Hybrid reactive power compensation system: advanced control strategy development

Electric arc furnaces are a major cause of line disturbance problems, in terms of flickers and of harmonic pollution. Various solutions had been proposed and applied, with the aim to compensate or control line disturbance phenomena. Optimal solutions can be found by using series and shunt devices, but system cost, reliability and efficiency become main issues. In the paper, authors propose a hybrid control and compensation system that allows an optimal tradeoff in performance and system cost, while providing high efficiency and reliability. The solution is a thyristor based series controller coupled with a high performance shunt compensator. The use of phase control thyristor and the fast changing characteristics of furnace load impose the development of an open loop advanced control strategy based on a load estimator and on the prediction of instantaneous active and reactive power associated with partialized waveforms. Power associated with harmonics is also computed on line, in order to achieve better performances under extreme load conditions and in order to minimize the power required by the expensive shunt compensator. Concept effectiveness is shown by extensive computer simulations.