OBSERVER-BASED DIRECT FIELD ORIENTATION - ANALYSIS AND COMPARISON OF ALTERNATIVE METHODS

This paper focuses on methods of achieving direct field orientation (D FO) of induction machines based on closed-loop, stator, and rotor flux observers which are well suited to both zero and very high-speed oper ation. Both observer topologies are dominated by a current model at ze ro and low speeds, and a voltage model at high speeds. Application of such rotor and stator flux observers to both stator and rotor direct f ield orientation is presented, including experimental results for thre e different methods. The influence which flux regulation has on parame ter sensitivity of the complete DFO system is analyzed. A rotor-flux-r egulated and -oriented system is shown to be sensitive to leakage indu ctance under high slip (i.e., field weakened) operation. Both a stator -flux-regulated and -oriented system and a stator-flux-regulated, roto r-flux-oriented system are shown to have reduced parameter sensitivity at high speeds. Unlike stator flux orientation using simple voltage i ntegration stator flux models, excellent zero and low-speed operation of an observer-based stator-flux-oriented system is demonstrated.