Voltage sag and momentary interruption ride-through for adjustable speed drives

Graduation date: 1999The awareness of electric power quality has increased over the past decade as electronic equipment\ud has become more susceptible to power disturbances. The most disruptive power disturbances are voltage\ud sags and momentary interruptions and their effect on adjustable speed drives (ASDs) is studied in this\ud thesis.\ud Several solutions have been suggested to provide only voltage sag ride-through to ASDs, but most\ud solutions focus on ASDs with passive rectifiers since they hold the largest share of the market. This thesis\ud focuses on ASDs with active rectifiers, which is an emerging and growing market due to the advantages\ud of four quadrant operation and reduced harmonics offered. A solution is presented which provides an\ud ASD with an active rectifier with the capability to ride through the most common sags in order to reduce\ud the frequency at which the ASD trips and thereby increase its reliability.\ud In order to provide ASDs with the capability to ride through momentary interruptions, it is\ud necessary to interface an energy storage system to the ASD. Flywheels, ultra-capacitors and batteries are\ud evaluated for use in an energy storage system to provide voltage sag and momentary interruption ride-through\ud and a detailed comparison of six systems based on these technologies is presented. The interface\ud circuit between the energy storage system and ASD has a significant influence on the performance of the\ud energy storage system and therefore interface circuits to ASDs with passive and active rectifiers are\ud studied.\ud The addition of an ultra-capacitor energy storage system to an ASD with an active rectifier in order\ud to provide ride-through of deeper sags and momentary interruptions is studied and a fuzzy logic controller\ud is designed to enhance system performance. Initially, no communication between the ASD and the ultra-capacitor\ud system is assumed and the ultra-capacitor system can therefore be added as a retro-fit to an\ud existing ASD. It is, however, foreseen that the market for ASDs with ride-through capability of voltage\ud sags and momentary interruptions will grow and the concepts for an integrated design of an ASD and an\ud energy storage system are presented