Suppression of AC Coupling Effects on HVdc Transmission System Based on MMC

As the number of dc transmission systems increases, more dc lines are constructed in close proximity to existing ac transmission lines. This article deals with ac coupling effect on dc transmission line of modular multilevel converter (MMC) based HVdc system due to neighboring ac lines. Based on a decoupled control of MMC, the operation of MMC is investigated with analytic expression. Furthermore, a new dc bus current controller is proposed to mitigate this effect. By applying the proposed controller, the MMC-HVdc system can operate without any interference from the ac coupling effect. The effectiveness of the proposed controller is demonstrated through both full-scale simulation and scaled experimental studies.