POWER SUPPLY SYSTEM OF VERTICAL TAKE-OFF AND LANDING AIRCRAFT

A controller (a control unit) of a power supply system of a vertical take-off and landing aircraft is configured to: after lift is generated by wings (a front wing and a rear wing), perform stop control of controlling electric power supplied to a motor so that rotation of a VTOL rotor continues to stop; temporarily cancel the stop control in response to the temperature of any one switching element detected by a temperature detection unit (a temperature sensor) becoming equal to or higher than a temperature threshold during the stop control; and resume the stop control after the stop control has been temporarily canceled.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-123032 filed on Aug. 2, 2022, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a power supply system of a vertical take-off and landing aircraft including VTOL rotors.

Description of the Related Art

Recently, vertical take-off and landing aircraft, so-called VTOL aircraft, have been developed. Some types of VTOL aircraft include a plurality of VTOL rotors and one or more cruise rotors. The VTOL rotors generate thrust in the vertical direction. The VTOL rotors are mainly used during takeoff and landing of the VTOL aircraft. The cruise rotors generate thrust in the horizontal direction. The cruise rotors are mainly used during cruising of the VTOL aircraft.

Blades of each VTOL rotor experience air resistance while the VTOL aircraft is cruising. That is, the VTOL rotor generates drag while the VTOL aircraft is cruising. While the VTOL aircraft is cruising, it is preferable to reduce drag caused by the VTOL rotors. JP 2015-147574 A discloses a technique for reducing drag by stopping rotation of each VTOL rotor while the VTOL aircraft is cruising. According to this technique, the rotation of the VTOL rotors is stopped by a mechanical stop mechanism. However, the mechanical stop mechanism increases the weight of the VTOL aircraft.

SUMMARY OF THE INVENTION

It is also possible to stop the rotation of the VTOL rotors by power control performed by a controller. Each VTOL rotor is connected to a rotation shaft of a motor. An inverter device is interposed between the motor and a power source. The controller can stop the rotation of each VTOL rotor by controlling electric power supplied to the motor by controlling the switching elements of the inverter device. According to this technique, the weight of the VTOL aircraft does not increase. On the other hand, according to this technique, since electric power is concentrated on a part of the switching elements, those switching elements generate heat. This may cause damage to the switching elements. Alternatively, the life of the switching elements may be shortened.

An object of the present invention is to solve the above-mentioned problems.

According to an aspect of the present invention, there is provided a power supply system of a vertical take-off and landing aircraft, the power supply system comprising: a vertical take-off and landing rotor configured to generate thrust in a vertical direction; a motor configured to rotate the vertical take-off and landing rotor; a power source; an inverter device configured to supply electric power from the power source to the motor using a plurality of switching elements, the electric power being multi-phase alternating current electric power; a controller configured to control the electric power supplied to the motor by controlling the plurality of switching elements; and a temperature detection unit configured to detect a temperature of each of the switching elements, wherein the controller is configured to: after lift is generated by a wing, perform stop control of controlling the electric power supplied to the motor in a manner so that rotation of the vertical take-off and landing rotor continues to stop; temporarily cancel the stop control in response to the temperature of any one of the switching elements detected by the temperature detection unit becoming equal to or higher than a temperature threshold during the stop control; and resume the stop control after the stop control has been temporarily canceled.

According to the present invention, it is possible to avoid various problems caused by heat, such as shortening of the life of the switching element and damage thereof, and as a result, it is possible to realize or maintain the stop control.

DETAILED DESCRIPTION OF THE INVENTION

1. Configuration of Vertical Take-Off and Landing Aircraft10

FIG.1is a top view of a vertical take-off and landing aircraft10. Hereinafter, the vertical take-off and landing aircraft10is also referred to as a VTOL aircraft10. The VTOL aircraft10is, for example, an electric vertical take-off and landing aircraft, a so-called eVTOL aircraft. The VTOL aircraft10includes a fuselage12, a front wing14, a rear wing16, two booms18, eight VTOL rotors20, and two cruise rotors22.

