JP5109316B2 - Fuel cell system and fuel cell impedance measurement method - Google Patents

Description

  The present invention relates to a fuel cell system and a fuel cell impedance measurement method, and more particularly to a fuel cell system and a fuel cell impedance measurement method that enable measurement of the impedance of the fuel cell in order to detect the operating state of the fuel cell.

  It is known that the output of the fuel cell is affected by the internal state of the fuel cell, for example, the wetness of the electrolyte membrane. Since the wetness of the electrolyte membrane has a correlation with the complex impedance of the fuel cell, conventionally, an AC signal is applied to the output of the fuel cell, and both the amplitude ratio of the current to the voltage and the phase shift are detected. It has been proposed to calculate the complex impedance and monitor the operating state of the fuel cell.

  For example, in Japanese Patent Application Laid-Open No. 2003-86220, the complex impedance of a fuel cell when a sine wave signal is applied to the output signal of the fuel cell while changing the frequency from a high frequency to a low frequency is obtained. A fuel cell system that estimates the moisture state of a fuel cell from a resistance component R1 that increases when the amount of water is insufficient and a resistance component R2 that increases when the amount of internal moisture is excessive is described (Patent Document 1). The resistance component R1 is measured by applying a high-frequency sine wave signal, and the resistance component R2 is measured by applying a low-frequency sine wave signal.

  As a similar technique, Japanese Patent Laid-Open No. 2003-297408 describes a fuel cell system configured to detect the water content of a gas to be measured from one of the voltage and current of an electrochemical cell (Patent Document 2). ).

  Japanese Patent Application Laid-Open No. 2005-209635 discloses an electrolyte membrane quality during the operation of the fuel cell by detecting residual moisture in both the electrolyte membrane quality and in the reaction gas flow path to control the wetness of the reaction gas. A fuel cell power generation operation control method is described in which the residual moisture of the fuel cell is optimally controlled, thereby reducing or eliminating the scavenging time when the fuel cell is stopped and improving the startability at the time of restart (Patent Document) 3).

  Furthermore, in Japanese Patent Application Laid-Open No. 2005-332702, a DC / DC converter that steps up and down the voltage of a fuel cell including n cells or cell modules is used, and an alternating current with a predetermined frequency is applied to the fuel cell. A fuel cell diagnostic device is described in which an internal resistance is measured by measuring a voltage change for each cell or the like, and an abnormality for each cell or the like is detected from the internal resistance and reactance (Patent Document 4).

By measuring the impedance of the fuel cell by the above-described conventional technology, the moisture state inside the fuel cell could be indirectly grasped.
JP 2003-86220 (paragraphs 0007, 0004, etc.) JP 2003-297408 A (paragraph 0007 etc.) JP 2005-209635 A (paragraph 0087 etc.) JP-A-2005-332702 (paragraph 0014, etc.)

By the way, in the impedance measuring method in the conventional fuel cell system described above, the influence of the ambient conditions (for example, gas pressure and environmental temperature ) of the fuel cell main body on the measured value is not taken into account, so that a measurement error occurs. In addition, since this measurement error fluctuates with time, there is a problem that impedance measurement with high accuracy cannot be stably performed.

More specifically, even when the impedance of the fuel cell obtained by measurement is constant, the estimated value of the water content increases as the pressure of the fuel cell (hereinafter referred to as “FC pressure”) and the environmental temperature increase. There was an error that it would be larger than the actual value.

Therefore, in order to solve the above problems, the present invention estimates the water content of the fuel cell after correcting the influence of the ambient conditions (for example, gas pressure and environmental temperature ) of the fuel cell body on the measured impedance value. It aims at providing the fuel cell system which can do.

In order to solve the above-mentioned problems, a fuel cell system according to the present invention is a fuel cell system capable of measuring the impedance of a fuel cell, an impedance measuring means for measuring the impedance of the fuel cell, and an impedance measured by the impedance measuring means. Water content estimating means for estimating the water content of the fuel cell based on the relationship of the estimated water content of the fuel cell , and the fuel content decreases as the gas pressure of the fuel cell increases, and the fuel Provided is a fuel cell system in which an estimated water content is corrected based on a gas pressure and an environmental temperature of a fuel cell so that the water content decreases as the environmental temperature of the battery increases. Is.

In order to solve the above-mentioned problems, a fuel cell impedance measurement method according to the present invention includes a fuel cell impedance measurement method provided in the fuel cell system, the impedance measurement step for measuring the impedance of the fuel cell, and the impedance measurement step. A moisture content estimation step for estimating the moisture content of the fuel cell based on the relationship of the estimated moisture content of the fuel cell to the measured impedance, so that the moisture content decreases as the gas pressure of the fuel cell increases, and A correction step of correcting the estimated water content based on the gas pressure and the environmental temperature of the fuel cell so that the water content decreases as the environmental temperature of the fuel cell increases. .

Since it was configured in this manner, the influence of the gas pressure, which is the ambient condition of the fuel cell, on the measured impedance value and the influence of the environmental temperature of the fuel cell on the measured impedance value were corrected, and the fuel cell was corrected. Thus, it is possible to measure impedance with high accuracy and time stability without causing a measurement error.

Note that, as described above, the fuel cell power generation operation control method disclosed in Patent Document 3 (Japanese Patent Laid-Open No. 2005-209635) detects residual moisture in both the electrolyte membrane and the reaction gas channel. By controlling the wetness of the reaction gas, the residual moisture of the electrolyte membrane during the operation of the fuel cell is optimally controlled.In contrast, the present invention provides the ambient conditions of the fuel cell body (for example, Since the water content of the fuel cell is estimated in consideration of the influence of the gas pressure and the environmental temperature on the measured value of the impedance, the invention differs from the above-mentioned invention of Patent Document 3.

