Fuel cell system and its control method

Abstract

The present invention provides a fuel cell system and a control method thereof. The system includes a hydrogen injection valve for controlling the input of high-pressure hydrogen, an ejector connected to the hydrogen injection valve, and a fuel cell stack and a gas-water separator respectively connected to the ejector. The system further includes a check valve and a reversing valve. The hydrogen injection valve includes a primary hydrogen injection valve and a secondary hydrogen injection valve. The ejector includes a primary ejector and a secondary ejector. The primary ejector has a primary ejector primary inlet, a primary ejector secondary inlet, and a primary ejector outlet. The secondary ejector has a secondary ejector primary inlet, a secondary ejector secondary inlet, and a secondary ejector outlet. The present invention can improve the entrainment ratio under low-power conditions, increase the hydrogen supply under high-power conditions, and broaden the working range of the ejector in fuel cells.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a fuel cell system and a control method thereof. Background Art

[0002] A fuel cell system is a power generation system that converts the chemical energy of fuel into electrical energy. Generally, a circulation pump or an ejector is used to achieve hydrogen circulation. The ejector has the outstanding advantages of simple structure, high reliability, low cost, and no additional power consumption when installed in the system. The ejector can suck out and reflux the hydrogen in the fuel cell stack, and after recombining with the supplied hydrogen, supply it to the fuel cell stack again.

[0003] However, in actual applications, the power of the fuel cell stack often changes, which requires the hydrogen circulation device to provide stable circulation ability within a wide power range. However, due to the structural characteristics of the ejector itself, it cannot meet the wide power range of the fuel cell stack. This is because when the fuel cell stack operates under high-power conditions, the required hydrogen flow rate is large, and the large-flow hydrogen passing through the primary flow nozzle of the ejector will cause excessive primary flow pressure, affecting the normal operation of the hydrogen injection valve. When the fuel cell stack operates under low-power conditions, the required metering ratio is large, and the ejector capacity of the ejector cannot meet the metering ratio required by the fuel cell stack. Summary of the Invention

[0004] The present invention provides a fuel cell system and a control method thereof to solve the problem that the ejector in the prior art cannot meet the wide power range of the fuel cell stack.

[0005] In a first aspect, a fuel cell system provided by the present invention includes a hydrogen injection valve for controlling the input of high-pressure hydrogen, an ejector connected to the hydrogen injection valve, and a fuel cell stack and a gas-water separator respectively connected to the ejector. The system further includes a check valve and a reversing valve. The hydrogen injection valve includes a primary hydrogen injection valve and a secondary hydrogen injection valve. The ejector includes a primary ejector and a secondary ejector. The primary ejector has a primary ejector primary inlet, a primary ejector secondary inlet, and a primary ejector outlet. The secondary ejector has a secondary ejector primary inlet, a secondary ejector secondary inlet, and a secondary ejector outlet;

[0006] The primary hydrogen injection valve is connected to the primary inlet of the primary ejector, the secondary hydrogen injection valve is connected to the primary inlet of the secondary ejector, the check valve is arranged in the entrained flow path between the primary ejector and the secondary ejector, the secondary inlet of the primary ejector is connected to the gas-water separator, the gas-water separator is connected to the fuel cell stack, the outlet of the primary ejector is connected to the secondary inlet of the secondary ejector through the first flow path led out by the reversing valve and the second flow path led out is connected to the fuel cell stack, and the outlet of the secondary ejector is connected to the fuel cell stack.

[0007] In an embodiment of the present invention, the system further includes a control module, and the control module controls the opening or closing of the primary hydrogen injection valve, the secondary hydrogen injection valve and the reversing valve according to the monitored power of the fuel cell stack; the check valve automatically closes under the action of the pressure difference in the series ejector mode to ensure that the primary ejector and the secondary ejector are in series, and at the same time automatically opens under the action of the pressure difference in the parallel mode to ensure that the primary ejector and the secondary ejector are in parallel; the power range of the fuel cell stack includes a first power range, a second power range and a third power range.

