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CSEE Journal of Power and Energy Systems 2023, 9(1): 365-379 https://doi.org/10.17775/CSEEJPES.2022.05460
Open Access | Issue | Published: 09 December 2022

Isolated Bipolar Modular Multilevel DC-DC Converter with Self-balancing Capability for Interconnection of MVDC and LVDC Grids

Show Author's Information Jinmu Lai1,  Xin Yin2 ( ),  Yaoqiang Wang1,  Lin Jiang2,  Zia Ullah3,  Xianggen Yin3
School of Electrical, and Information Engineering, Zhengzhou University, Zhengzhou 450001, China
Department of Electrical Engineering, and Electronics, University of Liverpool, Liverpool, UK
State Key Laboratory of Advanced Electromagnetic Engineering, and Technology, Huazhong University of Science, and Technology, Wuhan 430074, China
Keywords:
equivalent circuit, DC-DC converter, Bipolar, modular, monopolar operation, multilevel, self-balancing
Cite this article:
Lai J, Yin X, Wang Y, et al. Isolated Bipolar Modular Multilevel DC-DC Converter with Self-balancing Capability for Interconnection of MVDC and LVDC Grids. CSEE Journal of Power and Energy Systems, 2023, 9(1): 365-379. https://doi.org/10.17775/CSEEJPES.2022.05460
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Abstract Full text About this article

Bipolar medium-voltage DC (MVDC) and low-voltage DC (LVDC) grids have the advantages of flexible integration of distributed renewable-energy generation and reliable power supply. In order to achieve voltage conversion, power transfer, and electrical isolation for bipolar MVDC and LVDC grids, a high-power DC-DC converter is essential. Therefore, this paper proposes an isolated bipolar modular multilevel DC-DC converter (BiMMDC) with power self-balancing capability for interconnection of MVDC and LVDC grids. The proposed BiMMDC consists of two series connected MMCs in the MV stage to configure a bipolar MVDC interface, and interleaved converters combined with a dual-transformer are designed in the LV stage to configure the bipolar LVDC interface and to provide a self-balancing capability. Equivalent circuits of two series-connected MMCs and a dual-transformer with interleaved converters are derived. After that, operation principles of the proposed BiMMDC are introduced, considering balanced/unbalanced power transfer of bipolar LVDC grid and monopolar short-circuit or open-circuit faults at MVDC grid. The control scheme is also presented for the proposed BiMMDC under different operating conditions. Finally, a Matlab simulation and controller hardware-in-the-loop (CHIL) evaluation results are provided to validate the feasibility and effectiveness of the proposed typology and its operating performance.


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About this article

Isolated Bipolar Modular Multilevel DC-DC Converter with Self-balancing Capability for Interconnection of MVDC and LVDC Grids

Show Author's information Jinmu Lai1, Xin Yin2 ( ), Yaoqiang Wang1, Lin Jiang2, Zia Ullah3, Xianggen Yin3
School of Electrical, and Information Engineering, Zhengzhou University, Zhengzhou 450001, China
Department of Electrical Engineering, and Electronics, University of Liverpool, Liverpool, UK
State Key Laboratory of Advanced Electromagnetic Engineering, and Technology, Huazhong University of Science, and Technology, Wuhan 430074, China

Abstract

Bipolar medium-voltage DC (MVDC) and low-voltage DC (LVDC) grids have the advantages of flexible integration of distributed renewable-energy generation and reliable power supply. In order to achieve voltage conversion, power transfer, and electrical isolation for bipolar MVDC and LVDC grids, a high-power DC-DC converter is essential. Therefore, this paper proposes an isolated bipolar modular multilevel DC-DC converter (BiMMDC) with power self-balancing capability for interconnection of MVDC and LVDC grids. The proposed BiMMDC consists of two series connected MMCs in the MV stage to configure a bipolar MVDC interface, and interleaved converters combined with a dual-transformer are designed in the LV stage to configure the bipolar LVDC interface and to provide a self-balancing capability. Equivalent circuits of two series-connected MMCs and a dual-transformer with interleaved converters are derived. After that, operation principles of the proposed BiMMDC are introduced, considering balanced/unbalanced power transfer of bipolar LVDC grid and monopolar short-circuit or open-circuit faults at MVDC grid. The control scheme is also presented for the proposed BiMMDC under different operating conditions. Finally, a Matlab simulation and controller hardware-in-the-loop (CHIL) evaluation results are provided to validate the feasibility and effectiveness of the proposed typology and its operating performance.

Keywords: equivalent circuit, DC-DC converter, Bipolar, modular, monopolar operation, multilevel, self-balancing

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Received: 08 August 2022
Revised: 13 October 2022
Accepted: 24 October 2022
Published: 09 December 2022
Issue date: January 2023

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