Method of calibrating offset of pressure sensor

Abstract

A method of calibrating an offset of a pressure sensor, by which an offset of a sensing value of a pressure sensor, which detects a pressure of hydrogen in a fuel cell system, is accurately calibrated. The method includes receiving, by a controller, a sensing value of a pressure sensor which detects a hydrogen pressure in a state where a hydrogen supply starts after a start of a fuel cell system; counting, by the controller, a time for which the sensing value of the pressure sensor increases from a first pressure P.sub.1 to a second pressure P.sub.2; calculating, by the controller, an offset value corresponding to the counted time by use of stored setting data; and calibrating, by the controller, a subsequent sensing value of the pressure sensor by the calculated offset value in real time when the offset value is calculated.

Claims

1. A method of calibrating readings acquired from a pressure sensor, the method comprising: step (a) of receiving, by a controller, a sensing value of the pressure sensor which detects a hydrogen pressure in a state where a hydrogen supply starts after a start of a fuel cell system; step (b) of counting, by the controller, a time for which the sensing value of the pressure sensor increases from a first pressure P.sub.1 to a second pressure P.sub.2; step (c) of calculating, by the controller, an offset value corresponding to the counted time by use of stored setting data; and step (d) of adding, by the controller, the calculated offset value to a subsequent sensing value of the pressure sensor until a next start of the fuel cell system, wherein the setting data is a map in which an offset value is set as a value according to the time for which the sensing value of the pressure sensor increases from the first pressure P.sub.1 to the second pressure P.sub.2, or an equation wherein the time is set as a variable and based on the variable an offset value is calculated.

2. The method of claim 1, further comprising: determining, by the controller, whether a calibration permissible condition is satisfactory based on information collected in the fuel cell system before the hydrogen supply starts after the start of the fuel cell system, wherein only when the calibration permissible condition is satisfactory, all the steps: receiving of the sensing value; counting of the time; calculating of the offset value; and calibrating the sensing value of the pressure sensor in real time; are performed.

3. The method of claim 2, wherein the information includes the sensing value of the pressure sensor, and the calibration permissible condition includes a condition where the sensing value of the pressure sensor is within an initial pressure range that is a range between an initial pressure lower limit value P.sub.i1 and an initial pressure upper limit value P.sub.i2.

4. The method of claim 3, wherein the initial pressure lower limit value P.sub.i1 and the initial pressure upper limit value P.sub.i2 are set in the controller as pressure values equal to or lower than a value of atmospheric pressure.

5. The method of claim 3, wherein the information further includes a fuel cell stack voltage detected by a voltage detecting unit, and the calibration permissible condition further includes a condition where the detected fuel cell stack voltage is less than a predetermined voltage.

6. The method of claim 3, wherein the information further includes at least one of an operation state of hydrogen purging performed by a hydrogen purge valve and a drain operation state of a water trap, and the calibration permissible condition further includes at least one of a condition where hydrogen purging is in a non-operated state and a condition where a drain value of a water trap is in a closed state.

7. The method of claim 1, wherein the first pressure P.sub.1 and the second pressure P.sub.2 are set in the controller as pressure values larger than a value of atmospheric pressure.

8. The method of claim 7, wherein the first pressure P.sub.1 and the second pressure P.sub.2 are set in the controller as pressure values smaller than a value of a predetermined start target pressure.

9. The method of claim 1, wherein a duration measured while pressure is increasing from the first pressure P.sub.1 to the second pressure P.sub.2 in the pressure sensor in a normal state, without generation of an offset, is pre-stored in the controller, in the setting data, an offset value is set: a positive value when the counted time in step (b) is shorter than the pre-stored time of increasing pressure or a negative value when the counted time counted in step (b) is longer than the pre-stored time of increasing pressure.

10. The method of claim 9, wherein the real-time calibrated sensing value of the pressure sensor in step (d) is calculated by Equation E1 below by using the offset value calculated based on the sensing value of the pressure sensor before the calibration and the setting data,
P.sub.calibration=P.sub.measureP.sub.offset(E1) wherein, P.sub.measure is the sensing value of the pressure sensor before the calibration, P.sub.offset is an offset value calculated from the setting data, and P.sub.calibration is the real-time calibrated sensing value of the pressure sensor.

