The world’s first motor is a permanent magnet motor that generates an excitation magnetic field by a permanent magnet. The development of permanent magnet motors is actually accompanied by the development of permanent magnet materials.

The carbon steel used at the end of the 19th century has had little improvement in its remanence Br over the past century, and the improvement in energy product is due to the increase in coercivity Hc. The improvement in coercivity is mainly due to the understanding of its nature, the discovery of high magnetocrystalline anisotropic compounds, and the advancement of preparation technology.

In the early 20th century, people mainly used carbon steel, tungsten steel, chromium steel and cobalt steel as permanent magnet materials.

In the late 1930s, the successful development of AlNiCo permanent magnet materials made the large-scale application of permanent magnet materials possible.

In the 1950s, the emergence of barium ferrite not only reduced the cost of permanent magnets, but also expanded the application range of permanent magnet materials to the high-frequency field.

In the 1960s, the emergence of rare earth cobalt permanent magnets opened up a new era for the application of permanent magnets.

In 1967, Strnat et al. of Dayton University in the United States successfully made SmCo5 permanent magnets by powder bonding method, marking the arrival of the era of rare earth permanent magnets. So far, rare earth permanent magnets have gone through the first generation of SmCo5, the second generation of precipitation hardening Sm2Co17, and developed to the third generation of Nd-Fe-B permanent magnet materials.

The current output value of rare earth permanent magnet materials has greatly exceeded that of ferrite permanent magnet materials, and the production of rare earth permanent magnet materials has developed into a large industry.

Characteristics of permanent magnet motors:

The maximum power of permanent magnet motors has reached 1000kW, the minimum diameter is φ0.8mm, the maximum speed is 300000r/min, and the minimum speed is 0.01r/min. With the development of rare earth permanent magnet materials, rare earth permanent magnet motors have the following characteristics compared with electric excitation motors:

Simple structure and high reliability:

The use of rare earth permanent magnets can significantly reduce the weight of the motor and reduce the volume. Eliminating the collector ring and brushes for excitation not only improves the processability of the motor, but also greatly enhances the mechanical reliability of the motor operation and increases its lifespan.

Excellent performance:

Compared with traditional motors, permanent magnet motors have a simple structure. The use of rare earth permanent magnets can also increase the air gap flux density, adjust the motor speed to the optimal value, and improve the power-to-weight ratio. Almost all modern aviation and aerospace generators use rare earth permanent magnet generators.

Excellent control performance:

Due to the high performance of rare earth permanent magnet materials, the torque constant, torque-to-inertia ratio, power density, etc. of the motor are greatly improved. Through reasonable design, the indicators such as rotational inertia, electrical and mechanical time constants can be greatly reduced, which are the main indicators of servo control performance.

In modern permanent magnet motors, the design of permanent magnet magnetic circuits is relatively complete, and the coercive force of rare earth permanent magnet materials is high, so the ability of permanent magnet motors to resist armature reaction and other demagnetization is greatly enhanced, and the control parameters of the motor are greatly reduced with the influence of external disturbances.

Since permanent magnetic materials are used to replace electric excitation, the design of excitation winding and excitation magnetic field is reduced, thereby reducing many parameters such as excitation flux, excitation winding inductance, excitation current, etc., thereby directly reducing controllable variables or parameters.

High efficiency and energy saving:

Rare earth permanent magnet motor is a high efficiency and energy saving product, with an average power saving rate of more than 10%, and the power saving rate of special rare earth permanent magnet motor can be as high as 15% to 20%. Compared with the old series-excited DC starting motor, the neodymium iron boron permanent magnet starting motor developed by GM in the United States has increased its efficiency by 45%. The use of permanent magnet motors and variable frequency speed regulation technology in water pumps, fans, and compressors can save more than 30% of electricity.

The basic structure of rare earth permanent magnet motors is that the rotor is a permanent magnet structure that generates air gap flux, the stator is an armature, and there are multi-phase symmetrical windings. The emergence of rare earth coreless brushless motors is the result of the use of new materials and new processes.

The armature is made of a rigid whole made of materials with excellent heat resistance, which can operate stably for a long time under high temperature and high speed conditions; because the armature has no iron core and small inductance, the hysteresis loss and eddy current loss in the iron core are completely eliminated, and the torque fluctuation caused by the slot effect is eliminated, which has excellent control performance; high operating efficiency, low temperature rise, and wide speed range; the armature of the motor has no slots and adopts a fully plastic-sealed structure, and the noise and vibration are very low when the load is running.

The rare earth permanent magnet coreless motor is a major innovation, and it has achieved “three major” breakthroughs in technology. First, compared with the traditional radial magnetic field structure design, the axial magnetic field structure design is adopted, which greatly improves the power density and torque volume ratio. Second, the new winding process, high-pressure precision die-casting and polymer materials are adopted to effectively reduce the copper loss of the winding. Third, silicon steel sheets are not used as stator and rotor core materials, which eliminates magnetic damping and iron loss, reduces the driving power, and reduces the iron loss heat source.

Future Prospects of Permanent Magnet Motors

Electricity consumption of motor systems accounts for about 60% of the national electricity consumption, of which fans, pumps, compressors and air conditioners account for 10.4%, 20.9%, 9.4% and 6% of the national electricity consumption respectively. Motor systems are large in quantity and widespread in scope, with huge potential for energy saving.

According to statistics from the industry association, the total installed capacity of various types of motor systems in the country is about 700 million kW, and the operating efficiency is generally 10 to 20 percentage points lower than the advanced level abroad, equivalent to a waste of about 150 billion kWh of electricity each year.

The most notable performance characteristics of permanent magnet motors are lightweight, high performance, and high efficiency and energy saving. High-performance rare earth permanent magnet motors are the basis of many new technologies and high-tech industries.

The current status of rare earth permanent magnet motor applications at home and abroad:

(1) Aerospace: The United States has developed a 12.6kW, 9,000r/min rare earth permanent magnet brushless DC motor for driving the elevator ailerons of the space shuttle, with an efficiency of 95%.

(2) Ship electric propulsion: High-performance ships generally use all-electric propulsion systems. Permanent magnet motors are widely used as propulsion motors in electric propulsion systems abroad.

(3) Fan and water pump industry: mainly in oil field power drive systems, power plants and steel production enterprises, the number of mechanical loads such as water pumps and ventilators is the largest. This is also the main occasion for the promotion and application of permanent magnet rare earth motors.

China has promoted the use of rare earth permanent magnet synchronous motors in oil well pumping units, and has formed an annual production capacity of more than 10,000 units. The operation in oil fields is good and has achieved significant technical and economic benefits.

(4) Elevator industry: Most major foreign elevator manufacturers use permanent magnet synchronous motors to drive gearless traction machines. Their efficiency can be as high as 0.9 or above, which is more than 30% energy-saving than the AC asynchronous motor + reduction box structure system. Domestic Mitsubishi Elevator, Hitachi Elevator and Schindler Elevator have all adopted this technology.

At present, permanent magnet motors are developing towards high power (high speed, high torque), high functionality and miniaturization. As a product with broad application prospects in the 21st century, its industrialization level still needs to be improved.

Due to its various excellent performances and characteristics, it is believed that in the near future, it will be widely used in various fields and will penetrate into all aspects of daily life and industrial production. With the country’s attention and investment in the motor field, permanent magnet motors will surely flourish!