JP2006310182A - Fuel cell system and purge valve control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system correctly controlling a purge amount. <P>SOLUTION: In this fuel cell system for exhausting an anode off-gas by opening/closing a purge valve 18 arranged in an anode off-gas supply passage 15 of a fuel cell 10, a purge amount is calculated on the basis of a pressure difference ΔP(t) between anode off-gas pressure P1 in opening the purge valve 18 and anode off-gas pressure P2 when a certain time has passed, and an opening/closing time of the purge valve is corrected on the basis of the calculated purge amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a purge valve, and more particularly to an improvement in a purge control method.

In a system using a fuel cell, in a system that supplies fuel gas to an anode electrode, nitrogen contained in water and air generated by an electrochemical reaction is accumulated as impurities in the anode off gas. In order to discharge the hydrogen gas containing the impurities, the anode off gas may be purged. For example, Japanese Patent Laid-Open No. 2004-273427 discloses a technique for calculating an integral value obtained by integrating the amount of impurities at the hydrogen electrode, and controlling the purge valve to be opened when the integral value is equal to or greater than a threshold value. (Patent Document 1). Japanese Patent Laid-Open No. 2004-179000 discloses a fuel cell system configured to close a purge valve when the flow rate of the purge valve exceeds a predetermined value when the purge valve is opened (Patent Document 2). In addition, JP 2004-253259 A (Patent Document 3), JP 2004-39522 A (Patent Document 4), and the like have been known as means for controlling the purge flow rate.
JP 2004-273427 A JP 2004-179000 A JP 2004-253259 A JP 2004-39522 A

  However, the technique of purging by setting a threshold value or a predetermined value in advance may cause inconvenience in the long run. In a fuel cell system, the flow rate of a valve or piping varies due to secular change or the like, and the anode off gas flow rate varies depending on system factors. When the flow rate characteristic changes in this way, the flow rate of the purge valve discharged according to the threshold value that determines the timing of opening and closing the purge valve set in the initial conditions and the predetermined value and the flow rate of the purge valve that is actually discharged are changed. Deviation occurs. For this reason, there is a possibility that an error occurs in the amount of the anode off gas to be purged, and impurities cannot be properly removed.

  Therefore, an object of the present invention is to provide a fuel cell system capable of accurately controlling the purge amount.

  In order to solve the above-described problems, the present invention provides a fuel cell system that discharges anode off gas by opening and closing a purge valve disposed in an anode off gas passage of a fuel cell, and maintains a constant anode off gas pressure when the purge valve is opened. The purge amount is calculated based on the pressure difference from the anode off-gas pressure over time, and the opening / closing time of the purge valve is corrected based on the calculated purge amount.

  The fuel cell system of the present invention also includes a fuel cell, an anode off-gas passage for discharging the anode off-gas discharged from the anode of the fuel cell, and a purge valve for discharging impurities contained in the anode off-gas discharged to the anode off-gas passage. A purge amount based on a pressure sensor for detecting an anode off-gas pressure in the anode off-gas passage and a pressure difference between the anode off-gas pressure detected by the pressure sensor when the purge valve is opened and the anode off-gas pressure after a predetermined time has elapsed. And a control device that corrects the opening / closing time of the purge valve based on the calculated purge amount.

  Further, the present invention provides a fuel cell system that opens and closes a purge valve to discharge anode off gas, pressure detecting means for detecting the pressure of the anode off gas, and anode off gas detected by the pressure detecting means when the purge valve is opened. A pressure difference calculating means for calculating the pressure difference between the pressure and the anode off-gas pressure when a certain time has elapsed; an opening / closing time correcting means for correcting the opening / closing time of the purge valve based on the pressure difference calculated by the pressure difference calculating means; And purge valve control means for opening and closing the purge valve in accordance with the corrected opening / closing time.

  According to another aspect of the present invention, there is provided a purge control method for discharging an anode off gas from a purge unit disposed in an anode off gas passage of a fuel cell, the step of detecting the pressure of the anode off gas, and the anode off gas at the start of purge by the detected purge unit A step of calculating a pressure difference between the pressure and the anode off-gas pressure when a certain period of time elapses, and a step of changing the opening / closing time of the purge means up to the previous time based on the calculated pressure difference. To do.

  According to the present invention, the purge amount is obtained on the basis of the pressure when the purge valve is opened and the pressure after a certain period of time. Since the purge amount is the actual purge amount at that time, the opening / closing time of the purge valve is corrected based on the purge amount. With this process, the preset opening / closing time can be corrected to be a time during which an appropriate purge amount can be secured.

  Here, it is preferable to prohibit the correction of the opening / closing time of the purge valve when the pressure difference is within a predetermined reference range. When the pressure difference is not significantly different from the preset opening / closing time, it is assumed that there is little change with time and fluctuation of system factors. Therefore, in the present invention, when the pressure difference is within the reference range, that is, when the difference from the planned pressure difference is small, it is determined that the correction is unnecessary, and the correction is prohibited.

  For example, the correction of the opening / closing time of the purge valve is to change the valve opening time length from the opening time to the closing time of the purge valve. The valve opening time length directly corresponds to the purge amount. According to the present invention, the purge amount is corrected by changing the valve opening time length.

