In-depth study of the design of permanent magnet motor
3.1 permanent magnet material utilization rate
In permanent magnet motors, the cost of permanent magnet materials accounts for a large proportion of the total cost of the motor. Therefore, how to save materials and improve material utilization is one of the most concerned issues for permanent magnet motor manufacturers. In theory, the maximum magnetic energy point of a permanent magnet indicates that the magnet can provide the maximum energy to the outside, and the maximum operating point can also be obtained from the demagnetization curve. However, the actual application is not so simple. It is necessary to specifically study the use of the motor, analyze the predetermined function that the motor should complete, and find out the corresponding key indicators to determine the optimal position of the motor working point selection, and determine the Yong position reasonably. The shape and volume of the magnet must also take into account the effects of its processing. After considering various factors comprehensively, the optimal design of the motor in terms of function, performance and cost is achieved.
3.2 overload and demagnetization
Demagnetization of magnetic materials includes temperature demagnetization, time demagnetization, and environmental demagnetization. There are two types of reversible demagnetization and irreversible demagnetization. In-depth study of the relationship between coercivity and intrinsic coercivity of permanent magnet materials and stable working temperature; the influence of temperature coefficient on motor performance index and demagnetization safety factor; definition of maximum operating temperature of motor based on magnetic property change; reversible demagnetization And the proportion of irreversible demagnetization in the temperature range of the motor and the impact on the performance of the motor; re-magnetization and reuse of the permanent magnet material after demagnetization are necessary.
3.3 Analysis and design
The theory and design of modern permanent magnet motor are relatively mature. There are not only many design procedures and methods based on magnetic circuit analysis and calculation, but also the numerical analysis method of permanent magnet magnetic field has been widely used in engineering practice. However, in the permanent magnet motor, the permanent magnet is used as the field excitation source or the magnetic source of the magnetic circuit, and is also a component of the magnetic field and the magnetic circuit. At the same time, the permanent magnet material manufacturing process, shape size, magnetization tool, magnetization method, etc. The consistency and uniformity of the permanent magnet materials are not ideal, and sometimes the dispersion is large. Even the performance data of the same batch of permanent magnet materials of the same grade may have a large difference. Therefore, the dispersion of permanent magnets also brings certain difficulties to the design analysis of permanent magnet motors and the numerical calculation of permanent magnet magnetic fields, and the accuracy of design will be affected. For example, the establishment and equivalence of permanent magnet models in the theoretical and numerical analysis of the field; the problems of leakage magnetic coefficient, local demagnetization and accurate calculation of armature reaction in the calculation of engineering magnetic circuit are all more error than the analysis and calculation of electric excitation motor Big.
3.4 Magnetization and magnetic measurement
The permanent magnet motor design is based on the saturation magnetization of the permanent magnet material. Then, whether the magnet used on the motor has been fully magnetized and saturated, if the permanent magnet is magnetized by the magnetic material manufacturer and supplied with magnetic, there is generally no problem, but if it is magnetized on the motor, how to ensure The permanent magnet is sufficiently magnetized, and it is worthwhile to study how to maintain the uniformity and consistency of magnetic properties while saturating the magnetization.
Similarly, there are still many issues worth studying for the magnetic performance detection problem. For example, magnets supplied with magnetic materials can be effectively and easily tested in the motor manufacturer. However, most motor manufacturers cannot effectively measure the magnetic properties of permanent magnet materials in the component stage. Only when the performance test of the whole machine is unqualified can the magnetic material be found to have problems.
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