Analysis of electromagnetic field, temperature field and vibration characteristics of permanent magnet brushless direct drive motor
As an electromechanical conversion device, the motor realizes the mutual conversion of electrical energy and mechanical energy. As a power source in the industrial field and daily life, it plays an important role in industrial production and social life in today's society. The permanent magnet brushless direct drive motor uses torque as the main indicator of motor output. It is a motor with special performance. Its motor overload capacity is strong. It can directly drive the load without using planetary gears and other reduction transmission devices, thereby improving the operation accuracy of the servo system. The following mainly analyzes the electromagnetic field, temperature field, loss and vibration characteristics of permanent magnet motors.
1. Electromagnetic finite element analysis of permanent magnet motors
There is an interaction between electricity and magnetism inside the motor. It is an electromechanical device based on the law of electromagnetic induction. The interaction between the electromagnetic field and the current determines the output performance of the motor. The electromagnetic field inside the motor usually changes over time during operation.
2. Analysis of permanent magnet motor temperature field
The temperature rise of the motor is an important reference quantity in motor design. Excessive temperature rise will have many adverse effects on the motor. Excessive temperature will increase copper loss and reduce motor efficiency. High temperature will also cause irreversible demagnetization of the magnetic steel. The insulation material of the motor is prone to aging under high temperature conditions, which will reduce the insulation performance and affect the reliability and life of the motor.
3. Analysis of permanent magnet motor loss
Various losses will be generated during the operation of the motor. The more losses the motor generates, the higher the temperature of each component of the motor will be. If the loss of a motor is large, its efficiency must be low. In order to ensure the normal operation of the motor and provide a basis for the subsequent calculation of the motor temperature field, it is necessary to accurately calculate the loss of the motor.
The loss is composed of two parts, copper loss and iron loss. Iron loss is composed of hysteresis loss and eddy current loss. The direct current in the three-phase winding is the main source of copper loss. The stator core is filled with the alternating magnetic field and rotating magnetic field formed by the three-phase winding and is repeatedly magnetized. Each change in magnetization will cause friction and collision between magnetic domains. The energy loss caused by this is called hysteresis loss. Eddy current loss refers to the magnetic flux through the stator core. When the magnetic flux is constantly changing, the core will generate an induced electromotive force to prevent the magnetic flux from changing. The stator core, as a current conductor, will generate a circular current that moves in a vortex under the action of this induced electromotive force. The loss caused by this current is called eddy current loss.
4 Analysis of vibration characteristics of permanent magnet motors
(1) Mechanical vibration
Mechanical vibration is usually related to the processing accuracy and installation process of mechanical devices such as bearings. When the motor is working, the mechanical device will have friction and collision, which will cause vibration of various components.
(2) Vibration caused by aerodynamics
During the operation of the motor, the heat generated by the winding and the core causes the air pressure to change, resulting in different air pressures inside and outside the motor, causing air vibration of the motor.
(3) Electromagnetic vibration
Electromagnetic vibration is caused by the electromagnetic force inside the motor. There are many factors that affect the electromagnetic force of the motor. According to the previous discussion, the size of the stator slot, the shape of the permanent magnet, the selection of the pole arc coefficient, etc. will all cause high-frequency harmonic magnetic fields to be generated in the air gap, forming electromagnetic force harmonics that act on the stator core, thereby causing vibration.
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