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Application of Rare Earth Permanent Magnet Materials in Micro Motors (1)
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Application of Rare Earth Permanent Magnet Materials in Micro Motors (1)

Application of Rare Earth Permanent Magnet Materials in Micro Motors

Motors, transmissions and generators excited by permanent magnet materials work based on Faraday's law and Lorentz force. The magnetic properties of permanent magnet materials are remanence, coercivity, magnetic energy product, demagnetization curve shape, and temperature stability. , Size, weight, volume, manufacturing cost, etc. are the key factors that determine the quality and performance of permanent magnet motors. Generally speaking, the higher the magnetic energy product, the greater the output energy of the motor: the higher the output, the higher the air gap field provided, and the greater the torque of the motor, thereby improving the efficiency of the motor: The stronger the demagnetization ability, the wider the working range; the higher the rectangularity of the demagnetization curve, the smaller the dynamic loss of the motor: the higher the resistivity of the permanent magnet, the smaller the eddy current loss. For the high-precision small and special motors used in modern electronic information technology, the requirements are small size, light weight, large torque, high precision, and good controllability. Therefore, the requirements for permanent magnet materials are high, high, small and small. The installation size, and the price must be competitive. High-performance rare earth permanent magnet materials can meet the requirements of micro permanent magnet motors. The use of high-performance rare earth permanent magnet materials, especially neodymium iron boron permanent magnet materials in micro-permanent magnet motors is the development direction in recent years and a later period, and there have been many successful applications at home and abroad. This article comprehensively introduces these application examples.

1. Transverse magnetic field permanent magnet motor

Transverse magnetic field permanent magnet motor belongs to the category of synchronous motor. It is a brushless DC motor, which was invented by Professor Weh in Germany. The stator cogging structure of the motor and the armature coil are perpendicular to each other in space. The main magnetic flux in the motor is provided by rare earth permanent magnets and circulates along the axis of the motor. Therefore, the size of the stator and the size of the energized coil are independent of each other, within a certain range The internal can be selected arbitrarily. The early transverse motor was a magnetic-concentrating structure. In the ten years after its invention, researchers from various countries improved its complex structure, and combined the manufacturing process to invent flat-plate, magnetic-concentrating and magnetic Resistance type three structure (according to rotor magnet placement method).

The flat-plate structure is that the permanent magnets are evenly distributed on the surface of the rotor, and the adjacent permanent magnets are magnetized into different polarities. The laminated core can be used, which not only reduces the eddy current loss, but also facilitates processing, and can reduce the weight of the motor. The permanent magnets of the magnetism-reducing structure are located inside the rotor. The purpose is to concentrate magnetism. In order to improve the output torque and solve the problems of the stability of the rotor, the stator is made of a double stator structure, and the rotor adopts a bilateral permanent magnet structure. In order to make the coil easy to assemble, simplify the motor structure, save the core material, reduce the positioning torque without affecting the motor performance, in recent years, some people have changed its bilateral structure to a unilateral permanent magnet structure and rotated the original U-shaped stator 90 . When it becomes a C shape, the two teeth are staggered by one pole position, so that the permanent magnet can be fully utilized. The structure of the reluctance transverse magnetic field motor is very similar to that of the flat transverse magnetic field permanent magnet motor, except that its rotor part does not have permanent magnets. In order to reduce magnetic leakage, permanent magnets can be installed on the stator teeth for magnetic shielding, because the rotor of the motor Part of it is not placed with permanent magnets, so that its working principle is the same as that of a reluctance stepping motor. The magnetic flux is closed along the path with the largest magnetic permeability, generating magnetic pulling force and forming electromagnetic torque like reluctance.

At present, the research on the concentrating transverse magnetic field motor is the most widespread in the world, because it has the best output performance and its performance index is much greater than the other two transverse magnetic field motors. Although the structure is more complicated, with the improvement of manufacturing technology, it The most promising. Compared with other motors, the transverse magnetic field motor has the radial magnetic field of the normal motor and the transverse (axial) magnetic field; there is no coupling between the phases, which can be analyzed and controlled; each phase only needs one set of coils, and the winding composition is simple and convenient ; The rotor is composed of iron core punching pieces and rare earth permanent magnets to form a magnetic concentrating structure, which can produce a large air gap magnetic density when no-load, and the design freedom is large. The magnetic circuit size and the number of coil turns can be changed according to the needs, so it is particularly suitable for Low speed, high torque, high power industrial and military applications. Such as wind turbines, water turbines, cruise ships, warships, marine propulsion motors, etc.

