Patent Application
20240313245
This application claims priority to Japanese Patent Application No. 2023-041710 filed on Mar. 16, 2023, incorporated herein by reference in its entirety.
Technologies disclosed in the present specification relate to a fuel cell system that includes a fuel cell and a boost converter.
Japanese Unexamined Patent Application Publication No. 2011-23132 (JP 2011-23132 A) discloses a fuel cell system that includes a fuel cell and a boost converter. For preventing the overheating of the boost converter, the output of the boost converter is decreased when the temperatures of some capacitors included in the boost converter are equal to or higher than a threshold.
The technology in JP 2011-23132 A requires a temperature sensor that measures the temperature of the capacitor. When the number of capacitors included in the boost converter increases, it is necessary to include a plurality of temperature sensors. The present specification provides a technology for preventing the overheating of the boost converter without including the temperature sensor. Further, generally, for an electric device, a continuous rated electric power specifying the maximum electric power that allows continuous operation to be performed for one hour or more is prescribed. However, in the case of a short time, the overheating does not occur even when the electric power exceeds the continuous rated electric power. The present specification also provides a technology for allowing an output exceeding the continuous rated electric power for a short time depending on the situation.
An embodiment of a fuel cell system disclosed in the present specification includes: a fuel cell; a boost converter that boosts an output voltage of the fuel cell and outputs the output voltage to a predetermined load device; a voltage sensor; a current sensor: a controller that controls the boost converter based on measured values of the current sensor and the voltage sensor. The voltage sensor measures an input voltage to the boost converter. The current sensor measures an input current to the boost converter.
In the controller, the following data is previously stored.
The above data is previously obtained by simulations or experiments. The above correspondence relations may be indicated by mathematical expressions, or may be indicated by maps.
The controller decides a final upper limit electric power for the boost converter, using measured values of the current sensor and the voltage sensor and the above data. The controller controls the boost converter such that an output electric power of the boost converter does not exceed the final upper limit electric power.
A final upper limit electric power decision process that is executed by the controller is as follows.
The fuel cell system disclosed in the present specification can prevent the overheating of the boost converter without using a temperature sensor. Moreover, the final upper limit electric power for preventing the overheating is changed depending on the situation, and therefore it is possible to efficiently use the boost converter.
Details of the technologies disclosed in the present specification and further improvements will be described in “DETAILED DESCRIPTION OF EMBODIMENTS” shown later.
Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:
A fuel cell system 2 in an embodiment will be described with reference to the drawings. Hereinafter, for simplifying the description, “fuel cell” is occasionally referred to as “FC”. The “fuel cell system 2” is referred to as “FC system 2”, and “fuel cell stack” is referred to as “FC stack”.
An output terminal of the FC stack 11 is connected to an input terminal of the boost converter 20 through an input cable 41. The boost converter 20 includes a current sensor 22 that measures an input current, a voltage sensor 23 that measures an input voltage, and a boost circuit 21 that boosts the voltage of input electric power and outputs the electric power. The boost circuit 21 may be a conduction type boost circuit that is constituted by a coil, a switching element, and a capacitor, or may be a non-conduction type boost circuit in which a transformer is used.
An output terminal (an output terminal of the boost converter 20) of the boost circuit 21 is connected to a load device 90 through an output cable 42. The load device 90 is a device that consumes electric power, or a device that stores electric power. Specific examples of the load device 90 include an electric motor (the device that consumes electric power) and a battery (the device that stores electric power), and the like.
Measured values of the current sensor 22 and the voltage sensor 23 are sent to the controller 30. The controller 30 controls the boost converter 20 (boost circuit 21) and the FC 10 (auxiliary machine 12), based on the measured values of the current sensor 22 and the voltage sensor 23.
The controller 30 includes a storage device 32 that stores a program and a variety of data, and a central processing unit 31 (CPU 31) that executes the program stored in the storage device 32. The program that is executed by the controller 30 (CPU 31) is a program for a process (overheating prevention process) of controlling the boost converter 20 (boost circuit 21) and the FC 10 (auxiliary machine 12), such that the output electric power of the boost converter 20 (boost circuit 21) does not exceed a final upper limit electric power. In the overheating prevention process, the controller 30 appropriately sets the final upper limit electric power based on the measured values of the current sensor 22 and the voltage sensor 23.
The storage device 32 stores a variety of data for deciding the final upper limit electric power, in addition to the program for the overheating prevention process. The storage device 32 stores the following data.
The variety of correspondence relation data described above is previously obtained by simulations or experiments. The above correspondence relation may be given as mathematical expressions, or may be given as maps.
The controller 30 evaluates the estimated temperature of the input cable 41, using the measured value of the current sensor 22 and the first current-temperature correspondence relation (step S12). When current flows through the input cable 41, heat is generated by the internal resistance of the input cable 41. Further, some of the heat of the input cable 41 is dispersed to components (a protective tube and a terminal block that are made of resin) that contact with the input cable. Alternatively, some of the heat of the input cable 41 is dispersed to the air. The generated heat amount and the dispersed heat amount depend on the physical characteristic of the cable and the physical structure of the periphery of the cable. Accordingly, a constant relation is satisfied between the current that flows through the input cable 41 and the temperature of the input cable 41. The relation is formulated (or mapped) by simulations or experiments, so that the first current-temperature correspondence relation is obtained. The controller 30 refers to the first current-temperature correspondence relation, and obtains the estimated temperature of the input cable 41 with respect to the measured value of the current sensor 22.
