Field of the invention

[0001] The present invention concerns an electrical powering or drive system for a motor in an electrically driven aircraft.

Background [0002] Electric and hybrid vehicles have become increasingly significant for the transportation of people and goods. Such vehicles can desirably provide energy efficiency advantages over combustion-powered vehicles and may cause less air pollution than combustion-powered vehicles during operation. [0003] Although the technology for electric and hybrid automobiles has significantly developed in recent years, many of the innovations that enabled a transition from combustion-powered to electric-powered automobiles unfortunately do not directly apply to the development of electric or hybrid aircraft. The functionality of automobiles and the functionality of aircraft are sufficiently different in many aspects so that many of the design elements for electric and hybrid aircraft must be uniquely developed separate from those of electric and hybrid

automobiles.

[0004] Flying a manned or unmanned aircraft such an airplane can be dangerous. Problems with the aircraft may result in injury or loss of life for passengers in the aircraft or individuals on the ground, as well as damage to goods being transported by the aircraft or other items around the aircraft.

[0005] Therefore, any changes to an aircraft's design, such as to enable electric or hybrid operation, also require careful development and testing to ensure safety and reliability. If an aircraft experiences a serious failure during flight, the potential loss and safety risk from the failure may be very high as the failure could cause a crash of the aircraft and pose a safety or property damage risk to passengers or cargo, as well as individuals or property on the ground.

[0006] Several systems for driving electric motors of manned or unmanned aircrafts, comprising more reliable and robust electronic control systems already exist.

[0007] WO2019/006469 discloses an electric aircraft comprising a fault- tolerant electrical system designed to optimize concerns related to safety. The electrical system has a plurality of power sources (e.g., batteries) that are connected to other electrical components, such as motors for driving propellers or flight control surfaces, by a plurality of electrical buses. Each of such buses is electrically isolated from the other buses to help the system better withstand electrical faults. However, this electrical aircraft does not comprise an electrical system with a redundant motor controller to improve the reliability of the electrical system.

[0008] In order to attempt to mitigate potential problems associated with an aircraft, numerous organizations have developed certification standards for ensuring that aircraft designs and operations satisfy threshold safety requirements. The certification standards for electric or hybrid aircraft are further extremely stringent because of the risks posed by new aircraft designs. Designers of aircraft have struggled to find ways to meet the certification standards and bring new electric or hybrid aircraft designs to market.

[0009] Such certification standards have unfortunately had the effect of slowing commercial adoption and production of electric or hybrid aircraft. Electrical hybrid aircraft may, for example, utilize new aircraft designs relative to traditional aircraft designs to account for differences in operations of electric or hybrid aircraft versus traditional aircraft. The new designs however may be significantly different from the traditional aircraft designs. These differences may subject the new designs to extensive testing prior to certification. The need for extensive testing can take many resources, time and significantly drive up the ultimate cost of the aircraft.

[0010] The certification of prototypes may moreover not be sufficient to certify for commercial applications. Instead, a certification of each individual aircraft and its components may be required.

[0011] W02018/053680 discloses, for example, an UAV comprising an electric motor and two controllers for driving the electric motor. The two controllers use different control methods to drive the electric motor and are configured to: select one of the controllers as primary controller to drive the electric motor and the other one of the controllers as a secondary controller; monitor the control of the electric motor; and switch control of the electric motor from the primary controller to the secondary controller if an error condition is detected in the control of the electric motor. The electric motor is however developed primarily for unmanned aerial vehicles and therefore does not provide the highest safety level that can be expected for manned aircraft. Moreover, the vehicle comprises two controllers of different types which usually makes certification of the vehicle more difficult, since two different controllers need to be certified.

[0012] In view of these challenges, attempts to make electric and hybrid aircraft commercially viable have been largely unsuccessful. New

approaches for making and operating electric and hybrid aircraft thus continue to be desired.

[0013] There is therefore a need for simplified, yet robust, components and systems for an electric powered aircraft that simplify and streamline certifications requirements and reduce the cost and time required to produce a commercially viable electric aircraft.

Brief summary of the invention

[0014] It is an aim of the invention to improve the electrical drive system for electrically driven aircrafts. [0015] According to one embodiment of the invention, an electrical drive system for an electrically driven aircraft comprises the following:

a power source;

at least one motor;

a main motor controller using at least one sensor for controlling said at least one motor based on at least one parameter measured with said sensor;

a redundant motor controller for controlling said at least one motor, said redundant motor controller being sensorless.

