Basic frequency above speed
3.3.1 Direct Torque Control Strategy
The direct torque method, the starting point is to directly influence the torque output value by controlling the parameters in the torque formula. Select the moment angle as the control object.
Take the built-in rotor permanent magnet synchronous motor as an example to illustrate the specific method.
In the case of a constant supply voltage and stator magnetic field frequency, the motor outputs torque in real time, proportional to the sine of the moment angle.
The electromagnetic torque value corresponding to each torque angle can be calculated in an offline state to form a vector table and stored in the upper computer. During the operation of the motor controller, the torque and torque angles are observed in real time and the original values in the table are extracted for comparison. If there is any discrepancy between the value of the table and the value of the table, adjust the power supply voltage value and perform torque correction.
The direct torque method has good robustness, simple algorithm, and does not require coordinate transformation. In the early stage, it was a control method with more applications. However, in this method, the control accuracy drops sharply at low rotational speeds. Therefore, you can choose to use only below the fundamental frequency.
3.4 Maximum torque current ratio control strategy
The current is decoupled in the d-q coordinate system, and the maximum torque current ratio of each component is obtained separately, in order to obtain the maximum torque under the determined excitation current.
The existence of the maxima is determined by finding the second derivative. In the speed regulation interval, the torque current ratio is derived, and the second derivative is less than 0, then the torque current ratio maximum exists.
4 summary
Permanent magnet synchronous motor, its hard mechanical characteristics make it ideal for applications requiring speed regulation. The strong demand for power density and maneuverability of electric vehicles also makes permanent magnet synchronous motors particularly suitable for electric vehicle applications. If the problem of magnetic field stability of permanent magnets under high temperature can be further overcome, with the deepening of research on frequency conversion speed regulation technology, permanent magnet synchronous motors will occupy more electric vehicles.
