CCTV has reported successful underwater drone launches by us aircraft carriers and nuclear submarines.
European union member states and Israel are on the edge of developing drones.
Because in the future airspace will be dominated by drones.
The application of rare earth permanent magnet in uav is introduced below.
With the progress of rare earth permanent magnet materials, power electronics, microelectronics, microcomputer, new control theory and motor theory, the technology of rare earth permanent magnet motors has developed rapidly, showing a wide application prospect and strong vitality in the field of aviation.
The application of rare earth permanent magnet motor in aviation has the following characteristics:
1. Due to the high magnetic energy product of rare earth permanent magnet materials, the weight and volume of the motor can be significantly reduced.
Aviation motor has very strict requirements on its volume and weight.
In modern aircraft, about 15 to 30 kg of additional weight is required for each 1 kg of equipment.
2. Rare earth permanent magnet materials have high coercivity Hc and large residual magnetic Br, which can produce a large air gap flux and greatly reduce the outer diameter of the permanent magnet rotor, thus reducing the inertia of the rotor, reducing the time constant and improving the dynamic characteristics of the motor.
3. The air gap width can be selected as a larger value, which can reduce the torque fluctuation caused by tooth groove effect and inhibit the influence of armature reaction on torque fluctuation.
The armature reaction has little demagnetic effect on rare earth permanent magnet, so it is more suitable for the special performance requirements such as sudden reversal and blocking drive.
4, the use of brushless dc motor also has the following significant features:
Long service life.
Brush-dc motors are now widely used in aircraft and have a life span of only a few hundred hours.
With the continuous development of aviation technology, each aviation motor factory is facing the technical pressure of prolonging product life.
When the life requirements to 1000 to 2000 hours, brush dc motor with its own characteristics can not meet the requirements.
Brushless dc motor without brush and commutator, can greatly improve the life index.
Suitable for high speed operation.
The higher the speed, the smaller the volume and weight of the motor can be made.
However, due to the limitation of mechanical commutation, the speed of brush-dc motor can hardly be further improved on the existing basis.
The speed of brushless dc motor can increase exponentially under the condition that bearing allows.
High reliability.
High altitude reversing cremation increases, which affects the reliability and is not conducive to electromagnetic compatibility.
High - altitude brush wear, toner effect insulation performance, reduce the life of the motor.
Brushless dc motor does not have these problems.
Easy to dissipate heat.
The main heat source of brushless dc motor is on stator, and the natural heat dissipation condition is good.
At the same time, oil or water cooling can be carried out conveniently in the stator shell, especially oil cycle or oil injection cooling can greatly improve the power density of the motor.
This is very dangerous for brushless dc motors.
Easy redundancy control.
The reliability weakness of brushless dc motor lies in the controller and motor winding.
The weak link of brushless dc motor is commutating, and it is difficult to control the redundancy of single-axis output.
Rare earth permanent magnet materials have high intrinsic coercivity and good magnetic field orientation, so it is easy to establish magnetic field similar to rectangular wave in air gap, realize square wave drive, and improve motor output.
Because the rare earth permanent magnet motor has a series of advantages mentioned above, it is very suitable for the aviation field with special requirements on performance, volume and weight.
Especially rare earth permanent magnet brushless dc motor is considered as the most promising motor in aviation field.

Ii. Application status of rare earth permanent magnet motors in aviation
In developed countries, rare earth permanent magnet motors have been widely used in aviation, but their domestic application lags behind. So far, only a few new types of aircraft have been used.
The main applications of rare earth permanent magnet motors in aircraft are various electric actuation systems.
Electric power actuating system is a driving system with motor as the executive component, which is widely used in aircraft flight control system, environmental control system, brake system, fuel and starting system, etc.
The actuating systems used in aircraft are hydraulic, electric, pneumatic and mechanical.
Among them, hydraulic actuating system is the most widely used;
But the most promising actuating system is electric actuating system.
With the development of rare earth permanent magnet materials, high-power semi-conductor devices and microprocessors, the power actuating system has developed to compete with the hydraulic actuating system.
(1) flight control system
The electrical actuation system used in the flight control system, also known as the power telex actuator, is mainly used for the operation of the wing and rudder.
It is mainly divided into electro-hydraulic actuator and electromechanical actuator.
In the mid-1970s, the frequent failure of the hydraulic system of American helicopters in important international events prompted them to conduct research and development of the rare earth permanent magnet electric steering gear.
