DC resonance suppression for hybrid double-ended HVDC transmission systems

Abstract

In a high-voltage direct current (HVDC) transmission system, it is increasingly adopted to connect or replace a part of its traditional line commutated converters (LCCs) with modular multilevel converters (MMCs), forming a hybrid HVDC system. This hybrid topology achieves high performance at a relatively low cost and thus has gained lots of attention from industry. This paper analyzes the DC resonance issue of a hybrid double-ended HVDC system by simplifying the DC side of the MMC into a series-connected LC load. A new control method is proposed to inject damping into the resonance system. As a result, the DC resonance is eliminated by dynamically adjusting the total number of inserted submodules of the MMC, without changing the current and voltage on the AC side. The feasibility and performance of the proposed method is validated by simulations in PSCAD.