Motor control device

Abstract

A motor control device (MCU) (2i) comprises switching elements (211) and an electronic control device (22). The switching elements (211) control the state of conduction to windings (2u, 2v, 2w) of a motor (2m). The electronic control device (22) controls the state of conduction by controlling the operation of the switching elements (211), and thus controls the electrical angle of the motor (2m). The electronic control device (22) has a memory (222) (storage unit) and a lock maintenance control unit (221b). The memory (222) has stored therein a permissible range (Wθp) of rotation stop positions of a propeller. When a stoppage of rotation of the propeller is requested during flight, the lock maintenance control unit (221b) executes lock maintenance control for adjusting the electrical angle so as to cause the motor (2m) to exert a holding force for holding the rotation position of the propeller within a range that does not deviate from the permissible range (Wθp).

Description

Motor control device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-115016 filed in Japan on July 18, 2024, the contents of which are incorporated by reference in their entirety.

[0002] The disclosure herein relates to a motor control device applied to an electric aircraft.

[0003] Patent Document 1 describes an electric aircraft that flies by rotating a propeller with an electric motor. The electric aircraft is equipped with a motor control device. The motor control device controls the amount of power supplied to the motor by controlling the operation of a switching element that turns on and off the power supply to the motor windings.

[0004] However, there are cases where the rotation of the propeller is no longer necessary even during flight. In such cases, the motor control device stops the rotation of the propeller and then continues to supply power to the motor so that the propeller remains stopped (rotation lock).

[0005] However, if power supply that locks the rotation continues for a long period of time, the switching element will become hot and be damaged. Therefore, the motor control device described in Patent Document 1 temporarily stops the power supply when the switching element temperature reaches a threshold value during rotation lock, temporarily releasing the propeller rotation lock.

[0006] JP 2024-20679 A

[0007] Temporarily releasing the rotation lock as described above can protect the switching element from high-temperature damage. However, releasing the rotation lock may cause the propeller to rotate unintentionally, causing the motor to generate electricity. As a result, there is a concern that the voltage applied to the electrical components constituting the motor control device may exceed the withstand voltage, resulting in damage to the electrical components. In short, the motor control device described in Patent Document 1 has the problem of being unable to simultaneously protect the switching element from high-temperature damage and maintain the rotation lock state for a long period of time.

[0008] One disclosed object is to provide a motor control device that can achieve both thermal protection of switching elements and maintaining a rotation locked state for a long period of time.

[0009] In order to achieve the above object, a motor control device according to one aspect of the present disclosure is applied to an electric aircraft that flies using the thrust of a propeller rotated by a motor, and controls the operation of the motor, and includes: a switching element that controls the state of current flow to the motor windings; and an electronic control device that controls the state of current flow by controlling the operation of the switching element, and thereby controls the electrical angle of the motor, wherein the electronic control device has: a memory unit that stores an allowable range of the propeller rotation stop position; and a lock maintenance control unit that, when a request to stop the propeller rotation is made during flight, performs lock maintenance control to adjust the electrical angle so that the motor exerts a holding force that maintains the propeller rotation position within the allowable range.

[0010] The motor control device disclosed herein can reduce the thermal load on the switching elements when maintaining the propeller locked. This reduces the number of times the lock must be released due to thermal load, achieving both thermal protection for the switching elements and maintaining the locked state for extended periods of time. At the same time, the propeller position can be kept within the permitted range, preventing the flight resistance of the stopped propeller from exceeding the allowable range.

[0011] The reference numbers in parentheses above merely indicate an example of the correspondence with specific configurations in the embodiments described below, and do not in any way limit the technical scope.

[0012] 4 is a diagram showing a mechanical configuration of an eVTOL according to a first embodiment. FIG. 5 is a diagram showing an electrical configuration of an eVTOL according to a first embodiment. FIG. 6 is a schematic diagram of a propeller showing an allowable range stored in the memory of FIG. 2. FIG. 7 is a map showing the relationship between the electrical angle and a current command value of the motor of FIG. 2. FIG. 8 is a diagram showing the relationship between the map of FIG. 4 and the lock angle, and also showing the relationship between current values ​​of each phase. FIG. 9 is a flowchart showing a procedure for deceleration control executed by an electronic control device according to a first embodiment. FIG. 10 is a flowchart showing a procedure for lock maintenance control executed by an electronic control device according to a second embodiment. FIG. 11 is a flowchart showing a procedure for lock maintenance control executed by an electronic control device according to a third embodiment. FIG. 12 is a flowchart showing a procedure for lock maintenance control executed by an electronic control device according to a fourth embodiment. FIG. 13 is a flowchart showing a procedure for lock maintenance control according to a first modification of the fourth embodiment. FIG. 14 is a flowchart showing a procedure for lock maintenance control according to a second modification of the fourth embodiment. FIG. 15 is a flowchart showing a procedure for lock maintenance control according to a third modification of the fourth embodiment. 13 is an electrical circuit diagram showing a current path when lower arms of all phases are turned on in a sixth embodiment. FIG. 14 is an electrical circuit diagram showing a current path when upper arms of all phases are turned on in a sixth embodiment.

[0013] Hereinafter, several embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to matters described in the preceding embodiment may be assigned the same reference numerals, and duplicate descriptions may be omitted. In each embodiment, when only a part of the configuration is described, other previously described embodiments may be applied to the other parts of the configuration. In addition to combinations of parts that are specifically specified as being combinable in each embodiment, it is also possible to partially combine embodiments even if not specified, as long as there is no particular problem with the combination.

[0014] First Embodiment As shown in FIG. 1 , a motor control device (MCU 2i) according to this embodiment is applied to a motor 2m mounted on an electric aircraft 1. This electric aircraft 1 is also known as an eVTOL, a vertical take-off and landing aircraft capable of vertical take-off and landing. eVTOL stands for electric Vertical Take-Off and Landing aircraft. The eVTOL targeted by this embodiment is a manned aircraft carrying a crew member, but may also be an unmanned aircraft. The eVTOL airframe targeted by this embodiment has fixed wings that enable glider flight (gliding), but may also be an airframe without fixed wings. The eVTOL includes an EPU 2, propellers 3, a battery 4, an FCU 6, and the like.

[0015] A plurality of propellers 3 are provided on the airframe. The propellers 3 generate thrust and lift (propulsive force) for the eVTOL by rotating. Flight modes of the eVTOL include vertical takeoff, vertical landing, cruise, hovering, and the like. For example, during cruise flight, the rotation of the propellers 3 can be stopped to allow glider flight. The plurality of propellers 3 also includes propellers used during vertical flight and hovering, and propellers used during cruise flight. For example, during cruise flight, the cruise propellers may be rotated and the hovering propellers may be stopped. Furthermore, during hovering, the hovering propellers may be rotated and the cruise propellers may be stopped.

[0016] The EPU 2 is a device that propels the eVTOL by driving and rotating the propellers 3, and corresponds to an electric propulsion device. EPU is an abbreviation for Electric Propulsion Unit. An EPU 2 is provided for each of the multiple propellers 3. The EPU 2 includes an MCU 2i, a motor 2m, a gear 2g, a motor shaft 2a, a gear shaft 2b, a bus bar 2c, and the like.

[0017] The MCU 2i is a motor control device that controls the operation of the motor 2m. MCU is an abbreviation for Motor Control Unit. The MCU 2i functions as an inverter device that converts DC power supplied from the battery 4 into AC power. The AC power converted by the MCU 2i is supplied to the motor 2m.

[0018] The motor 2m is a polyphase motor having multiple phase windings 2u, 2v, and 2w. For example, the motor 2m may be a three-phase motor, with the MCU 2i controlling the energization state of each of the phase windings 2u, 2v, and 2w. Alternatively, the motor 2m may be a six-phase motor, with one MCU 2i controlling the energization state of three of the phase windings 2u, 2v, and 2w. In this case, another MCU 2i controls the remaining three phases. In other words, providing two MCUs for one six-phase motor provides redundancy so that the motor can continue to operate even if one MCU fails. The multiple windings 2u, 2v, and 2w are connected to each other. That is, the multiple windings 2u, 2v, and 2w are delta-connected or star-connected.