[0008] In an embodiment of the present invention, when it is monitored that the power of the fuel cell stack is in the first power range, the control module controls the primary hydrogen injection valve and the secondary hydrogen injection valve to open simultaneously so that high-pressure hydrogen is respectively input into the primary ejector and the secondary ejector to be entrained, and controls the reversing valve to switch to the first flow path so that the hydrogen coming out of the gas-water separator is entrained under the entraining action of the primary ejector and discharged from the outlet of the primary ejector to complete primary pressurization, and then passes through the first flow path and is input into the secondary ejector from the secondary inlet of the secondary ejector to complete secondary pressurization, and then enters the fuel cell stack from the outlet of the secondary ejector.

[0009] In an embodiment of the present invention, when it is monitored that the power of the fuel cell stack is in the second power range, the control module controls the secondary hydrogen injection valve to close and the primary hydrogen injection valve to open so that high-pressure hydrogen is input into the primary ejector to be entrained, and controls the reversing valve to switch to the second flow path so that the hydrogen coming out of the gas-water separator enters the fuel cell stack through the second flow path after being pressurized by the primary ejector.

[0010] In an embodiment of the present invention, when it is monitored that the power of the fuel cell stack is in the third power range, the control module controls the first-stage hydrogen injection valve and the second-stage hydrogen injection valve to open simultaneously so that high-pressure hydrogen is respectively input into the first-stage ejector and the second-stage ejector, and controls the reversing valve to switch to the second flow path so that the check valve automatically opens under the action of the pressure difference. The hydrogen gas coming out of the gas-water separator enters the first-stage ejector from the secondary inlet of the first-stage ejector to be ejected, and the gas discharged from the outlet of the first-stage ejector enters the fuel cell stack through the second flow path. At the same time, the hydrogen gas discharged from the outlet of the second-stage ejector also enters the fuel cell stack.

[0011] In an embodiment of the present invention, the first power range is [0 - 20) kW, the second power range is [20 - 50) kW, and the third power range is [50 - 100] kW.

[0012] In an embodiment of the present invention, the fuel cell system further includes a high-pressure gas cylinder for providing high-pressure hydrogen, a stop safety valve, and a pressure reducing valve. The high-pressure gas cylinder is connected to the stop safety valve through a flow path, the stop safety valve is connected to the pressure reducing valve through a flow path, and the pressure reducing valve is respectively connected to the first-stage hydrogen injection valve and the second-stage hydrogen injection valve through a flow path.

[0013] In a second aspect, a control method for a fuel cell system according to any one of the first aspect, the control method includes:

[0014] S1. Monitor the power of the fuel cell stack;

[0015] S2. Determine whether the power of the fuel cell stack is less than a first preset power. If it is less than the first preset power, execute step S3; otherwise, execute step S4;

[0016] S3. Control the first-stage hydrogen injection valve and the second-stage hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the first flow path. At this time, the fuel cell stack operates in the first power range;

[0017] S4. Determine whether the power of the fuel cell stack is less than a second preset power;

[0018] If it is less than the second preset power, control the first-stage hydrogen injection valve to open and the second-stage hydrogen injection valve to close, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the second power range;

[0019] If it is greater than or equal to the second preset power, control the first-stage hydrogen injection valve and the second-stage hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the third power range.

[0020] In an embodiment of the present invention, the control method further includes:

[0021] S5. Determine whether the fuel cell stack needs to be shut down. If it needs to be shut down, control the fuel cell stack to stop operating; otherwise, return to step S1.

[0022] In an embodiment of the present invention, the first preset power is 20 kW, and the second preset power is 50 kW.

[0023] A fuel cell system and its control method provided by the present invention, through the provided primary ejector, secondary ejector, check valve, and reversing valve, enable the primary ejector and the secondary ejector to operate in three different power ranges of low, medium, and high, and implement different ejector schemes in different power ranges, which can give full play to the performance of the ejector, improve the entrainment ratio under low power conditions, increase the hydrogen supply under high power conditions, and broaden the working range of the ejector in the fuel cell. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 is a schematic structural diagram of a fuel cell system provided by the prior art;

[0026] Figure 2 is a schematic structural diagram of a fuel cell system provided by the present invention;

