JP2009123550A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which air is supplied to a fuel cell using a turbo air compressor, in which operation instability of the turbo air compressor is suppressed when an air flow-rate to be supplied to the fuel cell is small. <P>SOLUTION: The fuel cell system is provided with a fuel cell, an air supply passage for supplying air to the fuel cell, a turbo air compressor to supply air to the fuel cell, a bypass passage which is communicated with the air supply passage and exhausts air without going through the fuel cell, a bypass flow-rate adjusting part for adjusting the air volume passing through the bypass passage, and a control part which controls the bypass flow-rate adjusting part according to a demand air flow-rate. The control part adjusts the air flow-rate to be supplied to the fuel cell while maintaining the supply air flow-rate of the turbo air compressor at the lower limit flow-rate or more by utilizing the air flow-rate passing through the bypass passage, when the demand air flow-rate is smaller than the lower limit flow-rate determined beforehand of the turbo air compressor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for supplying air to a fuel cell.

  Some fuel cell systems supply air as an oxidant gas to a fuel cell using an air compressor (see Patent Document 1 below).

JP 2007-123006 A

  There is a centrifugal air compressor as an air compressor used in a fuel cell system. In this centrifugal air compressor, a rotating body called an impeller (an impeller) rotates inside the casing to compress air. When this centrifugal air compressor is used to supply oxidant gas (air) to a fuel cell in a fuel cell system, the operation of the centrifugal air compressor becomes unstable if the flow rate of air supplied to the fuel cell is small. There was a problem.

  As a cause of such unstable operation of the centrifugal air compressor, for example, occurrence of surging can be considered. Surging is a phenomenon in which the air flow rate and air pressure fluctuate significantly (pulsates) periodically. When surging occurs, a strong impact is applied to the impeller and the casing (case) of the compressor to damage the air compressor and control of the supply air flow rate becomes impossible.

  The above-described problem may occur not only in a centrifugal air compressor but also in an axial flow compressor in which a moving blade (rotor) rotates and performs compression. That is, it can occur in a turbo air compressor.

  The present invention suppresses the operation of a turbo air compressor from becoming unstable when the flow rate of air supplied to the fuel cell is small in a fuel cell system that supplies air to the fuel cell using a turbo air compressor. It aims at providing the technology that can be.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A fuel cell system, a fuel cell, an air supply channel for supplying air to the fuel cell, and a turbo type for supplying air to the fuel cell via the air supply channel An air compressor, a bypass channel that communicates with the air supply channel and exhausts air without passing through the fuel cell, and a bypass that is disposed in the bypass channel and adjusts the amount of air passing through the bypass channel A flow rate adjusting unit; and a control unit that controls the bypass flow rate adjusting unit according to a required air flow rate required for the fuel cell, wherein the control unit has the required air flow rate of the turbo type air compressor. When the flow rate is smaller than a predetermined lower limit flow rate, the supply air flow rate of the turbo air compressor is maintained at the lower limit flow rate or more using the air flow rate through the bypass flow path. Adjusting the air flow rate supplied to the fuel cell, the fuel cell system.

  In the fuel cell system of Application Example 1, when the required air amount is less than the lower limit flow rate, the fuel cell is maintained while maintaining the supply air flow rate of the turbo air compressor at or above the lower limit flow rate using the air flow rate passing through the bypass flow path. Since the amount of air supplied to the fuel cell is adjusted, it is possible to prevent the operation of the turbo air compressor from becoming unstable when the flow rate of air supplied to the fuel cell is small. The phrase “turbo type air compressor” has a broad meaning including a turbo type blower. Further, the “lower limit flow rate” means a lower limit of an air flow range in which the turbo air compressor can normally operate. For example, it means a lower limit flow rate at which surging does not occur.

  Application Example 2 The fuel cell system according to Application Example 1, further including a pressure regulating valve that adjusts air pressure in the fuel cell, wherein the control unit responds to a required air pressure required for the fuel cell. And controlling the pressure regulating valve to bring the air pressure in the fuel cell closer to the required air pressure.

  In this way, the air flow rate required for the fuel cell can be supplied to the fuel cell at the required air pressure.

