Novel modulated equivalent model of point-to-point LCC-based high voltage AC/DC/AC system for geomagnetic storm-induced unbalanced harmonic studies

• Published in: International journal of electrical power & energy systems Vol. 122; p. 106173
• Main Authors: Shahsavarian, Tohid, Cao, Yang, Anagnostou, Emmanouil, Kalbfleisch, Roderick
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2020
• Subjects: Geomagnetic disturbance; Harmonic disturbances; HVDC grids; Line-commutated converters; Transformer half-cycle saturation; HVDC grids; Transformer half-cycle saturation; Harmonic disturbances; Geomagnetic disturbance; Line-commutated converters
• ISSN: 0142-0615; 1879-3517
• DOI: 10.1016/j.ijepes.2020.106173

•This work represents the first systematic study of harmonic disturbances for AC/DC interconnected system under GMD.•A novel complete equivalent time-variant model is proposed for wide ranges of harmonics.•The impact of the commutation overlap angle has been studied thoroughly.•The toolbox facilitates rapid and timely high-fidelity mitigation planning in the future event of GMD. Geomagnetically induced currents have been recognized as significant factors in causing power transformer saturation and damage to other key components of the power system via the injection of a wide range of harmonics to the system. Non-characteristic harmonics owing to transformer saturation during geomagnetic storms generates a wide range of reflected harmonics in HVDC/HVAC grids which cannot be filtered using conventional passive filters. These harmonics depending characteristic impedance of adjacent grid can be damped or amplified. Due to the nonlinear nature of converters, assessing the impact of each injected harmonics on the generation of different frequency components requires complete circuit analysis on both AC and DC sides, the complexity of which often necessitates mitigation solutions beyond a simple converter filter design. This work aims to introduce a novel numerical model to represent the HVDC system’s reaction for all harmonic components from disturbances. Also, accurate calculations have been provided to obtain time-variant transferred impedance by the modulation process of 12-pulse bridge converters behind the converter transformer. With proper parametrization of the converter and grid, this model enables the analysis of the whole system without requiring further calculations on the HVDC side. The impact of the commutation overlap angle has been studied thoroughly in this work. The accuracy of proposed model was verified by comparing the results obtained from a direct impedance method and fully-controlled LCC model in Electromagnetic Transient Program (EMTP) for both single and multiple injected harmonic scenarios. Grid voltage and current values at different frequencies for similar harmonic injection scenarios using the proposed reflected equivalent circuit and EMTP model were obtained and compared.