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Rare earth permanent magnet motor is a new type of permanent magnet motor that appeared in the early 1970s.
Due to the excellent magnetic properties of rare earth permanent magnet materials, they can establish a strong permanent magnetic field without external energy after magnetization.
Rare earth permanent magnet motor not only has high efficiency but also has a simple structure and reliable operation. It can also be small in size and light in weight.
Made into special motors that can meet specific operating requirements, such as elevator traction motors, special motors for automobiles, etc.
The combination of rare earth permanent magnet motors with power electronics technology and microcomputer control technology has improved the performance of the motor and transmission system to a new level.
Improving the performance and level of the supporting technical equipment is an important development direction for the motor industry to adjust the industrial structure.
Rare earth permanent magnet motors are widely used in almost every field of aviation, aerospace, national defense, equipment manufacturing, industrial and agricultural production, and daily life.
It includes permanent magnet synchronous motors, permanent magnet generators, DC motors, brushless DC motors, AC permanent magnet servo motors, permanent magnet linear motors, special permanent magnet motors, and related control systems, covering almost the entire motor industry.
On November 22, 2021, the Ministry of Industry and Information Technology and the State Administration for Market Regulation jointly issued the “Motor Energy Efficiency Improvement Plan (2021-2023)”, proposing that by 2023, the annual output of high-efficiency and energy-saving motors will reach 170 million kilowatts, and the proportion of the high-efficiency and energy-saving motors in service reached more than 20%, and the annual electricity saving was 49 billion kWh.
The document clearly mentions that “For fans, pumps, compressors, machine tools, and other general-purpose equipment, encourage the use of electric motors with energy efficiency level 2 and above.
For variable load operating conditions, promote variable-frequency permanent magnet motors with energy efficiency level 2 and above.”
According to the 2013 version of the “Permanent Magnet Synchronous Motor” standard, the current production of permanent magnet motors is distributed in the first-level and second-level energy consumption intervals; combined with the “Motor Energy Efficiency Limits and Energy Efficiency Grades” (GB 18613-2020) and “Motor Energy Efficiency Improvement Plan”, only some high-performance NdFeB rare earth permanent magnet motors can reach the efficiency of more than 95% of the first-level energy consumption standard (corresponding to IE5), and the rest of the rare-earth permanent magnet motors belong to the second-level energy consumption standard.
At present, rare earth permanent magnet motors can save more than 10% of electricity and increase their efficiency to more than 95%.
Using rare earth permanent magnet synchronous motor, the power saving rate of reactive power can reach 85%, and the power saving rate of active power can reach 23%~25%. The power-saving effect is remarkable.
Industrial motors are the areas that consume the most electricity in society.
In 2020, China’s motor holdings will be about 4 billion kilowatts, and the total power consumption will be about 4.8 trillion kwh, accounting for 64% of the total electricity consumption of the whole society.
Among them, the total power consumption of motors in the industrial field will be 3.84 trillion kWh, Accounting for 75% of industrial electricity consumption, every 1% increase in the energy efficiency of motors in the industrial field can save about 38.4 billion kWh of electricity per year, and a 3% increase in energy efficiency is equivalent to the annual power generation of the Three Gorges.
The State Council issued the “2030 Carbon Peak Action Plan”, which focuses on promoting energy conservation and efficiency enhancement of key energy-consuming equipment, focusing on motors, fans, pumps, compressors, transformers, heat exchangers, industrial boilers and other equipment to comprehensively improve energy efficiency standard.
High-efficiency and energy-saving motors refer to general-purpose standard motors with high-efficiency
In May 2020, China announced the latest motor energy efficiency standard “GB18613-2020 Motor Energy Efficiency Limits and Energy Efficiency Grades”, the standard is officially implemented on June 1, 2021, and energy-efficient motors below IE3 (international standard) were forced to stop production.
Motor types include three-phase asynchronous motors, rare earth permanent magnet motors, etc. Traditional asynchronous motors can be increased by increasing materials (increasing the outer diameter of the iron core, increasing the size of the stator slot, increasing the weight of copper wires, and using silicon steel sheets with good magnetic permeability).
However, due to its basic working principle, it is difficult to improve the efficiency of traditional asynchronous motors. For example, some IE4 and IE5 energy-efficient motors prefer to use permanent magnet mode.
More importantly, compared with asynchronous motors, rare earth permanent magnet motors have natural energy-saving advantages.
1) Energy saving:
Different from the asynchronous motor, the rotor of the permanent magnet motor does not need an excitation current, and the energy saving is about 15%-20%.
2) High efficiency:
The efficiency of permanent magnet motors is 2-19 percentage points higher than that of traditional motors.
3) Simple structure and low failure rate.
4) Long life:
The rotor of the permanent magnet motor adopts an embedded sealed structure, which is beneficial for reducing friction and oxidation during rotation and improving the stability and life of the motor.
The recovery cycle of replacing rare earth permanent magnet motors is about 1-2 years, and the economic benefits are actually obvious.
A permanent magnet motor is a DC/AC synchronous motor in which the stator is a permanent magnet and only the rotor is a coil. The stator of an ordinary motor is a coil (electromagnet).
The nature of the magnetic field.
After the permanent magnet motor is made, it can maintain its magnetic field without external energy; traditional motors need electric current to have a magnetic field.
Applicable occasions.
Traditional motors need to drive a reduction mechanism to achieve high torque, while rare earth permanent magnet motors can replace the reduction mechanism to achieve direct drive.
The permanent magnet motor has small vibration and good running stability.