11. The method of claim 1, further comprising: determining, by the controller, that the pressure sensor is broken down when an absolute value of the calculated offset value exceeds a predetermined value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 shows a diagram illustrating an installation state of a hydrogen pressure sensor in a general fuel cell system;

(3) FIG. 2 shows a diagram illustrating a controller and a pressure sensor performing an offset calibration process according to the present invention;

(4) FIG. 3 shows a flowchart illustrating the offset calibration process according to the present invention;

(5) FIG. 4 shows a diagram illustrating a comparison of pressure sensing values between a normal state of the pressure sensor and a state where an offset is generated in the present invention;

(6) FIG. 5 shows a diagram illustrating an example of setting data based on which an offset value is calculated based on a counted time in the present invention; and

(7) FIG. 6 shows a graph representing a comparison between an offset value and an increase time according to an offset state in the present invention.

(8) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

(9) In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

(10) Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

(11) Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings so that those with ordinary skill in the art to which the present invention pertains may easily carry out the exemplary embodiment. However, the present invention is not limited to the exemplary embodiment described herein, and may also be implemented in various different forms.

(12) Throughout the specification and the claims, unless explicitly described to the contrary, the word comprise and variations such as comprises or comprising will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

(13) In the description below, the present invention will be described based on a pressure sensor that is a target for a calibration of an offset according to the present invention, that is, a pressure sensor, on which a sensing value offset calibration and a failure determination are performed, according to the present invention is a pressure sensor 2 installed in a pipe (that is, a hydrogen supply pipe connected to an inlet of a hydrogen electrode of the fuel cell stack 3) at an inlet side of a fuel cell stack 3 so as to detect a hydrogen pressure (that is, a hydrogen supply pressure) supplied to a fuel cell stack 3 as illustrated in FIG. 2 as an example, as a pressure sensor detecting a hydrogen pressure in a fuel cell system.

(14) However, the present invention is not limited to the failure determination and the offset calibration for the hydrogen pressure sensor at the inlet side of the fuel cell stack 3 (that is, the inlet pressure sensor), and the failure determination and offset calibrating method according to the present invention may also be equally applied to an outlet pressure sensor 4 (FIG. 1) installed in a pipe at an outlet side of the fuel cell stack 3, that is, a pipe connected to an outlet side of the hydrogen electrode of the fuel cell stack 3.

(15) In this case, it is possible to individually determine failure and calibrate an offset by applying the method according to the present invention to each of the inlet pressure sensor and the outlet pressure sensor.

(16) In the description below, regarding a sensing value offset (deviation) of the pressure sensor, an offset state, in which a lower hydrogen pressure than an actual hydrogen pressure is sensed by the pressure sensor and a sensing value of the pressure sensor is smaller than a value of the actual hydrogen pressure, is defined as a offset.

(17) Regarding a sensing value offset, an offset state, in which a higher hydrogen pressure than an actual hydrogen pressure is sensed by the pressure sensor and a sensing value of the pressure sensor is larger than a value of the actual hydrogen pressure, is defined as a + offset.

(18) FIG. 2 shows a diagram illustrating a controller and the pressure sensor performing an offset calibration process according to the present invention, and FIG. 3 shows a flowchart illustrating the offset calibration process according to the present invention.

(19) As illustrated in FIG. 2, the hydrogen pressure sensor 2 detecting a hydrogen pressure may be installed in a hydrogen supply pipe, and a controller 10 receives a hydrogen pressure sensing value which is output from the pressure sensor 2 in a form of an electric signal.

(20) The controller 10 maybe an electronic circuitry that performs an offset calibration process according to the present invention illustrated in FIG. 3, and the offset calibration process performed by the controller 10 includes an operation S12 of determining whether a calibration is permissible performed after the fuel cell system starts (S11), operations S13 to S16 of measuring a time of increasing pressure, an operation S17 of calculating an offset value, an operation S18 of determining failure, and an operation S19 of calibrating an offset.

(21) First, as illustrated in FIG. 3, the controller 10 starts the fuel cell system (S11), and then determines whether a calibration is permissible based on information collected in the fuel cell system (S12), and only when all of the calibration permissible conditions are satisfied, a subsequent offset calibration process according to the present invention is performed.

