Systems and methods for inverter circuits in electric systems

Abstract

This disclosure generally relates to systems and methods for controlling electrical systems. A method for controlling an inverter circuit (820) is disclosed, comprising: receiving a first signal indicating a vertical flight mode; implementing a first switching sequence to control the inverter circuit (820) during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing a second switching sequence to control the inverter circuit (820) during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.

Description

PATENTAgent Ref. 16497-0029-00304SYSTEMS AND METHODS FOR INVERTER CIRCUITS IN ELECTRIC SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims priority to U.S. Provisional Application No. 63 / 736,451, titled “SYSTEMS AND METHODS FOR INVERTER CIRCUITS IN ELECTRIC SYSTEMS,” filed December 19, 2024, the contents of which are incorporated herein in their entirety for all purposes.TECHNICAL FIELD

[0002] This disclosure relates generally to the field of control of electric engines. More particularly, and without limitation, the present disclosure relates to innovations in tilt-rotor aircraft that use electrical propulsion systems. Certain aspects of the present disclosure generally relate to improvements in the electrical propulsion system of the tilt-rotor aircraft. Other aspects of the present disclosure generally relate to improvements in inverter circuits that may be used in other types of vehicles but provide particular advantages in aerial vehicles.BACKGROUND

[0003] The inventors here have recognized several problems that may be associated with inverter circuits of electric systems, including a tilt-rotor aircraft that uses electrical or hybrid-electric propulsion systems (hereinafter referred to as electric propulsion units or “EPUs”). Throughout its operational lifespan, an electric vehicle may need to stall one or more EPUs. Stalling an EPU may result in maintaining a position of an output end of the EPU (e.g., rotor, wheel), which may be desirable in certain situations. Further, some electric systems that do not include an EPU may need to stall one or more electric engines.

[0004] While some conventional aircraft may simply move and fix a propeller to a position and turn off the associated motor (e.g., feathering the propeller), some aircraft may be more architecturally complex than conventional aircraft, and could benefit from more sophisticated and energy-efficient methods to control a propeller. For example, for electric or hybridelectric aircraft, turning an EPU on and off may consume too much power and / or conventional propeller locking mechanisms may be incompatible (e.g., too heavy), requiring more advanced techniques for feathering a propeller. These techniques may also be used to provide similar benefits to electric or hybrid-electric vehicles, including automobiles.SUMMARY

[0005] The present disclosure relates generally to control of electric systems. More particularly, and without limitation, the present disclosure relates to innovations in electricPATENTAgent Ref. 16497-0029-00304 aircraft and other electric vehicles, including tilt-rotor aircraft that use electrical propulsion systems. For example, certain aspects of the present disclosure relate to controlling an inverter circuit. Further, certain embodiments may control an inverter circuit to maintain a propeller and / or rotor position. For example, during some portions of a flight or during some flight modes, it may be more energy efficient to stow or feather one or more propellers. While some aircraft may utilize mechanical means (e.g., locks, latches, ties) to rigidly position and secure a propeller in an aerodynamic position (e.g., align propeller blade along an axis parallel to the longitudinal axis of the aircraft or fuselage), such mechanical means add weight to the aircraft. This added weight may decrease the efficiency of an aircraft, especially electric or hybrid-electric aircraft. Furthermore, propellers are typically turned off while stowed or feathered. For electric or hybrid-electric aircraft, turning an electric engine powering a propeller off and on during a flight may be costly in terms of energy efficiency and may decrease the safety of the aircraft midflight. Accordingly, it may be desirable to implement a means to stow or feather a propeller in an active manner that reduces or minimizes energy costs while maintaining the ability to quickly return to normal operation (e.g., in response to an emergency). Moreover, each instance of switching (e.g., a switch transitioning from an open state to a closed state or vice versa) causes switching loss (e.g., energy lost as dissipated heat). Therefore, it may be desirable to implement a switching sequence that reduces or minimizes the number of switches to reduce or minimize switching loss.

[0006] Disclosed embodiments may include an inverter circuit control function configured to actively maintain a propeller and / or rotor position. For example, the inverter circuit control function may be configured to actively maintain a propeller and / or rotor position. Further, each time one or more switches of an inverter circuit are opened or closed, some power is lost due to switching losses and / or capacitance losses. The inverter circuit control function may be configured to provide effective switching strategies that reduce or minimize one or more losses associated with switching.

[0007] One aspect of the present disclosure comprises a method for controlling an inverter circuit, comprising: receiving a first signal indicating a vertical flight mode; implementing, by at least one hardware processor, a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing, by the at least one hardware processor, a second switching sequence toPATENTAgent Ref. 16497-0029-00304 control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.

[0008] Another aspect of the present disclosure comprises a system comprising: an inverter circuit; at least one hardware processor; and at least one non-transitory computer-readable medium containing instructions that, when executed by the at least one processor, cause the at least one processor to perform operations comprising: receiving a first signal indicating a vertical flight mode; implementing a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing a second switching sequence to control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.

[0009] Another aspect of the present disclosure comprises a non-transitory computer- readable medium storing instructions that, when executed by at least one hardware processor, cause the at least one hardware processor to perform operations comprising: receiving a first signal indicating a vertical flight mode; implementing a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing a second switching sequence to control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.

[0010] Yet another aspect of the present disclosure comprises an aircraft, comprising: an electric propulsion unit (EPU); an inverter circuit; at least one hardware processor; and at least one non-transitory computer-readable medium containing instructions that, when executed by the at least one hardware processor, cause the at least one hardware processor to perform operations comprising: receiving a first signal indicating a vertical flight mode; implementing a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing a second switching sequence to control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.BRIEF DESCRIPTIONS OF DRAWINGSPATENTAgent Ref. 16497-0029-00304

[0011] Fig. 1 is an illustration of a perspective view of an exemplary VTOL aircraft, consistent with disclosed embodiments.

[0012] Fig. 2 is another illustration of a perspective view of an exemplary VTOL aircraft in an alternative configuration, consistent with disclosed embodiments.

[0013] Fig. 3 is an illustration of a top plan view of an exemplary VTOL aircraft, consistent with disclosed embodiments.

[0014] Fig. 4 is a schematic diagram illustrating exemplary propeller rotation of a VTOL aircraft, consistent with disclosed embodiments.

[0015] Fig. 5 is a schematic diagram illustrating exemplary power connections in a VTOL aircraft, consistent with disclosed embodiments.

[0016] Fig. 6 is a block diagram illustrating an exemplary architecture and design of an electric propulsion unit of a VTOL aircraft, consistent with disclosed embodiments.

[0017] Fig. 7 is a schematic diagram illustrating an exemplary tilt electric propulsion system of a VTOL aircraft, consistent with disclosed embodiments.

[0018] Fig. 8 is a diagram illustrating a portion of an electrical propulsion system for a vertical take-off and landing (VTOL) aircraft, consistent with disclosed embodiments.

[0019] Fig. 9A is a diagram illustrating pulse width modulation (PWM) vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0020] Fig. 9B is a diagram illustrating an example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 9A, consistent with disclosed embodiments.

[0021] Fig. 10A is a diagram illustrating PWM vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0022] Fig. 10B is a diagram illustrating example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 10A, consistent with disclosed embodiments.

[0023] Fig. 11A is a diagram illustrating PWM vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0024] Fig. 1 IB is a diagram illustrating example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 11 A, consistent with disclosed embodiments.PATENTAgent Ref. 16497-0029-00304

[0025] Fig. 12A is a diagram illustrating PWM vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0026] Fig. 12B is a diagram illustrating example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 12A, consistent with disclosed embodiments.

[0027] Fig. 13A is a diagram illustrating PWM vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0028] Fig. 13B is a diagram illustrating example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 13A, consistent with disclosed embodiments.

[0029] Fig. 14A is a diagram illustrating PWM vectors for controlling an inverter circuit based on an example switching sequence, consistent with disclosed embodiments.

[0030] Fig. 14B is a diagram illustrating example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 14A, consistent with disclosed embodiments.

[0031] Fig. 15 illustrates a flow diagram of an exemplary inverter circuit control method, consistent with disclosed embodiments.DETAILED DESCRIPTION

[0032] The following disclosure provides different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0033] The terms used in this specification generally have their ordinary meanings in the art and in the specific context where each term is used. The use of examples in this specification, including examples of any terms discussed herein, is illustrative only, and in no way limits the scope and meaning of the disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given in this specification.

[0034] Although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a secondPATENTAgent Ref. 16497-0029-00304 element, and, similarly, a second element could be termed a first element, without departing from the scope of the embodiments. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0035] Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0036] As used herein, the term “coupled” may also be termed as “electrically coupled,” and the term “connected” may be termed as “electrically connected.” “Coupled” and “connected” may also be used to indicate that two or more elements cooperate or interact with each other.

[0037] The present disclosure addresses systems, components, and techniques primarily for use in an aircraft. The aircraft may be an aircraft with a pilot, an aircraft without a pilot (e.g., an unmanned aerial vehicle (UAV)), a drone, a helicopter, and / or an airplane. An aircraft includes a physical body and one or more components (e.g., a wing, a tail, a propeller) configured to allow the aircraft to fly. The aircraft may include any configuration that includes at least one propeller. In some embodiments, the aircraft is driven (e.g., provided with thrust) by one or more electric propulsion systems (hereinafter referred to as electric propulsion units or “EPUs”), which may include at least one engine, at least one partial motor, at least one rotor, at least one propeller, a nacelle, a housing, at least one ducted fan, at least one blade, or any combination thereof. The aircraft may be fully electric, hybrid, or gas powered. For example, in some embodiments, the aircraft is a tilt-rotor aircraft configured for frequent (e.g., over 50 flights per work day), short-duration flights (e.g., less than 100 miles per flight) over, into, and out of densely populated regions. The aircraft may be configured to carry 4-6 passengers or commuters, and as with all aircraft, safety is paramount. Accordingly, it is desirable to provide advanced inverter circuit control methods and schemes to improve aircraft efficiency.

[0038] Disclosed embodiments provide new and improved configurations of aircraft components that are not observed in conventional aircraft, and / or identified design criteria for components that differ from those of conventional aircraft. Such alternate configurations and design criteria, in combination addressing drawbacks and challenges with conventionalPATENTAgent Ref. 16497-0029-00304 components, yielded the embodiments disclosed herein for various configurations and designs of eVTOL aircraft components.

[0039] Disclosed embodiments provide new and improved configurations of aircraft components, some of which are not observed in conventional aircraft, and / or identified design criteria for components that differ from those of conventional aircraft. Such alternate configurations and design criteria, in combination addressing drawbacks and challenges with conventional components, yielded the embodiments disclosed herein for various configurations and designs of components for an aircraft (e.g., electric aircraft or hybridelectric aircraft) driven by a propulsion system.

[0040] In some embodiments, the aircraft driven by a propulsion system of the present disclosure may be designed to be capable of both vertical and conventional takeoff and landing, with a distributed propulsion system enabling vertical flight, horizontal and lateral flight, and transition (e.g., transitioning between vertical flight and horizontal flight). The aircraft may generate thrust by supplying high voltage electrical power to a plurality of engines of the distributed propulsion system, which may include components to convert the high voltage electrical power into mechanical shaft power to rotate a propeller.

[0041] Embodiments may include an electric engine (e.g., motor) connected to an onboard electrical power source, which may include a device capable of storing energy such as a battery or capacitor, and may optionally include one or more systems for harnessing or generating electricity such as a fuel powered generator or solar panel array. In some embodiments, the aircraft may comprise a hybrid aircraft configured to use at least one of an electric-based energy source or a fuel-based energy source to power the distributed propulsion system. In some embodiments, the aircraft may be powered by one or more batteries, internal combustion engines (ICE), generators, turbine engines, or ducted fans.