[0016] In the present application, a motor controller is considered to be sensorless if (apart from the motor coils) it does not comprise any

additional components for determining the position or speed of the rotor. For example, a motor controller without any position or speed encoder or sensor is considered to be sensorless, even if it might comprise other types of sensors.

[0017] In a preferred embodiment, the redundant motor controller does not comprise any sensor of any type, i.e., it is deprived of any position, speed, and/or temperature sensor for example.

[0018] The redundant motor controller is preferably a more simple controller than the main motor controller. For example, being sensorless, the sensors and the cable between the sensors and other electronic components do not need to be certified. Therefore, the certification of the redundant controller is usually easier than the certification of the main controller. Nevertheless, the redundant motor controller permits a control of the motor even if the main motor controller has a failure. Accordingly, since a redundant motor controller is available, a failure of the main motor controller is not critical so that less stringent certification criteria will be applied. Therefore, and unexpectedly, providing two motor controllers of different types makes the system easier to certificate, without any compromise on security. [0019] The redundant controller preferably does not use a field-oriented control. In a preferred embodiment, the redundant motor controller does not use a sinusoidal commutation. In a preferred embodiment, the redundant motor controller does not compute a prediction of the position of the sensor. A redundant motor controller that does not use one or any of those advanced motor control schemes is easier to certify than a motor controller which uses a field-oriented control and/or other methods for generating three sinusoidal waveforms based on a position of the rotor measured with sensors and/or predicted.

[0020] The main motor controller may use a plurality of sensors.

[0021] The main motor controller may measure a plurality of

parameters.

[0022] The parameter or parameters that are measured by the sensor or sensors are preferably parameters of the motor.

[0023] The motor might comprise a rotor.

[0024] The parameter or parameters that are measured by the sensor or sensors might include the speed and/or (angular) position of the rotor.

[0025] At least one sensor might be an encoder, such as a position encoder.

[0026] The redundant motor controller preferably comprises less components than said main motor controller. Certification of a controller with less components is usually easier than certification of a controller with more components.

[0027] The redundant motor controller preferably has a more limited weight and/or volume than the main motor controller. It might be designed for controlling said motor at a lower speed and torque. [0028] The maximal rotation speed of said at least one motor when controlled by the main motor controller is preferably higher than the maximal rotation speed of said motor controlled by the redundant motor controller.

[0029] The maximal torque of said at least one motor when controlled by the main motor controller is preferably higher than the maximal torque of said motor controlled by the redundant motor controller.

[0030] The efficiency of said at least one motor when controlled by the main motor controller is preferably higher than the efficiency of said motor controlled by the redundant motor controller.

[0031] The redundant motor controller is therefore only able to control the motor at lower speed and/or lower torque. This is not an issue, since the redundant motor controller is only used in case of failures of the main motor controller.

[0032] The motor is preferably a three-phase electric motor.

[0033] The motor is preferably a permanent magnet synchronous motor.

[0034] The main motor controller preferably uses a closed loop vector control method to generate three sinus signals dependent on said

parameter, one signal being applied to each of said phase. A closed-loop vector control method allows the motor to be operated in a very efficient way, i.e., with low losses.

[0035] The redundant motor controller is preferably arranged for generating a plurality of non-sinusoidal signals, each signal being applied to one of said phase. Applying non sinusoidal signals to the phases of a permanent magnet synchronous motor is less efficient than using sinusoidal signals, and increase torque ripples. Therefore, non-sinusoidal signals are usually not recommended especially in aeronautics where highly efficient motors are desired. However, generating non sinusoidal signals with a sensorless encoder is easier than generating sinusoidal signals, and does not require complex computations for predicting the position of the rotor at each instant. Therefore, the redundant motor controller will be easier to certificate than the main motor controller.

[0036] The redundant motor controller is preferably arranged for generating non-sinusoidal signals.

[0037] The redundant motor controller is preferably arranged for generating three non-sinusoidal signals, two of each being applied at each time to two phases of the motor.

[0038] The redundant motor controller is preferably arranged for using the voltage induced in the third said phase in order to determine the signals to apply to the two other phases. The redundant motor controller might be arranged for generating stepped signals.

[0039] The redundant motor controller might be arranged for

generating trapezoidal signals.

[0040] In one embodiment, the motor comprises a first rotor, and the electrical drive system further comprises:

a second transducer having a second rotor and drive coils;

a rotor shaft, the first rotor and the second rotor being both attached to said rotor shaft;

a circuit for measuring an electromotive force (EMF) induced in said drive coils of the second transducer when said rotor shaft is rotated by said motor,

wherein said redundant motor controller uses said electromotive force for controlling said motor.

