Fuel cell system

Abstract

A fuel cell system. The FC system of the present invention is provided with a first exhaust pipe connected to a first FC stack, a second exhaust pipe connected to a second FC stack, a common exhaust pipe for combining the first exhaust pipe and the second exhaust pipe, and a backflow prevention mechanism. The backflow prevention mechanism prevents oxygen backflow from the first exhaust pipe to the second exhaust pipe. A typical example of the backflow prevention mechanism includes a compressor, a bypass pipe, pressure regulating valves respectively provided in the bypass pipe, an oxygen supply pipe, and the second exhaust pipe, and a controller. The controller controls the compressor and the pressure regulating valves so that the second FC stack is supplied with an amount of oxygen required for matching the output of the second FC stack with a target output, and oxygen of the first exhaust pipe does not backflow to the second exhaust pipe.

Description

Technical Field

[0001] The technology disclosed in this specification relates to fuel cell systems having multiple fuel cell stacks. Background Technology

[0002] Fuel cell systems with multiple fuel cell stacks are known (e.g., Japanese Patent Application Publication No. 2023-102089, Japanese Patent Application Publication No. 2023-102090, and International Patent Application Publication No. 2017 / 010069). In Japanese Patent Application Publication No. 2023-102089 and Japanese Patent Application Publication No. 2023-102090, each fuel cell stack has an oxygen supply pipe for introducing oxygen (air) and an exhaust pipe for discharging excess oxygen, with multiple exhaust pipes connected to a common exhaust pipe. Furthermore, for ease of explanation, "fuel cell" will sometimes be referred to as "FC" below. "Fuel cell system" will be referred to as "FC system," and "fuel cell stack" will be referred to as "FC stack."

[0003] If the outputs of multiple FC groups differ, the amount of oxygen supplied to each FC group will also differ. The amount of oxygen supplied to the FC groups is adjusted by a compressor and pressure regulating valve located on the oxygen supply pipe. If the compressor output is determined solely based on the required oxygen amount, the pressure of the residual oxygen discharged from the FC groups will differ depending on the required oxygen amount. If the pressure of the residual oxygen discharged from multiple FC groups differs, oxygen may flow back to the FC group with the lower pressure because multiple exhaust pipes are connected through a common exhaust pipe. This specification provides a technique to prevent oxygen backflow in an FC system where the exhaust pipes of multiple FC groups are connected. Summary of the Invention

[0004] The FC system disclosed in this specification includes a first FC group, a second FC group, a first exhaust pipe, a second exhaust pipe, a common exhaust pipe for merging the first and second exhaust pipes, and a backflow prevention mechanism. The backflow prevention mechanism prevents oxygen backflow from the first exhaust pipe to the second exhaust pipe. A typical example of the backflow prevention mechanism includes a compressor, a bypass pipe, an intake pressure regulating valve located on the oxygen supply pipe, an exhaust pressure regulating valve located on the second exhaust pipe, a bypass pressure regulating valve located on the bypass pipe, and a controller. The compressor supplies oxygen to the second FC group through the oxygen supply pipe. The bypass pipe guides a portion of the oxygen discharged from the compressor around the second FC group to the second exhaust pipe. The intake pressure regulating valve adjusts the pressure of the oxygen supplied to the second FC group, the exhaust pressure regulating valve adjusts the pressure of the oxygen discharged from the second FC group, and the bypass pressure regulating valve adjusts the outlet pressure of the bypass pipe. The controller controls the compressor, the intake pressure regulating valve, the exhaust pressure regulating valve, and the bypass pressure regulating valve to supply the second FC group with the amount of oxygen required to make the output of the second FC group match the target output, and to prevent oxygen from flowing back from the first exhaust pipe to the second exhaust pipe. This control allows the second FC group to operate while preventing oxygen backflow. Furthermore, "oxygen" can be an oxygen-containing gas, typically air.

[0005] The controller can also control the compressor, intake pressure regulating valve, exhaust pressure regulating valve, and bypass pressure regulating valve to ensure that the required amount of oxygen for maintaining the second FC group at idle speed flows to the second FC group, and that oxygen does not flow backward from the first exhaust pipe to the second exhaust pipe. Idle speed means supplying a specified amount of oxygen to the FC group and controlling the output voltage of the FC group within a specified voltage range, thereby minimizing the output of the FC group. The minimum output depends on the physical and electrical characteristics of the FC group.

