The development history of rare earth permanent magnet motor
1.The development history of rare earth permanent magnet motor
A motor is a machine that converts mechanical energy and electrical energy into each other. This conversion process is inseparable from the excitation structure of the motor. There are two types of excitation structures for motors: one is current excitation, which relies on copper coil windings to excite currents, similar to electromagnets that generate a magnetic field. The size of the magnetic field depends on the number of turns of the windings and the size of the excitation current. Another is permanent magnet excitation, that is, a magnetic field is provided by a permanent magnet. The size of the magnetic field depends on the magnetic performance of the permanent magnet itself and the volume of the magnet used.
A motor with permanent magnet excitation is a permanent magnet motor. The big limitation of current excitation is that the coil generates a large amount of heat, the temperature of the motor increases, a larger winding space is required, and there is also a large copper loss, which makes the efficiency and specific power of the motor low. For permanent magnet excitation, as long as the magnetic performance of the permanent magnet is high, the above limitations do not exist, and the structure is simple and easy to maintain, especially for some motors with special requirements (ultra-high speed, ultra-high sensitivity) and special environments (explosion-proof, etc.) , permanent magnet excitation has outstanding advantages f2 than current excitation. Therefore, in terms of excitation structure, with the continuous improvement of the performance of permanent magnetic materials and the continuous emergence of new permanent magnetic materials, the permanent magnetic excitation structure will gradually replace the traditional current coil excitation structure. The development of permanent magnet motors is closely related to the development of permanent magnet materials, and the emergence of new permanent magnet materials will greatly promote the rapid development of permanent magnet motors.
The world's first motor is a permanent magnet motor, so the use of permanent magnets to manufacture motors has a long history. Due to the low magnetic properties of the permanent magnet material at that time, the motor made was very bulky, that is, it was replaced by an electric excitation motor. After the 1940s, AlNiCo with high remanence and ferrite permanent magnet materials with high coercivity appeared one after another, and permanent magnet motors gained vitality again, occupying an important position in the field of micro and special motors. However, AlNiCo permanent magnets have low coercivity and are easy to demagnetize, and ferrite permanent magnets have low remanence, which limits their application range.
Until the emergence of the first generation of rare earth permanent magnet alloys (SmCo5) in the late 1960s and the second generation of rare earth permanent magnet alloys (Sm2Co17) in the 1970s, although the raw materials of samarium and cobalt are expensive, the magnetic properties of the magnets are good, which makes the permanent magnet motor. With greater development. In the 1980s, NdFeB rare earth permanent magnets came out. In 1983, it was listed as the world's top ten important scientific and technological achievements and attracted worldwide attention. Due to the abundance of neodymium resources, cheap iron is used to replace expensive cobalt, and the price is relatively low. NdFeB rare earth permanent magnets have good magnetic properties, which greatly promotes the development of permanent magnet motors. Rare earth permanent magnets have excellent magnetic properties, and have the advantages of AlNiCo and ferrite permanent magnets. They have high remanence and coercivity, as well as a large magnetic energy product. The maximum magnetic energy product of rare earth permanent magnet is 5 to 8 times larger than that of AlNiCo; 10 to 15 times larger than that of ferrite; under the same effective volume conditions, it is 5 to 8 times larger than that of electric excitation, second only to Superconducting excitation. And the demagnetization curve is almost a straight line, the recovery curve and the demagnetization curve basically overlap, the anti-demagnetization ability is strong, and the thermal stability is good (samarium cobalt permanent magnet). Significantly improved, compared with electric excitation motors, the specific power (motor output power per unit weight) is more than 40% larger. Rare earth permanent magnets, together with power electronic devices and microcomputers, have been recognized as the three pillars to promote the development of electric motors. The development and application of rare earth permanent magnet motors are promising and promising.
In terms of product structure of permanent magnet motors, in the past period, AlNiCo and ferrite permanent magnets accounted for almost half of the market. In the future, the principle of material interchangeability and competition will be followed, and NdFeB will develop rapidly with its excellent magnetic properties. Ferrite permanent magnets occupy the market of low-end motors with a cheap advantage. The application market of AlNiCo will be relatively reduced, and finally most of them will be replaced by NdFeB. However, due to the high temperature stability of AlNiCo, it will still occupy a place in signal-based micromotors such as high-precision tachometer motors.
