Feasibility of applying inductive filtering technology to the HVDC transmission system

This study explores the feasibility of applying inductive filtering technology to high-voltage direct-current (HVDC) transmission system since only filtering in the net side may lead to a lot of harmonics in the converter transformer. Basic principles of inductive filtering technology are presented and detail analyses are discussed from the aspects of filtering, vibration, commutation, short circuit, and AC system strength. Simulations and experimental tests show that when inductive filtering technology is applied, most of the harmonics do not enter the net side of the converter transformer but are directly filtered in the valve side. Thus, the harmonics flowing in the converter transformer reduce and the vibration of the converter transformer becomes smaller. The commutation reactance decreases sharply which greatly reduces the overlap angle and improves the commutation characteristics. Moreover, the short-circuit reactance almost keeps unchanged and the short-circuit characteristics do not deteriorate, and so the requirement for the AC system strength is much lower. This study finally concludes that applying inductive filtering technology to the HVDC transmission system is feasible, based on a successful engineering application in the high-power rectifier system.