Design and Simulation of a Hybrid Active-Passive Filter for Power Quality Improvement in Electric Arc Furnaces

Electric arc furnaces (EAFs) represent one of the most demanding nonlinear loads in modern steelmaking industries, characterized by rapid and stochastic variations in arc impedance that generate severe power quality disturbances. These include high levels of current and voltage harmonics (predominantly odd orders such as ۵th, ۷th, ۱۱th, and ۱۳th), voltage flicker due to fluctuating reactive power demand, low power factor (typically ۰.۷–۰.۸۵ lagging), and voltage unbalance at the point of common coupling (PCC). Such disturbances not only increase energy losses and equipment stress but also violate international standards such as IEEE Std ۵۱۹-۲۰۲۲ and IEC ۶۱۰۰۰-۳-۶, potentially leading to penalties, process interruptions, and reduced lifespan of connected apparatus. Traditional mitigation techniques, including standalone passive filters or fully active power filters (APFs), suffer from limitations: passive filters are prone to resonance and detuning under varying load conditions, while pure APFs require high-rated inverters, resulting in elevated costs and switching losses.This research proposes a cost-effective hybrid active-passive filter (HAPF) topology specifically tailored for EAF applications. The passive section comprises shunt-connected single-tuned LC branches optimized for the dominant ۵th and ۷th harmonics, providing bulk harmonic absorption and partial reactive power compensation. The active section employs a three-phase voltage-source inverter (VSI) with insulated-gate bipolar transistor (IGBT) switches, a DC-link capacitor, and coupling inductors, controlled via the synchronous reference frame (SRF) theory with PI regulators for precise harmonic extraction and current tracking. This hybrid configuration leverages the strengths of both approaches: the passive filter handles high-power, fixed-frequency components at low cost, while the active filter dynamically compensates residual harmonics, interharmonics, and reactive power variations across the entire EAF operating cycle (boring, melting, and refining).The complete system, including a realistic EAF model based on a time-varying resistance-arc representation, was simulated in the MATLAB/Simulink environment using the SimPowerSystems toolbox. Comprehensive time-domain and frequency-domain analyses were performed under realistic operating conditions (۴۰۰ V, ۵۰ Hz supply, ۱۰ MVA transformer). Key performance metrics evaluated include total harmonic distortion (THD), individual harmonic content, displacement and true power factor, voltage flicker severity (short-term Pst and long-term Plt per IEC ۶۱۰۰۰-۴-۱۵), and dynamic response during arc fluctuations. Simulation results demonstrate exceptional performance: source current THD reduced from ۳۵.۱۳% to ۶.۲۲%, power factor improved to ۰.۹۸, and voltage flicker mitigated by over ۸۵%. The HAPF also maintains stability under distorted source voltages and parameter variations, confirming robustness.Compared with conventional solutions reported in the literature, the proposed HAPF achieves superior harmonic suppression and flicker reduction at approximately ۴۰–۵۰% lower inverter rating, offering a practical and economically viable solution for existing and new EAF installations. This work contributes to the advancement of power quality enhancement strategies in heavy industries and provides a validated simulation framework for further hardware-in-the-loop implementation.