AC main drives, such as cycloconverters, offer the possibility of higher speed and torque response over their DC counterparts. The price to be paid, however, is torque ripple which is a function of the operating frequency. Even a small value of ripple, at an underdamped plant resonant frequency, may be multiplied by the plant "Q" to a large enough value to cause trouble. Typical classical approaches used in the rolling mill industry to deal with mechanical resonance tend to fall apart with large values of time lag. We investigate a modified LQR/LQE approach using a torque sensor as the feedback element. The result is a low order SISO filter that suppresses the effects of the torque ripple on the underdamped plant. / Master of Science

This thesis is about the development and performance enhancement of an induction motor electric vehicle drive system. The fundamental operation of the induction motor drive hardware and control software are introduced, and the different modulation techniques tested are described. A software simulation package is developed to assist in the control design and analysis of the drive system. Next, to establish the efficiency gains obtained by using space vector modulation in the improved drive system, an inverter with hysteresis current control is compared to the same inverter with space vector modulation in steady state and on separate driving profiles. A method for determining induction motor harmonic losses is introduced and is based on obtaining the phase current harmonics from sampled induction motor stator phase currents obtained. Using a semi-empirical loss model, the induction motor losses are compared between different pulse width modulation control strategies throughout the torque versus speed operating region. Next, several issues related to the robustness of the control design are addressed. To obtain good performance in the actual vehicle, a new method for driveline resonance compensation is developed and proven to work well through simulation and experiment. Lastly, this thesis discusses the development of a new method to compensate for the gain and phase error obtained in the feedback of the d-axis and q-axis stator flux linkages. Improved accuracy of the measured stator flux linkages will be shown to improve the field oriented controller by obtaining a more accurate measurement of the feedback electromagnetic torque. / Master of Science