JP5119565B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system including a fuel cell that generates electric energy by a chemical reaction between hydrogen and oxygen, and is effective when applied to a moving body such as a vehicle, a ship, and a portable generator.
[0002]
[Prior art]
It is known that the internal resistance of a fuel cell affects the wetness of the electrolyte membrane inside the fuel cell. When the amount of moisture inside the fuel cell is low and the electrolyte membrane is dry, the internal resistance increases. The output voltage of the fuel cell decreases. On the other hand, when the internal water content of the fuel cell is excessive, the electrode of the fuel cell is covered with water, so that the diffusion of oxygen and hydrogen as reactants is hindered, and the output voltage decreases.
[0003]
For this reason, in order to operate the fuel cell with high efficiency, it is necessary to optimally manage the internal moisture content of the fuel cell, but at present there is no method for directly measuring the internal moisture content of the fuel cell.
[0004]
Since the internal moisture content of the fuel cell has a correlation with the complex impedance of the fuel cell, it is possible to indirectly grasp the moisture state inside the fuel cell by measuring the impedance of the fuel cell. Currently, there is an AC impedance method as a method for measuring impedance.
[0005]
[Problems to be solved by the invention]
However, in the current AC impedance method, impedance is measured at a number of points while changing the frequency of the applied sine wave, and thus it takes several minutes for one measurement. For this reason, it is difficult to measure the impedance of the fuel cell that changes over time, and it is difficult to grasp the moisture state inside the fuel cell in real time.
[0006]
An object of the present invention is to provide a fuel cell system that can measure the impedance of a fuel cell over time and can grasp the moisture state inside the fuel cell in real time.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 includes a fuel cell (10) that obtains electric power by electrochemical reaction of hydrogen and oxygen, and a sine wave while changing the frequency of the output signal of the fuel cell. Fuel is obtained from the resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficient and the resistance component (R2) that increases when the internal moisture content of the fuel cell is excessive, which is obtained by the complex impedance of the fuel cell when a signal is applied. A fuel cell system for estimating a moisture state inside a battery,
  A sine wave applying means (40) for applying a sine wave signal having an arbitrary frequency to the output signal of the fuel cell, a voltage detecting means (41) for detecting the output voltage of the fuel cell, and detecting the output current of the fuel cell Current detection means (42), and impedance calculation means (43 to 47) for calculating the complex impedance of the fuel cell when two sine wave signals of a predetermined frequency are applied,
  The impedance calculating means outputs the output voltage detected by the voltage detecting means (41) when one of the complex impedances of the fuel cell at two predetermined frequencies is applied by the sine wave applying means (40). And the output voltage is output when the sine wave signal is not applied to the other of the complex impedances of the fuel cell at two predetermined frequencies by the sine wave applying means. The value divided by the current is calculated as the complex impedance of the fuel cell at frequency 0And
  The impedance calculation means sets a complex plane for displaying the complex impedance of the fuel cell, and when one of the complex impedance coordinates (a3, b3) when a sine wave signal of a predetermined frequency is applied and when no sine wave signal is applied The coordinate (R2, 0) of the other complex impedance of is placed on a semicircle centered on the real axis of the complex plane;
  The impedance calculation means calculates the coordinates (a of the center of the semicircle from the coordinates (a3, b3), (R2, 0) of the two points. _c , 0) and the radius (R) of the semicircle,
  The resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficient is expressed as coordinates (a _c ) By subtracting the radius (R) of the semicircle from
  The resistance component (R2) that increases when the internal water content of the fuel cell is excessive is calculated from a value twice the radius (R) of the semicircle.It is characterized by that.
[0008]
  According to this, the coordinates (a3, b3) of one complex impedance when a sine wave signal of a predetermined frequency is applied to a semicircle centered on the real axis of the complex plane displaying the complex impedance of the fuel cell. , And the coordinates (R2, 0) of the other complex impedance when no sine wave signal is applied, and the coordinates of the center of the semicircle from the coordinates (a3, b3), (R2, 0) of these two points (A _c , 0) and the radius (R) of the semicircle, and the coordinates (a _c , 0) and radius (R),A resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficient and a resistance component (R2) that increases when the internal moisture content of the fuel cell is excessive can be obtained. For this reason, when estimating the internal moisture content of the fuel cell by the alternating current impedance method, it is not necessary to measure the complex impedance at many points while changing the frequency, and the impedance can be measured in a short time. Thereby, impedance measurement can be performed over time, and the moisture state (insufficient / excessive moisture) inside the fuel cell can be grasped in real time.
