Harmonic Mitigation in Power Transformers through Third Winding Current Injection

Abstract

Harmonic distortions in power distribution systems present a substantial challenge to electric power systems by lowering power quality. This leads to increased power losses, reduced system efficiency, and even damage to sensitive electrical equipment. The increasing use of power electronic-based nonlinear loads and renewable energy sources has increased these challenges, prompting the development of improved harmonic reduction solutions. Traditional mitigation approaches, such as passive and active filters, suffer from efficiency limitations, implementation complexity, and high costs. This research proposes a novel transformer-based harmonic mitigation strategy that leverages current injections into the tertiary winding of a three-winding transformer to dynamically suppress harmonic distortions while maintaining stable voltage and current waveforms. The proposed method exploits the magnetic flux in the transformers iron core to mitigate harmonics at the distribution level, reducing reliance on external filtering components. A key innovation of this research is developing a controlled current injection technique that introduces compensating currents into the tertiary winding, effectively canceling phase-shifted harmonics in the primary and secondary windings. This technique reduces THD and improves overall power quality. Despite traditional filtering systems, which passively absorb or block harmonics, this active compensation method neutralizes undesired harmonic components inside the system, making it a more efficient and scalable option. A comprehensive analysis of harmonic sources and their impact on power distribution networks was conducted to establish the foundation for this research. Conventional mitigation techniques, including passive filters, active filters, hybrid filtering solutions, and phase-shifting transformers, were reviewed to highlight their benefits and limitations. A detailed MATLAB/Simulink model was developed to simulate the behavior of a three-winding transformer under varying nonlinear load conditions, incorporating core nonlinearities such as saturation and hysteresis effects. The proposed injection technique was tested in simulations to evaluate its effectiveness in suppressing harmonics across multiple frequency orders. Experiments were conducted in a controlled laboratory environment to verify the modeling results. The results indicated a considerable reduction in harmonic content, with primary winding current harmonics decreasing from 6.79 to 2.9 in simulations and 4.61 to 2.51 in laboratory testing. These findings demonstrate the proposed approachs feasibility and practical application to real-world power distribution networks. This study and its theoretical contributions provide beneficial insights into the practical application of transformer-based harmonic mitigation strategies. The approach is especially well-suited for renewable energy integration, electric car charging stations, and smart grid applications since it provides a cost-effective and scalable alternative to traditional filtering systems. This research advances transformer-based harmonic suppression solutions, which improve power quality, enhance reliability, and eliminate harmonic-related losses in current electric power systems