The VTOL aircraft10shown inFIG.1is an example of an aircraft that employs the present invention. The present invention is applicable to any aircraft in which the plurality of VTOL rotors20are stopped in a state in which lift is generated by a fixed wing as the aircraft moves forward.

The front wing14is connected to a front portion of the fuselage12. The rear wing16is connected to a rear portion of the fuselage12. The front wing14and the rear wing16generate lift as the VTOL aircraft10moves forward.

A boom18R of the two booms18is disposed on the right side of the fuselage12. A boom18L of the two booms18is disposed on the left side of the fuselage12. Each boom18extends in the front-rear direction.

Four motors40(FIG.2) are arranged on the boom18L sequentially toward the rear. Similarly, four motors40are arranged on the boom18R sequentially toward the rear. The rotation shaft of each motor40is connected to the VTOL rotor20corresponding to the motor40. One or more gears may be interposed between the rotation shaft of the motor40and the VTOL rotor20. The axis of each VTOL rotor20is substantially parallel to the vertical direction. Alternatively, the axis of each VTOL rotor20may be inclined at a predetermined angle with respect to the vertical direction. The rotation of each VTOL rotor20is controlled so that the VTOL rotor20generates thrust in the vertical direction during vertical takeoff, during transition from takeoff and climb to cruising, during transition from cruising to descent and landing, during vertical landing, and during hovering. Each VTOL rotor20generates thrust in the vertical direction by rotation of the propeller.

Two motors40(FIG.2) are disposed in the fuselage12so as to be arranged side by side in the left-right direction. The rotation shaft of each motor40is connected to the cruise rotor22corresponding to the motor40. A plurality of gears may be interposed between the rotation shaft of the motor40and the cruise rotor22. The axis of each cruise rotor22is substantially parallel to the horizontal direction. The rotation of each cruise rotor22is controlled so that the cruise rotor22generates thrust in the horizontal direction during cruising, during transition from takeoff and climb to cruising, and during transition from cruising to descent and landing. Each cruise rotor22generates thrust in the horizontal direction by rotation of the propeller.

2. Configuration of Power Supply System30

The VTOL aircraft10includes a power supply system30shown inFIG.2.FIG.2is a block diagram of the power supply system30of the vertical take-off and landing aircraft10. The power supply system30includes a power storage device32, a power generation device34, a converter device36, an inverter device38, the motor40, a sensor group42, and a control device44. InFIG.2, solid arrows indicate power supply lines, and broken lines indicate signal lines. Although the power supply system30including the power generation device34is described in the present specification, the power supply system30may not include the power generation device34.

The power storage device32includes, for example, a high-voltage battery. The power generation device34includes a generator. The rotation shaft of the generator is connected to, for example, the rotation shaft of a gas turbine engine. The converter device36includes a converter circuit. One converter device36is provided for one power generation device34. The primary terminal of the converter circuit is connected to the power generation device34. The secondary terminal of the converter circuit is connected to the power storage device32and the inverter device38. The converter device36can convert AC power output from the power generation device34into DC power, and output the DC power to the power storage device32and the inverter device38. In addition, the converter device36can transform the voltage of electric power output from the power generation device34, and output the transformed voltage to the power storage device32and the inverter device38.

The inverter device38includes, for example, a three-phase inverter circuit. The inverter circuit includes a plurality of switching elements. The primary terminal of the inverter circuit is connected to the power storage device32and the converter device36. The secondary terminal of the inverter circuit is connected to the motor40. The inverter device38can convert DC power output from at least one of the power storage device32or the converter device36into AC power, and output the AC power to the motor40.

The motor40is, for example, a three-phase motor. As described above, the rotation shaft of the motor40is connected to a hub of one rotor (the VTOL rotor20or the cruise rotor22) directly or via one or more gears.