[0010]
  In particular, according to the first aspect of the present invention, when the sine wave signal is not applied, the value obtained by dividing the output voltage of the fuel cell by the output current is calculated as the complex impedance of the fuel cell at a frequency of 0.It is only necessary to measure the complex impedance at one frequency, and the impedance can be measured in a shorter time.
[0018]
  Claims2As described above, the output signal can be an output current and an output voltage of the fuel cell, and the sine wave signal can be a sine wave current or a sine wave voltage.
[0019]
  Moreover, in invention of Claim 3, the internal moisture content adjustment means (20-23, 30-33) which adjusts the internal moisture content of a fuel cell is provided,Based on the resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficientWhen it is determined that the internal moisture content of the fuel cell is insufficient, the internal moisture content of the fuel cell is increased by the internal moisture content adjusting means,Based on the resistance component (R2) that increases when the internal moisture content of the fuel cell is excessiveWhen it is determined that the internal moisture content of the fuel cell is excessive, the internal moisture content of the fuel cell is reduced by the internal moisture content adjusting means.
[0020]
Thereby, the internal moisture content of the fuel cell can be kept optimal.
[0021]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment to which the present invention is applied will be described below with reference to FIGS. In this embodiment, the fuel cell system of the present invention is applied to an electric vehicle.
[0023]
FIG. 1 shows the overall configuration of the fuel cell system of the first embodiment. As shown in FIG. 1, the fuel cell system according to the first embodiment includes a fuel cell (FC stack) 10, an air supply device 21, a hydrogen supply device 31, impedance detection units 40 to 47, a control unit 50, and the like. It has been.
[0024]
The fuel cell (FC stack) 10 generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen. In the first embodiment, a solid polymer electrolyte fuel cell is used as the fuel cell 10, and a plurality of single cells serving as basic units are stacked. In the fuel cell 10, when hydrogen and air (oxygen) are supplied, the following electrochemical reaction between hydrogen and oxygen occurs to generate electric energy.
(Hydrogen electrode side) H₂→ 2H⁺+ 2e^-
(Oxygen electrode side) 2H⁺+ 1 / 2O₂ + 2e^-→ H₂O
The fuel cell 10 is configured to supply electric power to an electric device such as an inverter (load) 11 or a secondary battery (not shown). The inverter 11 converts the direct current supplied from the fuel cell 10 into an alternating current and supplies it to a traveling motor (not shown) to drive the motor.
[0025]
In the fuel cell system, hydrogen is supplied to the air path (oxygen path) 20 for supplying air (oxygen) to the oxygen electrode (positive electrode) side of the fuel cell 10 and to the hydrogen electrode (negative electrode) side of the fuel cell 10. A hydrogen path 30 is provided. An air supply device (compressor) 21 is provided at the most upstream part of the air path 20. A hydrogen supply device 31 is provided at the most upstream part of the hydrogen path 30. As the hydrogen supply device 31, for example, a reforming device that generates hydrogen by a reforming reaction, or a hydrogen tank that stores pure hydrogen by incorporating a hydrogen storage material such as a hydrogen storage alloy can be used. The air supply device 21 and the hydrogen supply device 31 can adjust the flow rate by adjusting the supply amount of air and hydrogen.
[0026]
For the electrochemical reaction, the electrolyte membrane in the fuel cell 10 needs to be in a wet state containing moisture. For this reason, the air path 20 is provided with a humidifier 22 for humidifying the air supplied to the fuel cell 10. The humidifier 22 is configured to be able to adjust the humidification amount of air. Similarly, the hydrogen path 30 is also provided with a humidifier 32 for humidifying the hydrogen supplied to the fuel cell 10. By increasing the humidification amount by the humidifiers 22 and 32, the internal moisture amount can be increased, and by decreasing the humidification amount by the humidifiers 22 and 32, the internal moisture amount can be decreased.
