Observer-based direct field orientation for both zero and very high speed operation (of asynchronous machines)

This paper focuses on the design and analysis of a direct field orientation (DFO) approach based upon a closed-loop rotor flux observer. The approach is ideally suited for applications requiring both zero and very high (i.e. several times base) speed operation. The observer effectively combines the best accuracy attributes of rotor flux indirect (feedforward) field orientation (IFO) and stator flux DFO. The parameter sensitivity is similar to IFO at low and zero speeds and to stator flux DFO at high speeds. The closed-loop observer provides a smooth transition between two open-loop rotor flux observers referred to as the current and voltage models in a deterministic manner set by the closed-loop eigenvalues. The proposed DFO approach is analytically evaluated in comparison with both IFO and stator flux DFO. Experimental results verify the viability of this approach.<>