to improve the pressure detection accuracy, and hence the gas supply amount. The fuel cell system of the present invention may be configured as a stationary system that supplies power to a house, a plant, or the like, or may be configured as a system that can be mounted on a moving body such as a vehicle. In the former case, it is possible to realize operation control that takes into account fluctuations in atmospheric pressure due to weather conditions and the like. In the latter case, further, it is possible to realize operational control that takes into account fluctuations in atmospheric pressure accompanying changes in altitude caused by movement. Moreover, the influence by the error which arises in the detected value of a pressure sensor by a secular change etc. can also be suppressed.
[0010]
In the present invention, the atmospheric pressure may be read from the outside or detected by a sensor. For the purpose of suppressing errors due to secular change or the like, the atmospheric pressure may be a fixed value set in advance. When an atmospheric pressure sensor for detecting atmospheric pressure is used, the measurement range of the atmospheric pressure sensor is preferably narrower than the measurement range of the pressure sensor. In general, the narrower the measurement range, the higher the detection resolution. Therefore, by using such an atmospheric pressure sensor, the correction value of the pressure sensor can be set with high accuracy.
[0011]
In the present invention, the presence or absence of abnormality of the pressure sensor may be determined based on the difference between the detected value of the pressure sensor and the atmospheric pressure. For example, when the difference is larger than a predetermined value, it can be determined that the detected value of the pressure sensor is abnormal. When the atmospheric pressure is detected by a sensor, it may be specified which of the pressure sensor and the atmospheric pressure sensor is abnormal, for example, by comparison with a standard atmospheric pressure.
[0012]
In the present invention, the correction value can be set at various timings. For example, it is preferable to set a predetermined timing when the fuel cell system is started or after it is stopped. Generally, in a fuel cell system, the gas supply / exhaust mechanism is released to atmospheric pressure when stopped. Therefore, at such timing, it is possible to set the correction value with high accuracy without being affected by the gas remaining in the gas supply / discharge mechanism. The timing for executing the setting of the correction value may be, for example, the time when the fuel cell system is started or stopped, or the time when a predetermined time elapses after the start or stop instruction is input. .
[0013]
The setting of the correction value is not necessarily limited to when starting and stopping, and can be performed at various timings when the gas supply mechanism is released to atmospheric pressure. For example, when the fuel cell system is operated intermittently, the correction value may be set during a period when power generation is stopped.
[0014]
In the present invention, when the fuel cell system has a pump for supplying gas, the correction pressure value considering the correction value may be reflected in the drive control of the pump. The driving of the pump is also affected by the required power generation. Therefore, for example, it is possible to adopt a control method in which correction according to the difference between the reference pressure and the correction pressure value is performed based on the drive state of the pump set at a predetermined reference pressure in accordance with the required power generation amount. The driving state can be expressed by the number of revolutions of the pump, power consumption, and the like. When the correction pressure value is lower than the reference pressure, it is necessary to correct the rotational speed or power more than the reference driving state. When the correction pressure value is higher than the reference pressure, the reverse correction is necessary. In order to reduce the calculation load at the time of control, the driving state in consideration of the above correction is stored in advance as a map or function in association with the required power generation amount and the correction pressure value, and the pump is driven by referring to the stored content. You may control.
[0015]
The present invention is not limited to a fuel cell system, and may be configured as a power supply system equipped with a fuel cell system and a mobile body driven by electric power from the power supply system. Moreover, you may comprise as a control method of these fuel cell systems, a power supply system, and a moving body.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in the following order.
A. Device configuration:
B. Operation control processing:
[0017]
A. Device configuration:
FIG. 1 is an explanatory diagram showing the overall configuration of a fuel cell system as an embodiment. The fuel cell system of this embodiment is mounted as a power source in an electric vehicle driven by a motor. When the driver operates the accelerator, power generation is performed according to the operation amount detected by the accelerator opening sensor 101, and the vehicle can travel with the electric power. The fuel cell system of the embodiment does not need to be mounted on the vehicle, and can adopt various configurations such as a stationary type.
[0018]
The fuel cell stack 10 is a stack of cells that generate power by an electrochemical reaction between hydrogen and oxygen. Each cell has a configuration in which a hydrogen electrode (hereinafter referred to as an anode) and an oxygen electrode (hereinafter referred to as a cathode) are arranged with an electrolyte membrane interposed therebetween. In this embodiment, a solid polymer type cell using a solid polymer membrane such as Nafion (registered trademark) as an electrolyte membrane is used. However, the present invention is not limited to this, and various types can be used.
