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Multilevel Power Converters with Smart Control for Wave Energy Conversion
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-9599-9811
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 [en]
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: urn:nbn:se:uu:diva-332730ISBN: 978-91-513-0146-4 (print)OAI: oai:DiVA.org:uu-332730DiVA: diva2:1153926
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
List of papers
1. Control and Implementation of Three Level BoostConverter for Load Voltage Regulation
Open this publication in new window or tab >>Control and Implementation of Three Level BoostConverter for Load Voltage Regulation
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2013 (English)In: Industrial Electronics Society, IECON 2013 - 39th Annual Conference of the IEEE, IEEE conference proceedings, 2013, 561-565 p.Conference paper, Published paper (Refereed)
Abstract [en]

   The multilevel converters offer significant advantages for high power applications. The use of multilevel DC/DC converters provides improved efficiency for power conversion and transmission at high voltage. This paper investigates the control and implementation of a three level boost converter for regulating the load voltages. A PI controller based switch signal phase delay control (SSPDC) method is used for adjusting the load voltages at equal turn on and turn off time of the converter switches. The circuit simulation is done in Matlab/Simulink. The controller is realized by using the FPGA in Labview/Compact-Rio module. Software waiting loop length control technique is used for implementing the switch signal delay control. The hardware circuit is implemented and tested. The results show a validation of the controller for regulating the voltages. This method can easily be applied for voltage balancing in a three level neutral point clamped inverter where neutral voltage imbalance is always an issue.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2013
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-218177 (URN)10.1109/IECON.2013.6699196 (DOI)
Conference
39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2014-02-09 Created: 2014-02-09 Last updated: 2017-11-01
2. Pulse delay Control for Capacitor VoltageBalancing in a Three Level Boost Neutral PointClamped Inverter
Open this publication in new window or tab >>Pulse delay Control for Capacitor VoltageBalancing in a Three Level Boost Neutral PointClamped Inverter
2015 (English)In: IET Power Electronics, ISSN 1755-4543, Vol. 8, no 2, 268-277 p.Article in journal (Refereed) Published
Abstract [en]

The cross regulation effect in multi-output DC/DC converters offers a reliable support for the grid integration of multilevel inverters by balancing the capacitor voltages. The capacitor voltage balancing by single input dual output boost converter is often realised by conventional three-level switching scheme. The three-level operation benefits lower inductor ripple current, but it limits the maximum possible compensation voltages. In this study, the entire operating modes of the boost converter is presented and all the possible cases which contribute to the voltage balancing are employed for balancing the capacitor voltages in a three-level neutral point clamped inverter. A proportional-integral controller based duty ratio control and pulse delay control are used for DC link voltage regulation and capacitor voltage balancing. Since the classical state-space averaging technique is not suitable for SIDO converters, inductor current ripple averaging technique is utilised for controller design. The circuit simulation is performed in Matlab/Simulink. The digital controller is realised using the Virtex-5FPGA in Labview/CompactRIO module. Both simulation and experimental results are presented to validate the controller performance.

Keyword
invertors, DC-DC power convertors, PI control, control system synthesis, field programmable gate arrays, digital control, virtual instrumentation, voltage control, delays, pulse delay control, capacitor voltage balancing, three level boost neutral point clamped inverter, multioutput DC-DC converters, cross regulation effect, grid integration, single input dual output boost converter, three-level switching scheme, inductor ripple current, proportional-integral controller, DC link voltage regulation, state-space averaging technique, inductor current ripple averaging technique, controller design, Matlab, Simulink, digital controller, Vertex 5-FPGA, Labview-Compact-Rio module
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-218163 (URN)10.1049/iet-pel.2014.0103 (DOI)000349535400011 ()
Available from: 2014-02-09 Created: 2014-02-09 Last updated: 2017-11-01Bibliographically approved
3. Discontinuous conduction mode of a three-level boost DC-DC converter and its merits and limits for voltage cross regulation applications
Open this publication in new window or tab >>Discontinuous conduction mode of a three-level boost DC-DC converter and its merits and limits for voltage cross regulation applications
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2014 (English)In: Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE, IEEE conference proceedings, 2014, 4268-4272 p.Conference paper, Published paper (Refereed)
Abstract [en]

Distributed generation and smart grid integration of renewable energy sources introduce a lot of challenges for the enabling power electronic converter technology. Some of these challenges include wide controllability range, high power handling and good reliability. Three-level boost converter is one of the attractive solution for applications requiring voltage cross regulation such as three-level neutral point clamped inverter based grid integration of renewable sources. The present work shows the advantages and disadvantages of using discontinuous conduction mode of a Three-level boost converter for voltage cross regulation. The converter working principle, modes of operation and operating cases are listed briefly. The simulation results compare the DCM and CCM cross regulation effects. Based on these results, the controllability range of the converter is analyzed to understand the suitability of the converter for various applications.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-253956 (URN)10.1109/IECON.2014.7049144 (DOI)
Conference
Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the IEEE
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2015-06-04 Created: 2015-06-04 Last updated: 2017-11-01
4. Cross-Regulation Assessment of DIDO Buck-BoostConverter for Renewable Energy Application
Open this publication in new window or tab >>Cross-Regulation Assessment of DIDO Buck-BoostConverter for Renewable Energy Application
2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10Article in journal (Refereed) Published
Abstract [en]

