Small-Signal Modeling of LCC-HVDC Considering Switching Dynamics Based on the Linear Time-Periodic (LTP) Method

Line commutated converter-based high voltage direct currents (LCC-HVDCs) are receiving widespread application but tend to cause broadband small-signal stability issues. Due to the switching dynamics, the original mathematical expressions of LCCs present nondifferentiable, nonlinear, and time-varying characteristics, significantly challenging their accurate small-signal modeling. This paper proposes a novel small-signal state-space model (SSM) for an LCC considering switching dynamics based on the linear time-periodic (LTP) method. Compared to the existing LTP-SSMs, the proposed LTP state-space modeling method can be successfully applied to nondifferentiable systems. Then, comparisons between the proposed LTP-SSM and existing models, such as the dynamic phasor model and harmonic state-space model, are carried out using a two-terminal LCC-HVDC system and a real large-scale power electronic-based power system (PEPS). The comparative analysis demonstrates that the LTP-SSM can accurately describe the switching dynamics without increasing the model order. Therefore, the proposed LTP-SSM can balance analysis accuracy and computational efficiency, offering a distinct advantage over the existing models. Finally, the above analysis results are verified via electromagnetic transient simulation.