General electric, vexcor and HR derkstrang developed the electro-hydraulic actuator for the next generation of flight control rudder using ndfeb permanent magnet brushless dc motor technology.
The high voltage dc rare earth permanent magnet brushless dc motor technology and pulse width modulated power converter technology are used in the electromechanical actuator.
Motor controller receives the control commands from the aircraft flight control computer, after three-channel rudder servo amplifier circuit system of comprehensive and amplifier, signal processing, and then corresponding the output Angle of steering gear drive system in order to control the aircraft rudder and aileron rudder surface deflection, which changes the aircraft's attitude and heading, to realize automatic flight control system for aircraft flight control.
(2) electric environment control system
The electric environment control system adopts electromechanical actuation technology, which is characterized by high power and high speed variable speed drive motor.
The United States began to develop an electric steam circulating environmental control system in 1982, which was tested on p-3 anti-submarine aircraft.
The system USES a rare earth permanent magnet brushless dc motor with variable speed of 30,000-70000 r/min to drive the compressor.
The samarium-cobalt permanent magnet motor outputs 34.3 kW power at 45,000 r/min.
Domestic environment has also developed the electric control system of electric valve, rare earth permanent magnet brushless dc motor by the motor directly with the hall of the rotor position sensor output signal of indirect measurement of motor speed, motor in a wide range of high-precision steady speed varying load conditions, without the need for pure speed sensors, solved the original have a dc electric field series motor drive the time when the electric valve control precision problem.
(3) air oxygen production system
Oxygen concentrator is an important airborne equipment of advanced aircraft, which provides life endurance for pilots.
Only four countries, including the United States, have the technology.
The oxygen concentrator has been developed successfully in our country.
The motor used is a low-speed, high-precision brushless dc motor speed stabilizing system, which USES samarium cobalt permanent magnet excitation to drive the valve to rotate at 6 r/min.
(4) electric brake system
The electric brake system was developed in 1982 and tested on the a-10 attack plane.
In 1990, the third generation electric brake system was completed, which adopted large torque samarium cobalt permanent magnet brushless dc motor and pulley worm actuator.
1998 the U.S. f-16 fighter jet flew a new electric brake system.
Four rare earth permanent magnet brushless dc motors are used in the electric actuator of the system.
Because of the brushless motor and low inertia components, the response frequency of electromechanical actuator is 20~30 Hz, while that of hydraulic actuator is only 10 Hz.
The electric brake system can reduce the weight of fighter by 22.5~45kg.
(5) fuel system
System of hydraulic pumps, hydraulic valves in the past mostly used brush dc motor drive.
Brushless dc motor is now used.
The motor is immersed in fuel oil with the pump, and the controller is installed with the motor body in the same case, completely sealed.
The motor USES high-temperature ndfeb or smco permanent magnet and 1J22 high-permeability stator core material, which has digital control of speed closed-loop and soft start function.

Iii. Development trend of aviation rare earth permanent magnet motor
1. Rare earth permanent magnet brushless dc motor
Due to the unique advantages of rare earth permanent magnet brushless dc motor, its application speed in aircraft is also accelerating.
Both in function and performance are developing to a higher level.
In terms of reliability, redundancy technology is getting more and more attention.
Development of redundancy design technology, fault tolerant control technology, fault reconstruction technology.
Two kinds of redundancy forms are commonly developed: parallel type and serial type.
The parallel type is characterized by only one set of stator rotor, two sets of independent armature windings are embedded in the stator core, and each set of armature windings are connected to their respective controllers respectively. The two controllers are completely symmetrical and conduct fault monitoring with each other, forming a parallel type double redundancy structure.
The structure of serial type is characterized by the coaxial and identical shell installation of two independent motor bodies, forming a series type double redundancy structure.
The armature windings of each motor are connected to their respective controllers. The two controllers are completely symmetrical, and they monitor and coordinate with each other.
A variety of techniques are used to reduce volume and weight.
One is to improve the insulation grade, improve the magnetic steel high temperature resistance demagnetization ability.
Second, improve the working speed, using magnetic levitation, air levitation technology;
The third is to improve the cooling conditions by adopting circulating water cooling, circulating oil cooling, oil injection cooling, stator unilateral cooling, stator and rotor bilateral cooling and other technologies.
In addition, high power and high voltage direct current is one of the important development directions.