[0027]
A back pressure adjustment valve 23 for adjusting the pressure of the air flowing through the air path 20 is provided on the downstream side of the fuel cell 10 in the air path 20. The air pressure in the air path 20 can be increased by reducing the opening of the valve 23, and the air pressure can be decreased by increasing the opening. Similarly, a back pressure adjusting valve 33 for adjusting the pressure of hydrogen flowing through the hydrogen path 30 is also provided downstream of the fuel cell 10 in the hydrogen path 30.
[0028]
By increasing the opening degree of the back pressure adjusting valves 23 and 33, the pressure in the air path 20 and the hydrogen path 30 in the fuel cell 10 decreases, and the evaporation of moisture in these paths 20 and 30 can be promoted. And the amount of internal moisture can be reduced. Further, by reducing the opening degree of the back pressure adjusting valves 23 and 33, the pressure in the air path 20 and the hydrogen path 30 increases in the fuel cell 10, and moisture evaporation in these paths 20 and 30 is suppressed. And the amount of internal moisture can be increased.
[0029]
Furthermore, by increasing the flow rate of air supplied from the air supply device 21 or increasing the flow rate of hydrogen supplied from the hydrogen supply device 31, the moisture in the fuel cell 10 is blown away to reduce the amount of internal moisture. Can be made.
[0030]
The humidifiers 22, 32, back pressure adjustment valves 23, 33, air supply device 21, and hydrogen supply device 31 constitute internal water content adjusting means for adjusting the internal water content of the fuel cell 10 by increasing or decreasing it. ing. These may be used alone or in combination.
[0031]
Next, based on FIG. 2, the relationship between the output voltage drop of the fuel cell 10 and the amount of internal moisture will be described. FIG. 2 shows the relationship between the output voltage and output current of the fuel cell 10. In the fuel cell 10, if there is no loss inside the battery, a constant electromotive force is generated as shown by a broken line in FIG. 2.
[0032]
In practice, however, a voltage drop occurs as shown by the solid line in FIG. The breakdown is as follows: 1) activation overvoltage due to activation energy of electrochemical reaction, 2) resistance overvoltage due to internal resistance of fuel cell 10, and 3) diffusion due to inhibition of diffusion of hydrogen and oxygen. This is due to the occurrence of overvoltage.
[0033]
If the amount of water in the fuel cell 10 is insufficient, the water content of the polymer electrolyte membrane decreases, and the conductivity of the electrolyte membrane decreases. As a result, the electrical resistance of the electrolyte membrane increases, and 2) the resistance overvoltage increases. On the other hand, 1) active overvoltage and 3) diffusion overvoltage are not affected by insufficient water content.
[0034]
If the amount of water in the fuel cell 10 becomes excessive, the electrodes of the fuel cell 10 are covered with water, so that diffusion of hydrogen and oxygen as reactants is hindered, and 3) diffusion overvoltage increases. On the other hand, 1) activation overvoltage and 2) resistance overvoltage are not affected by excessive water content.
[0035]
From the above points, if 2) increase in resistance overvoltage and 3) increase in diffusion overvoltage can be measured separately, it can be determined from the increase in resistance overvoltage that the internal moisture content is insufficient. Can be judged. These resistance overvoltage and diffusion overvoltage can be separated by using the AC impedance method.
[0036]
Next, a method for separating resistance overvoltage and diffusion overvoltage by the AC impedance method will be described with reference to FIGS.
[0037]
FIG. 3 shows an equivalent circuit of the fuel cell 10. In the equivalent circuit of FIG. 3, R1 corresponds to the resistance of the electrolyte membrane, and R2 corresponds to the resistance-converted activation overvoltage and diffusion overvoltage. When a sine wave current having a predetermined frequency is applied to the equivalent circuit of FIG. 3, the voltage response is delayed with respect to the change in current.