[0019]
The cathode of the fuel cell stack 10 is supplied with compressed air as a gas containing oxygen. The air is sucked from the filter 40, compressed by the compressor 41, humidified by the humidifier 42, and supplied to the fuel cell stack 10 from the pipe 35. The pipe 35 is provided with a temperature sensor 102 for detecting the intake air temperature. Exhaust gas from the cathode (hereinafter referred to as “cathode off gas”) is discharged to the outside through the pipe 36 and the muffler 43. The supply pressure of air is detected by a pressure sensor 53 provided in the pipe 36 and is controlled by the opening degree of the pressure regulating valve 27. The pressure sensor 53 has a measurement range of 0 to 660 Kpa in general, the supply pressure of the fuel cell 10.
[0020]
Hydrogen is supplied to the anode of the fuel cell stack 10 from high-pressure hydrogen stored in the hydrogen tank 20 via the pipe 32. Instead of the hydrogen tank 20, hydrogen may be generated by a reforming reaction using alcohol, hydrocarbon, aldehyde or the like as a raw material and supplied to the anode.
[0021]
The hydrogen stored in the hydrogen tank 20 at a high pressure is supplied to the anode after the pressure and supply amount are adjusted by a shut valve 21, a regulator 22, a high pressure valve 23, and a low pressure valve 24 provided at the outlet thereof. Exhaust gas from the anode (hereinafter referred to as anode off gas) flows out to the pipe 33. A pressure sensor 51 and a valve 25 are provided at the outlet of the anode, and are used for controlling supply pressure and amount to the anode.
[0022]
The pipe 33 is branched into two on the way, one is connected to a discharge pipe 34 for discharging the anode off gas to the outside, and the other is connected to the pipe 32 via a check valve 28. As a result of the consumption of hydrogen by power generation in the fuel cell stack 10, the pressure of the anode offgas is relatively low. Therefore, the pipe 33 is provided with a pump 45 for pressurizing the anode offgas.
[0023]
While the discharge valve 26 provided in the discharge pipe 34 is closed, the anode off gas is circulated again to the fuel cell stack 10 via the pipe 32. Since hydrogen that has not been consumed in power generation remains in the anode off gas, hydrogen can be effectively used by circulating in this way.
[0024]
During the circulation of the anode off gas, hydrogen is consumed for power generation, while impurities other than hydrogen, for example, nitrogen that has permeated the electrolyte membrane from the cathode remain without being consumed, so that the impurity concentration gradually increases. When the discharge valve 26 is opened in this state, the anode off-gas passes through the discharge pipe 34 and is diluted with air in the diluter 44 and then discharged to the outside, thereby reducing the amount of impurities circulating. However, at this time, since hydrogen is also discharged at the same time, it is preferable from the viewpoint of improving fuel efficiency to suppress the opening amount of the discharge valve 26 as much as possible.
[0025]
The fuel cell stack 10 is supplied with cooling water in addition to hydrogen and oxygen. The cooling water flows through the cooling pipe 37 by the pump 46, is cooled by the radiator 38, and is supplied to the fuel cell stack 10. A temperature sensor 103 for detecting the temperature of the cooling water is provided at the outlet from the fuel cell stack 10.
[0026]
The operation of the fuel cell system is controlled by the control unit 100. The control unit 100 is configured as a microcomputer including a CPU, a RAM, and a ROM therein, and controls the operation of the system according to a program stored in the ROM. In the figure, an example of a signal input / output to / from the control unit 100 for realizing this control is indicated by a broken line. Examples of the output destination of the control signal include the low pressure valve 24, the discharge valve 26, the pressure regulating valve 27, and the compressor 41.
[0027]
As an input, the detection signal of the temperature sensor 102, the temperature sensor 103, and the accelerator opening degree sensor 101 is mentioned, for example. Detection signals from the pressure sensor 53 and the atmospheric pressure sensor 105 for detecting the outlet pressure of the cathode are also input to the control unit 100. The atmospheric pressure sensor 105 is a sensor for detecting atmospheric pressure, and has a measurement range of about 70 to 110 Kpa. The atmospheric pressure sensor 105 has a narrower measurement range than the pressure sensor 53, and has characteristics of high measurement resolution and measurement accuracy.
[0028]
The fuel cell system of the present embodiment is stopped in the following state. Regarding the gas supply system to the anode, all the valves 21 to 26 are closed so that hydrogen does not leak to the outside. Regarding the gas supply system to the cathode, since the operation of the compressor 41 is stopped and the pressure regulating valve 27 is released, the entire system becomes equal to the atmospheric pressure.
[0029]
B. Operation control processing:
FIG. 2 is a flowchart of the operation control process. This process is repeatedly executed by the control unit 100 when the fuel cell is operated.