  Specifically, when the pressure difference is greater than or equal to a predetermined reference value, the valve opening time length of the purge valve is decreased. When the pressure difference is large, it means that the purge flow rate per unit time is increased. Therefore, if the valve opening time length is decreased, the purge amount can be maintained appropriately.

  Conversely, when the pressure difference is equal to or smaller than a predetermined reference value, the valve opening time length of the purge valve is increased. When the pressure difference is small, it means that the purge flow rate per unit time is small. Therefore, if the valve opening time length is increased, the purge amount can be kept appropriate.

  For example, the predetermined time elapses is a predetermined time after the purge valve is opened and before the valve is closed. This is because the pressure can be measured when the pressure change has settled to some extent, and therefore it can be measured without necessarily waiting until the valve is closed.

  Here, when the pressure difference can be measured before the valve is closed, the opening / closing time of the purge valve is corrected while the purge valve is open after a certain period of time, and the purge valve is closed after the corrected valve opening time has elapsed. Can be controlled. This is because when the pressure difference is measured before the valve is closed, the pressure difference can be grasped during the valve opening period, so that the correction can be ended during the valve opening and the valve closing time can be changed.

  It is also possible to set the purge valve when the fixed time has elapsed. In this case, the next purge valve is opened and closed with the corrected valve opening time length. Since the pressure difference can be grasped after the valve is closed, the correction result is reflected in the opening / closing time of the purge valve because the next purge is performed.

  In the present invention, it is preferable to further provide a flow rate limiting portion on the upstream side of the purge valve. The flow restriction unit restricts the flow rate when the purge valve is opened and can sufficiently lower the downstream pressure. On the other hand, when the purge valve is closed, the downstream pressure is the same as that of the anode off-gas passage. Since the pressure difference before and after the opening and closing of the purge valve can be increased, the detection accuracy can be increased.

  In the present invention, the opening / closing time of the purge valve may be controlled to be updated by the corrected opening / closing time every time the opening / closing time is corrected. Each time correction is performed, the reference opening / closing time is changed, and the prescribed opening / closing time is changed in accordance with a change with time and a change in system factors.

  In the present invention, the correction of the opening / closing time of the purge valve can be performed by changing the interval time length from the closing of the purge valve to the next opening. This is because even if the purge valve opening time length is constant, the purge amount per unit time can be changed by changing the time length of the interval. The purge valve opening time length and the interval time length may be changed together.

  In this case, specifically, the interval time length is increased when the pressure difference is equal to or larger than a predetermined reference value. When the pressure difference is large, it means that the purge flow rate per unit time is increased. Therefore, if the interval time length is increased, the purge amount can be properly maintained.

  Conversely, when the pressure difference is equal to or smaller than a predetermined reference value, the interval valve opening time length is decreased. When the pressure difference is small, it means that the purge flow rate per unit time is small. Therefore, if the valve opening time length is decreased, the purge amount can be kept appropriate.

  As described above, according to the present invention, the actual purge amount at that time can be grasped based on the pressure when the purge valve is opened and the pressure when a certain time has elapsed from that. It is possible to correct and secure an appropriate purge amount.

Next, preferred embodiments for carrying out the present invention will be described with reference to the drawings. The following embodiment is merely one embodiment of the present invention, and the present invention is not limited thereto and can be applied.
(Embodiment 1)
Embodiment 1 of the present invention relates to an example in which the opening time length of a purge valve is corrected by comparing a reference pressure difference with an actually measured pressure difference.
FIG. 1 shows an overall system diagram of the fuel cell system. As shown in FIG. 1, the fuel cell system includes a gas supply unit 1 for supplying a fuel cell 10 with hydrogen gas as a fuel gas and air as an oxidizing gas, and a control unit 2 of the fuel cell. Configured.

The fuel cell 10 has a stack structure in which a plurality of cells (single cells) are stacked. Each cell has MEA power generation, termed (M embrane E lectrode A ssembly) , hydrogen gas, air, sandwiched between separators pair having a flow path of the cooling water. The MEA has a structure in which a polymer electrolyte membrane is sandwiched between two electrodes, a fuel electrode and an air electrode. The fuel electrode is configured by providing a fuel electrode catalyst layer on a porous support layer, and the air electrode is configured by providing an air electrode catalyst layer on a porous support layer.

Since a fuel cell causes reverse reaction of water electrolysis, hydrogen gas, which is anode gas, is supplied to the fuel electrode side, which is the anode (cathode), and hydrogen gas, which is cathode (anode), is supplied to the air electrode side. Cathode gas (air) containing oxygen is supplied, and a reaction such as equation (1) is generated on the fuel electrode side and a reaction such as equation (2) is generated on the air electrode side to circulate electrons and flow current. Is.
H ₂ → 2H ⁺ + 2e ^{^} (1)
2H ⁺ + 2e ^{^} + (1/2) O ₂ → H ₂ O (2)
In the present embodiment, the anode gas discharged from the fuel cell 10 through the electrochemical reaction is referred to as an anode off gas, and the discharged cathode gas is referred to as a cathode off gas.

