Blue Direct Drive Permanent Magnet Motor

What Is The Permanent Magnet Synchronous Motor?

The Permanent Magnet Synchronous Motor (PMSM) is an AC synchronous motor whose field excitation is provided by permanent magnets and has a sinusoidal back EMF waveform. The PMSM is a cross between an induction motor and a brushless DC motor. Like a brushless DC motor, it has a permanent magnet rotor and windings on the stator. However, the stator structure with windings constructed to produce a sinusoidal flux density in the air gap of the machine resembles that of an induction motor. Its power density is higher than induction motors with the same ratings since there is no stator power dedicated to magnetic field production.

With permanent magnets the PMSM can generate torque at zero speed, it requires a digitally controlled inverter for operations. PMSMs are typically used for high-performance and high-efficiency motor drives. High-performance motor control is characterized by smooth rotation over the entire speed range of the motor, full torque control at zero speed, and fast acceleration and deceleration.

To achieve such control, vector control techniques are used for PMSM. The vector control techniques are usually also referred to as field-oriented control (FOC). The basic idea of the vector control algorithm is to decompose a stator current into a magnetic field-generating part and a torque-generating part. Both components can be controlled separately after decomposition.

Working of Permanent Magnet Synchronous Motor

The permanent magnet synchronous motor working principle is similar to the synchronous motor. It depends on the rotating magnetic field that generates electromotive force at synchronous speed. When the stator winding is energized by giving the 3-phase supply, a rotating magnetic field is created in between the air gaps.

This produces the torque when the rotor field poles hold the rotating magnetic field at synchronous speed and the rotor rotates continuously. As these motors are not self-starting motors, it is necessary to provide a variable frequency power supply.

Analysis of the principle of the technical advantages of permanent magnet motor

The principle of a permanent magnet synchronous motor is as follows: In the motor's stator winding into the three-phase current, after the pass-in current, it will form a rotating magnetic field for the motor's stator winding. Because the rotor is installed with the permanent magnet, the permanent magnet's magnetic pole is fixed, according to the principle of magnetic poles of the same phase attracting different repulsion, the rotating magnetic field generated in the stator will drive the rotor to rotate, The rotation speed of the rotor is equal to the speed of the rotating pole produced in the stator.

Back-emf waveform:

Back emf is short for back electromotive force but is also known as the counter-electromotive force. The back electromotive force is the voltage that occurs in electric motors when there is a relative motion between the stator windings and the rotor’s magnetic field. The geometric properties of the rotor will determine the shape of the back-emf waveform. These waveforms can be sinusoidal, trapezoidal, triangular, or something in between.

Both induction and PM machines generate back-emf waveforms. In an induction machine, the back-emf waveform will decay as the residual rotor field slowly decays because of the lack of a stator field. However, with a PM machine, the rotor generates its own magnetic field. Therefore, a voltage can be induced in the stator windings whenever the rotor is in motion. Back-emf voltage will rise linearly with speed and is a crucial factor in determining maximum operating speed.