Vector Control Frequency Inverters (Adjustable Speed Drives, AFDs) (part 1)
As one main speed control technique implemented by modern-age variable speed drives (variable frequency drives), vector control is also known as the "field oriented control", "flux oriented control" or "indirect torque control".
Using field orientation (Clarke-Park transformation), three-phase current vectors are converted to a two-dimensional rotating reference frame (d-q) from a three-dimensional stationary reference frame. The "d" component represents the flux producing component of the stator current. The "q" component represents the torque producing component.
These two decoupled components (d-q) can be independently controlled by passing though separate PI controllers. The outputs of the PI controllers are transformed back to the three-dimensional stationary reference plane using the inverse of the Clarke-Park transformation. The corresponding switching pattern is pulse width modulated (PWM) and implemented using the Space Vector Modulation (SVM). This control simulates a separately exited DC motor model, which provides an excellent torque-speed curve.
Vector control frequency converters from Shenzhen POWTRAN Technology Co., Ltd.:
The transformation from the stationary reference frame to the rotating reference frame is done and controlled with reference to a specific flux linkage space vector (stator flux linkage, rotor flux linkage or magnetizing flux linkage). Generally there exists 3 possibilities for such selection and hence, three different vector controls. They are:
Stator flux oriented control
Rotor flux oriented control
Magnetizing flux oriented control
We will introduce these 3 different vector controls of frequency inverters (variable speed drives, VFDs) later.
(To be continued)