[0042] The engines may be mounted directly to the wing, or mounted to one or more booms attached to the wing. The amount of thrust each engine generates may be governed by a torque command from a Flight Control System (FCS) over a digital communication interface to each engine. Embodiments may include forward engines (and associated propellers) that are capable of altering their orientation, or tilt.

[0043] The engines may rotate the propellers in a clockwise (CW) or counterclockwise (CCW) direction. In some embodiments, the difference in propeller rotation direction may be achieved using the direction of engine rotation. In other embodiments, the engines may allPATENTAgent Ref. 16497-0029-00304 rotate in the same direction, and gearing may be used to achieve different propeller rotation directions.

[0044] In some embodiments, an aircraft may possess quantities of engines in various combinations of forward and aft engine configurations. A forward engine may be considered an engine that is positioned predominantly towards the leading edge of a wing. An aft engine may be considered an engine that is positioned predominantly towards the trailing edge of a wing. For example, an aircraft may possess six forward and six aft engines, five forward and five aft engines, four forward and four aft engines, three forward and three aft engines, two forward and two aft engines, or any other combination of forward and aft engines, including embodiments where the number of forward engines and aft engines are not equivalent.

[0045] In some embodiments, for a vertical takeoff and landing (VTOL) mission, the forward and aft engines may provide vertical thrust during takeoff and landing. During flight phases where the aircraft is moving forward, the forward engines may provide horizontal thrust, while the propellers of the aft engines may be stowed at a fixed position in order to reduce or minimize drag. The aft engines may be actively stowed with position monitoring.

[0046] Transition from vertical flight to horizontal flight and vice-versa may be accomplished via the tilt propeller subsystem. The tilt propeller subsystem may redirect thrust between a primarily vertical direction during vertical flight phase (e.g., hover-phase) to a horizontal or near-horizontal direction during a forward-flight cruising phase, based on a tilt of one or more propellers (e.g., determining directionality of one or more propellers). A variable pitch mechanism may change the forward engine’s propeller-hub assembly blade collective angles for operation during phases of flight, such as a hover-phase, transition phase, and cruise-phase. Vertical lift may be thrust in a primarily vertical direction (e.g., during a hover-phase). Horizontal thrust may be thrust in a primarily horizontal direction (e.g., during a cruise-phase).

[0047] In some embodiments, a “phase of flight,” or “flight mode,” (e.g., hover, cruise, forward flight, takeoff, landing, transition) may be defined by a combination flight conditions (e.g., a combination of flight conditions within particular ranges), which may include one or more of an airspeed, altitude, pitch angle (e.g., of the aircraft), tilt angle (e.g., of one or more propellers), roll angle, rotation speed (e.g., of a propeller), torque value, pilot command, or any other value indicating a current or requested (e.g., commanded) state of at least part of the aircraft.PATENTAgent Ref. 16497-0029-00304

[0048] In some embodiments, the distributed electrical propulsion system may include twelve electrical engines, which may be mounted on booms forward and aft of the main wings of the aircraft. The forward electrical engines may be tiltable mid-flight between a horizontally oriented position (e.g., to generate forward thrust) and a vertically oriented position (e.g., to generate vertical lift). The forward electrical engines may be of a CW type or CCW type in terms of direction of propeller rotation. The aft electrical engines may be fixed in a vertically oriented position (e.g., to generate vertical lift). They may also be of a CW type or CCW type in terms of direction of propeller rotation. In some embodiments, an aircraft may possess various combinations of forward and aft electrical engines. For example, an aircraft may possess six forward and six aft electrical engines, four forward and four aft electrical engines, or any other combination of forward and aft engines, including embodiments where the number of forward electrical engines and aft electrical engines are not equivalent. In some embodiments, an aircraft may possess four forward and four aft propellers, where at least four of these propellers comprise tiltable propellers.

[0049] In some embodiments, for a vertical takeoff and landing (VTOL) mission, the forward electrical engines as well as aft electrical engines may provide vertical thrust during takeoff and landing. During flight phases where the aircraft is in forward flight-mode, the forward electrical engines may provide horizontal thrust, while the propellers of the aft electrical engines may be stowed at a fixed position in order to reduce or minimize drag. The aft electrical engines may be actively stowed with position monitoring. Transition from vertical flight to horizontal flight and vice-versa may be accomplished via the tilt propeller subsystem. The tilt propeller subsystem may redirect thrust between a primarily vertical direction during vertical flight mode to a mostly horizontal direction during forward-flight mode. A variable pitch mechanism may be configured to change the forward electrical engine’s propeller-hub assembly blade collective angles for operation during the hover-phase, transition phase, and cruise-phase.

[0050] In some embodiments, in a conventional takeoff and landing (CTOL) mission, the forward electrical engines may provide horizontal thrust for wing-borne take-off, cruise, and landing. In some embodiments, the aft electrical engines may not be used for generating thrust during a CTOL mission and the aft propellers may be stowed in place.

[0051] As detailed herein, embodiments of the aircraft may include multiple EPUs, each of which have one or more propellers. The propellers are critical to controlling the aircraft. ItPATENTAgent Ref. 16497-0029-00304 may be desirable to idle some EPUs (e.g., lifter EPUs) during some phases of flight (e.g., cruise, forward flight) to improve energy and aerodynamic efficiency.

[0052] As further detailed below with reference to Figs. 9A-14B, there may be many different inverter circuit switching strategies that may be employed to idle or feather one or more propellers of an EPU. By actively feathering one or more propellers of an EPU by utilizing the switching techniques disclosed herein, the overall efficiency of the aircraft during flight may be increased.

[0053] In some embodiments, an electric engine may be housed or connected to a boom of an aircraft and include a motor, inverter, and gearbox. In some embodiments, the motor, inverter, and gearbox may be interfaced such that they share a central axis. In some embodiments, the torque originating in the motor may be sent away from the propellers of the propulsion system and to a gearbox. In some embodiments, a gearbox may provide a gear reduction and then send the torque, via a main shaft, back through a bearing located inside the motor and to the propeller. In some embodiments, an inverter may be mounted on the rear of a gearbox such that a main shaft does not travel through the inverter when outputting torque to the propeller. In some embodiments, the motor, gearbox, and inverter may be interfaced such that a coolant, such as oil, may be used to service the motor, inverter, and / or gearbox, while sharing a common heat exchanger. In some embodiments, the amount of oil used to lubricate and cool the electric engine may vary, including amounts less than one quart, two quarts, three quarts, or any other measured amount of oil.

[0054] In some embodiments, a tilt propeller system may include a linear or rotary actuator to change the orientation of a propulsion system during operation. In some embodiments, the pitch of the propulsion system may be changed as a function of the orientation of the propulsion system. In some embodiments, a rotary actuator may include a motor, inverter, and gearbox. In some embodiments, a gearbox may include various types of gears interfacing to provide a gear reduction capable of orienting the propulsion system. In some embodiments, a tilt propeller system may include a redundant configuration such that multiple motors, inverters, and gearboxes are present and interface using a gear. In some embodiments, a configuration utilizing multiple motors, gearboxes, and inverters may allow a failed portion of the redundant configuration to be driven by the motor, inverter, and gearbox of another portion of the configuration. In some embodiments, a gearbox configuration may also allow the tilt propeller system to maintain a propulsion system orientation with the help of, or without, additional power being provided by the system.PATENTAgent Ref. 16497-0029-00304

[0055] In some embodiments, an electrical propulsion system as described herein may generate thrust by supplying High Voltage (HV) electric power to an electric engine, which in turn converts HV power into mechanical shaft power which is used to rotate a propeller. As mentioned above, an aircraft as described herein may possess multiple electric engines which are boom-mounted forward and aft of the wing. The amount of thrust each electric engine generates may be governed by a torque command from the FCS over a digital communication interface to each electric engine. Embodiments may include forward electric engines, and may be able to alter their orientation, or tilt. Additional embodiments include forward engines that may be a CW type or CCW type. The forward electric engine propulsion subsystem may consist of a multi-blade adjustable pitch propeller, as well as a variable pitch subsystem.

[0056] In some embodiments, an aircraft may include aft engines, or lifters, that can be of a CW type or CCW type. Additional embodiments may include aft electric engines that utilize a multi-blade fixed pitch propeller.

[0057] As described herein, the orientation and use of EPUs may change throughout the operation of the aircraft. In some embodiments, during vertical takeoff and landing, the forward propulsion systems as well as aft propulsion systems may provide vertical thrust during takeoff and landing. During the flight phases where the aircraft is in forward flightmode, the forward propulsion systems may provide horizontal thrust, while the aft propulsion system propellers may be stowed at a fixed position (or near-fixed position) in order to reduce or minimize drag. The aft EPUs may be actively stowed with position monitoring. Some embodiments may include a transition from vertical flight to horizontal flight and vice- versa. In some embodiments, the transitions may be accomplished via a tilt propeller system (TPS) (e.g., for tilting one or more EPUs of the aircraft). The TPS redirects thrust between a primarily vertical direction during vertical flight mode to a mostly horizontal direction during forward-flight mode. Additional embodiments may include a variable pitch mechanism that may change the forward propulsion system propeller-hub assembly blade collective angles for operation during the hover-phase, cruise-phase and transition phase. Some embodiments may include a Conventional Takeoff and Landing (CTOL) configurations such that the tilters provide horizontal thrust for wing-borne take-off, cruise, and landing. The aft electronic engines are not used for generating thrust during a CTOL mission and the aft propellers are stowed in place.PATENTAgent Ref. 16497-0029-00304

[0058] As disclosed herein, an electrical engine may include an inverter and motor; or inverter, gearbox, and motor across various configurations, such as representative configurations as described herein. For example, an electrical engine may include an electrical motor, gearbox, and inverter that all share the same central axis. Additionally, the central axis may be configured along an axis of an output shaft going to the propeller of the aircraft. In such an exemplary configuration, the motor, gearbox, and inverter would all share the output shaft as a central axis and would be circularly oriented around the output shaft. Additional embodiments may include a motor, gearbox, and inverter that are mounted together in a sequence, or a configuration where some of the components are mounted together, such as the motor and gearbox, and another component is located elsewhere, such as the inverter, but wiring systems are used to connect the electrical engine.

[0059] As mentioned above, an electrical engine for an aircraft as described here may include some or all of a motor, inverter, and gearbox. Various configurations may include an inverter and motor such that the output shaft of a motor directly provides the speed and torque for a propeller shaft. Additional embodiments of an electrical engine may include a motor, inverter, and a gearbox, where the output of a motor may travel through a gearbox that is connected to the output shaft for the propeller; a motor, inverter, and gearbox where the output from the motor travels away from the propeller, through a gearbox, where the output shaft for the propeller travels back through the gearbox and motor to the propeller. As described herein, an electrical engine may account for any combination or orientation of some or all of a motor, inverter, and gearbox. Additionally, each configuration or orientation of the electrical engine as disclosed herein may include cooling via air-cooling, coolant liquid, or a mixture of both.

[0060] For example, a configuration of an electrical engine may include a motor and inverter where the motor is in between the propeller of the aircraft and the inverter. Additionally, a motor may include a gearbox. Further, an inverter may share the same central axis as a motor where the inverter may be located in an enclosure that is cantilevered off of the rear of the motor and may be air cooled. It is recognized that such an inverter orientation may not be an optimum configuration in terms of the enclosure required to achieve such a cantilevered orientation. Additionally, a motor in this configuration utilizing air cooling may comprise potting material and air fins to assist with cooling of the motor may lead to an even larger increase in mass of the system.PATENTAgent Ref. 16497-0029-00304

[0061] Some embodiments may include an EPU and / or inverter modules, which may be mounted on the outside of a motor enclosure and / or configured to supply power to an EPU, consistent with disclosed embodiments. An inverter module may include an inverter, associated circuitry for managing current flow to and through the inverter, including from a high voltage bus, and / or housing to hold the same. Additional embodiments may include an EPU where an inverter may be mounted on top of an electrical motor such that the air-cooling fins of the inverter are underneath the propeller. Further embodiments may include an inverter mounted to the back of a motor with air-cooling fins facing out radially, an inverter mounted to the front of a motor with the air-cooling fins facing out radially, an inverter mounted to a motor where the inverter is cooled by a liquid, such as oil, or any other position of the inverter relative to a motor.

