A topology-based simplified dynamic model and solving algorithm for LCC-HVDC converters considering commutation failure

• Topology-based dynamic model preserves LCC valve switching and commutation behaviour. • Structure-stable solver enables fast simulation under changing converter topologies. • Model captures commutation failure dynamics with high accuracy and efficiency. Dynamic modeling of line-commutated converter (LCC) based high-voltage direct current (HVDC) systems faces a trade-off between computational efficiency and accuracy in capturing commutation failure (CF) behavior. Existing electromagnetic transient (EMT) models are highly accurate but computationally intensive, whereas simplified models often neglect valve-level switching dynamics and CF mechanisms. To overcome these limitations, this paper proposes a topology-based simplified dynamic (TBSD) model for LCC-HVDC converters. The model adopts ideal switch representations to preserve the discrete switching behavior of thyristors, and decomposes the converter circuit into a main network and a valve-level auxiliary network based on topological states. Then, a structure-stable solving algorithm is developed to maintain consistent matrix dimensions across different switching configurations. Furthermore, an adaptive time-step control strategy is introduced, which dynamically adjusts the simulation step based on the rate of change in DC current, achieving both computational acceleration during steady-state and high-resolution tracking during transients. The proposed model and solution method are implemented in the PSModel simulation platform and validated against PSCAD/EMTDC under steady-state and fault conditions. Simulation results confirm that the TBSD model accurately captures commutation failure dynamics while significantly improving computational efficiency.