[0006] The detailed description of the technology disclosed in this specification and further improvements are described in the following "Detailed Description". Attached Figure Description

[0007] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements, wherein,

[0008] Figure 1 This is a block diagram of the FC system of the first embodiment.

[0009] Figure 2 This is a flowchart of the backflow prevention process.

[0010] Figure 3 This is a flowchart of the backflow prevention process (variant example).

[0011] Figure 4 This is a block diagram of the FC system of the second embodiment. Detailed Implementation

[0012] First Embodiment

[0013] Reference Figure 1 , Figure 2 The FC system 2 of the first embodiment will now be described. As mentioned above, "FC" is short for "fuel cell". Figure 1 This is a block diagram showing FC system 2. FC system 2 has two FC groups 10a and 10b. Although the diagram is omitted, voltage converters are connected to the output terminals of each of the two FC groups 10a and 10b, and the output terminals of the two voltage converters are connected to the output terminal of FC system 2. That is, the outputs of the two FC groups 10a and 10b are added together to output from FC system 2.

[0014] The first FC group 10a is connected to an oxygen supply pipe 11a, an exhaust pipe 12a, a hydrogen supply pipe 14a, and an exhaust pipe 15a. The oxygen supply pipe 11a supplies oxygen (external air) to the cathode of the first FC group 10a. A compressor 17a, an intake pressure regulating valve 18a, and a flow meter 21a are connected to the oxygen supply pipe 11a. The hydrogen supply pipe 14a connects a hydrogen tank 37 to the anode of the first FC group 10a and supplies hydrogen from the hydrogen tank 37 to the anode of the first FC group 10a. Furthermore, the hydrogen supply pipe 14a includes a pressure regulating valve, a pressure sensor, and an injector, but their illustrations are omitted. As is well known, the hydrogen supplied to the anode of the first FC group 10a reacts with the oxygen supplied to the cathode to generate electricity and water. The electricity is supplied to the aforementioned voltage converter. The water and the reacted gas are discharged from the exhaust pipe 15a. Additionally, the remaining oxygen (air) not used in the reaction with hydrogen is discharged from the exhaust pipe 12a. An exhaust pressure regulating valve 19a is provided in the exhaust pipe 12a. In the following explanation, "oxygen" refers to pure oxygen or oxygen-containing gases (typically air).

[0015] Oxygen supply pipe 11a and exhaust pipe 12a are connected via bypass pipe 13a. Oxygen (air) compressed by compressor 17a is bypassed from the first FC group 10a and delivered to exhaust pipe 12a via bypass pipe 13a. One end of bypass pipe 13a is connected to oxygen supply pipe 11a between compressor 17a and intake pressure regulating valve 18a. The other end of bypass pipe 13a is connected to exhaust pipe 12a between exhaust pressure regulating valve 19a and common exhaust pipe 32.

[0016] A bypass pressure regulating valve 20a is provided in the bypass pipe 13a. Pressure regulating valves 18a, 19a, and 20a are valves that adjust the pressure on the secondary side (downstream side of the valve) to the desired pressure; they are also called pressure reducing valves. However, the pressure on the secondary side cannot exceed the pressure on the primary side (upstream side of the valve). Furthermore, pressure regulating valves 18a, 19a, and 20a can also be completely closed. That is, pressure regulating valves 18a, 19a, and 20a can disconnect the primary side from the secondary side.

[0017] The controller 40 determines the amount of oxygen and hydrogen to be supplied to the first FC group 10a based on the target output of the first FC group 10a. The amount of hydrogen supplied to the first FC group 10a is adjusted by a pressure regulating valve (not shown) and an injector provided with the hydrogen supply pipe 14a. The amount of oxygen supplied to the first FC group 10a is adjusted by the compressor 17a and pressure regulating valves 18a, 19a, and 20a. Additionally, the amount of oxygen supplied to the first FC group 10a is measured by the flow meter 21a. Based on the measurement results from the flow meter 21a, the controller 40 controls the compressor 17a, pressure regulating valves 18a, 19a, and 20a to supply an appropriate amount of oxygen to the oxygen supply port of the first FC group 10a.

[0018] The exhaust pipe 12a is equipped with a pressure sensor 22a for measuring the internal pressure of the exhaust pipe 12a. The pressure sensor 22a is installed in the exhaust pipe 12a downstream of the exhaust pressure regulating valve 19a. In addition, the first FC group 10a also includes several pressure sensors and valves, but their illustrations are omitted.

