New approaches to improve the performance of adjustable speed drive (ASD) systems under power quality disturbances

Modern pulse-width modulated (PWM) adjustable speed drive (ASD) systems provide improved efficiency, energy savings and process control in commercial and industrial facilities. However, PWM ASD systems are often susceptible to electric power quality disturbances such as: voltage sags, voltage swells, short-term power interruptions (STPIs), capacitor-switching transients (CSTs), flicker, etc. Numerous power quality surveys have shown that utility transients like sags, swells, short-term power interruptions and CSTs are responsible for numerous nuisance tripping on ASD equipment installed in critical commercial and industrial continuous processes. In response to these concerns, this dissertation analyzes the effects of power quality disturbances on ASD equipment. Extended analyses on the effect of single-phase and polyphase sags, short-term power interruptions (STPIs) and capacitor-switching transient (CST) events on ASD equipment are presented.;In this dissertation, several new approaches to provide ride-through capability for ASDs in the event of voltage sags, short-term power interruptions and CSTs are presented. The main goal of these approaches is to provide the required full output power to the ASD by maintaining the dc-link voltage within its nominal value, through the use of power electronic converters. The full output power to ASD equipment is provided from the remaining voltage in the ac supply or by other energy source such as supercapacitors. Simulation and experimental results validate the proposed approaches to achieve ride-through under voltage sags using the remaining ac supply and also for STPIs using alternative sources of energy.;Additionally, new approaches to mitigate the nuisance tripping issue of PWM ASDs due to CST events are presented. Extensive analysis of the CST event on the distribution system, as well as on the ASD dc-link is presented to evaluate their effects on ASD equipment. The proposed approach facilitates electronic damping of a CST event and protects the ASD from nuisance tripping. Experimental results on a 480 V, 16 kVA ASD are presented to validate the approach.