[0038]
FIG. 4 shows the impedance of the fuel cell 10 on a complex plane when a sinusoidal current from high frequency to low frequency is applied to the circuit of FIG. When the frequency of the applied sine wave current is infinitely large (ω = ∞), the impedance is R1 in FIG. Further, when the frequency of the sine wave current is very small (ω = 0), the impedance is R1 + R2. The impedance when the frequency is changed between a high frequency and a low frequency draws a semicircle as shown in FIG.
[0039]
From these things, it becomes possible to isolate | separate and measure R1 and R2 in the equivalent circuit of the fuel cell 10 by using the alternating current impedance method. When R1 is larger than a predetermined first predetermined value and the output is reduced, the polymer electrolyte membrane is dried, the resistance overvoltage is increased, and the conductivity is reduced, which is the cause of the output decrease. It can be judged. In addition, when R2 is larger than a predetermined second predetermined value and the output is reduced, it can be determined that water is excessively present on the electrode surface and the diffusion overvoltage is increased. .
[0040]
The fuel cell system of the first embodiment is provided with impedance detectors 40 to 47 that detect the impedance of the fuel cell 10 by the AC impedance method.
[0041]
The impedance detection unit detects a sine wave oscillator (sine wave applying means) 40 that generates a sine wave current at an arbitrary frequency, a voltage sensor (voltage detection means) 41 that detects an output voltage of the fuel cell 10, and an output current. Current sensor (current detection means) 42, filter units 43 and 44 for removing noise from voltage signals and current signals, FFT processing units 45 and 46 for performing fast Fourier transform processing, voltage components and current components subjected to FFT processing And an impedance analyzer 47 for calculating impedance from The filter units 43 and 44, the FFT processing units 45 and 46, and the impedance analysis unit 47 constitute impedance calculation means.
[0042]
In the fuel cell system of the first embodiment, a control unit 50 that performs various controls is provided. The control unit 50 determines the moisture state inside the fuel cell 10 based on the impedance of the fuel cell 10 calculated by the impedance analysis unit 47, and controls the moisture content inside the fuel cell 10 based on this. It is configured.
[0043]
Next, the operation of the fuel cell system according to the first embodiment will be described.
[0044]
First, the required vehicle power required for vehicle travel is detected from the accelerator opening by the driver. The fuel cell 10 generates power so as to supply the vehicle required power. Next, impedance measurement of the fuel cell 10 is performed by the impedance detection units 40 to 47.
[0045]
FIG. 5 shows an impedance measurement procedure. First, a sine wave current having a predetermined frequency is applied to the direct current output from the fuel cell 10 by the sine wave oscillator 40. At this time, the output voltage of the fuel cell 10 is detected by the voltage sensor 41, and the output current is detected by the current sensor 42. In the voltage signal and the current signal, the filter units 43 and 44 remove the high-frequency noise component and the current fluctuation component for satisfying the low-frequency vehicle power requirement.
[0046]
In the FFT processing units 45 and 46, fast Fourier transform is performed, and the voltage signal and current signal that have passed through the filter units 43 and 44 are converted into real and imaginary components (a_V+ Jb_V, A_I+ Jb_I). The impedance analyzer 47 calculates the real component and imaginary component of the impedance by dividing the FFT-processed voltage signal by the FFT-processed current signal, and calculates the distance (absolute value) r and the phase angle θ from the origin on the complex plane. Is output.
[0047]
With the above procedure, the impedance of the fuel cell 10 at a predetermined frequency can be detected.
[0048]
Next, the resistance overvoltage and the diffusion overvoltage of the fuel cell 10 are separated and detected. As described above, if R1 and R2 in the equivalent circuit of FIG. 3 are obtained by the AC impedance method, the resistance overvoltage and the diffusion overvoltage of the fuel cell 10 can be separated and detected. FIG. 6 shows a procedure for calculating R1 and R2. In the first embodiment, R1 and R2 are calculated by measuring impedances at two points at different frequencies.
[0049]
First, the impedance of the fuel cell 10 at two different frequencies f1 and f2 is measured. As shown in FIG. 6, the coordinates of these two points on the complex plane are (a1, b1) and (a2, b2), respectively. The coordinates of these two points are located on the circumference of a semicircle centered on the real axis shown in FIG.