[0019] The second FC group 10b also includes the same equipment as the first FC group 10a. In the above description related to the first FC group 10a, if the suffix "a" in the reference numerals is changed to "b", it becomes a description related to the second FC group 10b.

[0020] Exhaust pipes 12a and 12b are connected to a common exhaust pipe 32. Exhaust pipes 15a and 15b are connected to a common exhaust pipe 33. The common exhaust pipe 33 is connected to a gas-liquid separator 34, where the exhaust gas from FC groups 10a and 10b is separated into residual hydrogen not used in the reaction and water generated in the reaction. The residual hydrogen is returned to hydrogen supply pipes 14a and 14b. The water is transported to a muffler 35. The common exhaust pipe 32 is also connected to the muffler 35. The residual oxygen from FC groups 10a and 10b is transported to the muffler 35 via exhaust pipes 12a and 12b and the common exhaust pipe 32, and is discharged to the outside along with the water. By converging multiple exhaust pipes 12a and 12b into a single common exhaust pipe 32 and installing the muffler 35 on the common exhaust pipe 32, the cost of the FC system can be reduced, and space-saving design of the FC system can be achieved.

[0021] To ensure that the outlets for residual oxygen and water are unified, exhaust pipes 12a and 12b are connected to a common exhaust pipe 32. On the other hand, the amount of oxygen supplied to FC group 10a (10b) is adjusted by the compressor 17a (17b) and the intake pressure regulating valves 18a (18b) and 19a and 20a (19b, 20b) of the oxygen supply pipe 11a (11b). If the output of compressor 17a (17b) is determined solely based on the required oxygen amount, the pressure of the residual oxygen discharged from FC groups 10a and 10b will differ depending on the required oxygen amount. If the pressure of the residual oxygen discharged from FC groups 10a and 10b differs, oxygen may flow back towards the FC group with lower pressure because multiple exhaust pipes 12a and 12b are connected via the common exhaust pipe 32. Especially when the internal pressure of the exhaust pipe of one FC group is high and the internal pressure of the exhaust pipe of another FC group is close to atmospheric pressure, some of the residual oxygen discharged from the exhaust pipe of one FC group may flow back to the exhaust pipe of the other FC group. FC system 2 has a structure to prevent the backflow of residual oxygen.

[0022] Figure 2 This is a flowchart illustrating the backflow prevention process performed by controller 40. Controller 40 receives a command (request output) from a higher-level controller (not shown) requesting output from FC system 2. Controller 40 divides the requested output into target outputs for the first FC group 10a and the second FC group 10b, respectively. Various calculation formulas can be used to divide the requested output into two target outputs. Furthermore, if the requested output can be supplied by one FC group, one FC group can be stopped or put into an idle state (described later). The case where the requested output can be supplied by one FC group will be described later. Figure 2 The flowchart below illustrates the processing when target outputs are assigned to the two FC groups respectively. Hereinafter, the target output of the first FC group 10a will be referred to as the first target output, and the target output of the second FC group 10b will be referred to as the second target output.

[0023] The controller 40 compares the two determined target outputs (step S12). If the first target output is equal to the second target output (step S12: Yes), the controller 40 drives each FC group in such a way that the output of each FC group follows its respective target output (step S13). In step S13, the controller 40 calculates the amount of oxygen (target oxygen amount) and hydrogen (target hydrogen amount) to be supplied to each FC group in such a way that the output of each FC group follows its respective target output. The compressor 17a, pressure regulating valves 18a, 19a, and 20a are controlled to supply the target oxygen amount to the first FC group 10a. In addition, the pressure regulating valve and injector of the hydrogen supply pipe 14a are controlled to supply the target hydrogen amount to the first FC group 10a. The controller 40 performs the same control on the second FC group 10b. Furthermore, in this case, the bypass pressure regulating valves 20a and 20b can also be closed.

[0024] Since the target output of the two FC groups is the same, the exhaust pressure is also equal. Therefore, in this case, no special treatment to prevent backflow is required. However, due to individual differences in the FC groups, even with the same target output, the exhaust pressure may sometimes differ slightly. But such slight differences in exhaust pressure will not cause backflow.

[0025] If the first target output is greater than the second target output (step S12: No, S14: Yes), the controller 40 drives the first FC group 10a in such a way that the output of the first FC group 10a follows the first target output (step S15). In step S15, similar to step S13, the controller 40 controls the injectors and pressure regulating valves of the compressor 17a, pressure regulating valves 18a, 19a, 20a, and hydrogen supply pipe 14a in a way that achieves the first target output. Here, the controller 40 closes the bypass pressure regulating valve 20a.

