Recently, CCTV reported that the US aircraft carrier and nuclear submarine have successfully launched unmanned aerial vehicles (Uavs) underwater. Eu member states and Israel are intensively developing Uavs, because the future airspace will be dominated by Uavs. The following is the application of rare earth permanent magnets on Uavs. With the progress of rare earth permanent magnet materials, power electronics,
microelectronics, microcomputer, new control theory and motor theory, rare earth permanent magnet motor technology has developed rapidly, showing broad application prospects and strong vitality in the field of aviation. The application of rare earth permanent magnet motor in aviation has the following characteristics :
Due to the high magnetic energy product of rare earth permanent magnet material, the motor can significantly reduce the weight and volume. The volume and weight requirements of aero-engines are very strict. In modern aviation aircraft, for every additional kilogram of equipment weight, approximately 15 to 30 kg of additional weight is needed.
2. The coercivity Hc of rare earth permanent magnet material is high, and the remanence Br is large, so it can produce a large air gap flux, greatly reducing the outer diameter of the permanent magnet rotor, thereby reducing the rotor moment of inertia, time constant and dynamic characteristics of the motor.
3. The width of the air gap can be selected to be large, which can reduce the torque fluctuation caused by the cogging effect and inhibit the influence of the armatoid reaction on the torque fluctuation. The armature reaction has little effect on the demagnetization of rare earth permanent magnets, which is more suitable for special performance requirements such as sudden reversal and locked-off drive.
4. The use of brushless DC motor also has the following remarkable characteristics: long service life. At present, a large number of brushable DC motors are used in aircraft, and their service life is only a few hundred hours. With the continuous development of aviation technology, all aviation motor manufacturers are facing technical pressure to extend product life. When the service life is increased to 1000-2000 hours, the characteristics of the brushless DC motor can no longer meet the requirements. Brushless DC motors have no brush and commutator, which can greatly improve the life index. Suitable for high speed operation.
The higher the speed, the smaller the volume weight of the motor can be. However, due to the limitation of mechanical commexation, it is difficult to further improve the speed of brushless DC motors. When the bearing allows, the speed of the brushless DC motor can be doubled. High reliability. The increase of high altitude commutation cremation affects the reliability and is not conducive to electromagnetic compatibility. Brush wear is aggravated at high altitude, and the toner affects the insulation performance and reduces the motor life. Brushless DC motors do not have these problems. Easy to dissipate heat. The main heat source of brushless DC motor is on the stator, and the natural heat dissipation condition is good. At the same time, oil cooling or water cooling can be easily carried out in the stator housing, especially oil circulation or oil injection cooling can greatly improve the power density of the motor. This is very dangerous for brushable DC motors. Redundancy control is convenient. The reliability weakness of the brushless DC motor lies in the controller and the motor winding, and the redundant control mode is flexible. The weak link of the brushable DC motor is the commutation, which makes it difficult to realize the redundant control of the single axis output.
Rare earth materials have high intrinsic coercivity and good magnetic field orientation, so it is easy to establish a magnetic field similar to rectangular wave in the air gap, realize square wave drive, and improve the output of the motor. Due to the above series of advantages, rare earth permanent magnet motors are very suitable for the aviation field with special requirements for performance, volume and weight. Rare earth permanent magnet brushless DC motors, in particular, are considered the most promising motors in the aviation field.
