Advanced modular multilevel converters for high-voltage direct current grids swegrids-logo

SweGRIDS research area Controllable Power Components
SweGRIDS project code CPC4
Project type PhD
Status completed
Researcher Stefanie Heinig   (webpage)
University KTH (EPE)
Project period 2015-05-26 to 2020-06-30    migrated from earlier Elektra funding
Project supervisor Hans-Peter Nee   (webpage)
Industrial sponsors ABB


back to project index


Project abstract

This project addresses the need to investigate new submodule (SM) topologies for modular multilevel converters (MMC) with extended functionality which can be applied in future demanding applications such as meshed high-voltage direct current (HVDC) grids. Supergrids based on HVDC technology are foreseen to be the most attractive solution for handling of massive power variations in electricity grids where most of the generated power originates from renewable power sources. As the direction of power in such grids may change on many of the interconnections voltage source converters (VSCs) are preferable. The state-of-the-art VSC for HVDC transmission is the MMC. When planning HVDC grids with MMCs, one of the most important aspects to consider is DC side fault handling. Even if HVDC circuit breakers have been proposed, cost savings are highly probable if the DC side fault current can be controlled by the converter itself and ancillary services can be provided to the connected AC power system during fault conditions. One promising approach to find advanced SM topologies is based on the idea to equip SMs with more than one capacitor each. This approach leads to improved SM topologies with essentially reduced power losses, such as the semi-full-bridge (SFB) or the double-connection of the novel Double-Zero-Submodule (DZ-SM). Both topologies enable efficient handling of DC side short circuits, whereas the SFB also uses less semiconductors than two conventional full-bridge (FB) SMs. Both SMs provide the possibility to operate the converter at increased modulation indices which can significantly reduce the energy storage requirements of the submodule capacitors. Many aspects of the SFB and the DZ-SM topologies have not been investigated extensively. Moreover, the application of advanced silicon carbide (SiC) power semiconductors is a further option to improve future SM topologies.


Summary of work

2015. The requirements on power electronic converters compatible with DC grids have been determined during the first phase of the project. It entailed the investigation of an HVDC grid test system in the EMT-type software PSCAD. The purpose was first to get familiar with PSCAD and second to study a point-to-point HVDC transmission system with different converter configurations (e.g. symmetrical monopole and bipole). The influence of various grounding schemes has thereby been considered and examined.

2015-2016. A rather in-depth study of state-of-the-art HVDC converter topologies and specifically their energy storage requirements has been conducted. Particular attention has been given to analyzing converters capable of handling DC-side short-circuits, e.g. full-bridge MMC and the alternate arm converter (AAC). These topologies have been benchmarked with focus on the cell capacitor requirements. One conference publication has been presented at the 18th European Conference on Power Electronics and Applications, EPE’16 ECCE Europe, 5-9 September 2016, Karlsruhe, Germany.

2016. Work on a flexible MMC laboratory prototype that will be used among several PhD students has been established. Tasks have been the selection of an appropriate FPGA, redesigning the existing controller as well as implementing and testing it. The applied methods involved programming in VHDL, PCB designs and working with the Xilinx design tools.

2016. The study of the surge current capability of the body diode of silicon carbide (SiC) MOSFETs for HVDC applications has been supported. The results of these investigations have been presented at the 18th European Conference on Power Electronics and Applications, EPE’16 ECCE Europe, 5-9 September 2016, Karlsruhe, Germany.

2016-2017. Research activities on the SFB SM topologies have been initiated, incl. the analysis of possible switching sequences and control methods for the capacitor balancing. A full-scale implementation of the SFB has been constructed and experimental work has been initiated.

2017. Theoretical and experimental results regarding the SFB activities have been presented in a lecture presentation at the 19th European Conference on Power Electronics and Applications, EPE’17 ECCE Europe, 11-14 September 2017, Warsaw, Poland.

2018. Further investigations concerning improved switching sequences of the SFB. By using the proposed alternative bypass state the switching losses can be reduced by up to 60%. These findings have been presented in a lecture presentation at the 20th European Conference on Power Electronics and Applications, EPE’18 ECCE Europe, 17-21 September 2018, Riga, Latvia.

2018. Experimental work on the MMC prototype platform. Conference paper published at EPE’17 has been extended and submitted as journal article to IEEE Transactions on Power Electronics. The article got accepted in November 2018.


Event log

2015. Attended the CIGRE Symposium, 27-28 May 2015, Lund, Sweden.

2015. Attended the “Powering the offshore grid: legal and technical solutions” Conference, 26 June 2015, Amsterdam, Netherlands.

2015. Attended the 17th European Conference on Power Electronics and Applications, EPE’15 ECCE Europe, 8-10 September 2015, Geneva, Switzerland.

2016. Attended the IEEE International Energy Conference ENERGYCON, 4-8 April 2016, Leuven, Belgium.

2016. Research visit at ABB Corporate Research, 15-31 August 2016. A detailed switched model of a full-bridge MMC has been implemented in PSCAD during that time. Furthermore, semiconductor devices and submodules that are available today and high-voltage devices of the future have been investigated regarding their properties.

2016. Attended the 18th European Conference on Power Electronics and Applications, EPE’16 ECCE Europe, 5-9 September 2016, Karlsruhe, Germany.

