HVDC converter simulation model with turn-off characteristics of series thyristors

• Dynamic dissipation characteristics of charge carriers during the turn-off process are analyzed and the key influence factors of the turn-off characteristics are extracted. • A thyristor simulation model that considers the dynamic dissipation characteristics of charge carriers during the turn-off process is proposed. • A converter simulation model that considers the turn-off characteristics of series thyristors is proposed. The converter models in common electromagnetic transient simulation software cannot reflect the dynamic turn-off process and the dispersity of series thyristors, which leads to inaccurate judgment and simulation of the commutation failure (CF). To characterize the turn-off process of the thyristor precisely from the micro-physical mechanism, the dynamic dissipation characteristics of charge carriers during the turn-off process are analyzed. The current zero-crossing rate, forward current, and junction temperature are extracted as the key influence factors of turn-off characteristics. Then, based on the analysis of the difference in the dynamic dissipation characteristics of charge carriers, a novel nonlinear segmentation mathematical model describing the turn-off process of thyristor is proposed. Considering the dispersity of the reverse recovery charge between series thyristors, a converter model with turn-off characteristics of series thyristors is proposed. The experiment results from the thyristor test platform and the LCC experiment platform verify the accuracy of the proposed thyristor and converter models separately. The simulation errors of peak turn-off current, reverse recovery charge, and turn-off time are less than 5%. Under the single-phase and three-phase short-circuit ground faults, the proposed converter model can judge the CF and simulate the characteristics of the CF more accurately.