  The system for handling the anode gas includes a hydrogen tank 11 as a hydrogen gas supply source, an anode gas supply path 12, a circulation path 13, a circulation pump 14, and an anode off-gas path 15. The main valve, the regulating valve, the shutoff valve, the check valve, the gas-liquid separator and the like necessary for the management control of the anode gas are not shown.

  The hydrogen tank 11 is filled with high-pressure anode 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 12 is a pipe that supplies high-pressure anode gas, and may be provided with a pressure regulating valve (regulator) or the like not shown in the middle. The circulation path 13 supplies the regulated anode gas to the fuel electrode 10 </ b> A of the fuel cell 10. After the electrochemical reaction, the anode off-gas discharged from the fuel electrode 10A is returned to the anode gas supply path 12 again via a check valve and an ejector (not shown) to form a circulation path. The circulation pump 14 forcibly circulates the anode off gas based on the control of the control unit 2. On the way, moisture and other impurities in the anode off-gas are removed by a gas-liquid separator (not shown).

  In the circulation path 13, the anode off gas passage 15 is branched upstream of the circulation pump 14. The anode off gas passage 15 is provided with a flow restriction unit 16, a pressure sensor 17, and a purge valve 18.

  The flow restriction unit 16 relates to the present invention and is provided by selection and is not an essential configuration. The flow rate restricting unit has a structure capable of restricting the gas flow rate passing therethrough, and is configured by, for example, an orifice with a reduced diameter. Since the flow restriction unit 16 restricts the flow rate of the anode off-gas flowing through the anode off-gas passage 15, the pressure downstream of the purge valve can be sufficiently reduced by restricting the flow rate when the purge valve 18 is opened, while the flow rate restriction is performed when the purge valve 18 is closed. The pressure between the part 16 and the purge valve 18 is made equal to the upstream side of the flow restriction part 16.

  The pressure sensor 17 is configured to detect the primary pressure of the purge valve 18, that is, the pressure of the anode off gas passage 15. When the flow restriction unit 16 is not provided, the pressure sensor 17 always detects the pressure downstream of the circulation pump 14. On the other hand, when the flow restriction unit 16 is provided, when the purge valve 18 is open, a relatively low pressure with a restricted flow rate is applied when the purge valve 18 is closed. Will detect the pressure downstream of the circulation pump 14. The pressure sensor 17 outputs the detected internal pressure of the anode offgas passage 15 to the control unit 2 as a detection signal Sd.

  The purge valve 18 according to the present invention is configured to open and close according to the purge valve control signal Spc of the control unit 2. The opening / closing control of the purge valve 18 is a feature of the present invention. The anode off gas passage 15 on the downstream side of the purge valve 18 is connected to a diluter 25 so as to be mixed and diluted with the anode off gas.

  As a system for handling the cathode gas, an air cleaner 21, a cathode gas supply path 22, a compressor 23, a cathode off gas supply path 24, and a diluter 25 are provided. Various shut-off valves, pressure regulating valves, humidifiers for increasing the humidity of the cathode gas, etc. are not shown.

  The air cleaner 21 purifies outside air and takes it into the fuel electric system as air containing oxidizing gas. The cathode gas supply path 22 circulates this air, and the compressor 23 compresses the air taken into the cathode gas supply path 22 based on the control signal of the control unit 2 and supplies it to the air electrode 10C of the fuel cell 10. It has become.

  The cathode offgas supply path 24 circulates the cathode offgas discharged from the air electrode 10 </ b> C of the fuel cell 10 and supplies it to the diluter 25. The diluter 25 generates turbulent flow between the anode off gas discharged from the purge valve 18 and the cathode off gas supplied from the cathode off gas supply path 24 to dilute the anode off gas. The diluter 25 discharges the off gas diluted to such an extent that an abnormal oxidation phenomenon does not occur through the exhaust path 26.

  Although not shown, the fuel cell 10 is provided with a cooling system for flowing a coolant over the separator to cool the inside of the fuel cell.

The controller 2 is a known computer system, such as ECU (E lectric C ontrol U nit ), CPU (not shown) (central processing unit), a RAM, ROM, interface circuits and the like. The control unit 2 causes the fuel cell system to execute the purge control method of the present invention by sequentially executing software programs stored in a ROM or the like.

  FIG. 1 shows functional blocks realized by the control unit 2. The control unit 2 is functionally divided into a pressure detection unit 200, a pressure difference calculation unit 202, an open / close time correction unit 204, and a purge valve control unit 206.

  The pressure detection means 200 detects the pressure of the anode off gas in the anode off gas passage 15 with reference to the detection signal Sd from the pressure sensor 17. That is, the pressure detecting means 200 refers to the detection signal Sd of the pressure sensor 17 that is a measuring device, and converts it into a relative pressure value suitable for the arithmetic processing. The pressure detection means 200 and the pressure sensor 17 correspond to the pressure detection means according to the present invention.

  The pressure difference calculating means 202 calculates the pressure difference detected by the pressure detecting means 200 between the anode off gas pressure P1 when the purge valve 18 is opened and the anode off gas pressure P2 when a certain time has elapsed, at the time t. This is calculated as the difference ΔP (t). That is, the anode off-gas pressure when the purge valve 18 is opened is temporarily stored as P1, and the anode off-gas pressure P2 when a certain time has elapsed is subtracted from the anode off-gas pressure P1 when the purge valve 18 is opened. The fixed time is the following time.

