Ride-through alternatives for adjustable-speed drives-computational analysis

Adjustable speed drives (ASD) are recognized as very sensitive to power disturbances. Of the various power quality problems, the voltage sag appears to be the most relevant phenomenon. The device dependence on power quality problems can be attributed to the use of a highly sensitivity protection philosophy to prevent the equipment from high cost damages. Typical voltage sag occurrences may cause the frequency converter to completely shutdown with consequent loss of production and other undesired effects. To prevent this, some strategies can be used to improve the overall system/converter/load performance. Some are quite simple while others involve more complex solutions. Aiming to study the above, this paper uses a time domain simulation to represent the equipment, supply and corresponding load in a comprehensive way. By using this model in the SABER simulator, studies are carried out to illustrate the converter performance under voltage sag conditions with and without the inclusion of ride-through improvement strategies. The aim is to increase the equipment immunity to voltage disturbance considered. Computational results associated with a commercial type of VSI-PWM unit are given to clarify the work.