ECS-9712596 Shireen Typical low voltage electric power distribution systems are increasingly being contaminated with excessive amounts of harmonic currents due to the growing use of nonlinear loads. The resulting electrical "pollution", often propagates for miles along the distribution feeders. More publicized problem cases have been caused by large single source offenders such as arc furnaces and megawatt-sized adjustable speed drive systems. These situations have been handled by electric utilities on a case by case basis. However, cumulative problems because of the aggregation of thousands of small residential, commercial and industrial nonlinear loads are much more difficult to deal with. Thus, there exists the need for new and innovative circuits that can be placed at end user facilities and on distribution feeders to reduce harmonic distortions. This research project proposes a Digital Signal Processor(DSP) based active power filter to cancel harmonic currents in low voltage electric power distribution systems. In recent years, DSPs have become an attractive means for the implementation of measurement and control algorithms, mainly because of their computing speed and low cost compared to conventional microprocessors used in control applications. The objectives of the proposed research are: To develop a DSP based control algorithm for a single phase active power filter to cancel harmonic currents in low voltage electric power distribution systems. To experimentally evaluate the algorithm on a laboratory prototype. To verify that the DSP-based active power filter is capable of providing localized low cost solution to the harmonic problem in power distribution systems. In view of the proliferation of power electronics equipment connected to the utility system, various national and international agencies have been considering limits on harmonic current injection to maintain a good power quality. The revised IEEE-519-1992 sta ndard, specifies requirements for the users as well as for the utility companies. Therefore, the proposed research will make significant contributions that serve the interests of the utility companies as well as the consumers. DSP-based single phase active power filters as proposed in this project can have significant contribution in isolating and neutralizing harmonics generated by a group of single phase nonlinear loads (such as computers and other electronic office equipment) and thereby protecting the upstream distribution system. This would provide a localized low cost solution, that will also be light in weight and occupy minimum space. The use of a DSP based controller will improve the system performance significantly compared to existing methods. Digital control by a DSP will provide fast transient response, high performance and increased reliability, in addition to the inherent advantages like computational power and immunity to noise and drift. Also, being programmable the DSP-based controller can easily be upgraded or modified to meet specific system requirements.