  FIG. 3 shows how the anode off-gas passage 15 changes in pressure as the purge valve 18 is opened and closed. As shown in FIG. 3, when the purge valve 18 is opened at time t1, the anode off gas flows according to the pressure difference between the primary side and the secondary side of the purge valve 18, and the pressure in the anode off gas passage 15 rapidly decreases. . As the pressure difference between the primary side and the secondary side of the purge valve 18 decreases, the pressure drop becomes slow and the pressure gradually becomes stable. For example, there is almost no pressure drop after time t2. Thus, an appropriate time t2 during which the pressure change can be expected to be slow during the opening period of the purge valve is determined as the elapse of a certain time for measuring P2.

  The opening / closing time correcting means 204 corrects the opening / closing time of the purge valve 18 based on the pressure difference ΔP (t) calculated by the pressure difference calculating means 202. Specifically, the opening / closing time correction unit 204 includes a functional block including a correction coefficient calculation unit 212, a multiplication unit 216, and an addition unit 219. Further, the opening / closing time correction means 204 stores an opening time length of the purge valve 18 appropriate as a purging time when it is assumed that the fuel cell system operates as designed as a specified opening time length T (0). (Reference numeral 218). Further, the pressure difference from the purge valve opening time t1 to the time t2 when a certain time has elapsed, which should be detected when the fuel cell system is assumed to operate as designed, is stored as the specified pressure difference ΔP (0) ( Reference numeral 214). The opening / closing time correction unit 204 multiplies the correction coefficient calculated by the correction coefficient calculation unit 212 and the specified valve opening time length T (0) by the multiplication unit 216 to obtain a correction time length ΔT (t), and adds this to the addition unit 219. Is added to the specified valve opening time length T (0), and the corrected valve opening time length T (0) + ΔT (t) is output. The purge valve control means 206 outputs a purge valve control signal Spc for opening and closing the purge valve 18 according to a schedule according to the corrected valve opening time length.

Next, the principle of the purge valve control method in the present invention will be described.
In general, when the pressure difference between the primary side and the secondary side of the valve means is ΔP for the fluid passing through the valve means, the volume flow rate Q of the fluid passing through the valve means may be proportional to the square root of the pressure difference ΔP. Are known.
Q ∝ √ΔP (1)
According to the equation (1), the flow rate Qp passing through the purge valve 18 is
Qp∝√ΔP (t) = √ (P1−P2) (2)
It becomes. Here, the specified flow rate Qp (0) assumed when the system operates as designed uses the pressure difference ΔP (0) in this case, the proportionality constant is A,
Qp (0) = A√ΔP (0) (3)
It becomes. Similarly, the flow rate Qp (t) passing through the purge valve at the current time t using the pressure difference ΔP (t) (= P1−P2) measured at the current time is
Qp (t) = A√ΔP (t) = A√ (P1−P2) (4)
It becomes. Here, a (= ΔP (t) / ΔP (0)) is a ratio of the pressure difference ΔP (t) at the current time t to the initial specified pressure difference ΔP (0).
ΔP (t) = a · ΔP (0) (5)
It is. Further, the change amount ΔQ of the volumetric flow rate from the initial state at the current time t is expressed by using equation (5):
ΔQ = Qp (0) −Qp (t)
= A (√ΔP (0) −√ΔP (t))
= A√ΔP (0) · (1−√a) (a = ΔP (t) / ΔP (0)) (6)
It becomes.

となる。従って、現時刻ｔにおいてパージ弁の開弁時間長Ｔ（ｔ）は、この補正時間長と規定開弁時間長とを加算したもの、すなわち、
Ｔ（ｔ） ＝ Ｔ（０）＋ΔＴ（ｔ） …（７）
となる。このようにして補正された開弁時間長Ｔ（ｔ）に対応するように、パージ弁の開閉が制御されればよいことが判る。本実施形態の制御部２では、補正係数演算部２１２において補正係数（１−√ａ）が演算され、乗算部２１６において規定開弁時間長Ｔ（０）と乗算されることによって、数１のように補正時間長ΔＴ（ｔ）が求められ、加算部２２０においてさらに規定開弁時間長Ｔ（０）と加算されることによって、補正された開弁時間長が求められるのである。 Here, the purge amount flowing through the purge valve by one purge is considered to be proportional to the valve opening time length of the purge valve. The purge amount in the initial state is the specified flow rate Qp (0), and the purge amount changes from this by ΔQ. Therefore, the purge valve correction time is set to the specified valve opening time length T (0) with a correction coefficient (1−√a). Multiplied by. That is, the correction time length ΔT (t) necessary to compensate for the change amount ΔQ using the equation (5) is

It becomes. Therefore, the opening time length T (t) of the purge valve at the current time t is the sum of the correction time length and the specified valve opening time length, that is,
T (t) = T (0) + ΔT (t) (7)
It becomes. It can be seen that the opening and closing of the purge valve should be controlled so as to correspond to the valve opening time length T (t) corrected in this way. In the control unit 2 of the present embodiment, a correction coefficient (1−√a) is calculated in the correction coefficient calculation unit 212 and multiplied by the specified valve opening time length T (0) in the multiplication unit 216, whereby In this way, the corrected time length ΔT (t) is obtained and further added to the specified valve opening time length T (0) in the adding unit 220, whereby the corrected valve opening time length is obtained.