[0027] Figure 3 is Figure 2 an enlarged view of the structure of the compound ejector;

[0028] Figure 4 is a schematic diagram of the operation of the system in the low power range provided by the present invention;

[0029] Figure 5 is a schematic diagram of the operation of the system in the medium power range provided by the present invention;

[0030] Figure 6 is a schematic diagram of the operation of the system in the high power range provided by the present invention;

[0031] Figure 7 is a schematic diagram of the working mode of the ejector in different power ranges provided by the present invention;

[0032] Figure 8 is a schematic flowchart of the control method of the fuel cell system provided by the present invention. Detailed implementation manners

[0033] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0034] The terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned accompanying drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments described herein can be implemented in an order different from that shown or described herein.

[0035] Please refer to Figure 1 , Figure 1 , which is a schematic structural diagram of a fuel cell system provided by the prior art. A fuel cell system includes a high-pressure hydrogen cylinder 2, a stop safety valve 3, a pressure reducing valve 4, a hydrogen injection valve 5, a conventional ejector 6, an ejector primary flow inlet 601, an ejector secondary flow inlet 602, an ejector outlet 603, a fuel cell stack 7, a fuel cell stack inlet 71, a fuel cell stack outlet 72, a gas-liquid separator 8, and a drain and nitrogen discharge valve 9.

[0036] Exemplarily, the high-pressure hydrogen cylinder 2 is used to store high-pressure hydrogen as the fuel of the fuel cell stack 7. The high-pressure hydrogen cylinder 2 is connected to the stop safety valve 3, and the stop safety valve 3 and the pressure reducing valve 4 are connected. The high-pressure hydrogen cylinder 2 supplies high-pressure hydrogen to the hydrogen injection valve 5 through the stop safety valve 3 and the pressure reducing valve 4, and then the high-pressure hydrogen supplied through the hydrogen injection valve 5 enters the primary flow inlet 601 of the ejector 6. The ejector outlet 603 of the ejector 6 is connected to the fuel cell stack inlet 71 of the fuel cell stack 7 to pump hydrogen to the fuel cell stack 7.

[0037] Hydrogen undergoes an electrochemical reaction with oxygen on the cathode side in the fuel cell stack 7 to generate electric energy. The unconsumed hydrogen carries the generated liquid water and water vapor and is discharged from the fuel cell stack outlet 72 in the fuel cell stack 7, generating a recycle gas that needs to be recycled. The recycle gas is a gas-liquid two-phase fluid containing liquid water droplets, hydrogen, etc. The liquid water is separated by the gas-liquid separator 8, and the remaining gas enters the secondary flow inlet 602 of the ejector and is entrained. The drain and nitrogen discharge valve 9 opens and closes periodically to discharge the accumulated nitrogen and liquid water.

[0038] An ejector is a jet compression pump, and its performance is manifested as the effects of entrainment and pressurization, that is, the pressure of a certain flow rate of fluid is increased. Under the same working conditions, the greater the entrained flow rate, the smaller the increased pressure; conversely, the smaller the pressure increase of the ejector, the greater the entrained flow rate. Therefore, for the case where a higher entrainment flow rate is required, the pressure increase of the ejector should be reduced as much as possible. And Figure 1 The shown ejector has only one ejector. When the fuel cell stack operates under high-power conditions, the hydrogen flow rate required by the fuel cell stack is relatively large. When a large flow rate of hydrogen passes through the primary flow nozzle of the ejector, it will cause the primary flow pressure to be too high, affecting the normal operation of the hydrogen injection valve. When the fuel cell stack operates under low-power conditions, the required metering ratio is relatively large, and the entrainment capacity of the ejector cannot meet the metering ratio required by the fuel cell stack.

[0039] Therefore, in order to solve the problem that the ejector in the prior art cannot meet the wide power range of the fuel cell stack, the present invention provides a fuel cell system and its control method. By providing a primary ejector, a secondary ejector, a check valve, and a reversing valve, the primary ejector and the secondary ejector work in three different power ranges of low, medium, and high, and different entrainment schemes are implemented in different power ranges, which can give full play to the performance of the ejector, improve the entrainment ratio under low-power conditions, increase the hydrogen supply under high-power conditions, and broaden the working range of the ejector in the fuel cell.