According to the present invention, the moisture content of the fuel cell can be estimated after correcting the influence of the gas pressure and the environmental temperature, which are one of the ambient conditions of the fuel cell main body, on the measured impedance value. In addition, it is possible to measure impedance with high accuracy and time stability.

  Next, preferred embodiments for carrying out the present invention will be described with reference to the drawings.

  In the embodiment of the present invention, the present invention is applied to a hybrid fuel cell system mounted on an electric vehicle. The following embodiments are merely examples of the application form of the present invention, and do not limit the present invention.

(Embodiment 1)
In the first embodiment, when estimating the water content of the fuel cell in the fuel cell system, the measured impedance value of the fuel cell is corrected by the environmental temperature of the fuel cell.

FIG. 1 is a configuration diagram showing an overall configuration of an electric system of a fuel cell system according to Embodiment 1 of the present invention.
The electric system of the fuel cell system shown in FIG. 1 includes a fuel cell 100, an anode gas supply system 1 that supplies hydrogen gas as an anode gas to the fuel cell 100, and a cathode that supplies air as a cathode gas to the fuel cell 100. The gas supply system 2 includes a control unit 3 that executes the impedance measurement method according to the present invention, and a power system 4 that is an impedance measurement target.

  The fuel cell 100 has a stack structure in which a plurality of cells (single cells) are stacked. Each cell has a structure in which a power generation body called MEA (Membrane Electrode Assembly) is sandwiched between a pair of separators having flow paths of hydrogen gas, air, and cooling water. The MEA has a structure in which a polymer electrolyte membrane is sandwiched between two electrodes, an anode electrode and a cathode electrode. The anode electrode is configured by providing a fuel electrode catalyst layer on a porous support layer, and the cathode electrode is configured by providing an air electrode catalyst layer on a porous support layer. In addition, as the form of the fuel cell, a phosphoric acid type, a molten carbonate type, or the like can be used.

  The fuel cell 100 undergoes a reverse reaction of water electrolysis, and hydrogen gas, which is anode gas, is supplied from the anode gas supply system 1 to the anode (cathode) electrode side. Air, which is a cathode gas containing oxygen, is supplied from the cathode gas supply system 2 to the cathode (anode) electrode side. A reaction such as the formula (1) is caused on the anode electrode side, and a reaction such as the formula (2) is caused on the cathode electrode side to circulate electrons and to pass a current.

H ₂ → 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)

  The anode gas supply system 1 includes a hydrogen tank 10 as a hydrogen gas supply source, an anode gas supply path 11, and an anode off gas discharge path 12. In addition, although not shown, a hydrogen pump for circulating hydrogen gas, a main valve and a regulating valve, a shut-off valve, a check valve, a gas-liquid separator, etc. necessary for hydrogen gas management control may be provided. .

  The hydrogen tank 10 is filled with high-pressure hydrogen gas. As a hydrogen supply source, various types such as a hydrogen tank using a hydrogen storage alloy, a hydrogen supply mechanism using a reformed gas, a liquid hydrogen tank, and a liquefied fuel tank can be applied in addition to a high-pressure hydrogen tank. The anode gas supply path 11 is a pipe for supplying high-pressure hydrogen gas, and may be provided with a pressure regulating valve (regulator) or the like not shown. The hydrogen gas supplied from the anode gas supply path 11 is supplied to the anode electrode side of each single cell via the manifold in the fuel cell 100, and after an electrochemical reaction occurs at the anode of the MEA, the anode offgas (hydrogen offgas). As discharged. The anode off-gas discharge path 12 is a path for discharging the anode off-gas discharged from the fuel cell 100, and may form a circulation path. In order to form the circulation path, the anode off-gas is again returned to the anode gas supply path 11 via a check valve and an ejector (not shown).

  The cathode gas supply system 2 includes a compressor 20, a cathode gas supply path 21, and a cathode offgas discharge path 22. In addition, although not shown in FIG. 1, a humidifier for controlling the humidity of the air that is the cathode gas, a gas-liquid separator that removes the cathode offgas (air offgas), and a diluter for mixing the anode offgas with the cathode offgas. A silencer or the like may be provided.

The compressor 20 compresses air taken in from an air cleaner or the like by rotating at a rotational speed based on a compressor control signal C _COMP from the control unit 3, changes the air amount and air pressure, and the cathode side of the fuel cell 100. To supply. In the fuel cell 100, the air supplied from the cathode gas supply path 21 is supplied to the cathode electrode side of each single cell via the manifold in the same manner as the hydrogen gas, and causes an electrochemical reaction at the cathode of the MEA as a cathode off gas. Discharged. The cathode offgas discharged from the fuel cell 100 is discharged after being diluted with the anode offgas.

  The power system 4 includes a battery 40, a DC-DC converter 41, a traction inverter 42, a traction motor 43, an auxiliary inverter 44, a high voltage auxiliary machine 45, a battery computer 46, a current sensor 47, a voltage sensor 48, a backflow prevention diode 49, and the like. I have.

  The battery 40 is a chargeable / dischargeable secondary battery. As the battery, various types of secondary batteries such as a nickel-hydrogen battery can be used. Instead of the secondary battery, a chargeable / dischargeable power storage device such as a capacitor can be used. The battery 40 can output a high voltage by stacking a plurality of battery units that generate power at a constant voltage and connecting them in series.

  The battery computer 46 is provided at the output terminal of the battery 40 and can communicate with the control unit 3. The battery computer 46 monitors the state of charge of the battery 40, maintains the battery within an appropriate charge range that does not lead to overcharge or overdischarge, and controls the control unit if the battery becomes overcharged or overdischarged. 3 is notified.