[0062] Embodiments of an electrical motor may comprise a stator enclosure, a wound stator assembly, a rotor, various bearings, and / or any additional components to assist in transferring the speed and torque generated by the motor to a propeller.

[0063] In some embodiments, an aircraft of any of the disclosed embodiments may be simulated. For example, the aircraft may be simulated in a simulation environment, such as in a simulator (e.g., a simulator for flight training), a testing simulation environment, or a virtual environment in a video game. Additionally or alternatively, in some embodiments, at least one device of an aircraft may be simulated. For example, the at least one device (e.g., EPU, display wing, effector, and / or actuator, etc.) may be simulated in a simulation environment, such as in a simulator (e.g., a simulator for flight training), a simulated testing environment, or a virtual environment in a video game. A representation of the simulated display may be displayed on at least one display device (e.g., monitor, tablet, smartphone, computer screen, or any other display device) operatively connected to at least one processor configured to execute software code stored in a storage medium for performing flight controls operations. To the extent that any of the disclosed embodiments describe functionality with respect to a real aircraft using sensors, actuators, aircraft structures or other aircraft components, this disclosure contemplates equivalent simulated and virtual aircraft embodiments in which similar or identical functionality may be enabled by using equivalent sensors, actuators, or other hardware components in the simulated / virtual embodiment, by modeling the described functionality using one or more software modules, or by a combination of such hardware and software. Persons having ordinary skill in the art would be able to make and use suchPATENTAgent Ref. 16497-0029-00304 functionalities in equivalent simulated / virtual embodiments using known hardware sensors and / or actuators and known software modeling techniques.

[0064] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the subject matter recited in the appended claims.

[0065] Fig. 1 is an illustration of a perspective view of an exemplary VTOL aircraft, consistent with disclosed embodiments. Fig- 2 is another illustration of a perspective view of an exemplary VTOL aircraft in an alternative configuration, consistent with embodiments of the present disclosure. Figs. 1 and 2 illustrate VTOL aircraft 100, 200 in a cruise configuration and a vertical take-off, landing and hover configuration (also referred to herein as a “lift” configuration), respectively, consistent with embodiments of the present disclosure. Elements corresponding to Figs. 1 and 2 may possess like numerals and refer to similar elements of aircraft 100, 200. Aircraft 100, 200 may include fuselage 102, 202, wings 104, 204 mounted to the fuselage 102, 202 and one or more rear stabilizers 106, 206 mounted to the rear of the fuselage 102, 202. A plurality of lift propellers 112, 212 may be mounted to wings 104, 204 and may be configured to provide lift for vertical take-off, landing, and hover. A plurality of tilt propellers 114, 214 may be mounted to wings 104, 204 and may be tiltable (e.g., configured to tilt or alter orientation) between the lift configuration in which they provide a portion of the lift required for vertical take-off, landing and hovering, as shown in Fig. 2, and the cruise configuration in which they provide forward thrust to aircraft 100 for horizontal flight, as shown in Fig. 1. As used herein, a tilt propeller lift configuration refers to any tilt propeller orientation in which the tilt propeller thrust is providing primarily lift to the aircraft and tilt propeller cruise configuration refers to any tilt propeller orientation in which the tilt propeller thrust is providing primarily forward thrust to the aircraft.

[0066] While the term “tilt propeller” is used herein, it is appreciated that this term does not necessarily apply to just propellers themselves, but may also include other components of an electric propulsion unit (EPU) of which the propellers are a part, and accordingly may refer to an EPU that can tilt about an axis (e.g., using an actuator). While the term “lift propeller” is used herein, it is appreciated that this term does not necessarily apply to just propellersPATENTAgent Ref. 16497-0029-00304 themselves, but may also include other components of an EPU of which the propellers are a part, and accordingly may refer to an EPU that cannot tilt.

[0067] In some embodiments, lift propellers 112, 212 may be configured for providing lift only, with all horizontal propulsion being provided by the tilt propellers. For example, lift propellers 112, 212 may be configured with fixed positions and may only generate thrust during take-off, landing, and hover phases of flight. Meanwhile, tilt propellers 114, 214 may be tilted upward into a lift configuration in which thrust from propellers 114, 214 is directed downward to provide additional lift.

[0068] For forward flight, tilt propellers 114, 214 may tilt from their lift configurations to their cruise configurations. In other words, the orientation of tilt propellers 114, 214 may be varied from an orientation in which the tilt propeller thrust is directed downward (to provide lift during vertical take-off, landing and hover) to an orientation in which the tilt propeller thrust is directed rearward (to provide forward thrust to aircraft 100, 200). The tilt propellers assembly for a particular electric engine may tilt about an axis of rotation defined by a mounting point connecting the boom and the electric engine. When the aircraft 100, 200 is in full forward flight, lift may be provided entirely by wings 104, 204. Meanwhile, in the cruise configuration, lift propellers 112, 212 may be shut off. The blades 120, 220 of lift propellers 112, 212 may be held in low-drag positions for aircraft cruising. In some embodiments, lift propellers 112, 212 may each have two blades 120, 220 that may be locked, for example while the aircraft is cruising, in minimum drag positions in which one blade is directly in front of the other blade as illustrated in Fig. 1. In some embodiments, lift propellers 112, 212 have more than two blades. In some embodiments, tilt propellers 114, 214 may include more blades 116, 216 than lift propellers 112, 212. For example, as illustrated in Figs. 1 and 2, lift propellers 112, 212 may each include, e.g., two blades, whereas tilt propellers 114, 214 may each include more blades, such as the five blades shown. In some embodiments, each of the tilt propellers 114, 214 may have 2 to 5 blades, and possibly more depending on the design considerations and requirements of the aircraft.

[0069] In some embodiments, the aircraft may include a single wing on each side of fuselage 102, 202 (e.g., wings 104 in Fig. 1, wings 204 in Fig. 2). In other embodiments, the aircraft may include a single wing that extends across the entire aircraft. At least a portion of lift propellers 112, 212 may be located rearward of wings 104, 204 (e.g., rotation point of propeller is behind a wing from a bird’s eye view) and at least a portion of tilt propellers 114, 214 may be located forward of wings 104, 204 (e.g., rotation point of propeller is in front of aPATENTAgent Ref. 16497-0029-00304 wing from a bird’s eye view). In some embodiments, all of lift propellers 112, 212 may be located rearward of wings 104, 204 and all of tilt propellers 114, 214 may be located forward of wings 104, 204. According to some embodiments, all lift propellers 112, 212 and tilt propellers 114, 214 may be mounted to the wings — e.g., no lift propellers or tilt propellers may be mounted to the fuselage. In some embodiments, lift propellers 112, 212 may be all located rearwardly of wings 104, 204 and tilt propellers 114, 214 may be all located forward of wings 104, 204. According to some embodiments, all lift propellers 112, 212 and tilt propellers 114, 214 may be positioned inwardly of the ends of the wing 104, 204.

[0070] In some embodiments, lift propellers 112, 212 and tilt propellers 114, 214 may be mounted to wings 104, 204 by booms 122, 222. Booms 122, 222 may be mounted beneath wings 104, 204, on top of the wings, and / or may be integrated into the wing profile. In some embodiments, lift propellers 112, 212 and tilt propellers 114, 214 may be mounted directly to wings 104, 204. In some embodiments, one lift propeller 112, 212 and one tilt propeller 114, 214 may be mounted to each boom 122, 222. Lift propellers 112, 212 may be mounted at a rear end of boom 122, 222 and tilt propellers 114, 214 may be mounted at a front end of boom 122, 222. In some embodiments, lift propellers 112, 212 may be mounted in a fixed position on boom 122, 222. In some embodiments, tilt propellers 114, 214 may mounted to a front end of boom 122, 222 via a hinge. Tilt propellers 114, 214 may be mounted to boom 122, 222 such that tilt propellers 114, 214 are aligned with the body of boom 122, 222 when in its cruise configuration, forming a continuous extension of the front end of boom 122, 222 that reduces or minimizes drag for forward flight.

[0071] In some embodiments, aircraft 100, 200 may include, e.g., one wing on each side of fuselage 102, 202 or a single wing that extends across the aircraft. According to some embodiments, the at least one wing 104, 204 is a high wing mounted to an upper side of fuselage 102, 202. According to some embodiments, the wings include control surfaces, such as flaps, ailerons, and / or flaperons (e.g., configured to perform functions of both flaps and ailerons). According to some embodiments, wings 104, 204 may have a profile that reduces drag during forward flight. In some embodiments, the wing tip profile may be curved and / or tapered to reduce or minimize drag.

[0072] In some embodiments, rear stabilizers 106, 206 include control surfaces, such as one or more rudders, one or more elevators, and / or one or more combined rudder-elevators. The wing(s) may have any suitable design for providing lift, directionality, stability, and / or anyPATENTAgent Ref. 16497-0029-00304 other characteristic beneficial for aircraft. In some embodiments, the wings have a tapering leading edge.

[0073] In some embodiments, lift propellers 112, 212 or tilt propellers 114, 214 may be canted relative to at least one other lift propeller 112, 212 or tilt propeller 114, 214, where canting refers to a relative orientation of the rotational axis of the lift propeller / tilt propeller about a line that is parallel to the forward-rearward direction, analogous to the roll degree of freedom of the aircraft.

[0074] In some embodiments, one or more lift propellers 112, 212 and / or tilt propellers 114, 214 may be canted relative to a cabin of the aircraft, such that the rotational axis of the propeller in a lift configuration is angled away from an axis perpendicular to the top surface of the aircraft.

[0075] Fig. 3 is an illustration of a top plan view of an exemplary VTOL aircraft, consistent with embodiments of the present disclosure. Aircraft 300 shown in the figure may be a top plan view of the aircraft 100, 200 shown in Figs. 1 and 2, respectively. As discussed herein, an aircraft 300 may include twelve EPUs distributed across the aircraft 300. In some embodiments, a distribution of EPUs may include six forward EPUs 314 and six aft EPUs 312 mounted on booms forward and aft of wings 304 of the aircraft 300. In some embodiments, forward EPUs may be mounted to wings 304 by booms 322. In some embodiments, aft EPUs may be mounted to wings 304 by booms 324. In some embodiments, a length of the rear end of the boom 324 from wings 304 to a lift propeller (part of EPU 312) may comprise a similar rear end of the boom 324 length across the numerous rear ends of the booms. In some embodiments, the length of the rear ends of the booms may vary, for example, across the six rear ends of the booms. Further, Fig. 3 depicts an exemplary embodiment of a VTOL aircraft 300 with forward propellers (part of EPU 314) in a horizontal orientation for horizontal flight and aft propeller blades 320 in a stowed position for a forward phase of flight.

[0076] Fig. 4 is a schematic diagram illustrating exemplary propeller rotation of a VTOL aircraft, consistent with disclosed embodiments. Aircraft 400 shown in the figure may be a top plan view of the aircraft 100, 200, and 300 shown in Figs. 1, 2, and 3, respectively. An aircraft 400 may include six forward EPUs with three of the forward EPUs being of CW type 424 and the remaining three forward EPUs being of CCW type 426. In some embodiments, three aft EPUs may be of CCW type 428 with the remaining three aft EPUs being of CW type 430. Some embodiments may include an aircraft 400 possessing four forward EPUs and fourPATENTAgent Ref. 16497-0029-00304 aft EPUs, each with two CW types and two CCW types. In some embodiments, aircraft 400 may include a fuselage 402, wing(s) 404 mounted to the fuselage 402, and one or more rear stabilizers 406 mounted to the rear of the fuselage 402. In some embodiments, each forward EPU may include propeller blades 416. In some embodiments, each aft EPU may include propeller blades 420. In some embodiments, EPUs may be mounted to wing(s) 404 by booms 422. In some embodiments, propellers may counter-rotate with respect to adjacent propellers to cancel torque steer, generated by the rotation of the propellers, experienced by the fuselage or wings of the aircraft. In some embodiments, the difference in rotation direction may be achieved using the direction of engine rotation. In other embodiments, the engines may all rotate in the same direction, and gearing may be used to achieve different propeller rotation directions.

