Regarded as constant). Equations derived for the current-fed machine remain to be valid. Two coordinate transformations are required: one transforms stator voltage d-q axis references into phase voltage references, while the other one transforms measured phase currents into d-q axis components. | HIGH PERFORMANCE DRIVES 50 regarded as constant . Equations derived for the current-fed machine remain to be valid. Two coordinate transformations are required one transforms stator voltage d-q axis references into phase voltage references while the other one transforms measured phase currents into d-q axis components. Hence the equations that are relevant for a voltage-fed rotor flux oriented induction machine are the following 1 vds vds ed 1 Vqs Vqs eq ed - r Lsiqs eq r- Vr m V T Li dt r - VrT L íqS t -3 . Va Vds C0S Or - VqS Sin O . vb vds cos Or - 2n 3 - vqs sin Or - 2n 3 v Vds cos Or - 4n 3 - sin Or - 4n 3 ids 2 3 ia cos Or ib cos Or - 2n 3 ic cos Or - 4n 3 iqs - 2 3 ia sinOr ib sin Or -2n 3 ic sin Or -4n 3 It should be noted that the control system in both the voltage fed and current fed drive processes DC quantities see discussion in Sub-section . and that it fully corresponds to the one met in DC machines. The principal difference is the need for co-ordinate transformation in the case of an induction machine. . ESTIMATION OF MAGNITUDE AND POSITION OF ROTOR FLUX SPACE VECTOR . Methods for direct rotor flux oriented control If the decoupled flux and torque control is to be achieved it is absolutely necessary to know instantaneous position of the rotor flux space vector because the stator current space vector has to be orientated with respect to the rotor flux space vector. Estimation method suggested at the earliest stage of vector control development applies convenient induction machine model and measured values of stator currents and air gap flux main magnetising flux . Hall sensors are utilised for assessment of main flux components. Stator phase currents are measured and converted into alfa-beta components using ia 2 3Wa - - i - 2 3 -i 3 2 i 3 2 while Hall sensors directly provide main flux components in the stationary reference frame yrm y two fixed sensors are used in the air-gap of the machine displaced by 90 .
