In flexible high-voltage source converter high-voltage direct current (VSC-HVDC) transmission systems integrated with renewable energy (RE) and thermal power units, the ratio between thermal and renewable energy units, the proportion of grid-following (GFL) to grid-forming (GFM) renewable units, and the electrical distance between thermal units and the collection bus may affect system stability. However, due to challenges in system modeling, the underlying mechanisms of their potential impacts remain unclear. To address this issue, this paper proposes a modeling method specifically designed for such systems, comprehensively considering the dynamic characteristics and interactions among all components. First, mathematical models of renewable energy units, thermal power units, and transmission lines are established based on the impedance method. Subsequently, an open-loop transfer function model for the flexible HVDC converter is developed, followed by integration at the bus. Using this model, the study investigates the impact of progressively increasing renewable energy penetration on system stability, identifies key influencing factors, and determines the safe and stable operational boundaries of the system. Finally, leveraging the proposed model, MATLAB-based analysis evaluates the effects of critical variables on system dynamics, leading to principal conclusions.
Li et al. (Mon,) studied this question.
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