The sensor group42includes sensors included in the VTOL aircraft10. For example, the sensor group42includes a plurality of temperature sensors58, one angle sensor60, and a plurality of current sensors62. One temperature sensor58is provided for one switching element of the inverter device38. The temperature sensor58detects the temperature of the switching element (switch temperature). Instead of the temperature sensor58, a control unit64described later may estimate each switch temperature based on a current value or the like. The angle sensor60detects a rotation angle of each VTOL rotor20. Each current sensor62detects one phase current supplied to the motor40. Each sensor outputs a signal indicating the detected information to the control device44.

The control device44controls the power supply system30. The control device44may be, for example, a flight controller of the VTOL aircraft10or a slave controller controlled by the flight controller. The control device44includes a control unit64, a storage unit66, and a driver68.

The control unit64includes processing circuitry. The processing circuitry may be a processor such as a CPU. The processing circuitry may be an integrated circuit such as an ASIC or an FPGA. The processor can execute various processes by executing programs stored in the storage unit66. At least some of the plurality of processes may be executed by an electronic circuit including a discrete device.

The control unit64outputs a control signal to the driver68in order to control each motor40. As a result, the control unit64can supply electric power to each motor40and can stop the supply of electric power to each motor40. The control unit64can stop the rotation of each VTOL rotor20by controlling the inverter device38. The control of the inverter device38performed by the control unit64in order to stop the rotation of each VTOL rotor20is referred to as stop control. Further, the control unit64may fix the rotation angle of each VTOL rotor20at a predetermined angle. Furthermore, the control unit64can change the torque of the motor40by controlling the inverter device38.

The storage unit66includes a volatile memory and a non-volatile memory. Examples of the volatile memory include a RAM and the like. The volatile memory is used as a working memory of the processor. The volatile memory temporarily stores data and the like necessary for processing or computation. Examples of the non-volatile memory include a ROM, a flash memory, and the like. The non-volatile memory is used as a storage memory. The non-volatile memory stores programs, tables, maps, and the like. At least a part of the storage unit66may be included in the processor, the integrated circuit, or the like as described above.

The non-volatile memory stores the relationship between the amount of change in the rotation angle of the VTOL rotor20and the amount of change in the electrical angle of the motor40. The amount of change in the rotation angle of the VTOL rotor20and the amount of change in the electrical angle of the motor40are determined according to the number of magnetic poles of the motor40. When a gear is interposed between the VTOL rotor20and the motor40, the amount of change in the rotation angle of the VTOL rotor20and the amount of change in the electrical angle of the motor40are determined according to the gear ratio.

The driver68includes a gate driver circuit. In response to the control signal output from the control unit64, the driver68outputs an ON/OFF signal to each switching element included in the inverter circuit of the inverter device38. Further, in a case where the converter device36includes switching elements, the driver68outputs an ON/OFF signal to each switching element of the converter device36.

3. State of Blade70in Stop Control

FIG.3is a top view of a stopped VTOL rotor20. As shown inFIG.3, the control unit64stops the VTOL rotor20with one blade70extending generally straight forward. The air resistance experienced by the blade70varies depending on the shape, size, and the like of the blade70. In the present specification, it is assumed that the attitude shown inFIG.3minimizes the total air resistance experienced by the blades70. That is, the attitude shown inFIG.3can minimize drag caused by the VTOL rotor20.

Note thatFIG.3illustrates the VTOL rotor20including three blades70. However, the number of the blades70is not limited. Regardless of the number of the blades70, by stopping the VTOL rotor20with one blade70extending generally straight forward, drag caused by the VTOL rotor20can be minimized. If the angle of the blade70with respect to the front-rear direction is within 0°±a°, the drag can be minimized. The angle a° is determined according to the shape and the like of the blade70. In the present specification, the angle range of 0°±a° is referred to as a “stop angle range”.