[0019] The gear 2g transmits the rotational torque of the motor 2m to the propeller 3 while reducing the rotational speed. Specifically, a motor shaft 2a is connected to the rotor of the motor 2m. The gear 2g has multiple gear stages, and a gear shaft 2b is connected to the output gear stage. The gear 2g outputs the rotational torque of the motor shaft 2a from the gear shaft 2b while reducing the rotational speed of the motor shaft 2a. The propeller 3 is connected to the gear shaft 2b.

[0020] The MCU 2i, motor 2m, and gear 2g are housed in a common housing and unitized as the EPU 2. A bus bar 2c is housed within the housing. The bus bar 2c connects the upper and lower arms of the inverter in the MCU 2i to the winding 2u. The battery 4 and MCU 2i are connected by a harness 5. The harness 5 supplies DC power from the battery 4 to the MCU 2i. The bus bar 2c supplies AC power converted by the MCU 2i to the motor 2m.

[0021] 2, the MCU 2i includes an inverter circuit 21, an electronic control unit 22, a gate signal generating unit 23, and a gate driving circuit 24. These components are housed in a single common case.

[0022] The inverter circuit 21 includes a switching element 211, a flywheel diode 212, a smoothing capacitor 213, a current sensor 214, and the like. The switching element 211 is, for example, an insulated gate bipolar transistor (IGBT). However, the switching element 211 is not limited to an IGBT and may be a field effect transistor (MOSFET). A pair of switching elements 211 forms an upper and lower arm circuit for each of the windings 2u, 2v, and 2w of each phase. The upper and lower arm circuits for the three phases form a bridge circuit. A flywheel diode 212 is connected in anti-parallel to each switching element 211. A pair of a flywheel diode 212 and a switching element 211 connected in anti-parallel to each other forms an upper arm circuit or a lower arm circuit. In other words, the bridge circuit is formed by six pairs of arms.

[0023] The smoothing capacitor 213 is connected in parallel to the bridge circuit and the battery 4. The smoothing capacitor 213 smoothes the voltage of the battery 4. The current sensor 214 is connected to the bus bar 2c. For example, the current sensor 214 is a shunt resistor, and outputs the potential difference across the shunt resistor as a current value detection signal. In the example shown in FIG. 2, the current sensor 214 is connected to the U-phase and W-phase bus bars 2c. The U-phase current sensor 214 detects the current flowing in the winding 2u. The W-phase current sensor 214 detects the current flowing in the winding 2w.

[0024] The electronic control device 22 is mainly composed of a computer. This computer has a processor 221, a memory 222, an input / output interface, a bus connecting these, etc. The processor 221 executes a control program PG stored in the memory 222, thereby controlling the driving state of the motor 2m. Specifically, the electronic control device 22 controls the current and electrical angle flowing through the windings 2u, 2v, and 2w by controlling the on / off operation of the switching element 211. This controls the rotational speed and rotational position of the motor shaft 2a, and ultimately the rotational speed and rotational position of the propeller 3.

[0025] The processor 221 is hardware for arithmetic processing coupled to the memory 222. The processor 221 accesses the memory 222 to execute various processes such as motor drive control and lock control (described later). The memory 222 is a storage medium that stores a program PG and the like. For example, the memory 222 is a non-transitory tangible storage medium that non-temporarily stores computer-readable programs and data. The non-transitory tangible storage medium serving as the memory 222 is a non-transitory tangible storage medium, and is realized by a semiconductor memory, a magnetic disk, or the like.

[0026] The electronic control device 22 receives a torque command signal, a lock command signal, a current detection signal, and a rotational position signal, which will be described below.

[0027] The torque command signal is a signal output from the FCU 6. The FCU 6 is an abbreviation for Flight Control Unit, and is a flight control device that controls the flight status of the eVTOL. The FCU 6 mainly controls the MCU 2i to control the drive status of the multiple EPUs 2, and ultimately the drive status of the multiple propellers 3. In other words, the FCU 6 performs flight control for flying the eVTOL. Like the electronic control unit 22, the FCU 6 is mainly composed of a computer. The FCU 6 outputs a required output torque value corresponding to flight control as a torque command signal to each EPU 2 installed in the eVTOL. The lock command signal is a signal that commands lock control, which will be described later, and is output from the FCU 6 to each EPU 2 installed in the eVTOL.

[0028] The current detection signal is a signal output from the current sensor 214 and indicates the value of the current flowing through the windings 2u and 2w. The electronic control device 22 calculates the value of the current flowing through the winding 2v from the values ​​of the current flowing through the windings 2u and 2w. Instead of the above calculation, a current sensor 214 may also be provided for the winding 2v to detect the current value.

[0029] The rotational position signal is a signal output from the rotational position sensor 2d and indicates the rotational position of the motor shaft 2a. The rotational position sensor 2d may be a sensor that detects the rotational position of the gear shaft 2b, or may be a sensor that detects the rotational position of the propeller 3. The electronic control device 22 calculates the rotational speed and rotational position of the propeller 3 based on the rotational position signal.

[0030] The electronic control device 22 controls the operation of the inverter circuit 21 based on the torque command signal, the current detection signal, the rotational position signal, etc. For example, the electronic control device 22 generates a U-phase switching signal Su, a V-phase switching signal Sv, and a W-phase switching signal Sw based on these signals. These switching signals are signals that command the current value for each phase.

[0031] The gate signal generation unit 23 outputs upper arm signals and lower arm signals for each phase based on the respective phase switching signals Su, Sv, and Sw output from the electronic control unit 22. These upper arm signals and lower arm signals have dead times added to them. The gate drive circuit 24 outputs on / off signals to each of the six switching elements 211 based on the arm signals output from the gate signal generation unit 23. In short, the MCU 2i converts the DC power supply of the battery 4 into three-phase AC using the three-phase switching signals Su, Sv, and Sw generated by the electronic control unit 22 to drive the motor 2m.

[0032] In flight control by the FCU 6, torque commands to multiple EPUs 2 are controlled according to flight conditions. For example, in lift flight such as vertical takeoff, the lift propeller 3 is rotated while the motor 2m for the cruise propeller 3 is stopped. Also, in cruise flight such as cruising, the cruise propeller 3 is rotated while the motor 2m for the lift propeller 3 is stopped. In this way, the FCU 6 may stop the motor 2m during eVTOL flight.

[0033] It is desirable to lock the propeller 3 that does not need to rotate in this way to prevent unintended rotation. If the propeller 3 were to rotate unintendedly due to air resistance during flight, the motor 2m could generate electricity. As a result, there is a concern that the voltage applied to the electrical components constituting the MCU 2i would exceed their withstand voltage and cause damage to the electrical components. Therefore, the FCU 6 outputs a lock command signal to the MCU 2i of the corresponding EPU 2 for the propeller 3 that does not need to rotate. When the MCU 2i receives a lock command from the FCU 6, it executes lock control, described below, to apply a braking force to the motor 2m. This braking force acts to maintain the propeller 3's rotational position. The lock control controls the flow of current through the windings 2u, 2v, and 2w to prevent the motor 2m from rotating. This current application generates the braking force.

[0034] When locking the propeller 3, it is ideal to fix (lock) the propeller position at a position where flight resistance is minimized. However, when control errors are taken into consideration, it may be difficult to strictly fix the propeller at a position where flight resistance is minimized. Furthermore, when the thermal load of the switching element 211 of the inverter circuit 21 is taken into consideration, it may be difficult to keep the propeller 3 fixed at the position where flight resistance is minimized for a long period of time.