  The DC-DC converter 41 increases / decreases the voltage between the primary side and the secondary side to distribute power. For example, the output voltage of the primary side battery 40 is boosted to the output voltage of the secondary side fuel cell 100, and power is supplied to load devices such as the traction motor 43 and the high voltage auxiliary machine 45. On the contrary, surplus power of the fuel cell 100 and regenerative power from the load device are allowed to pass down on the secondary side in order to charge the primary battery 40 in a step-down manner.

In particular, the DC-DC converter 41 can control the power line voltage on the fuel cell side based on the converter control signal C _CONV from the control unit 3. The converter control signal C _CONV includes a superimposed signal for causing the output voltage of the DC-DC converter 41 to sine-wave with a predetermined amplitude around a predetermined target voltage. This superimposed signal is preferably configured to include two types of frequency components, high and low. Since the frequency characteristics of the impedance change according to the internal state of the electrolyte membrane, such as the moisture retention amount of the electrolyte membrane, the residual moisture content of the electrolyte membrane is detected by measuring the impedance at at least two different frequencies. Because it is possible. For example, the internal state of the fuel cell can be inferred by setting a frequency around 300 Hz as a high-frequency AC signal and a frequency below 10 Hz as a low-frequency AC signal.

  The traction inverter 42 converts direct current into three-phase alternating current and supplies it to the traction motor 43. The traction motor 43 is, for example, a three-phase motor and is a main power source of an automobile on which the fuel cell system is mounted.

  The auxiliary machine inverter 44 is a DC-AC converting means for driving the high-voltage auxiliary machine 45. The high-pressure auxiliary machine 45 is various motors necessary for the operation of the fuel cell system, such as the compressor 20, a hydrogen pump, and a cooling system motor.

  The current sensor 47 can detect a current on the secondary side of the DC-DC converter 41 and supply it to the control unit 3 as a current detection signal Si. The voltage sensor 48 can detect the secondary side voltage and supply it to the control unit 3 as the voltage detection signal Se.

  The control unit 3 includes a CPU (Central Processing Unit), RAM, ROM, interface circuit, and the like as a general-purpose computer. The control unit 3 sequentially controls the entire fuel cell system including the anode gas supply system 1, the cathode gas supply system 2, and the power system 4 by sequentially executing software programs stored in a built-in ROM or the like. The impedance measurement method of the present invention can be executed in a fuel cell system.

  Specifically, the control unit 3 is divided into the following several operation blocks. In particular, filters 30 and 31, FFT processing units 32 and 33, a correction processing unit 34, an impedance analysis unit 35, a determination unit 36, a storage device 37, a temperature sensor 38, and a pressure sensor 39 are provided as blocks related to impedance measurement. ing.

  The filters 30 and 31 are band-pass filters and allow only the frequency component superimposed on the power line by the DC-DC converter 41 to pass therethrough. The filter 30 allows only a frequency component related to impedance measurement to pass through the current detection signal Si detected by the current sensor 47. The filter 31 allows only a frequency component related to impedance measurement to pass through the voltage detection signal Se detected by the voltage sensor 48.

The FFT processing units 32 and 33 perform a fast Fourier transform operation on the current detection signal Si and the voltage detection signal Se, and the current detection signal Si and the voltage detection signal Se in the measurement frequency component are respectively a real part and an imaginary part (a _i + jb _i , a _e + jb _e ).

The impedance analyzer 35 calculates an impedance X (aX + jbX) based on the FFT-processed voltage detection signal and current detection signal, and a distance (effective value) r (= √ ((aX ) ² + (bX) ² ) and the phase angle θ (= tan ⁻¹ (b / a)), and the impedance in the AC signal of the applied frequency is obtained.

Here, the correction processing unit 34 corrects a phase lag or gain fluctuation that occurs according to the filter characteristics of the filters 30 and 31. Based on the phase delay and gain fluctuation of the filters 30 and 31 that are measured in advance, the correction processing unit 34 uses the coefficients (a _i , b _i , a _e , b _e) of the real and imaginary parts in the FFT processing units 32 and 33. ). By this correction processing, an actual voltage detection signal and current detection signal from which the phase delay and gain fluctuation caused by the filter characteristics are removed can be obtained.

Determining unit 36, the effective value and phase angle obtained in the impedance analyzer 35, or the real part of the complex plane at two different frequencies f1 and f2 and the imaginary part _{(aX f1, bX f1) (} aX f2, bX f2 ) Is stored in the storage device 37. To obtain the resistance overvoltage and diffusion overvoltage of the fuel cell, obtain the impedance curve in the complex plane by geometric calculation based on two points in the complex plane, and set the resistance value when the frequency is zero to the resistance of the electrolyte membrane. And the resistance value when the frequency is infinite is the resistance conversion value of the activation overvoltage and the diffusion overvoltage.

  If the impedance is obtained and stored while changing the frequency of the AC signal to be superimposed, the impedance curve can be obtained without performing a special geometric operation.

The temperature sensor 38 measures the temperature at the outlet of the coolant that cools the fuel cell 100, that is, the environmental temperature of the fuel cell 100, and outputs the temperature detection signal _ST to the control unit 3. The pressure sensor 39, the inlet pressure of the anode gas to the fuel cell 100 in the anode gas supply system 1 to the fuel cell 100 is measured and output to the control unit 3 as a pressure detection signal S _P.

  Here, the control unit 3 is configured to perform various controls of the fuel cell system based on the impedance measurement result, and scavenging for reducing the residual water content in the fuel cell to an appropriate value when the fuel cell system is stopped. Processing is also configured to be executable.

In particular, in the present invention, the control unit 3 receives the temperature detection signal S _T from the temperature sensor 38 and the pressure detection signal S _P from the pressure sensor 39, and is measured in order to grasp the appropriate water content for judgment. It is configured to correct impedance or moisture content. In the first embodiment, correction based on temperature is performed, correction based on pressure is performed in the second embodiment, and correction based on temperature and pressure is performed in the third embodiment. This will be described in detail below.

