JP6908881B2 - Fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

The fuel cell has a stack structure in which a plurality of single cells are stacked in series, and each single cell has an anode electrode arranged on one surface of the electrolyte membrane and a cathode electrode arranged on the other surface. It has a membrane-electrode assembly. By supplying fuel gas (hydrogen gas) and oxidation gas (air) to the membrane-electrode assembly, an electrochemical reaction occurs and chemical energy is converted into electrical energy. Among them, the polymer electrolyte electrolyte fuel cell, which uses a polymer electrolyte membrane as an electrolyte, is expected to be used as an in-vehicle power source for electric vehicles because it is low in cost, easy to be compact, and has a high output density. Has been done. In this type of electric vehicle, from the viewpoint of downsizing the in-vehicle power source and reducing the cost, for example, as proposed in Japanese Patent Application Laid-Open No. 2009-123550, for humidifying the air supplied to the fuel cell. There is a tendency to adopt a so-called non-humidifying system without a humidifying device and to adopt a turbo compressor as an air compressor for supplying air to a fuel cell. Further, in such a non-humidifying system, in order to maintain the electrolyte membrane of the fuel cell in an appropriate wet state, the back pressure of the air supplied to the fuel cell is increased to reduce the volume flow rate, and the air is taken away from the inside of the fuel cell. The amount of water is reduced.

Japanese Unexamined Patent Publication No. 2009-123550

However, if the air flow rate required for the fuel cell is also reduced as the load required for the fuel cell is reduced, the operation of the turbo compressor may become unstable. Surging may occur as a cause of unstable operation of the turbo compressor. Surging is a phenomenon in which air flow rate and air pressure fluctuate violently (pulsate) periodically. In order to stabilize the operation of the turbo compressor, it is desirable to suppress the occurrence of surging.

Therefore, an object of the present invention is to propose a fuel cell system capable of stabilizing the operation of a turbo compressor.

In order to solve the above-mentioned problems, the fuel cell system according to the present invention includes (i) a fuel cell, (ii) an air supply flow path for supplying air to the fuel cell, and (iii) a fuel cell through the air supply flow path. A turbo compressor that supplies air to the fuel cell, and (iv) a bypass passage that branches off from the air supply flow path and discharges the air supplied from the turbo compressor by bypassing the fuel cell, and (v). ) A flow rate adjusting valve for adjusting the flow rate of air flowing through the bypass flow path, and (vi) a control device for controlling the rotation speed of the turbo compressor and the valve opening degree of the flow rate adjusting valve are provided. The control device estimates that the operating point of the turbo compressor falls within the surging region, which is determined by the air flow rate and air pressure required for the fuel cell to generate the target power, and the operating point of the turbo compressor falls within the surging region. Compared to when it is estimated that the operating point of the turbo compressor does not enter the surging area so that it does not enter, the rotation speed of the turbo compressor is gradually reduced, and the surplus caused by the gradual decrease in the rotation speed of the turbo compressor. The valve opening of the flow control valve is controlled so that air is discharged through the bypass flow path.

According to the fuel cell system according to the present invention, the operation of the turbo compressor can be stabilized.

It is explanatory drawing which shows the outline of the structure of the fuel cell system which concerns on this embodiment. It is explanatory drawing of the surging characteristic map which concerns on this embodiment. It is explanatory drawing which shows the control method of the turbo compressor when the required load of a fuel cell is reduced. It is explanatory drawing which shows the control method of the turbo compressor when the required load of a fuel cell is reduced. It is explanatory drawing which shows the control method of the turbo compressor when the required load of a fuel cell is reduced. It is explanatory drawing which shows the control method of the turbo compressor when the required load of a fuel cell is reduced. It is a flowchart which shows the control flow of the turbo compressor which concerns on this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to each figure. Here, the same reference numerals indicate the same elements, and duplicate description will be omitted.
FIG. 1 is an explanatory diagram showing an outline of the configuration of the fuel cell system 10 according to the present embodiment. The fuel cell system 10 mainly includes a fuel cell 20, an oxidation gas supply system 30, a fuel gas supply system 40, and a control device 50. The fuel cell 20 has a stack structure in which a plurality of single cells are stacked. The single cell sandwiches the anode pole 21 formed on one surface of the electrolyte membrane made of an ion exchange membrane, the cathode pole 22 formed on the other surface of the electrolyte membrane, and the anode pole 21 and the cathode pole 22 from both sides. It has a pair of separators. At the anode pole 21, the electrochemical reaction of the formula (1) occurs, and at the cathode pole 22, the electrochemical reaction of the formula (2) occurs. By such an electrochemical reaction, a single cell generates an electromotive force of about 1 volt. When the fuel cell 20 is used as an in-vehicle power supply system, hundreds of single cells are stacked.

