Magnetization requirements and design methods of permanent magnet motors

A permanent magnet motor is a motor that uses permanent magnets to establish a magnetic field. It is also a common motor. After being made, a permanent magnet motor can maintain its magnetic field without external energy. So what are the magnetizing requirements and design methods of permanent magnet motors? Let’s learn together below!

The design method is as follows:

1. Magnetic circuit method: The unevenly distributed alternating magnetic field in a permanent magnet motor can be equivalent to a corresponding magnetic circuit, so that magnetic field calculations are converted into magnetic circuit calculations. Since many correction coefficients are used in the equivalent magnetic circuit calculation, its accurate value cannot be calculated theoretically. Usually empirical data is used. If the initially designed solution does not meet the original design requirements, the designer must re-select the correction value and calculate it again.

2. Finite element method: In order to make the calculation accurate, the electromagnetic field needs to be analyzed, such as the shape and size of the permanent magnet poles, partial demagnetization phenomenon, etc. Using finite element software to numerically calculate and analyze electromagnetic fields saves product development costs and provides an accurate basis for the design of this motor. The improvement of computer performance has enabled the development of various analysis methods for electromagnetic field numerical calculation theory. The essence of the finite element method is to transform the problem into a structural problem suitable for numerical solution. It idealizes a connected system with infinite degrees of freedom into a set of units with a limited number of degrees of freedom. Nowadays, the commonly used finite element simulation software is Ansoft, which can jointly simulate the entire motor system.

3. Field-circuit combination method: Although the magnetic circuit method has fast calculation speed, its accuracy is not high. Computer calculation has high accuracy, but its calculation is slow and has high computer requirements. Therefore, combining the finite element method with the traditional magnetic circuit method in the numerical calculation of motor electromagnetism can not only improve the calculation power, but also improve the accuracy. This has great practical value for motor parameter design. The basic idea of ​​the field-circuit combination method is to refer to the magnetic circuit calculation results, start to establish a geometric model, and then conduct magnetic field analysis through finite element to accurately calculate the coefficients that need to be corrected in the equivalent magnetic circuit method.

Magnetization requirements are as follows:

In the permanent magnet motor, the commutator is equipped with brushes, which can convert the external DC power into the alternating current in the armature coil, so that the direction of the electromagnetic torque is stable and unchanged. It is a widely used motor now. The following Let’s take a look at its magnetization requirements.

Different uses of permanent magnet motors require different functions. The different functions depend on the electromagnetic structural parameters inside the motor. In terms of magnetic parameters, different air gap magnetic field distribution shapes are required, such as permanent magnet DC motors for pure output driving. , its performance requires higher output power and power, so the internal air gap magnetic field distribution of this type of motor should use a flat-top wave equal to or slightly larger than 2/3 of the pole pitch, so as to provide as much magnetic flux as possible and make the motor have a larger large electromagnetic torque. Another example is that for permanent magnet DC motors that have small oscillation, low noise, small sparks, and low output power and power requirements, the internal air gap magnetic field distribution should use a flat-top wave or a sine wave that is less than 1/3 of the pole pitch. , to ensure the suitability of this type of motor. In order to obtain air gap magnetic field waveforms with different distribution shapes, it is not only related to the reasonable design of the structural shape of the magnet and the selection of the magnetic orientation of the magnet, but also related to the magnetization method of the magnet, that is, the design of the magnetization technology.

Regarding the magnetization requirements of this kind of equipment, the article has now explained it clearly. The structure of the permanent magnet motor will be more complex, the calculation structure will be more accurate, and the manufacturing process will be more advanced and applicable. These complex problems require the use of multidisciplinary theory and system engineering for design, improve cost performance, and promote the further development of electrical disciplines and professions.