2.The development trend of rare earth permanent magnet motors
China is rich in rare earth resources, and the reserves of rare earth mines rank first in the world. The scientific research level of rare earth permanent magnet materials and rare earth permanent magnet motors has reached the international advanced level, giving full play to the advantages of China's rich rare earth resources, vigorously researching and promoting the application of various permanent magnet motors represented by rare earth permanent magnet motors, and accelerating the realization of It is of great significance for our country to enter a well-off society in an all-round way.
Rare earth permanent magnet motors are developing towards high power (high speed, high torque), high functionality and miniaturization, and are constantly expanding new motor varieties and application fields, and the application prospects are very optimistic. In order to meet the needs, the design and manufacturing process of rare earth permanent magnet motors still need to be continuously innovated, the electromagnetic structure will be more complex, the calculation structure will be more accurate, and the manufacturing process will be more advanced and applicable. These complex problems require the application of multidisciplinary theory and systems engineering to optimize design, improve cost performance, and promote the further development of electrical machinery and other disciplines and industries.
3.Advantages of rare earth permanent magnet motors
The rare earth permanent magnet motor is based on the Y series motor, and the motor rotor is embedded with rare earth permanent magnet material. Compared with ordinary motors, it has the following advantages:
1. Small size, light weight and less consumables. Due to the high magnetic energy product and high coercivity of rare earth permanent magnet materials, the miniaturization and light weight of the motor magnetic circuit system are realized. Comparison of motor volume and weight parameters. It can be seen that the volume and weight of the NdFeB permanent magnet motor are greatly reduced and reduced compared with the AlNiCo permanent magnet motor.
Under the same power, the ZYN40 rare earth permanent magnet DC motor is reduced by one frame size compared with the AlNiCo motor, and the weight and volume are 70% and 68% of the AlNiCo motor respectively; compared with the ferrite motor, Reduced by two frame sizes, the weight and volume are 40% and 36% of those of ferrite motors: compared with SZ series electric excitation motors, the weight and volume are 40% of those of electric excitation motors, reduced by two frame sizes
2.Efficient. First, due to the miniaturization of the magnetic circuit system, the windings also become smaller, thereby reducing the copper loss and iron loss of the motor, and improving the efficiency; Synchronous operation, there is no induced current in the rotor winding, and there is no rotor resistance and hysteresis loss; third, there is no excitation current component in the stator current, the power factor is high, the stator current is small, and the copper loss on the stator side is reduced, which improves the motor efficiency. Some people have analyzed], a high-speed brushed motor above 20000r/min, the output power is 316W, the efficiency is 69%, that is, the loss is 31%. Among them, the excitation copper loss is 6%, the excitation loss is 3%, the armature copper loss is 3%, the brush loss is 8%, the armature iron loss is 8%, the mechanical loss is 2%, and the stray loss is 1%.
Induction motors that are widely used, such as refrigerator compressors, air conditioners, washing machines, fans, etc., if the output power is 18.4W, the efficiency is 83%, and the loss is 17%, including the primary winding copper loss 6%, iron loss 7% , the secondary copper loss and stray loss account for 4%: when the output power is 420W and the efficiency is 85%, the loss is 15%, which includes the primary winding copper loss 6%, iron loss 4%, secondary copper loss and stray loss 5% loss.
If a permanent magnet is used to generate a magnetic field (as a rotor) and a brush commutator is not used to form a permanent magnet motor (brushless motor), the losses are only the copper loss of the armature winding, the iron loss of the armature core and the mechanical loss. Therefore, the brush loss unique to the brushed motor and the secondary copper loss caused by the primary current excitation in the brushed motor and the induction motor can be eliminated, which will greatly improve the efficiency of the motor.
3.High power factor. There is no induced current excitation in the rotor of the rare earth permanent magnet motor, the stator winding presents a resistive load, and the power factor of the motor is close to 1; the stator current is reduced, and the efficiency of the motor is further improved. At the same time, the improvement of the power factor improves the quality factor of the power grid, reduces the loss of power transmission and transformation lines, and reduces the power transmission and transformation capacity, saving power grid investment.
4.Large starting torque. In equipment that requires large starting torque (such as oil field pumping unit motors), smaller capacity rare earth permanent magnet motors can be used to replace larger capacity Y series motors, such as 37kW permanent magnet motors to replace 45~55kW Y series motors The motor can better solve the phenomenon of "big horse-drawn trolley", save the investment cost of equipment, and improve the operating efficiency of the system.