2. Rare earth permanent magnet brushless DC motors for hybrid electric vehicles

In recent years, due to increasingly prominent resource and environmental issues worldwide, and soaring oil prices, countries have stepped up the implementation of electric vehicle research and development plans, and hybrid electric vehicles (HEV) and fuel cell vehicles (FCEV) have become new hot spots. Hybrid electric vehicles have both motor-driven and engine-driven systems. This new type of transportation using oil and electricity will be favored by people. The rare earth permanent magnet brushless DC motor is the core component of hybrid electric vehicles. It is the key to realize various working modes and directly affects the performance of hybrid electric vehicles. The basic composition of the rare earth permanent magnet brushless DC motor system for hybrid electric vehicles is the same as that of ordinary brushless motors. It is mainly composed of the permanent magnet motor body, power electronic commutation controller and rotor position sensor. The main feature is the small axial thickness. , Light weight, high output power, high efficiency, integrating electric, power generation and braking functions in one, and can frequently perform electric and power reversible work.

Ford Motor Company uses hybrid electric vehicle technology and advanced new fuel cell batteries to create the industry's first "hybrid fuel cell, zero-emission, high-efficiency" Ford Focus car. It combines the advantages of hybrid technology to improve driving range and power performance with the comprehensive benefits of fuel cells.

3. Rare earth permanent magnet generators for automobiles

With the continuous development of the rural economy, the production of agricultural transport vehicles in my country is increasing, with an annual output of more than 3 million vehicles. At present, the generators used in small agricultural vehicles are mainly permanent magnet AC generators, which have the problem of poor lighting effects at low speeds. This causes such agricultural vehicles to be prone to traffic accidents when driving at night or when the road is poorly turned. The windshield wipers and heaters in the driving shed provide DC power. Therefore, it is necessary to develop a rare earth permanent magnet DC generator device with stable voltage output, low cost, reliable performance, and suitable for various vehicles. The rare earth permanent magnet DC power generation device includes an electronic voltage stabilizer, a generator shell cover, a stator composed of a stator core and coils, and a rotor assembly composed of a rotor shaft, a rotor core and NdFeB permanent magnets.

12 poles are evenly arranged on the rotor core, of which 6 are salient poles at the same interval, and the other 6 are grooved poles. The equivalent NdFeB permanent magnet is fixed on the grooved poles, close to the polarity of the groove of the rotor core, and passes through the rotor. The iron core is led to the salient pole, so that the magnetism of each magnet can be fully utilized, thereby improving the material utilization rate and reducing the production cost. The generator rated voltage is 14V, rated power 200W, rated speed 400r/min, 12 poles, star rotor type. The NdFeB permanent magnet material used has a remanence of 1.12T, a coercivity of 790kA/m, and a maximum energy product of 224~256kJ/m. This kind of power generation device that integrates a generator and an electronic voltage stabilizer and uses high-performance rare earth permanent magnets as magnetic poles can achieve DC constant voltage output, small in size, light in weight, low in cost, safe and reliable in use, and can solve T car (agricultural use) The DC power supply required for the night lighting of automobiles, steering indicators, electric horns, wipers, heaters and other electrical facilities.

4. NdFeB permanent magnet synchronous motors for inverter air conditioners

With the development of society, people have higher and higher requirements for environmental protection and a comfortable environment, so that inverter technology has been introduced into household electrical control. Inverter air conditioners are proposed in this context because inverter air conditioners have control accuracy. High temperature, low temperature fluctuation, energy saving, low noise, etc., which are well received by the market. The core component of the inverter air conditioner is the compressor, and its executive component is an asynchronous motor. Asynchronous motors are low in efficiency and variable frequency controllers are more complex, prompting people to develop new motors to replace them. Research shows that: neodymium iron boron permanent magnet synchronous motors have high performance indicators, low temperature rise, good starting performance, high efficiency, single-phase Compared with the three-phase NdFeB permanent magnet motor, the starting and running performance is better at the rated frequency and below the rated frequency; and above the rated frequency, the frequency conversion effect of the three-phase permanent magnet synchronous motor is better than that of the single-phase permanent magnet synchronous motor. The starting time is short, the speed is stable after synchronization, and there is almost no vibration: if the frequency conversion starting is adopted, the starting frequency gradually rises to high frequency, and the starting and running performance of the three-phase permanent magnet synchronous motor is better. Experiments have proved that the NdFeB permanent magnet synchronous motor is an ideal replacement motor for the asynchronous motor in the compressor of the air conditioner.
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