In Embodiment 1, measures the environmental temperature T of the fuel cell 100, a temperature sensor 38 for outputting a temperature detection signal S _T corresponding to the environmental temperature becomes essential component, the gas of the fuel cell 100 the pressure P a pressure sensor 39 that outputs a pressure detection signal S _P measured becomes optional components.

FIG. 2 is a functional block diagram relating to impedance measurement and scavenging processing of the fuel cell system according to Embodiment 1 of the present invention.
As shown in FIG. 2, the control unit 3 includes a target voltage determination unit 51, a superimposed signal generation unit 52, a converter control signal generation unit 53, and an impedance measurement / scavenging process control unit 54 as functional blocks.

  The target voltage determination unit 51 determines an output target voltage, that is, a secondary side voltage (for example, 300 V) that serves as a reference voltage before superimposing the sine wave, and outputs it to the converter control signal generation unit 53.

  The superimposed signal generation unit 52 determines the frequency (for example, 300 Hz, 10 Hz) and amplitude (for example, 2 V) of the superimposed signal, which is a sine wave signal for impedance measurement to be superimposed on the power system, and generates the converter control signal. To the unit 53.

The converter control signal generator 53 is a secondary voltage value to be commanded to the converter 41 when the superimposed signal supplied from the superimposed signal generator 52 is superimposed on the output target voltage supplied from the target voltage determiner 51. _Are continuously generated and output to the DC-DC converter 41 as a converter control signal C _CONV . As the DC-DC converter 41 continuously changes the power line voltage on the secondary side in accordance with the command of the converter control signal C _CONV , a sine wave is superimposed on the secondary side of the DC-DC converter 41.

  The impedance measurement / scavenging process control unit 54 relates to the present invention, and is means for calculating the impedance of the fuel cell, means for estimating the water content of the fuel cell, means for correcting the impedance or / and the water content, water content And a means for controlling the scavenging process based on the above. The impedance measurement / scavenging processing control unit 54 is realized by the filters 30 and 32, the FFT processing units 32 and 33, the correction processing unit 34, the impedance analysis unit 35, and the determination unit 36 described in FIG.

FIG. 3 shows a more detailed functional block diagram of the impedance measurement / scavenging process control unit 54 in the first embodiment.
The impedance measurement / scavenging process control unit 54 shown in FIG. 3 includes impedance calculation means 1040, impedance temperature correction means 1041, moisture content estimation means 1042, scavenging amount calculation means 1043, and compressor control means 1044.

  The impedance calculation means 1040 uses the output voltage (FC voltage) Vf of the fuel cell 1 detected by the voltage sensor 48 and the output current (FC current) If of the fuel cell 100 detected by the current sensor 47 at a predetermined sampling rate. Sampling is performed, and the impedance X of the fuel cell 100 is output.

  The impedance temperature correction unit 1041 corrects the impedance of the fuel cell 100 measured by the impedance calculation unit 1040 based on the environmental temperature T of the fuel cell 100 detected by the temperature sensor 38.

  The water content estimation means 1042 is a functional block that estimates the water content of the fuel cell 100 based on the temperature-corrected impedance temperature correction value Xat. Details will be described later.

  The scavenging amount calculation means 1043 calculates the amount of air necessary to reduce the estimated water content in the fuel cell 100 to an appropriate water content. Details will be described later.

The compressor control means 1044 calculates the rotation speed and scavenging time of the compressor 20 for obtaining the necessary air amount calculated by the scavenging amount calculation means 1043, and drives the compressor at the calculated rotation speed for the calculated scavenging time. The compressor control signal C _COMP is output to the compressor 20.

Next, the water content estimation / scavenging operation in the present embodiment will be described.
First, an impedance correction method performed by the impedance temperature correction unit 1041 will be described.
FIG. 4 shows the relationship between the impedance and the environmental temperature in the fuel cell.

  As shown in FIG. 4, in an actual fuel cell system, the water content of the fuel cell varies depending on the environmental temperature even if the impedance value is the same. Conversely, the impedance for estimating the same water content tends to decrease as the temperature increases. Therefore, in the first embodiment, the impedance temperature correction means 1041 takes into account the temperature characteristics as shown in FIG. 4 so that the impedance decreases as the environmental temperature T of the fuel cell 100 increases at the impedance X. The impedance X of the battery 100 is corrected. More specifically, the impedance X measured by the following procedure is corrected.

  First, the impedance temperature correction unit 1041 inputs the measured impedance X. Next, a temperature compensation calculation is performed on the input impedance X based on the environmental temperature T of the fuel cell 100, and an impedance temperature correction value Xat is output.

The correction method based on the environmental temperature T can be performed, for example, by a method according to the equation (3) (that is, Arrhenius law). Here, X _T impedance at environmental temperature T, R0 is the impedance at the reference temperature (reference impedance), C1, C2 is a predetermined coefficient which depends on the type of water and fuel cells.
X _{T /} X0 = −C1 + C2 / ( _{T [} ° C.] + 273.15) (3)
(3) by equation can be calculated impedance X _T corresponding to the environmental temperature T on the basis of the reference impedance X0 with respect to the reference temperature. Therefore, the impedance temperature correction unit 1041 calculates the temperature correction value Xat from the measured impedance X based on the equation (3), and outputs it to the water content estimation unit 1042.

FIG. 5 shows a timing chart of how the impedance and water content of the fuel cell change due to the scavenging process.
As shown in FIG. 5, there is a correlation between the water content of the fuel cell and the impedance of the fuel cell. For example, the relationship between the water content of the fuel cell 100 and the impedance of the fuel cell 100 in the fuel cell system is measured and stored as a relationship table under conditions of a specific environmental temperature (for example, 25 ° C.) and pressure (for example, 1 atm). If so, the correct water content of the fuel cell can be estimated from the measured impedance.