2017. Attended the 13th IET International Conference on AC and DC Power Transmission (ACDC), 14-16 February 2017, Manchester, United Kingdom.

2017. Attended the ECPE Workshop “Current Measurement for PE Applications in Lab Scale”, 17-18 October 2017, Hamburg, Germany.

2017. Attended the 19th European Conference on Power Electronics and Applications, EPE’17 ECCE Europe, 11-14 September 2017, Warsaw, Poland.

2018. Attended the ECPE Workshop “DC Grids, Technologies and Applications”,

17-18 April 2018, Aachen, Germany.

2018. Attended the PCIM Europe Conference, 5-7 June 2018, Nuremberg, Germany.

2018. Attended the CIGRE Session, 26-31 August 2018, Paris, France.

2018. Attended the 20th European Conference on Power Electronics and Applications, EPE’18 ECCE Europe, 17-21 September 2018, Riga, Latvia.

2018.”Outstanding Young EPE Member Award” at the 20th European Conference on Power Electronics and Applications, EPE’18 ECCE Europe


Project reference-group

Alireza Nami,  ABB Corporate Research
Kalle Ilves,  ABB Corporate Research (and affiliated with KTH)
Jan Svensson,  ABB Corporate Research
Lennart Harnefors,  ABB Corporate Research (and affiliated with KTH)
Frans Dijkhuizen,  ABB Corporate Research (and affiliated with KTH)
Nan Chen,  ABB Corporate Research
Hans-Peter Nee,  KTH


MSc etc theses connected to the project

2017. Kandidatexjobb, KTH. Kontext N: Mikronät för eldistribution, Projekt N1: “Systemfrågor för DC-baserade mikronät”, https://www.kth.se/Kandidatexjobbsprojekt2017

2018. Kandidatexjobb, KTH. Kontext N: HVDC Grids, Projekt N1: "Operation and Control of HVDC Grids".


Publications by this researcher

See alternatively the researcher's full DiVA list of publications, with options for sorting.
Publications in journals and conferences usually will not show until a while after they are published.

Main Circuits, Submodules, and Auxiliary Power Concepts for Converters in HVDC Grids
Stefanie Heinig.
2020,   Thesis (PhD), KTH Royal Institute of Technology, TRITA-EECS-AVL 2020:41

Auxiliary Power Supplies for High-Power Converter Submodules: State-of-the-Art and Future Prospects
Stefanie Heinig,   Keijo Jacobs,   Kalle Ilves,   Staffan Norrga,   Hans-Peter Nee.

Single-Fiber Combined Optical Power and Data Transmission for High-Voltage Applications
Stefanie Heinig,   Keijo Jacobs,   Staffan Norrga,   Hans-Peter Nee.
2020,   The 46th Annual Conference of the IEEE Industrial Electronics Society, IECON 2020, Singapore, October 18-21, 2020

Implications of Capacitor Voltage Imbalance on the Operation of the Semi-Full-Bridge Submodule
Stefanie Heinig,   Keijo Jacobs,   Kalle Ilves,   Luca Bessegato,   Panagiotis Bakas,   Staffan Norrga,   Hans-Peter Nee.
2019,   IEEE transactions on power electronics, vol. 34(10)

Low Loss Submodule Cluster for Modular Multilevel Converters Suitable for Implementation with SiC MOSFETs
Keijo Jacobs,   Stefanie Heinig,   Baris Ciftci,   Staffan Norrga,   Hans-Peter Nee.
2019,   IEEE Energy Conversion Congress and Exposition - IEEE-ECCE 2019, Baltimore, MD, Sept. 29 – Oct. 3, 2019

Reduction of Switching Frequency for the Semi-Full-Bridge Submodule Using Alternative Bypass States
Stefanie Heinig,   Keijo Jacobs,   Kalle Ilves,   Staffan Norrga,   Hans-Peter Nee.
2018,   20th European Conference on Power Electronics and Applications (EPE ECCE Europe), SEP 17-21, 2018, Riga, LATVIA

Implications of Capacitor Voltage Imbalance on the Operation of the Semi-Full-Bridge Submodule
Stefanie Heinig,   Keijo Jacobs,   Kalle Ilves,   Staffan Norrga,   Hans-Peter Nee.
2017,   2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe), SEP 11-14, 2017

Investigation of the Surge Current Capability of the Body Diode of SiC MOSFETs for HVDC Applications
Diane-Perle Sadik,   Stefanie Heinig,   Keijo Jacobs,   Daniel Johannesson,   Jan-Kwon Lim,   Muhammad Nawaz,   Frans Dijkhuizen,   Mietek Bakowski,   Staffan Norrga,   Hans-Peter Nee.
2016,   18th European Conference on Power Electronics and Applications (EPE), SEP 05-09, 2016, GERMANY

On Energy Storage Requirements in Alternate Arm Converters and Modular Multilevel Converters
Stefanie Heinig,   Kalle Ilves,   Staffan Norrga,   Hans-Peter Nee.
2016,   18th European Conference on Power Electronics and Applications (EPE), SEP 05-09, 2016, GERMANY

Publication list last updated from DiVA on 2021-09-18 22:00.


back to project index

Page started: 2018-01-01
Last generated: 2021-09-18