[0077] Some embodiments may include an aircraft 400 possessing forward and aft EPUs where the amount of CW types 424 and CCW types 426 is not equal among the forward EPUs, among the aft EPUs, or among the forward and aft EPUs.

[0078] Fig. 5 is a schematic diagram illustrating exemplary power connections in a VTOL aircraft, consistent with disclosed embodiments. A VTOL aircraft may have multiple power systems connected to diagonally opposing EPUs. In some embodiments, the power systems may include high voltage power systems. Some embodiments may include high voltage power systems connected to electric engines via high voltage channels. In some embodiments, an aircraft 500 may include six power systems (e.g., battery packs), including power systems 526, 528, 530, 532, 534, and 536 stored within the wing 570 of the aircraft 500. The power systems may power EPUs and / or other electric components of the aircraft 500. In some embodiments, the aircraft 500 may include six forward EPUs having six electric engines 502, 504, 506, 508, 510, and 512 and six aft EPUs having six electric engines 514, 516, 518, 520, 522, and 524. In some embodiments, one or more power systems (e.g., battery packs) may include a battery management system (“BMS”) (e.g., one BMS for each battery pack). While six power systems are shown in Fig. 5, the aircraft 500 may include any number and / or configuration of power systems.

[0079] In some embodiments, the one or more battery management systems may communicate with an FCS of the aircraft (e.g., FCS 612 shown in Fig 6). For example, the FCS may monitor the status of one or more battery packs and / or provide commands to the one or more battery management systems which make corresponding adjustments to the high voltage power supply.PATENTAgent Ref. 16497-0029-00304

[0080] Fig. 6 illustrates block diagram of an exemplary architecture and design of an electric propulsion unit 600 consistent with disclosed embodiments. Exemplary electric propulsion unit 600 includes an electric propulsion system 602, which may be configured to control aircraft propellers. Electric propulsion system 602 may include an electric engine subsystem 604 that may supply torque, via a shaft, to a propeller subsystem 606 to produce the thrust of the electric propulsion system 602. Some embodiments may include the electric engine subsystem 604 receiving low voltage direct current (LV DC) power from a Low Voltage System (LVS) 608. In some embodiments, the electric engine subsystem 604 may be configured to receive high voltage (HV) power from a High Voltage Power System (HVPS) 610 comprising at least one battery or other device capable of storing energy. In some embodiments, electric propulsion system 602 may include one or more energy generation devices, such as a hydrocarbon-fueled turbine or generator, which may provide power to HVPS 610 and / or directly to electric propulsion system 602. HV power may refer to power that is higher in voltage than voltage provided by Low Voltage System (LVS) 608. For example, HV power may include electric power having a voltage of at least 50 V (e.g., 270 V, 400 V, 800 V, 1000 V, etc.) and LV power may include electric power having a voltage of less than 50 V (e.g., 12 V, 28 V, 48 V, etc.).

[0081] Some embodiments may include an electric propulsion system 602 including an electric engine subsystem 604 receiving signals from and transmitting signals to an FCS 612. In some embodiments, an FCS 612 may comprise a flight control computer (FCC) capable of using Controller Area Network (“CAN”) data bus signals to transmit commands to the electric engine subsystem 604 and receive status and data from the electric engine subsystem 604. An FCC may include a device configured to perform one or more operations (e.g., computational operations) for an aircraft, such as at least one processor and a memory component, which may store instructions executable by the at least one processor to perform the operations, consistent with disclosed embodiments. It should be understood that while CAN data bus signals are used between the FCC and the electric engine(s), some embodiments may include any form of communication with the ability to transmit and receive data from an FCC to an electric engine. Some embodiments may include electric engine subsystems 604 capable of receiving operating parameters from and communicating operating parameters to an FCC in FCS 612, including speed, voltage, current, torque, temperature, vibration, propeller position, and / or any other value of operating parameters.PATENTAgent Ref. 16497-0029-00304

[0082] In some embodiments, FCS 612 may also include a Tilt Propeller System (“TPS”) 614 capable of transmitting and receiving analog and / or discrete data to and from the electric engine subsystem 604 of the tilt propellers. A tilt propeller system (TPS) 614 may include an apparatus capable of communicating operating parameters to an electric engine subsystem 604 and articulating an orientation of the propeller subsystem 606 to redirect the thrust of the tilt propellers during various phases of flight using mechanical means such as a gearbox assembly, linear actuators, and any other configuration of components to alter an orientation of the propeller subsystem 606. In some embodiments, electric engine subsystem may communicate an orientation of the propeller system (e.g., an angle between lift and forward thrust) to TPS 614 and / or FCS 612 (e.g., during flight).

[0083] As discussed throughout, an exemplary VTOL aircraft may possess various types of electric propulsion systems including tilt propellers and lift propellers, including forward electric engines with the ability to tilt during various phases of flight, and aft electric engines that remain in one orientation and may only be active during certain phases of flight (i.e., take off, landing, and hover).

[0084] Fig. 7 is a schematic diagram illustrating an exemplary tilt EPU of a VTOL aircraft, consistent with disclosed embodiments. A tiltable EPU 700 may include an electric engine assembly 702 aligned along a shaft 724 that is connected to an output shaft 738 that is mechanically coupled to a propeller assembly 720, which may comprise a hub, a spinner, and tilt propeller blades. In some embodiments, an electric engine assembly 702 may include a motor and gearbox assembly 704 aligned along and mechanically coupled to the shaft 724. In some embodiments, a motor and gearbox assembly 704 may include an electric motor assembly comprising a stator 706 and a rotor 708. As shown in Fig. 7, and present in some embodiments, a stator 706 may include multiple stator windings connected to the inverter 716. In such a configuration, a stator 706 may incorporate one or more redundances so that, in the event one set of windings were to fail, power would still be transmitted to the stator 706 via one or more remaining windings, so that the electric engine assembly 702 retains power and continues to generate thrust at the propeller assembly 720.

[0085] In some embodiments, a motor and gearbox assembly 704 may contain a gearbox 710 aligned along the shaft 724 to provide a gear reduction between the torque of the shaft 724 from the electric engine assembly, comprising a stator 706 and rotor 708, and the output shaft 738 Torque applied to the output shaft 738 may be transferred to the propeller assembly 720. Some embodiments may include a gearbox 710 containing an oil pump. In such anPATENTAgent Ref. 16497-0029-00304 embodiment, the oil pump may drive a circulation of oil throughout the motor and gearbox assembly 704 at a speed equivalent to the rotation of the output shaft 738 to cool and lubricate the gearbox and electric motor components. In some embodiments, the oil pump may drive a circulation of oil at a speed greater than or less than the rotation of the output shaft 738. Some embodiments of a motor and gearbox assembly 704 may include propeller position sensors 712 present within the housing that may detect a magnetic field produced by the electric engine assembly to determine a propeller position. Further embodiments may include propeller position sensors 712 that are powered by an inverter 716 and send collected data to an inverter 716.

[0086] In some embodiments, an electric engine assembly 702 may also include an inverter assembly 714 substantially aligned along the shaft 724. An inverter assembly 714 may include an inverter 716 and an inverter power supply 740 An inverter power supply 740 may accept low voltage DC power from a low voltage system 734 located outside the electric engine assembly 702. An inverter power supply 740 may accept low voltage DC power originating from a high voltage power system 732, located outside the electric engine assembly 702, that has been converted to low voltage DC power via a DC-DC converter 742. An inverter 716 may supply high voltage alternating current (AC) to the stator 706 of the electric engine assembly located within the motor and gearbox assembly 704 via at least one three-phase winding. An inverter assembly 714 may include an inverter 716 that may receive flight control data from a flight control computing subsystem 736.

[0087] In some embodiments, a motor and gearbox 704 may be located between an inverter assembly 714 and a propeller assembly 720. Some embodiments may also include a divider plate 744 coupled to the motor and gearbox assembly 704 and inverter assembly 714. A divider plate 744 may create an enclosed environment for an upper portion of the motor and gearbox assembly 704 via an end bell assembly, and create an enclosed environment for a lower portion of the inverter assembly 714 via a thermal plate. In some embodiments, divider plate 744 may serve as an integral mounting bracket for supporting heat exchanger 718. Heat exchanger 718 may comprise, for example, a folded fin or other type of heat exchanger. In some embodiments, the EPU 700 may circulate oil or other coolant throughout the electric engine assembly 702, motor and gearbox assembly 704, or inverter assembly 714 to transfer heat generated from the components to the oil or other coolant liquid. The heated oil or other coolant liquid may circulate through heat exchanger 718 to transfer the heat to an air flow 722 passing through the fins of the heat exchanger.PATENTAgent Ref. 16497-0029-00304

[0088] In some embodiments, the electric engine assembly 702 may be mounted or coupled to a boom structure 726 of the aircraft. A variable pitch mechanism 730 may be mechanically coupled to the propeller assembly 720. In some embodiments, the variable pitch mechanism may abut the electric engine assembly 702. In some embodiments, the variable pitch mechanism 730 may be coupled to the variable pitch mechanism 730 such it may be remotely mounted within the boom, wing, or fuselage of the aircraft. In some embodiments, the variable pitch mechanism 730 may include a shaft or component traveling within or adjacent to the shaft 724 to the propeller assembly 720. A variable pitch mechanism 730 may serve to change the collective angle of the forward electric engine’s propeller assembly blades as needed for operation during the hover-phase, transition phase, and cruise-phase. Some embodiments may include the electric engine assembly 702 being mechanically coupled to a tilt propeller subsystem 728 that may redirect thrust between a primarily vertical direction during vertical flight mode to a mostly horizontal direction during forward-flight mode. In some embodiments, the tilt propeller subsystem may abut the variable pitch mechanism 730. Some embodiments may include a tilt propeller subsystem 728 comprising various components located in various locations. For example, a component of the tilt propeller subsystem may be coupled to the electric engine assembly 702 and other components may be coupled to the variable pitch mechanism 730. These various components of the tilt propeller subsystem 728 may work together to redirect the thrust of the tiltable EPU 700.

[0089] Fig. 8 illustrates a portion of an electrical propulsion system 800 for a vertical takeoff and landing (VTOL) aircraft, consistent with disclosed embodiments. The electrical propulsion system 800 may provide a dual three-phase system for motor control. As shown in Fig- 8, the electrical propulsion system 800 includes a first inverter circuit 810, a second inverter circuit 820, an electrical motor Ml configured to drive one or more propellers of the VTOL aircraft, and a bus capacitor 870 configured to stabilize a direct current (DC) bus voltage Vbus. The first inverter circuit 810 is coupled to the bus capacitor 870 and configured to convert the DC bus voltage Vbus on the bus of the first inverter circuit 810 to alternate current (AC) voltages to drive a first set of stator windings of the electrical motor Ml, in response to a first pulse width modulation (PWM) vector. The second inverter circuit 820 is configured to convert the DC bus voltage Vbus on the bus of the second inverter circuit 820 to AC voltages to drive a second set of stator windings of the electrical motor Ml, in response to a second PWM vector. In some embodiments, the first PWM vector and the second PWM vector are substantially equal and opposite vectors. For example, the delayPATENTAgent Ref. 16497-0029-00304 between PWM signals corresponding to the first PWM vector and the second PWM vector may equal to or less than 0.25%, 0.5 %, 1%, or 2% of the switching cycle period. For example, the delay may be within 50 nanoseconds. Accordingly, the first inverter circuit 810 is configured to output a first set of three-phase AC voltages (e.g., based on a state of pairs of switches ul, vl, wl) and the second inverter circuit 820 is configured to output a second set of three-phase AC voltages (e.g., based on a state of pairs of switches ul’, vl’, wl’), and a phase of the first set of three-phase AC voltages and a corresponding phase of the second set of three-phase AC voltages are two interleaved phases with a phase-shift of substantially 180 degrees (e.g., plus or minus 5 degrees).