[0035] Therefore, in the lock control, the electronic control unit 22 sets a predetermined angle range including the position where flight resistance is minimum as the stop position range. The electronic control unit 22 allows the propeller 3 to stop within this stop position range. Alternatively, the electronic control unit 22 allows the propeller 3 to move within the stop position range. The rotational position θp0 of the propeller 3 shown in FIG. 3 is the rotational position where flight resistance is minimum. The angle range from rotational position θp1 to rotational position θp2 corresponds to the allowable range Wθp. In other words, the allowable range Wθp includes the rotational position where flight resistance is minimum. The allowable range Wθp is the rotational position range of the propeller 3 where flight resistance falls within an allowable range. For example, the rotational position θp1 is set to an angle of minus 10 degrees and the rotational position θp2 is set to an angle of plus 10 degrees relative to the rotational position θp0. The allowable range Wθp is set in advance before flight and stored in the memory 222 (storage unit).

[0036] For example, of the six switching elements 211, the U-phase switching elements 211 for the upper arm and the V-phase and W-phase switching elements 211 for the lower arm are repeatedly turned on for a moment (e.g., a few μs). This allows the motor 2m to exert a braking force without rotating the motor shaft 2a. However, if the above repetition is performed for a long period of time, the thermal load on the U-phase upper arm switching element 211 increases. Therefore, in lock control, it is desirable to transition the combination of switching elements 211 to be turned on. For example, it is desirable to distribute the thermal load by transitioning from the combination that turns on the U-phase of the upper arm as described above to a combination that turns on the V-phase of the upper arm or a combination that turns on the W-phase of the upper arm.

[0037] As shown in Figures 4 and 5, in the case of a three-phase AC motor 2m, for example, the current value for one winding can be set to zero when the electrical angle θe is set to any of 0, 60, 120, 180, 240, 300, and 360 degrees. In the following description, the electrical angle θe shown in Figure 4 is referred to as the lock angle. Figure 4 is a map showing the correspondence between the command value for each phase current and the lock angle. As shown in Figure 4, for example, when the lock angle is set to 0 degrees or 180 degrees, the U-phase current value becomes zero.

[0038] The vertical axis of Figure 5 represents the current value of each phase, and the horizontal axis represents the electrical angle θe. When driving the motor 2m to rotate, the current value of each phase is changed as shown in Figure 5. For example, when lock control is performed with the lock angle set to 120 degrees, the U-phase current value is fixed to Ia amperes, the W-phase current value is fixed to -Ia amperes, and the V-phase current value is fixed to zero.

[0039] The rotational position θp0 at which flight resistance is minimum does not necessarily coincide with the lock angle. In other words, if braking force is exerted at the rotational position θp0 to lock the propeller, the thermal load may not be reduced. Therefore, in lock control, the electrical angle θe is set to a lock angle within a range in which the propeller 3 does not deviate from the allowable range Wθp. However, if the lock angle is fixed and maintained for a long period of time, there is a high concern about the thermal load for the switching elements 211 that form the current paths of the phases whose current values ​​are not zero. In consideration of these points, in lock control, it is desirable to appropriately change the lock angle to a different angle so as not to maintain the same lock angle for a long period of time.

[0040] The procedure of the lock control performed by the processor 221 executing the program PG will be described below with reference to Figures 6 and 7. The lock control includes deceleration control and lock maintenance control. The electronic control unit 22, which is provided with the memory 222 that stores the program PG and the processor 221, can be said to have a deceleration control unit 221a that executes deceleration control and a lock maintenance control unit 221b that executes lock maintenance control. In the lock control shown in Figure 6 and the lock maintenance control shown in Figure 7, the processor 221 repeatedly executes the processing of each illustrated step at a predetermined interval.

[0041] The deceleration control shown in Figure 6 is executed when the propeller 3 is rotating at a predetermined rotational speed or higher. In this deceleration control, first in step S10, it is determined whether or not there is a request to lock the propeller. For example, if a lock command is output from the FCU 6 to the MCU 2i for a propeller 3 that does not need to rotate, it is determined that there is a request to lock the propeller. In the following step S11, a target stop position for the propeller 3 is set. For example, the rotational position θp0 at which flight resistance is minimized is set as the target stop position. Alternatively, the rotational position of the propeller 3 corresponding to the lock angle closest to the rotational position θp0 is set as the target stop position.

[0042] In the following step S12, deceleration control related to lock control is executed. In deceleration control, the inverter circuit 21 is controlled so that the motor 2m exerts a braking force (negative torque) on the forward-rotating propeller 3. The deceleration control may be regenerative control, which will be described below, or non-regenerative control. Regenerative control is control that operates the inverter circuit 21 to cause the motor 2m to generate electricity. With regenerative control, the rotational energy of the propeller 3 is converted into electrical energy, thereby decelerating the propeller rotation. Non-regenerative control is control that operates the inverter circuit 21 so that the electrical energy generated by the motor 2m is consumed by the resistance components of the motor 2m and the inverter circuit 21, without returning it to the battery 4. With non-regenerative control, the rotational energy of the propeller 3 is converted into thermal energy, thereby decelerating the propeller rotation.

[0043] Furthermore, in the deceleration control of step S12, feedback control, which will be described below, is executed. In the feedback control, the state of energization to the inverter circuit 21 is feedback-controlled so that the actual propeller rotation position (actual propeller position) stops at the target stop position set in step S11. The actual propeller position is calculated based on the detection signal of the rotation position sensor 2d.

[0044] In the following step S13, it is determined whether the motor speed is equal to or less than a predetermined value. The motor speed is the rotational speed of the motor shaft 2a and is calculated based on the detection signal of the rotational position sensor 2d. If the motor speed is not equal to or less than the predetermined value, the deceleration control in step S12 continues. If it is determined that the motor speed is equal to or less than the predetermined value, it is determined in the following step S14 whether the actual propeller position is within the allowable range Wθp. Note that the allowable range Wθp is the angle range of the propeller 3, and the corresponding range of electrical angle is larger than the angle range of the propeller 3. For example, the allowable range Wθp is a propeller angle range of plus or minus 1 to 2 degrees, and the corresponding range of electrical angle control for lock control is plus or minus 60 degrees. If the actual propeller position is not within the allowable range Wθp, the feedback control related to the deceleration control in step S12 continues. If it is determined that the motor speed is equal to or less than the predetermined value and within the allowable range Wθp, the process transitions from deceleration control to lock maintenance control in the following step S15.

[0045] The lock maintenance control shown in Figure 7 is executed as a subroutine process of step S15 in Figure 6. In the lock maintenance control, the lock angle is periodically switched within a range that does not deviate from the allowable range Wθp. Specifically, first, in step S20, a plurality of stop target positions A, B, and C are set. In the following description, the first stop target position A will be simply referred to as position A, the second stop target position B will be simply referred to as position B, and the third stop target position C will be simply referred to as position C.

[0046] Position A is set to a propeller rotation position corresponding to the lock angles shown below. For example, it is set to the lock angle closest to the forward rotation side from the current electrical angle θe0. In the example shown in FIG. 5, the lock angle closest to the forward rotation side from the electrical angle θe0 is 120 degrees. Alternatively, it is set to a lock angle that makes the current value of the phase with the largest absolute current value at the electrical angle θe0 zero. In the example shown in FIG. 5, the phase with the largest absolute current value at the electrical angle θe0 is the U-phase. The lock angle that makes the current value of the U-phase zero and is closest to the forward rotation side from the electrical angle θe0 is 180 degrees. Position B is set to a propeller rotation position corresponding to a lock angle shifted 60 degrees toward the forward rotation side from position A. Position C is set to a propeller rotation position corresponding to a lock angle shifted 60 degrees toward the reverse rotation side from position A.

[0047] In the next step S21A, it is determined whether the current stop target position is position A. The initial value of the stop target position is set to position A. If it is set to position A, in the next step S22A, the time during which the actual propeller position has continued to be at position A is measured. In the next step S23A, it is determined whether the time measured in step S22A has continued for a predetermined time T1 or more. If it is determined that the time has continued, in the next step S24A, the stop target position is changed from position A to position B.

[0048] If it is determined in the previous step S21A that the target stop position is not set to position A, then in step S21B it is determined whether the current target stop position is position B. If it is set to position B, then in step S22B it is measured how long the actual propeller position has continued to be at position B. Then in step S23B it is determined whether the time measured in step S22B has continued for a predetermined time T1 or more. If it is determined that the time has continued, then in step S24B the target stop position is changed from position B to position C.

