Fuel cell system

Abstract

To prevent overheating of a boost converter without using a temperature sensor, in a fuel cell system disclosed herein including a fuel cell and a boost converter.SOLUTION: A fuel cell system disclosed herein includes a sensor that measures an input voltage and an input current of a boost converter. The controller determines a continuous rated electric power on the basis of the input current and an input power of the boost converter 20. The controller sets a time rated electric power as a final upper limit electric power when the time rated electric power is higher than the continuous rated electric power and is lower than an instantaneous upper limit electric power, and sets the instantaneous upper limit electric power as the final upper limit electric power when the time rated electric power is higher than the continuous rated electric power and is higher than the instantaneous upper limit electric power. In contrast, when the time rated electric power is lower than the continuous rated electric power, the continuous rated electric power is set as the final upper limit electric power. The controller controls one of the boost converter 20 and an FC 10 such that the output of the boost converter 20 does not exceed the final upper limit electric power.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The technology disclosed in this specification relates to a fuel cell system including a fuel cell and a boost converter.

Background Art

[0002] Patent Document 1 discloses a fuel cell system including a fuel cell and a boost converter. To prevent overheating of the boost converter, when the temperature of some capacitors included in the boost converter becomes equal to or higher than a threshold value, the output of the boost converter is reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technology of Patent Document 1 requires a temperature sensor for measuring the temperature of the capacitor. When the number of capacitors included in the boost converter increases, a plurality of temperature sensors must be provided. This specification provides a technology for preventing overheating of the boost converter without providing a temperature sensor. Also, generally, an electric device is defined with a continuous rated power that defines the maximum power allowing continuous operation for one hour or more, but overheating does not occur even if the continuous rated power is exceeded for a short time. This specification also provides a technology for allowing an output exceeding the continuous rated power according to the situation for a short time.

Means for Solving the Problems

[0005] One embodiment of an electric vehicle disclosed herein includes a fuel cell, a boost converter that boosts the output voltage of the fuel cell and outputs it to a predetermined load device, a voltage sensor, a current sensor, and a controller that controls the boost converter based on the measured values ​​of the current sensor and the voltage sensor. The voltage sensor measures the input voltage to the boost converter. The current sensor measures the input current to the boost converter.

[0006] The controller has the following data pre-stored: (1) Continuous rated power, which is the upper limit that the boost converter is allowed to output continuously for more than one hour. (2) Instantaneous power limit, which is the upper limit that the boost converter is allowed to output from the standpoint of protecting its components. (3) The first current-temperature correspondence relationship, which determines the estimated temperature of a conductive component that connects the boost converter and the fuel cell and through which current from the fuel cell flows (this component is referred to as the "pre-boost component") from the measured value of the current sensor. (4) The first temperature limit value correspondence for determining the input current limit value of the boost converter from the estimated temperature of the components before boosting. (5) A second current-temperature correspondence relationship that determines the estimated temperature of a conductive component connecting the boost converter and the load device, through which current from the boost converter flows (referred to as the "post-boost component"), based on the measured values ​​of the current sensor and the voltage sensor. (6) A second temperature limit relationship for determining the output current limit of the boost converter from the estimated temperature of the components after boosting. (7) Time rating correspondence to determine the time rating power that the boost converter is allowed to output continuously for up to one hour, based on the input current limit and the output current limit.

[0007] The above data has been obtained in advance through simulations and experiments. The above correspondences may be in the form of mathematical formulas or maps.

[0008] The controller uses the measurements from the current and voltage sensors, along with the data mentioned above, to determine the final upper limit power for the boost converter. The controller then controls the boost converter to ensure that its output power does not exceed the final upper limit power.

[0009] The final power limit determination process performed by the controller is as follows: (1) The controller uses the measured value from the current sensor and the first current-temperature correspondence to determine the estimated temperature of the component before voltage boosting. (2) The estimated temperature of the component after voltage boosting is determined using the measured values ​​from the current sensor and voltage sensor and the second current-temperature correspondence relationship. (3) The input current limit value is determined using the estimated temperature of the components before voltage boosting and the correspondence between the first temperature limit value and the obtained relationship. (4) The output current limit value is determined using the estimated temperature of the boosted component obtained and the correspondence between that temperature and the second temperature limit value. (5) The time-rated power is determined using the obtained input current limit value, output current limit value, and time-rated correspondence. (6) If the obtained time-rated power is greater than the continuous-rated power and less than the instantaneous upper limit power, the time-rated power is set to the final upper limit power. (7) If the obtained time-rated power is greater than the continuous-rated power and also greater than the instantaneous upper limit power, the instantaneous upper limit power is set as the final upper limit power. (8) If the obtained time-rated power is less than the continuous-rated power, the continuous-rated power is set as the final upper limit power.