[0041] This embodiment allows a control of the first motor by the redundant motor controller based on the position or speed of its rotor which is determined by the second transducer, without any additional sensor. [0042] The system might comprise a switch for manually activating said redundant motor controller instead of said main motor controller.

Manually means here that the commutation from the main motor controller to the redundant motor controller might be commanded by the pilot, for example when a signal in the cockpit indicates to the pilot a failure of the main motor controller.

[0043] The switch might be connected so as to connect said at least one motor either with the main motor controller or with the redundant motor controller. [0044] The switch might be connected so as to connect said power source either with the main motor controller or with the redundant motor controller.

[0045] The system preferably comprises a main motor controller monitoring system for detecting failures of the main motor controller. [0046] The motor controller monitoring system is preferably distinct from the redundant motor controller. Therefore, a defect redundant motor controller will not trigger a switch from the main motor controller to the redundant motor controller.

[0047] The main motor controller monitoring system might trigger a switch from said main motor controller to said redundant motor controller when a failure has been detected.

[0048] The redundant motor controller preferably comprises only non programmable components, so that its certification will be easier.

[0049] The main motor controller preferably comprises silicon carbides components and a digital signal processor in order to generate drive signals in a very precise and effective way.

[0050] The redundant motor controller might be more conventional. [0051] The redundant motor controller might comprise IGBT

components.

[0052] The system preferably comprises a first cooling system for dissipating heat produced by said main motor controller and a second cooling system for dissipating heat produced by said redundant motor controller.

[0053] The second cooling system is preferably of a different type than the first cooling system, so that a failure of the first cooling system is less likely to affect at the same time the second cooling system.

[0054] The system might comprise a liquid based cooling system for dissipating heat produced by said main motor controller; and an air-based cooling system for dissipating heat produced by said redundant motor controller.

[0055] This disclosure provides at least some approaches for constructing electric powered aircraft from components and systems that have been designed to pass certification requirements so that the aircraft itself may pass certification requirements and proceed to active commercial use.

Brief Description of the Drawings

[0056] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the figures, in which:

^■ Fig. 1 illustrates an aircraft, such as an electric or hybrid aircraft;

^■ Fig. 2 illustrates a simplified block diagram of an aircraft;

^■ Fig. 3 illustrates the components of a system for operating an aircraft; Fig. 4 illustrate an example circuit comprising a power source, one or a plurality of motors, and motor controllers;

^■ Fig. 5 illustrates a simplified block diagram of a drive

system of an aircraft in an embodiment with two distinct transducers.

Detailed Description

[0057] Fig. 1 illustrates an aircraft 100, such as an electric or hybrid aircraft, and Fig. 2 illustrates a simplified block diagram of the aircraft 100. The aircraft 100 includes at least one motor 1 10, a motor controller 222, and a power source 130. The motor 1 10 can be used to propel the aircraft 100 and cause the aircraft 100 to fly and navigate. The motor controller 222 can control and monitor the motor 1 10. The power source 130 can power the motor 1 10 to drive the aircraft 100 and power the motor controller 222 to enable operations of the motor controller 222. The motor controller 222 includes a plurality of controllers, as well as other electronic circuitry for controlling and monitoring the components of the aircraft 100.

[0058] The power source 130 comprises one or more battery packs including multiple battery cells, such as lithium-ion cells. The battery cells can be connected in series and/or in parallel to deliver an appropriate voltage and current.

[0059] Each, some, or one of the at least one motor 1 10 can be a three- phase motor, such as a brushless motor or a permanent magnet

synchronous motor, which is connected via a three phase AC power line RST with the motor controllers 222. However, the at least one motor 1 10 can instead be a different type of motor, such as any type of DC motor or a one phase AC motor. The at least one motor 1 10 can move a vehicle, such as an airborne vehicle like an aircraft. The at least one motor 1 10 can drive a (thrust-generating) propeller or a (lift-generating) rotor. In addition, the at least one motor 1 10 can also function as a generator. The electrical powering system or the at least one motor 1 10 can include two or more electrical motors as described further herein.

[0060] The motor controller 222 can, for example, be connected over a two phase or DC power line with the power source 130 or connected over a three-phase power line with the at least one motor 1 10. The motor controller 222 can transform, convert, or control the power received from the power source into motor driving signals for driving the at least one motor 1 10. The motor controller 222 can include a power converter for converting the DC current of the power source 130 into a (three phase)

(AC) current for the at least one motor 1 10 (power converter working as inverter). The power converter can treat different input DC voltages (if the power source 130 has a plurality of battery packs with different DC voltages). If the at least one motor 1 10 acts as generator, the power controller can convert the current generated from each phase of the at least one motor 1 10 into a DC current for loading the power source 130 (power converter working as rectifier). The motor controller 222 can create the motor driving signals for the at least one motor 1 10 based on user input, for example with a throttle.

