The difference between permanent magnet motors and ordinary motors
The difference between permanent magnet motors and ordinary motors
Permanent magnet motors, also known as permanent magnet synchronous motors, are mostly permanent magnet variable frequency motors that are excited by permanent magnets without excitation windings and without excitation losses. Compared with ordinary motors (or ordinary three-phase asynchronous motors), permanent magnet variable frequency motors do not have electrical excitation and corresponding losses. The permanent magnet rotor does not generate heat, and the electrical load can be selected very high, resulting in small size and high power density.
With the rapid development of new motor control theories and rare earth permanent magnet materials, the performance of permanent magnet motors has been further improved,
The advantages are as follows:
1. Efficient and energy-saving. As the excitation magnetic field is provided by permanent magnets, the permanent magnet rotor does not require excitation, and the efficiency can reach over 90%. Compared with asynchronous motors, permanent magnet motors have a wide range of efficient operating speeds and significant energy savings. Especially during low speed operation, the advantages are more obvious.
2. Low temperature rise. No electric excitation of the rotor means no loss and heating, therefore, permanent magnet motors generally have a low temperature rise.
3. Good starting performance. Due to the ineffective rotor winding during normal operation of permanent magnet motors, the rotor winding can be designed to fully meet the requirements of high starting torque, such as increasing from 1.8 times to 2.5 times or even greater.
4. High power factor. The impact on the operation of the power grid lies in the fact that asynchronous motors absorb a large amount of reactive current from the grid, causing a large amount of reactive current in the power transmission and transformation system of the grid, thereby reducing the quality factor of the grid and increasing the load on the transmission and transformation equipment and power generation equipment. At the same time, reactive current consumes a portion of electrical energy in the power grid or transmission and transformation system, resulting in low operating efficiency of the power grid. In addition, coupled with low efficiency of asynchronous motors and excessive absorption of electrical energy from the grid, the loss of electrical energy intensifies, and the load on the grid becomes even more severe. The unique advantages of non electric excitation and high power factor of permanent magnet motor rotors can help improve the quality factor of the power grid or eliminate the need to install compensators in the power grid. An increase in power factor can also increase the utilization rate of transformers.
5. High power density. Due to the use of high-performance permanent magnet materials to provide magnetic field, the air gap magnetic field of permanent magnet motors is greatly enhanced compared to ordinary motors, while the volume and weight of permanent magnet motors are greatly reduced compared to ordinary motors, with light weight. The motor can be designed and installed according to the size of a regular motor and one to two smaller frame sizes, making it very convenient to use in energy-saving transformation and upgrading.
