JP7452502B2 - fuel cell system - Google Patents

Description

The technology disclosed herein relates to a fuel cell system.

Patent Document 1 discloses a fuel cell system. This fuel cell system includes a fuel cell that supplies power to a motor, and a secondary battery that is connected in parallel to the fuel cell without a converter. A relay is provided between the fuel cell and the secondary battery, and charging and discharging of the secondary battery is controlled by controlling the relay.

JP2006-318818A

In the above configuration, the secondary battery is connected to the fuel cell without a converter. With such a configuration, the configuration of the fuel cell system can be simplified. On the other hand, since the secondary battery is passively charged or discharged depending on the output voltage of the fuel cell, there is a risk that the secondary battery may be overcharged depending on the output voltage of the fuel cell. In this regard, if a relay is provided between the fuel cell and the secondary battery, when the secondary battery approaches a fully charged state, the relay is opened to prevent overcharging of the secondary battery. It can be prevented. However, if the relay is turned on and off while a relatively large current is flowing, there is a risk that the contacts of the relay will weld. This specification discloses a technique that can avoid overcharging of a secondary battery without necessarily requiring a relay in a fuel cell system in which the secondary battery is connected to a fuel cell without going through a converter.

A fuel cell system disclosed in this specification includes a fuel cell that supplies power to at least one load, and a fuel cell that is connected in parallel to the fuel cell without a converter, passively depending on the output voltage of the fuel cell. It includes a secondary battery that is charged or discharged, and a controller that monitors the output voltage of the fuel cell and executes a protective operation mode when the output voltage of the fuel cell exceeds a first threshold. In the protected operation mode, an operation command corresponding to a predetermined minimum power consumption is given to some or all of at least one load.

As described above, when the secondary battery is connected to the fuel cell without going through a converter, the secondary battery is passively charged or discharged according to the output voltage of the fuel cell. Here, the output voltage of the fuel cell changes depending on the output current of the fuel cell, and the output voltage becomes larger as the output current becomes smaller. Therefore, when the power consumption of the load connected to the fuel cell is small and the output current of the fuel cell is also small, the output voltage of the fuel cell increases and there is a risk that the secondary battery will be overcharged. In this regard, in the fuel cell system described above, for example, when the power consumption by the load is small and the output voltage of the fuel cell exceeds the first threshold, the controller executes the protective operation mode. In the protected operation mode, an operation command corresponding to a predetermined minimum amount of power consumption is given to some or all of at least one load connected to the fuel cell. As a result, the output current of the fuel cell increases and the output voltage of the fuel cell decreases, thereby preventing overcharging of the secondary battery. Note that the first threshold value related to the output voltage and the minimum power consumption amount related to the protection operation mode can be determined as appropriate depending on the state of charge (SOC) allowed for the secondary battery. According to such a configuration, overcharging of the secondary battery can be avoided without necessarily requiring a relay.

FIG. 1 is a block diagram showing the configuration of an aircraft according to an embodiment. The current-voltage curves of a secondary battery and a fuel cell are shown.

In one embodiment of the present technology, the controller may discontinue the protected operating mode when the output voltage of the fuel cell exceeds a first threshold and then the output voltage falls below a second threshold. The second threshold may be smaller than the first threshold. According to such a configuration, the protective operation mode can be stopped when the output voltage of the fuel cell has sufficiently decreased. Thereby, it is possible to suppress excessive switching between execution and cancellation of the protection operation mode.

In one embodiment of the present technology, the controller may execute the protective operating mode even during startup of the fuel cell. Further, the controller may cancel the protection operation mode after a predetermined time has elapsed from the start of activation of the fuel cell. According to such a configuration, a certain amount of power is consumed when starting up the fuel cell, so that the fuel cell can be appropriately protected.

In one embodiment of the present technology, the at least one load may include a first load that receives power from the fuel cell system and a second load that is included in the fuel cell system. In the protected operation mode, an operation command may be given to the second load.