Next, a series of operations in the control unit 2 will be described with reference to the flowchart of FIG.
First, it is determined whether or not the purge time has come (S1). The purge schedule is grasped by the control unit 2. After the end of the previous purge, the purge is not performed until the impurity concentration in the circulation path 13 increases to some extent (S1: NO), and the transition is made to the purge process when an interval at which the impurity concentration is assumed to have increased (S1: YES) has elapsed. In this embodiment, it is assumed that this interval is constant.

  First, the detection signal Sd of the pressure sensor 17 is referred to, and the pressure P1 when the purge valve 18 is opened is grasped (S2). Immediately thereafter, the purge valve control signal Spc is output, and the purge valve 18 is opened (S3). When the purge valve 18 is opened, the anode off gas in the circulation path 13 is discharged through the purge valve 18, and diluted and mixed with the cathode off gas in the diluter 25. The pressure detected by the pressure sensor 17 changes with the characteristics shown in FIG.

  The purge is continued until a certain time elapse t2 that is assumed to be sufficient for the pressure to stabilize (S4: NO). When a certain time elapses (S4: YES), the anode off-gas pressure is again measured by the pressure sensor 17 and set to P2 (S5). Then, the pressure difference ΔP (t) (= P1-P2) at the current time t is calculated (S6).

Next, a determination is made according to the pressure difference.
First, when the pressure difference ΔP (t) is within a predetermined reference range, that is, when the pressure difference ΔP (0) in the initial state is hardly different (S8: YES), the correction time length ΔT (t) is zero. Is set (S9). The case where the measured pressure difference ΔP (t) is approximately equal to the specified pressure difference ΔP (0) means that the system has not changed over time or system factors, and is operating as expected. Conceivable. In such a case, since it is not necessary to correct the valve opening time length of the purge valve, the correction time length is set to zero. By this process, it is possible to avoid an extra correction calculation even though the error is small.

  Next, when the pressure difference ΔP (t) deviates from the specified pressure difference ΔP (0) from the reference range (S8: NO), the correction time length ΔT (t) is calculated according to the deviation. For example, when the pressure difference ΔP (t) is larger than the specified pressure difference ΔP (0) (S10: NO), it means that the cathode off-gas pressure is higher than the specified value and the purge amount per unit time is increased. . According to Equation 1, the correction time length ΔT (t) shows a negative value, and as a result, it works to reduce the valve opening time length of the purge valve (S11). On the other hand, when the pressure difference ΔP (t) is equal to or less than the specified pressure difference ΔP (0) (S10: YES), it means that the cathode offgas pressure is lower than the specified value and the purge amount per unit time is reduced. To do. According to Equation 1, the correction time length ΔT (t) indicates a positive value, and works to increase the valve opening time length of the purge valve (S12).

  Through these series of procedures, the correction time length ΔT (t) set in accordance with the detected pressure difference ΔP (t) is added to the specified valve opening time length T (0) (S13). When the corrected valve opening time length T (t) has elapsed (S14: YES), the purge valve control signal Spc for closing the purge valve is output and the purge valve is closed (S15).

  As described above, according to the first embodiment, the purge amount Q is obtained on the basis of the pressure P1 at the time t1 when the purge valve 18 is opened and the pressure P2 at the time t2 after the passage of a certain time. This purge amount is the actual purge amount at that time, and based on the purge amount, a predetermined opening / closing time T (0) is set to a time (T (0) + ΔT ( t)). Therefore, even if the pressure state changes due to aging or system factors, purge control can be performed with an appropriate purge amount following the pressure state.

  According to the first embodiment, when the pressure difference ΔP (t) is within a predetermined reference range, the purge valve opening / closing time is not corrected, and therefore it is confirmed that there is no change in the system state. The correction calculation can be omitted.

  According to the first embodiment, the pressure difference is detected at the time t2 when the purge valve 18 is closed before the valve is closed. Therefore, the correction calculation is performed immediately after the fixed time has elapsed, and the correction result is changed to the current open state. This can be reflected in the valve closing timing adjustment of the purge valve 18. That is, it is possible to quickly respond to changes in the system state.

  According to the first embodiment, the flow restriction unit 16 is provided on the upstream side of the purge valve 18 and the pressure difference before and after the opening and closing of the purge valve can be increased, so that the detection accuracy can be increased.

(Embodiment 2)
As in the first embodiment, the second embodiment of the present invention compares the reference pressure difference with the actually measured pressure difference to correct the purge valve opening time length. It relates to the example used.
The fuel cell system in the present embodiment is the same as that in the first embodiment (see FIG. 1). However, in the control unit 2, the pressure detection means 200 detects the pressure P1 at the time t1 when the purge valve 18 is opened and the pressure P2 at the time t2 when the purge valve 18 is closed, and the pressure difference calculation means 202 is the next time (nth). The difference is that the pressure difference ΔP (n) for purging is calculated. Other configurations are the same as those in the first embodiment.