  Application Example 3 In the fuel cell system according to Application Example 1 or Application Example 2, the control unit may prevent the air from flowing through the bypass flow path when the required air flow rate is equal to or higher than the lower limit flow rate. A fuel cell system that controls a bypass flow rate adjustment unit and controls the bypass flow rate adjustment unit so that air flows through the bypass flow path when the required air flow rate is smaller than the lower limit flow rate.

  In this way, when the required air amount is equal to or greater than the lower limit flow rate, air does not flow through the bypass flow path, so the total air amount sent out by the turbo air compressor is compared to when air flows through the bypass flow path. Less power is required, and the power consumption of the turbo air compressor can be kept low.

Hereinafter, the best mode for carrying out the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Fourth embodiment:
E. Variations:

A. First embodiment:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system as an embodiment of the present invention. The fuel cell system 1000 can be used for an electric vehicle, for example, and includes a fuel cell 100, an air cleaner 32, an air compressor 34, a muffler 36, a flow meter 52, a thermometer 54, and two pressures. 56, 58, flow control valve 42, back pressure valve 44, control unit 20, bypass flow path 70, two air supply flow paths 62, 64, and two air discharge flow paths 92, 94 It is equipped with.

  The fuel cell 100 is a solid polymer type fuel cell and includes an electrolyte membrane (not shown). Hydrogen gas as a fuel gas supplied from a hydrogen tank (not shown) is supplied to the anode 100a through the fuel gas passage 82 and used for the electrochemical reaction. The hydrogen gas that has not been used for the electrochemical reaction is discharged to the outside of the fuel cell 100 as an off gas. On the other hand, air as an oxidant gas is supplied to the cathode 100 c of the fuel cell 100 through the oxidant gas flow path 80. Air that has not been used for the electrochemical reaction at the cathode 100c is discharged to the outside of the fuel cell 100 as off-gas. As the fuel cell 100, other types of fuel cells such as phosphoric acid fuel cells may be employed instead of the solid polymer fuel cells.

  The air cleaner 32 removes impurities from the air sucked by the air compressor 34. The air compressor 34 sucks air from the atmosphere through the air cleaner 32 and compresses it, and sends the compressed air toward the cathode 100 c of the fuel cell 100. The air compressor 34 is a so-called turbo-type air compressor that compresses air by rotating a rotating body within a casing. As the air compressor 34, for example, a centrifugal compressor in which an impeller rotates and compresses, or an axial flow compressor in which a moving blade (rotor) rotates and compresses can be used. Here, the rotating body (such as an impeller) is driven by an electric motor (not shown). Therefore, by adjusting the voltage and current applied to the electric motor (not shown), the rotation speed of the rotating body can be controlled to control the output of the air compressor 34. In addition, it can also be set as a belt drive instead of the drive by an electric motor. Moreover, it can replace with an air compressor and can also employ | adopt a blower (blower).

  The flow meter 52 is disposed in the air supply channel 64 and can measure the flow rate of air flowing through the air supply channel 64. The thermometer 54 can measure the temperature in the air supply channel 64. The pressure gauge 56 is disposed in the air discharge passage 92 and can measure the air pressure in the air discharge passage 92. The pressure gauge 58 is disposed in the air supply flow path 62 and can measure the pressure on the discharge side of the air compressor 34.

  The back pressure valve 44 is disposed in the air discharge channel 92 and can be adjusted so as to keep the air pressure on the cathode 100c side, which is the primary side, constant. The flow rate adjustment valve 42 is disposed in the bypass flow path 70 and can adjust the amount of air passing through the bypass flow path 70. The flow rate adjustment valve 42 and the back pressure valve 44 are both electromagnetic valves. The flow rate adjusting valve 42 corresponds to a bypass flow rate adjusting unit in claims. The back pressure valve 44 corresponds to the pressure regulating valve in the claims.

  The control unit 20 includes a CPU 20a, a RAM 20c, and a ROM 20d. The CPU 20a functions as the control unit 20b by executing a control program (not shown) stored in the ROM 20d. In the ROM 20d, a surging characteristic map 20e, an air compressor operation map 20f, and a flow rate adjustment valve operation map 20g are stored in advance. The operation maps 20e, 20f, and 20g will be described later. The control unit 20 is connected to the flow rate adjustment valve 42 by a cable. Similarly, the control unit 20 is connected to the back pressure valve 44, the flow meter 52, the thermometer 54, the pressure gauge 56, and the pressure gauge 58 by cables. Therefore, the control unit 20 b can acquire the measurement values in the flow meter 52, the thermometer 54, the pressure gauge 56, and the pressure gauge 58, and can control the flow rate adjustment valve 42 and the back pressure valve 44.

