Electric Arc Furnaces are considered one of the major achievements in the steel industry. In recent years, these furnaces have attracted significant attention due to their lower investment cost an‎d reduced energy consumption compared to blast furnaces an‎d oxygen-based furnaces. Despite their advantages, electric arc furnaces represent nonlinear, highly fluctuating, an‎d strongly time-varying loads, which lead to power quality issues such as instantaneous fluctuations of active an‎d reactive power, harmonics, low power factor, an‎d flicker. Arc furnaces are generally classified into two categories: AC arc furnaces an‎d DC arc furnaces. With the advancement of iron an‎d steelmaking technologies, along with the rapid an‎d remarkable progress in semiconductor devices an‎d high-power power-electronic converters, the application of DC arc furnaces in these industries has also increased. Therefore, this thesis focuses on DC arc furnaces. The power supplies used for DC arc furnaces are generally divided into two categories: Thyristor-based rectifier power supplies an‎d IGBT-based chopper power supplies. First, through a comparative study, it is shown that power supplies based on IGBT switches have advantages over those based on thyristor rectifiers. Subsequently, through a comprehensive review of arc furnace models, an accurate an‎d practical model is derived for simulating the nonlinear an‎d stochastic behavior of DC electric arc furnaces. This model belongs to the class of chaotic models, which are suitable for simulating the unpredictable an‎d time-varying behavior of DC arc furnaces. The chaotic model used in this thesis is the Chua model, which is also combined with the static model of the furnace, ultimately providing a comprehensive an‎d complete model for simulation. Next, after studying high-power DC–DC converters, the full-bridge converter based on IGBT switches is selec‎ted as the power supply of the DC arc furnace. An advanced control strategy is also proposed for the control of this converter. This control strategy is designed based on the melting process, which consists of two stages: the melting stage an‎d the heating stage. Since arc current fluctuations during the melting stage are very high, the constant-current control strategy is applied. In contrast, during the heating stage, where arc current fluctuations are considerably reduced an‎d relatively a constant power is required to be transferred to the furnace, the constant-power control strategy is employed. Finally, the simulation results carried out in the MATLAB/Simulink clearly demonstrate that the proposed system is capable of successfully mitigating severe arc fluctuations during different stages of the melting process.

حميدرضا كارشناس

محمد سعيد مهدوي , فاطمه زارع