(22) Herein, the satisfaction of the calibration permissible condition means a case where a condition in which a hydrogen pressure in the fuel cell stack 3 approximately maintains a uniform value, that is, a condition in which a hydrogen pressure is steady, before a supply of hydrogen starts after the start of the fuel cell system is satisfied.

(23) More particularly, the satisfaction of the calibration permissible condition means a case where a condition in which a hydrogen pressure maintains a uniform value or a condition in which a hydrogen pressure may maintain a uniform value is satisfied, and the calibration permissible condition includes a condition in which a sensing value of the pressure sensor is maintained within an initial pressure range.

(24) That is, when the controller receives a sensing value of the pressure sensor and the sensing value of the pressure sensor is maintained within a predetermined initial pressure range, the controller determines that the calibration permissible condition is satisfied.

(25) In addition to this, the calibration permissible condition may further include a condition in which a voltage of the fuel cell stack 3 is less than a predetermined voltage, and may further include a condition in which hydrogen purging is not operated, and may further include a condition in which a drain valve 9 of a water trap 8 is in a closed state.

(26) The controller 10 is a controller of the fuel cell system, and as illustrated in FIG. 2, when it is set that the controller 10 controls the operations of a hydrogen purge valve 5 and the drain valve 9, the controller 10 may recognize non-operated states of the hydrogen purge valve 5 and the drain valve 9.

(27) The hydrogen purging is performed by a periodical opening and closing operation of the hydrogen purge valve 5, and a condition in which the hydrogen purging is not operated means a condition in which there is no opening/closing operation of the hydrogen purge valve 5.

(28) A typical fuel cell system includes the water trap 8 storing water discharged from the fuel cell stack 3, and the drain valve 9 which is opened for discharging stored water to the outside is installed in the water trap 8.

(29) When the drain valve 9 is opened and water within the water trap 8 is discharged, particularly, water of the anode water trap is discharged, a hydrogen pressure of the fuel cell may be changed, and thus, the controller 10 determines that the calibration permissible condition is satisfied when the non-operation state, that is, a closed state, of the drain valve 9 is maintained.

(30) This will be described in more detail. In order to determine whether the calibration is permissible, an initial pressure lower limit value P.sub.i1 and an initial pressure upper limit value P.sub.i2 are preset and stored in the controller, and in a process of determining whether the calibration is permissible, the controller determines whether an initial pressure value detected by the pressure sensor, that is, an initial sensing value of the pressure sensor, is within an initial pressure range that is a range between the initial pressure lower limit value P.sub.i1 and the initial pressure upper limit value P.sub.i2.

(31) That is, when the initial sensing value of the pressure sensor is equal to or greater than the initial pressure lower limit value and is equal to or lower than the initial pressure upper limit value (P.sub.i1initial sensing valueP.sub.i2), it is determined that the initial sensing value of the pressure sensor is within the initial pressure range.

(32) Herein, both the initial pressure lower limit value P.sub.i1 and the initial pressure upper limit value P.sub.i2 may be set to pressure values equal to or lower than a value of the atmospheric pressure, and the initial pressure upper limit value is set to a larger pressure value than the initial pressure lower limit value.

(33) Both the initial pressure lower limit value and the initial pressure upper limit value are set to smaller pressure values than a value of a first pressure P.sub.1 to be described below.

(34) In the process of determining whether the calibration is permissible, the controller compares a fuel cell stack voltage detected by a voltage detecting unit with a predetermined voltage and determines whether the fuel cell stack voltage is less than the predetermined voltage, and checks whether the hydrogen purging is in a non-operation state and the drain of the water trap is in a non-operation state.

(35) The calibration permissible condition is a condition predetermined in the controller in order to confirm the steady state of the hydrogen pressure of the fuel cell at an initial stage of the start of the fuel cell, and when the calibration permissible condition is satisfied, the controller may determine that the hydrogen pressure of the fuel cell is in a steady state.

(36) That is, the controller determines whether the calibration is permissible by confirming the steady state of the hydrogen pressure of the fuel cell, and only in the steady state of the hydrogen pressure, an offset of the pressure sensor is calibrated by the controller.

(37) The hydrogen pressure during the operation of the fuel cell system is changed according to a current output of the fuel cell, a material transmission within the fuel cell, the hydrogen purging, and the operation of the drain of the water trap, so that it is difficult to secure the steady state of the hydrogen pressure.

