page 1/9 Shunt Active Filter for Power Quality Improvement João Afonso * , Maurício Aredes + , Edson Watanabe + , Júlio Martins * * University of Minho - Industrial Electronics Dept. Campus de Azurém – 4800 Guimarães – Portugal e-mail: lafonso@dei.uminho.pt e-mail: jmartins@dei.uminho.pt + Federal University of Rio de Janeiro – COPPE/UFRJ Cx.P.2754 – CEP: 21945-970 Rio de Janeiro, RJ, Brazil e-mail: aredes@coe.ufrj.br e-mail: watanabe@coe.ufrj.br Abstract This paper describes the development of a low cost shunt active power filter with digital control, which allows dynamic power factor correction and both harmonics and zero-sequence current compensation. The active filter controller is based on the instantaneous power theory (p-q theory) and was implemented using a standard 16 bits microcontroller. The p-q theory is introduced followed by the presentation of some active power filters topologies. Then a brief description of the implemented solution is made, including references to software tools used for simulation and system development. Experimental results are also presented, showing the good performance of the developed active filter. 1. Introduction Due the intensive use of power converters and other non-linear loads in industry and by consumers in general, it can be observed an increasing deterioration of the power systems voltage and current waveforms. The explanation is simple. Accordingly to Fig. 1, which presents a single-phase system, the voltage across the load terminals is: v v v S L ∆ ⋅ − = 2 where v ∆ is the voltage drop in the power lines impedances. Even if the supply voltage v s is a pure sinusoid, the non-linear load input current is not, and as a result, the supply current 2 1 L L S i i i + = includes harmonics which makes both the voltage drop v ∆ and the load voltage (v L ) non-sinusoidal. NON- LINEAR LOAD POWER SOURCE LINEAR LOAD 1 L i 2 L i S i L R S v L R ∆v ∆v L v Fig. 1 – Problems caused by a non-linear load connected to the power system. The presence of harmonics in the power lines results in greater power losses in distribution, interference problems in communication systems and, sometimes, in operation failures of electronic equipments, which are more and more sensitive since they include microelectronic control systems, which work with very low energy levels. Because of these problems, the issue of the power quality delivered to the end consumers is, more than ever, an object of great concern. International standards concerning electrical energy consumption impose that electrical equipments should not produce harmonic contents greater than specified values. Meanwhile it is mandatory to solve the harmonic problems caused by those equipments already installed. International Conference UIE 2000 – “Electricity for a Sustainable Urban Development” Lisboa, Portugal, 1-4 Novembro 2000, pp. 683-691