[0030]
When this process is started, the control unit 100 inputs various parameters necessary for operation control (step S10). This parameter includes, for example, the accelerator opening degree related to the required power generation amount, the pressure of each part related to the supply amount control of hydrogen and compressed air, and the like.
[0031]
Next, the control unit 100 determines whether or not it corresponds to the correction timing of the pressure sensor 53 (step S11). In this embodiment, the time when the fuel cell system is started is set as the correction timing. As described above, since the cathode gas supply system is released to atmospheric pressure when the fuel cell system is stopped, it is assured that the gas supply system is also at atmospheric pressure even during startup.
[0032]
As the correction timing, various timings at which the cathode gas supply system becomes atmospheric pressure can be applied. For example, the time when a predetermined time has elapsed after the stop instruction of the fuel cell system is issued and the pressure regulating valve 27 is released may be used as the correction timing. When the fuel cell system is intermittently operated, the correction timing may be a time point after a predetermined time has elapsed after power generation is stopped. These “predetermined times” can be set based on the time required for the pressure of the cathode gas supply system to drop to atmospheric pressure.
[0033]
When it corresponds to the correction timing (step S11), the control unit 100 measures the atmospheric pressure (step S20). In this embodiment, values measured by both the pressure sensor 53 and the atmospheric pressure sensor 105 are acquired. In the case of a stationary fuel cell system, instead of the measurement value of the atmospheric pressure sensor 105, it may be acquired via a network from a server that provides weather information such as atmospheric pressure. Further, instead of the measurement value of the atmospheric pressure sensor 105, a user may input a separately measured value. Hereinafter, the measured value of the atmospheric pressure sensor 105 or a value corresponding thereto is referred to as a true value of the atmospheric pressure.
[0034]
Next, the control unit 100 calculates a pressure difference ΔP between the measured value Ps of the pressure sensor 53 and the true value Pa of atmospheric pressure by the following equation (step S21).
ΔP = Ps−Pa
[0035]
When the absolute value of the obtained pressure difference ΔP is larger than the predetermined determination reference value Tp (step S22), the control unit 100 determines that either the pressure sensor 53 or the atmospheric pressure sensor 105 is abnormal, and the abnormality Time processing is executed (step S23). As the processing at the time of abnormality, for example, abnormality notification by an alarm, prohibition of operation of the fuel cell system, etc. can be taken.
[0036]
When the absolute value of the pressure difference ΔP is equal to or less than a predetermined determination reference value Tp, it is determined that both the pressure sensor 53 and the atmospheric pressure sensor 105 are normal, and the pressure difference ΔP is set as the pressure correction value Pc. . This correction value is a set value for correcting the measurement value of the pressure sensor 53 on the assumption that the measurement value of the atmospheric pressure sensor 105 is a true value.
[0037]
In step S11, when it is determined that it is not the sensor correction timing, the control unit 100 executes normal operation processing. In order to control the supply amount of the compressed air on the cathode side, the control unit 100 corrects the measured value of the pressure sensor 53 by the following equation (step S30).
P = Ps−Pc;
P: Pressure after correction (hereinafter referred to as “correction pressure value”);
Ps: Pressure sensor measurement value;
Pc: correction value;
[0038]
The control unit 100 determines the rotation speed of the pump based on this corrected pressure value (step 31). The example of the map referred in order to determine the rotation speed of a pump in the figure was shown. The control unit 100 stores this map in advance, and sets the rotation speed of the pump by referring to the map based on the required power and the outlet pressure.
[0039]
As shown in the figure, when the cathode outlet pressure is a preset reference pressure, for example, 660 Kpa, the supply amount of air increases as the required power increases. When the outlet pressure is different from the reference pressure, the amount of oxygen in the unit volume of air varies. Therefore, in order to perform stable power generation, it is necessary to correct the rotational speed of the pump and change the air supply amount so as to compensate for the fluctuation of the oxygen amount. As a result, the map is set to increase the pump rotation speed when the outlet pressure is lower than the reference pressure, and to decrease the pump rotation speed when the outlet pressure is higher than the reference pressure. The correction based on the difference between the outlet pressure and the reference pressure is not necessarily prepared as a map, and may be prepared as a correction formula. Furthermore, all the pump rotation speeds including the pump rotation speed with respect to the reference pressure may be calculated by a function of the required power and the outlet pressure.
[0040]
As a gas supply control, the control unit 100 drives the pump at the pump rotation speed thus set, and supplies hydrogen corresponding to the required power generation amount from the hydrogen tank (step S32). The control unit 100 repeatedly generates the requested power by the fuel cell system by repeatedly executing the above processing.