[0049] If it is determined in the previous step S21B that the actual propeller position is not set to position B, the current stop target position is considered to be position C. Next, in step S22C, the time that the actual propeller position has continued to be position C is measured. In the following step S23C, it is determined whether the time measured in step S22C has continued for a predetermined time T1 or more. If it is determined that the time has continued, in the following step S24C, the stop target position is changed from position C to position A.

[0050] According to the locking control shown in FIG. 7 , the actual propeller position repeatedly changes from position A to position B to position C to position A again every predetermined time T1. The angle range from the propeller position corresponding to position B to the propeller position corresponding to position C is extremely small compared to the allowable range Wθp. Therefore, although the actual propeller position changes due to the locking control, the actual propeller position does not deviate from the allowable range Wθp. Furthermore, the target stop position is set to an electrical angle different from the electrical angle at which the absolute value of the current value in any of the windings 2u, 2v, and 2w is maximized. Specifically, the electrical angle set to 30, 90, 150, 210, 270, or 330 degrees is prohibited from continuing for more than the predetermined time T1. In the following description, the electrical angle at which these maximum current values ​​occur is referred to as the maximum current electrical angle.

[0051] <Effects of the First Embodiment> The MCU 2i according to this embodiment includes a switching element 211 and an electronic control unit 22. The electronic control unit 22 has a memory 222 as a storage unit and a lock maintenance control unit 221b. The memory 222 stores the allowable range Wθp for the rotation stop position of the propeller 3. When a request to stop the rotation of the propeller 3 is made during flight, the lock maintenance control unit 221b executes lock maintenance control, adjusting the electrical angle so that the motor 2m exerts a holding force that maintains the rotation position of the propeller 3 within the allowable range Wθp. This reduces the thermal load on the switching element 211 when maintaining the propeller 3 locked. This reduces the number of times that the lock must be released due to thermal load, thereby achieving both thermal protection for the switching element 211 and long-term maintenance of the rotation locked state. At the same time, the actual propeller position can be maintained within the allowable range Wθp, preventing the flight resistance of the stopped propeller 3 from increasing beyond tolerance.

[0052] Furthermore, in this embodiment, the rotational position of the propeller 3 is changed within the permissible range Wθp while the lock maintenance control is being executed. Therefore, the lock control that exhibits the above-described effects can be realized with simple control.

[0053] Furthermore, in this embodiment, the propeller 3 is stopped from rotating within the allowable range Wθp, and the rotation stop position is switched at a predetermined cycle. The predetermined cycle corresponds to the predetermined time T1. Therefore, the lock control that exhibits the above-mentioned effects can be realized with simple control.

[0054] Furthermore, in this embodiment, the motor 2m is a three-phase motor, and the electronic control device 22 controls the energization state of the three-phase windings 2u, 2v, and 2w. When switching the rotation stop position of the propeller 3 to switch the phase of the electrical angle θe, the phase difference is switched to a multiple of 60 degrees. Specifically, electrical angles θe of 0, 60, 120, 180, 240, 300, and 360 degrees are set as lock angles, and lock maintenance control switches to one of these lock angles. At each lock angle, the current value in one of the windings of each phase becomes zero. This helps reduce the thermal load on the switching element 211.

[0055] Furthermore, in this embodiment, when changing the rotational position of the propeller 3 within the allowable range Wθp, the change is made by repeatedly rotating forward and backward. Therefore, unlike when the rotation direction is set to one direction, forward or backward, when changing the target stop position within the allowable range Wθp, the chances of the actual propeller position deviating from the allowable range Wθp and flight resistance increasing can be reduced.

[0056] Second Embodiment In the first embodiment, the target stop position is repeatedly changed in the order of position A, position B, position C, and position A. That is, first, when changing from position A to position B, the electrical angle θe changes by 60 degrees. Next, when changing from position B to position C, the electrical angle θe changes by 120 degrees. In this way, the target stop position changes each time it changes.

[0057] In contrast, in this embodiment, the target stop position is repeatedly changed in the order of position A, position B, position A, position C, and position A. That is, when first changing from position A to position B, the phase difference of the electrical angle θe is 60 degrees, and when next changing from position B to position A, the phase difference is also 60 degrees. Thereafter, the phase difference of 60 degrees continues. For example, as shown by arrows (1), (2), (3), and (4) in FIG. 5 , when the electrical angle at position A is 180 degrees, the electrical angle θe changes in the order of (1), (2), (3), and (4).

[0058] In this embodiment, the number of times the robot is set to position A is increased compared to the first embodiment. In consideration of this, the time for stopping the robot at position A (predetermined time T1) is set to half the time for stopping the robot at positions B and C (predetermined time T2).

[0059] In this embodiment, the lock maintaining control shown in Fig. 7 is changed to the lock maintaining control shown in Fig. 8. The same explanation will be used for processes designated by common reference symbols in the figures. If it is determined in step S23A of Fig. 8 that the measurement time has continued for a predetermined time T1 or more, it is determined in the following step S25 whether the previous stop target position was position C. If it is determined that it was position C, the stop target position is changed from position A to position B in the following step S26. If it is determined that it was not position C, the stop target position is changed from position A to position C in the following step S27.

[0060] If it is determined in step S21B that the current stop target position is position B, the following step S22B measures the time that the actual propeller position has continued to be at position B. If it is determined that the current stop target position is not position B, the following step S22C considers the current stop target position to be position C, and measures the time that the actual propeller position has continued to be at position C.

[0061] In the next step S23Bx, it is determined whether the measured time has continued for a predetermined time T2 or more. The predetermined time T2 is set to be longer than the predetermined time T1. For example, the predetermined time T2 is set to be twice as long as the predetermined time T1. If it is determined that the measured time has continued for the predetermined time T2 or more, in the next step S28, the stop target position is changed from position B or position C to position A.

[0062] As described above, according to this embodiment, the target stop position changes while the phase difference is constant, so that the stability of control can be improved when lock maintenance control is executed.

[0063] (Variation 1 of the First and Second Embodiments) In the second embodiment, the lock angle is changed in increments of 60 degrees, but it may also be changed in increments of 30 degrees. In other words, when switching the phase of the electrical angle θe by switching the rotation stop position of the propeller 3, the phase difference may be changed so that it is a multiple of 30 degrees. Specifically, electrical angles θe of 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, and 360 degrees are set as the lock angle, and the lock maintenance control switches to one of these lock angles. According to this variation, the amount of phase change in the lock angle is small, thereby reducing the risk of step-out when switching the phase of the electrical angle θe.

[0064] Here, when the electrical angle θe is set to 30, 90, 150, 210, 270, or 330 degrees, i.e., the maximum current electrical angle, the absolute value of the current value in any of the phase windings 2u, 2v, and 2w is maximized. For example, as illustrated in Fig. 5 , when the electrical angle θe is set to the maximum current electrical angle of 270 degrees, the maximum current Ib flows through the W-phase winding 2w. Therefore, if the electrical angle θe is fixed at 270 degrees, contrary to this embodiment, a holding force can be exerted to hold the rotational position of the propeller 3, but the thermal load on the W-phase switching element 211 increases.

[0065] In contrast, in this embodiment, although the propeller position at the maximum current electrical angle is included in the target stop position, the target stop position is not fixed but is changed to an electrical angle different from the maximum current electrical angle. In other words, fixing the target stop position at the maximum current electrical angle is prohibited. This makes it possible to avoid a large thermal load on a specific switching element 211.

[0066] (Variation 2 of the First and Second Embodiments) In the first and second embodiments described above, the actual propeller position is always within the allowable range Wθp while the lock maintenance control is being executed. In contrast, when the propeller 3 is rotated in accordance with changing the target stop position within the allowable range Wθp, the actual propeller position may temporarily be outside the allowable range Wθp. For example, the lock maintenance control may be limited to propeller rotation in the forward direction only. If the target stop position is at the end of the allowable range Wθp on the forward rotation side, the next time the target stop position is changed, the actual propeller position will temporarily deviate from the allowable range Wθp by rotating the propeller toward the forward rotation side. Such deviation from the allowable range Wθp is permitted as long as the target stop position is within the allowable range Wθp.