(38) Accordingly, in the present invention, when the condition in which the sensing value of the pressure sensor at the initial stage of the start of the fuel cell system is within the initial pressure range, the condition in which the fuel cell stack voltage is less than the predetermined voltage, and the condition in which the hydrogen purging of the fuel cell is not operated and the drain (water discharge) of the water trap is not operated are satisfied, the controller determines that the hydrogen pressure is in the steady state to perform the process of calibrating the offset of the pressure sensor.

(39) The hydrogen pressure of the fuel cell is not sharply changed at the initial state of the start (including a re-start) of the fuel cell system, and the initial pressure lower limit value P.sub.i1 and the initial pressure upper limit value P.sub.i2 which regulate the initial pressure range are set to pressure values which satisfy the condition in which the hydrogen pressure is maintained in the steady state and are equal to or lower than the value of the atmospheric pressure.

(40) As is known, cathode oxygen depletion (COD) which removes residual hydrogen or oxygen within the fuel cell stack 3 is performed by connecting an electric load device acting as the kind of resistance to the fuel cell stack 3 when the starting of the fuel cell system is terminated, and in this case, a lower negative pressure than the atmospheric pressure is formed in the hydrogen electrode (the anode) within the fuel cell stack 3.

(41) Accordingly, the hydrogen pressure in the condition in which the hydrogen pressure maintains the steady state at the initial state of the start represents a pressure equal to or lower than the atmospheric pressure, and thus, the initial pressure lower limit value P.sub.i1 and the initial pressure upper limit value P.sub.i2 are preset in the controller 10 with the pressure values equal to or lower than the value of the atmospheric pressure.

(42) The setting voltage for determining whether the calibration is permissible at the initial stage of the starting of the fuel cell is set to a specific value for confirming a state where there is no reaction of the fuel cell inside the fuel cell stack 3.

(43) Next, when the controller 10 determines that all of the calibration permissible conditions are satisfied after the start of the fuel cell system, the controller 10 starts to count a time when the pressure value detected by the pressure sensor 2, that is, the sensing value of the pressure sensor, reaches a predetermined first pressure P.sub.1 after the hydrogen supply starts (S13 and S14).

(44) Then, when the hydrogen pressure, that is, the sensing value of the pressure sensor, increases and reaches a second pressure P.sub.2 (S15), the controller terminates the counting of the time and records and stores the counted time in the memory (S16).

(45) Herein, the first pressure P.sub.1 and the second pressure P.sub.2 are preset in the controller 10 with specific larger pressure values than a value of the atmospheric pressure.

(46) As described above, the controller 10 counts a time for which the sensing value of the pressure sensor 2 continuously increases after reaching the first pressure P.sub.1 and then reaches the second pressure P.sub.2, that is, a time of increasing pressure t for which the sensing value of the pressure sensor 2 reaches from the first pressure P1 to the second pressure P.sub.2, and then the controller 10 calculates an offset value by using setting data from the counted time t (S17).

(47) The setting data is setting information input and stored in the memory of the controller in advance, and is data defining a correlation between the time (a time of the pressure increase from P.sub.1 to P.sub.2), for which the sensing value of the pressure sensor increases from the first pressure P.sub.1 to the second pressure P.sub.2 and the offset value, and may be a map or an equation wherein the time is set as a variable and based on the variable the offset value is calculated.

(48) In the case of the map, the offset value may be preset as a map value according to the counted time, and the equation, which is a function by which the offset value is calculated based on the counted time as a variable, may be pre-obtained and used.

(49) The setting data of the map or the equation may be calculated by use of data obtained through an advanced test and an evaluation, and the same fuel cell system and the sensor having the same specification are used in the advanced test and evaluation process.

(50) In this case, a predetermined offset (an offset value is already known) is pre-generated in the pressure sensor, and the fuel cell system is soaked for a sufficient time, and then the controller records the time for which the sensing value of the pressure sensor reaches from the first pressure to the second pressure by supplying hydrogen under the same start operation and the same operation condition.

(51) The map, in which a correlation between the time and the offset value is defined, that is, the map, by which an offset value corresponding to a time is calculated based on a time as an input variable, is written by repeating the process while changing the offset (the already-known offset value) of the pressure sensor, and then the map is input and stored in the controller to be used.

