Observer-based direct fiels orientation : analysis and comparison of alternative methods

This paper focuses on methods of achieving direct field orientation (DFO) of induction machines based on closed-loop, stator, and rotor flux observers which are well suited to both zero and very high-speed operation. Both observer topologies are dominated by a current model at zero and low speeds, and a voltage model at high speeds. Application of such rotor and stator flux observers to both stator and rotor direct field orientation is presented, including experimental results for three different methods. The influence which flux regulation has on parameter sensitivity of the complete DFO system is analyzed. A rotor-flux-regulated and -oriented system is shown to be sensitive to leakage inductance under high slip (i.e., field weakened) operation