Why do permanent magnet motor magnets fall off and what are the serious consequences?
The permanent magnet motor uses permanent magnets to generate the magnetic field of the motor. It does not require an excitation coil or excitation current. It has high efficiency and simple structure. It is a good energy-saving motor. With the advent of high-performance permanent magnet materials and the rapid development of control technology. The application of permanent magnet motors will become more widespread. Compared with traditional electric excitation motors, permanent magnet motors, especially rare earth permanent magnet motors, have significant advantages such as simple structure, reliable operation, small size and light weight, low loss and high efficiency, and the shape and size of the motor can be flexible and diverse. . Therefore, it has an extremely wide range of applications, covering almost all fields of aerospace, national defense, industrial and agricultural production, and daily life.
The picture below is a simple working principle model of a permanent magnet DC motor. Two permanent magnets generate a magnetic field at the central coil. The coil is passed through current, and the electromagnetic force (left-hand rule) is generated by the magnetic field, which then rotates. The motor The rotating part is called the rotor, and the non-moving part is called the stator. Obviously, the permanent magnet in the picture below belongs to the stator, and the coil belongs to the rotor.
Permanent magnet motor magnets have the following characteristics :
1. Magnetic circuit structure and design calculation
In order to give full play to the magnetic properties of various permanent magnet materials, especially the excellent magnetic properties of rare earth permanent magnets, and create a cost-effective permanent magnet motor, we cannot simply apply the structure and design calculation methods of traditional permanent magnet motors or electric excitation motors. , a new design concept must be established, and the magnetic circuit structure must be reanalyzed and improved. With the rapid development of computer hardware and software technology, as well as the continuous improvement of modern design methods such as electromagnetic field numerical calculation, optimization design and simulation technology, through the joint efforts of the electrical academic and engineering circles, the design theory and design of permanent magnet motors have been Breakthrough progress has been made in calculation methods, structural technology and control technology, and a complete set of analysis research methods and computer-aided analysis and design software that combine electromagnetic field numerical calculations and equivalent magnetic circuit analytical solutions have been formed, and are being continuously improved. .
2. Control issues
After the permanent magnet motor is made, it can maintain its magnetic field without external energy, but it also makes it extremely difficult to adjust and control its magnetic field from the outside. It is difficult to adjust the output voltage and power factor of the permanent magnet generator from the outside, and the permanent magnet DC motor can no longer adjust its speed by changing the excitation. These limit the application range of permanent magnet motors. However, with the rapid development of power electronic devices and control technologies such as MOSFET and IGBT, most permanent magnet motors can be used without magnetic field control and only armature control. The design needs to combine three new technologies, rare earth permanent magnet materials, power electronic devices and microcomputer control, so that the permanent magnet motor can operate under new working conditions.
3. Irreversible demagnetization problem
If improperly designed or used, the permanent magnet motor will operate at too high (neodymium iron boron permanent magnet) or too low (ferrite permanent magnet) temperature, under the action of armature reaction caused by inrush current, or under severe mechanical vibration. Irreversible demagnetization, or loss of magnetization, may occur, which may reduce the performance of the motor or even make it unusable. Therefore, it is necessary to not only research and develop methods and devices for checking the thermal stability of permanent magnet materials suitable for motor manufacturers, but also to analyze the anti-demagnetization capabilities of various structural forms, so that corresponding measures can be taken to ensure that during design and manufacturing Permanent magnet motors do not lose magnetism.
4. Cost issue
Ferrite permanent magnet motors, especially miniature permanent magnet DC motors, are widely used due to their simple structure and process, reduced weight, and generally lower total cost than electric excitation motors. Since rare earth permanent magnets are currently relatively expensive, the cost of rare earth permanent magnet motors is generally higher than that of electric excitation motors, which needs to be compensated by its high performance and operating cost savings. In some cases, such as the voice coil motor of computer disk drives, the performance of NdFeB permanent magnets is improved, the volume and mass are significantly reduced, and the total cost is reduced. During design, it is necessary to compare performance and price before deciding on a choice based on specific use occasions and requirements. It is also necessary to innovate structural processes and design optimization to reduce costs.