In one embodiment of the present technology, the second load is at least one of an air pump that supplies air to the fuel cell, a cooling pump that supplies cooling water to the fuel cell, and a cooling fan that radiates heat from the cooling water. may include.

In one embodiment of the present technology, an air vehicle may include a motor driving a propeller and a fuel cell system, and the motor may be included in the at least one load powered by the fuel cell.

The fuel cell system 12 of this embodiment will be explained with reference to the drawings. The fuel cell system 12 of this embodiment is employed in the aircraft 10. The flying object 10 is a so-called multicopter. However, the flying object 10 is not limited to a multicopter, and may be any helicopter that obtains lift from a propeller. Further, the flying object 10 may be an unmanned flying object with no humans on board, or a manned flying vehicle with humans on board.

As shown in FIG. 1, the flying object 10 includes a fuel cell system 12, a propeller 14, and a motor 16. The propeller 14 is connected to and driven by the motor 16. When the propeller 14 rotates in accordance with the operation of the motor 16, lift is generated on the flying object 10. The number of propellers 14 is not limited.

Next, the fuel cell system 12 will be explained. The fuel cell system 12 includes a fuel cell unit 18, a power controller 20, a secondary battery 22, and a diode 32. Fuel cell unit 18 includes a fuel cell 24, an air pump 26, a cooling pump 28, and a cooling fan 30.

The fuel cell 24 generates electricity by using fuel gas supplied from a fuel container (not shown). Fuel cell 24 is connected to motor 16 through power line 34 . Electric power generated by fuel cell 24 is supplied to motor 16 through power line 34 .

Secondary battery 22 is connected to power line 34 . The secondary battery 22 is connected in parallel to the fuel cell 24 via a power line 34, and is connected to the motor 16 together with the fuel cell 24. A diode 32 is inserted between the fuel cell 24 and the secondary battery 22 to cut off the current flowing to the fuel cell 24. The current generated by the secondary battery 22 is prohibited from flowing to the fuel cell 24 by the diode 32, and is supplied to the motor 16 through the power line 34. The secondary battery 22 can also be charged with power generated by the fuel cell 24. Specifically, since the secondary battery 22 is connected to the fuel cell 24 without going through a converter, it is passively charged or discharged according to the voltage of the fuel cell 24.

Power supply controller 20 is electrically connected to fuel cell system 12 . The power supply controller 20 can control the output power of the fuel cell 24 by controlling the amount of fuel gas supplied to the fuel cell 24 . The power supply controller 20 is configured to be driven by electric power supplied from the fuel cell 24.

The power supply controller 20 stores in advance a first threshold value Vth1, a second threshold value Vth2, and an upper limit output voltage Vmax. These values Vth1, Vth2, and Vmax are parameters used in the protection operation mode described later. The power supply controller 20 monitors the voltage of the fuel cell 24, and executes the protection operation mode when the voltage exceeds the first threshold Vth1. Details of the protection operation mode will be explained later. The power supply controller 20 further cancels the protection operation mode when the voltage of the fuel cell 24 exceeds the first threshold Vth1 and then falls below the second threshold Vth2. Note that the second threshold value Vth2 is smaller than the first threshold value Vth1.

Air pump 26 supplies air to fuel cell 24 . Specifically, air outside the aircraft 10 is compressed by the air pump 26 and supplied to the fuel cell 24 through an air flow path (not shown).

Cooling pump 28 supplies cooling water to fuel cell 24 . For example, the cooling pump 28 circulates cooling water between the fuel cell 24 and a radiator (not shown). The cooling water pumped from the cooling pump 28 circulates through the radiator and the fuel cell 24 in order through a circulation path (not shown). That is, the temperature of the cooling water increases as it passes through the fuel cell 24, which is a heat source, and absorbs heat. Thereafter, the cooling water is cooled by exchanging heat with air in a radiator.