[0067] As described above, it is desirable to rotate the propeller faster when the aircraft is outside the allowable range Wθp than when the propeller is rotated within the allowable range Wθp, thereby shortening the time during which flight resistance increases due to deviation from the allowable range Wθp.

[0068] (Third Embodiment) In the first and second embodiments, a plurality of target stop positions are set and periodically switched. In other words, the actual propeller position repeatedly stops and rotates at predetermined time intervals. In contrast, in this embodiment, the actual propeller position is constantly rotated within the allowable range Wθp without being stopped. Note that in this embodiment, forward and reverse rotation is repeated when constantly rotating within the allowable range Wθp. In contrast, in the first and second embodiments, the direction of rotation may be either forward or reverse.

[0069] In the lock maintenance control shown in Figure 9, first, in step S30, a stop target position +a and a stop target position -a are set. These two stop target positions may be either end of the allowable range Wθp or may be within a narrower predetermined range. The stop target position +a is a position advanced by a predetermined angle a from a predetermined position, and the stop target position -a is a position retarded by the predetermined angle a from the predetermined position. The predetermined positions may be the stop target positions set in step S11 of Figure 6 related to the deceleration control, or may be, for example, the rotational position θp0 at which flight resistance is minimum.

[0070] If it is determined in the following step S31 that this is the first execution of lock maintenance control, the following step S32 sets the stop target position to +a. If it is determined in the following step S33 that the current stop target position is +a, the following step S34 determines whether the actual propeller position has reached +a. If it is determined in step S34 that the actual propeller position has reached +a, the following step S35 changes the stop target position to -a.

[0071] On the other hand, if it is determined in step S33 that the current stop target position is not +a, it is determined in the following step S36 whether the actual propeller position has reached -a. If it is determined in the following step S36 that it has reached -a, the stop target position is changed to +a in the following step S37.

[0072] 9, the propeller 3 continues to oscillate, repeatedly rotating forward and backward, without stopping within the range of the target stop position +a and the target stop position −a. The purpose of this lock maintenance control is to distribute the thermal load of the switching element 211. Therefore, the oscillation speed can be slow within a range that meets this purpose.

[0073] As described above, the electronic control device 22 according to this embodiment continues to rotate the propeller 3 within the permissible range Wθp while executing the lock maintenance control, which can promote the distribution of the thermal load of the switching element 211 compared to the case of the lock maintenance control in which the propeller 3 is repeatedly stopped and rotated.

[0074] Fourth Embodiment In the first to third embodiments, the propeller 3 is rotated within the permissible range Wθp during lock maintenance control to distribute the thermal load on the switching element 211. In contrast, in this embodiment, the propeller 3 is fixed at a predetermined position within the permissible range Wθp, provided that the position does not result in the maximum current electrical angle. The processing procedure for the lock maintenance control according to this embodiment will be described below with reference to FIG. 10. As in the first embodiment, the lock maintenance control in FIG. 10 is started when the deceleration control in FIG. 6 is completed and the processing of step S15 is executed.

[0075] As shown in Figure 10, first, in step S40, the current value of each phase is measured. For example, the electronic control unit 22 calculates the current value flowing through the winding 2u and the winding 2w based on the detection value of the current sensor 214. Furthermore, from these calculated current values, the electronic control unit 22 calculates the current value flowing through the winding 2v. If, in the subsequent step S41, it is determined that the absolute value of the current in any of the phases is equal to or greater than a predetermined value, in the subsequent step S42, the motor 2m is operated at an extremely low speed to shift the actual propeller position. At this time, the motor 2m is operated within the allowable range Wθp.

[0076] Thereafter, steps S40, S41, and S42 are repeated to continue operating the motor 2m until the current detection value of the phase with the maximum current absolute value falls below a predetermined value. When operating the motor 2m in step S42, the motor 2m may be shifted stepwise by a preset electrical angle increment, or the motor may be continuously swept to search for a position where a negative determination is made in step S41.

[0077] As described above, according to this embodiment, the electronic control device 22 controls the electrical angle θe so that the current detection value of the phase with the maximum current absolute value is less than a predetermined value. During lock maintenance control, fixing the energized state at the maximum current electrical angle is prohibited. This reduces the thermal load on the switching element 211 when maintaining the propeller 3 locked. This reduces the number of occasions when the lock must be released due to thermal load, achieving both thermal protection for the switching element 211 and maintaining the rotation locked state for a long period of time. At the same time, the actual propeller position can be maintained within the allowable range Wθp, preventing the flight resistance of the stopped propeller 3 from becoming unacceptably large.

[0078] (First Modification of Fourth Embodiment) In the fourth embodiment, the current value is actually measured, and if the maximum current is equal to or less than a predetermined value, control is performed to permit locking to be maintained. However, the electrical angle θe may be controlled so that the current detection value of the phase with the maximum current absolute value is minimized. This can further reduce the thermal load on the switching element 211.

[0079] Specifically, as shown in FIG. 11 , first, in step S40, the current value of each phase is measured. If it is determined in the subsequent step S41x that the current value of one phase is zero, then in the subsequent step S42x, the current energization state is maintained so that the current actual propeller position is fixed. Note that the determination in step S41x is not limited to determining whether the current value is strictly zero, but may instead determine whether it is within a predetermined range including zero. On the other hand, if the determination in step S41x is negative, then in step S42, the motor 2m is operated at an extremely low rotation speed within the allowable range Wθp to shift the actual propeller position.

[0080] Thereafter, by repeating steps S40, S41x, and S42x, the motor 2m continues to operate until the current value of one phase becomes approximately zero. The electrical angle θe at which the current value of one phase becomes zero is the lock angle described above. At the lock angle, the current value of one phase becomes zero, and the remaining two phases correspond to the phases whose absolute current values ​​are maximum. For example, as illustrated in FIG. 5 , when the electrical angle θe is 120 degrees, the current value of the V phase becomes zero, and the U and W phases correspond to the phases whose absolute current values ​​are maximum. These current absolute values ​​are then minimum. In short, the lock angle is the condition under which the detected current value of the phase whose absolute current value is maximum becomes minimum.

[0081] 12 , after measuring the current value of each phase in step S40, the target stop electrical angle is set in the following step S43. Specifically, when the propeller 3 has been decelerated to an extent that it can be stopped at any time and the propeller 3 is within the permissible range Wθp, the target stop electrical angle is set to the nearest lock angle on the forward rotation side from the current rotation position.

[0082] If it is determined in the next step S44 that the propeller 3 has stopped near the target stop electrical angle, then in step S45, the current energization state is maintained so that the propeller 3 is fixed at the current actual propeller position. On the other hand, if the determination in step S44 is negative, then in step S46, it is determined whether the target stop electrical angle has been passed. If it is determined in step S46 that the propeller 3 has passed the target stop electrical angle, then in step S47, it is determined whether the propeller 3 will exceed the permissible range Wθp at the lock angle closest to the forward rotation side from the current electrical angle. If it is determined in step S47 that the propeller 3 will exceed the permissible range Wθp, then in step S48, the motor 2m is rotated in the reverse direction without changing the target stop electrical angle set in step S43. If the determination in step S47 is negative, then in step S49, the target stop electrical angle is changed to the lock angle closest to the forward rotation side from the current electrical angle.

[0083] In short, if the electrical angle of the motor 2m exceeds the target stop electrical angle while the motor 2m is rotating in the forward direction, the lock-up maintaining control unit according to this modification reverses the rotation of the motor 2m to adjust the electrical angle to the target stop electrical angle. This reduces the chances of the propeller 3 exceeding the allowable range Wθp. Note that, if it is determined in step S47 that the propeller 3 will exceed the allowable range Wθp, the following control may be performed instead of the motor reverse control in step S48. That is, the propeller 3 may be rotated in the forward direction to temporarily exceed the allowable range Wθp, and this control may be resumed when the propeller 3 returns to the allowable range Wθp.