  The moisture content estimation means 1042 stores a relationship table between the impedance of the fuel cell 100 and the moisture content accurately measured at a specific reference environmental temperature. The moisture content estimation means 1042 reads the moisture content from the relation table based on the input impedance, and outputs the read moisture content as the estimated moisture content at the impedance. In addition to storing the reference table in advance, the estimated water content with respect to the impedance may be calculated based on a predetermined relational expression.

  Here, if the fuel cell 100 is operating at a reference environmental temperature, the correct moisture content can be measured only by directly inputting the impedance X measured by the impedance computing means 1040 to the moisture content estimating means 1042. Is possible. However, as described above, it can be said that the impedance has temperature characteristics. Moreover, since the impedance corresponds to the water content, it can be said that the water content has temperature characteristics.

  Therefore, in the present embodiment, the impedance X is measured by the impedance temperature correction means 1041 based on the environmental temperature T in a fuel cell that is normally operated at a relatively high temperature, and is used as a reference for estimating the water content. The impedance temperature correction value Xat converted to the environmental temperature is calculated, and the appropriate water content can be estimated even at the environmental temperature T deviating from the reference environmental temperature.

Furthermore, the flow from the stop of the fuel cell operation to the scavenging process will be described with reference to the timing chart of FIG.
In FIG. 5, the target moisture content value of the fuel cell is the optimum moisture content that should remain when the fuel cell is stopped. The impedance target value is an impedance to be measured in order to achieve the water content target value at the reference environmental temperature.

When the power generation of the fuel cell 100 is stopped at time T0, the impedance measurement / scavenging process control unit 54 measures the impedance and estimates the water content of the fuel cell 100 when the power generation is stopped. Then, the rotation speed of the compressor 20 is determined so that the water content of the fuel cell decreases to the water content target value at a time T1 after a predetermined time suitable for the scavenging process, and the compressor 20 starts scavenging at this rotation speed. Compressor control signal C _COMP is output. When scavenging is started, the water content of the fuel cell decreases as shown in FIG. 5, but simultaneously with the start of scavenging, the environmental temperature of the fuel cell also decreases, and the water content decreases and the temperature decreases according to the characteristics of FIG. As a result, the impedance also rises. Thereafter, the impedance measurement / scavenging process control unit 54 measures the impedance periodically (ideally immediately before time T1), and determines whether the water content has approached the water content target value as planned.

  Here, if the reference ambient temperature remains constant, the impedance changes as shown in the ideal impedance curve of FIG. 5 and reaches the impedance target value at time T1, at which time the water content converges to the water content target value. Should be. However, as described above, the impedance X to be measured has a temperature characteristic, and the degree of deviation of the impedance measurement value from the ideal impedance value due to the change of the environmental temperature can be understood from FIG. The less it becomes, the more noticeable it becomes. If the water content is estimated without performing the temperature correction of the impedance, the impedance measurement value has a characteristic as shown by the solid line in FIG. 5 and tends to measure an impedance higher than the ideal impedance curve. For this reason, at the time ta when the preset impedance target value is reached, the actual water content of the fuel cell is larger than the target value.

  In this regard, in the first embodiment, the water content is estimated based on the impedance temperature correction value Xat obtained by correcting the impedance X measured by the impedance temperature correction unit 1041 based on the environmental temperature T. In FIG. 5, the error of the impedance temperature correction value subjected to temperature correction is reduced toward the impedance ideal curve. Therefore, the impedance temperature correction value Xat reaches the impedance target value at time tb, and the water content can be brought close to the target value by scavenging for the time length Δt (= tb−ta). Since the water content at time tb is substantially close to the water content target value, there is no problem even if the scavenging process is terminated at this time.

The impedance measurement / scavenging process control unit 54 determines that the impedance Xat has reached the impedance target value and has reached the moisture content target value, and outputs a compressor control signal C _COMP for stopping the operation of the compressor 20. Move to a total stop.

  In the above-described embodiment, the moisture content is estimated after calculating the impedance temperature correction value Xat obtained by converting the measured impedance X into the impedance at the reference environmental temperature. However, the present invention is not limited to this. As described above, it can be said that the impedance has temperature characteristics, but the estimated water content can also be said to have temperature characteristics.

  Thus, instead of providing the impedance temperature correction means 1041, a similar effect can be obtained by providing a means for correcting the temperature of the water content estimated by the water content estimation means 1042. For example, referring to FIG. 5, the moisture content estimation means 1042 estimates the moisture content based on the measured impedance measurement value (solid line), but further includes the moisture content estimated from the impedance. Correction for estimating that the value obtained by subtracting the water amount correction amount Δq is the correct water content is performed. Whether or not to stop the scavenging process may be determined based on the estimated and corrected water content instead of the impedance.

  As described above, according to the first embodiment, even if the impedance measurement value of the fuel cell 100 is different from the actual impedance value due to the influence of the environmental temperature, the impedance measurement / scavenging process control unit 54 actually Since the scavenging process is controlled based on the corrected impedance value close to the impedance value, the scavenging process for obtaining an appropriate water content can be performed.

(Embodiment 2)
In the second embodiment, when estimating the water content of the fuel cell in the fuel cell system, the measured impedance value of the fuel cell is determined by the gas pressure of the gas (anode gas or cathode gas) supplied to the fuel cell. It is configured to correct.

  The overall configuration of the electrical system and the overall configuration of the mechanical system of the fuel cell system according to Embodiment 2 of the present invention are the same as the overall configuration of the electrical system of the fuel cell system according to Embodiment 1 of the present invention. Since only the processing of the impedance measurement / scavenging process control unit 54 is different, the difference will be mainly described below.