The cooling fan 30 is provided, for example, near a circulation path (for example, a radiator). When air is applied to the circulation path by a cooling fan, a radiator having a circulation path for cooling water exchanges heat between the cooling water and the air. This causes the cooling water to radiate heat.

As described above, when the secondary battery 22 is connected to the fuel cell 24 without using a converter, the secondary battery 22 is passively charged or discharged according to the output voltage of the fuel cell 24. Here, FIG. 2 shows a current-voltage curve (hereinafter sometimes referred to as "IV curve") L1 of the fuel cell 24 and an IV curve L2 of the secondary battery 22. As shown by the IV curve L1 in FIG. 2, the output voltage of the fuel cell 24 changes depending on the output current of the fuel cell 24, and the smaller the output current, the larger the output voltage. Therefore, when the power consumption of the load connected to the fuel cell 24 is small and the output current of the fuel cell 24 is also small, there is a risk that the secondary battery 22 will be overcharged due to the increase in the output voltage of the fuel cell 24. There is.

Regarding the above problem, in the flying object 10 of this embodiment, for example, when the power consumption by the load is small and the output voltage of the fuel cell 24 exceeds the first threshold value Vth1, the power supply controller 20 executes the protective operation mode. . With reference to FIG. 2, the protection operation mode processing executed by the power supply controller 20 will be described.

In the protection operation mode, an operation command corresponding to a predetermined minimum power consumption P1 is given to the load connected to the fuel cell 24. The load connected to the fuel cell 24 here is, for example, at least one or all of the air pump 26, the cooling pump 28, and the cooling fan 30. A load such as the air pump 26 receives an operation command from the power supply controller 20 and operates so as to consume power equal to or more than the minimum power consumption amount P1.

The minimum power consumption amount P1 can be determined based on the IV curve L1 of the fuel cell 24 and the IV curve L2 of the secondary battery 22. As shown in the IV curve L2 of the secondary battery 22, the open circuit voltage (output voltage when the current becomes zero) of the secondary battery 22 changes depending on the charging rate of the secondary battery 22, and The higher the charging rate of the secondary battery 22, the higher the open circuit voltage of the secondary battery 22 becomes. Furthermore, an allowable upper limit value is set for the charging rate of the secondary battery 22 in order to avoid overcharging. For example, assume that the open-circuit voltage of the secondary battery 22 becomes Vmax when the charging rate of the secondary battery 22 is at the upper limit value. In this case, if the output voltage of the fuel cell 24 exceeds the voltage value Vmax, the charging rate of the secondary battery 22 will exceed its upper limit. Therefore, the output voltage of the fuel cell 24 needs to be limited to the voltage value Vmax or less, and is hereinafter referred to as the upper limit output voltage Vmax. As shown in the IV curve L1 of the fuel cell 24, in order to limit the output voltage of the fuel cell 24 to below the upper limit output voltage Vmax, it is sufficient to maintain the output current of the fuel cell 24 above Imin. Hereinafter, this will be referred to as the lower limit output current Imin. Therefore, the minimum power consumption P1 can be appropriately determined so that the output current of the fuel cell 24 is equal to or higher than the lower limit output current Imin. Note that the lower limit value of the minimum power consumption P1 is a value obtained by multiplying the upper limit output voltage Vmax of the fuel cell 24 by the lower limit output current Imin of the fuel cell 24 corresponding to the upper limit output voltage Vmax. That is, the minimum power consumption P1 is the area of the region P surrounded by the point a1 (Imin, Vmax), the point a2 (0, Vmax), the point a3 (0, 0), and the point a4 (Imin, 0) in FIG. be equivalent to.