The storage unit66stores, as a predetermined angle range, the rotation angle range of the VTOL rotor20in which the angle of the blade70is within the stop angle range. It is preferable that the control unit64fixes the rotation angle of the VTOL rotor20within the predetermined angle range in the cruising state of the VTOL aircraft10.

4. Stop Process Performed by Control Unit64

4-1. First Embodiment

FIG.4is a flowchart of a stop process according to a first embodiment. The control unit64executes the process shown inFIG.4at predetermined time intervals after the VTOL aircraft10transitions from takeoff to cruising. For example, in a state where the VTOL aircraft10is moving forward at or above a predetermined speed, the wings (the front wing14and the rear wing16) generate sufficient lift. Therefore, after operating the cruise rotors22, the control unit64may stop the rotation of each VTOL rotor20in response to the forward speed becoming equal to or higher than the predetermined speed.

In step S1, the control unit64performs stop control. Here, the control unit64controls the inverter device38to stop each VTOL rotor20and supplies electric power to the motor40. The power storage device32or the power generation device34supplies appropriate electric power to the inverter device38. The inverter device38supplies electric power to the motor40through the switching elements that are turned on. As a result, the motor40and the VTOL rotor20can remain in a stopped state. When the process of step S1is ended, the process proceeds to step S2.

In step S2, the control unit64compares the switch temperature detected by each temperature sensor58with a temperature threshold. The temperature threshold is stored in advance in the storage unit66. If any one of the switch temperatures is equal to or higher than the temperature threshold (step S2: YES), the process proceeds to step S3. On the other hand, when all of the switch temperatures are lower than the temperature threshold (step S2: NO), the stop process at this timing is ended. In this case, the control unit64continues the stop control. As a result, the motor40and the VTOL rotor20remain in a stopped state.

When the process proceeds from step S2to step S3, the control unit64temporarily cancels the stop control. For example, the control unit64turns off each switching element of the inverter device38to temporarily stop the power supply to the motor40. The time during which the power supply is stopped can be arbitrarily set. The control unit64may reduce the torque of the motor40instead of stopping the power supply. When the process of step S3is ended, the process proceeds to step S4.

In step S4, the control unit64resumes the stop control. When the power supply is stopped in step S3, the control unit64resumes the power supply to the motor40to stop the VTOL rotor20. When the torque is reduced in step S3, the control unit64increases the torque. When the process of step S4is ended, the stop process is tentatively ended.

As shown inFIG.5A, the torque of the motor40is temporarily reduced by the temporary cancellation of the stop control, and is restored by the resumption of the stop control. As shown inFIG.5B, the electrical angle (the phase of the current of the motor40) is changed by the temporary cancellation and the resumption of the stop control. As shown inFIG.5C, the current value of each of three phase (U-phase, V-phase, and W-phase) currents is changed by the temporary cancellation and the resumption of the stop control. As shown inFIG.5D, the temperature of the switching element having the highest temperature among the switching elements through which the three phase (U-phase, V-phase, and W-phase) currents flow decreases after the temporary cancellation of the stop control.

Note that, inFIG.5A, the torque of the motor40becomes 0 due to the temporary cancellation of the stop control. However, the control unit64may not set the torque of the motor40to 0. For example, the control unit64may control the motor40so that the torque of the motor40is smaller than the external force acting on the propeller of the VTOL rotor20.

In the first embodiment, when the temperature of one of the switching elements of the inverter device38becomes equal to or higher than the temperature threshold, the process of step S3is performed. For example, the control unit64temporarily stops the power supply to the motor40. As a result, the heated switching element is turned off. Then, the temperature of the switching element decreases. Alternatively, the control unit64reduces the torque of the motor40. As a result, the phases of the three phase currents supplied to the motor40change. Then, the energization state of the heated switching element changes, and the temperature of the switching element decreases. Therefore, according to the first embodiment, it is possible to prevent the switching element from being damaged. According to the first embodiment, as a result, the life of the switching element can be extended.