[0040] The following combines Figures 2 - 8 to describe the fuel cell system and its control method of the present invention.

[0041] Please refer to Figure 2 、 Figure 3 , Figure 2 is a schematic structural diagram of the fuel cell system provided by the present invention, Figure 3 is Figure 2 The enlarged view of the composite ejector structure. A fuel cell system, which is a fuel cell system with a composite ejector, includes a high-pressure hydrogen cylinder 2, a stop safety valve 3, a pressure reducing valve 4, a primary hydrogen injection valve 51, a secondary hydrogen injection valve 52, a primary ejector 61, a secondary ejector 62, a check valve 63, a reversing valve 64, a fuel cell stack inlet 71, a fuel cell stack outlet 72, a gas-water separator 8, and a drain and nitrogen discharge valve 9. Among them, the primary ejector 61 has a primary ejector primary inlet 610, a primary ejector secondary inlet 612, and a primary ejector outlet 611. The secondary ejector 62 has a secondary ejector primary inlet 620, a secondary ejector secondary inlet 622, and a secondary ejector outlet 621.

[0042] Exemplarily, the high-pressure hydrogen cylinder 2 is used to store high-pressure hydrogen as the fuel for the fuel cell stack 7. The high-pressure hydrogen cylinder 2 is connected to the cut-off safety valve 3, and the cut-off safety valve 3 is connected to the pressure reducing valve 4. The pressure reducing valve 4 is respectively connected to the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52. The primary hydrogen injection valve is connected to the primary inlet 610 of the primary ejector, and the secondary hydrogen injection valve 52 is connected to the primary inlet 620 of the secondary ejector.

[0043] Exemplarily, the one-way valve 63 is disposed in the entrained flow path between the primary ejector 61 and the secondary ejector 62 to control whether the entrained flow path is connected. When the one-way valve 63 is opened, the entrained flow path between the primary ejector 61 and the secondary ejector 62 is connected. When the one-way valve 63 is closed, the entrained flow path between the primary ejector 61 and the secondary ejector 62 is not connected.

[0044] Exemplarily, the secondary inlet 612 of the primary ejector is connected to the gas-water separator 8, the gas-water separator 8 is connected to the fuel cell stack outlet 72 of the fuel cell stack 7. The primary ejector outlet 611 is connected to the secondary inlet 622 of the secondary ejector through the first flow path S1 led out by the reversing valve 64 and is connected to the fuel cell stack inlet 71 of the fuel cell stack 7 through the second flow path S2 led out by the reversing valve 64. That is to say, one outlet of the reversing valve 64 is connected to the secondary inlet 622 of the secondary ejector to form the first flow path S1, and the other outlet of the reversing valve 64 is connected to the fuel cell stack inlet 71 to form the second flow path S2. The secondary ejector outlet 621 is directly connected to the fuel cell stack inlet 71 of the fuel cell stack 7.

[0045] In an embodiment of the present invention, the fuel cell system further includes a control module (not shown in the figure). The control module controls the opening or closing of the primary hydrogen injection valve 51, the secondary hydrogen injection valve 52, and the reversing valve 64 according to the monitored power of the fuel cell stack 7.

[0046] Exemplarily, a one-way valve 63 is added to the entrained flow path between the primary ejector 61 and the secondary ejector. Its function is to automatically close under the pressure difference in the series ejector mode to ensure that the primary ejector 61 and the secondary ejector 62 are in series; at the same time, it automatically opens under the pressure difference in the parallel mode to ensure that the primary ejector 61 and the secondary ejector 62 are in parallel.

[0047] The power range of the fuel cell stack 7 is divided into a first power interval, a second power interval, and a third power interval. The first power interval is a low power interval, the second power interval is a medium power interval, and the third power interval is a high power interval. For example, if the maximum power of the fuel cell stack 7 is 100 kW, then it can be set that 0 - 20 kW is the low power interval, 20 - 50 kW is the medium power interval; 50 - 100 kW is the high power interval.

