Decoupled flux and torque control of an induction machine can be realised by control of instantaneous phase current values, which in turn can be achieved by stator current space vector magnitude and position control with respect to the chosen flux space vector. As already discussed in the Section ., a vector is composed of appropriate d-q axis components, d-axis component being the real part and qaxis component being the imaginary part of the vector (. d-q axes are mutually perpendicular, as already emphasised). . | HIGH PERFORMANCE DRIVES 41 3. ROTOR FLUX ORIENTED CONTROL OF INDUCTION MACHINES . FIELD ORIENTATION POSSIBILITIES IN INDUCTION MACHINES Decoupled flux and torque control of an induction machine can be realised by control of instantaneous phase current values which in turn can be achieved by stator current space vector magnitude and position control with respect to the chosen flux space vector. As already discussed in the Section . a vector is composed of appropriate d-q axis components d-axis component being the real part and q-axis component being the imaginary part of the vector . d-q axes are mutually perpendicular as already emphasised . Stator current space vector can be orientated with respect to space vector of rotor flux stator flux or air gap flux and machine can be fed from either voltage or current type source. Comparative analysis of different orientation possibilities reveals the main reasons for prevailing application of current-fed induction machines with rotor flux oriented control. If the decoupled flux and torque control are to be achieved in an induction machine by means of either stator flux or air gap flux oriented control an appropriate decoupling circuit has to be inserted in the control part of the system regardless of whether the machine is fed from a voltage or a current type source. A similar conclusion is valid for a voltage-fed induction machine with rotor flux oriented control. Orientation along air gap flux space vector has been a rarely discussed and applied orientation possibility until recently. Orientation along stator flux remained as well beyond the scope of interest for a long time. Recent advancement in development of microprocessors and DSPs enables however significantly easier implementation of decoupling circuits. As a consequence an increase in amount of research devoted to these two orientation methods has occurred recently with emphasis on orientation along stator flux. If the flux space vector is to be .
