Digital Modeling Method of HVDC Converter Considering the Turn-Off Characteristics of Thyristors

Introduction: Existing simulation models of thyristors ignore the dynamic turn-off characteristics, resulting in inaccurate simulation of commutation failure in HVDC converters. To accurately characterize the turn-off characteristics of thyristors and simulate commutation failure characteristics of converters, custom digital models of thyristors and converters have been established in this study. Methods: The influence of current zero-crossing rate (di/dt|t=t1), forward current peak (IF), and junction temperature (Tj) on the turn-off characteristics of the thyristor was analyzed. A characterization method for the influence of di/dt|t=t1, IF, and Tj on the turn-off characteristics has been proposed, and a custom digital simulation model of thyristors considering turn-off characteristics has been established. An electromagnetic transient model of the converter that can accurately reflect the characteristics of commutation failure has also been constructed. Results: Compared to the experimental results, the simulation error of the peak reverse recovery current of the proposed thyristor model has been found to be less than 5%, and the simulation error of the turn-off time has been found to be less than 4%. Discussion: The proposed digital model of converters has addressed the problem of inaccurate simulation of commutation failure found in traditional models. This model has significantly enhanced simulation accuracy, providing reliable support for the research on commutation failure in HVDC systems and being of great significance for ensuring system stability. Conclusion: The turn-off process of thyristors and influencing factors have been analyzed in this study, the digital simulation models for thyristors and converters have been established, and the validity and accuracy of the digital models have been verified through simulation.