Novel modulated equivalent model of point-to-point LCC-based high voltage AC/DC/AC system for geomagnetic storm-induced unbalanced harmonic studies
Novel modulated equivalent model of point-to-point LCC-based high voltage AC/DC/AC system for geomagnetic storm-induced unbalanced harmonic studies
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DOI：
10.1016/j.ijepes.2020.106173
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发表时间：
2020-11
影响因子：
5.2
通讯作者：
Tohid Shahsavarian;Yang Cao;E. Anagnostou;Roderick Kalbfleisch
中科院分区：
文献类型：
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作者：
Tohid Shahsavarian;Yang Cao;E. Anagnostou;Roderick Kalbfleisch
地磁感应电流已被认为是导致电力变压器饱和和电力系统其他关键部件损坏的重要因素，因为它向电力系统注入了广泛的谐波。地磁风暴期间变压器饱和产生的非特征谐波在高压直流/高压交流电网中产生了广泛的反射谐波，而这些谐波不能用传统的无源滤波器滤除。这些依赖于相邻电网特性阻抗的谐波可以被抑制或放大。由于变流器的非线性特性，要评估每次注入的谐波对不同频率分量产生的影响，需要对交流侧和直流侧进行完整的电路分析，其复杂性往往需要除简单的变流器滤波器设计之外的缓解方案。这项工作的目的是引入一种新的数值模型来描述高压直流系统对来自扰动的所有谐波分量的反应。同时，对换流变压器后12脉冲桥式变流器的调制过程进行了精确的计算，得到了时变传递阻抗。通过对换流站和电网进行适当的参数化处理，该模型可以对整个系统进行分析，而不需要在高压直流输电侧进行进一步的计算。本文对换相重叠角的影响进行了深入的研究。通过比较电磁暂态程序(EMTP)中直接阻抗法和完全受控LCC模型在单次和多次注入谐波情况下的计算结果，验证了该模型的准确性。利用所提出的反射等效电路模型和EMTP模型对相似的谐波注入场景下不同频率下的电网电压和电流值进行了计算和比较。
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.