Calculation of harmonic interference in HVDC systems with unbalance

A technique which is useful in analyzing the nontheoretical harmonics in the converters is the modulation theory of converters. The authors outline the basic theory and then use it to calculate the nontheoretical harmonics in HVDC systems under unbalanced AC supply conditions. The effects of the commutation overlap and the commutation impedance in the harmonic calculations have been taken into consideration. Examples are given for some typical HVDC schemes with unbalanced AC supplies. The results are compared with those produced by a time domain digital simulation package, SABER. The good agreement shows the effectiveness of the analytical method