[0090] As used herein, an “inverter circuit” may include an electrical circuit that includes one or more switches, is configured to convert direct current to alternating current (or vice versa), and / or is configured to supply and / or adjust voltage from a power source (e.g., battery) to a rotational device (e.g., motor, EPU, roller, etc.).

[0091] In particular, in the electrical propulsion system 800, two inverter circuits 810 and 820 are electrically coupled to the internal high voltage DC supply bus and configured to provide corresponding three-phase AC voltages (e.g., based on a state of pairs of switches ul, vl, and wl) and three-phase AC voltages (e.g., based on a state of pairs of switches ul’, vl’, and wl’) to drive a dual 3-phase motor Ml. The dual-inverter drive system shown in Fig. 8 may improve the motor performance, and improve the system reliability by increasing the number of phases.

[0092] As shown in the figure, the inverter circuits 810 and 820 are respectively configured to convert the bus voltage Vbus on the high voltage DC supply bus to three-phase AC power to drive the motor Ml. When inverter circuits 810 and 820 convert the DC power to the AC power, there is a voltage difference between the power source and the neutral point of the load, which is referred to as a common-mode voltage. Common-mode currents due to common-mode voltages in the inverters may be detrimental to the electrical systems. Specifically, the common-mode voltage may result in faults in motors, premature failure of bearings, glitches in the control equipment, etc. In an effort to reduce common mode noises, filter components may be installed in the electrical propulsion system 800.

[0093] For example, the electrical propulsion system 800 may include a DC common-mode filter 830 and AC common-mode chokes 840 and 850. The DC common-mode filter 830 may be coupled to the bus capacitor 870 and configured to reduce common mode signals at a DC- side of the first inverter circuit 810 and the second inverter circuit 820. The one or more ACPATENTAgent Ref. 16497-0029-00304 common-mode chokes 840 and 850 may be coupled to an AC-side of the first inverter circuit 810 or the second inverter circuit 820 to reduce common mode signals.

[0094] For example, the DC common-mode filter 830 may be located between the DC power source 860 and the bus capacitor 870 and formed by a set of DC-side chokes 832 and a set of DC common-mode filter capacitors 834, 836. The DC-side chokes 832 may be configured such that positive and negative lines are wound around the same magnetic core. Thus, the DC-side chokes 832 and the DC common-mode filter capacitors 834, 836 may be configured to reduce the common mode signals at the DC-side. However, a larger filter may add volume and mass and may incur additional losses.

[0095] In some embodiments, the electrical propulsion system 800 may achieve a common mode voltage cancelation by applying proper space vector modulations (SVM) to the inverter circuits 810 and 820.

[0096] The winding arrangement of the motor Ml applied in the electrical propulsion system 800 may be different in various embodiments. For example, the phase difference in electrical angle between the two sets of 3-phase windings may be designed to reduce the harmonic components. In some embodiments, the first set of stator windings and the second set of stator winding of the motor Ml are shifted by substantially 180 degrees (e.g., plus or minus 5 degrees). That is, the motor phasing between independent winding sets may be 180 degrees, or there abouts, out of phase.

[0097] In some embodiments, the first inverter circuit 810 is controlled using a standard center aligned SVM while the second inverter circuit 820 is controlled using an inverted center aligned space vector modulation. In such operation mode, the common mode voltage can be canceled through the equal and opposite PWM vectors.

[0098] While the exemplary electrical propulsion system 800 depicted in Fig. 8 may be described with respect to a VTOL aircraft, it may be understood that the disclosed embodiments (e.g., as described and exemplified with respect to Figs. 9A-15) may be similarly applied to any system comprising a rotational device controlled by at least one inverter circuit, including in an electric or hybrid-electric automobile, wind turbine, ski lift, or conveyor belt system. Further, the term “propeller” may be replaced by a suitable driven component, such as a rotor, wheel, a drive pulley, or drive roller.

[0099] Embodiments described herein address technical challenges associated with stowing or feathering a propeller of an EPU, such as using components of the systems described above. Feathering or stowing a propeller may refer to maintaining a position or orientation ofPATENTAgent Ref. 16497-0029-00304 one or more propellers. For example, propellers not actively being used to generate thrust or lift may be feathered or stowed to increase an aerodynamic efficiency of the aircraft. For example and without limitation, lifter propellers (e.g., propellers that cannot tilt and are primarily used to generate lifting thrust) may be stowed or feathered during phases of flight during which vertical thrust is not required (e.g., forward flight, cruise). Further, by leveraging a particular control scheme, propellers may be actively controlled to maintain a particular orientation while removing the need to install separate electromechanical components to stow or feather a propeller, thereby reducing an overall weight of an aircraft implementing such a control scheme.

[0100] Fig. 9A is an example diagram 900A illustrating PWM vectors for controlling an inverter circuit, such as first inverter circuit 810 in electrical propulsion system 800 of Fig. 8, consistent with disclosed embodiments. For example, the illustrated PWM vectors may be transmitted to control one or more switches, consistent with disclosed embodiments.

[0101] In some embodiments, the PWM vectors and switching sequences or techniques depicted in Figs. 9A-14B may be implemented (e.g., transmitted, used, generated, etc.) by at least one processor, such as a controller or FCC. For example, at least one processor may transmit instructions to one or more switches to open or close according to a waveform or sequence of values (e.g., voltage values, reference values, binary values, etc.), such as those shown in the figures below. While Figs. 9A-14B are described with reference to first inverter circuit 810, it may be understood that any other number of inverter circuits (e.g., second inverter circuit 820) configured to control a same electric engine may perform similar or opposite switching operations. Further, while Figs. 9A-14B are described as separate control schemes, it may be understood that a same aircraft may implement any combination of the switching techniques disclosed herein. For example, one or more EPUs may utilize the switching strategy described with respect to Figs. 9A and 9B, while one or more other EPUs may utilize the switching strategy described with respect to Figs. 10A and 10B.

[0102] Fig. 9B is a diagram 900B illustrating an example switching sequence for controlling an inverter circuit in one period based on the PWM vectors of Fig. 9A, consistent with disclosed embodiments. For example, diagram 902 depicts the states (e.g., open or “OFF,” or closed or “ON”) for upper switches ul, vl, and wl and lower switches ul’, vl’, and wl’ of a two-level three-phase inverter circuit (e.g., first inverter circuit 810, second inverter circuit 820). A period may be considered one iteration of a switching sequence.PATENTAgent Ref. 16497-0029-00304

[0103] In some embodiments, an SVM algorithm is applied to control the PWM and used for generating the AC voltages from the DC voltage to drive the three-phase motor at varying speeds. Different SVM algorithms may have different quality and computational requirements. As shown in Fig. 9A, there are eight possible switching vectors SV0-SV7 for a two-level three-phase inverter circuit using SVM. A switching vector may represent a state of one or more switches of an inverter circuit, and may be used by at least one processor (e.g., FCC, EPU controller) to determine, generate, and / or send waveform signals to the one or more switches. Waveform signals may be based on a single switching vector or multiple switching vectors.

[0104] An example PWM reference vector VINV for an inverter circuit is also shown in Fig. 9A. A reference vector may refer to, represent, or include a desired output voltage vector to control a motor. For example, a reference vector may refer to, represent, or include the voltage vector required to drive a motor or control a motor to actively maintain a propeller position and / or alignment. Additionally or alternatively, a reference vector may refer to, represent, or include a voltage value at or beyond which a switch state will be considered “on.” A voltage value may be expressed relative to a total voltage supplied by a bus (e.g., VBUS / 2, VBUS / 6). Further, a reference vector may be implemented as an average of two or more switching PWM switching vectors. For example and as further discussed herein, actively stowing a propeller may include maintaining a propeller position by outputting, by the inverter circuit, a constant voltage vector at a predetermined angle. If the predetermined angle does not lie along an active switching vector (i.e., lies between two active switching vectors), the inverter circuit may switch between the two neighboring active switching vectors to, in a time-based average, output the reference vector.

[0105] Referring to a switch as “on” or “off’ may mean that the switch has a switch state that is closed and / or allows current to flow through the switch, or has a switch state that is open and / or does not allow current to flow (or does not allow current beyond an expected tolerance amount to flow), respectively. In some embodiments, an “on” state may correspond to a scenario in which a switch is allowing flow of current reaching a threshold amount, and an “off’ state may correspond to a scenario in which a switch is not permitting current flow that reaches the threshold amount. A switch state of inverter circuitry may be considered a combination of switching states of components (e.g., switches) that are part of the inverter circuitry.PATENTAgent Ref. 16497-0029-00304

[0106] As used herein, a switching sequence may refer to a combination, order, and / or group of switch states for one or more switches. For example, a switching sequence may refer to an order of different switch states for multiple switches, which may occur (e.g., as instructed or commanded) one after another. In some embodiments, a switching sequence may be repeated, such as according to a predetermined frequency. For example, a switching sequence may be repeated at a frequency of at least 1 kHz (e.g., 1 kHz, 2 kHz, 10 kHz, etc.). The input waveforms (e.g., as depicted in Figs. 9B, 10B, 11B, 12B, 13B, 14B) to implement the switching sequences or techniques described and exemplified herein may be accessed, generated, and / or transmitted to the corresponding switches by at least one processing device (e.g., FCC, EPU controller).

[0107] While some disclosed embodiments may describe switching sequences or techniques with respect to a single inverter circuit (e.g., inverter circuit 810), it may be understood that similar switching sequences or techniques may be implemented with respect to multiple inverter circuits, including multiple inverter circuits controlling a same electric engine (e.g., inverter circuits 810 and 820). Further, one inverter circuit may implement one switching sequence or technique while another inverter circuit may implement another switching sequence or technique. Additionally, one inverter circuit may implement a switching sequence or technique while another inverter circuit may implement the same switching sequence or technique but phase-shifted.

[0108] Additionally or alternatively, a combination of different switching sequences may be used when a propeller and / or rotor controlled by the inverter circuit is stowed. For example, a switching sequence in use may rotate to another switching sequence after a predetermined amount of time (e.g., 5 periods, 10 periods, 100 periods). By way of further example, one of the switching sequences depicted in and described with respect to Figs. 10B, 11B, 12B, or 13B may be applied to the switches of an inverter (e.g., by an inverter controller) for one or more cycles, and then another set of switching vectors of one of the switching sequences depicted in and described with respect to Figs. 10B, 11B, 12B, or 13B may be applied to the switches of the inverter for one or more cycles. The number of cycles during which each switching sequence is used may be the same or different. Any number and combination of sets of switching vectors may be applied in a pattern.

[0109] During the operation, the switches within the inverter circuits 810 and 820 are controlled so that both switches (i.e., the upper switch and the lower switch) in the same leg are not turned on at the same time to avoid the DC supply being shorted. A switch mayPATENTAgent Ref. 16497-0029-00304 include a solid state switch, such as a field-effect transistor (FET), a metal-oxide- semiconductor field-effect transistor (MOSFET), a relay, a contactor, an insulated gate bipolar transistor (IGBT), or any electrical device capable of changing a state to influence current flow. This can be achieved by the complementary operation of the switches within the same leg. That is, for each leg, when the upper switch is on, then the lower switch is off, and vice versa. Accordingly, the switching vectors SV0-SV7 include six active switching vectors (i.e., SV1-SV6) and two zero vectors (i.e., SVO and SV7).