  The bypass channel 70 has one end communicating with the air supply channel 62 and the other end communicating with the air discharge channel 94. That is, the bypass flow path 70 forms an air flow path that does not pass through the fuel cell 100. Therefore, a part of the air sent from the air compressor 34 flows into the bypass flow path 70 in accordance with the opening degree of the flow rate adjustment valve 42 and goes from the air discharge flow path 94 to the atmosphere without passing through the fuel cell 100. And discharged. When the flow rate adjustment valve 42 is closed, all the air sent from the air compressor 34 is supplied to the fuel cell 100.

  FIG. 2 is an explanatory diagram showing operating characteristics of the air compressor 34 shown in FIG. In FIG. 2, the horizontal axis indicates the flow rate of air sent from the air compressor 34, and the vertical axis indicates the discharge side pressure of the air compressor 34. In addition, operation lines La, Lb, Lc, Ld, and Le are described as examples of operation lines of the air compressor 34. In the air compressor 34, when the back pressure is changed while the rotation speed of the rotating body (impeller, etc.) is kept constant, the operation point is changed along the operation line (for example, the operation lines La, Lb, Lc) corresponding to the rotation speed. Moving. Here, the rotation speeds of the three operation lines La, Lb, and Lc are decreased in this order. For example, when the back pressure is gradually lowered, the operating point moves from the upper left to the lower right on the operating lines La, Lb, and Lc. On the other hand, when the back pressure is gradually increased, the operation lines La, Lb, and Lc are moved from the lower right to the upper left.

  In the air compressor 34, when the rotational pressure of the rotating body is changed while the back pressure is constant, the operating point moves along an operating line (for example, operating lines Ld and Le) corresponding to the back pressure. Here, the back pressure of the two operation lines Ld and Le decreases in this order. When the rotational speed of the rotating body is gradually lowered, the operating point moves from the upper right to the lower left on the operating lines Ld and Le. Such air compressor operating characteristics can be obtained by experiments in the fuel cell system 1000 shown in FIG.

  Here, since the air compressor 34 is a turbo type air compressor, surging can occur when the air flow rate is relatively small as a feature of this type of air compressor. Surging is a phenomenon in which the air flow rate and air pressure fluctuate significantly (pulsates) periodically.

  FIG. 3 is an explanatory view showing the occurrence characteristics of surging in the air compressor 34 shown in FIG. In FIG. 3, the horizontal axis represents the air flow rate in the air compressor 34, and the vertical axis represents the air pressure on the discharge side of the air compressor 34. In FIG. 3, the limit condition where surging does not occur is shown as a surging limit line L1. The left side of the surging limit line L1 is a region where surging occurs (hereinafter referred to as “surging region”), and the right side including the surging limit line L1 is a region where surging does not occur (hereinafter “normal”). Area).

  In the air compressor 34, surging occurs when the flow rate is relatively small at the same air pressure, and surging tends to occur when the air pressure is relatively high at the same flow rate. The surging limit line L1 can be obtained by experiment. Specifically, for example, in the fuel cell system 1000 (FIG. 1), the output (air flow rate) of the air compressor 34 is lowered stepwise while the flow rate adjustment valve 42 is closed, so that surging does not occur. Find the flow rate (lower flow rate). Then, by performing this operation while changing the discharge side pressure of the air compressor 34, a surging limit line L1 as shown in FIG. 2 can be obtained. Even if the flow rate adjustment valve 42 is open, the surging limit line L1 is substantially the same line. In the fuel cell system 1000, this surging characteristic (surging limit line L1) is stored as a surging characteristic map 20e in the ROM 20d (FIG. 1).

