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DC-Link Stress Analysis for the Grid Connection of Point Absorber Type Wave Energy Converters
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-9599-9811
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Univ Bologna, Dept Elect Engn, Bologna, Italy.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2015 (English)In: 2015 International Conference On Clean Electrical Power (ICCEP), 2015, 61-66 p.Conference paper, Oral presentation only (Refereed)
Abstract [en]

Highly random nature of input power from wave energy converters (WEC), especially from direct-driven point absorbers, demands customized power electronic converters for grid connection. In this paper, analysis and comparison of the DC-link stresses in the converter systems for two cases - a single and three collective units, of wave energy converters is given. The AC/DC/AC converter system includes a conventional uncontrolled three phase rectifier, a DC/DC converter to boost the DC-link voltage and an inverter with RL load. The system has been studied under two different controller actions for the DC/DC converter: with constant boost factor and with constant DC-link voltage. A Proportional Integral controller has been used to regulate the voltage in the latter case. Matlab/Simulink based system simulation has been done to compare the DC-link stress. The analysis shows the comparison in DC-link stresses and the requirements of the system for different cases, proving the advantages and the importance of having customized active power conversion methods for minimizing the DC-link stresses.

Place, publisher, year, edition, pages
2015. 61-66 p.
Keyword [en]
DC-link stress analysis; harmonic distortion; passive rectifier; wave energy converter
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-258208DOI: 10.1109/ICCEP.2015.7177601ISI: 000380609800010ISBN: 9781479987047 (print)OAI: oai:DiVA.org:uu-258208DiVA: diva2:841225
Conference
5th International Conference on Clean Electrical Power (ICCEP)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2015-07-10 Created: 2015-07-10 Last updated: 2017-11-01Bibliographically approved
In thesis
1. Multilevel Power Converters with Smart Control for Wave Energy Conversion
Open this publication in new window or tab >>Multilevel Power Converters with Smart Control for Wave Energy Conversion
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis is on the power electronic converter system challenges associated with the grid integration of variable-renewable-energy (VRE) sources like wave, marine current, tidal, wind, solar etc. Wave energy conversion with grid integration is used as the key reference, considering its high energy potential to support the future clean energy requirements and due the availability of a test facility at Uppsala University. The emphasis is on the DC-link power conditioning and grid coupling of direct driven wave energy converters (DDWECs). The DDWEC reflects the random nature of its input energy to its output voltage wave shape. Thereby, it demands for intelligent power conversion techniques to facilitate the grid connection.

One option is to improve and adapt an already existing, simple and reliable multilevel power converter technology, using smart control strategies. The proposed WECs to grid interconnection system consists of uncontrolled three-phase rectifiers, three-level boost converter(TLBC) or three-level buck-boost converter (TLBBC) and a three-level neutral point clamped (TLNPC) inverter. A new method for pulse delay control for the active balancing of DC-link capacitor voltages by using TLBC/TLBBC is presented. Duty-ratio and pulse delay control methods are combined for obtaining better voltage regulation at the DC-link and for achieving higher controllability range. The classic voltage balancing problem of the NPC inverter input, is solved efficiently using the above technique. A synchronous current compensator is used for the NPC inverter based grid coupling. Various results from both simulation and hardware testing show that the required power conditioning and power flow control can be obtained from the proposed multilevel multistage converter system.

The entire control strategies are implemented in Xilinx Virtex 5 FPGA, inside National Instruments’ CompactRIO system using LabVIEW. A contour based dead-time harmonic analysis method for TLNPC and the possibilities of having various interconnection strategies of WEC-rectifier units to complement the power converter efforts for stabilizing the DC-link, are also presented. An advanced future AC2AC direct power converter system based on Modular multilevel converter (MMC) structure developed at Siemens AG is presented briefly to demonstrate the future trends in this area.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1597
Keyword
Multilevel power converter, FPGA control, Wave Energy, Three-level boost converter, Three-level buck-boost converter, Variable-renewable-energy, Three-level neutral point clamped inverter, Linear generator, DC-link, AC2AC direct converter, Modular multilevel converter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-332730 (URN)978-91-513-0146-4 (ISBN)
Public defence
2017-12-04, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2017-11-13 Created: 2017-11-01 Last updated: 2017-11-13

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Elamalayil Soman, DeepakLoncarski, JelenaLeijon, Mats

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