[0050]
Therefore, from the coordinates (a1, b1) and (a2, b2) of the two points, the coordinates (a_C, 0) and the radius R can be calculated. In this way, the impedance when the frequency is changed from a high frequency (ω = ∞) to a low frequency (ω = 0) can be calculated using the impedances at two points. At this time, R1 = (center X coordinate−circle radius) = (a_C-R), R2 = circle diameter = 2R. As described above, R1 and R2 can be calculated from the impedances at two points.
[0051]
Next, the state of the internal moisture content of the fuel cell 10 is determined. As described above, R1 corresponds to the resistance of the electrolyte membrane, and R2 corresponds to the resistance-converted activation overvoltage and diffusion overvoltage. For this reason, when R1 is larger than the preset first predetermined value and R2 is smaller than the second predetermined value, it is estimated that the resistance overvoltage has increased and the internal moisture content of the fuel cell 10 is insufficient. it can. Further, when R1 is smaller than the first predetermined value and R2 is larger than the second predetermined value, it can be estimated that the diffusion overvoltage has increased and the internal moisture content of the fuel cell 10 is excessive.
[0052]
When it is determined that the internal moisture content of the fuel cell 10 is insufficient, control is performed so that the internal moisture content of the fuel cell 10 is increased by the internal moisture content adjusting means such as the humidifiers 22 and 32. On the other hand, when it is determined that the internal moisture content of the fuel cell 10 is excessive, the internal moisture content of the fuel cell 10 is decreased by the humidifiers 22 and 32 and the like. Thereby, the internal moisture content of the fuel cell 10 can be maintained appropriately.
[0053]
As described above, according to the first embodiment, when the internal moisture content of the fuel cell 10 is estimated by the AC impedance method, it is only necessary to measure the impedance of the fuel cell 10 at two different frequencies. For this reason, since impedance can be measured in a short time, impedance measurement can be performed over time, and the moisture state (insufficient / excessive moisture) inside the fuel cell 10 can be grasped in real time. Become.
[0054]
(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is different from the first embodiment in the method for obtaining R1 and R2 in the equivalent circuit of FIG. The same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
[0055]
  FIG. 7 shows a procedure for calculating R1 and R2 in the second embodiment. Book number2In the embodiment, the impedance at one point at a predetermined frequency is measured, and R1 and R2 are calculated.
[0056]
First, the impedance of the fuel cell 10 at the predetermined frequency f3 is measured. As shown in FIG. 7, the coordinates of this point on the complex plane are (a3, b3). Next, when no sine wave current is applied by the sine wave oscillator 40, the value obtained by dividing the output voltage of the fuel cell 10 by the output current is set as R2 = (output voltage) as the impedance of the fuel cell 10 at frequency = 0. ) / (Output current). Consider this point at the coordinates of (R2,0).
[0057]
  (A3, b3) and (R2, 0) are bothFIG.It is located on the circumference of a semicircle centered on the real axis shown in FIG. Therefore, as in the first embodiment, the coordinates (a3, b3) and (R2, 0) of the two points are used as the coordinates (a_c, 0) and the radius R can be calculated. At this time, R1 = (center X coordinate−circle radius) = (a_c-R), R2 = circle diameter = 2R.
[0058]
As described above, R1 and R2 can be calculated in the same manner as in the first embodiment by measuring the impedance at one point at a predetermined frequency and measuring the output voltage and output current in the steady state.
[0059]
After thus seeking R1 and R2, similar to the first embodiment estimates the internal fuel cell 10 of the water status, and controls the internal moisture content of the fuel cell 10 by an internal water content adjusting means.
[0060]
As described above, according to the second embodiment, when estimating the internal moisture content of the fuel cell 10 by the AC impedance method, it is only necessary to measure the impedance of the fuel cell 10 in one predetermined frequency. For this reason, since the impedance can be measured in a short time as in the first embodiment, the impedance can be measured over time, and the moisture state in the fuel cell 10 (insufficient / excessive moisture). Can be grasped in real time.
[0061]
(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is different from the above embodiments in the method of estimating the internal water content from the impedance of the fuel cell 10.