  If the required operating point determined by the air flow rate and air pressure required by the fuel cell 100 is included in the surging area, surging will occur if the air compressor 34 or the like is controlled to be the required operating point. If surging occurs, there is a risk of damaging the rotating body such as an impeller and the casing of the air compressor 34 with an extreme impact. Moreover, in the turbo type air compressor, the air flow rate can be adjusted by the rotational speed of the rotating body. However, if surging occurs, the air flow becomes unstable and it becomes difficult to adjust the air flow rate. Therefore, in the fuel cell system 1000, the flow rate of air passing through the bypass flow path 70 is adjusted to suppress the occurrence of surging. When the required operating point is within the normal range, the flow rate adjustment valve 42 is closed and no air flows through the bypass flow path 70.

  Specifically, when the current operating point is the operating point A in the normal range (FIG. 3), the operating point required by the fuel cell 100 is the operating point B in the surging range. This operating point B is an air flow rate Q1 that is less than the air flow rate Q0 at the current operating point A, and an air pressure P1 that is lower than the air pressure P0 at the operating point A. In addition, as a case where such an operating point B is requested | required, the case where the fuel cell system 1000 is mounted in the electric vehicle and the user lifts his / her foot from the accelerator to decelerate the electric vehicle can be considered, for example. . The control unit 20b determines whether or not the requested operating point is included in the surging area based on the surging characteristic map 20e (FIGS. 1 and 3).

  When it is determined that the requested operating point is included in the surging area, the control unit 20b sets the target operating point to the operating point C instead of the operating point B that is the requested operating point. This operating point C has the same air pressure P1 as the operating point B, but the air flow rate Q2 is larger than the air flow rate Q1 at the operating point B, and is included in the normal range. Then, the control unit 20b controls the air compressor 34, the flow rate adjusting valve 42, and the back pressure valve 44 toward the operating point C that is the target operating point.

  As a specific control operation, the control unit 20b first increases the air pressure by controlling the back pressure valve 44 without changing the rotational speed of the rotating body (step [1]). In this case, the operating point moves to the upper left as described in the operating characteristics (FIG. 2). At this time, since the air pressure rises with the rotational speed of the rotating body as it is, air hardly flows and the air flow rate decreases. When the air pressure rises to a predetermined pressure, the control unit 20b then controls the air compressor 34 based on the air compressor operation map 20f (FIG. 1) while keeping the back pressure constant to rotate the rotating body. And the air flow rate is adjusted to be Q2 (step [2]).

  FIG. 4 is an explanatory diagram schematically showing the air compressor operation map 20f shown in FIG. In FIG. 4, the horizontal axis indicates the required air pressure for the fuel cell 100, and the vertical axis indicates the target air flow rate of the air compressor 34. The surging limit line L1 shown in FIG. 3 is shown for reference. In the air compressor operation map 20f, a target air flow rate (target air flow line L2) corresponding to the required air pressure is determined in advance. Here, the target air flow rate line L2 is located slightly above the surging limit line L1. That is, at each required air pressure, the target air flow rate is set to be slightly higher than the lower limit flow rate at which surging does not occur. Therefore, based on the target air flow line L2, the control unit 20b can obtain Q2 slightly higher than Q1 as the target air flow rate when the required air pressure is P1 described above, and the air flow rate becomes Q2. In addition, the air compressor 34 can be controlled.

  Then, when the air compressor 34 operates at the operating point C (FIG. 3), the control unit 20b controls the flow rate adjusting valve 42, and the flow rate corresponding to the difference in air flow rate between the required operating point B and the required operating point C. It adjusts so that the air of Q3 (Q2-Q1) may flow into bypass channel 70. At this time, the control unit 20b controls the opening degree of the flow rate adjustment valve 42 based on the flow rate adjustment valve operation map 20g (FIG. 1).

  FIG. 5 is an explanatory diagram schematically showing the flow rate adjustment valve operation map 20g shown in FIG. In FIG. 5, the horizontal axis indicates the required air flow rate, and the vertical axis indicates the opening degree of the flow rate adjustment valve 42. In the flow rate adjustment valve operation map 20g, the opening degree of the flow rate adjustment valve 42 corresponding to the required air flow rate is predetermined for each required air pressure. For example, as described above, when the required air pressure is P1 and the required air flow rate is Q1, the opening degree of the flow rate adjusting valve 42 is R1. The opening R1 is determined in advance by experiments so that the air flow rate through the bypass flow path 70 is Q3 when the cathode-side air pressure is P1 in the fuel cell system 1000. Therefore, when the controller 20b controls the opening of the flow rate adjusting valve 42 to be R1, the air flow rate flowing through the bypass flow path 70 becomes Q3, and the air flow rate flowing into the cathode 100c via the air supply flow path 64. Becomes Q1 (Q2-Q3). Then, the air with the required air flow rate Q1 can be supplied to the fuel cell 100 at the required air pressure P1. At this time, since the air compressor 34 operates at the operating point C in the normal range, it is possible to avoid the occurrence of surging.

