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Design and Control of Unidirectional DC/DCModular Multilevel Converter for Offshore DC Collection Point: Theoretical Analysis and Experimental Validation

Lookup NU author(s): He Liu Liu, Dr Mohamed Dahidah, Dr James Yu, Dr Naayagi Ramasamy, Dr Matthew Armstrong



This is the authors' accepted manuscript of an article that has been published in its final definitive form by IEEE, 2019.

For re-use rights please refer to the publisher's terms and conditions.


This paper presents the design and control of an advanced unidirectional DC/DC Modular Multilevel Converter (MMC) which enables the integration of off-shore windfarms with the High-Voltage Direct Current (HVDC) transmission system. The proposed converter consists of a single-phase MMC inverter, coupled with series-connected rectifier modules through a medium frequency transformer of multiple secondary windings. The modularity feature of the proposed converter enables scalability for different voltage levels. In addition to the galvanic isolation, the transformer also provides stepping gain to the output voltage. The proposed converter shows superior performance in terms of efficiency, losses and devices utilization, when compared with the most competitive unidirectional cascaded DC/DC converters such as input series output series (ISOS) and input parallel output series (IPOS). Furthermore, unlike the conventional d-q control method, which involves multiple transformations, this paper employs a simple proportional resonant (PR) control strategy that directly acts on the AC output of the MMC, under the stationary reference frame. The analytical design along with the simulation and experimentally validated results, confirmed the excellent performance of the proposed converter.

Publication metadata

Author(s): Liu H, Dahidah MSA, Yu J, Ramasamy NT, Armstrong M

Publication type: Article

Publication status: Published

Journal: IEEE Transactions on Power Electronics

Year: 2019

Volume: 34

Issue: 6

Pages: 5191-5208

Print publication date: 01/06/2019

Online publication date: 22/08/2018

Acceptance date: 08/08/2018

Date deposited: 30/08/2018

ISSN (print): 0885-8993

ISSN (electronic): 1941-0107

Publisher: IEEE


DOI: 10.1109/TPEL.2018.2866787


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