4-2. Second Embodiment

FIG.6is a flowchart of a stop process according to a second embodiment. The second embodiment is an application example of the first embodiment. The processes of steps S11to S13and step S15shown inFIG.6are the same as the processes of steps S1to S4shown inFIG.4. Hereinafter, description of steps S11to S13and step S15will be omitted, and step S14will be described.

In step S13, the power supply to the motor40is stopped. Thus, there is no torque applied to the VTOL rotor20by the motor40. In this state, the VTOL rotor20can be rotated by an external force.

In step S14, the control unit64determines whether or not the rotation angle of the VTOL rotor20detected by the angle sensor60is within the predetermined angle range. As described above, the predetermined angle range is stored in advance in the storage unit66. When the rotation angle of the VTOL rotor20is within the predetermined angle range (step S14: YES), the process proceeds to step S15. In this case, the control unit64resumes the stop control. On the other hand, when the rotation angle of the VTOL rotor20is not within the predetermined angle range (step S14: NO), the control unit64continues the determination of step S14.

In step S14, the control unit64may gradually increase the torque of the motor40at the time when the rotation angle of the VTOL rotor20falls within a range of the stop angle range±b°.

According to the second embodiment, in the same manner as in the first embodiment, it is possible to prevent the switching element from being damaged. According to the second embodiment, as a result, the life of the switching element can be extended. Further, according to the second embodiment, any one of the blades70of the VTOL rotor20can be reliably stopped within the stop angle range.

FIG.7is a flowchart of a stop process according to a third embodiment. The third embodiment is an application example of the second embodiment. In the second embodiment described above, the external force causes the VTOL rotor20to rotate. In the third embodiment, the motor40rotates the VTOL rotor20. The processes of steps S21to S24and step S26shown inFIG.7are the same as the processes of steps S11to S15shown inFIG.6. Hereinafter, description of steps S21to S24and step S26will be omitted, and step S25will be described.

In step S24, when the rotation angle of the VTOL rotor20is not within the predetermined angle range (step S24: NO), the process proceeds to step S25. In step S25, the control unit64supplies electric power to the motor40to rotate the VTOL rotor20. The control unit64switches ON/OFF of each switching element of the inverter device38to supply electric power to the motor40. The motor40rotates in response to the supply of electric power. The VTOL rotor20rotates in response to the rotation of the motor40. The control unit64continuously performs the process of step S25until the rotation angle of the VTOL rotor20falls within the predetermined angle range.

According to the third embodiment, in the same manner as in the first embodiment and the second embodiment, it is possible to prevent the switching element from being damaged. According to the third embodiment, as a result, the life of the switching element can be extended. Further, according to the third embodiment, any one of the blades70of the VTOL rotor20can be reliably stopped within the stop angle range. Further, according to the third embodiment, any one of the blades70of the VTOL rotor20can be rapidly rotationally moved to the stop angle range. As a result, drag can be minimized.

The control unit64may control the rotation direction of the VTOL rotor20in step S25. The motor40is rotatable in two directions, namely, a forward direction and a reverse direction. For example, the control unit64acquires the latest rotation angle of the VTOL rotor20. The control unit64compares the angle difference between the latest rotation angle in the forward direction and the predetermined angle range, with the angle difference between the latest rotation angle in the reverse direction and the predetermined angle range. The control unit64selects the direction in which the angle difference is smaller, and rotates the motor40in this direction. As a result, any one of the blades70of the VTOL rotor20can be more rapidly rotationally moved to the stop angle range. As a result, drag can be minimized.

The third embodiment can be modified. In the above-described embodiment, the control unit64determines the rotation direction of the VTOL rotor20based on the rotation angle. Instead, the control unit64may determine the rotation direction of the VTOL rotor20based on the power consumption of the motor40. For example, based on the current value detected by each current sensor62, the control unit64calculates the power consumption when the VTOL rotor20is rotated in two directions. The control unit64may supply electric power to the motor40so as to rotate the VTOL rotor20in a rotation direction for making the power consumption of the motor40smaller.