[0062]
A method for estimating the moisture state inside the fuel cell 10 based on the impedance of the fuel cell 10 according to the third embodiment will be described with reference to FIGS. FIG. 8 shows the relationship between the impedance of the fuel cell 10 and the moisture state inside the fuel cell 10 when a sine wave having a predetermined frequency is applied.
[0063]
In FIG. 4, when the internal moisture content of the fuel cell 10 is insufficient and the resistance overvoltage increases, R1 increases on the complex plane. As R1 increases, the impedance Z at a predetermined frequency mainly increases the real component a and moves away from the origin on the complex plane. As a result, the absolute value r of the impedance Z increases and the phase angle θ of the impedance Z decreases. This means that the phase delay (response delay) of the voltage signal with respect to the current signal of the fuel cell 10 is reduced.
[0064]
On the other hand, when the internal moisture content of the fuel cell 10 is excessive and the diffusion overvoltage increases, R2 increases on the complex plane of FIG. As R2 increases, the impedance Z at a predetermined frequency mainly increases the imaginary component b and moves away from the origin on the complex plane. As a result, the absolute value r of the impedance Z increases, and the phase angle θ of the impedance Z increases. This means that the phase delay of the output voltage with respect to the output current of the fuel cell 10 becomes large.
[0065]
As described above, the moisture state in the fuel cell 10 has a correlation with the impedance phase angle of the fuel cell 10 (the phase delay of the voltage signal with respect to the current signal) and the absolute value. FIG. 8 shows these relationships, and three areas are set on the complex plane: 1) the optimal area, 2) the excessive area, and 3) the insufficient area. These areas are determined according to the load of the fuel cell 10.
[0066]
As shown in FIG. 8, the state of the internal moisture content of the fuel cell 10 can be estimated based on the phase angle of the impedance of the fuel cell 10. That is, when the phase angle of the impedance of the fuel cell 10 at a predetermined frequency is in the vicinity of the predetermined phase angle θo, the internal water content of the fuel cell is appropriate, and when the phase angle is smaller than the predetermined phase angle θo, the internal water content is insufficient. If the phase angle is larger than the predetermined phase angle θo, it can be determined that the amount of internal moisture is excessive. The predetermined phase angle θo, which is a criterion for determining the internal moisture content, is set in advance by the frequency of the applied sine wave or the like.
[0067]
Further, as shown in FIG. 8, the optimum region of the internal moisture amount is a region in which the real component and the imaginary component of the impedance of the fuel cell 10 are each smaller than a predetermined value. Therefore, when the absolute value of the impedance is smaller than the predetermined value, it can be determined that the internal moisture content is in the appropriate region.
[0068]
As described above, in the third embodiment, the moisture state in the fuel cell 10 can be estimated as follows by measuring the impedance of the fuel cell 10 at one predetermined frequency.
[0069]
1) Based on the phase angle of the impedance of the fuel cell 10, the state of the internal moisture content of the fuel cell can be determined.
[0070]
2) If the absolute value of the impedance is smaller than a predetermined value, it can be determined that the internal moisture content is in the optimum region.
[0071]
3) Moreover, after determining the output decrease of the fuel cell 10 with the voltage sensor 41, it is also possible to determine whether the moisture is insufficient or excessive based on the phase angle of the impedance.
[0072]
4) In addition, the optimum area, excess area, and insufficient area of the internal moisture amount on the complex plane are set in advance, and the moisture in the fuel cell 10 depends on which of the three areas the coordinates of the impedance on the complex plane are located. The state can be estimated.
[0073]
As described above, according to the third embodiment, when estimating the internal moisture content of the fuel cell 10 by the AC impedance method, it is only necessary to measure the impedance of the fuel cell 10 in one predetermined frequency. For this reason, as in the first embodiment, since the impedance can be measured in a short time, the impedance can be measured over time, and the moisture state inside the fuel cell 10 (insufficient / excessive moisture). Can be grasped in real time.
[0074]
(Other embodiments)
In each of the above embodiments, the sine wave oscillator 40 is configured to generate a sine wave current. However, the sine wave oscillator 40 may be configured to generate a sine wave voltage, and the DC voltage output from the fuel cell 10 is a sine wave. A wave voltage may be applied.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an overall configuration of a fuel cell system according to a first embodiment.
