Vector Control Frequency Inverters (Adjustable Speed Drives, AFDs) (part 2)
Continued from the previous article: Vector Control Frequency Inverters (Adjustable Speed Drives, AFDs) (part 1) , we still introduce this kind of speed control technique implemented by modern-age frequency converters.
As the torque producing component in vector control is controlled only after transformation is done, and is not the main input reference, the vector control is known as "indirect torque control".
Vector control variable frequency drives from Shenzhen POWTRAN Technology Co., Ltd.: 
The most challenging and ultimately, the limiting feature of the field orientation, is the method whereby the flux angle is measured or estimated. Depending on the method of measurement, the vector control is divided into two subcategories: direct vector control and indirect vector control.
In the direct vector control, the flux measurement is done by using the flux sensing coils or the Hall devices. This adds to additional hardware cost and in addition, measurement is not highly accurate. Therefore, the direct vector control is not a very good control technique for frequency changers (variable speed drives, VSDs).
The more common method of vector control is indirect vector control. In indirect vector control, the flux angle is not measured directly, but is estimated from the equivalent circuit model and from measurements of the rotor speed, the stator current and the voltage.
