Abstract
With the advances of power electronics technologies, the switching frequency of power semiconductors has reached several kilo-Hz for hundreds of kilo-watt ratings. Such progress leads to the development of voltage source inverters and high speed drives technologies.Pulse Width Modulation (PWM) techniques have been widely used in inverters and motor drives systems. For high speed drives applications, the PWM operation often face the limit of the switching frequency of the power semiconductors and the limit of the inverter DC bus voltage. Therefore, how to obtain a high quality voltage output waveform with sufficient magnitude under the constraints of switching frequency and DC bus voltage becomes an important issue for high-speed motor drives.In this thesis, a combination of PWM techniques will be presented. The proposed scheme uses conventional sinusoidal PWM (SPWM) in the linear modulation region, and switches to the Discontinuous PWM (DPWM) in the over modulation region to extract wider linear modulation range. Both modes of PWM operate under the principle of synchronous PWM to avoid undesirable sub-harmonics under limited switching frequency. A Proportional-Integral current regulator under the synchronous reference frame will also be included in this system to evaluate the effectiveness of the proposed PWM schemes.This thesis will provide a survey of related literature, and discuss the distinct phenomena in different modulation regions. Simulation results and experimental results will be provided to validate the performance of the proposed strategies.