Abstract
The rotor flux oriented control theory of induction motors has been presented for more than thirty years and there are also related commercial products available in the market. Its main characteristic lies in the instantaneous torque response to achieve as fast dynamic response as a separately excited dc motor drive. However, in spite of the fast torque response, maximization of the resulting torque is still a subject for further improvement. In fact, it is the main motivation of this thesis to propose a new rotor flux oriented maximum torque control strategy for the induction motor drives.Major contributions of this thesis may be summarized as follows. First, a closed form truly maximum torque analytic expression is derived without neglecting the stator resistance and imposing the constraint such as the rotor flux oriented control condition. Second, a closed form analytic expression of the corresponding slip angular frequency as a function of rotor speed is also derived. Based on the previous results, a new rotor flux oriented maximum torque control strategy is then presented to further increase the dynamic response speed under four-quadrant operation. Third, to reduce the effect of variations of the stator and rotor time constants, an on-line estimation method is proposed to correct the time constants. Fourth, a soft starting control is presented to build up the initial rotor flux to achieve very fast starting response without violating the current and voltage constraints of the inverter. Finally, a prototype is also constructed to implement the proposed control strategy by using a digital signal processor, namely TMS320F2407. Both simulation and experimental results verify the validity of the proposed control strategy.