[0084] (Variation 3 of Fourth Embodiment) In this variation 3 shown in FIG. 13 , after measuring the current value of each phase in step S40, it is determined in the following step S41 whether the absolute current value of any of the phases is equal to or greater than a predetermined value. If it is determined in step S41 that the current value is equal to or greater than the predetermined value, it is determined in the following step S43 whether the state in which the current value is equal to or greater than the predetermined value has continued for a predetermined time. If it is determined in step S43 that the state has continued, the target stop position is changed in the following step S44. In other words, if there is no condition in which all phase currents are equal to or less than the predetermined value within the allowable range Wθp, the stop position cannot be kept fixed at the same position, so the stop position is changed periodically.

[0085] As described above, according to the third modification, a state in which the current detection value of the phase with the largest current absolute value is equal to or greater than a predetermined value is determined to be a high-load state. If the high-load state continues for a predetermined time or longer, the electrical angle θe is changed. This improves the reliability of reducing the thermal load on the switching element 211.

[0086] Instead of the determination in step S43, if the cumulative current value is equal to or greater than a predetermined value, the target stop position may be changed in step S44.

[0087] Fifth Embodiment In this embodiment shown in FIG. 14 , the configuration of the inverter circuit 21 formed by the switching elements 211 is changed from the configuration shown in FIG. 2 . The inverter circuit 21 shown in FIG. 14 has a pair of three-phase half-bridge circuits 21A and 21B. These three-phase half-bridge circuits 21A and 21B are connected to one end and the other end of the windings 2u, 2v, and 2w, respectively, and are also connected to a common battery 4. In other words, the motor 2m shown in FIG. 2 is a star-connected motor, in which one end of the windings 2u, 2v, and 2w of each phase is connected to one another. In contrast, the motor shown in FIG. 14 is an open-winding motor, in which both ends of the windings 2u, 2v, and 2w of each phase are connected to the three-phase half-bridge circuits 21A and 21B.

[0088] In the star-connected motor shown in Figure 2, the current of each phase cannot be controlled independently, as shown in Figure 5. For example, when the U-phase current value is Ia amperes and the W-phase current value is -Ia amperes, the V-phase current value is set to zero. In contrast, in the open-winding motor shown in Figure 14, the current of each phase can be controlled independently. Therefore, the current of each phase can be adjusted without changing the propeller position.

[0089] For example, as shown in FIG. 5 , if you want to lock the rotation of the propeller 3 at an electrical angle of 330 degrees, the current of one phase (W-phase) will have the maximum amplitude (maximum current Ib). In the case of star connection, there is a constraint that the current values ​​of the remaining two phases must be −Ib / 2. Therefore, for example, if the maximum current Ib of the W-phase is reduced, the current values ​​of the remaining two phases will also be reduced accordingly, reducing the holding force for propeller lock. In contrast, in the case of open winding, if the current values ​​of the two phases other than the maximum current phase are equal and the signs of the current values ​​of these two phases are opposite to those of the maximum current phase, static torque can be generated. Therefore, for example, by reducing the absolute value of the current of the maximum current phase within a range that does not change the sign, it is possible to suppress heat generation in the switching element 211 associated with the maximum current phase while ensuring holding force.

[0090] As shown in Fig. 15 , in the lock maintenance control according to this embodiment, first, in step S50, the current value of each phase is measured, similar to step S40 in Fig. 10 . In the following step S511, it is determined whether the absolute value of the U-phase current is at a maximum based on the current measurement value acquired in step S50. If it is determined in step S511 that the U-phase current is at a maximum, in the following step S521, a U-phase current command value is set so that the absolute value of the U-phase current is equal to or less than a predetermined value without changing the sign of the U-phase current. As a result, when the current values ​​of the remaining two phases (V and W phases) are equal to each other, the resultant vector obtained by combining the current vectors of each phase (U, V, and W phases) becomes smaller without changing direction.

[0091] If the determination in step S511 is negative, the next step S512 determines whether the absolute value of the V-phase current is at its maximum based on the current measurement value. If the determination in step S512 is that the V-phase current is at its maximum, the next step S522 sets a V-phase current command value so that the V-phase current absolute value is equal to or less than a predetermined value without changing the sign of the V-phase current. As a result, if the current values ​​of the remaining two phases (U and W phases) are equal to each other, the resultant vector obtained by combining the current vectors of each phase becomes smaller without changing direction.

[0092] If the determination in step S512 is negative, the next step S513 determines whether the absolute value of the W-phase current is maximum based on the current measurement value. If the determination in step S513 is that the absolute value is maximum, the next step S523 sets a W-phase current command value so that the absolute value of the W-phase current is equal to or less than a predetermined value without changing the sign of the W-phase current. As a result, when the current values ​​of the remaining two phases (U and V phases) are equal to each other, the resultant vector obtained by combining the current vectors of each phase decreases without changing its direction. For example, as shown in FIG. 5 , when the electrical angle is 330 degrees, the absolute value of the W-phase current is maximum. Therefore, by making the absolute value of the W-phase current equal to or less than a predetermined value without changing the sign of the W-phase current, the resultant vector of the equal U-phase current, the V-phase current, and the W-phase current decreases without changing its direction.

[0093] As described above, in this embodiment, the motor 2m to be controlled is an open-winding motor, and the electronic control device 22 independently controls the current flowing through the windings of each phase. Therefore, as described above, the propeller lock retention force can be ensured while suppressing heat generation in the switching element 211 associated with the maximum current phase. This reduces the number of occasions where the lock must be released due to thermal load, achieving both thermal protection for the switching element 211 and maintaining the rotation locked state for a long period of time. At the same time, the actual propeller position can be maintained within the allowable range Wθp, preventing the flight resistance of the stopped propeller 3 from exceeding the allowable range.

[0094] In the lock maintenance control according to each of the above embodiments, a braking force is exerted on the motor 2m by passing a current through the windings 2u, 2v, and 2w. In contrast, in this embodiment, the following braking control is executed without passing a current through the windings 2u, 2v, and 2w, so that the motor 2m exerts a holding force (braking force) that maintains the rotational position of the propeller 3.

[0095] The processing procedure of the lock maintenance control according to this embodiment will be described below with reference to Fig. 16. As in the first embodiment, the lock maintenance control in Fig. 16 is started when the deceleration control in Fig. 6 is completed and the processing of step S15 is executed.

[0096] First, in step S60 of Fig. 16, it is determined whether a predetermined time has elapsed as measured by a counter (described later), or whether this is the first time that a counter measurement has not been performed. If it is determined in step S60 that the predetermined time has elapsed or this is the first time, the next step S61 is performed. In step S61, it is determined whether the upper arms of all phases are on and the lower arms of all phases are off, as shown in Fig. 17. Alternatively, it is determined whether this is the first time that the processes of steps S62 and S63 have not been performed.

[0097] If it is determined in step S61 that the upper arms of all phases are on or that this is the first time, then in step S62, the upper arms of all phases are turned off and the lower arms of all phases are turned on, as shown in Fig. 18. If the determination in step S61 is negative, then in step S63, the upper arms of all phases are turned on and the lower arms of all phases are turned off, as shown in Fig. 17. In this embodiment, all of the switching elements 211 constituting the upper arms correspond to first switching elements, and all of the switching elements 211 constituting the lower arms correspond to second switching elements.

[0098] In the state shown in Figure 17 or 18, both ends of the windings 2u, 2v, and 2w of each phase are short-circuited. In this state, if the propeller 3 attempts to rotate due to an external force such as flight resistance, a braking force is generated in the motor 2m due to electromagnetic induction. The processing shown in Figure 16 is started when the rotational position of the propeller 3 has been stopped within the allowable range Wθp by the deceleration control shown in Figure 6. In other words, with the propeller 3 within the allowable range Wθp, braking control is performed to set the connection state shown in Figure 17 or 18. Therefore, a holding force (braking force) is exerted on the motor 2m to maintain the rotational position of the propeller 3 within the allowable range Wθp.

[0099] In this way, in braking control in which the motor 2m exerts a holding force without supplying power from the battery 4 to the windings 2u, 2v, and 2w, the propeller rotation position is locked at the electrical angle when the upper arms or lower arms of all phases are turned on. Therefore, it can be said that the braking control shown in Figure 16 adjusts the electrical angle depending on the timing at which the control is started.

