Abstract
Squirrel-cage induction motors, due to their simple structure, cheaper cost and ruggedness, have been widely used in various applications. However, due to the complex dynamic model, the corresponding field oriented control characteristics are not well grasped by general engineers. Hence, in this thesis, a general flux oriented control is first proposed to unify the existing field oriented controls for easy understanding the principle. In other words, the existing field oriented controls become special cases of the proposed general flux oriented control. Also, new flux oriented controls can be derived from the proposed general control. In addition, contributions of this thesis can be summarized as follows. First, accurate theoretical maximum torque of the familiar rotor flux oriented control is derived. It is found that if the stator resistance is neglected as usually done in the literature, then the corresponding maximum torque may either be over estimated or under estimated in the field weakening region. Second, detailed steady state characteristics of the proposed general flux oriented control are analyzed. It is interesting to see that, in spite of different choices of the parameters, the maximum torque in the constant torque region, and the corresponding slip as well as copper loss are identical. Moreover, the flux linkage magnitude of the existing field oriented controls happen to be located near the local minimum which implies the resulting core loss will also be smaller. Finally, due to limitation of time, a general equivalent impedance expression is derived for the general flux oriented control for convenient transforming the voltage constraint into corresponding current constraint such that the accurate maximum torque in the field weakening region can be explored in the future.