(52) Otherwise, when the offset value and the time data are calculated through a repeated test, the equation as the setting data, that is, the equation, wherein the time is set as a variable and based on the variable the offset value is calculated, may be obtained through a polynomial curve fitting process by using the data.

(53) Here, for example, an equation of a quadric function may be obtained through the 2.sup.nd polynomial curve fitting process, and the equation below represents a more particular example.
P.sub.offset=Ax.sup.2+Bx+C[Equation 2]

(54) Herein, as an example of a simulation, A=5.571, B=11.85, C=3.714, x=(t60)/36.1, and in this case, t represents a time of increasing pressure for which the sensing value of the pressure sensor reaches from the first pressure P.sub.1 to the second pressure P.sub.2.

(55) The calculation of the offset value will be further described. In the present invention, the controller confirms that the hydrogen electrode (anode) of the fuel cell stack 3 is in a steady state with respect to the hydrogen pressure, and subsequently, the controller calibrates the offset based on the pressure (the sensing value of the pressure sensor) increase time (which is related to a pressure increase speed) after the start of the hydrogen supply.

(56) FIG. 4 shows a diagram illustrating a comparison of pressure sensing values between a normal state of the pressure sensor and a state where an offset is generated, and an increase speed of a sensing value of the pressure sensor at the initial stage of the starting after the start of the hydrogen supply during the start of the fuel cell system is changed according to the sensor state.

(57) Referring to FIG. 4, in regards to the hydrogen pressure during the start of the fuel cell system, a start target pressure may be set, and the first pressure P.sub.1 and the second pressure P.sub.2 may be set to hydrogen pressure values in the state where the hydrogen pressure is increased to a predetermined pressure or more after the start of the hydrogen supply.

(58) In this case, the first pressure P.sub.1 and the second pressure P.sub.2 may be set to specific pressure values larger than the value of the atmospheric pressure, and the second pressure P.sub.2 has the larger value than the value of the first pressure P.sub.1, but is set to a value smaller than that of the set start target pressure.

(59) The first pressure and the second pressure are set so that some time is taken for the sensing value of the pressure sensor to increase from the first pressure P.sub.1 to reach the second pressure P.sub.2.

(60) In FIG. 4, t.sub.offset,+ represents a time counted while the sensing value is increased from the first pressure P.sub.1 to reach the second pressure P.sub.2 in the state where a + offset is generated in the pressure sensor, and t.sub.offset, represents a time counted in the state where a offset is generated in the pressure sensor.

(61) t.sub.normal represents a time counted when the pressure sensor is in a normal state without the generation of the offset.

(62) Referring to FIG. 4, in counting the time taken for the sensing value of the pressure sensor to increase from the first pressure P.sub.1 to reach the second pressure P.sub.2 at the initial stage of the starting, at which the hydrogen supply starts, when the +offset (deviation) is generated in the pressure sensor, the sensing value of the pressure sensor generally has a larger value than that of the case where the pressure sensor is normal.

(63) When the offset is generated in the pressure sensor, the sensing value of the pressure sensor generally has a smaller value than that of the case where the pressure sensor is normal.

(64) Particularly, when the + offset is generated, the time counted while the sensing value of the pressure sensor reaches from the first pressure P.sub.1 to the second pressure P.sub.2 is shorter than the time counted when the pressure sensor is normal.

(65) When the offset is generated, the time counted while the sensing value of the pressure sensor reaches from the first pressure P.sub.1 to the second pressure P.sub.2 is longer than the time counted when the pressure sensor is normal.

(66) That is, in summarizing, the relationship is established as t.sub.offset,+<t.sub.normal<t.sub.offset, and it is possible to determine whether the + offset is generated in the pressure sensor, the offset is generated in the pressure sensor, or the pressure sensor is in the normal state based on the counted time by using the relationship.

(67) FIG. 5 shows a diagram illustrating an example of setting data based on which an offset value is calculated based on a counted time in the present invention, and as illustrated in FIG. 5, when the counted time has a value smaller than t.sub.normal, the + offset is generated in the pressure sensor, and in contrast to this, when the counted time has a value larger than t.sub.normal, the offset is generated in the pressure sensor.

(68) Finally, the time t.sub.normal when the pressure sensor 2 is in the normal state is input and stored in the controller 10 in advance, and the counted time is compared with the time t.sub.normal after the termination of the counting of the time, it is possible to determine whether the offset is generated in the pressure sensor and the state of the generated offset (the offset or the + offset).