[0061] The motor controller 222 can comprise a control circuit and a power stage controlled by the control circuit. The control circuit of the main motor controller can comprise a processor, such as for example a digital signal processor or a FPGA, and a memory for executing a control program, such as a regulation program in order to regulate the speed and torque of the motor(s) in function of parameters measured with sensors 1 15. The control circuit of the redundant motor controller is sensorless and preferably does not include any processor nor any FPGA for regulating the speed and torque of the motor.

[0062] The power stage can include power electronic components, such as IGBTs, MOSFETs, H bridges and/or EMC filters, in order to generate the drive currents sent to the coils of the controlled motor(s) 1 10. The power stage can include silicon carbide components. [0063] As will be described, the motor controller 222 includes one main motor controller 222A and one redundant motor controller 222B.

[0064] In addition, the motor controller 222 can include, for instance, a first controller for powering the at least one motor from at least one of the first battery pack and a second controller for powering the at least one motor from at least one other battery pack.

[0065] As will be described later, the main motor controller 222A is a sensored motor controller and uses at least one sensor 1 15, such as an encoder, Hall sensors, etc. for determining the position and/or speed of a rotor 1 1 10 of the motor 1 10. The motor controller 222A determine the speed and/or position of the rotor 1 1 10 and compare it to the set speed and/or set position that the motor controller is trying to achieve - any discrepancies is then adjusted in a closed loop system.

[0066] The main motor controller 22A preferably generates three sinus drive signals, one drive signal being applied to each phase of the three- phase motor 1 10. A sinus signal means here a signal which has substantially a sinusoidal waveform when the motor 1 10 is controlled at constant speed.

[0067] The redundant motor controller 222B is sensorless and thus does not comprise any sensor 1 15 for determining the position or speed of the rotor 1 1 10. It might control the motor 1 10 in a closed loop system.

Alternatively, the sensorless redundant motor controller 222B might use the back electromotive force (EMF) of the motor 1 10 (i.e., the voltage generated by the motor acting as a generator) or of another motor on the same rotor shaft to determine its speed and/or position and control the motor 1 10 in a controlled-loop system.

[0068] In one embodiment, the redundant motor controller 222B generates three drive signals; at each time, only two of those three drive signals are applied to two of the phases of the three-phases motor 1 10 while the third phase is open, and no signal is applied to it. An

electromotive signal induced in this third phase by the rotation of the rotor is measured in order to determine its speed and/or position and to control the generation of the two signals.

[0069] The redundant motor controller 222B preferably generates non sinusoidal drive signals, such as trapezoidal signals or stepped signals, that are applied to at least two phases of the motor 1 10. Generating non sinusoidal signals does not require any mathematical prediction of the future position of the rotor 1 1 10, so that the redundant motor controller 222B does not rely on failure-prone software methods for generating the drive currents, making the system more robust and easier to certify.

[0070] Fig. 3 illustrates components 200 of a system for operating an aircraft, such as the aircraft 100 of Figs. 1 and 2. The components 200 can include a power management system 210, a motor management system 220, and a recorder 230, as well as a power source 130 comprising one or a plurality of battery packs, one or a plurality of motor controllers 222, one or more motors 100, and a throttle 226.

[0071] The power management system 210, the motor management system 220, and the recorder 230 can monitor communications on a communication bus, such as a controller area network (CAN) bus and/or analog lines, and communicate via the communication bus. The battery pack can, for instance, communicate on the communication bus enabling the power management system 210 to monitor and control the battery pack 212. As another example, the motor controller 222 can communicate on the communication bus enabling the motor management system 220 to monitor and control the motor controller 222. One of the motor controller, for example the main motor controller 222A, can use a CAN bus while the other motor controller might use a communication system that is easier to certificate, such as for example analog lines.

[0072] The recorder 230 can store some or all data communicated (such as component status, temperature, or over/undervoltage information from the components or other sensors) on the communication bus to a memory device for later reference, such as for reference by the power management system 210 or the motor management system 220 or for use in

troubleshooting or debugging by a maintenance worker. The power management system 210 and the motor management system 220 can each output or include a user interface that presents status information and permits system configurations. The power management system 210 can control a charging process (for instance, a charge timing, current level, or voltage level) for the aircraft when the aircraft is coupled to an external power source to charge a power source of the aircraft, such as the battery pack 212.