Subsequently, the controller 30 evaluates the estimated temperature of the output cable 42, using the measured values of the current sensor 22 and the voltage sensor 23 and the second current-temperature correspondence relation (step S13). The temperature of the output cable 42 depends on the electric power after the boost. The electric power after the boost is nearly equal to the electric power before the boost. The second current-temperature correspondence relation is obtained by previously formulating (or mapping) the relation between the electric power before the input (that is, the product of the measured values of the current sensor 22 and the voltage sensor 23) and the temperature of the output cable 42. The controller 30 evaluates the estimated temperature of the output cable 42, using the second current-temperature correspondence relation.
Subsequently, the controller 30 evaluates the input current limit of the boost converter 20, using the estimated temperature of the input cable 41 that is obtained in step S12 and the first temperature-limit correspondence relation (step S14). In the first temperature-limit correspondence relation, the relation between the estimated temperature and the input current limit is prescribed such that the input current limit is lower as the estimated temperature is higher.
Subsequently, the controller 30 evaluates the output current limit of the boost converter 20, using the estimated temperature of the output cable 42 that is obtained in step S13 and the second temperature-limit correspondence relation (step S15). In the second temperature-limit correspondence relation, the relation between the estimated temperature and the output current limit is prescribed such that the output current limit is lower as the estimated temperature is higher.
The controller 30 evaluates the time rated electric power of the boost converter 20, using the input current limit obtained in step S14, the output current limit obtained in step S15, and the time rated correspondence relation (step S16). The “time rated electric power” means the upper limit of an output electric power at which the overheating does not occur even when the boost converter continuously performs output for equal to or less than one hour. In the time rated correspondence relation, the relation between the product of the input current limit and the output current limit and the time rated electric power is prescribed such that the time rated electric power is higher as the product of the input current limit and the output current limit is larger.
Subsequently, the controller 30 compares the time rated electric power obtained in step S16 and the continuous rated electric power stored in the storage device 32 (step S22). In the case where the time rated electric power is higher than the continuous rated electric power, the controller 30 compares the time rated electric power and the instantaneous upper limit electric power stored in the storage device 32 (step S22: YES, S23). In the case where the time rated electric power is lower than the instantaneous upper limit electric power, the controller 30 sets the time rated electric power as the final upper limit electric power (step S23: YES, S24). The “final upper limit electric power” is a variable that is defined in the overheating prevention process, and is decided in one of step S24, step S25, and step S26.
In the case where the time rated electric power is lower than the instantaneous upper limit electric power in the determination in step S23 (step S23: YES), the controller 30 sets the time rated electric power as the final upper limit electric power (step S24). In the case where the time rated electric power is higher than the instantaneous upper limit electric power in the determination in step S23 (step S23: NO), the controller 30 sets the instantaneous upper limit electric power as the final upper limit electric power (step S25).
In the case where the time rated electric power is lower than the continuous rated electric power in step S22 (step S22: NO), the controller 30 sets the continuous rated electric power as the final upper limit electric power (step S26).
After the final upper limit electric power is decided in one of step S24, step S25, and step S26, the controller 30 controls the boost converter 20 and/or the FC 10, such that the output electric power of the boost converter 20 does not exceed the final upper limit electric power (step S27). Specifically, the controller 30 decreases the boost rate of the boost converter 20, when the output of the boost converter 20 is close to the final upper limit electric power. Alternatively, the controller 30 controls the auxiliary machine 12, to decrease the output of the FC stack 11. The controller 30 controls the FC 10 such that the input current to the boost converter 20 does not exceed the input current limit obtained in step S14. Further, the controller 30 controls the boost converter 20 such that the output current of the boost converter 20 does not exceed the output current limit obtained in step S15.
By the above process, the output electric power of the boost converter 20 does not exceed the final upper limit electric power, so that the overheating is prevented.
The FC system 2 can prevent the overheating of the boost converter 20 without using a temperature sensor. Further, the FC system 2 adjusts the final upper limit electric power of the boost converter 20 depending on the measured values of the current sensor 22 and the voltage sensor 23. Accordingly, it is possible to effectively use the boost converter 20.
The process in
Next, the controller 30 compares the continuous rated electric power and the time rated electric power (step S22). When the time rated electric power is higher than the continuous rated electric power (step S22: YES), the controller 30 compares the time rated electric power and the instantaneous upper limit electric power (step S23). When the time rated electric power is lower than the instantaneous upper limit electric power (step S23: YES), the controller 30 sets the time rated electric power as the final upper limit electric power (step S24). On the other hand, when the time rated electric power is higher than the instantaneous upper limit electric power (step S23: NO), the controller 30 sets the instantaneous upper limit electric power as the final upper limit electric power (step S25).
Further, when the time rated electric power is lower than the continuous rated electric power in the process of step S22 (step S22: NO), the controller 30 sets the continuous rated electric power as the final upper limit electric power (step S26). Then, the controller 30 controls at least one of the boost converter 20 and the FC 10 such that the output of the boost converter 20 does not exceed the final upper limit electric power (step S27).
Notes relevant to the technologies described in the embodiment will be described. The input cable 41 corresponds to an example of the pre-boost component that connects the boost converter 20 and the FC 10. The output cable 42 corresponds to an example of the post-boost component that connects the boost converter 20 and the load device 90. The pre-boost component only needs to be a component through which the output current of the FC 10 flows, and may be a terminal or a relay, instead of the input cable. The post-boost component only needs to be a component through which the output current of the boost converter 20 flows, and may be a terminal or a relay, instead of the output cable.
Specific examples of the present disclosure have been described above in detail. They are just examples, and do not limit the scope of the claims. The technologies described in the claims include various modifications and alterations of the above-exemplified specific examples. The technical elements described in the present specification or the drawings exert technical utility independently or by various combinations, and are not limited to the combinations described in the claims at the filing time. Further, the technologies exemplified in the present specification or the drawings can concurrently achieve a plurality of purposes, and have technical utility simply by achieving one of the plurality of purposes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-041710 | Mar 2023 | JP | national |