[0110] An upper switch and a lower switch may be considered two or more switches that are wired in series with respect to one another, with that group of two or more switches being referred to as a “leg.” For example, the two switches shown in Fig. 8 near ul may be considered to form a “leg,” with the switch above ul being considered the upper switch and the switch below ul being considered the lower switch. A leg may also be associated with a phase. For example, a phase may include similarly placed and / or electrically coupled legs in different inverter circuits.

[0111] As shown in Fig. 9A, the switching vector SVO = {000} represents that the upper switches of three phases U, V, and W are OFF (e.g., ul, vl, wl are open), while the lower switches of three phases U, V, and W are ON (e.g., ul’, vl’, wl’ are closed). The switching vector SV1 = { 100} represents that the upper switch of the U phase is ON and the upper switches of the V phase and the W phase are OFF. The switching vector SV2 = {110} represents that the upper switches of the U phase and the V phase are ON and the upper switch of the W phase is OFF. The switching vector SV3 = {010} represents that the upper switch of the V phase is ON and the upper switches of the U phase and the W phase are OFF. The switching vector SV4 = {011 } represents that the upper switches of the V phase and the W phase are ON and the upper switch of the U phase is OFF. The switching vector SV5 = {001 } represents that the upper switch of the W phase is ON and the upper switches of the U phase and the V phase are OFF. The switching vector SV6 = { 101 } represents that the upper switches of the U phase and the W phase are ON and the upper switch of the V phase is OFF. The switching vector S V7 = { 111 } represents that the upper switches of three phases U, V, and W are ON, while the lower switches of three phases U, V, and W are OFF.

[0112] In some embodiments, the first inverter circuit 810 is controlled according to a standard center-aligned SVM starting from the switching vector SVO with the upper switches of three phases U, V, and W being OFF, and the second inverter circuit 820 is controlled according to the inverted center-aligned SVM starting from the switching vector SV7 withPATENTAgent Ref. 16497-0029-00304 the upper switches of three phases U, V, and W being ON. In some embodiments, an inverter circuit may be controlled according to another SVM modulation strategy. For example, first inverter circuit 810 and / or second inverter circuit 810 may be controlled according to asymmetric (e.g., leading-edge or trailing edge) SVM.

[0113] Accordingly, as shown in Fig. 9B, in each stage of the operation period, a PWM reference vector VINV-CM can be obtained by controlling upper switches ul, vl, and wl and lower switches ul’, vl’, and wl’ using the depicted input waveforms. The waveforms may represent when a switch is ON (e.g., non-zero voltage input) and when a switch is OFF (e.g., zero or near-zero voltage input). For example, at least one processor (e.g., FCC, controller of EPU) may output a voltage waveform to upper switch ul that is low (e.g., zero) for SVO and high (e.g., non-zero, greater than a predetermined threshold) for SV1, SV2, and SV7.

[0114] In some embodiments, a six-phase machine may thus be implemented to achieve similar functionality of the three-phase machine but with a reduction in the common mode noises experienced by the system. In some embodiments, the common mode voltage cancellation across any number of phases may be implemented, such that the combination of the PWM vectors can cancel or reduce the common mode noises experienced by the system. In some embodiments, the first and the second inverter circuits 810 and 820 may be configured to pull the power from the power source (e.g., from the DC bus capacitor 870) at the same time, and the first and the second inverter circuits 810 and 820 operate according to PWM signals with equal duty cycle but substantially 180 degrees out of phase.

[0115] In some embodiments, at least one processor may output control signals commanding switches of an inverter circuit to open or to close based on the waveforms depicted in diagram 900B. For example, during a vertical flight mode, one or more inverter circuits controlling an EPU may switch, according to the exemplary depiction in Fig. 9B, to cause the inverter circuit to output a reference PWM vector, as depicted in Fig. 9A. A vertical flight mode may be considered a flight mode where a tilt angle of one or more EPUs (e.g., tilters) is beyond a first threshold, where a total amount of vertical lift supplied by one or more EPUs is beyond a second threshold, where lift supplied to an aircraft is predominantly supplied by one or more EPUs rather than wings, where thrust provided by one or more EPUs exceeds a third threshold, and / or any combination thereof.

[0116] In some embodiments, one or more EPU propellers may be stowed. For example, while an aircraft is in a horizontal flight mode, one or more EPUs may be stowed. Stowing a propeller may refer to maintaining a propeller rotational position and / or retracting a propellerPATENTAgent Ref. 16497-0029-00304 into a supporting structure. For example, while in a horizontal flight mode, one or more aft EPUs may be stowed such that their respective propellers are fixed or near-fixed in a predetermined position. For example, a propeller and / or rotor maybe be prevented from rotating beyond a tolerance amount, such as 1 / 10thof a full rotation. By maintaining a fixed or near-fixed predetermined position (e.g., to reduce or minimize drag) for a propeller and / or rotor, the efficiency of the aircraft may increase. While disclosed techniques may be described as relating to “stowing” a propeller, they may similarly be applied to actively feather one or more propellers of an EPU.

[0117] One or more EPUs may be stowed based on at least one processor determining that the aircraft is in a predetermined flight mode (e.g., propeller stow mode), such as a flight mode where the aircraft’s forward speed exceeds a threshold, the aircraft’s vertical speed exceeds a threshold, the aircraft’s altitude exceeds a threshold, any combination of the foregoing, or any phase of flight, discussed above.

[0118] In some embodiments, at least one processor may be configured to determine a flight mode of an aircraft. For example, at least one processor (e.g., FCC, controller) may be configured to determine a flight mode of an aircraft (e.g., vertical flight mode, horizontal flight mode) based on one or more of received measurements from one or more sensors, an airspeed of the aircraft, an altitude of the aircraft, a pilot command, a tilt angle of a tiltable propeller, a thrust of the aircraft, a flight plan, or any combination of the foregoing. For example, based on an airspeed, an orientation, and / or an altitude of an aircraft (e.g., as measured by one or more sensors, as determined by at least one processor), at least one processor (e.g., FCC, controller) may determine an aircraft is in a horizontal flight mode or a vertical flight mode. In some embodiments, one or more EPU propellers may be stowed during only a portion of a flight. For example, one or more aft EPUs may be stowed only during (e.g., as determined by at least one processor) a horizontal flight mode of an aircraft and may not be stowed during (e.g., as determined by at least one processor) a vertical flight mode of the aircraft.

[0119] Due to one or more constraints, it may be undesirable to stow one or more propellers by shutting down the EPU. For example, the time and energy cost to shut down and turn back on an EPU may be too high. Further, shutting down an engine while in flight, including to stow a propeller, may be unsafe. A propeller that has been stowed may be referred to as having, reflecting, or being in a “stow mode.” While propellers are referred to herein withPATENTAgent Ref. 16497-0029-00304 respect to stowing, being stowed, and a stow mode, it is appreciated that rotors and / or other parts associated with rotation may also be treated in the same fashion.

[0120] In some embodiments, a propeller position can be actively maintained using PWM control of the EPU inverter circuit. For example, the inverter circuit can be controlled, based on a measured position of the propeller, to maintain a desired position using SVM, as described and exemplified above with respect to Figs. 8, 9A, and 9B. However, this switching method may induce more losses than a reduced switching method, as described and exemplified below. Losses may include switching loss and capacitance loss. Switching loss may refer to energy lost due to the transition of a switch (e.g., OFF to ON, ON to OFF) and may occur each time a switch transitions. Capacitance loss may include energy lost due to the charging or discharging of parasitic or intentional capacitances during a switch. One way to reduce switching loss and / or capacitance loss is to reduce the number of switch transitions within a period of a time. For example, the exemplary switching pattern depicted in Fig. 9B includes 6 instances of switching losses and 6 instances of motor capacitance losses.

[0121] Fig. 10A depicts an example diagram 1000A illustrating PWM vectors for controlling an inverter circuit during a propeller stow mode, and Fig. 10B depicts an example diagram 1000B illustrating the three-phase voltages output by upper and lower switches of an inverter circuit, consistent with disclosed embodiments. As depicted in Fig. 10B, a reduced number of switching vectors (e.g., SVO, SV1, and SV2) are used to maintain a same PWM reference vector VINV as compared to Fig. 9B. In some embodiments, the number of switching vectors is reduced by eliminating switching vector SV7 and adding an amount of time allocated previously to switching vector SV7 to switching vector SVO instead. Additionally or alternatively, in some embodiments, the number of switching vectors is reduced by eliminating switching vector SVO and adding an amount of time allocated previously to SVO to switching vector SV7 instead. The switching vectors SVO and SV7 are the zero vectors, and it may be understood that a similar replacement can be implemented for other inverter circuits with a different number of switches and including at least two zero vectors.

[0122] As depicted in Fig. 10B, first graph 1002 depicts a first switching method that includes using a 3-phase short for switching vector SVO. A 3-phase short configuration may refer to a switch configuration in which all the upper switches are open and all the lower switches are closed, or vice versa. In this exemplary embodiment, there are 4 instances of switching losses and 6 instances of motor capacitance losses. Further, the 3-phase short mayPATENTAgent Ref. 16497-0029-00304 result in higher 3 -phase short currents across the switches and windings of the inverter circuit.

[0123] Further, as depicted in Fig. 10B, second graph 1004 depicts a second switching method that includes using a 6-switch open state (e.g., where six switches are simultaneously set to open for at least a portion of a switching sequence) in place of switching vector SVO. For example, instead of implementing a 3-phase short for switching vector SVO, each switch is opened. By opening each switch of the six switches, the current and / or voltage of the inverter circuit is unregulated and may freely vary. For example, during a 6-switch open state, the electric engine may not be applying a torque on a propeller, allowing the propeller to freely spin. However, due to the high switching frequency and / or additional design considerations associated with stowing a propeller (e.g., propeller only needs to stay at or near a predefined position), a 6-switch open state can be utilized (e.g., by an inverter, such as by a processing unit thereof) to mimic the results of a 3-phase short switching vector SVO. In this embodiment, there are 5 instances of switching losses and 3 instances of capacitance losses. Further, the 6-switch open state may result in lower motor and switch currents and higher diode losses. A 6-switch open state may also be referred to as a 6-switch open configuration (e.g., a configuration of six switches where each of the switches is in an open state).

[0124] A propeller angle may be based on and / or defined relative to a reference point. A propeller angle may refer to the physical position or orientation of a propeller. For example, a particular propeller rotational position (e.g., for a two-blade propeller, aligning the blades along an axis parallel a longitudinal axis of the aircraft) may be considered to be at “0 degrees,” which may be set at a processing device and / or memory device. In some embodiments, at least one processor may be configured to determine a reference vector based on a predetermined position. For example, at least one processor (e.g., FCC, EPU controller) may be configured to determine a reference vector VINV that corresponds to a desired propeller stow position (e.g., as measured or determined by a position sensor, including a resolver, encoder, and / or Hall effect sensor) using one or more algorithms or look-up tables. Additionally or alternatively, at least one processor (e.g., FCC, EPU controller) may be configured to determine a reference vector that is aligned along (e.g., same angle as) an active switching vector. For example, when a desired stow position (e.g., as measured or determined by a position sensor, including a resolver, encoder, and / or Hall effect sensor) is not aligned with an active switching vector, at least one processor may determine a nearest activePATENTAgent Ref. 16497-0029-00304 switching vector that, if maintained over time, would result in a propeller angle that is within a predetermined threshold of the desired stow position (e.g., within 0.1 degrees, 1 degree, 5 degrees, etc.). The at least one processor may then utilize the determined nearest active switching vector as the reference vector, as further described below.

