3 speed control method
Compared with asynchronous motors, the relationship between electric, magnetic and force of permanent magnet synchronous motors is simpler. After a certain coordinate transformation, the decoupling of current and torque can be realized.
3.1 coordinate transformation
Listed, the relevant coordinate transformation used in the variable frequency speed regulation of permanent magnet synchronous motor. The A-B-C coordinate system takes the center of the stator core as the origin, and the three phases of the stator are A, B, and C in the axial direction, and the angle between the shaft and the shaft is 120°.
The α-β coordinate system, in the same plane as the A-B-C coordinate system, shares the same origin, the α-axis coincides with the A-axis, and the β-axis forms an angle of 90° with the α-axis.
In the d-q coordinate system, the d-axis coincides with the rotor permanent magnet pole N and follows the rotor. The q-axis is at an angle of 90° to the d-axis in the counterclockwise direction.
3.2 Basic frequency adjustment
Field oriented control
The magnetic field orientation, that is, in the d-q coordinate system, the motor parameters, such as the excitation current, the part that affects the moment, is the component of the parameter projection to the q-axis. The part projected onto the d-axis is not considered, that is, the so-called id=0 method. Under this method, the decisive factor of the maximum output speed of the motor is the maximum supply voltage of the controller.
The limitation of the field-oriented control strategy is that it cannot reflect the change of some parameters of the magnetic field affected by the excitation current, so the field weakening control cannot be performed.