Next, a series of operations in the control unit 2 will be described with reference to the flowchart of FIG.
In the second embodiment, the correction time length is obtained using the pressure P1 when the purge valve 18 is opened and the pressure P2 when the purge valve 18 is closed as the pressure difference. This is different from the first embodiment in which the pressure of t2 is P2. The purge control with the corrected correction time length is reflected in the next purge. In the second embodiment, the valve opening time length T (n) reflected in the next (n-th) purge is obtained by calculation in the (n-1) th purge. The object to be obtained is the correction time length ΔT (n) to be added or subtracted in the nth purge.
First, it is determined whether or not the purge time has come (S21). When a predetermined interval has elapsed (S21: YES), the process proceeds to a purge process.

  As in the first embodiment, the detection signal Sd of the pressure sensor 17 is referred to, and the pressure P1 when the purge valve 18 is opened is grasped (S22). Immediately thereafter, the purge valve control signal Spc is output, and the purge valve 18 is opened (S23). And in this embodiment, it will be in a waiting state until the valve opening time length T (n-1) set by the last time for this time (n-1 time) passes (S24: NO). When the valve opening time length T (n−1) has elapsed (S24: YES), the anode off-gas pressure at the time of closing is first detected as P2 (S25), and then the purge valve control signal Spc for closing the purge valve 18 is reached. Is output and the purge valve is closed (S26).

Next, the same correction calculation as in the first embodiment is performed.
First, a pressure difference ΔP (n) (= P1-P2) for the next time (n-th) is calculated (S26). When the pressure difference ΔP (t) is within a predetermined reference range, that is, when the pressure difference ΔP (0) that is the initial state is hardly different (S28: YES), the correction time length ΔT (n) is zero. Is set (S29).

  When the pressure difference ΔP (n) deviates from the reference range from the specified pressure difference ΔP (0) (S28: NO), the correction time length ΔT (n) is calculated according to the deviation. For example, when the pressure difference ΔP (n) is larger than the specified pressure difference ΔP (0) (S30: NO), it means that the cathode off-gas pressure is higher than the specified value and the purge amount per unit time is increased. Therefore, a correction time length ΔT (n) indicating a negative value is obtained (S31). On the other hand, when the pressure difference ΔP (n) is equal to or less than the specified pressure difference ΔP (0) (S30: YES), it means that the cathode off-gas pressure is lower than the specified value and the purge amount per unit time is reduced. Thus, a correction time length ΔT (n) indicating a positive value is obtained (S32). The correction time length ΔT (n) is added to the specified valve opening time length T (0) and stored for the next purge valve control (S33). The corrected valve opening time length T (n) is used as the opening / closing time length in the next purge valve opening / closing control.

FIG. 5 shows a timing chart of the purge valve opening / closing control in the second embodiment.
As shown in FIG. 5, in the (n-1) th purge, the opening / closing control is performed with the purge valve opening time length T (n-1), and after the time t2 when the purge valve is closed, the correction calculation is performed, and the nth time The correction time length ΔT (n) in purging is obtained, and the valve opening time length T (n) added with the specified valve opening time length T (0) is set. As described above, in the second embodiment, the calculation of the next correction time length may be completed during a relatively long interval after the purge valve is closed.

  As described above, according to the second embodiment, the same effect as that of the first embodiment is obtained, and the timing of the pressure difference measurement of the purge valve is set when the valve is opened and closed, such as when the purge valve is opened and closed. It can also be simplified. For this reason, it is not necessary to consider the factor of output stability after the purge valve is opened.

  Further, according to the second embodiment, since a certain period is assumed from the closing of the purge valve to the next opening, the calculation time can be increased. Thereby, when the calculation speed of the control unit 2 is slow or when the purge period is set to be short in the first place, it is possible to give a margin to the calculation time.

(Embodiment 3)
As in the first embodiment, the third embodiment of the present invention compares the reference pressure difference with the actually measured pressure difference to correct the purge valve opening time length. The specified value is updated.
FIG. 6 shows an overall system diagram of the fuel cell system. The fuel cell system according to the third embodiment is substantially the same as that of the first embodiment, but differs in the configuration of the control unit 2b.

  That is, in the third embodiment, the pressure difference ΔP (n) obtained by the pressure detection means 200 and the pressure difference calculation means 202 in the control unit 2b is a pressure difference for determining the valve opening time length of the nth purge. . As in the first embodiment, the pressure difference is detected as a differential pressure between the pressure P1 at the time t1 when the purge valve is opened and the pressure P2 at the time t2 when the purge valve is opened, as in the second embodiment. The pressure P1 at the valve time t1 and the pressure P2 at the valve close time t2 may be used.