[0026] Next, the controller 40 calculates a target value (target internal pressure) for the internal pressure of the exhaust pipe 12b to prevent backflow in the exhaust pipe 12b, based on the internal pressure of the exhaust pipe 12a. Furthermore, in Figure 2 In this context, the internal pressure of exhaust pipe 12a is referred to as the first internal pressure, and the internal pressure of exhaust pipe 12b is referred to as the second internal pressure. As described above, the first internal pressure is measured by pressure sensor 22a located downstream of exhaust pressure regulating valve 19a, and the second internal pressure is measured by pressure sensor 22b located downstream of exhaust pressure regulating valve 19b.

[0027] If the first internal pressure and the second internal pressure are approximately equal, the residual oxygen in exhaust pipe 12a and exhaust pipe 12b is discharged to the outside through the common exhaust pipe 32 and muffler 35. If the first internal pressure is much greater than the second internal pressure, a portion of the residual oxygen in exhaust pipe 12a may flow backwards into exhaust pipe 12b. Alternatively, if the second target output is small and the second internal pressure is close to atmospheric pressure, a portion of the residual oxygen in exhaust pipe 12a may also flow backwards into exhaust pipe 12b. Whether backward flow occurs depends on the flow path resistance of the common exhaust pipe 32, including the muffler 35, and the first internal pressure. The target internal pressure to prevent backward flow is calculated using a relationship (or mapping) with the first internal pressure as a variable. The flow path resistance can be determined in advance. The relationship (or mapping) is determined in advance and installed in the controller 40. The controller 40 refers to the relationship (or mapping) and calculates the target internal pressure based on the first internal pressure (step S16).

[0028] The controller 40 controls the compressor 17b and pressure regulating valves 18b, 19b, and 20b (and the injector and pressure regulating valve attached to the hydrogen supply pipe 14b) in a manner that the output of the second FC group 10b follows the second target output and the second internal pressure follows the target internal pressure (step S17). The amount of oxygen to be supplied to the second FC group 10b (target oxygen quantity) is determined by the second target output. The controller 40 controls the compressor 17b, the intake pressure regulating valve 18b, and the exhaust pressure regulating valve 19b in a manner that supplies the second FC group 10b with the target oxygen quantity. At the same time, the controller 40 controls the compressor 17b and the bypass pressure regulating valve 20b in a manner that the second internal pressure follows the target internal pressure. Specifically, if the second internal pressure is lower than the target internal pressure, the controller 40 increases the output of the compressor 17b and readjusts the pressure regulating valves 18b, 19b, and 20b.

[0029] Furthermore, if the second internal pressure is equal to the first internal pressure, oxygen backflow will not occur. Therefore, the controller 40 can also replace the processing in steps S16 and S17, controlling the compressor 17b and pressure regulating valves 18b, 19b, and 20b in such a way that the output of the second FC group 10b follows the second target output and the second internal pressure is equal to the first internal pressure. Through the processing in steps S16 and S17 or their alternative processing, oxygen backflow from the exhaust pipe 12a to the exhaust pipe 12b is prevented.

[0030] If the first target output is less than the second target output, the judgment result of step S12 is "No", the judgment result of S14 is "No", and the processing of controller 40 moves to step S20. Controller 40 in Figure 2In the processing instructions, "first" and "second" are swapped to execute steps S15, S16, and S17 (step S20). Controller 40 repeats the above processing until a stop command for the FC system is received from the upper controller (step S18: No, S12). If a stop command for the FC system is received from the upper controller, controller 40 stops the operation of all FC groups and ends the processing (step S18: Yes, S19).

[0031] Through the above processing, even when the outputs of the two FC groups 10a and 10b are different, FC system 2 can prevent oxygen backflow in the exhaust pipe.

[0032] Figure 3 This is another example (modified example) of backflow prevention processing. When the required output from the upper controller exceeds the maximum output of one FC group, controller 40 sets the target output of each of the two FC groups 10a and 10b to half of the required output (step S22: No, S23). Then, controller 40 drives each FC group in such a way that the output of each FC group follows its respective target output (step S24). The processing in step S24 is similar to... Figure 2 The processing in step S13 is the same. Since the target output of the two FC groups is the same, the exhaust pressure is also equal. Therefore, in this case, no special treatment to prevent backflow is required.

