Low-loss HVDC transmission system with self-commutated power converter introducing zero-current soft-switching technique

In recent years, application of self turn-off devices for the HVDC transmission system is very important for flexible and high efficient power transport and supply. However, for self turn-off devices that are applied to high-power system, excessive switching losses due to voltage/current surges occurred on hard switching and the current tail characteristics on turn-off lead to the considerable switching loss. Therefore switching-loss reduction by using a soft-switching technique is very effective for improvement of the considerable switching losses. A self-commutated HVDC circuit topology with soft-switching characteristics is discussed. The proposed topology is able to achieve a zero-current switching in self-commutated power converters. In order to examine the effectiveness of the proposed system, the system is analysed in terms of the characteristics of switching losses through a theoretical approach and computer simulations.