  The opening / closing time correction means 220 according to the third embodiment is characterized in that the specified pressure difference ΔP is updated every purge, and the valve opening time length T is also updated every purge. The correction coefficient calculation unit 222 uses the pressure difference ΔP (n−1) updated last time (n−1) instead of the specified pressure difference ΔP (0) of the first embodiment, and this updated pressure The difference ΔP (n−1) is substituted into Equation 1 for correction calculation. Further, the specified valve opening time length is also updated for each purge, and the valve opening time length T (n-1) updated last time is used instead of the specified valve opening time length T (0) of the first embodiment. It is done. Then, the correction coefficient calculated by the correction coefficient calculation unit 212 and the valve opening time length T (n−1) updated last time are multiplied by the multiplication unit 226, and the current (n-th) correction time length ΔT (n) is obtained. This is calculated and added to the valve opening time length T (n−1) updated in the adding unit 230, and the corrected valve opening time length T (n) (= T (n−1) + ΔT (n)) is obtained. Is output. The corrected valve opening time length T (n) is stored as the next opening / closing time length (symbol 228).

Next, a series of operations in the control unit 2 will be described with reference to the flowchart of FIG.
First, it is determined whether or not the purge time has come (S41). When a predetermined interval has elapsed (S41: YES), the process proceeds to a purge process.

  As in the first embodiment, the detection signal Sd of the pressure sensor 17 is referred to, and the pressure P1 when the purge valve 18 is opened is grasped (S42). Immediately thereafter, the purge valve control signal Spc is output, and the purge valve 18 is opened (S43). Next, as in the first embodiment, the process waits until a certain time t2 when the pressure stabilizes has elapsed (S44: NO). When the certain time t2 has elapsed (S44: YES), the anode off-gas pressure is detected as P2. (S45). Note that, as in the second embodiment, the valve closing pressure may be detected as P2.

Next, the same correction calculation as in the first embodiment is performed.
First, the pressure difference ΔP (n) (= P1-P2) for the next time (n-th time) is calculated (S46). When the pressure difference ΔP (t) is within a predetermined reference range, that is, when the pressure difference ΔP (n−1) updated last time is almost the same (S48: YES), the correction time length ΔT (n) is It is set to be zero (S49).

  When the pressure difference ΔP (n) deviates from the reference range from the pressure difference ΔP (n−1) (S48: NO), the correction time length ΔT (n) is calculated according to the deviation. For example, when the pressure difference ΔP (n) is larger than the previous pressure difference ΔP (n−1) (S50: NO), the cathode off-gas pressure is higher than specified and the purge amount per unit time is increased. Therefore, a correction time length ΔT (n) indicating a negative value is obtained (S51). On the other hand, when the pressure difference ΔP (n) is equal to or smaller than the previous pressure difference ΔP (n−1) (S50: YES), the cathode off-gas pressure is lower than specified and the purge amount per unit time is small. This means that a correction time length ΔT (n) indicating a positive value is obtained (S52). And this correction | amendment time length (DELTA) T (n) is added with the valve opening time length T (n-1) of the last update. Then, the newly calculated valve opening time length T (n) is stored for the next purge valve correction calculation (S53). Then, until the corrected valve opening time length T (n) is reached (S54: NO), when the time length has elapsed (YES), the purge valve 18 is closed (S55).

  As described above, according to the configuration of the third embodiment, the same effect as that of the first and second embodiments is obtained, and the valve opening time length of the purge valve is updated every time the opening / closing time is corrected. For this reason, the appropriate valve opening time length always follows the change in diameter and the fluctuation of the system factor by the correction calculation, so that accurate purge control can be performed over a long period of time.

(Modification)
The present invention is not limited to the above embodiments and can be used with various modifications.
For example, in the above embodiment, the opening time length of the purge valve is corrected. However, the interval time length from the closing of the purge valve to the next opening may be changed. This is because even if the purge valve opening time length is constant, the purge amount per unit time can be changed by changing the time length of the interval. Both the purge valve opening time length and the interval time length may be changed.

  When correcting the interval period, the interval time length is increased when the pressure difference ΔP is equal to or larger than a predetermined reference value. When the pressure difference is large, it means that the purge flow rate per unit time is increased. Therefore, if the interval time length is increased, the purge amount can be properly maintained.

  Conversely, when the pressure difference is equal to or smaller than a predetermined reference value, the interval valve opening time length is decreased. When the pressure difference is small, it means that the purge flow rate per unit time is small. Therefore, if the valve opening time length is decreased, the purge amount can be kept appropriate.

  Further, when the purge valve has a structure capable of adjusting the opening degree, the flow rate may be adjusted by controlling the valve opening degree instead of controlling the valve opening time length or the interval time length. When the pressure difference is equal to or smaller than a predetermined reference value, the opening degree is increased, and when the pressure difference is larger than the reference value, the opening degree is decreased.

  In the above embodiment, the correction calculation is performed according to the pressure difference ΔP. However, an appropriate constant may be added or subtracted as the correction time length. For example, when the pressure difference is equal to or smaller than the reference value, a certain time length Tc is added, and when the pressure difference is larger than the reference value, the time length Tc is subtracted. Since it is not the correction time length ΔT obtained from the principle as in the above embodiment, it cannot be converged to the optimum value by a single calculation. However, since the purge is repeated, it is expected that the optimum purge time is converged for each purge.

