FIRING ANGLE MODULATION FOR ELIMINATING TRANSFORMER DC CURRENTS IN COUPLED AC-DC SYSTEMS

A method of eliminating de components of the currents in the transform er windings of a de converter is presented. The method uses the techni que of firing angle modulation. It is shown that merely eliminating th e fundamental frequency component on the de side may not remove this d e component. The impact of such control action at one converter on the other converters in the de transmission system is also presented, It is also shown that the undesirable side effects of such a scheme inclu de increased generation of non-characteristic harmonics on both the ac and de sides. The study is performed using an electromagnetic transie nts simulation program and theoretical calculations.