[0041]
According to the fuel cell system of the embodiment described above, the detection accuracy of the outlet pressure can be improved by correcting the detection value of the pressure sensor 53 based on the true value of the atmospheric pressure. As a result, the air supply amount can be controlled with high accuracy, and loss due to unnecessary pump driving and power shortage due to air shortage can be suppressed.
[0042]
C. Variations:
In step S21 of the embodiment, a preset standard value, for example, 100 Kpa may be used instead of the atmospheric pressure measurement value. The pressure difference ΔP obtained based on this value can be used for determining the abnormality of the pressure sensor 53. In this case, the correction (steps S24 and S30) when the pressure sensor 53 is determined to be normal may be omitted.
[0043]
In the embodiment, the case of correcting the pressure sensor 53 on the cathode side is illustrated. Similar processing can be applied to the pressure sensor 51 on the anode side. In this case, it is desirable to release the anode-side valves 25 and 26 when the fuel cell system is stopped, and to release the anode gas supply / discharge system to atmospheric pressure.
[0044]
As mentioned above, although the various Example of this invention was described, it cannot be overemphasized that this invention is not limited to these Examples, and can take a various structure in the range which does not deviate from the meaning.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an overall configuration of a fuel cell system as an embodiment.
FIG. 2 is a flowchart of an operation control process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell 20 ... Hydrogen tank 21 ... Shut valve 22 ... Regulator 23 ... High pressure valve 24 ... Low pressure valve 25 ... Valve 26 ... Discharge valve 27 ... Pressure regulating valve 28 ... Check valves 32, 33, 35, 36, 37 ... Pipe 34 ... Discharge pipe 38 ... Radiator 40 ... Filter 41 ... Compressor 42 ... Humidifier 43 ... Muffler 44 ... Diluter 45, 46 ... Pump 51, 53 ... Pressure sensor 100 ... Control unit 101 ... Accelerator opening sensor 102, 103 ... Temperature sensor 105 ... Atmospheric pressure sensor

Claims (5)

A fuel cell system,
A fuel cell that generates electricity by supplying hydrogen and oxidizing gas;
A gas supply and discharge mechanism for supplying and discharging the hydrogen or oxidizing gas to and from the fuel cell;
A pressure sensor for detecting the pressure of the hydrogen or oxidizing gas in the gas supply / discharge mechanism;
A pressure difference obtained by subtracting the atmospheric pressure from the pressure detected by the pressure sensor in a state where the gas supply / discharge mechanism is released to the atmospheric pressure at the time of starting or stopping the fuel cell system, A correction amount setting unit that is set as a correction amount for correcting the detected value of
A fuel cell comprising: a supply control unit that controls a supply amount of hydrogen or oxidizing gas that is a pressure detection target of the pressure sensor, based on a correction pressure value obtained by subtracting the correction amount from the pressure detected by the pressure sensor; system. The fuel cell system according to claim 1, wherein
The measurement range is narrower than the pressure sensor, and has an atmospheric pressure sensor for measuring atmospheric pressure,
The correction amount setting unit is a fuel cell system that uses a detection value of the atmospheric pressure sensor as the atmospheric pressure. The fuel cell system according to claim 1 or 2, wherein
In addition, the correction amount setting unit determines that the pressure sensor is abnormal when the absolute value of the pressure difference is larger than a determination reference value for determining whether the pressure sensor is abnormal. Battery system. A fuel cell system according to any one of claims 1 to 3, wherein
The gas supply / discharge mechanism has a pump for supplying the hydrogen or oxidizing gas to the fuel cell,
The supply control unit increases the drive amount of the pump when the correction pressure value is lower than a reference pressure value preset to a pressure value for causing the fuel cell to perform stable power generation, A fuel cell system that reduces the drive amount of the pump when the corrected pressure value is higher than a reference pressure value. A control method for controlling the operation of a fuel cell system including a fuel cell that generates power by receiving supply of hydrogen and oxidizing gas,
Detecting a pressure of the hydrogen or oxidizing gas in a gas supply / discharge mechanism for supplying / exhausting the hydrogen or oxidizing gas to / from the fuel cell by a pressure sensor;
A pressure difference obtained by subtracting the atmospheric pressure from the pressure detected by the pressure sensor in a state where the gas supply / discharge mechanism is released to the atmospheric pressure at the time of starting or stopping the fuel cell system, Setting as a correction amount for correcting the detected value of
Controlling the supply amount of hydrogen or oxidizing gas, which is a pressure detection target of the pressure sensor, based on a corrected pressure value obtained by subtracting the correction amount from the pressure detected by the pressure sensor.

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