Decoupled Modeling and Control of the Modular Multilevel Converter

摘要

The modular multilevel converter (MMC) has become a very popular topology in the field of HVDCs. However, the MMC control strategies still inherit from traditional two-level voltage source converter, in which the DC voltage regulation relies on an AC current control loop. In this paper, according to the specific energy storage characteristic of the MMC sub-module capacitors, a decoupled control strategy is proposed which can independently control the AC and DC loops. This strategy not only has a faster response of DC voltage regulation, but also has DC current control capability which avoids overcurrent/oscillation. In addition, a new average-value model is further designed to reflect the energy storage and control decoupling features of MMC. Effectiveness of the proposed control strategy and accuracy of the proposed model are both verified by simulation results.