Rare earth permanent magnet limited angular torque motor
The motor can drive the load directly in a certain range of angles for fast movement and accurate positioning.
Its characteristics are: in the limited Angle of output, fast response, high positioning accuracy, high reliability, small volume, light weight.
With the motor as the core, a special high precision and high reliability position servo system can be composed.
The system is composed of rare earth permanent magnet finite torque motor, position sensor and controller.
The motor consists of single redundancy permanent magnet rotor and double redundancy winding stator, and the controller consists of double redundancy control circuit corresponding to the motor winding.
The system can work normally under the condition of double redundancy or single channel, thus greatly improving the reliability of the system.
When the operating range is ± theta °, the motor can achieve the maximum torque output under the minimum volume through special design, and obtain a wide range of frequency response characteristics.
It is because of the unique advantages of this system that foreign countries began to study this aspect in the late 1980s and has been successfully applied in the aerospace field.
The system in the flight control system and electric brake system, can be used as a new direct drive actuator drive system, directly drive the actuator servo valve open, rather than drive through the gear reduction drive;
Thus, the error of the gear train drive system can be overcome, and the shortcomings of the hydraulic drive system can be reduced.
Rare earth permanent magnet brushless dc motor
Brush dc motor is still the most widely used motor in aircraft in China.
Although the motor has some inherent shortcomings, but because of its relatively low cost, mature technology, good characteristics, so in some systems still play an important role, and continue to seek technological progress.
Using rare earth permanent magnet excitation can effectively improve the power density;
Adopting multiple redundancy forms to improve fault tolerance;
Adopt multi-alloy precious metal brush and commutator to improve commutating performance and prolong service life;
The hollow cup armature structure is adopted to reduce the moment of inertia.
4. Rare earth permanent magnet linear motor
The electro-hydraulic servo valve, oxygen valve, emergency oil drain valve, electric valve, the engine throttle lever load thrust linear motion occasions is not large, use the worm gear and worm institutions or rotating screw structure only wants to make rotation movement into linear motion, but I don't adapt to the plane fast actuation valve high reliability, high frequency and direct drive performance requirements.
Hybrid Linear Stepping Motor (HLSM) is a digital impulse Motor that converts pulse signal into Linear motion with small step distance. It can achieve precise positioning control even under open-loop condition without Linear displacement sensor.
The motor has the advantages of simple structure, long travel distance, energy saving, low temperature rise, easy digital control, no cumulative positioning error, small inertia, strong interchangeability and direct drive.
The motor is a high-torque linear motor. The rare earth permanent magnet sheet is embedded in the plane of stator teeth facing the air gap, and the rotor is designed as an induction form.
Due to the effect of inductive rotor teeth, this kind of motor is suitable for the occasion of low speed and high torque.
The key technologies include stability control to reduce thrust fluctuation, stroke end impact and noise elimination.
5. Rare earth permanent magnet generator
At present, 500 ~ 2000 VA rare earth permanent magnet synchronous generator series for uavs and 45 ~ 150 kVA large capacity rare earth permanent magnet generator for airborne power system have been developed at home and abroad.
In order to meet the increasingly high demand of aviation power supply quality, an adaptive compound excitation rare earth permanent magnet generator is attracting more and more attention at home and abroad.
The generator combines the characteristics of rare earth permanent magnet and electric excitation generator, and has high efficiency and good voltage self-adjustment ability.
Rare earth permanent magnet double salient pole motor
Rare earth permanent magnet double salient pole motor is a new type of motor developed on the basis of switched reluctance motor. Rare earth permanent magnet is implanted in stator or rotor, which has higher output torque, high reliability and fault tolerance, so it shows a good application prospect in aviation field.

Four, conclusion
Although a lot of researches have been carried out in the field of rare earth permanent magnet motor for aviation in China, there are still many gaps between the speed and scale of practical application and the technical level and engineering application level of developed countries.
Further efforts should be made in the following areas:
1. Further improve reliability and accelerate the pace of engineering application.
Especially in rare earth permanent magnet high temperature anti-demagnetization ability, control circuit, position sensor reliability test and exploration;
2. Develop high performance rare earth permanent magnet motor speed regulation system and servo system with high precision and wide speed ratio to meet the needs of high precision power actuation system;
3. Research on redundant (three redundant, four redundant) electric actuation technology to replace hydraulic actuation technology;
4. Study the high performance and practical control strategy of rare earth permanent magnet motor servo system.