_{^{2H 2 → 4H + + 4e -}} ... (1)
_{^{H + + 4e - + O 2}} → 2H 2 O ... (2)

The oxidation gas supply system 30 supplies air as an oxidation gas to the cathode electrode 22 of the fuel cell 20. The oxidation gas supply system 30 includes an air supply flow path 31 that supplies air to the fuel cell 20, an air off gas flow path 32 that discharges air off gas from the fuel cell 20, and an air off gas branching from the air supply flow path 31. A bypass flow path 33 connected to the flow path 32 is provided. A turbo compressor CP is provided on the upstream side of the air supply flow path 31 from the position where the bypass flow path 33 branches from the air supply flow path 31. The turbo compressor CP supplies the air taken in from the atmosphere through the air cleaner AC to the fuel cell 20 through the air supply flow path 31. The turbo compressor CP is a turbo type blower. For example, a centrifugal air compressor in which an impeller called an impeller rotates to compress air, or an axial flow type air in which a moving blade called a rotor rotates to compress air. Including compressor etc. The air supply flow path 31 is supplied to the fuel cell 20 with a shutoff valve V1 that selectively shuts off the supply of air to the fuel cell 20, a pressure gauge P1 that measures the pressure on the discharge side of the turbo compressor CP, and the fuel cell 20. A flow meter Q for measuring the flow rate of air is provided. The air-off gas flow path 32 is provided with a pressure regulating valve V2 for adjusting the air pressure in the fuel cell 20 and a pressure gauge P2 for measuring the air pressure in the air-off gas flow path 32. The bypass flow path 33 bypasses the fuel cell 20 and discharges the air supplied from the turbo compressor CP. The bypass flow path 33 is provided with a flow rate adjusting valve V3 that adjusts the flow rate of air flowing through the bypass flow path 33. The air off gas flowing through the air off gas flow path 32 is discharged to the atmosphere through the muffler MF.

The fuel gas supply system 40 supplies hydrogen gas as a fuel gas to the anode pole 21 of the fuel cell 20. The fuel gas supply system 40 is provided with a hydrogen supply flow path 41 that supplies hydrogen gas released from the hydrogen supply device AS to the fuel cell 20, and a hydrogen off gas flow path 42 that discharges hydrogen off gas from the fuel cell 20. There is. The hydrogen supply device AS is, for example, a hydrogen tank for storing high-pressure hydrogen gas.

The control device 50 is an electronic control unit including a processor 51, a storage resource 52, and an input / output interface 53. The processor 51 has an air flow rate (target air flow rate) and a hydrogen flow rate (target air flow rate) required for the fuel cell 20 to generate the generated power (target power) required for the fuel cell 20 according to the required load of the fuel cell 20. The target hydrogen flow rate) is calculated, measurement signals from various sensors (for example, flow meter Q and pressure gauges P1 and P2) are input through the input / output interface 53, and the target air flow rate and the target hydrogen flow rate are supplied to the fuel cell 20. Each part of the fuel cell system 10 (for example, the rotation speed of the turbo compressor CP and the valve opening degree of each of the shutoff valve V1, the pressure regulating valve V2, and the flow rate adjusting valve V3) is controlled so as to be performed. The storage resource 52 is a storage area provided by various memories such as a random access memory and a read-only memory. The surging characteristic map 60 is stored in the storage resource 52.

The surging characteristic map 60 will be described with reference to FIG. The horizontal axis of FIG. 2 shows the air flow rate of the turbo compressor CP, and the vertical axis shows the air pressure on the discharge side of the turbo compressor CP. The line connecting the operating points of the turbo compressor CP at the limit where surging does not occur is called the surging limit line 61. Here, the operating point of the turbo compressor CP means an operating state determined by the air flow rate and the air pressure of the turbo compressor CP. The surging characteristic map 60 holds the surging limit line 61 as map data. Under the same air flow rate, surging occurs at air pressures higher than the air pressure on the surging limit line 61 corresponding to that air flow rate. The set of operating points of the turbo compressor CP where surging occurs is called a surging region. On the other hand, a set of operating points of the turbo compressor CP in which surging does not occur is called a non-surging region. For example, the air pressure on the surging limit line 61 corresponding to the air flow rate Q0 is set to P2, and 0 <P1 <P2 <P3. In this case, the operating point A1 of the turbo compressor CP when the air flow rate is Q0 and the air pressure is P1 exists in the non-surging region. On the other hand, the operating point A3 of the turbo compressor CP when the air flow rate is Q0 and the air pressure is P3 exists in the surging region.