[0073] The motor management system 220 can provide control commands to the motor controller 222, which can in turn be used to operate the one or more motors 100. The motor controller 222 may further operate according to instructions from the throttle 226 that may be controlled by a pilot of the aircraft. The one or more motors can include an electric brushless motor.

[0074] The power management system 210 and the motor management system 220 may include the same or similar computer hardware. A single hardware may perform both functions.

System Architecture

[0075] Certification requirements can be related to a safety risk analysis. A condition that may occur with an aircraft or its components can be assigned to one of multiple safety risk assessments, which may in turn be associated with a particular certification standard. The condition can, for example, be catastrophic, hazardous, major, minor, or no safety effect. A catastrophic condition may be one that likely results in multiple fatalities or loss of the aircraft. A hazardous condition may reduce the capability of the aircraft or the operator ability to cope with adverse conditions to the extent that there would be a large reduction in safety margin or functional capability crew physical distress/excessive workload such that operators cannot be relied upon to perform required tasks accurately or completely or serious or fatal injury to small number of occupants of aircraft (except operators) or fatal injury to ground personnel or general public. A major condition can reduce the capability of the aircraft or the operators to cope with adverse operating condition to the extent that there would be a significant reduction in safety margin or functional capability, significant increase in operator workload, conditions impairing operator efficiency or creating significant discomfort physical distress to occupants of aircraft (except operator), which can include injuries, major occupational illness, major environmental damage, or major property damage. A minor condition may not significantly reduce system safety such that actions required by operators are well within their capabilities and may include a slight reduction in safety margin or functional capabilities, slight increase in workload such as routine flight plan changes, some physical discomfort to occupants or aircraft (except operators), minor occupational illness, minor environmental damage, or minor property damage. A no safety effect condition may be one that has no effect on safety.

[0076] An aircraft can be designed so that different subsystems of the aircraft are constructed to have a robustness corresponding to their responsibilities and any related certification standards, as well as

potentially any subsystem redundancies.

[0077] In particular, damages to motor controllers 222 can be very serious incidents that may prevent a motor 110 or all motors of the aircraft from working properly, and cause a crash. Therefore, a reliable motor controller system can be critical for the safety of electric airplanes.

[0078] However, motor controllers 222 can have failings in rare occurrences that cause problems with the motor driving and/or with monitoring the condition parameters of the motor controller. For example, power semiconductors used in the inverters may be damaged by

overcurrent, overvoltage, overheating or chocks. In other occurrences, hardware and/or software modules used for monitoring motor parameters fail to work properly or to deliver correct parameters, so that the motors are not controlled correctly or that failures of the motor or of the motor controller is either not detected or not reported correctly. [0079] The present disclosure provides at least approaches to increase the reliability of motor controllers 222 in an electric aircraft. In order to prevent risks of incident due to failures of a motor controller, redundant control of electric motors can be performed with two different motor controllers 222A and 222B of different types, so that at least motor 110 can be controlled with a first motor controller 222A and/or with a second, redundant motor controller 222B for example in case of failure of the main motor controller 222A.

[0080] As an example, and according to Fig. 4, a plurality of motor controllers 222A, 222B are used for redundantly controlling the one or plurality of motors 110, so that even if one of the motor controllers 222A or 222B becomes defective, the one or more motors can still be controlled with the remaining motor controller, at least to insure low speed or low power operation.

[0081] Both motor controllers 222 can be supported by an aircraft housing.

[0082] Both motor controllers 222A and 222B can include solid-state power electronics components for converting the DC current from the battery packs 130 into AC currents, such as for example tri-phase currents R, S, T, required for driving the motor(s). The main motor controller 222A can use silicon carbide components. The redundant motor controller 222B can use more conventional components, such as for example IGBTs.

[0083] Each controller can include one or more power inverters for controlling the speed and/or torque of the motorsl 10 by varying motor input frequency, current and/or voltage.

[0084] The power inverters can be implemented can be, for example, as simple inverters, multilevel inverters or power inverter devices with the possibility of an impedance adjustment using an additional amplifier stage, or any combination between those solutions. [0085] At least the motor controller 222A further comprises hardware and/or software modules for monitoring the power inverters and the other components of the motor controller. Those parameters can be used for controlling the power inverters in real time, for example as input of a feedback loop.

[0086] If both motor controllers 222 are of the same type, a defect or conception flaw that affects one motor controller may also affect the redundant motor controller as well, so that the gain in reliability can be limited. Therefore, in order to increase the reliability of the motor controller function, one of the motor controllers 222A is of a first type and the redundant motor controller 222B is of a different type.