[0033] When the required output is less than the maximum output of one FC group, the controller 40 drives the first FC group 10a in such a way that the output of the first FC group 10a follows the required output (step S22: Yes, S25). The processing of step S25 is the same as that of step S15.

[0034] Next, the controller 40 calculates a target value (target internal pressure) for a second internal pressure that will not cause backflow in the exhaust pipe 12b based on the first internal pressure (step S26). The processing in step S26 is the same as that in step S16. Then, the controller 40 controls the compressor 17b and pressure regulating valves 18b, 19b, and 20b in a manner that maintains the second FC group 10b at idle speed and the second internal pressure follows the target internal pressure (step S27). The specific control of the compressor 17b and pressure regulating valves 18b, 19b, and 20b in step S27 is the same as that in step S17.

[0035] Idle state refers to the state in which the voltage of the FC (Fuel Concentrator) is maintained within a specified idle voltage range, and the output of the FC is suppressed to a minimum. In idle state, the reaction of oxygen and hydrogen continues within the FC, and the output of the FC remains minimal. As mentioned above, a voltage converter is connected to the output of the FC. The output of the FC is adjusted by changing the transformation ratio of the voltage converter. By reducing the output voltage of the voltage converter in idle state, the output current from the FC can be made substantially zero. Furthermore, the magnitude of the minimum output depends on the physical and electrical configuration of the FC.

[0036] By keeping the FC (FC) group in an idling state instead of stopping it completely, degradation of the FC group can be suppressed. Furthermore, keeping the FC group in an idling state allows for a rapid increase in its output current. Once the FC group is stopped, a predetermined startup time is required from restarting it until output current is obtained. In other words, the idling state refers to putting the FC group into a standby state in preparation for future increases in output demand.

[0037] At idle, the second FC group 10b requires a small amount of oxygen. If the bypass pressure regulating valve 20b is closed at this time, the second internal pressure approaches atmospheric pressure, increasing the likelihood of oxygen backflow. Therefore, the controller 40 increases the second internal pressure by increasing the output of the compressor 17b and opening the bypass pressure regulating valve 20b more fully to prevent oxygen backflow.

[0038] Controller 40 repeats the above process until it receives a stop command from FC system 2 from the higher-level controller (step S28: No, S22). If a stop command from FC system 2 is received from the higher-level controller, controller 40 stops all FC groups and ends the process (step S28: Yes, S29). Figure 3 In terms of processing, FC system 2 can maintain the second FC group 10b at idle speed and prevent oxygen backflow from exhaust pipe 12a to exhaust pipe 12b. Additionally, in Figure 3 In the flowchart, "first" and "second" can also be interchanged.

[0039] Second Embodiment

[0040] use Figure 4 The FC system 2a of the second embodiment will now be described. Figure 4This is a block diagram of FC system 2a. FC system 2a adds a third FC group 10c and its associated equipment to the FC system 2 of the first embodiment. Specifically, the third FC group 10c includes an oxygen supply pipe 11c, an exhaust pipe 12c, a hydrogen supply pipe 14c, an exhaust pipe 15c, a bypass pipe 13c, a compressor 17c, pressure regulating valves 18c, 19c, and 20c, and a pressure sensor 22c. The construction and function of these devices are the same as those of the oxygen supply pipe 11a, exhaust pipe 12a, hydrogen supply pipe 14a, exhaust pipe 15a, bypass pipe 13a, compressor 17a, pressure regulating valves 18a, 19a, 20a, and pressure sensor 22a in the FC system 2 of the first embodiment.

[0041] When the power required by FC system 2a is less than the maximum output of one FC, controller 40a performs the following processing as a reverse current prevention process. (1) Controller 40a drives the first FC group 10a in such a way that the output of the first FC group 10a follows the required output. This processing is consistent with... Figure 3 The process of step S25 is the same. (2) Controller 40a stops the third FC group 10c. That is, controller 40a closes the pressure regulating valves 18c, 19c, and 20c of the third FC group 10c. As described above, pressure regulating valves 18a, 19a, and 20a (18b, 19b, 20b, 18c, 19c, and 20c) can adjust the pressure on the secondary side (downstream side of the valve) and can cut off the connection between the primary side (upstream side of the valve) and the secondary side (downstream side of the valve). Oxygen and hydrogen are not supplied to the third FC group 10c, and the third FC group 10c stops completely. In addition, since the exhaust pressure regulating valve 19c and the bypass pressure regulating valve 20c are closed, oxygen will not flow back to the exhaust pipe 12c.