[0010] The fuel cell system disclosed herein can prevent overheating of the boost converter without using a temperature sensor. Moreover, since the final upper limit power for overheating prevention is changed according to the situation, the boost converter can be used efficiently.

[0011] Details of the technology disclosed herein and further improvements are described in the following "Modes for Carrying Out the Invention". [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram of the fuel cell system in the embodiment. [Figure 2] This is a flowchart of the overheating prevention process performed by the controller. [Figure 3] This is a flowchart of the overheating prevention process (continuation of Figure 2). [Modes for carrying out the invention]

[0013] The fuel cell system 2 of the embodiment will be described with reference to the drawings. For the sake of simplicity, "fuel cell" may be abbreviated as "FC" below. "Fuel cell system 2" will be referred to as "FC system 2," and "fuel cell stack" will be referred to as "FC stack."

[0014] Figure 1 shows a block diagram of FC system 2. FC system 2 comprises FC10 (fuel cell 10), a boost converter 20, and a controller 30. FC10 includes an FC stack 11 that generates power and auxiliary equipment 12 for operating the FC stack 11. In this embodiment, "auxiliary equipment" is a general term for all devices necessary to operate the FC stack 11, such as a fuel tank, compressor, and injectors.

[0015] The output terminal of the FC stack 11 is connected to the input terminal of the boost converter 20 via the input cable 41. The boost converter 20 includes a current sensor 22 for measuring the input current, a voltage sensor 23 for measuring the input voltage, and a boost circuit 21 that boosts the voltage of the input power and outputs it. The boost circuit 21 may be a conductive type boost circuit composed of a coil, a switching element and a capacitor, or it may be a non-conductive type boost circuit using a transformer.

[0016] The output terminal of the boost circuit 21 (the output terminal of the boost converter 20) is connected to the load device 90 via the output cable 42. The load device 90 is a device that consumes power or a device that stores power. Specific examples of the load device 90 include an electric motor (a device that consumes power) and a battery (a device that stores power).

[0017] The 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.

[0018] The controller 30 includes a storage device 32 that stores programs and various types of data, and a CPU 31 (central processing unit 31) that executes the programs stored in the storage device 32. The program executed by the controller 30 (CPU 31) is a process (overheat prevention process) that controls the boost converter 20 (boost circuit 21) and the FC 10 (auxiliary machine 12) so that the output power of the boost converter 20 does not exceed the final upper limit power. In the overheat prevention process, the controller 30 appropriately sets the final upper limit power based on the measured values of the current sensor 22 and the voltage sensor 23.

[0019] In addition to the program for the overheat prevention process, the storage device 32 stores various types of data for determining the final upper limit power. The following data is stored in the storage device 32. (1) Continuous rated power, which is the upper limit value that allows the boost converter to output continuously for 1 hour or more. In other words, the continuous rated power is a constant that determines the upper limit power that the boost converter can output continuously for 1 hour or more. (2) Instantaneous upper limit power, which is the upper limit value that allows the boost converter to output from the perspective of component protection. (3) The first current-temperature correspondence relationship for obtaining the estimated temperature of a conductive component that connects the boost converter and the fuel cell and through which the current from the fuel cell flows (this component is referred to as the "front-boost component") from the measured value of the current sensor. (4) The first temperature-limit value correspondence relationship for obtaining the input current limit value of the boost converter from the estimated temperature of the front-boost component. (5) The second current-temperature correspondence relationship for obtaining the estimated temperature of a conductive component that connects the boost converter and the load device and through which the current from the boost converter flows (this component is referred to as the "rear-boost component") from the measured values of the current sensor and the voltage sensor. (6) A second temperature limit relationship for determining the output current limit of the boost converter from the estimated temperature of the components after boosting. (7) Time rating correspondence to determine time rating power from input current limit value and output current limit value. Time rating power is a variable that defines the upper limit power that the boost converter is allowed to output continuously for a period of one hour or less. In other words, time rating power is the upper limit power that the boost converter is allowed to output continuously for a period of one hour or less.

[0020] The various correspondence data described above have been obtained in advance through simulations and experiments. These correspondences may be given in the form of mathematical formulas or in the form of maps.

[0021] Figures 2 and 3 show flowcharts of the overheat prevention process for the boost converter 20. The overheat prevention process will be explained below with reference to Figures 2 and 3.