As described above, the power supply controller 20 executes the protection operation mode when the output voltage of the fuel cell 24 exceeds the first threshold value Vth1. In the protective operation mode, an operation command corresponding to the minimum power consumption P1 is given to the load connected to the fuel cell 24. As a result, the output current of the fuel cell 24 increases and the output voltage of the fuel cell 24 decreases. That is, the relationship between the output voltage and the output current of the fuel cell 24 moves in the direction of the arrow x1 along the IV curve of the fuel cell 24 from a point a5 corresponding to the first threshold value Vth1. In this way, as the output voltage of the fuel cell 24 decreases, the relationship between the output voltage and the output current of the fuel cell 24 can move from point a5 in the direction of arrow x2 along the IV curve of the fuel cell. suppressed. That is, since the output voltage of the fuel cell 24 does not reach the upper limit output voltage Vmax that can cause overcharging of the secondary battery 22, overcharging of the secondary battery 22 is avoided. According to such a configuration, overcharging of the secondary battery 22 can be avoided without necessarily requiring a relay.

The first threshold value Vth1 is set by giving a certain margin to the upper limit output voltage Vmax, for example, taking into consideration the existence of unavoidable errors. Unavoidable errors are, for example, those caused by the response time of each load when the power supply controller 20 gives an operation command to the loads connected to the fuel cell 24, the rate of voltage change of the fuel cell 24, etc. .

Moreover, by executing the protection operation mode, not only can overcharging of the secondary battery 22 be avoided, but also catalyst deterioration of the fuel cell 24 can be suppressed. Generally, when the output voltage of a fuel cell exceeds a predetermined value, catalyst deterioration of the fuel cell is accelerated. In this regard, in this embodiment, the power supply controller 20 executes the protection operation mode when the output voltage of the fuel cell 24 exceeds the first threshold Vth1. As a result, the output current of the fuel cell 24 increases and the output voltage of the fuel cell 24 decreases. This suppresses deterioration of the catalyst in the fuel cell 24.

For example, when the power supply controller 20 executes the protection operation mode and the air pump 26 is given an operation command corresponding to the minimum power consumption P1, the air pump 26 adjusts the opening degrees of the air inlet valve and outlet valve. Enlarge. At this time, the air taken in by the air pump 26 is divided as necessary before flowing into the fuel cell 24, so the flow rate of the air flowing into the fuel cell 24 does not change. That is, the reaction rate within the fuel cell 24 does not change. Therefore, the air pump 26 can increase the amount of air flowing into and out of the air pump 26 as a whole, without changing the flow rate of air flowing into the fuel cell 24, thereby increasing power consumption. As a result, the output current of the fuel cell 24 increases and the output voltage of the fuel cell 24 decreases. This prevents overcharging of the secondary battery 22 and suppresses catalyst deterioration of the fuel cell 24.

As another example, when an operation command corresponding to the minimum power consumption P1 is given to the cooling pump 28, the power consumption can be increased by increasing the rotation speed of the pump. Further, for example, when the cooling fan 30 is given an operation command corresponding to the minimum power consumption amount P1, the power consumption can be increased by increasing the rotation speed of the fan. In these cases, the cooling efficiency of the cooling water supplied to the fuel cell 24 by the cooling pump 28 is improved.

When the protection operation mode is executed, which of the air pump 26, the cooling pump 28, and the cooling fan 30 is given an operation command is determined depending on, for example, the power consumption generated by each device. It's fine. For example, since the air pump 26 consumes relatively large power, an operation command may be given to it preferentially.

The power supply controller 20 further cancels the protection operation mode when the output voltage of the fuel cell 24 exceeds the first threshold Vth1 and then falls below the second threshold Vth2. As shown in FIG. 2, the second threshold Vth2 is smaller than the first threshold Vth1. According to such a configuration, the protective operation mode can be stopped when the output voltage of the fuel cell has sufficiently decreased. Thereby, it is possible to suppress excessive switching between execution and cancellation of the protection operation mode. The second threshold value Vth2 is set by giving a certain margin to the first threshold value Vth1, taking into account, for example, the voltage change rate of the fuel cell 24. In a modification, the second threshold Vth2 may be equal to the first threshold Vth1.