Next, a method of controlling the turbo compressor CP when the required load of the fuel cell 20 is reduced will be described with reference to FIGS. 3 to 7. Here, the horizontal axis of FIGS. 3 to 5 shows the air flow rate of the turbo compressor CP, and the vertical axis shows the ratio of the air pressure between the intake side and the discharge side of the turbo compressor CP. As shown in FIG. 3, when the operating point A of the turbo compressor CP exists in the non-surging region away from the surging limit line 61, the turbo compressor CP responds to the reduction of the required load of the fuel cell 20. The locus 62 of the operating point A of the turbo compressor CP remains in the non-surging region even if the rotation speed of the turbo compressor CP is reduced. Therefore, even if the rotation speed of the turbo compressor CP is reduced in response to the reduction in the required load of the fuel cell 20, surging does not occur. On the other hand, as shown in FIG. 4, when the operating point A of the turbo compressor CP exists in the non-surging region near the surging limit line 61, the rate of decrease in the rotation speed of the turbo compressor CP is limited. If the rotation speed of the turbo compressor CP is reduced in response to the reduction of the required load of the fuel cell 20, the locus 62 of the operating point A of the turbo compressor CP enters the surging region from the non-surging region. As a result, surging will occur.

Therefore, as shown in FIG. 5, when the operating point A of the turbo compressor CP exists in the non-surging region near the surging limit line 61, the operating point A of the turbo compressor CP does not enter the surging region. As described above, the rotation speed of the turbo compressor CP is gradually reduced as compared with the case where the operating point A of the turbo compressor CP is estimated not to enter the surging region (FIG. 3). Here, "gradually reducing the rotation speed of the turbo compressor CP" means lowering the upper limit of the reduction speed of the rotation speed of the turbo compressor CP. In this way, when the required load of the fuel cell 20 is reduced, the rotation speed of the turbo compressor CP is gradually reduced so that the locus 62 of the operating point A of the turbo compressor CP stays in the non-surging region. can. The torque rate of the turbo compressor CP is calculated so that the operating point A of the turbo compressor CP is closer to the surging limit line 61, the rotation speed of the turbo compressor CP is reduced more slowly, and the turbo is calculated according to the calculated torque rate. It is desirable to reduce the rate of decrease in the number of revolutions of the compressor CP. The torque rate is a factor that affects the system design (for example, the characteristics of the turbo compressor CP and the capacity of the battery that stores the generated power of the fuel cell 20) and the air flow rate in the fuel cell 20 (for example, the cathode volume, etc.). And the response characteristics of the valve, etc.) should be taken into consideration to determine the optimum value. When the rotation speed of the turbo compressor CP is gradually reduced, the air flow rate supplied from the turbo compressor CP exceeds the target air flow rate of the fuel cell 20. Therefore, it is desirable to control the valve opening degree of the flow rate adjusting valve V3 so that the excess air generated by the gradual decrease in the rotation speed of the turbo compressor CP is discharged through the bypass flow path 33. Here, reference numeral 601 in FIG. 6 indicates the air flow rate supplied from the turbo compressor CP, and reference numeral 602 indicates the air flow rate supplied to the fuel cell 20. The surplus air means air having an air flow rate obtained by subtracting the air flow rate 602 supplied to the fuel cell 20 from the air flow rate 601 supplied from the turbo compressor CP.

When the responsiveness of the flow control valve V3 is lower than the responsiveness of the turbo compressor CP, the turbo does not gradually reduce the rotation speed of the turbo compressor CP, but the turbo responds to the reduction of the required load of the fuel cell 20. When the rotation speed of the compressor CP is reduced, the turbo compressor CP is kept closed (that is, the ratio of the air pressure between the intake side and the discharge side of the turbo compressor CP is high). Since the air flow rate from the turbo is reduced, surging occurs.

FIG. 7 is a flowchart showing a control flow of the turbo compressor CP when the required load of the fuel cell 20 is reduced. When the control device 50 detects that the required load of the fuel cell 20 has been reduced (step 701; YES), the control device 50 obtains the operating point of the turbo compressor CP (step 702). The operating point of the turbo compressor CP can be obtained based on the measurement signals from the pressure gauge P1 and the flow meter Q. Next, the control device 50 estimates whether or not the operating point of the turbo compressor CP, which is determined by the air flow rate and air pressure required for the fuel cell 20 to generate the target electric power, falls within the surging region (step). 703). For example, when the operating points of the turbo compressor CP are separated from the surging limit line 61 at intervals equal to or greater than the threshold value, even if the rotation speed of the turbo compressor CP is reduced in response to the reduction of the required load of the fuel cell 20, the turbo It can be estimated that the operating point of the compressor CP remains in the non-surging region. On the other hand, when the operating points of the turbo compressor CP are close to the surging limit line 61 at intervals less than the threshold value, if the rotation speed of the turbo compressor CP is reduced in accordance with the reduction of the required load of the fuel cell 20, the turbo compressor It can be estimated that the operating point of the CP enters the surging region from the non-surging region. This threshold value can be obtained in advance from, for example, the characteristics of the turbo compressor CP and factors that affect the air flow rate in the fuel cell 20 (for example, the cathode volume and the response characteristics of the valve).

