An Improved AC-Link Voltage Matching Control for the Multiport Modular Multilevel DC Transformer in MVDC Applications

Yong Chen, Songtao Yu (), Yizhen Wang (), Ruixiong Yang and Xu Cheng
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Yong Chen: DC Power Distribution and Consumption Technology Research Center of Guangdong Power Grid, Zhuhai 519099, China
Songtao Yu: State Key Laboratory of HVDC, Electric Power Research Institute, CSG, Guangzhou 510663, China
Yizhen Wang: Key Laboratory of the Ministry of Education on Smart Power Grids, Tianjin University, Tianjin 300072, China
Ruixiong Yang: DC Power Distribution and Consumption Technology Research Center of Guangdong Power Grid, Zhuhai 519099, China
Xu Cheng: DC Power Distribution and Consumption Technology Research Center of Guangdong Power Grid, Zhuhai 519099, China

Energies, 2024, vol. 17, issue 6, 1-14

Abstract: In this paper, an improved AC-link voltage matching control (IVM) strategy is proposed for the multiport modular multilevel DC transformer (M3DCT), which comprises a single-phase modular multilevel converter (MMC) and a series of cascaded H-bridge units. The objective of the proposed IVM strategy is to address the AC-link voltage mismatch phenomenon. Distinct from existing control methods, such as various phase-shifting control methods and the conventional AC-link voltage matching control strategy, the proposed IVM strategy orchestrates the operation of the M3DCT in an innovative fashion. It allows the sum of inserted submodule (SM) numbers in the upper and lower arms to be flexible, no longer confined to a specific SM number per arm. Consequently, the AC-link voltage of the M3DCT is maintained proximate to the matched operating condition, regardless of the degree of mismatch in the DC side voltage of the M3DCT. This enables the enhancement of the M3DCT’s overall operational performance, particularly under conditions of light loads within medium-voltage DC (MVDC) distribution systems. The correctness and effectiveness of the proposed control strategy and the corresponding analysis are substantiated through simulation results.

Keywords: MVDC distribution networks; multiport modular multilevel DC transformer (M3DCT); AC-link voltage mismatch phenomenon; current stress; phase-shift control (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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