[0087] More complex systems are generally more likely to have defects; therefore, a complex motor controller 222, i.e., a motor controller that comprises many different components, such as one or a plurality of external sensors 1 15 and cables 1 16 between those sensors and other components of the motor controller, is more prone to defect than a simpler motor controller. Such a complex motor controller is also more difficult to certify. On the other hand, a simple motor controller might not offer all the functionalities of a complex controller, or might not be able to drive a motor at full speed or full torque.

[0088] Therefore, in order to increase the reliability of the motor controller function, one of the motor controllers 222A is more complex than the other, redundant motor controller 222B.

[0089] In particular, a first, main motor controller 222A controls the one or more motors 1 10 with a large set of components in order to provide a full set of functionalities in order to control the motor at full speed and/or full torque and/ with an increased efficiency or additional parameters.

[0090] Another, redundant motor controllers 222B can be designed to be simple and robust and thus may be able to satisfy difficult certification standards. The motor controller 222B, for instance, can be composed of a limited number of individual components, so as to reduce the number of individual components and cables or interconnexions 116 to certify.

[0091] A failure of the main motor controller 222A is less catastrophal, since the other redundant motor controller 222B can be used as a backup. Therefore, even if the main motor controller 222A comprises a large set of components, its certification can be made less stringent since a failure of this motor controller is unlikely to have a catastrophic impact as the main motor controller 222A can be easily and immediately replaced by the redundant, simple motor controller 222B.

[0092] According to one aspect, a main motor controller 222A might have a more complex structure than a redundant motor controller 222B redundantly used for driving the same motor or motors 110. In one example, the first motor controller 222A might comprise and use at least one external hardware sensor 115, such as a speed and/or position sensor (encoder), heat sensors, and/or current sensors, for monitoring parameters of the motor. The second, redundant motor controller 222B might be sensorless and be deprived of any external hardware sensors for controlling its operations.

[0093] In one embodiment, the redundant motor controller 222B comprises a motor temperature sensor and/or a motor controller

temperature sensor (not shown) but is nevertheless considered to be sensorless in the present application since it does not comprise or use any position or speed sensor. The temperature sensor can be used for reducing the intensity of the currents delivered to the motor when the temperature of the motor and/or the temperature of the motor controller exceeds a threshold.

[0094] In another embodiment, the redundant motor controller 222B does not comprise any position, speed, temperature or other sensor.

[0095] In one example, the main motor controller 222A can include hardware and/or software modules for monitoring the speed and/or position of the motors, as well as other parameters of the motor(s) 1 10 or of the motor controller 222A itself, and for controlling the currents applied to each coil of each controlled motor in order to achieve the desired rotation speed and/or torque. The hardware modules can comprise at least one sensor 1 15, such as for example speed and/or position sensors for monitoring the rotation speed and/or position of the rotor, and optionnally additional sensors such as temperature sensors, current sensors, etc.

[0096] The main motor controller 222A preferably uses a closed loop vector control method to generate three sinus signals dependent on the parameter(s) measured with the sensor(s), one signal being applied to each of said phase. A closed-loop vector control method allows the motor to be operated in a very efficient way, i.e., with low losses. Moreover, applying sinus signals to the phases of the motor 1 10 allows for a high efficiency mode of operation. It requires however a more complex controller system, such as for example a fast processor or DSP, in order to generate the signals, and is therefore more failure-prone and more difficult to certify.

[0097] The redundant motor controller 222B is sensorless. It can control the moor in an open-loop system (i.e., without any feedback about the current speed or position of the motor). Alternatively, it can detect speed and possibly position of the rotor 1 1 10 for example by measuring and analyzing the back electromotive force (back EMF) generated in the coils when the rotor is rotating. For example, the redundant motor controller 222B can detect zero crossings of the back EMF signal in order to determine the rotation speed of the rotor, and, by interpolating or integrating, its angular position. In one embodiment, the redundant motor controller generates three drive signals, only two of which are applied at each time to the phase coils of the motor 1 10. The zero-crossing of the electromotive signal induced in the third phase by the rotation of the rotor 1 10 is measured in order to determine its speed and/or position and to control the generation of the two drive signals in a closed-loop, sensorless system.

[0098] Because a second, redundant motor controller 222B may include less components, and in particular less or no hardware sensors for monitoring speed and position parameters of the motors, its certification can be easier, and its reliability may be increased. For example, because the second, redundant controller may be sensorless, it can be made simple, easy to certify, and reliable.

