Study on the Effects of the DC Bias on the Harmonic Characteristics of the New Converter Transformer

DC bias is the problem that must be faced in the course of the design of the converter transformer for the high-voltage direct current (HVDC) transmission system, especially the new converter transformer that has the unique wiring scheme. This paper will theoretically analyze the basic cause of the dc bias of the new converter, and then according to the real no-load characteristic of the new converter transformer, its simulation model, which considers the hysteresis loss of the core of the new converter transformer, will be established by the means of data fitting. Based on the established simulation model, the harmonic characteristic of the new converter transformer caused by the dc bias will be simulated and analyzed in detail. Furthermore, this paper will propose a new inductive filtering technology to suppress the harmonic caused by the dc bias. Finally, compared with the traditional converter transformer, the superiority that the new suppression scheme has will be revealed.