Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids

Ahmed Aboushady, Khaled Ahmed, Dragan Jovcic

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Abstract

This paper presents a modular multilevel converter (MMC) based DC/DC converter with LCL inner circuit for HVDC transmission and DC grids. Three main design challenges are addressed. The first challenge is the use of MMCs with higher operating frequency compared to common transformer-based DC/DC converters where MMC operating frequency is limited to a few hundred hertz due to core losses. The second issue is the DC fault response. With the LCL circuit, the steady state fault current is limited to a low magnitude which is tolerable by MMC semiconductors. Mechanical DC circuit breakers can therefore be used to interrupt fault current for permanent faults and extra sub-module bypass thyristors are not necessary to protect antiparallel diodes. Thirdly, a novel controller structure is introduced with multiple coordinate frames ensuring zero local reactive power at both bridges in the whole load range. The proposed controller structure is also expandable to a DC hub with multiple ports. Detailed simulations using PSCAD/EMTDC are performed to verify the aforementioned design solutions in normal and fault conditions.
Original languageEnglish
Title of host publication2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe)
PublisherIEEE
Number of pages6
Publication statusPublished - 2015

Fingerprint

DC power transmission
Electric fault currents
DC-DC converters
Controllers
Networks (circuits)
Electric circuit breakers
Reactive power
Thyristors
Diodes
Semiconductor materials

Keywords

  • DC grids
  • LCL DC/DC converter
  • modular multilevel converter
  • MMC
  • nearest level modulation
  • NLM

Cite this

Aboushady, A., Ahmed, K., & Jovcic, D. (2015). Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids. In 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe) IEEE.
Aboushady, Ahmed ; Ahmed, Khaled ; Jovcic, Dragan. / Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids. 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe). IEEE, 2015.
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title = "Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids",
abstract = "This paper presents a modular multilevel converter (MMC) based DC/DC converter with LCL inner circuit for HVDC transmission and DC grids. Three main design challenges are addressed. The first challenge is the use of MMCs with higher operating frequency compared to common transformer-based DC/DC converters where MMC operating frequency is limited to a few hundred hertz due to core losses. The second issue is the DC fault response. With the LCL circuit, the steady state fault current is limited to a low magnitude which is tolerable by MMC semiconductors. Mechanical DC circuit breakers can therefore be used to interrupt fault current for permanent faults and extra sub-module bypass thyristors are not necessary to protect antiparallel diodes. Thirdly, a novel controller structure is introduced with multiple coordinate frames ensuring zero local reactive power at both bridges in the whole load range. The proposed controller structure is also expandable to a DC hub with multiple ports. Detailed simulations using PSCAD/EMTDC are performed to verify the aforementioned design solutions in normal and fault conditions.",
keywords = "DC grids, LCL DC/DC converter, modular multilevel converter, MMC, nearest level modulation, NLM",
author = "Ahmed Aboushady and Khaled Ahmed and Dragan Jovcic",
year = "2015",
language = "English",
booktitle = "2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe)",
publisher = "IEEE",

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Aboushady, A, Ahmed, K & Jovcic, D 2015, Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids. in 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe). IEEE.

Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids. / Aboushady, Ahmed; Ahmed, Khaled; Jovcic, Dragan.

2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe). IEEE, 2015.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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T1 - Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids

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N2 - This paper presents a modular multilevel converter (MMC) based DC/DC converter with LCL inner circuit for HVDC transmission and DC grids. Three main design challenges are addressed. The first challenge is the use of MMCs with higher operating frequency compared to common transformer-based DC/DC converters where MMC operating frequency is limited to a few hundred hertz due to core losses. The second issue is the DC fault response. With the LCL circuit, the steady state fault current is limited to a low magnitude which is tolerable by MMC semiconductors. Mechanical DC circuit breakers can therefore be used to interrupt fault current for permanent faults and extra sub-module bypass thyristors are not necessary to protect antiparallel diodes. Thirdly, a novel controller structure is introduced with multiple coordinate frames ensuring zero local reactive power at both bridges in the whole load range. The proposed controller structure is also expandable to a DC hub with multiple ports. Detailed simulations using PSCAD/EMTDC are performed to verify the aforementioned design solutions in normal and fault conditions.

AB - This paper presents a modular multilevel converter (MMC) based DC/DC converter with LCL inner circuit for HVDC transmission and DC grids. Three main design challenges are addressed. The first challenge is the use of MMCs with higher operating frequency compared to common transformer-based DC/DC converters where MMC operating frequency is limited to a few hundred hertz due to core losses. The second issue is the DC fault response. With the LCL circuit, the steady state fault current is limited to a low magnitude which is tolerable by MMC semiconductors. Mechanical DC circuit breakers can therefore be used to interrupt fault current for permanent faults and extra sub-module bypass thyristors are not necessary to protect antiparallel diodes. Thirdly, a novel controller structure is introduced with multiple coordinate frames ensuring zero local reactive power at both bridges in the whole load range. The proposed controller structure is also expandable to a DC hub with multiple ports. Detailed simulations using PSCAD/EMTDC are performed to verify the aforementioned design solutions in normal and fault conditions.

KW - DC grids

KW - LCL DC/DC converter

KW - modular multilevel converter

KW - MMC

KW - nearest level modulation

KW - NLM

M3 - Conference contribution

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Aboushady A, Ahmed K, Jovcic D. Modular multilevel converter based LCL DC/DC converter for high power DC transmission grids. In 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe). IEEE. 2015