  As described above, in the fuel cell system 1000, when the required air flow rate of the fuel cell 100 is less than the lower limit flow rate, the air compressor 34 is controlled with a flow rate slightly higher than the lower limit flow rate as the target air flow rate, and the required air flow Since the air of the flow rate Q3 corresponding to the difference between the flow rate and the target air flow rate is discharged through the bypass flow path 70, the occurrence of surging in the air compressor 34 can be suppressed, and air can be stably supplied to the fuel cell 100. Can be supplied. Further, since the back pressure valve 44 and the air compressor 34 are controlled so as to obtain the required air pressure, the required air pressure required by the fuel cell 100 can be realized. In addition, since the target air flow rate is set to a level slightly higher than the lower limit flow rate, the power consumption in the air compressor 34 can be suppressed lower than when a flow rate sufficiently higher than the lower limit flow rate is set as the target air flow rate. it can.

B. Second embodiment:
FIG. 6 is an explanatory diagram showing changes in the operating point of the air compressor 34 in the second embodiment. The fuel cell system according to the second embodiment is different from the fuel cell system 1000 (FIG. 1) in that the target operating point when the required operating point is within the surging region is the operating point D. This is the same as the first embodiment.

  Specifically, the target operating point D in the second embodiment has the same air pressure as the required air pressure P1 at the required operating point B, and the air flow rate is Q4, which is higher than the required flow rate Q1. Here, the flow rate Q4 is larger than the air flow rate Q2 at the operating point C, which was the target operating point in the first embodiment. That is, the operating point C in the first embodiment is set in a region relatively close to the surging limit line L1, but the operating point D is set in a region relatively far from the surging limit line L1. In this case, unlike the first embodiment, the controller 20b controls the back pressure valve 44 to reduce the air pressure while maintaining the rotational speed of the rotating body in step [1]. Then, the operating point moves to the lower right. At this time, since the air pressure decreases with the rotational speed of the rotating body as it is, air easily flows and the air flow rate increases. When the air pressure drops to a predetermined pressure, the control unit 20b executes step [2] as in the first embodiment. At this time, the controller 20b adjusts the air flow rate to be Q4. Note that whether to increase or decrease the air pressure in step [1] can be determined by the control unit 20b in consideration of the current operating point, the target operating point, and the operating line (FIG. 2).

  In the fuel cell system according to the second embodiment having such a configuration, the difference Q5 between the required air flow rate Q1 and the air flow rate Q4 at the operating point D is discharged through the bypass flow path 70. The same effect as the fuel cell system 1000 in the example is achieved.

C. Third embodiment:
FIG. 7 is an explanatory diagram showing changes in the operating point of the air compressor 34 in the third embodiment. The fuel cell system according to the third embodiment is different from the fuel cell system 1000 (FIG. 1) in that the air flow rate in the air compressor 34 is not adjusted when the required operating point is within the surging region. This is the same as the first embodiment.

  Specifically, when the current operating point is the operating point A and the required operating point is the operating point B in the surging area, the control unit 20b controls the back pressure valve 44 so that the air pressure becomes P1. Adjust (step [1]). At this time, since the air pressure decreases from P0 to P1, air easily flows, the air flow rate increases to Q6 (> Q0), and the operating point A shifts to the operating point E. Then, the controller 20b adjusts the opening degree by controlling the flow rate adjusting valve 42 without adjusting the air flow rate in the air compressor 34 (without executing Step [2]). At this time, the flow rate adjustment valve 42 is opened so that the amount of air passing through the bypass flow path 70 becomes a differential flow rate Q7 between the required air flow rate Q1 and the flow rate Q6 at the operating point E. Such a relationship between the required air flow rate and the opening degree of the flow rate adjustment valve 42 is obtained in advance by experiments and stored in the ROM 20d as a flow rate adjustment valve operation map 20g.

