Power quality measurements and mitigation of disturbances due to PWM AC drives

Abstract

Variable speed AC drives are finding their place in all types of industrial and commercial loads. One important application of these drives is in process control, controlling the speed of fans, compressors, pumps and blowers. However, there are many line (source) design parameters frequently overlooked. A pipeline for transporting synthetic crude oil was installed in Argentina and variable frequency drives (VFD) were employed to control the centrifugal pumps, in order to provide flow and pressure control. During the commissioning and start-up program, the IITREE-LAT performed Power Quality measurements and EMC studies in the petroleum process plants. The first part of the paper deals with the problem of commonmode voltages and its mitigation. In the second part of the paper, the preservation of the reference levels for the supply voltage and emission limits for the petroleum plant as a customer is evaluated by measurements of harmonics content in both voltage and current. An LC resonance problem was found and a practical solution was implemented. The fulfillment of power quality limits for both International and Argentinian standards is assessed. Finally, the behavior of the VFD – in terms of PQ indicators – under different load conditions is analyzed in detail.