[0100] Returning to the description of FIG. 16 , in step S64, the time measured by the counter is reset to zero, and measurement of the elapsed time is restarted. Thereafter, in step S60, measurement by the counter continues until the time measured by the counter reaches a predetermined time. In other words, measurement of the elapsed time is started at the timing when the state of FIG. 17 is switched to the state of FIG. 18 . Thereafter, when the predetermined time has elapsed since the state of FIG. 18 was switched to the state of FIG. 17 , a positive determination is made in step S60, and the state of FIG. 18 is switched to the state of FIG. 17 . Similarly, when a predetermined time has elapsed since the state of FIG. 18 was switched to the state of FIG. 17 , a positive determination is made in step S60, and the state of FIG. 17 is switched to the state of FIG. 18 .

[0101] As described above, in this embodiment, the switching element 211 constituting either the upper arm or the lower arm is referred to as the first switching element, and the other is referred to as the second switching element. The lock maintenance control includes braking control that turns on the first switching element and turns off the second switching element. By executing this braking control, a braking force is exerted on the propeller 3 by electromagnetic induction when the propeller 3 attempts to rotate.

[0102] Therefore, the motor 2m can exert a holding force that maintains the rotational position of the propeller 3 without supplying power from the battery 4 to the windings 2u, 2v, and 2w. This reduces the number of times that the lock must be released due to thermal load, achieving both thermal protection for the switching element 211 and maintaining the rotation locked state for a long period of time. At the same time, the actual propeller position can be kept within the allowable range Wθp, preventing the flight resistance of the stopped propeller 3 from exceeding the allowable range.

[0103] When braking force is exerted by braking control, electricity generated by electromagnetic induction flows through the switching element 211 of the arm that is turned on. As a result, the thermal load on the switching element 211 that is turned on is greater than that on the switching element 211 that is turned off. In consideration of this, in this embodiment, the state in which all upper arms are turned on for all phases shown in Figure 17 and the state in which all lower arms are turned on for all phases shown in Figure 18 are alternately switched over every predetermined time. As a result, the thermal load on the switching element 211 can be distributed between the upper arm and the lower arm.

[0104] (First Modification of Sixth Embodiment) In the braking control shown in Fig. 16, the state in which the upper arms of all phases are on as shown in Fig. 17 and the state in which the lower arms of all phases are on as shown in Fig. 18 are alternately switched over at predetermined time intervals. However, this switching may be abolished and the state in Fig. 17 or the state in Fig. 18 may be continued.

[0105] (Variation 2 of Sixth Embodiment) The braking control according to the sixth embodiment is lock maintenance control that exerts a holding force without supplying power to the motor 2m from the battery 4. In contrast, in the lock maintenance control according to the first to fifth embodiments, the holding force is exerted by supplying power to the motor 2m from the battery 4. Such lock maintenance control using power supply will be referred to as energized lock control in the following description. In other words, in energized lock control, an arbitrary element of the plurality of first switching elements is turned on while an arbitrary element of the plurality of second switching elements is turned on.

[0106] The lock maintenance control unit may stop braking control and switch to energized lock control if, during execution of braking control, the propeller rotational position falls outside the permissible range Wθp or if it is determined that the propeller rotational position is likely to fall outside the permissible range Wθp. Since the holding force provided by energized lock control is stronger than the holding force provided by braking control, according to this second modification, it is possible to achieve both the advantage of braking control, which does not require energization, and the advantage of energized lock control, which provides a strong holding force.

[0107] In Modification 3 of the Sixth Embodiment, when the propeller rotational position is within the permissible range Wθp during execution of the lock maintenance control, braking control and power-on locking control are alternately repeated at predetermined time intervals. Alternatively, Modifications 2 and 3 may be combined to alternate braking control and power-on locking control when the propeller rotational position is within the permissible range Wθp, and switch to power-on locking control when the propeller rotational position is outside the permissible range Wθp.

[0108] (Other Embodiments) The disclosure of this specification is not limited to the exemplified embodiments. The disclosure encompasses the exemplified embodiments and modifications thereto by those skilled in the art. For example, the disclosure is not limited to the combinations of parts and elements shown in the embodiments, and can be implemented in various modifications. The disclosure can be implemented in various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure encompasses embodiments in which parts and elements of the embodiments are omitted. The disclosure encompasses the substitution or combination of parts and elements between one embodiment and another embodiment. The disclosed technical scope is not limited to the description of the embodiments. The disclosed technical scope is defined by the claims, and should be interpreted as including all modifications within the meaning and scope of the claims.

[0109] In each of the above embodiments, the allowable range Wθp is stored in advance in the memory 222 before the start of flight. However, the allowable range Wθp may be set and stored in the memory 222 during flight.

[0110] The EPU 2 according to each of the above embodiments includes one motor 2 m and one MCU 2 i, but two or more MCUs 2 i may be provided for one motor 2 m to provide redundancy in motor control. Furthermore, in each of the above embodiments, the electric aircraft 1 equipped with the EPU 2 may be an aircraft without fixed wings or an unmanned aircraft.

[0111] In each of the above embodiments, the electronic control unit 22 is provided by a control system including at least one computer. The control system includes at least one processor that is hardware. If this processor is referred to as a hardware processor, the hardware processor can be provided by the following (i), (ii), or (iii).

[0112] (i) A hardware processor may be a hardware logic circuit. In this case, the computer is provided by a digital circuit including a number of programmed logic units. The logic units may be, for example, gate circuits. The digital circuit may include a memory that stores at least one of a program and data. The computer may be provided by an analog circuit. The computer may be provided by a combination of a digital circuit and an analog circuit.

[0113] (ii) The hardware processor may be at least one processor core that executes a program stored in at least one memory. In this case, a computer is provided by at least one memory and at least one processor core. The processor core is referred to as a CPU, for example. The memory is also referred to as a storage medium. The memory is a non-transitory, tangible storage medium that non-temporarily stores "programs and / or data" that can be read by the processor.

[0114] (iii) The hardware processor may be a combination of (i) above and (ii) above, where (i) and (ii) are located on different chips or on a common chip.

[0115] (Disclosure of Technical Ideas) This specification discloses multiple technical ideas described in the following multiple clauses. Some clauses may be described in a multiple dependent form, with the subsequent clause alternatively referring to the preceding clause. Furthermore, some clauses may be described in a multiple dependent form, with the subsequent clause referring to another multiple dependent clause. These multiple dependent clauses define multiple technical ideas.

[0116] (Technical Idea 1) A motor control device (2i) applied to an electric aircraft (1) that flies using the thrust of a propeller (3) rotated by a motor (2m), and that controls the operation of the motor, comprises: a switching element (211) that controls the state of current supply to windings (2u, 2v, 2w) of the motor; and an electronic control device (22) that controls the state of current supply by controlling the operation of the switching element, and thereby controls the electrical angle of the motor, wherein the electronic control device has: a memory unit (222) that stores an allowable range (Wθp) of a rotation stop position of the propeller; and a lock maintenance control unit (221b) that, when a stop of rotation of the propeller is requested during flight, executes lock maintenance control to adjust the electrical angle so that the motor exerts a holding force that holds the rotation position of the propeller within the allowable range (Wθp).

[0117] (Technical Concept 2) The motor control device according to Technical Concept 1, wherein the lock maintenance control unit changes the rotational position of the propeller within the permissible range while the lock maintenance control is being executed.

[0118] (Technical Concept 3) The motor control device according to Technical Concept 2, wherein the lock maintenance control unit stops the rotation of the propeller within the permitted range and switches the rotation stop position at a predetermined cycle.

[0119] (Technical Idea 4) A motor control device according to Technical Idea 3, wherein the motor is a polyphase motor having windings for a plurality of phases, and the lock maintenance control unit controls the energization state of the windings for three phases, and when switching the rotation stop position of the propeller to switch the phase of the electrical angle, the phase difference is switched to a multiple of 60 degrees.