[0042] (3) The controller 40a determines a target internal pressure for the exhaust pipe 12b based on the internal pressure (first internal pressure) of the exhaust pipe 12a, to prevent backflow of oxygen from the exhaust pipe 12a to the exhaust pipe 12b. Furthermore, the controller 40a controls the compressor 17b and pressure regulating valves 18b, 19b, and 20b in a manner that maintains the second FC group 10b at idle speed and the second internal pressure follows the target internal pressure. These processes are related to... Figure 3 Steps S26 and S27 are processed in the same way. The controller 40a repeatedly performs the above processes (1), (2), and (3) until it receives a system stop command. The above processes (1), (2), and (3) are collectively referred to as the first standby mode.

[0043] If the first standby mode is maintained for a specified time, the controller 40a will perform the following processes (4) and (5) instead of the processes (2) and (3) above. (4) The controller 40a stops the second FC group 10b. That is, the controller 40a closes the pressure regulating valves 18b, 19b, and 20b of the second FC group 10b. (5) The controller 40a determines the target internal pressure of the exhaust pipe 12c based on the internal pressure (first internal pressure) of the exhaust pipe 12a, so as to prevent the backflow of oxygen from the exhaust pipe 12a to the exhaust pipe 12c. Moreover, the controller 40a controls the compressor 17c and the pressure regulating valves 18c, 19c, and 20c in such a way that the third FC group 10c is kept in an idle state and the internal pressure (third internal pressure) of the exhaust pipe 12c follows the target internal pressure. The controller 40a repeats the processes (1), (4), and (5) until it receives a system stop command. The processes (1), (4), and (5) above are collectively referred to as the second standby mode. The controller 40a alternately cycles between a first standby mode and a second standby mode at predetermined intervals. This process prevents oxygen backflow and suppresses the degradation of the second FC group 10b and the third FC group 10c. Furthermore, these processes enable rapid response even when power demands exceed the maximum output of one FC group.

[0044] The controller 40a can also switch between the first standby mode and the second standby mode alternately at certain time intervals, and switch between the first standby mode and the second standby mode according to the dryness status of each FC group.

[0045] As described above, even when the outputs of multiple FC groups are different, the FC systems 2 and 2a of the embodiments are able to prevent oxygen backflow in the exhaust pipes of the FC groups.

[0046] The features of FC system 2 are summarized as follows. FC system 2 includes: a first FC group 10a, a second FC group 10b, a first exhaust pipe (exhaust pipe 12a) connected to the first FC group 10a and discharging oxygen not used in the reaction, a second exhaust pipe (exhaust pipe 12b) connected to the second FC group 10b and discharging oxygen not used in the reaction, a common exhaust pipe 32 for merging the first and second exhaust pipes, and a backflow prevention mechanism to prevent oxygen backflow from the first exhaust pipe to the second exhaust pipe. Figure 1 A specific component of the backflow prevention mechanism includes a bypass pipe 13b, a compressor 17b, an intake pressure regulating valve 18b, an exhaust pressure regulating valve 19b, a bypass pressure regulating valve 20b, and a controller 40. Figure 1Compressor 17b is located on oxygen supply pipe 11b, which supplies oxygen to the second FC group 10b, and pressurizes oxygen (air) to the second FC group 10b. Intake pressure regulating valve 18b is located on oxygen supply pipe 11b and adjusts the pressure of the oxygen supplied to the second FC group 10b. Exhaust pressure regulating valve 19b is located on the second exhaust pipe and adjusts the pressure of the oxygen discharged from the second FC group 10b. Bypass pipe 13b guides oxygen discharged from compressor 17b around the second FC group 10b to the second exhaust pipe (exhaust pipe 12b). Bypass pressure regulating valve 20b can adjust the outlet pressure of bypass pipe 13b. Controller 40 controls compressor 17b, intake pressure regulating valve 18b, exhaust pressure regulating valve 19b, and bypass pressure regulating valve 20b to supply the second FC group 10b with the amount of oxygen (oxygen flow rate) required to make the output of the second FC group 10b match the target output, and to prevent backflow of oxygen from the first exhaust pipe to the second exhaust pipe.

