A physically insightful approach to the design and accuracy assessment of flux observers for field oriented induction machine drives

Rotor flux observers can provide an attractive means for achieving direct field oriented control of induction machines. The authors present a physics-based design methodology and use it to evaluate open loop observers and to develop a novel closed loop flux observer. It is shown that the new flux observer is a straightforward structure with properties that combine the best features of known methods. A distinction is made between observers which use only integration and feedback summation operations, and those estimation methods requiring approximate differentiation which are, in essence, cancellation methods. Furthermore, a clear distinction is made between accuracy and dynamic robustness of the observer. This distinction is important because the accuracy of flux observers for induction machines is inherently parameter sensitive. A distinctive form of frequency response function analysis similar to that used in classical control engineering is demonstrated to be a useful and insightful tool even though flux observers are multiple-input, multiple-output systems