However, in the second embodiment, the gas pressure P of the fuel cell 100 is measured and the pressure detection signal _SP is output in the overall configuration (FIG. 1) of the electric system of the fuel cell system according to the first embodiment of the present invention described above. a pressure sensor 39 which is a mandatory component, measuring the environmental temperature T of the fuel cell 100, a temperature sensor 38 for outputting a temperature detection signal S _T corresponding to the environmental temperature becomes optional components.

FIG. 6 shows a more detailed functional block diagram of the impedance measurement / scavenging process control unit 54 in the second embodiment.
The impedance measurement / scavenging process control unit 54 shown in FIG. 6 includes impedance calculation means 1040, impedance pressure correction means 2041, moisture content estimation means 1042, scavenging amount calculation means 1043, and compressor control means 1044.

  The impedance calculation means 1040, the water content estimation means 1042, the scavenging amount calculation means 1043, and the compressor control means 1044 are substantially the same as in the first embodiment.

  The impedance pressure correction unit 2041 corrects the impedance of the fuel cell 100 measured by the impedance calculation unit 1040 based on the gas pressure P of the fuel cell 100 detected by the pressure sensor 39. Hereinafter, an impedance correction method will be described.

FIG. 7 shows the relationship between the impedance and gas pressure in the fuel cell.
As shown in FIG. 7, in an actual fuel cell system, the water content of the fuel cell varies depending on the gas pressure even with the same impedance value. Conversely, the impedance for estimating the same water content tends to decrease as the gas pressure increases. Therefore, in the second embodiment, the impedance pressure correction means 2041 takes into account the pressure characteristics as shown in FIG. 7 so that the impedance decreases as the gas pressure P of the fuel cell 100 increases at the impedance X. The impedance X of the battery 100 is corrected. More specifically, the impedance X measured by the following procedure is corrected.

  The impedance pressure correction means 2041 first inputs the measured impedance X. Next, the input impedance X is subjected to a pressure compensation calculation based on the gas pressure P of the fuel cell 100, and an impedance pressure correction value Xap is output.

  The correction method based on the gas pressure P is, for example, by converting the surface pressure from the gas pressure P, obtaining the relationship between the surface pressure and the contact resistance per unit area, and calculating the change in the overall resistance value. Impedance can be corrected. Regarding the pressure, a relational expression between the gas pressure and the impedance according to the Arrhenius law described in the embodiment can also be used. The relationship between pressure and resistance value change can be obtained experimentally in advance and stored as a relationship table for use, or an approximate expression can be obtained in advance from experimental results, etc., and an operation based on the approximate expression can be performed. It is also possible to configure as described above. The impedance pressure correction unit 2041 calculates a pressure correction value Xap from the measured impedance X based on the correction method and outputs the pressure correction value Xap to the water content estimation unit 1042.

The water content estimation means 1042 estimates the water content of the fuel cell 100 based on the pressure-corrected impedance pressure correction value Xap. The scavenging amount calculation means 1043 calculates the amount of air necessary to reduce the estimated water content in the fuel cell 100 to an appropriate water content. Then, the compressor control means 1044 calculates the rotation speed and scavenging time of the compressor 20 for obtaining the necessary air amount calculated by the scavenging amount calculation means 1043, and drives the compressor at the calculated rotation speed for the calculated scavenging time. A compressor control signal C _COMP for causing the compressor 20 to output is output to the compressor 20.

Next, the water content estimation / scavenging operation in the second embodiment will be described with reference to FIG.
In FIG. 8, the target moisture content value of the fuel cell is the optimum moisture content that should remain when the fuel cell is stopped. The impedance target value is an impedance to be measured in order to achieve the water content target value at the reference gas pressure.

When the power generation of the fuel cell 100 is stopped at time T0, the impedance measurement / scavenging process control unit 54 measures the impedance and estimates the water content of the fuel cell 100 when the power generation is stopped. Then, the rotation speed of the compressor 20 is determined so that the water content of the fuel cell decreases to the water content target value at a time T1 after a predetermined time suitable for the scavenging process, and the compressor 20 starts scavenging at this rotation speed. Compressor control signal C _COMP is output. When scavenging is started, the water content of the fuel cell decreases as shown in FIG. 8, but the gas pressure also decreases with the start of scavenging. With the decrease in the water content and gas pressure according to the characteristics of FIG. Impedance also increases. Thereafter, the impedance measurement / scavenging process control unit 54 measures the impedance periodically (ideally immediately before time T1), and determines whether the water content has approached the water content target value as planned.

  Here, if the reference gas pressure remains constant, the impedance changes as shown in the ideal impedance curve of FIG. 8, reaches the impedance target value at time T1, and at that time the water content converges to the water content target value. Should be. However, as described above, the impedance X to be measured has a pressure characteristic, and the degree of deviation of the impedance measured value from the ideal impedance value due to the change in gas pressure can be understood from FIG. The less it becomes, the more noticeable it becomes. If the moisture content is estimated without performing impedance pressure correction, the impedance measurement value has a characteristic as shown by the solid line in FIG. 8 and tends to measure an impedance higher than the ideal impedance curve. For this reason, at the time ta when the preset impedance target value is reached, the actual water content of the fuel cell is larger than the target value.

  In this regard, in the second embodiment, the water content is estimated based on the impedance pressure correction value Xap obtained by correcting the impedance X measured by the impedance pressure correction means 2041 based on the gas pressure P. In FIG. 8, the error of the impedance pressure correction value subjected to pressure correction is reduced toward the ideal impedance curve. Therefore, the impedance pressure correction value Xap reaches the impedance target value at time tb, and the water content can be brought close to the target value by scavenging for the time length Δt (= tb−ta). Since the water content at time tb is substantially close to the water content target value, there is no problem even if the scavenging process is terminated at this time.