High power density and efficiency
Compared with ordinary motors, permanent magnet motors have high power density, which mainly means that permanent magnet motors are small in size and large in power generation or output.
Compared with ordinary motors, energy saving can reach 20%-40%. The rotor structure of the permanent magnet motor is different from that of the ordinary motor.
The permanent magnet poles are installed on the rotor of the permanent magnet motor; the excitation coil is installed on the rotor of the ordinary motor, and the magnetic field needs to be supplied with current.
Compared with traditional motors, any speed point saves power, especially at low speeds.
Small size, lightweight, low-temperature rise
The permanent magnet motor has a simple structure.
Due to the use of high-performance permanent magnets to provide the magnetic field, the air gap magnetic field of the permanent magnet motor is greatly enhanced compared with ordinary motors, while the volume and weight of permanent magnet motors are greatly reduced compared with ordinary motors.
Sizes and shapes are also flexible. The non-electric excitation of the rotor means that there is no loss and heat generation.
Therefore, the temperature rise of permanent magnet motors is generally very low.
Lower failure rate, widely used
Due to the use of high-performance rare earth permanent magnet materials to provide the magnetic field, the failure rate is lower and the use is more common.
Large starting torque and good performance
Since the rotor winding does not work when the permanent magnet motor works normally, the rotor winding can be designed to fully meet the requirements of high starting torque, for example, from 1.8 times to 2.5 times, or even greater.
The service life of the permanent magnet motor is generally 15-20 years, and the service life of the motor mainly depends on the maintenance of the user.
In addition, the quality of the permanent magnet motor’s use environment, and the factors such as electricity, magnetism, heat, vibration, and other factors that the motor receives during use will affect the life of the permanent magnet synchronous motor!
General magnets have a service life. When used for a certain number of years, the magnetism will weaken, but the magnetic properties of NdFeB permanent magnet materials change very little with time, and rare earth permanent magnets are within the design life of the motor (10-20 years).
The magnetic performance attenuation is less than 3%. Under the existing motor design and electronic control technology, it has little impact on the overall performance of the motor.
Improper selection of magnetic steel-grades
If the calculation of the motor design is not accurate enough, and a lower grade is wrongly selected, such as the permanent magnet of 180°C should be selected but 155°C is wrongly selected, there may be such a situation: the initial test record index of the test process is very good, As the motor gradually tends to be thermally stable, the relevant indicators of the motor begin to deteriorate and deviate from the design expectations more and more. At a certain moment, the current increases sharply, the inverter stops quickly, and an overcurrent code is displayed. Test the no-load characteristics of the motor again, indicating that the motor has lost its magnetism, and the magnetic steel must be replaced.
Overheating the demagnetization problem
Overheating loss of magnetism is a sensitive topic, and the decrease in the magnetic properties of magnets can also lead to overcurrent and overheating problems. If the influence of the magnetic properties of the magnetic steel is excluded and only the thermal factor is considered, it can be determined that there are two situations in which the phenomenon of overheating demagnetization will occur: first, the circulation ventilation path in the motor is unreasonable, which violates the natural law of cold and heat conduction, resulting in localized heat accumulation; second, The heat load of the winding is too high, and the heat generation exceeds the heat exchange level of the motor heat exchange system.
The problem of excessive demagnetization current
When the motor is running, when the load current exceeds the anti-demagnetization ability of the magnet, it will cause irreversible demagnetization of the magnet, which will further increase the load current and aggravate the irreversible demagnetization of the magnet. This reciprocation accelerates irreversible demagnetization until demagnetization.
Correct selection of permanent magnet motor power:
Demagnetization is related to the power selection of permanent magnet motors. Correct selection of PM motor power can prevent or delay demagnetization. The main reason for the demagnetization of the permanent magnet synchronous motor is that the temperature is too high, and the overload is the main reason for the high temperature. Therefore, a certain margin should be left when selecting the power of the permanent magnet motor. According to the actual situation of the load, generally, about 20% is more appropriate.
Avoid heavy load starting and frequent starting:
Permanent magnet synchronous motors try to avoid direct starting or frequent starting of heavy loads. During the starting process, the starting torque is oscillating, and in the valley section of the starting torque, the stator magnetic field is demagnetizing the rotor magnetic pole. Therefore, try to avoid the heavy load and frequent starting of the permanent magnet synchronous motor.
Improve the design:
(1) Appropriately increase the thickness of the permanent magnet:
From the perspective of permanent magnet synchronous motor design and manufacture, the relationship between armature reaction, electromagnetic torque, and permanent magnet demagnetization should be considered.
Under the combined action of the magnetic flux produced by the torque winding current and the magnetic flux produced by the radial force winding, the permanent magnets on the rotor surface easily cause demagnetization.
Under the condition that the air gap of the motor remains unchanged, to ensure that the permanent magnet does not demagnetize, the most effective method is to appropriately increase the thickness of the permanent magnet.
(2) There is a ventilation groove circuit inside the rotor to reduce the temperature rise of the rotor:
If the temperature of the rotor is too high, the permanent magnet will cause irreversible loss of magnetism. In the structural design, the internal ventilation circuit of the rotor can be designed to directly cool the magnetic steel. Not only reduces the temperature of the magnetic steel but also improves its efficiency.
The days of choosing between profits or environment are over. Enneng is a China leading permanent magnet motor and generator provider. With the Enneng’s products, users are discovering that energy-saving, low carbon driving and generation costs less than conventional practices for their industry. In the near future, we hope energy saving green permanent magnet motors and generators will be more used in various of fields.