[0048] Exemplarily, under low power conditions, the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 work simultaneously, and the primary ejector 61 and the secondary ejector 62 are connected in series for boosting, reducing the pressure difference of a single ejector, thereby increasing the circulation flow rate and improving the stack circulation metering ratio.

[0049] Exemplarily, under medium power conditions, only the primary hydrogen injection valve 51 works, so only the primary ejector 61 works. The closing of the secondary hydrogen injection valve 52 causes the secondary ejector 62 to close, and the circulation flow rate works normally through the primary ejector 61.

[0050] Exemplarily, under high power conditions, the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 work simultaneously. At this time, the flow direction of the switching valve 64 is switched so that the fluid does not pass through the first flow path S1, and the check valve 63 automatically opens under the action of the pressure difference. At this time, the primary ejector 61 and the secondary ejector 62 are in a parallel working state, and can supply a large flow of hydrogen to meet the large flow demand of the stack under high power conditions.

[0051] That is to say, the compound ejector provided by the present invention uses different ejector schemes in different power ranges. In the low power range, the ejectors are connected in series for ejection, reducing the pressure difference of a single ejector and improving the metering ratio of the system; in the high power range, the two-stage ejectors work in parallel, improving the ability to supply a large flow of hydrogen.

[0052] It can be understood that the ejection ratio of the ejector described in the present invention is the ratio of the secondary flow mass flow rate to the primary flow mass flow rate. Only when the ejection ratio of the ejector is higher than the stack demand metering ratio can the stack work normally. Under low power conditions, the primary flow rate of the ejector is small, and the ejection ability of the ejector is insufficient. Therefore Figure 1 the ejection ratio of a single ejector shown is small. In order to improve the ejection ratio of the ejector in the present invention, it is necessary to reduce the ejector pressure difference, that is, it is necessary to reduce the difference between the secondary flow pressure and the outlet pressure of the ejector. By Figure 2 connecting two ejectors in series as shown, the pressure difference of a single ejector can be reduced, thereby increasing the ejection ratio of the ejector.

[0053] The working process of the fuel cell system described in the present invention will be described below.

[0054] Please refer to Figure 4 , Figure 4 which is a schematic diagram of the system working in the low power range provided by the present invention. Figure 4 The dotted line in

[0055] Exemplarily, when it is monitored that the power of the fuel cell stack 7 is in the first power (such as low power) range, the control module controls the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 to open simultaneously so that high-pressure hydrogen is respectively input into the primary ejector 61 and the secondary ejector 62, and the primary ejector 61 and the secondary ejector 62 both have the ability to eject and boost pressure.

[0056] The gas-liquid mixture discharged from the fuel cell stack outlet 72 is separated from most of the liquid water by the gas-liquid water separator 8, enters the primary ejector 61 at the secondary inlet 612 of the primary ejector, and is ejected under the ejection action of the primary ejector 61, and then is discharged from the primary ejector outlet 611 of the primary ejector to complete primary pressure boosting. Then, it is switched to the first flow path S1 through the reversing valve 64 and supplied to the secondary ejector 62 from the secondary inlet 622 of the secondary ejector for secondary pressure boosting, and then the gas discharged from the secondary ejector outlet 621 of the secondary ejector enters the fuel cell stack 7 through the fuel cell stack inlet 71.

[0057] It can be seen that under low power conditions, the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 work simultaneously, and the primary ejector 61 and the secondary ejector 62 are connected in series for pressure boosting, reducing the pressure difference of a single-stage ejector, thereby increasing the circulation flow rate and improving the stack circulation metering ratio.

[0058] Please refer to Figure 5 , Figure 5 which is a schematic diagram of the system working in the medium power range provided by the present invention. Figure 5 The dotted line in

[0059] Exemplarily, when it is monitored that the power of the fuel cell stack 7 is in the second power (such as medium power) range, the control module controls the secondary hydrogen injection valve 52 to close and the primary hydrogen injection valve 51 to open so that high-pressure hydrogen is input into the primary ejector, and only the primary ejector 61 is used for conventional ejection.