FIG. 2 is a characteristic diagram showing the content of a voltage drop in a fuel cell.
FIG. 3 is a circuit diagram showing an equivalent circuit of a fuel cell.
FIG. 4 is a characteristic diagram showing the impedance of the fuel cell.
FIG. 5 is a conceptual diagram illustrating the operation of an impedance detection unit.
FIG. 6 is a characteristic diagram showing an impedance calculation procedure when the frequency is changed from two impedance points.
FIG. 7 is a characteristic diagram showing an impedance calculation procedure when the frequency is changed from one point of impedance.
FIG. 8 is a characteristic diagram showing the relationship between the impedance of the fuel cell and the state of the internal moisture content.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 11 ... Inverter, 20 ... Air supply path, 21 ... Air supply apparatus, 22 ... Humidifier, 23 ... Back pressure adjustment valve, 30 ... Hydrogen supply path, 31 ... Hydrogen supply apparatus, 32 ... Humidifier, 33 ... Back pressure adjusting valve, 40 ... Sine wave oscillator, 41 ... Voltage sensor, 42 ... Current sensor, 43, 44 ... Filter unit, 45, 46 ... FFT processing unit, 47 ... Impedance analysis unit, 50 ... Control unit.

Claims (3)

Obtained by the complex impedance of the fuel cell when a fuel cell (10) is provided that obtains electric power by electrochemically reacting hydrogen and oxygen, and a sine wave signal is applied to the output signal of the fuel cell while changing the frequency. A fuel cell system for estimating a moisture state inside the fuel cell from a resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficient and a resistance component (R2) that increases when the internal moisture content of the fuel cell is excessive Because
Sine wave applying means (40) for applying a sine wave signal having an arbitrary frequency to the output signal of the fuel cell;
Voltage detection means (41) for detecting the output voltage of the fuel cell;
Current detection means (42) for detecting the output current of the fuel cell;
Impedance calculating means (43 to 47) for calculating the complex impedance of the fuel cell when two sine wave signals having a predetermined frequency are applied;
The impedance calculation means is the voltage detection means (41) when one of the complex impedances of the fuel cell at the two predetermined frequencies is applied with the sine wave signal of the predetermined frequency by the sine wave application means (40). ) And the output current detected by the current detection means (42),
When the other of the complex impedances of the fuel cell at the two predetermined frequencies is not applied by the sine wave applying means, the value obtained by dividing the output voltage by the output current is the frequency at 0. Calculated as the complex impedance of the fuel cell ,
The impedance computing means, said fuel and set the complex plane for displaying the complex impedance of the battery, the predetermined frequency of the one of the complex impedance when applying a sinusoidal signal coordinates (a3, b3), and the sine wave The coordinates (R2, 0) of the other complex impedance when no signal is applied are located on a semicircle centered on the real axis of the complex plane;
The impedance calculation means calculates the coordinates (a _c , 0) of the center of the semicircle and the radius (R) of the semicircle from the coordinates (a3, b3), (R2 , 0) of the two points ,
The resistance component (R1) that increases when the internal moisture content of the fuel cell is insufficient is calculated by subtracting the radius (R) of the semicircle from the coordinates ( _ac ) on the real axis at the center of the semicircle. ,
The fuel cell system, wherein the resistance component (R2) that increases when the internal moisture content of the fuel cell is excessive is calculated from a value that is twice the radius (R) of the semicircle . The fuel cell system according to claim 1 , wherein the output signal is an output current and an output voltage of the fuel cell, and the sine wave signal is a sine wave current or a sine wave voltage. An internal water content adjusting means (20-23, 30-33) for adjusting the internal water content of the fuel cell;
If the internal water content of the fuel cell based on the resistance component increases in the internal water content on low (R1) of the fuel cell is determined to be insufficient, the fuel cell by the internal water amount adjusting means Increase the internal moisture content,
When the internal water content of the fuel cell based on the fuel resistance component increases when the internal water volume overload of the battery (R2) is determined to be excessive, the interior of the fuel cell by the internal water amount adjusting means The fuel cell system according to claim 1 or 2, wherein the amount of water is reduced.

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