[0120] (Technical Idea 5) The motor control device according to Technical Idea 3 or 4, wherein when rotating the propeller to switch the rotation stop position through the lock maintenance control, the lock maintenance control unit increases the rotation speed when the propeller rotates outside the permitted range compared to when the propeller rotates within the permitted range.

[0121] (Technical Concept 6) The motor control device according to Technical Concept 2, wherein the lock maintenance control unit continues to rotate the propeller within the permitted range while the lock maintenance control is being executed.

[0122] (Technical Idea 7) The motor control device according to any one of Technical Ideas 2 to 6, wherein the lock maintenance control unit repeatedly changes the rotational position of the propeller between forward and reverse rotations when changing the rotational position of the propeller within the permissible range.

[0123] (Technical Idea 8) A motor control device according to any one of Technical Ideas 1 to 7, further comprising a current sensor (214) that detects a value of a current flowing through the winding, and the electronic control device controls the energization state based on a value detected by the current sensor.

[0124] (Technical Idea 9) The motor control device according to Technical Idea 8, wherein the motor is a polyphase motor having windings for a plurality of phases, and the lock maintenance control unit controls the electrical angle so that the detected value of the phase having the largest current absolute value is less than a predetermined value.

[0125] (Technical Idea 10) The motor control device according to Technical Idea 8 or 9, wherein the motor is a polyphase motor having windings for multiple phases, and the lock maintenance control unit controls the electrical angle so that the detection value of the phase having the maximum current absolute value is minimized.

[0126] (Technical Idea 11) The motor control device according to Technical Idea 8, wherein the motor is a polyphase motor having windings of multiple phases, a state in which the detection value of the phase with the largest current absolute value is equal to or greater than a predetermined value is regarded as a high load state, and the lock maintenance control unit changes the electrical angle when the high load state continues for a predetermined time or longer.

[0127] (Technical Idea 12) The motor control device according to Technical Idea 8, wherein, when the electrical angle exceeds a target stop electrical angle while the motor is rotating in the forward direction, the lock maintenance control unit reverses the rotation of the motor to adjust the electrical angle to the target stop electrical angle.

[0128] (Technical Idea 13) The motor control device according to Technical Idea 1, wherein the motor is a polyphase motor having windings of multiple phases, and is an open winding motor in which the windings of the multiple phases are independent of each other, and the electronic control device independently controls the value of current flowing through the windings of each phase.

[0129] (Technical Idea 14) The motor is a polyphase motor having windings of multiple phases, the switching elements include a first switching element that configures one of an upper arm and a lower arm, and a second switching element that configures the other of the upper arm and the lower arm, the lock maintenance control includes braking control that turns on all of the first switching elements for the windings of the multiple phases while turning off all of the second switching elements for the windings of the multiple phases, and the lock maintenance control unit executes the braking control so that a braking force is exerted on the propeller by electromagnetic induction when the propeller attempts to rotate, a motor control device according to Technical Idea 1.

[0130] (Technical Idea 15) The motor control device according to Technical Idea 14, wherein the lock maintenance control includes an energized lock control that turns on any one of the plurality of first switching elements while turning on any one of the plurality of second switching elements, and the lock maintenance control unit stops the braking control and switches to the energized lock control when, during execution of the braking control, the rotational position of the propeller falls outside the permissible range or determines that it is likely to fall outside the permissible range.

[0131] (Technical Idea 16) The motor control device according to Technical Idea 14 or 15, wherein the lock maintenance control includes an energization lock control that turns on any one of the plurality of first switching elements while turning on any one of the plurality of second switching elements, and wherein the braking control and the energization lock control are alternately repeated while the lock maintenance control is being executed.

Claims

1. A motor control device (2i) applied to an electric aircraft (1) that flies using the thrust of a propeller (3) rotated by a motor (2m), and that controls the operation of the motor, comprising: a switching element (211) that controls the state of current supply to the windings (2u, 2v, 2w) of the motor; and an electronic control device (22) that controls the state of current supply by controlling the operation of the switching element, and thereby controls the electrical angle of the motor, wherein the electronic control device has: a memory unit (222) that stores an allowable range (Wθp) for the rotation stop position of the propeller; and a lock maintenance control unit (221b) that, when a stop of the propeller rotation is requested during flight, executes lock maintenance control to adjust the electrical angle so that the motor exerts a holding force that holds the rotation position of the propeller within the allowable range (Wθp).

2. The motor control device according to claim 1, wherein the lock maintenance control unit changes the rotational position of the propeller within the permissible range while the lock maintenance control is being executed.

3. The motor control device according to claim 2, wherein the lock maintenance control unit stops the rotation of the propeller within the permitted range and switches the rotation stop position at a predetermined interval.

4. A motor control device as described in claim 3, wherein the motor is a polyphase motor having windings for multiple phases, and the lock maintenance control unit controls the state of current flow to the windings for three phases, and when switching the rotation stop position of the propeller to switch the phase of the electrical angle, switches the phase difference to a multiple of 60 degrees.

5. A motor control device as described in claim 3 or 4, wherein when the lock maintenance control unit rotates the propeller through the lock maintenance control to switch the rotation stop position, when the propeller rotates outside the allowable range, the rotation speed is increased compared to when the propeller rotates within the allowable range.

6. The motor control device according to claim 2, wherein the lock maintenance control section continues to rotate the propeller within the permissible range while the lock maintenance control is being executed.

7. A motor control device according to any one of claims 2 to 4, wherein the lock maintenance control unit, when changing the rotational position of the propeller within the permissible range, alternates between forward and reverse rotation.

8. A motor control device according to any one of claims 1 to 4, further comprising a current sensor (214) that detects the value of the current flowing through the winding, and wherein the electronic control device controls the energization state based on the value detected by the current sensor.

9. The motor control device according to claim 8, wherein the motor is a polyphase motor having windings for multiple phases, and the lock maintenance control unit controls the electrical angle so that the detected value of the phase having the largest current absolute value is less than a predetermined value.

10. The motor control device according to claim 8, wherein the motor is a polyphase motor having windings for multiple phases, and the lock maintenance control unit controls the electrical angle so that the detected value of the phase having the maximum current absolute value is minimized.

11. The motor control device according to claim 8, wherein the motor is a polyphase motor having windings for multiple phases, and the high load state is a state in which the detected value of the phase in which the current absolute value is greatest is equal to or greater than a predetermined value, and the lock maintenance control unit changes the electrical angle when the high load state continues for a predetermined time or longer.

12. A motor control device according to claim 8, wherein the lock maintenance control unit reverses the rotation of the motor to adjust the electrical angle to the target stop electrical angle when the electrical angle exceeds the target stop electrical angle while the motor is rotating in the forward direction.

13. The motor control device according to claim 1, wherein the motor is a polyphase motor having windings for multiple phases, and is an open winding motor in which the windings for the multiple phases are independent of each other, and the electronic control device independently controls the value of the current flowing through the windings for each phase.

14. A motor control device as described in claim 1, wherein the motor is a polyphase motor having windings of multiple phases, the switching elements include a first switching element that constitutes one of the upper arm and the lower arm, and a second switching element that constitutes the other of the upper arm and the lower arm, the lock maintenance control includes braking control that turns on all of the first switching elements for the windings of multiple phases while turning off all of the second switching elements for the windings of multiple phases, and the lock maintenance control unit executes the braking control so that a braking force is exerted on the propeller by electromagnetic induction when the propeller attempts to rotate.

15. A motor control device as described in claim 14, wherein the lock maintenance control includes energization lock control for turning on any one of the plurality of first switching elements while turning on any one of the plurality of second switching elements, and the lock maintenance control unit stops the braking control and switches to the energization lock control if, during execution of the braking control, it determines that the rotational position of the propeller has deviated from the permissible range or is likely to deviate from it.

16. A motor control device as described in claim 14 or 15, wherein the lock maintenance control includes energization lock control for turning on any one of the plurality of first switching elements while turning on any one of the plurality of second switching elements, and wherein the braking control and the energization lock control are alternately repeated while the lock maintenance control is being executed.

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