The impedance measurement / scavenging process control unit 54 determines that the impedance Xap has reached the impedance target value and has reached the moisture content target value, and outputs a compressor control signal C _COMP for stopping the operation of the compressor 20. Move to a total stop.

  In the second embodiment, the moisture content is estimated after calculating the impedance pressure correction value Xap obtained by converting the measured impedance X into the impedance at the reference gas pressure. However, the present invention is not limited to this. As described above, it can be said that the impedance has pressure characteristics, but the estimated water content can also be said to have pressure characteristics.

  Therefore, instead of providing the impedance pressure correcting means 2041, a similar effect can be obtained by providing means for correcting the pressure of the water content estimated by the water content estimating means 1042. For example, referring to FIG. 8, the moisture content estimation means 1042 estimates the moisture content based on the measured impedance measurement value (solid line), but further includes the moisture content estimated from the impedance. Correction for estimating that the value obtained by subtracting the water amount correction amount Δq is the correct water content is performed. Whether or not to stop the scavenging process may be determined based on the estimated and corrected water content instead of the impedance.

  As described above, according to the second embodiment, even when the measured impedance value of the fuel cell 100 is different from the actual impedance value due to the influence of the gas pressure, the impedance measurement / scavenging process control unit 54 actually Since the scavenging process is controlled based on the corrected impedance value close to the impedance value, the scavenging process for obtaining an appropriate water content can be performed.

(Embodiment 3)
In the third embodiment, when the water content of the fuel cell in the fuel cell system is estimated, the measured impedance value of the fuel cell is determined based on the ambient temperature of the fuel cell and the gas (anode gas or The gas pressure of the cathode gas is corrected.

  The overall configuration of the electrical system and the overall configuration of the mechanical system of the fuel cell system according to Embodiment 3 of the present invention are the same as the overall configuration of the electrical system of the fuel cell system according to Embodiment 1 of the present invention. Since only the processing of the impedance measurement / scavenging process control unit 54 is different, the difference will be mainly described below.

In particular, in the third embodiment, the temperature sensor 38 and measures the gas pressure P the pressure sensor 39 that outputs a pressure detection signal S _P and outputs the measured environmental temperature T of the fuel cell 100 temperature detection signal S _T are both An essential component.

FIG. 9 shows a more detailed functional block diagram of the impedance measurement / scavenging process control unit 54 in the third embodiment.
9 includes an impedance calculation unit 1040, an impedance temperature correction unit 1041, an impedance pressure correction unit 2041, a water content estimation unit 1042, a scavenging amount calculation unit 1043, and a compressor control unit 1044. .

  Among these, the impedance calculation means 1040, the impedance temperature correction means 1041, the water content estimation means 1042, the scavenging amount calculation means 1043, and the compressor control means 1044 are substantially the same as those in the first embodiment, and the impedance pressure correction means 2041. Is substantially the same as in the second embodiment.

  In the third embodiment, the temperature of the impedance is corrected as in the first embodiment and then the pressure of the impedance is corrected as in the second embodiment. is there.

Based on FIG. 10, the water content estimation / scavenging operation in the third embodiment will be described.
In FIG. 10, the target moisture content value of the fuel cell is the optimum moisture content that should remain when the fuel cell is stopped. The impedance target value is an impedance to be measured in order to achieve the water content target value at the reference environmental temperature and the reference gas pressure.

When the power generation of the fuel cell 100 is stopped at time T0, the impedance measurement / scavenging process control unit 54 measures the impedance and estimates the water content of the fuel cell 100 when the power generation is stopped. Then, the rotation speed of the compressor 20 is determined so that the water content of the fuel cell decreases to the water content target value at a time T1 after a predetermined time suitable for the scavenging process, and the compressor 20 starts scavenging at this rotation speed. Compressor control signal C _COMP is output. When scavenging is started, the water content of the fuel cell decreases as shown in FIG. 10, but the environmental temperature and gas pressure also decrease with the start of scavenging, and according to the characteristics of FIG. 4 and FIG. As the ambient temperature and gas pressure decrease, the impedance also increases. Thereafter, the impedance measurement / scavenging process control unit 54 measures the impedance periodically (ideally immediately before time T1), and determines whether the water content has approached the water content target value as planned.

  Here, if the reference ambient temperature and gas pressure remain constant, the impedance changes as shown in the ideal impedance curve of FIG. 10, reaches the impedance target value at time T1, and the water content at that time is the water content target. It should converge to the value. However, as described above, the measured impedance X has temperature characteristics and pressure characteristics, and the degree of deviation of the impedance measurement value from the ideal impedance value due to changes in environmental temperature and gas pressure is low in water content. It will become more prominent.

  In the third embodiment, both the impedance temperature correction unit 1041 and the impedance pressure correction unit 2041 in the first embodiment are provided. First, the impedance temperature correction means 1041 corrects the measured impedance X based on the environmental temperature T to obtain an impedance temperature correction value Xat. The impedance pressure correction means 2041 further corrects the correction value Xat based on the gas pressure P, thereby obtaining the impedance temperature pressure correction value Xatp. The water content estimation means 1042 estimates the water content based on the impedance temperature pressure correction value Xatp.

  As can be seen from FIG. 10, the impedance temperature / pressure correction value subjected to both temperature correction and pressure correction has a characteristic that is substantially similar to an ideal impedance curve because a factor that greatly affects impedance is corrected. For this reason, the time when the impedance temperature / pressure correction value Xatp reaches the impedance target value has almost no error from the time T1 when the impedance ideal curve reaches the impedance target value. Therefore, according to the third embodiment, the operation of the entire system can be stopped in a state that is substantially close to the water content target value.

