A linearised small-signal model of an HVDC converter for harmonic calculation

In this paper a new method is presented for calculation of the harmonics in the ac current and dc voltage of a six-pulse HVDC converter. Instead of fast Fourier transform, FFT, the Fourier series is used in this method. The HVDC converter is represented by a linearised small-signal model in mixed time- frequency domain in which the effects of on and off states resistances, forward voltage drop, and snubber circuits of the thyristors are taken into account. RL series circuits are used for modeling of the converter transformer and ac system. To validate the method a comparison is made with PSCAD/EMTDC time domain simulation program.