[0125] Fig. 11A depicts an example diagram 1100A illustrating PWM vectors for controlling an inverter circuit during a propeller stow mode, and Fig. 11B depicts an example diagram 1100B illustrating the three-phase voltages output by upper and lower switches of an inverter circuit, consistent with disclosed embodiments. As depicted in Fig. 11B, a reduced number of switching vectors are used by eliminating a non-zero and a zero vector and by aligning the reference vector along a non-zero vector. For example, as depicted in Fig. 11 A, the switching vector SV2 and the zero vector SV7 may be eliminating, and the reference vector VINV may be aligned along switching vector SV1. In this way, the inverter circuit can be switched between a zero state (e.g., SVO) and a single active state (e.g., SV1).

[0126] As depicted in Fig. 11B, first graph 1102 depicts a first switching method that includes using a 3-phase short for switching vector SVO. In this embodiment, there are 2 instances of switching losses and 2 instances of motor capacitance losses. Further, the 3- phase short may result in higher 3-phase short currents across the switches and windings of the inverter circuit and in more unbalanced losses between phases.

[0127] Further, as depicted in Fig. 11B, second graph 1104 depicts a second switching method that includes using a 6-switch open state in place of switching vector SVO. In this embodiment, there are 3 instances of switching losses and 1 instance of capacitance losses. Further, the 6-switch open state may result in lower motor and switch currents and higher diode losses and in more balanced losses between phases.

[0128] In some embodiments, at least one processor may use a dynamic mode of control based on an angle of a propeller. For example, after aligning an open loop angle corresponding to the propeller angle (e.g., 30 degrees may correspond to 0.67 degrees propeller angle) to the nearest sector boundary (e.g., 0 degrees, 60 degrees, 120 degrees, etc.), either SVO or SV7 may be used as the zero switching vector. A zero switching vector may refer to a switch configuration (e.g., all upper switches ON, all lower switches ON), that produces an output voltage vector of zero at an inverter such that a connected motor does not produce any active torque. If the aligned angle of the propeller is 0 degrees (SV1), 120 degrees (SV3), or 240 degrees (SV5), SVO may be used as the zero switching vector. If the aligned angle of the propeller is 60 degrees (SV2), 180 degrees (SV4), or 300 degrees (SV6),PATENTAgent Ref. 16497-0029-00304SV7 may be used as the zero switching vector. By determining the zero vector most similar to the aligned angle of the propeller, switching losses may be reduced, e.g., by two-thirds, because a fewer number of switches are required to switch between the active switching vector acting as the reference vector and the determined zero vector.

[0129] Fig. 12A depicts an example diagram 1200 A illustrating PWM vectors for controlling an inverter circuit during a propeller stow mode, and Fig. 12B depicts an example diagram 1200B illustrating the three-phase voltages output by upper and lower switches of an inverter circuit, consistent with disclosed embodiments. As depicted in Fig. 12B, a reduced number of switching vectors are used by only using three switching vectors (e.g., SV1, SV3, and SV5; SV2, SV4, and SV6).

[0130] As depicted in Fig. 12B, first graph 1202 depicts a first switching method that includes only using switching vectors SV1, SV3, and SV5. In this embodiment, there are 6 instances of switching losses and 0 instances of motor capacitance losses. Further, the switch states implemented by this method do not include or use any 3-phase short currents across the windings and switches. Additionally, the zero vector may be formed using a combination of all three switching vectors.

[0131] Further, as depicted in Fig. 12B, second graph 1204 depicts a second switching method that includes only using switching vectors SV2, SV4, and SV6. In this embodiment, there are 6 instances of switching losses and 0 instances of capacitance losses. Further, the switch states implemented by this method do not include or use any 3-phase short currents across the windings and switches.

[0132] Fig. 13A depicts an example diagram 1300A illustrating PWM vectors for controlling an inverter circuit during a propeller stow mode, and Fig. 13B depicts an example diagram 13006 illustrating the three-phase voltages output by upper and lower switches of an inverter circuit, consistent with disclosed embodiments. As depicted in Fig. 13B, a reduced number of switching vectors are used by only using two active switching vectors (e.g., SV1 and SV3, SV2 and SV4) and one zero switching vector (e.g., SV0, SV7).

[0133] As depicted in Fig. 13B, first graph 1302 depicts a first switching method that includes using a 3-phase short for switching vector SV0. In this embodiment, there are 4 instances of switching losses and 1 instance of motor capacitance losses. Further, there may be 3-phase short currents during some periods of time (e.g., during switching).

[0134] Further, as depicted in Fig. 13B, second graph 1304 depicts a second switching method that includes using a 6-switch open state for switching vector SV0. In thisPATENTAgent Ref. 16497-0029-00304 embodiment, there are 5 instances of switching losses and 0 instances of capacitance losses. Further, there may be low motor and switch short currents and high diode losses.

[0135] Fig. 14A depicts an example diagram 1400A illustrating PWM vectors for controlling an inverter circuit during a propeller stow mode, and Fig. 14B depicts an example diagram 1400B illustrating the three-phase voltages output by upper and lower switches of an inverter circuit, consistent with disclosed embodiments. As depicted in Fig. 14B, bursts of pulses can be used instead of the longer switch durations depicted in Figs. 10B, 11B, 12B, and 13B. For example, the bursts of pulses may have a frequency approximately ten times faster (e.g., 8 times faster, 10 times faster, 15 times faster) than a switching frequency used in non-stow mode (e.g., vertical flight mode). In some embodiments, the burst of pulses may be used (e.g., by at least one processor configured to control one or more switches of an inverter circuit) based on a propeller position exceeding a threshold. For example, a burst of pulses may be run in response to determining (e.g., by at least one processor and / or at least one sensor) that the propeller position is more than 5 degrees from a predetermined position (e.g., stow position).

[0136] As depicted in Fig. 14B, top graph 1402 depicts a first switching method that includes using a 3-phase short when not pulsing. In some embodiments, the first switching method may further include alternating between a plurality of inverter circuits. For example, first inverter 810 and second inverter circuit 820 may alternate (e.g., after a predetermined amount of time) between which circuit’s switches are ON to implement a 3-phase short.

[0137] Further, as depicted in Fig. 14B, bottom graph 1404 depicts a second switching method that includes using a 6-switch open state when not pulsing.

[0138] In some embodiments, a switching method may be run constantly or continuously (e.g., by at least one processor). For example, instead of only using bursts of pulses based on a propeller position (e.g., propeller position is more than 5 degrees from a predetermined position for stow), bursts of pulses are used to constantly or continuously and actively control a propeller position. While this embodiment may be more architecturally and / or energy- intensive, it may provide a more precise position control.

[0139] In some embodiments, only one inverter circuit may operate at a time. For example, considering two inverter circuits (e.g., as depicted in Fig. 8), first inverter circuit 810 may be the only inverter circuit operating while second inverter circuit 820 is switched off (i.e., all switches open). Additionally or alternatively, second inverter circuit 820 may be the only inverter circuit operating while first inverter circuit 810 is switched off (i.e., all switchesPATENTAgent Ref. 16497-0029-00304 open). In some embodiments, the operating inverter circuit may alternate with a switched-off inverter circuit. For example, first inverter circuit 810 may be the only inverter circuit operating until a threshold is reached (e.g., temperature, duration), at which point second inverter circuit 820 beings operating and first inverter circuit 810 is switched off. This process may repeat or be similarly implemented for any plurality of inverter circuits.

[0140] Fig. 15 illustrates a flow diagram of an exemplary inverter circuit control method, consistent with disclosed embodiments. Process 1500 may be implemented as software (e.g., in at least one module, at least one program, at least one application, and / or at least one function, etc.), hardware (e.g., at least one processor, such as an FCC, etc.), or a combination of both. For purposes of explanation, the steps of process 1500 are described as being carried out by at least one processor. The at least one processor may be, for example, part of a controller, computer, FCC, or any processing circuitry. In some embodiments, the at least one processor may be included in a housing of an inverter. The at least one processor may be communicably connected to one or more switches, consistent with disclosed embodiments. For example, the at least one processor may be communicably connected to one or more gates of inverter switches. An inverter circuit may be part of an aircraft and / or used to control power to at least one EPU, consistent with disclosed embodiments.

[0141] In step 1502, process 1500 may include receiving a first signal indicating a vertical flight mode. For example, at least one processor configured to control an inverter circuit may receive (e.g., from FCC, sensor) a signal indicating a vertical flight mode. A vertical flight mode may be considered a flight mode during which a driven component (e.g., rotor, wheel, and / or propeller) is permitted to rotate according to commands received (e.g., directly or indirectly from an FCC), beyond a particular threshold amount of rotation, and / or according to natural forces (e.g., windmilling). Additionally or alternatively, a vertical flight mode may be considered a state where a rotor and / or propeller are in a state other than a propeller stow mode. For example, a vertical flight mode may include any phase of flight during which at least one lifter EPU generates thrust, including, for example, during vertical take-off and landing, hover, and / or transition.

[0142] In step 1504, process 1500 may include implementing a first switching sequence during the vertical flight mode. Implementing a switching sequence may include instructing one or more switch states of one or more switches, which may include accessing (e.g., as predetermined and / or stored in a memory) one or more signals (e.g., signals corresponding to the waveforms and voltage vectors depicted in Figs. 9A-14B), determining one or morePATENTAgent Ref. 16497-0029-00304 signals, generating one or more signals, and / or transmitting one or more signals to the one or more switches, consistent with disclosed embodiments. For example, implementing a switching sequence may include at least one processor (e.g., FCC, EPU controller) transmitting instructions to inverter circuits (or switches, which may be part of inverter circuits) to maintain or change, according to the first switching sequence, a switch state. For example, at least one processor may transmit signals to one or more switches to cause them to switch states (e.g., ON to OFF or vice versa) according to a defined switching sequence, consistent with disclosed embodiments. For example, the at least one processor may cause (e.g., instruct, transmit instruction signals to) the inverter circuits to cause them to switch using SVM (e.g., as depicted and described with respect to Figs. 9A and 9B). The first switching sequence may include two zero vectors and six active vectors (e.g., SV0-SV7). However, one having ordinary skill in the art would appreciate that other inverter circuits (e.g., three-level, three-phase inverter circuit) may include more switching vectors, and similar switching sequences and techniques as disclosed herein may similarly be applied to such other inverter circuits.

[0143] Implementing a switching sequence during a particular mode may include using the switching sequence based on that particular mode. For example, at least one processing device may determine that a mode is present or in effect for at least one EPU, at least one propeller, and / or an aircraft, and in response to the determination, may implement a particular switching sequence (e.g., a switch state designated for that mode).

[0144] In step 1506, process 1500 may include receiving a signal indicating a propeller stow mode. For example and as discussed above, it may be desirable to actively stow a propeller based on a particular switching sequence configured to maintain a propeller position (e.g., in an aerodynamic position aligned parallel to or along a longitudinal axis of the aircraft). Further, it may be desirable to reduce or minimize the number of switching instances during a propeller stow mode to reduce losses (e.g., switching loss, motor capacitance loss). A propeller stow mode for an EPU and / or its propellers may refer to mode during which the EPU is controlled (e.g., by at least one processor, FCC, controller) via its one or more inverter circuits to maintain (e.g., fixed, near-fixed) a propeller position (e.g., to reduce or minimize drag). For example, a propeller stow mode may be implemented during a phase of flight during which lifter EPUs may not be needed or utilized to generate thrust, including, for example, horizontal phases of flight, such as cruise.PATENTAgent Ref. 16497-0029-00304

[0145] Further, a stow mode may refer to a mode of operation for an electric engine and / or its driven component during which mode the electric engine is controlled (e.g., by at least one processor, controller) via its one or more inverter circuits to maintain (e.g., fixed, near-fixed) a driven component position. In general, it may be understood that the embodiments disclosed herein may apply to any system with one or more inverter circuits where it may be desirable to actively maintain a position of an end effector (e.g., propeller, blade, wheel). For example, an electric or hybrid-electric automobile may initiate a stow mode to actively maintain a wheel position (e.g., not moving) on a sloped surface (e.g., hill). By way of another example, a wind turbine may initiate a stow mode to actively maintain blade positions (e.g., not moving) during high wind speed events. As used herein, “propeller stow mode” and “stow mode” may be understood to be interchangeable and equivalent, wherein “propeller stow mode” refers to a “stow mode” as applied to an aircraft.