5.Good performance indicators. At low load rates (i.e. not operating at the rated point), asynchronous motors suffer severe reductions in efficiency and power factor. When the Y series motor works under 60% load, the efficiency drops by 15%, the power factor drops by 30%, and the power index drops by 4o%. However, the efficiency and power factor of the permanent magnet motor decrease very little. When the motor is only 20% loaded, its performance index is still more than 80% of the full load. The efficiency of the permanent magnet motor maintains high efficiency with a flat change in a large load variation range, and the energy saving effect is outstanding. Especially for the oil field pumping units with large starting load and small running load, the energy saving effect is better.
6.Low temperature rise. There is no copper loss in the rotor winding and almost no reactive current in the stator winding, so the motor temperature rise is low. The excitation current of the electric excitation motor is provided by the winding. Due to the limitation of the temperature rise of the excitation coil, the excitation winding occupies a large space, and the high-performance rare earth permanent magnet excitation can reduce the excitation space and provide a higher average magnetic density of the air gap. The output of the motor can be increased under the same volume.
7.Can be air-gap, easy to form a new magnetic circuit
8.The armature reaction is small and the overload resistance is strong.
4.Application of rare earth permanent magnet motor
Due to the above advantages of rare earth permanent magnet motors, their applications are becoming more and more extensive, and the main application fields are as follows:
1.Rare earth permanent magnet high efficiency and energy saving motor
Focus on the high efficiency and energy saving of rare earth permanent magnet motors. The main application objects are large power consumers, such as rare earth permanent magnet synchronous motors for textile and chemical fiber industries, rare earth permanent magnet synchronous motors for various mining and transportation machinery used in oil fields and coal mines, and rare earth permanent magnet synchronous motors for driving various pumps and fans. Magnetic synchronous motors, etc.
2.Various rare earth permanent magnet motors for vehicles
Rare earth permanent magnet motors for various types of vehicles (cars, motorcycles, trains) are the largest market for rare earth permanent magnet motors. According to foreign statistics, about 70% of permanent magnets are used in automobiles. A luxury car has more than 70 motors for various purposes. Due to the different requirements of various automobile motors, the selected permanent magnet materials are also different. The motor magnets used in air conditioners, fans, electric windows, etc., will still be dominated by ferrite in the future from the perspective of price. Ignition coils, transmissions, sensors, etc. still use Sm-Co sintered magnets, but they will be developed to NdFeB sintered permanent magnets from the perspective of price.
In addition to the above-mentioned automotive components, electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are environmentally friendly cannot be ignored. The brushless synchronous motors used for their drive and power generation mostly use sintered NdFeB permanent magnets with high heat resistance and high magnetic properties.
3.Rare earth permanent magnet motor AC servo system
The system is a mechatronics high-performance speed control system integrating electronics and mechanics. The main body of the system is a self-controlled rare earth permanent magnet synchronous motor. This system is used in CNC machine tools to develop flexible manufacturing technology; it is also used in electric vehicles to replace traditional thermal power vehicles, and the vehicles have no emissions. This is a very promising high-tech industry.
4.Rare earth permanent magnet motor for new household appliances
This field is mainly for the low-power rare earth permanent magnet synchronous motor frequency control system for new air conditioners and refrigerators, rare earth permanent magnet micro DC motors for various small wireless power tools, and rare earth permanent magnets for various power instruments. Magnetic brushless DC motor. Such motors are also in high demand.
5.Applications in Aerospace
The advantages of rare earth permanent magnets make them very suitable for applications in aerospace motors. Although there are still some problems to be solved in some applications of rare earth permanent magnet motors in aviation (such as generator voltage regulation and short-circuit protection, etc.), domestic and foreign experts agree that rare earth permanent magnet motors will be an important development of a new generation of aviation motors. direction.
6.Medical Precision Rare Earth Permanent Magnet Brushless DC Motor
As the power for medical equipment, single-phase AC commutator motors are currently used. This high-speed rotating commutator motor not only has a high failure rate, but also has a short lifespan, high noise, and cannot be sterilized. It is imperative to replace with electronically commutated brushless DC permanent magnet motors, which will effectively improve work reliability, reduce noise and prolong life, which is the key to developing a new generation of medical devices. Such as high-speed micro medical grinding and drilling rigs, used for oral diagnosis and treatment, ENT and orthopedic surgery.
(The above information comes from the Internet, if there is any infringement, please contact the author to change it)