When the control device 50 estimates that the operating point of the turbo compressor CP falls within the surging region (step 703; YES), the control device 50 calculates the target air flow rate of the fuel cell 20 (step 704), and the operating point of the turbo compressor CP is determined. The torque rate required to gradually reduce the rotation speed of the turbo compressor CP so as not to enter the surging region is calculated (step 705). Next, the control device 50 calculates the valve opening degree of the flow rate adjusting valve V3 for flowing the excess air into the bypass flow path 33 (step 706). Next, the control device 50 controls the rotation of the turbo compressor CP at the torque rate calculated in step 705, and opens the flow rate adjusting valve V3 at the valve opening degree calculated in step 706 (step 707). On the other hand, assuming that the operating point of the turbo compressor CP does not fall within the surging region (step 703; NO), the control device 50 requests the fuel cell 20 without gradually reducing the rotation speed of the turbo compressor CP. The rotation speed of the turbo compressor CP is reduced as the load is reduced (step 708).

As described above, according to the present embodiment, assuming that the operating point of the turbo compressor CP falls within the surging region, the rotation speed of the turbo compressor CP is determined so that the operating point of the turbo compressor CP does not fall within the surging region. The suction side of the turbo compressor CP is controlled by controlling the valve opening degree of the flow rate adjusting valve V3 so that the excess air generated by the gradual decrease in the rotation speed of the turbo compressor CP is discharged through the bypass flow path 33. When the ratio of the air pressure between the turbo compressor and the discharge side is high, it is possible to suppress a decrease in the air flow rate from the turbo compressor CP. As a result, it is possible to prevent the occurrence of surging.

Further, by increasing the back pressure of the air supplied to the fuel cell 20 by using the turbo compressor CP, a humidifying device for humidifying the air supplied to the fuel cell 20 becomes unnecessary, and the configuration of the fuel cell system 10 is simplified. And miniaturization becomes possible. Further, the generation of surplus electric power can be suppressed by discharging the surplus air through the bypass flow path 33 without supplying the surplus air to the fuel cell 20. This eliminates the need for a large-capacity battery for storing surplus electric power, and makes it possible to simplify and downsize the configuration of the fuel cell system 10.

The embodiments described above are for facilitating the understanding of the present invention, and are not for limiting and interpreting the present invention. The present invention can be modified / improved without departing from the spirit of the present invention, and the present invention also includes an equivalent thereof. That is, those skilled in the art with appropriate design changes are also included in the scope of the present invention as long as they have the features of the present invention. For example, each element included in the embodiment and its arrangement are not limited to those illustrated, and can be changed as appropriate. Further, the positional relationship such as up, down, left, and right is not limited to the ratio shown in the figure unless otherwise specified. In addition, the elements included in the embodiment can be combined as much as technically possible, and the combination thereof is also included in the scope of the present invention as long as the features of the present invention are included.

10 ... Fuel cell system 20 ... Fuel cell 21 ... Anode pole 22 ... Cathode pole 30 ... Oxidation gas supply system 31 ... Air supply flow path 32 ... Air off gas flow path 33 ... Bypass flow path 40 ... Fuel gas supply system 41 ... Hydrogen supply Flow path 42 ... Hydrogen off-gas flow path 50 ... Control device CP ... Turbo compressor V1 ... Shutoff valve V2 ... Pressure regulating valve V3 ... Flow control valve

Claims (1)

With a fuel cell
An air supply flow path that supplies air to the fuel cell and
A turbo compressor that supplies air to the fuel cell through the air supply flow path,
A bypass passage that branches from the air supply flow path and discharges the air supplied from the turbo compressor by bypassing the fuel cell.
A flow rate adjusting valve that adjusts the flow rate of air flowing through the bypass flow path,
A control device for controlling the rotation speed of the turbo compressor and the valve opening degree of the flow rate adjusting valve is provided.
The control device estimates that the operating point of the turbo compressor, which is determined by the air flow rate and air pressure required for the fuel cell to generate the target power, falls within the surging region, and the operating point of the turbo compressor is determined. The rotation speed of the turbo compressor is gradually reduced as compared with the case where it is estimated that the operating point of the turbo compressor does not enter the surging region so as not to enter the surging region. A fuel cell system that controls the valve opening degree of the flow rate adjusting valve so that excess air generated by a gradual decrease in the number of revolutions is discharged through the bypass flow path.

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