[0022] The controller 30 determines the estimated temperature of the input cable 41 using the measured value from the current sensor 22 and the first current-temperature correspondence relationship (step S12). When current flows through the input cable 41, it generates heat due to its internal resistance. Some of the heat from the input cable 41 is dissipated to the components it is in contact with (such as a resin protective tube or terminal block). Alternatively, some of the heat from the input cable 41 is dissipated into the air. The amount of heat generated and dissipated depends on the physical characteristics of the cable and the surrounding physical structure. Therefore, a certain relationship exists between the current flowing through the input cable 41 and the temperature of the input cable 41. The first current-temperature correspondence relationship is a formalization (or mapping) of this relationship through simulations and experiments. The controller 30 refers to the first current-temperature correspondence relationship to obtain the estimated temperature of the input cable 41 for the measured value from the current sensor 22.

[0023] Next, the controller 30 uses the measured values ​​from the current sensor 22 and the voltage sensor 23 and the second current-temperature correspondence relationship to determine the estimated temperature of the output cable 42 (step S13). The temperature of the output cable 42 depends on the power after voltage boosting. The power after voltage boosting is approximately equal to the power before voltage boosting. The second current-temperature correspondence relationship is a pre-formulated (or mapped) relationship between the power before input (i.e., the product of the measured values ​​from the current sensor 22 and the voltage sensor 23) and the temperature of the output cable 42. The controller 30 uses the second current-temperature correspondence relationship to determine the estimated temperature of the output cable 42.

[0024] Next, the controller 30 uses the estimated temperature of the input cable 41 obtained in step S12 and the first temperature limit relationship to determine the input current limit value for the boost converter 20 (step S14). In the first temperature limit relationship, the relationships are defined such that the higher the estimated temperature, the lower the input current limit value.

[0025] Next, the controller 30 uses the estimated temperature of the output cable 42 obtained in step S13 and the second temperature limit relationship to determine the output current limit for the boost converter 20 (step S15). In the second temperature limit relationship, the relationship is defined such that the output current limit decreases as the estimated temperature increases.

[0026] The controller 30 determines the time-rated power for the boost converter 20 using the input current limit value obtained in step S14 and the output current limit value obtained in step S15, along with the time rating correspondence (step S16). "Time rating vs. power" refers to the upper limit of output power at which overheating will not occur even if the boost converter continuously outputs for less than one hour. In the second temperature limit correspondence, the relationship between the input current limit value and the output current limit value is defined such that the larger the product of the input current limit value and the output current limit value, the larger the time-rated power.

[0027] Next, the controller 30 compares the time-rated power obtained in step S16 with the continuous-rated power stored in the memory device 32 (step S22). If the time-rated power is greater than the continuous time-rated power, the controller 30 compares the time-rated power with the instantaneous upper limit power stored in the memory device 32 (step S22: YES, S23). If the time-rated power is less than the instantaneous upper limit power, the controller 30 sets the time-rated power as the final upper limit power (step S23: YES, S24). The "final upper limit power" is a variable defined in the overheat prevention process and is determined in one of steps S24, S25, or S26.

[0028] In the determination in step S23, if the time-rated power is less than the instantaneous upper limit power (step S23: YES), the controller 30 sets the time-rated power as the final upper limit power (step S24). In the determination in step S23, if the time-rated power is greater than the instantaneous upper limit power (step S23: NO), the controller 30 sets the instantaneous upper limit power as the final upper limit power (step S25).

[0029] In step S22, if the time-rated power is less than the continuous-rated power (step S22: NO), the controller 30 sets the final upper limit power to the continuous-rated power (step S26).

[0030] After the final upper limit power is determined in step S24, S25, or S26, the controller 30 controls the boost converter 20 and / or FC10 so that the output power of the boost converter 20 does not exceed the final upper limit power (step S27). Specifically, when the output of the boost converter 20 approaches the final upper limit power, the controller 30 reduces the boost ratio of the boost converter 20. Alternatively, the controller 30 controls the auxiliary equipment 12 to reduce the output of the FC stack 11. The controller 30 also controls the FC10 so that the input current to the boost converter 20 does not exceed the input current limit value obtained in step S14. Furthermore, the controller 30 controls the boost converter 20 so that the output current of the boost converter 20 does not exceed the output current limit value obtained in step S15.

[0031] Through the above process, the output power of the boost converter 20 does not exceed the final upper limit power, and overheating is prevented.

[0032] The FC system 2 can prevent overheating of the boost converter 20 without using a temperature sensor. Furthermore, the FC system 2 adjusts the final upper limit power of the boost converter 20 according to the measured values ​​of the current sensor 22 and the voltage sensor 23. Therefore, the boost converter 20 can be used effectively.