[0060] The gas-liquid mixture discharged from the fuel cell stack outlet 72 is separated from most of the liquid water by the gas-liquid water separator 8, enters the primary ejector 61 through the secondary inlet 612 of the primary ejector, and is ejected under the ejection action of the primary ejector 61, and then is discharged from the primary ejector outlet 611 of the primary ejector to complete pressure boosting. The control module controls the reversing valve 64 to switch the flow path to the second flow path S2, and the gas discharged from the primary ejector outlet 611 enters the fuel cell stack inlet 71 of the fuel cell stack 7 through the second flow path S2.

[0061] It can be seen that under medium power conditions, only the primary hydrogen injection valve 51 works, so only the primary ejector 61 works, and the closing of the secondary hydrogen injection valve 52 causes the secondary ejector 62 to close, and the circulation flow rate is normal through the normal operation of the primary ejector 61.

[0062] Please refer to Figure 6 , Figure 6 which is a schematic diagram of the operation of the high-power interval system provided by the present invention. Figure 6 The dotted line in

[0063] exemplarily, when it is monitored that the power of the fuel cell stack 7 is in the third power (such as high power) interval, the control module controls the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 to open simultaneously so that high-pressure hydrogen is respectively input into the primary ejector 61 and the secondary ejector 62, and the primary ejector 61 and the secondary ejector 62 both have the ejecting ability.

[0064] The control module controls the reversing valve 64 to switch to the second flow path S2, so that the fluid does not pass through the first flow path S1, and the check valve 63 automatically opens under the action of the pressure difference. At this time, the entrained flow path between the primary ejector 61 and the secondary ejector 62 is connected.

[0065] After the gas-liquid mixture discharged from the fuel cell stack outlet 72 is separated from most of the liquid water by the gas-water separator 8, it enters the primary ejector 61 from the secondary inlet 612 of the primary ejector and is entrained under the entraining action of the primary ejector 61. The reversing valve 64 switches the flow path to the second flow path S2, and the gas discharged from the ejector outlet 611 of the primary ejector 61 enters the fuel cell stack 7 through the second flow path S2. At the same time, under the entraining action of the secondary ejector 62, part of the circulating fluid is entrained into the ejector 62, and the gas discharged from the secondary ejector outlet 621 of the secondary ejector 62 also enters the fuel cell stack 7. In this state, the primary ejector 61 and the secondary ejector 62 are in a parallel working state, and the hydrogen flow rate that can be supplied increases, meeting the large flow rate demand of the fuel cell stack under high power conditions.

[0066] It can be seen that under high power conditions, the primary hydrogen injection valve 51 and the secondary hydrogen injection valve 52 work simultaneously. At this time, the flow direction of the reversing valve 64 is switched so that the fluid does not pass through the first flow path S1, and the check valve 63 automatically opens under the action of the pressure difference. At this time, the primary ejector 61 and the secondary ejector 62 are in a parallel working state, and a large flow rate of hydrogen can be supplied to meet the large flow rate demand of the fuel cell stack under high power conditions.

[0067] Please refer to Figure 7 , Figure 7 which is a schematic diagram of the working modes of the ejector in different power intervals. Series entrainment is performed in the low power interval, conventional entrainment is performed in the medium power interval, and parallel entrainment is performed in the high power interval.

[0068] Exemplarily, the ranges of the low, medium, and high power intervals are 20%, 30%, and 50% of the rated power respectively. For example, for a 100 kW fuel cell stack, the 0 - 20 kW range is the low power interval, the 20 - 50 kW range is the medium power interval; and the 50 - 100 kW range is the high power interval. By implementing different ejector schemes in different power intervals, the performance of the ejector is fully utilized, the entrainment ratio under low power conditions is increased, the hydrogen supply under high power conditions is increased, and the working range of the ejector in the fuel cell is broadened.

[0069] The control method of the fuel cell system provided by the present invention will be described below. The control method described below can be correspondingly referred to the fuel cell system described above.

[0070] Please refer to Figure 8 , Figure 8 which is a schematic flowchart of the control method of the fuel cell system provided by the present invention. A control method based on the above - mentioned fuel cell system, the control method includes:

[0071] Step S110. Monitor the power of the fuel cell stack.