[0099] Since the redundant motor controller 222B has no sensors, it can only determine the speed and position of the rotor 1110 when a back EMF signal is generated, for example in the third phase. This makes the control of the motor 110 at 0 RPM difficult, but since the redundant motor controller 222B is only used as a backup in flight when the first motor controller 222A has a failure, this is not problematic. Moreover, since the start torque that is requested for starting the rotation of the rotor 1110 and its associated propeller is very low as compared to the start torque in an electric car for example, the redundant motor controller might be used for starting turning the rotor from 0 RPM.

[00100] The redundant motor controller 222B preferably generates a set of two or three non-sinusoidal drive signals R, S, T that are applied to the phases of the motor 110. For example, the redundant motor controller 222B might generate two or three trapezoid signals or stepped signals. The generation of trapezoidal or stepped signals can be performed without any interpolation or complex mathematical predictions, and is therefore easier to certificate.

[00101] Fig. 5illustrates another embodiment of a drive system for an electric airplane. In this embodiment, the system comprises two transducers 110A and 110B. The first transducer 110A is controlled by the main motor controller 222A or by the redundant motor controller 222B, as previously described. The second transducer 110B is controlled by the main motor controller 223A; in a preferred embodiment, it can also be controlled by the redundant motor controller 223B for example when the motor controller 223A has a failure.

[00102] The main transducer 110A can work as a motor and preferably as a generator for charging at least one battery pack 130, for example at landing. The second transducer 110B can work as a generator for charging at least one battery pack 130, for example at landing, and preferably also as a motor for assisting the main motor 110A when additional power is needed, for example at take-off, and/or for replacing this main motor 110A in case of failure.

[00103] Each of the motors 110A and 110B have a rotor. The two rotors are attached to a common rotor shaft 1110 so that the angular position of the two rotors are related.

[00104] At some instants, the main transducer 110A can be used as a motor for propelling the airplane while the second transducer 110B is either freewheeling or used as a generator, for example in order to charge a battery pack or equilibrate charges between different battery packs. The electromotive force (EMF) induced in this second transducer 110B is measured by a circuit (not shown) that generate a position signal 224 used in the redundant motor controller 222B of the main motor 110A for determining the position or speed of this first motor 110A, and for generating the drive signals that are applied to this first motor 110A.

[00105] The main motor controller 222A might use more complex software modules and/or more complex algorithms to control the motor(s) 110 than the redundant motor controller 222B. For example, the main motor controller can feature a more complex regulation, based on feedback signals provided by at least one sensor 115, than the redundant motor controller that only offers a simple regulation using no sensors.

[00106] The motor controllers 222A, 222B can exchange information in real time with the motor management system 220 in order to control the motor(s) in the desired way, and to send parameters and diagnosis, including parameters measured by the sensor(s), to the motor management system 220. [00107] The second, redundant motor controller 222B can provide for a redundant control of the driven motor(s) 110 and for a redundant transmission of parameters measured on this motor(s).

[00108] The main motor controller 222A may be used to drive the motor(s) 110 at full speed and/or full torque. The redundant motor controller 222B might be used to drive the same motor(s) 110 only up to a more limited speed and/or torque. For example, the redundant motor controller 222B might deliver a maximal power (such as for example 65KW) that is sufficient for driving the motor(s) 110 at a maximum speed (such as for example rpm) and torque required during continuous or cruisier flight, but that would be insufficient for take-off. The first motor controller might deliver a higher maximal power (for example 90KW).

[00109] Since the main motor controller 222A can control the motor at a higher speed and/or torque than the redundant motor controller 222B, and since it may be commuted more often, it might dissipate more heat in its power semiconductors than the redundant motor controller 222B. In one aspect, the main motor controller might comprise a heat dissipating system 111, such as for example a liquid cooling system, that is more efficient than the heat dissipating system 112, such as for example an air-based system, used for cooling the redundant motor controller 222B.

[00110] The heat dissipating system 111 used for cooling the first motor controller 222A is preferably of a different type than the heat dissipating system used for cooling the redundant motor controller 222B. Since two different cooling systems are used, the system is more reliable. Moreover, a defect or conception flaw that affects one cooling system of a first type is less likely to affect the other cooling system of a different type.

[00111] The redundant motor controller 222B might have a more limited weight and volume than the main motor controller 222A, due to the more limited set of components, more limited power it needs to apply to the motor 110, and more limited functionalities. It might also be easier to design a redundant motor controller able to work in a broad range of temperature and/or radiation since this motor controller 222B has less components. Therefore, the addition of this redundant motor controller has only a limited impact on the weight, volume, operability and/or range of the aircraft.