  In the fuel cell system of the third embodiment having such a configuration, the difference Q7 between the required air flow rate Q1 and the air flow rate Q6 at the operating point E is discharged via the bypass flow path 70, so the first embodiment The same effect as the fuel cell system 1000 in FIG.

D. Fourth embodiment:
FIG. 8 is an explanatory diagram showing changes in the operating point of the air compressor 34 in the fourth embodiment. In the fuel cell system according to the fourth embodiment, the current operating point is the operating point F (air pressure P2, air flow rate Q10), and the back pressure is not adjusted when the required operating point is within the surging range. Unlike the fuel cell system 1000 (FIG. 1), other configurations are the same as those of the first embodiment.

  Specifically, when the current operating point is the operating point F (air pressure P2, air flow rate Q10) in the normal range and the required operating point is the operating point B in the surging range, the control unit 20b includes the back pressure valve 44. Without controlling the air compressor 34, the air compressor 34 is controlled to adjust the air flow rate to Q8, and the operating point F is shifted to the operating point G (step [2]). Then, the control unit 20b controls the flow rate adjustment valve 42 to open the flow rate adjustment valve 42 so that the amount of air passing through the bypass flow path 70 becomes the differential flow rate Q9 between the required air flow rates Q1 and Q8. By doing in this way, the air of the required flow rate Q1 can be supplied to the fuel cell 100, and the occurrence of surging in the air compressor 34 can be suppressed.

E. Fifth embodiment:
FIG. 9 is an explanatory diagram showing a schematic configuration of the fuel cell system according to the fifth embodiment. This fuel cell system 1000a differs from the fuel cell system 1000 (FIG. 1) in that one end of the bypass flow path 70 is not in communication with the air discharge flow path 94, and the other configuration is the same as that of the first embodiment. is there.

  Specifically, the downstream side of the flow rate adjustment valve 42 in the bypass channel 70 does not communicate with the air discharge channel 94. Therefore, the air flowing into the bypass flow path 70 from the air compressor 34 is released to the atmosphere without passing through the air discharge flow path 94 and the muffler 36. The fuel cell system 1000a having such a configuration has the same effects as the fuel cell system 1000 in the first embodiment.

F. Variations:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in each of the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

F1. Modification 1:
In each of the above-described embodiments, the flow rate adjustment valve 42 is opened when the required operating point is in the surging range and closed when the required operating point is in the normal range. Even if the point is in the normal range, it can be opened at a predetermined opening. In this configuration, when the current operating point is in the normal range and the required operating point is to be shifted to the surging range, the opening of the flow rate adjustment valve 42 is increased and the opening determined based on the flow rate adjustment valve operation map 20g. The occurrence of surging can be suppressed by controlling so as to be the degree. As can be understood from the above embodiments and modifications, the air compressor 34 is controlled by controlling the flow rate adjusting valve 42 to increase the air flow rate through the bypass flow path 70 when the required operating point is within the surging region. Any configuration that adjusts the air flow rate supplied to the cathode 100c side of the fuel cell 100 without reducing the supply air flow rate below the lower limit flow rate can be applied to the fuel cell system of the present invention.

F2. Modification 2:
In the first embodiment described above, in order to shift from the current operating point A (FIG. 3) to the operating point C, the back pressure valve 44 is first controlled to adjust to a predetermined air pressure (step [1] Next, the air compressor 34 is controlled to adjust the air flow rate to be Q2 (step [2]). Instead, these steps [1] and [2] are performed. It can also be executed at the same time. Further, the order in which these steps [1] and [2] are executed can be changed, and step [1] can be executed after step [2].

F3. Modification 3:
In the above-described embodiment, the reason why the supply of air to the fuel cell 100 becomes unstable is the occurrence of surging, but when the supply of air at a low flow rate can become unstable due to any other reason, By applying the fuel cell system of the present invention, it is possible to stably supply air. In this case, instead of determining whether or not the operating point is in the surging region, it is determined whether or not the required air flow rate is less than the lower limit flow rate at which the air compressor 34 can stably operate at the required air pressure. Can be. This lower limit flow rate can be obtained in advance by experiments and stored in the ROM 20d as a map, as in the above-described embodiments.

