The characteristics and advantages of permanent magnet motors

Motor From the source of excitation can be divided into two categories: permanent magnet motor, and electric excitation motor. A permanent magnet motor is an electric motor that produces an excitation magnetic field from a permanent magnet. The most widely used three-phase asynchronous motors in industry and civil use, such as Y-Series, Y2-Series, YE2-Series, YX3 Series, Series YB, series YB2 series, etc. all belong to electric excitation motors. ENNENG Motor products are ultra-efficient permanent magnet synchronous motors.

Compared with traditional electric excitation motors, permanent magnet motors, especially rare earth permanent magnet motors, have the advantages of simple structure, reliable operation, small size, lightweight, small loss and high efficiency, and flexible and diverse shape and size of the motor. The application is extremely wide, covering almost all areas of aerospace, national defense, industrial and agricultural production, and daily life.

The permanent magnet synchronous motor has the following characteristics:

• Rated efficiency is 2% to 5% higher than normal asynchronous motors;
• The efficiency rises rapidly with the increase of the load. When the load changes within the range of 25% to 120%, it maintains high efficiency. The high-efficiency operating range is much higher than that of ordinary asynchronous motors. Light-load, variable-load, and full-load all have significant energy-saving effects;
• Power factors up to 0.95 and above, no reactive compensation required;
• The power factor is greatly improved. Compared with asynchronous motors, the running current is reduced by more than 10%. Due to the decrease in operating current and system losses, energy-saving effects of about 1% can be achieved.
• Low-temperature rise, high power density: 20K lower than three-phase asynchronous motor temperature rise, design temperature rise is the same and can be made into a smaller volume, saving more effective materials;
• High starting torque and high overload capacity: according to requirements, it can be designed with high starting torque (3-5 times) and high overload capacity;
• The variable frequency speed control system is used, which is better in dynamic response and better than that of asynchronous motors.
• The installation dimensions are the same as the asynchronous motors currently widely used, and the design and selection are very convenient.
• Due to the increase in power factor, the visual power of the power supply system transformer is greatly reduced, which improves the power supply capacity of the transformer, and can also greatly reduce the cost of the system cable (new project);
• When the new project is built, all the drive systems use permanent magnet synchronous motors, the project investment is basically the same as the use of asynchronous motors, and the project can continue to obtain energy-saving benefits after the project is put into operation;

In the general industrial sector, the replacement of low-voltage(380/660/1140V) high-efficiency asynchronous motors, the system saves 5% to 30% energy, and the high-voltage(6kV/10kV) high-efficiency asynchronous motors, system saves 2% to 10%.

Application of rare earth permanent magnet motor

Due to the superiority of rare earth permanent magnet motors, their applications are becoming more and more extensive. The main application areas are as follows:

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.

How to prevent the demagnetization of permanent magnet motors?

01. 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.

02. 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.

03. 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 the efficiency.