[0146] In some embodiments, implementing the first switching sequence and / or using the second switching sequence may include commanding the inverter circuits to change respective switch states with a frequency of at least 1 kHz.

[0147] In step 1508, process 1500 may include implementing a second switching sequence (e.g., different from the first switching sequence) during the propeller stow mode. For example, the inverter circuits may switch using reduced SVM (e.g., as depicted in and described with reference to Figs. 10A-14B). In some embodiments, the vertical flight mode, propeller stow mode, or both, may correspond to an aircraft being airborne. For example, a vertical flight mode may correspond to a flight mode as described above (e.g., including taking off or landing), and the propeller stow mode may correspond to another flight mode as described above (e.g., horizontal flight, cruise). The second switching sequence may include fewer switching vectors than the first switching sequence. For example, the second switching sequence may include two active vectors and one zero vector (e.g., as described and exemplified above with respect to Figs. 10A and 10B, or Figs. 13A and 13B). Further, the second switching sequence may include one active vector and one zero vector (e.g., as described and exemplified above with respect to Figs. HA and 11B). Moreover, the second switching sequence may include three non-adjacent active vectors (e.g., as described and exemplified above with respect to Figs. 12A and 12B). In general, the second switching sequence may include any of the disclosed switching sequences that involve a fewer number of switching vectors and / or a fewer number of instances of switching in a single period.PATENTAgent Ref. 16497-0029-00304

[0148] In some embodiments, a mode may be based on one or more of a pilot command, tilt angle of at least one EPU, thrust from at least one EPU, thrust vector direction, airspeed of an aircraft, etc. For example, responsive to receiving a pilot command indicating a propeller stow mode, at least one processor may control one or more EPUs (e.g., tilter EPUs) using the second switching sequence. By way of another example, responsive to receiving a measurement from one or more sensors indicating a horizontal airspeed that exceeds a predetermined threshold, at least one processor may control one or more EPUs (e.g., tilter EPUs) using the second switching sequence. In some embodiments, a mode of operation may include a phase of flight, as discussed above.

[0149] Additional aspects of the present disclosure may be further described via the following clauses:1. A computer-implemented method for controlling an inverter circuit, comprising: receiving, by at least one hardware processor, a first signal indicating a vertical flight mode; implementing, by the at least one hardware processor, a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing, by the at least one hardware processor, a second switching sequence to control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.2. The method of clause 1, wherein the second switching sequence includes switching between two active vectors and one zero vector.3. The method of clause 2, wherein the zero vector is implemented using a three-phase short configuration.4. The method of clause 2, wherein the zero vector is implemented using a six-switch open configuration.5. The method of any preceding clause, wherein the second switching sequence includes commanding, by the at least one hardware processor, one or more switches of the inverter circuit to switch between an active vector and a zero vector.6. The method of clause 5 wherein the second switching sequence includes implementing, by the at least one hardware processor, a dynamic mode of control, the dynamic mode of control comprising:PATENTAgent Ref. 16497-0029-00304 determining, by the at least one hardware processor, the active vector based on an angle associated with a propeller, wherein the active vector is associated with a predetermined angle; determining, by the at least one hardware processor, a zero vector that is most similar to the active vector; and commanding, by the at least one hardware processor, one or more switches of the inverter circuit to switch between the active vector and the zero vector.7. The method of clause 5 or 6, wherein the zero vector is implemented using a three-phase short configuration.8. The method of clause 5 or 6, wherein the zero vector is implemented using a six-switch open configuration.9. The method of any preceding clause, wherein the second switching sequence includes switching between three non-adjacent active vectors.10. The method of any preceding clause, wherein the second switching sequence includes switching between two non-adjacent active vectors and one zero vector.11. The method of clause 10, wherein the zero vector is implemented using a three-phase short configuration.12. The method of clause 10, wherein the zero vector is implemented using a six-switch open configuration.13. The method of any preceding clause, wherein the second switching sequence includes switching between one or more active vectors and one zero vector, wherein the one or more active vectors are implemented as a burst of pulses.14. The method of clause 13, wherein the burst of pulses are implemented responsive to determining, by the at least one hardware processor, that an angle of a propeller exceeds a predetermined threshold.15. The method of clause 13 or 14, wherein the zero vector is implemented using a three- phase short configuration.16. The method of clause 13 or 14, wherein the zero vector is implemented using a six-switch open configuration.17. The method of any preceding clause, further comprising, during the propeller stow mode: commanding, by the at least one hardware processor and during the propeller stow mode, a first set of six switches to open to a six-switch open configuration; andPATENTAgent Ref. 16497-0029-00304 commanding, by the at least one hardware processor and during the propeller stow mode, a second set of six switches to switch based on the second switching sequence.18. The method of clause 17, wherein the operations further comprise, after a predetermined period of time: commanding, by the at least one hardware processor and during the propeller stow mode, the first set of six switches to switch based on the second switching sequence; and commanding, by the at least one hardware processor and during the propeller stow mode, the second set of six switches to open to a six-switch open configuration.19. A non-transitory computer-readable medium storing instructions that, when executed by at least one hardware processor, cause the at least one hardware processor to perform operations comprising the method of any one of clauses 1-18.20. A system, comprising: an inverter circuit; at least one hardware processor; and a non-transitory computer readable medium storing instructions that, when executed by at least one hardware processor, cause the at least one hardware processor to perform operations comprising the method of any one of clause 1-18.21. An aircraft, comprising: an electric propulsion unit (EPU); and the system of clause 20, wherein the EPU is controlled by the inverter circuit.22. The aircraft of clause 21, wherein the propeller stow mode is associated with a horizontal flight mode.23. The aircraft of clause 21 or 22, wherein a number of EPUs is twelve.24. The aircraft of clause 23, wherein a number of inverter circuits is twenty four, wherein each EPU is controlled by two inverter circuits.

[0150] The foregoing description has been presented for purposes of illustration. It is not exhaustive and does not limit the invention to the precise forms or embodiments disclosed. Modifications and adaptations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments of the inventions disclosed herein.

[0151] The features and advantages of the disclosure are apparent from the detailed specification, and thus, it is intended that the appended claims cover all systems and methodsPATENTAgent Ref. 16497-0029-00304 falling within the true spirit and scope of the disclosure. As used herein, the indefinite articles “a” and “an” mean “one or more.” Similarly, the use of a plural term does not necessarily denote a plurality unless it is unambiguous in the given context. Words such as “and” or “or” mean “and / or” unless specifically directed otherwise. Also, words such as “be” or “is” or “are” may refer to “include” or “includes” unless specifically directed otherwise. As used herein, unless specifically stated otherwise, being “based on” may include being dependent on, being interdependent with, being derived from (e.g., using), being associated with, being defined at least in part by, being influenced by, occurring upon, occurring after, and / or being responsive to. As used herein, “related to” may include being inclusive of, being expressed by, being indicated by, or being based on. Further, since numerous modifications and variations will readily occur from studying the present disclosure, it is not desired to limit the disclosure to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the disclosure.

[0152] Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the implementations disclosed herein. It is intended that the architectures and circuit arrangements shown in figures are only for illustrative purposes and are not intended to be limited to the specific arrangements and circuit arrangements as described and shown in the figures. It is also intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims. The foregoing description has been presented for purposes of illustration. It is not exhaustive and does not limit the invention to the precise forms or embodiments disclosed. Modifications and adaptations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments of the inventions disclosed herein. It is also intended that the sequence of steps shown in figures is only for illustrative purposes and is not intended to be limited to any particular sequence of steps. Moreover, steps may be combined from multiple different figures into a single embodiment. As such, those skilled in the art can appreciate that these steps can be performed in a different order while implementing the same method.

Claims

PATENTAgent Ref. 16497-0029-00304CLAIMS:

1. A method for controlling an inverter circuit, comprising: receiving a first signal indicating a vertical flight mode; implementing, by at least one hardware processor, a first switching sequence to control the inverter circuit during the vertical flight mode, wherein the first switching sequence includes two zero vectors and six active vectors; receiving a second signal indicating a propeller stow mode; and implementing, by the at least one hardware processor, a second switching sequence to control the inverter circuit during the propeller stow mode, wherein the second switching sequence includes fewer switching vectors than the first switching sequence.

2. The method of claim 1, wherein the second switching sequence includes switching between two active vectors and one zero vector.

3. The method of claim 2, wherein the zero vector is implemented using a three-phase short configuration.

4. The method of claim 2, wherein the zero vector is implemented using a six-switch open configuration.

5. The method of any preceding claim, wherein the second switching sequence includes commanding, by the at least one hardware processor, one or more switches of the inverter circuit to switch between an active vector and a zero vector.

6. The method of claim 5 wherein the second switching sequence includes implementing, by the at least one hardware processor, a dynamic mode of control, the dynamic mode of control comprising: determining, by the at least one hardware processor, the active vector based on an angle associated with a propeller, wherein the active vector is associated with a predetermined angle; determining, by the at least one hardware processor, a zero vector that is most similar to the active vector; and commanding, by the at least one hardware processor, one or more switches of the inverter circuit to switch between the active vector and the zero vector.

7. The method of claim 5 or 6, wherein the zero vector is implemented using a three-phase short configuration.

8. The method of claim 5 or 6, wherein the zero vector is implemented using a six-switch open configuration.PATENTAgent Ref. 16497-0029-003049. The method of any preceding claim, wherein the second switching sequence includes switching between three non-adjacent active vectors.

10. The method of any preceding claim, wherein the second switching sequence includes switching between two non-adjacent active vectors and one zero vector.

11. The method of claim 10, wherein the zero vector is implemented using a three-phase short configuration.

12. The method of claim 10, wherein the zero vector is implemented using a six-switch open configuration.

13. The method of any preceding claim, wherein the second switching sequence includes switching between one or more active vectors and one zero vector, wherein the one or more active vectors are implemented as a burst of pulses.

14. The method of claim 13, wherein the burst of pulses are implemented responsive to determining, by the at least one hardware processor, that an angle of a propeller exceeds a predetermined threshold.

15. The method of claim 13 or 14, wherein the zero vector is implemented using a three- phase short configuration.

16. The method of claim 13 or 14, wherein the zero vector is implemented using a six-switch open configuration.

17. The method of any preceding claim, further comprising, during the propeller stow mode: commanding, by the at least one hardware processor and during the propeller stow mode, a first set of six switches to open to a six-switch open configuration; and commanding, by the at least one hardware processor and during the propeller stow mode, a second set of six switches to switch based on the second switching sequence.

18. The method of claim 17, further comprising, after a predetermined period of time: commanding, by the at least one hardware processor and during the propeller stow mode, the first set of six switches to switch based on the second switching sequence; and commanding, by the at least one hardware processor and during the propeller stow mode, the second set of six switches to open to a six-switch open configuration.

19. A computer-readable medium storing instructions that, when executed by at least one hardware processor, cause the at least one hardware processor to perform operations comprising the method of any one of claims 1-18.

20. A system, comprising: an inverter circuit; andPATENTAgent Ref. 16497-0029-00304 at least one hardware processor configured to perform operations comprising the method of any one of claim 1-18.

21. An aircraft, comprising: an electric propulsion unit (EPU); and the system of claim 20, wherein the EPU is controlled by the inverter circuit.

22. The aircraft of claim 21, wherein the propeller stow mode is associated with a horizontal flight mode.

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