Multi-object control of an isolated DC–DC modular multilevel converter

Yu Chen; Shanshan Zhao; Zuoyu Li; Yong Kang

Multi-object control of an isolated DC–DC modular multilevel converter

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Author(s): Yu Chen^{1, 2} ; Shanshan Zhao^{1, 2} ; Zuoyu Li^{1, 2} ; Yong Kang^{1, 2}
- Affiliations: 1: State Key Laboratory of Advanced Electromagnetic Engineering and Technology (AEET), Huazhong University of Science and Technology (HUST) , Wuhan , People's Republic of China ;
  2: School of Electrical and Electronic Engineering (SEEE) , Huazhong University of Science and Technology (HUST) , Wuhan , People's Republic of China
Source: Volume 11, Issue 8, 10 July 2018, p. 1338 – 1349
DOI: 10.1049/iet-pel.2017.0151 , Print ISSN 1755-4535, Online ISSN 1755-4543

Received 25/02/2017, Accepted 10/01/2018, Revised 07/01/2018, Published 10/01/2018

Two medium voltage direct current (MVDC) grids can be connected via an isolated DC–DC modular multilevel converter (DC–DC MMC) to enhance the power transmission and supporting abilities. DC power, DC terminal currents, arm energy balancing and active/reactive power through inner AC link need to be controlled in such a DC–DC MMC, and the submodule and grid fault situations should also be addressed. Therefore, a multi-object controller is inherently required. This study thus proposes a multi-object control frame that can realise not only DC power regulation but also inner dynamic control, reactive power optimisation and fault riding through. To facilitate the controller design, a detailed dynamic model of DC–DC MMC is also derived, and such a model is turned into different forms according to different control objects. The proposed control method and the main design considerations are given in a detailed mathematical way. A full-scale simulation system containing a 6 MW DC–DC MMC, a 20 kV MVDC grid, a 10 kV MVDC grid, and several sources and loads is built to verify the control compatibility, and a down-scale low-power prototype is also built to test the control performance.

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