[0072] Exemplarily, when the fuel cell stack is operating, the control module is used to monitor the power of the fuel cell stack and control the opening or closing of the primary hydrogen injection valve, secondary hydrogen injection valve, and the reversing valve by outputting control signals.

[0073] S120. Determine whether the power of the fuel cell stack is less than a first preset power. If it is less than the first preset power, then execute step S130; otherwise, execute step S140.

[0074] Exemplarily, the first preset power is 20 kW, and it is determined whether the power of the fuel cell stack is less than 20 kW, that is, whether it is operating in the low - power interval.

[0075] S130. Control the primary hydrogen injection valve and the secondary hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the first flow path. At this time, the fuel cell stack operates in the first power interval.

[0076] Exemplarily, when the power of the fuel cell stack is less than 20 kW, control the primary hydrogen injection valve and the secondary hydrogen injection valve to work, and the reversing valve switches to the first flow path. At this time, the primary ejector and the secondary ejector work in series.

[0077] S140. Determine whether the power of the fuel cell stack is less than a second preset power. If it is less than the second preset power, then execute step S150; otherwise, execute step S160.

[0078] Exemplarily, the second preset power is 50 kW. If the power of the fuel cell stack is not less than 20 kW (i.e., greater than or equal to 20 kW), it is simultaneously determined whether the power of the fuel cell stack is less than 50 kW.

[0079] S150. Control the first hydrogen injection valve to open and the second hydrogen injection valve to close, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the second power range, and step S170 is executed.

[0080] Exemplarily, if the power of the fuel cell stack is less than 50 kW, the fuel cell stack is in the medium power range at this time. Control the first hydrogen injection valve to open and the second hydrogen injection valve to close, and control the reversing valve to switch to the second flow path. At this time, only the first ejector is in the normal ejector state.

[0081] S160. Control the first hydrogen injection valve and the second hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the third power range.

[0082] Exemplarily, if the power of the fuel cell stack is not less than 50 kW (i.e., greater than or equal to 50 kW), the fuel cell stack operates in the high power range. At this time, control the first hydrogen injection valve and the second hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the second flow path. At this time, the first ejector and the second ejector work in parallel.

[0083] S170. Determine whether the fuel cell stack needs to be shut down. If it needs to be shut down, control the fuel cell stack to stop running; otherwise, return to the above step S110.

[0084] Exemplarily, determine whether the fuel cell stack continues to operate. If so, return to step S110 to continue monitoring the power of the fuel cell stack; if not, shut down the fuel cell stack.

[0085] It should be noted here that the control method of the fuel cell system provided by the embodiments of the present invention can achieve the control functions implemented by the above-mentioned embodiments of the fuel cell system and can achieve the same technical effects. The same parts and beneficial effects as those in the embodiments of the fuel cell system in this embodiment will not be specifically described herein.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fuel cell system, the system comprising a hydrogen injection valve for controlling the input of high-pressure hydrogen, an ejector connected to the hydrogen injection valve, and a fuel cell stack and a gas-water separator respectively connected to the ejector, characterized in that, the system further comprises a check valve and a reversing valve, the hydrogen injection valve comprises a primary hydrogen injection valve and a secondary hydrogen injection valve, the ejector comprises a primary ejector and a secondary ejector, the primary ejector has a primary ejector primary inlet, a primary ejector secondary inlet and a primary ejector outlet, and the secondary ejector has a secondary ejector primary inlet, a secondary ejector secondary inlet and a secondary ejector outlet; the primary ejector outlet is connected to the secondary ejector secondary inlet through a first flow path led out by the reversing valve and is connected to the fuel cell stack through a second flow path led out; the secondary ejector outlet is connected to the fuel cell stack; the check valve is arranged in the entrained flow path between the primary ejector and the secondary ejector; the system further comprises a control module, and the control module controls the opening or closing of the primary hydrogen injection valve, the secondary hydrogen injection valve and the reversing valve according to the monitored power of the fuel cell stack; the power range of the fuel cell stack includes a first power range, a second power range and a third power range; when it is monitored that the power of the fuel cell stack is in the first power range, the control module controls the primary hydrogen injection valve and the secondary hydrogen injection valve to be opened simultaneously so that high-pressure hydrogen is respectively input into the primary ejector and the secondary ejector to be entrained, and controls the reversing valve to switch to the first flow path so that the hydrogen coming out of the gas-water separator is entrained under the entrainment action of the primary ejector and discharged from the primary ejector outlet to complete primary pressurization, then passes through the first flow path and is input into the secondary ejector from the secondary ejector secondary inlet to complete secondary pressurization, and then enters the fuel cell stack from the secondary ejector outlet; when it is monitored that the power of the fuel cell stack is in the second power range, the control module controls the secondary hydrogen injection valve to be closed and the primary hydrogen injection valve to be opened so that high-pressure hydrogen is input into the primary ejector to be entrained, and controls the reversing valve to switch to the second flow path so that the hydrogen coming out of the gas-water separator enters the fuel cell stack through the second flow path after being pressurized by the primary ejector; when it is monitored that the power of the fuel cell stack is in the third power range, the control module controls the primary hydrogen injection valve and the secondary hydrogen injection valve to be opened simultaneously so that high-pressure hydrogen is respectively input into the primary ejector and the secondary ejector, and controls the reversing valve to switch to the second flow path so that the check valve is automatically opened under the action of the pressure difference, the hydrogen coming out of the gas-water separator enters the primary ejector from the secondary inlet of the primary ejector to be entrained, the gas discharged from the primary ejector outlet enters the fuel cell stack through the second flow path, and at the same time the hydrogen discharged from the secondary ejector outlet also enters the fuel cell stack.