[00112] In one embodiment, the main motor controller 222A and the redundant motor controller 222B share a common electronic power stage, including for example common IGBTs, MOSFETs, H bridges and/or EMC filters, but use two different control circuits for controlling this power stage. In that case, the control circuit of the main motor controller uses a more complex software and relies on external sensors for controlling the speed and torque of the controlled motor(s) 110, while the control circuit of the redundant motor controller uses a simpler regulation, with a more simple software, or no software, and no external sensors.

[00113] The redundant motor controller 222B preferably comprises a switch 2222 for activating it, in replacement of the main motor controller 222A, in case of failure of the main motor controller 222A. This switch can preferably be operated by the pilot and has the effect of powering the redundant motor controller, disconnecting the motor(s) 110 from the main motor controller 222A, and/or connecting the motor controller 222B with the moto(s) 110. The switch might also have the effect of disconnecting the power source (battery pack) 130 from the main motor controller 222A.

[00114] The system can comprise at least one motor controller

monitoring system 113 for detecting failures of at least the main motor controller 222A. In a preferred embodiment, the system comprises one main motor controller monitoring system 1 13 for detecting failures of at least the main motor controller 222A, and optionally one redundant motor controller monitoring system (114) for detecting failures of this main motor controller 222A. The redundant motor controller monitoring system 114 is preferably of a different type than the main motor controller monitoring system 113; in one preferred embodiment, the main motor controller monitoring system 113 uses programmable components and delivers more functionalities than the redundant motor controller monitoring system 114 which uses only non-programmable components, and therefore offers less functionalities but is easier to certifiy.

[00115] The motor controller monitoring system 113 that detects failures of the main motor controller 222A is preferably distinct from the

redundant motor controller monitoring system 114 that detects failures of the redundant motor controller 222B.

[00116] A detection of a failure of the main motor controller 222A by the motor controller monitoring system 113 can trigger an automatic and preferably immediate commutation from the main motor controller 222A to the redundant motor controller 222B.

[00117] The main motor controller 222A and/or the second, redundant motor controller 222B are connected with a digital bus, such as a CAN bus, of the vehicle. The CAN bus can be used for diagnostic purposes of the main motor controller 222A and for controlling the main motor controller using signals sent over the bus from the motor management system 2220 and the throttle 226. The CAN bus can also be used for diagnostic purposes of the redundant motor controller 222B. Preferably, the redundant motor controller cannot be controlled over the CAN bus, in order to keep the certification of this motor controller and of the CAN bus simple.

Additional Features and Terminology

[00118] Although examples provided herein may be described in the context of an aircraft, such as an electric or hybrid aircraft, one or more features may further apply to other types of vehicles usable to transport passengers or goods. For example, the one or more futures can be used to enhance construction or operation of automobiles, trucks, boats, submarines, spacecrafts, hovercrafts, or the like.

[00119] As used herein, the term "sensorless," in addition to having its ordinary meaning, can refer to a component or system or device that can measure a physical parameter without any additional, external sensors. For example, any motor controller that can determine the speed and/or position of a rotor from EMC currents generated in the coils of the motors, without any independent or separate speed or position sensor, is said to be sensorless. A motor controller is also said to be sensorless if the closed-loop control system used for regulating the speed of the rotor does not rely on any external hardware sensors, such as Hall sensors. A motor controller is considered to be sensorless even if it comprises or uses sensors for

determining parameters other than the speed or position of the rotor; for example, a motor controller comprising or using a temperature sensor will be considered to be sensorless.

[00120] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (for example, not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, for instance, through multi threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines or computing systems that can function together.

[00121] The various illustrative logical blocks, modules, and algorithm steps described herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative

components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure. [00122] The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, a microprocessor, a state machine, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a FPGA, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A hardware processor can include electrical circuitry or digital logic circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an FPGA or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. A

computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[00123] The steps of a method, process, or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non-transitory computer- readable storage medium, media, or physical computer storage known in the art. An example storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The storage medium can be volatile or nonvolatile. The processor and the storage medium can reside in an ASIC. [00124] Conditional language used herein, such as, among others, "can," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements or states. Thus, such conditional language is not generally intended to imply that features, elements or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements or states are included or are to be performed in any particular embodiment. The terms "comprising," "including," "having," and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term "or" is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Further, the term "each," as used herein, in addition to having its ordinary meaning, can mean any subset of a set of elements to which the term "each" is applied.