What is a permanent magnet synchronous AC motor with no excitation loss?

ndustry development and market dynamics:
With the increasing demand for high-efficiency and energy-saving motors, the share of permanent magnet synchronous motors in the motor market has gradually expanded, and the development prospects of related industries have received attention. For example, in industrial automation, home appliances, rail transit and other fields, the application of permanent magnet synchronous motors is more and more extensive, which has promoted the development and upgrading of the industry.
The importance of rare earth resources in the manufacturing of permanent magnet synchronous motor has become increasingly prominent, China, as a country rich in rare earth resources, has certain advantages in the development of permanent magnet synchronous motor industry, and the development of related industries has also attracted attention.

 

Definition and principle
A Permanent Magnet Synchronous Motor (PMSM) is a synchronous motor that generates a synchronous rotating magnetic field excited by a permanent magnet. Its stator winding will generate a rotating magnetic field after the three-phase alternating current, and the rotor is composed of permanent magnets, relying on the magnetic field generated by the permanent magnet to interact with the stator rotating magnetic field, so that the motor rotor rotates synchronically with the stator rotating magnetic field.
Its operating principle is based on the law of electromagnetic induction and the principle of magnetic field interaction. There is an electromagnetic torque between the rotating magnetic field generated by the stator current and the permanent magnetic field of the rotor. The torque drives the rotor of the motor to rotate, and the rotor speed is strictly synchronized with that of the stator rotating magnetic field.

 

Structural characteristics
The stator structure is similar to that of the ordinary three-phase asynchronous motor, which is composed of the stator core and the stator winding. The stator core is usually made of silicon steel sheet laminated to reduce core loss. The stator winding is a three-phase winding, which is embedded in the stator slot according to certain rules, and is used to generate a rotating magnetic field by passing three-phase AC current.
The rotor structure is the key part of permanent magnet synchronous motor. A permanent magnet is installed on the rotor, and the material of the permanent magnet is usually NdFeb (Nd-Fe-B) and other high-performance permanent magnet materials. According to the different installation methods of permanent magnets on the rotor, it can be divided into surface permanent magnet rotor and built-in permanent magnet rotor. The permanent magnet of the surface type permanent magnet rotor is installed on the surface of the rotor core, which is simple in structure and process, but the permanent magnet is easy to be interfered by external magnetic field; The permanent magnet of the built-in permanent magnet rotor is embedded in the inner core of the rotor, its structure is relatively complex, but it has better magnetic circuit characteristics and mechanical properties.

advantage
High efficiency: Because of the use of permanent magnet excitation, no additional excitation current is required, reducing the excitation loss, and compared with traditional asynchronous motors, it has higher efficiency under the same working conditions. This can significantly reduce energy consumption and save energy costs for long-term operating equipment.
High power factor: the power factor of permanent magnet synchronous motor can be close to 1, which means that when the power grid is supplied, the reactive power absorbed by the motor from the grid is very small, reducing the reactive power burden of the grid and improving the power supply quality of the grid.
Fast response speed: its torque response is rapid, and it can quickly adjust the speed and torque according to the control signal, which is suitable for occasions requiring high-precision control, such as industrial automated production lines, robots and other fields.
Compact structure: Because there is no need for excitation windings and related excitation devices, the overall structure of the motor is more compact and smaller, which has great advantages in some equipment with high space requirements.

Application field
Industrial field: widely used in industrial automation equipment, such as CNC machine tools, textile machinery, printing machinery, etc. For example, in CNC machine tools, permanent magnet synchronous motors can precisely control the speed and position of the tool, improving the machining accuracy.
Transportation field: permanent magnet synchronous motors are widely used as driving motors in electric vehicles, electric trains and other transportation vehicles. Permanent magnet synchronous motor in electric vehicle has the advantages of high efficiency, energy saving and good torque characteristics, which can improve the driving range and power performance of electric vehicle.
Home appliances: It is also used in air conditioners, refrigerators, washing machines and other home appliances. For example, the use of permanent magnet synchronous motors for air conditioning compressors can improve the energy efficiency ratio of air conditioners and reduce operating noise.
Second, the understanding and actual situation of "no loss"

 

Ideally no loss
Under ideal circumstances, if the iron loss (hysteresis loss and eddy current loss in the iron core) and mechanical loss (bearing friction loss, wind resistance loss, etc.) in the motor are ignored, the energy conversion efficiency of the permanent magnet synchronous motor can be close to 100% because there is no excitation loss, that is, the so-called "no loss". This is based on the theoretical assumption that under this assumption, the electrical energy input to the stator winding is almost completely converted into mechanical energy output.
Actual loss condition
Iron loss: In actual operation, the silicon steel sheet in the stator core will produce hysteresis loss and eddy current loss under the action of alternating magnetic field. Hysteresis loss is due to the hysteresis characteristics of the core material, which makes the magnetic domain inside the core flip over and consume energy when the magnetic field changes. Eddy current loss is caused by the eddy current induced by the alternating magnetic field in the core, which generates heat on the resistance of the core and consumes energy.
Mechanical loss: the rotor of the motor in the rotation process, the bearing will produce friction loss, while the motor rotation and the surrounding air there is relative motion, will produce wind resistance loss. These mechanical losses reduce the efficiency of the motor.
Stray loss: including the loss caused by the interaction of high order harmonic magnetic fields in the stator and rotor, and the additional loss caused by manufacturing process and other factors. Although the efficiency of permanent magnet synchronous motors is relatively high, these actual losses cannot be ignored.
Third, the characteristics of the AC motor are related
Adaptability of AC power supply
Permanent magnet synchronous motor is a kind of AC motor, it can be directly connected to the three-phase AC power supply operation. In practical applications, it is necessary to match the corresponding AC power supply according to the rated voltage and rated frequency of the motor. Different application scenarios may need to make appropriate adjustments to the AC power supply, such as in some industrial occasions, when the power grid voltage fluctuations are large, it may be necessary to use a voltage regulator to ensure the normal operation of the motor.
Comparison with other AC motors
Compared with asynchronous motors, as mentioned earlier, permanent magnet synchronous motors have higher efficiency, power factor and other advantages. The asynchronous motor has simple structure, low cost and high reliability, and is widely used in some occasions where the efficiency requirement is not particularly high and the cost is more sensitive.
Compared with synchronous reluctance motor, permanent magnet synchronous motor has higher torque density, and can output greater torque under the same volume and power. Synchronous reluctance motor mainly depends on the reluctance torque operation, its efficiency and performance are not as good as permanent magnet synchronous motor in some aspects.