2. The fuel cell system according to claim 1, characterized in that, The one-way valve automatically closes under the action of pressure difference in the series ejector mode to ensure that the primary ejector and the secondary ejector are in series, and at the same time, it automatically opens under the action of pressure difference in the parallel mode to ensure that the primary ejector and the secondary ejector are in parallel.

3. The fuel cell system according to claim 1, characterized in that the primary hydrogen injection valve is connected to the primary inlet of the primary ejector, the secondary hydrogen injection valve is connected to the primary inlet of the secondary ejector, the secondary inlet of the primary ejector is connected to the gas-water separator, and the gas-water separator is connected to the fuel cell stack.

4. The fuel cell system according to claim 1, characterized in that the first power range is [0 to 20) kW, the second power range is [20 to 50) kW, and the third power range is [50 to 100] kW.

5. The fuel cell system according to claim 1, characterized in that the fuel cell system further includes a high-pressure gas cylinder for providing high-pressure hydrogen, a stop safety valve, and a pressure reducing valve. The high-pressure gas cylinder is connected to the stop safety valve through a flow path, the stop safety valve is connected to the pressure reducing valve through a flow path, and the pressure reducing valve is connected to the primary hydrogen injection valve and the secondary hydrogen injection valve through flow paths respectively.

6. A control method for a fuel cell system according to any one of claims 1-5, characterized in that the control method includes: S1. Monitoring the power of the fuel cell stack; S2. Judging whether the power of the fuel cell stack is less than a first preset power. If it is less than the first preset power, execute step S3; otherwise, execute step S4; S3. Controlling the primary hydrogen injection valve and the secondary hydrogen injection valve to open simultaneously, and controlling the reversing valve to switch to the first flow path. At this time, the fuel cell stack operates in the first power range; S4. Judging whether the power of the fuel cell stack is less than a second preset power; If it is less than the second preset power, control the primary hydrogen injection valve to open and the secondary hydrogen injection valve to close, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the second power range; If it is greater than or equal to the second preset power, control the primary hydrogen injection valve and the secondary hydrogen injection valve to open simultaneously, and control the reversing valve to switch to the second flow path. At this time, the fuel cell stack operates in the third power range.

7. The control method for a fuel cell system according to claim 6, characterized in that the control method further includes: S5. Judging whether the fuel cell stack needs to be shut down. If it needs to be shut down, control the fuel cell stack to stop running; otherwise, return to step S1.

8. The control method for a fuel cell system according to claim 6, characterized in that the first preset power is 20 kW, and the second preset power is 50 kW.

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