F4. Modification 4:
In each of the above-described embodiments, the two pressure gauges 56 and 58 are disposed in the air discharge flow path 92 or the air supply flow path 62, but instead of these positions, the oxidant gas flow path 80 is provided. It may be arranged. In this case, as a surging characteristic, the relationship between the air pressure in the oxidant gas flow path 80 and the air flow rate in the air compressor 34 can be obtained in advance by experiments and stored in the ROM 20d as a surging characteristic map 20e. Note that the pressure gauge 56 may be disposed in the air supply flow path 64. Further, the number of pressure gauges is not limited to two, and may be an arbitrary number. Similarly, the arrangement position of the flow meter 52 is not limited to the air supply flow path 64, and may be disposed in other places such as the oxidant gas flow path 80, the air discharge flow path 92, and the air supply flow path 62. Further, the number of the flow meters 52 is not limited to one and may be an arbitrary number.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows schematic structure of the fuel cell system as one Example of this invention. Explanatory drawing which shows the operating characteristic of the air compressor 34 shown in FIG. Explanatory drawing which shows the generation | occurrence | production characteristic of the surging in the air compressor 34 shown in FIG. Explanatory drawing which shows typically the air compressor operation | movement map 20f shown in FIG. Explanatory drawing which shows typically the flow volume adjustment valve operation map 20g shown in FIG. Explanatory drawing which shows the change of the operating point of the air compressor 34 in a 2nd Example. Explanatory drawing which shows the change of the operating point of the air compressor 34 in a 3rd Example. Explanatory drawing which shows the change of the operating point of the air compressor 34 in a 4th Example. Explanatory drawing which shows schematic structure of the fuel cell system in a 5th Example.

Explanation of symbols

20 ... Control unit 20a ... CPU
20b ... Control unit 20c ... RAM
20d ... ROM
20e ... Surging characteristics map 20f ... Air compressor operation map 20g ... Flow adjustment valve operation map 32 ... Air cleaner 34 ... Air compressor 36 ... Muffler 42 ... Flow adjustment valve 44 .. Back pressure valve 52 ... Flow meter 54 ... Thermometer 56, 58 ... Pressure gauge 62 ... Air supply flow path 64 ... Air supply flow path 70 ... Bypass flow path 80 .. Oxidant gas flow path 82 ... Fuel gas flow path 92 ... Air discharge flow path 94 ... Air discharge flow path 100 ... Fuel cell 100a ... Anode 100c ... Cathode 1000, 1000a. ..Fuel cell system A to F ... Operating points Q0 to Q10 ... Air flow rate P0 to P2 ... Air pressure L1 ... Surging limit line L2 ... Target air flow rate line R1 ... Opening

Claims (3)

A fuel cell system,
A fuel cell;
An air supply channel for supplying air to the fuel cell;
A turbo air compressor for supplying air to the fuel cell through the air supply flow path;
A bypass passage communicating with the air supply passage and exhausting air without passing through the fuel cell;
A bypass flow rate adjusting unit for adjusting the amount of air passing through the bypass channel disposed in the bypass channel;
A control unit for controlling the bypass flow rate adjusting unit according to a required air flow rate required for the fuel cell;
With
When the required air flow rate is less than a predetermined lower limit flow rate of the turbo air compressor, the control unit uses the air flow rate through the bypass flow path to reduce the supply air flow rate of the turbo air compressor. A fuel cell system that adjusts a flow rate of air supplied to the fuel cell while maintaining the flow rate at or above the lower limit flow rate. The fuel cell system according to claim 1, further comprising:
A pressure regulating valve for adjusting the air pressure in the fuel cell;
The said control part is a fuel cell system which controls the said pressure regulation valve according to the request | requirement air pressure requested | required of the said fuel cell, and makes the air pressure in the said fuel cell approach the said request | requirement air pressure. The fuel cell system according to claim 1 or 2,
The control unit controls the bypass flow rate adjusting unit so that air does not flow in the bypass flow path when the required air flow rate is equal to or higher than the lower limit flow rate, and the required air flow rate is less than the lower limit flow rate. In the fuel cell system, the bypass flow rate adjusting unit is controlled so that air flows through the bypass flow path.

Images