(69) As illustrated in FIG. 5, the offset value P.sub.offset in the state where the + offset is generated is set to a positive (+) value, and the offset value P.sub.offset in the state where the offset is generated is set to a negative () value.

(70) Next, when the offset value is calculated based on the counted time as illustrated in FIG. 3 and when an absolute value of the calculated offset value is an offset excessive state of exceeding a predetermined value, the controller 10 determines that the pressure sensor 2 is broken down (S18).

(71) When the controller 10 determines that the pressure sensor has the failure that is the offset value excessive state, the controller 10 may be set to immediately shut down the fuel cell system.

(72) In the meantime, in the case where the absolute value of the calculated offset value is less than the predetermined value, when the offset is calibrated for the sensing value of the pressure sensor 2, the fuel cell system is in an operable state by using the sensing value of the pressure sensor, so that the sensing value of the pressure sensor is calibrated in real time by using the calculated offset value (S19).

(73) Herein, when it is assumed that a real-time sensing value before the calibration of the sensing value of the pressure sensor is P.sub.measure, the calculated offset value is P.sub.offset, and the real-time calibrated sensing value of the pressure sensor is P.sub.calibration, the calibrated sensing value of the pressure sensor may be represented as the equation below.
P.sub.calibration=P.sub.measureP.sub.offset[Equation 2]

(74) When the absolute value of the calculated offset value exceeds the predetermined value in operation S18, the controller determines that the pressure sensor 2 is broken down, and more particularly, when the calculated offset value P.sub.offset exceeds a predetermined offset upper limit value P.sub.offset,high or is less than a predetermined offset lower limit value P.sub.offset,low, the controller 10 may be set to determine that the pressure sensor 2 has the failure by the excessive offset.

(75) Herein, as illustrated in FIG. 5, P.sub.offset,high is set as a positive value and P.sub.offset,low is set as a negative value.

(76) Table 1 below represents a comparison between an offset value P.sub.offset (kPa) during an increase in a pressure and an increase time t (msec) according to an offset by setting the first pressure P.sub.1 to 110 kPa and the second pressure P.sub.2 to 120 kPa, and FIG. 6 shows a graph representing a comparison between an offset value and an increase time according to an offset state.

(77) TABLE-US-00001 TABLE 1 Time Time to P.sub.offset to reach P.sub.1 reach P.sub.2 t (kPa) (sec) (sec) (msec) Note 10 0.15 0.17 20 Rapidly increase compared to normal state 0 0.1 0.17 70 Normal 10 0.08 0.17 90 Slowly increase compared to normal state

(78) Accordingly, the present invention may determine, whenever the fuel cell system starts, whether an offset is generated in the pressure sensor, determine a state of the generated offset (the discrimination between the offset and the + offset), calculate an offset value, and accurately calibrate the offset of the pressure sensor by using the time of increasing pressure t for which the sensing value of the pressure sensor at the initial stage of the starting increases from the first pressure to the second pressure in the state where the hydrogen supply starts, thereby preventing the fuel cell stack 3 from being operated in the state where the hydrogen supply is excessive or short.

(79) According to the present invention, it is possible to expect an effect in improving reliability of the pressure sensor and improving reliability of the calibration for the offset.

(80) It is possible to solve a problem of fuel efficiency degradation due to an increase of the quantity of hydrogen crossover generated due to the higher pressure of the hydrogen electrode (anode) than a required numerical value when the offset is generated in the pressure sensor, and solve a problem of deterioration of a fuel cell due to a lack of hydrogen generated due to the lower pressure of the hydrogen electrode than the required numerical value when the + offset is generated in the pressure sensor.

(81) Unlike the method in the related art, when an offset is calibrated, the hydrogen electrode is not exposed to the air, so that it is possible to prevent carbon corrosion of the cathode due to the forming of the interface between hydrogen and oxygen generated when the hydrogen electrode is exposed to the air, and solve a problem in the related art in that fuel cell deteriorates when the offset is calibrated.

(82) It is possible to periodically diagnose failure and calibrate an offset for the continuously degraded pressure sensor, and when the offset of the pressure sensor is excessive, the present invention diagnoses that the pressure sensor is broken down to induce a replacement of the sensor.

(83) The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.