Permanent magnet synchronous motor
Determine the size and material of each part of the magnetic circuit
Permanent magnets and their properties are diverse. How to choose the right permanent magnet material is directly related to the performance and economy of the motor. The selection of permanent magnets should meet the following requirements:
The permanent magnet shall be capable of generating the required magnetic field in the designated working space;
The magnetic field established by the permanent magnet should have a certain stability, and the magnetic properties should be within the allowable range according to the change of working temperature and environment;
Has good corrosion resistance;
Has good mechanical properties, good toughness, high compressive strength, and processability;
The choice of permanent magnet materials with reasonable price and good economy.
• Ferrite: Suitable for applications where the size, weight and performance of the motor are not critical and the economics of the motor are high.
• AlNiCo: Suitable for applications where the size, weight and performance of the motor are not high, but the operating temperature exceeds 300 degrees or the temperature stability is required and the cost of the motor is not high.
• NdFeB: Suitable for applications where the size, weight and performance of the motor are very high, the operating environment temperature is not high, and the temperature stability of the permanent magnet is not high.
• Rare Earth Cobalt: Suitable for applications where the motor's volume, weight and performance are very high, the working environment temperature is high, temperature stability is required, and manufacturing costs are not a major consideration.
• Bonded permanent magnet material: suitable for occasions with large batch size, complex magnetic pole shape and low motor performance requirements.
The choice of permanent magnet size:
• When designing the motor, in order to make full use of the permanent magnet material, reduce the size of the permanent magnet and the entire motor, it is necessary to establish the magnetic field with the largest magnetic energy in the air gap with the smallest permanent magnet volume.
Using the equivalent magnetic circuit calculation method to calculate whether the characteristic judgment error of the magnetic circuit is within the allowable range
• Using the equivalent magnetic circuit method, the uneven magnetic field existing in the motor space is converted into an equivalent multi-segment magnetic circuit, and the magnetic flux is uniformly distributed along the cross-section and length in each magnetic circuit, and the magnetic field is calculated. The calculation is converted into a magnetic circuit, and then corrected by various coefficients, that is, the magnetic position difference of each magnetic circuit is equal to the magnetic difference between the corresponding points in the magnetic field. After accumulating certain experience and obtaining various actual correction factors, the calculation accuracy can meet the actual needs of the project.
• Through the calculation of the magnetic circuit of the permanent magnet motor, the performance of the initial design is checked by the relevant formula, and it is judged whether the error between the calculated result and the performance requirement of the motor is within the allowable range. If it is within the allowable range, the magnetic circuit design is completed; otherwise, the size, material, magnetic circuit structure, etc. of the magnetic circuit need to be adjusted until a reasonable magnetic circuit is obtained.
