Abstract
The development of a speed sensorless indirect field-oriented (IFO) induction motor drive fed by a soft-switching inverter is studied in this dissertation. The zero-voltage transition (ZVT) technique is employed to reduce the switching losses and voltage stresses of inverter switches. The proposed soft-switching inverter is formed from the traditional pulse width modulated (PWM) inverter by simply augmenting with auxiliary resonant circuits, and the soft switching is achieved through applying PWM switching control signals with suitable delays for the main and auxiliary switches. No additional voltage and current sensors are required in implementation. In the development of the proposed soft-switching inverter, the circuit operations and derivations of governing equations in various modes are described in detail. And accordingly, the circuit design procedure is derived. Next, an improved speed estimator via parameter uncertainty cancellation and its application to the IFO induction motor drive are presented. The speed estimation errors of a V-I model based adaptive speed observer due to motor parameter variations are analyzed. Then a novel compensation scheme is developed to cancel the effects of parameter variations on the speed estimation performance. The variable structure system (VSS) controller with the detected estimation error signal as its input is employed to realize the proposed compensation scheme. As to the development of high-performance speed controllers, a proportional plus integral-derivative (PI-D) two-degrees-of-freedom controller (2DOFC) is first designed for an ideal IFO induction motor drive at nominal case to meet the desired speed responses. In addition to the tracking and regulation speed control specifications, the effects of command change rate as well as control effort are also considered in the proposed design procedure. As the variations of motor drive parameters occur, the control performance of the detuned IFO induction motor drive will be greatly degraded. A compensation signal is yielded by the proposed fuzzy robust controller (FRC) to preserve the prescribed responses. In the generation of compensation signal, the compromise between the control effort and the performance is considered through a varying weighting factor, which is tuned by a fuzzy controller. Finally, the system dead-time of motor drive using estimated speed as feedback signal will be significantly enlarged, and this may significantly affect the closed-loop operating stability. Thus the fuzzy robust speed controller design for the sensorless IFO motor drive considering the effect of dead-time is further presented. The validities of all the proposed circuits and controllers are verified by some simulation and measured results.