To make the control system open for motoring & generating, we shall consider that only torque vs speed is performed. In core, a functional generator produces the desired torque versus speed curve desired from the IG (Fig 5.2-a to Fig 5.2-c). For motor starting, the torque vs. speed may decrease notably with speed (Fig 5.2-a)
. the essential is, by an a priori applied optimization procedure that involves the prime-mover characteristics & IG capability, the optimal torque(speed) curves are calculated. From now on +ive or -ive torque control is performed by the help of various torque speed curves stored in tables & are called upon depending to the operation mode. For the purpose of generating, the reference power P is set, but after this its value is termed into the torque/speed The direct torque & flux control (DTFC) seems to be natural to the application once torque control is required. Stator flux control is added, & therefore the control system comes in state of robust & presents fast response. We can express the stator flux functional in terms of flux vs. torque, for minimizing the losses in the IG over the whole speed & power range. The space vector modulation (SVM) is added for reduction of the IG current harmonics, converter losses, & noise.
The 2 major components of DTFC for SCIGs are the state observers & the DTFC–SVM strategy. Vector control strategies are carried out similarly but apparently with to some extent larger online computation efforts & higher sensitivity to machine parameter variation.
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