[0047] The controller 40 can also control the compressor 17b, the intake pressure regulating valve 18b, the exhaust pressure regulating valve 19b and the bypass pressure regulating valve 20b to supply the second FC group 10b with the amount of oxygen (oxygen flow) required to maintain the second FC group 10b at idle speed, and the oxygen will not flow backward from the first exhaust pipe (exhaust pipe 12a) to the second exhaust pipe (exhaust pipe 12b).

[0048] In addition to FC system 2, the second embodiment of FC system 2a also includes: a third FC group 10c, having a third exhaust pipe (exhaust pipe 12c) connected to a common exhaust pipe 32; and another backflow prevention mechanism, having the same constituent elements as the backflow prevention mechanism of the first embodiment, to prevent oxygen backflow from the first exhaust pipe (exhaust pipe 12a) to the third exhaust pipe (exhaust pipe 12c). Figure 4 The controller 40a of the FC system 2a alternately executes the first standby mode and the second standby mode described above.

[0049] In the case of FC system 2a, the FC groups that make the output consistent with the required output can be switched in turn, and the remaining two FC groups can be used to alternately execute the first standby mode and the second standby mode.

[0050] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the technical solutions. The technology described in the technical solutions includes various modifications and variations of the specific examples described above. The technical elements described in this specification or drawings exert their technical usefulness individually or in various combinations, and are not limited to the combinations described in the technical solutions at the time of application. Furthermore, the technology illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

Claims

1. A fuel cell system, characterized in that, The fuel cell system comprises: First fuel cell stack and second fuel cell stack; The first exhaust pipe is connected to the first fuel cell stack and discharges oxygen that is not used in the reaction. The second exhaust pipe is connected to the second fuel cell stack and discharges oxygen that is not used in the reaction. A shared exhaust pipe is provided for the first exhaust pipe and the second exhaust pipe to merge; and A backflow prevention mechanism prevents oxygen from flowing back from the first exhaust pipe to the second exhaust pipe.

2. The fuel cell system according to claim 1, characterized in that, The backflow prevention mechanism includes: A compressor is installed in the oxygen supply pipe that supplies oxygen to the second fuel cell stack; A bypass pipe guides oxygen discharged from the compressor to bypass the second fuel cell stack and direct it to the second exhaust pipe; An intake pressure regulating valve is installed in the oxygen supply pipe to adjust the pressure of the oxygen supplied to the second fuel cell stack. An exhaust pressure regulating valve is installed in the second exhaust pipe to adjust the pressure of oxygen discharged from the second fuel cell stack; A bypass pressure regulating valve is installed in the bypass pipe to adjust the outlet pressure of the bypass pipe; as well as The controller controls the compressor, the intake pressure regulating valve, the exhaust pressure regulating valve, and the bypass pressure regulating valve to supply the second fuel cell stack with the amount of oxygen required to make the output of the second fuel cell stack match the target output, and to prevent oxygen from flowing back from the first exhaust pipe to the second exhaust pipe.

3. The fuel cell system according to claim 2, characterized in that, The controller controls the compressor, the intake pressure regulating valve, the exhaust pressure regulating valve, and the bypass pressure regulating valve to ensure that the amount of oxygen required to keep the second fuel cell stack at idle flows to the second fuel cell stack, and that oxygen does not flow backward from the first exhaust pipe to the second exhaust pipe.

4. The fuel cell system according to claim 3, characterized in that, The idling state is a state in which the voltage of the second fuel cell stack is maintained within a specified idling voltage range and the output of the second fuel cell stack is suppressed to a minimum.

5. The fuel cell system according to claim 4, characterized in that, The fuel cell system also features: A third fuel cell stack, comprising a third exhaust pipe connected to the shared exhaust pipe; and Another backflow prevention mechanism, having the same components as the aforementioned backflow prevention mechanism, prevents oxygen backflow from the first exhaust pipe to the third exhaust pipe. The controller alternately executes a first standby mode and a second standby mode. In the first standby mode, the third fuel cell stack is stopped, and the oxygen required to keep the second fuel cell stack idling flows to the second fuel cell stack, while the backflow prevention mechanism is controlled in such a way that oxygen does not flow back from the first exhaust pipe to the second exhaust pipe. In the second standby mode, the second fuel cell stack is stopped, and the oxygen required to keep the third fuel cell stack idling flows to the third fuel cell stack, and the oxygen does not flow back from the first exhaust pipe to the third exhaust pipe, thereby controlling the other backflow prevention mechanism.

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