5. Invention Obtained from Embodiments

The invention that can be grasped from the above embodiments will be described below.

According to the aspect of the present invention, provided is the power supply system (30) of the vertical take-off and landing aircraft (10), the power supply system including: the VTOL rotor (20) configured to generate thrust in the vertical direction; the motor (40) configured to rotate the VTOL rotor; the power source (32,34); the inverter device (38) configured to supply electric power to the motor from the power source using the plurality of switching elements, the electric power being multi-phase AC electric power; the controller (64) configured to control the electric power supplied to the motor by controlling the plurality of switching elements; and the temperature detection unit (58) configured to detect the temperature of each of the switching elements, wherein the controller is configured to: after lift is generated by the wing (14,16), perform stop control of controlling the electric power supplied to the motor in a manner so that rotation of the VTOL rotor continues to stop; temporarily cancel the stop control in response to the temperature of any one of the switching elements detected by the temperature detection unit becoming equal to or higher than the temperature threshold during the stop control; and resume the stop control after the stop control has been temporarily canceled.

In the above configuration, the stop control is temporarily canceled. By canceling the stop control, the temperature of the heated switching element decreases. Therefore, according to the above configuration, it is possible to prevent the switching element from being damaged. According to the above configuration, as a result, shortening of the life of the switching element due to heat generation can be avoided and the life thereof can be extended.

In the above aspect, the controller may temporarily cancel the stop control by temporarily stopping supply of the electric power to the motor.

According to the above configuration, by turning off the heated switching element, the temperature of the heated switching element decreases. Therefore, according to the above configuration, it is possible to prevent the switching element from being damaged. According to the above configuration, as a result, shortening of the life of the switching element due to heat generation can be avoided and the life thereof can be extended.

In the above aspect, the controller may temporarily cancel the stop control by making the torque of the motor smaller than the torque of the motor generated before the temperature of any one of the switching elements becomes equal to or higher than the temperature threshold.

According to the above configuration, by reducing the torque of the motor, the balance between the external force and the torque is lost. As a result, the motor rotates and the phase of the current supplied to the motor changes. Then, the temperature of the heated switching element decreases. Therefore, according to the above configuration, it is possible to prevent the switching element from being damaged. According to the above configuration, as a result, shortening of the life of the switching element due to heat generation can be avoided and the life thereof can be extended.

In the above aspect, the power supply system may further include the angle detection unit (60) configured to detect the rotation angle of the VTOL rotor, and the controller may resume the stop control in response to the rotation angle detected by the angle detection unit falling within the predetermined angle range after the stop control has been temporarily canceled.

According to the above configuration, it is possible to reliably stop any one of the blades of the VTOL rotor within the stop angle range.

In the above aspect, the power supply system may further include the angle detection unit configured to detect the rotation angle of the VTOL rotor, and after the stop control has been temporarily canceled, the controller may supply the electric power to the motor so as to rotate the VTOL rotor, and the controller may resume the stop control in response to the rotation angle detected by the angle detection unit falling within the predetermined angle range.

According to the above configuration, it is possible to reliably stop any one of the blades of the VTOL rotor within the stop angle range. Further, according to the above configuration, it is possible to rapidly rotationally move any one of the blades of the VTOL rotor to the stop angle range.

In the above aspect, the controller may supply the electric power to the motor so as to rotate the VTOL rotor in a rotation direction in which an angle between the latest rotation angle of the VTOL rotor and the predetermined angle range is smaller among the two rotation directions of the VTOL rotor.

According to the above configuration, it is possible to more rapidly rotationally move any one of the blades of the VTOL rotor to the stop angle range.

In the above aspect, the controller may supply the electric power to the motor so as to rotate the VTOL rotor in a rotation direction for making the power consumption of the motor smaller among the two rotation directions of the VTOL rotor.

Note that the present invention is not limited to the above disclosure, and various modifications are possible without departing from the essence and gist of the present invention.