  Note that various modifications can be made to the temperature correction and the pressure correction as described in the first and second embodiments. In addition, the water content estimation means 1042 can reduce the water content correction amount Δq considering the environmental temperature T and the gas pressure P to estimate an appropriate water content, as in the above embodiment.

  As described above, according to the third embodiment, even when the measured impedance value of the fuel cell 100 is different from the actual impedance value due to the influence of the environmental temperature and the gas pressure, the impedance measurement / scavenging process control unit 54. Since the scavenging process is controlled based on the corrected impedance value close to the actual impedance value, the scavenging process for obtaining an appropriate water content can be performed.

  In particular, in the third embodiment, since the moisture content of the fuel cell is estimated after correcting the influence of the ambient temperature and gas pressure, which are ambient conditions of the fuel cell body, on the measured impedance value, a measurement error occurs. In addition, there is an effect that it is possible to provide a fuel cell system that enables more accurate impedance measurement that is time-stable and more accurate.

(Other embodiments)
The present invention can be applied with various modifications other than the above embodiment.
For example, in the third embodiment, the correction for the gas pressure is performed after the correction of the environmental temperature. However, this order is changed, and the correction for the environmental temperature is performed after the correction for the gas pressure. It is also possible.

  Furthermore, the present invention can be applied to other fuel cell systems as long as a device for measuring the impedance of the fuel cell is provided, for example, since a converter is not used, the impedance is different from the above-described method. The present invention can also be applied to a fuel cell system that performs measurement.

  In each of the above embodiments, the hybrid fuel cell system mounted on a vehicle that is a moving body has been exemplified. However, the present invention is mounted not only on an automobile but also on other moving bodies such as ships, aircrafts, and the like. There may be. Of course, the present invention may be applied to a stationary hybrid fuel cell system.

1 is a configuration diagram showing an overall configuration of a fuel cell system according to an embodiment of the present invention. The block diagram which shows the functional block of the control part 3 which concerns on embodiment of this invention is shown. The functional block diagram which concerns on the impedance measurement and scavenging process control of Embodiment 1 of this invention is shown. In the graph which shows the relationship between an impedance and temperature, even if it is the same impedance value, it is explanatory drawing which shows a mode that the moisture content of a fuel cell changes with temperature. It is a timing chart which shows change of environmental temperature, impedance, and moisture content from the power generation stop of a fuel cell to the end of scavenging processing. The functional block diagram which concerns on the impedance measurement and scavenging process control of Embodiment 2 of this invention is shown. In the graph which shows the relationship between an impedance and a pressure, it is explanatory drawing which shows a mode that the moisture content of a fuel cell changes with pressure even if it is the same impedance value. 6 is a timing chart showing changes in gas pressure, impedance, and moisture content from when the fuel cell stops generating power to when the scavenging process ends. The functional block diagram which concerns on the impedance measurement and scavenging process control of Embodiment 3 of this invention is shown. 10 is a timing chart showing changes in impedance and water content from the stop of power generation of the fuel cell to the end of the scavenging process in Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Anode gas supply system, 2 ... Cathode gas supply system, 3 ... Control part, 4 ... Electric power system, 10 ... Hydrogen tank, 11 ... Anode gas supply path, 12 ... Anode off-gas discharge path, 20 ... Compressor, 21 ... Cathode Gas supply path, 22 ... Cathode off gas discharge path, 30 · 31 ... Filter, 32 · 33 ... FFT processing section, 34 ... Correction processing section, 35 ... Impedance analysis section, 36 ... Judging section, 37 ... Storage device, 38 ... Temperature Sensor, 39 ... Pressure sensor, 40 ... Battery, 41 ... Converter, 42 ... Traction inverter, 43 ... Traction motor, 44 ... Auxiliary inverter, 45 ... High voltage auxiliary machine, 46 ... Battery computer, 47 ... Current sensor, 48 ... Voltage Sensors 49... Backflow prevention diode 100. Fuel cell 51. Target voltage determination unit 52. Superimposition signal generation unit 53 Converter control signal generator 53, 54 ... Impedance measurement / scavenging control unit, 1040 ... Impedance calculation means, 1041 ... Impedance temperature correction means, 2041 ... Impedance pressure correction means, 1042 ... Water content estimation means, 1043 ... Scavenging amount calculation means , 1044 ... compressor control unit, Sa ... accelerator opening signal, Se ... voltage detection signal, Si ... current detection signal, S _P ... gas pressure detection signal, Ss ... shift position signal, S _T ... temperature detection signal, S _SOC ... Detection signal, X ... impedance, θ ... phase angle, ω ... frequency

Claims (2)

In a fuel cell system capable of measuring the impedance of a fuel cell,
Impedance measuring means for measuring the impedance of the fuel cell;
Water content estimation means for estimating the water content of the fuel cell based on the relationship of the estimated water content of the fuel cell to the impedance measured by the impedance measurement means;
With
The gas pressure of the fuel cell so that the water content decreases as the gas pressure of the fuel cell increases and the water content decreases as the environmental temperature of the fuel cell increases. And the estimated water content is corrected based on the ambient temperature .
A fuel cell system. In the fuel cell impedance measurement method provided in the fuel cell system,
An impedance measuring step for measuring the impedance of the fuel cell;
A moisture content estimating step for estimating the moisture content of the fuel cell based on the relationship of the estimated moisture content of the fuel cell to the impedance measured by the impedance measuring step;
The gas pressure of the fuel cell so that the water content decreases as the gas pressure of the fuel cell increases and the water content decreases as the environmental temperature of the fuel cell increases. And a correction step of correcting the estimated water content based on the environmental temperature ;
A method for measuring the impedance of a fuel cell, comprising:

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