Permanent Magnet Synchronous Motor
Permanent magnet synchronous motor is a synchronous motor that generates a synchronous rotating magnetic field by excitation of a permanent magnet. The permanent magnet acts as a rotor to generate a rotating magnetic field. The three-phase stator winding reacts through the armature under the action of the rotating magnetic field, inducing a three-phase symmetrical current. At this time, the kinetic energy of the rotor is converted. For electric energy, the permanent magnet synchronous motor is used as a generator; in addition, when the three-phase symmetrical current is passed to the stator side, because the three-phase stator is 120 degrees different in spatial position, the three-phase stator current generates a rotating magnetic field in the space, and the rotor rotates Under the action of electromagnetic force in the magnetic field, the electric energy is converted into kinetic energy at this time, and the permanent magnet synchronous motor is used as a motor.
Asynchronous motor
When the three-phase stator winding of the motor is fed with three-phase symmetrical alternating current, a rotating magnetic field will be generated, which will cut the rotor winding, thereby generating an induced current in the rotor winding (the rotor winding is a closed path), and the current-carrying rotor conductor is in the Under the action of the rotating magnetic field of the stator, an electromagnetic force will be generated, thereby forming an electromagnetic torque on the rotating shaft of the motor, driving the motor to rotate, and the rotation direction of the motor is the same as that of the rotating magnetic field. When a conductor cuts magnetic lines of force within a magnetic field, an induced current is generated in the conductor, hence the name "induction motor". The combined action of the induced current and the magnetic field applies a driving force to the motor rotor.
The difference between permanent magnet motor and asynchronous motor
1. High efficiency
The high efficiency mentioned here not only means that the efficiency of the rated power point is different from that of the ordinary three-phase asynchronous motor, but also refers to its average efficiency in the entire speed regulation range. The excitation magnetic field of the permanent magnet synchronous motor is provided by the permanent magnet, the rotor does not need excitation current, and the motor efficiency is improved. Compared with the asynchronous motor, electricity can be saved at any speed point, especially when the speed is low.
2. Starting torque
The permanent magnet synchronous motor generally also adopts the asynchronous starting method. Since the rotor winding does not work when the permanent magnet synchronous motor is working normally, when designing the permanent magnet motor, the rotor winding can fully meet the requirements of high starting torque, such as making the starting torque 1.8 times. times rose to 2.5 times, or even larger.
3. Impact on power grid operation
Due to the low power factor of the asynchronous motor, the motor needs to absorb a large amount of reactive current from the power grid, resulting in a large amount of reactive current in the power grid's substation equipment and power generation equipment, which in turn reduces the quality factor of the power grid and aggravates the power grid and gun transformers. At the same time, the reactive current consumes part of the electric energy in the power grid, substation equipment and power generation equipment, resulting in lower efficiency of the power grid and affecting the effective use of electric energy. Also due to the low efficiency of the asynchronous motor, in order to meet the power requirements, it is necessary to absorb more power from the grid, which further increases the loss of electrical energy and increases the load on the grid. There is no induced current excitation in the rotor of the permanent magnet motor, and the power factor of the motor is high, which improves the quality factor of the power grid and eliminates the need to install a compensator in the power grid. At the same time, due to the high efficiency of the permanent magnet motor, electricity is also saved.
4. Small size and light weight
Due to the use of high-performance permanent magnet materials to provide the magnetic field, the air gap magnetic field of the permanent magnet motor is stronger than that of the induction motor, and the volume and weight of the permanent magnet motor can be greatly reduced compared with that of the induction motor. For example, the 11kW asynchronous motor weighs the most at 220kg, while the permanent magnet motor is only 92kg, which is equivalent to 45.8% of the weight of the asynchronous motor.
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