A personal computer based controller for an active power filter

This paper presents the development of controllers used in active power filters, applied to improve power quality in electrical systems. These active filters can be able to compensate for the following current or voltage related problems: short blackouts, current or voltage distortion due to harmonies, current or voltage unbalance in three-phase systems, flicker (subharmonics) and momentary over or under voltages. There are several causes for current and voltage distortion, namely, non linear loads, some types of voltage sources and thunderstorms. These problems cause instant and long term effects on the electrical equipment. The short term effects are imperfections, malfunctioning, interferences and degradation of the performance of devices or equipments. Effects in the long run are, basically, overheating and premature aging of the electric devices. The main goal of the work described in this paper is to develop an active power filter controller based on a personal computer and a standard multifunction data acquisition PCI bus card, due to its relative low cost, high processing capability, versatility and the numerous possibilities offered by such a computer-based system. Four different approaches were tested: using C++ on Microsoft Windows with the manufacturer's device driver, using a new device driver for Windows, using Linux with real-time application interface; and using LabVIEW for Windows. Experimental and simulation results of the developed controllers are also presented.