Block diagram of a fuel cell system according to Embodiment 1 A flowchart for explaining a purge control method of the fuel cell system according to the first embodiment. Relationship diagram between purge valve open / close state and anode off-gas pressure in Embodiment 1 Flowchart for explaining a purge control method of the fuel cell system according to the second embodiment. FIG. 4 is a relationship diagram between the purge valve open / close state and the anode off-gas pressure according to the second embodiment. Block diagram of a fuel cell system according to Embodiment 3 Flowchart for explaining the purge control method of the fuel cell system according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas supply part, 2, 2b ... Control part, 10C ... Air electrode, 10A ... Fuel electrode, 10 ... Fuel cell, 11 ... Hydrogen tank, 12 ... Anode gas supply path, 13 ... Circulation path, 14 ... Circulation pump, DESCRIPTION OF SYMBOLS 15 ... Anode off-gas supply path, 16 ... Flow control part, 17 ... Pressure sensor, 18 ... Purge valve, 21 ... Air cleaner, 22 ... Cathode gas supply path, 23 ... Compressor, 24 ... Cathode off-gas supply path, 25 ... Diluter, 26: Exhaust path, 200 ... Pressure detection means, 202 ... Pressure difference calculation means, 204, 220 ... Opening / closing time correction means, 206 ... Purge valve control means, 212, 222 ... Correction coefficient calculation section, 216, 226 ... Multiplication section, 219, 230: Adder, Sd: Detection signal, Spc: Purge valve control signal, ΔP: Pressure difference, ΔT: Correction time length

Claims (16)

In the fuel cell system for discharging the anode off gas by opening and closing the purge valve disposed in the anode off gas passage of the fuel cell,
The purge amount is calculated based on the pressure difference between the anode off-gas pressure when the purge valve is opened and the anode off-gas pressure when a predetermined time has elapsed,
A fuel cell system, wherein the opening and closing time of the purge valve is corrected based on the calculated purge amount. A fuel cell;
An anode off-gas supply path for discharging anode off-gas discharged from the anode of the fuel cell;
A purge valve for discharging impurities contained in the anode offgas discharged to the anode offgas passage;
A pressure sensor for detecting an anode offgas pressure in the anode offgas supply path;
The purge amount is calculated based on the pressure difference between the anode off-gas pressure detected by the pressure sensor when the purge valve is opened and the anode off-gas pressure after a predetermined time has elapsed, and the purge amount is calculated based on the calculated purge amount. A fuel cell system comprising: a control device that corrects the opening and closing time of the valve. In a fuel cell system that opens and closes a purge valve to discharge anode off gas,
Pressure detecting means for detecting the pressure of the anode off gas;
Pressure difference calculating means for calculating a pressure difference detected by the pressure detecting means between the anode off gas pressure when the purge valve is opened and the anode off gas pressure when a predetermined time has elapsed;
Open / close time correcting means for correcting the open / close time of the purge valve based on the pressure difference calculated by the pressure difference calculating means;
Purge valve control means for opening and closing the purge valve according to the corrected opening and closing time;
A fuel cell system comprising:   4. The fuel cell system according to claim 1, wherein when the pressure difference is within a predetermined reference range, correction of the opening / closing time of the purge valve is prohibited. 5.   The fuel cell system according to any one of claims 1 to 4, wherein the correction of the opening and closing time of the purge valve is to change a valve opening time length from a valve opening time to a valve closing time of the purge valve. .   The fuel cell system according to claim 5, wherein when the pressure difference is equal to or greater than a predetermined reference value, a valve opening time length of the purge valve is decreased.   6. The fuel cell system according to claim 5, wherein when the pressure difference is equal to or less than a predetermined reference value, the valve opening time length of the purge valve is increased.   The fuel cell system according to claim 5, wherein the predetermined time elapses is a predetermined time after the purge valve is opened and before the valve is closed.   9. The fuel according to claim 8, wherein an opening / closing time of the purge valve is corrected while the purge valve is opened after the fixed time has elapsed, and the purge valve is closed after the corrected valve opening time has elapsed. Battery system.   6. The fuel cell system according to claim 5, wherein when the predetermined time has elapsed, the purge valve is closed, and the next purge valve is opened and closed with the corrected valve opening time length. 7.   The fuel cell system according to any one of claims 1 to 10, further comprising a flow restriction unit on an upstream side of the purge valve.   The fuel cell system according to any one of claims 1 to 11, wherein the opening / closing time of the purge valve is updated by the corrected opening / closing time each time the opening / closing time is corrected.   The fuel cell system according to any one of claims 1 to 4, wherein the correction of the opening / closing time of the purge valve is to change an interval time length from the closing of the purge valve to the next opening.   The fuel cell system according to claim 13, wherein the interval time length is increased when the pressure difference is equal to or greater than a predetermined reference value.   The fuel cell system according to claim 13, wherein the interval valve opening time length is decreased when the pressure difference is equal to or smaller than a predetermined reference value. In the purge control method for discharging the anode off gas from the purge means arranged in the anode off gas passage of the fuel cell,
Detecting the pressure of the anode offgas;
Calculating a pressure difference between the detected anode off-gas pressure at the start of purge by the purge means and the anode off-gas pressure after a certain period of time;
And a step of changing the opening / closing time of the purge means up to the previous time based on the calculated pressure difference.

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