A novel CCSC for circulating current suppression in modular multilevel converters

摘要

Aiming at the problem of circulating current in MMCs, a novel circulating current suppressing controller (CCSC) is proposed based on the internal-model principle in stationary αβ0 frame in dc-loop control, with the proportional-resonant (PR) regulator adopted. Compared with the existing one, the proposed CCSC seems better, since it does not need the massive amount of computation for estimating the sub-module(SM) capacitor voltages, and is capable of suppressing the 2nd harmonics in circulating currents under both balanced and unbalanced AC system as well. The implementation, steady-state and dynamic performance of the two dc-loop controllers are elaborated in this paper. Simulations prove the feasibility of the new CCSC dc-loop controller, and show good dynamic performance superior to the existing ones.