[0033] The processes shown in Figures 2 and 3 can be summarized as follows: The controller 30 determines the continuous rated power based on the input current and input power of the boost converter 20 (steps S12-S16). The correspondence between the input current and input voltage for determining the continuous rated power is stored in the controller 30 beforehand.

[0034] Next, the controller 30 compares the continuous rated power with the time rated power (step S22). If the time rated power is greater than the continuous rated power (step S22: YES), the controller 30 compares the time rated power with the instantaneous upper limit power (step S23). If the time rated power is less than the instantaneous upper limit power (step S23: YES), the controller 30 sets the time rated power to the final upper limit power (step S24). On the other hand, if the time rated power is greater than the instantaneous upper limit power (step S23: NO), the controller 30 sets the instantaneous upper limit power to the final upper limit power (step S25).

[0035] Furthermore, in the process of step S22, if the time-rated power is less than the continuous-rated power (step S22: NO), the controller 30 sets the continuous-rated power to the final upper limit power (step S26). Then, the controller 30 controls at least one of the boost converter 20 and FC10 so that the output of the boost converter 20 does not exceed the final upper limit power (step S27).

[0036] The following are points to note regarding the technology described in the embodiment. The input cable 41 corresponds to an example of a pre-boost component connecting the boost converter 20 and FC10. The output cable 42 corresponds to an example of a post-boost component connecting the boost converter 20 and load device 90. The pre-boost component can be any component through which the output current of FC10 flows, and may include terminals and relays in addition to the input cable. The post-boost component can be any component through which the output current of the boost converter 20 flows, and may include terminals and relays in addition to the output cable.

[0037] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness. [Explanation of Symbols]

[0038] 2: Fuel cell system 10: Fuel cell) 11: Fuel cell stack 12: Auxiliary equipment 20: Boost converter 21: Boost circuit 22: Current sensor 23: Voltage sensor 30: Controller 31: Central processing unit 32: Memory device 41: Input cable 42: Output cable 90: Load device

Claims

[Claim 1] Fuel cells and A boost converter that increases the output voltage of the fuel cell and outputs it to a predetermined load device, A voltage sensor for measuring the input voltage to the boost converter, A current sensor for measuring the input current to the boost converter, A controller that controls the aforementioned boost converter, It is equipped with, The aforementioned controller, The continuous rated power is the upper limit that the boost converter is allowed to output continuously for more than one hour, From the perspective of protecting components, the instantaneous upper limit power, which is the upper limit value that the boost converter is allowed to output, A first current-temperature correspondence relationship is obtained from the measured value of the current sensor to determine the estimated temperature of the conductive component connecting the boost converter and the fuel cell, which is a pre-boost component through which current from the fuel cell flows, A first temperature limit value correspondence relationship for determining the input current limit value of the boost converter from the estimated temperature of the component before boosting, A second current-temperature correspondence is obtained by determining the estimated temperature of a conductive component connecting the boost converter and the load device, which is a boosted component through which current from the boost converter flows, from the measured values ​​of the current sensor and the voltage sensor. A second temperature limit value correspondence relationship for determining the output current limit value of the boost converter from the estimated temperature of the boosted component, A time rating correspondence is determined from the input current limit value and the output current limit value to find the time-rated power that the boost converter is allowed to output continuously for up to one hour, and I remember, Using the measured value of the current sensor and the first current-temperature correspondence relationship, the estimated temperature of the component before voltage boosting is determined. Using the measured values ​​of the current sensor and the voltage sensor and the second current-temperature correspondence relationship, the estimated temperature of the boosted component is determined. Using the estimated temperature of the component before voltage boosting obtained and the correspondence between that temperature and the first temperature limit, the input current limit is determined. The output current limit value is determined using the estimated temperature of the boosted component obtained and the correspondence between that temperature and the second temperature limit value. Using the obtained input current limit value, output current limit value, and time rating correspondence relationship, the time rating power is determined. If the obtained time-rated power is greater than the continuous-rated power and less than the instantaneous upper limit power, the time-rated power is set to the final upper limit power. If the obtained time-rated power is greater than the continuous-rated power and also greater than the instantaneous upper limit power, the instantaneous upper limit power is set to the final upper limit power. If the obtained time-rated power is less than the continuous-rated power, the continuous-rated power is set to the final upper limit power. A fuel cell system that controls the boost converter so that the output power of the boost converter does not exceed the final upper limit power.

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