The power supply controller 20 executes the protection operation mode not only at the timing after the output voltage of the fuel cell 24 exceeds the first threshold value Vth1 as described above, but also at the timing when the fuel cell 24 starts to be activated. In the protective operation mode executed after the output voltage of the fuel cell 24 exceeds the first threshold value Vth1, the minimum power consumption P1 is set for at least one of the air pump 26, the cooling pump 28, and the cooling fan 30. A corresponding operation command is given, but in the protective operation mode executed when the fuel cell 24 is started, an operation command may be given to the motor 16 in addition to or in place of the above.

When the motor 16 is given an operation command corresponding to the minimum power consumption P1, the rotation speed of the propeller 14 increases as the rotation speed of the motor 16 increases. As described above, the rotation of the propeller 14 generates lift on the flying object 10. However, if the minimum power consumption amount P1 is relatively small, even if the minimum power consumption amount P1 is consumed by the motor 16, the lift force necessary for takeoff of the aircraft 10 will not be generated. Therefore, for example, when executing the protective operation mode when starting up the fuel cell 24, even if the motor 16 (and propeller 14) consumes the minimum amount of power P1, the aircraft 10 does not take off and the motor 16 is operated on land without taking off. (and the propeller 14) will be in a state of rotation. In this way, the aircraft 10 can increase power consumption by the motor 16 without taking off unintentionally. For this reason, the fuel cell 24 can be appropriately protected.

When the power supply controller 20 executes the protection operation mode when starting the fuel cell 24, it is preferable to cancel the protection operation mode after a predetermined period of time has elapsed from the start of the start of the fuel cell 24. In this case, the predetermined time can be determined as appropriate depending on the structure of the fuel cell 24 and the like, taking into consideration the time required for the fuel cell 24 to be properly activated.

In the aircraft 10 of this embodiment, a relay may be provided between the fuel cell 24 and the secondary battery 22. According to the technology disclosed in this specification, even if a relay is present, the frequency at which the relay operates is relatively reduced. Therefore, welding of the contacts of the relay can be suppressed.

Although the embodiments of the present technology have been described above in detail, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims as filed. Further, the techniques illustrated in this specification or the drawings simultaneously achieve a plurality of objectives, and achieving one of the objectives has technical utility in itself.

10: Aircraft 12: Fuel cell system 14: Propeller 16: Motor 18: Fuel cell unit 20: Power controller 22: Secondary battery 24: Fuel cell 26: Air pump 28: Cooling pump 30: Cooling fan 32: Diode 34: Power line

Claims (8)

a fuel cell for powering at least one load;
a secondary battery that is connected in parallel to the fuel cell without a converter and passively charged or discharged according to the output voltage of the fuel cell;
a controller that monitors the output voltage of the fuel cell and executes a protected operating mode when the output voltage of the fuel cell exceeds a first threshold;
In the protected operation mode, an operation command corresponding to a predetermined minimum power consumption is given to some or all of the at least one load.
fuel cell system. The fuel cell according to claim 1, wherein the controller discontinues the protective operation mode when the output voltage of the fuel cell exceeds the first threshold and then falls below a second threshold. battery system. The fuel cell system according to claim 2, wherein the second threshold is smaller than the first threshold. The fuel cell system according to any one of claims 1 to 3, wherein the controller executes the protective operation mode even when starting up the fuel cell. 5. The fuel cell system according to claim 4, wherein the controller cancels the protective operation mode after a predetermined time has elapsed from the start of activation of the fuel cell. The at least one load includes a first load receiving power supply from the fuel cell system and a second load included in the fuel cell system,
The fuel cell system according to any one of claims 1 to 5, wherein in the protective operation mode, the operation command is given to the second load. Claim: The second load includes at least one of an air pump that supplies air to the fuel cell, a cooling pump that supplies cooling water to the fuel cell, and a cooling fan that radiates heat from the cooling water. 7. The fuel cell system according to any one of 1 to 6. A motor that drives a propeller,
The fuel cell system according to any one of claims 1 to 7,
Equipped with
the motor is included in the at least one load to which the fuel cell supplies power;
flying object.

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