When medium- or high-voltage power conversion is preferred for renewable energy sources, multilevel power converters have received much of the interest in this area as methods for enhancing the conversion efficiency and cost effectiveness. In such cases, multilevel, multi-input multi-output (MIMO) configurations of DC-DC converters come to the scenario for integrating several sources together, especially considering the stringent regulatory needs and the requirement of multistage power conversion systems. Considering the above facts, a three-level dual input dual output (DIDO) buck-boost converter, as the simplest form of MIMO converter, is proposed in this paper for DC-link voltage regulation. The capability of this converter for cross regulating the DC-link voltage is analyzed in detail to support a three-level neutral point clamped inverter-based grid connection in the future. The cross-regulation capability is examined under a new type of pulse delay control (PDC) strategy and later compared with a three-level boost converter (TLBC). Compared to conventional boost converters, the high-voltage three-level buck boost converter (TLBBC) with PDC exhibits a wide controllability range and cross regulation capability. These enhanced features are extremely important for better regulating variable output renewable energy sources such as solar, wind, wave, marine current, etc. The simulation and experimental results are provided to validate the claim.

Keyword
dual input dual output (DIDO) converter; three-level buck boost converter (TLBBC); pulse delay control (PDC); neutral point clamped inverter; cross-regulation; renewable energy conversion
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-332725 (URN)10.3390/en10070846 (DOI)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2017-11-01
5. Analysis of Three-level Buck-Boost Converter Operation for Improved Renewable Energy Conversion and Smart Grid Integration
Open this publication in new window or tab >>Analysis of Three-level Buck-Boost Converter Operation for Improved Renewable Energy Conversion and Smart Grid Integration
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2014 (English)In: 2014 IEEE International Energy Conference (ENERGYCON 2014), IEEE conference proceedings, 2014, 76-81 p.Conference paper, Published paper (Refereed)
Abstract [en]

The increased smart grid integration of renewable energy sources demands high power handling and wide controllability for the enabling power conversion technologies. The conventional energy conversion techniques are inadequate to efficiently handle the highly varying nature of renewable energy sources like wave, solar, tidal and wind. The present work examines the advantages of using a three-level buck-boost DC-DC converter to aid three-level neutral-point-clamped inverter based grid integration. There are two main reasons for using this converter. It can provide the conventional buck-boost capability at higher power levels for absorbing and conditioning the renewable source output. Besides, it can be used as a voltage balancing device to satisfy the input requirement for the three-level neutral-point-clamped inverter. The work includes complete operating range analysis of the converter for the combined buck-boost action and voltage balancing effects to understand its suitability for various applications. The converter switching modes of operation are also presented in detail along with essential example waveforms. The final results show good controllability bandwidth for the converter which makes it an attractive solution for smart grid integration of renewable energy sources.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
Series
IEEE International Energy Conference, ISSN 2164-4322 ; 76-81
Keyword
Three-level buck-boost converter, Renewable energy conversion, Smart grid integration, Neutral-point-clamped inverter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-240677 (URN)10.1109/ENERGYCON.2014.6850409 (DOI)000343646400013 ()978-1-4799-2449-3 (ISBN)
Conference
IEEE International Energy Conference (ENERGYCON), MAY 13-16, 2014, Dubrovnik, CROATIA
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2017-11-01
6. Contour-Based Dead-Time Harmonic Analysis in a Three-Level Neutral-Point-Clamped Inverter
Open this publication in new window or tab >>Contour-Based Dead-Time Harmonic Analysis in a Three-Level Neutral-Point-Clamped Inverter
2015 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 62, no 1, 203-210 p.Article in journal (Refereed) Published
Abstract [en]

The term dead time refers to a prime safety factor for most power electronic converter topologies, and it is included either in the control software or in the gate/base driver hardware, depending on the application as well as the control requirements. In this paper, the authors present a comprehensive numerical analysis of dead-time effects on the output voltage of a three-level neutral-pointclamped (NPC) inverter. To incorporate the dead-time effect in the output voltage, 3-D models of three-level carrier pulse width modulation (PWM) methods are modified for two dead-time implementations. Closed-form expressions of inverter phase voltage harmonics for phase opposition disposition (POD) PWM are derived based on the double Fourier series approach and modified contour plots. The harmonic spectra from numerical evaluations, simulations, and experiments for natural sampling (NS), symmetrical regular sampling (SRS), and asymmetrical regular sampling (ARS) are compared to validate the mathematical models. In addition, the fundamental voltage with respect to the dead time and the load phase angle is presented based on analytical results and simulation.

Place, publisher, year, edition, pages
IEEE, 2015
Keyword
DC–AC power conversion, dead time, neutral-point-clamped (NPC) inverter, pulse width modulation (PWM), voltage harmonics
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-218169 (URN)10.1109/TIE.2014.2327579 (DOI)000346767400022 ()
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy StorageSwedish Energy AgencyStandUp
Available from: 2014-02-09 Created: 2014-02-09 Last updated: 2017-11-01Bibliographically approved
7. Synchronous Current Compensator for a Self Balanced Three-Level Neutral Point Clamped Inverter
Open this publication in new window or tab >>Synchronous Current Compensator for a Self Balanced Three-Level Neutral Point Clamped Inverter
2014 (English)In: Advances in Power Electronics, ISSN 2090-181X, E-ISSN 2090-1828, 620607Article in journal (Refereed) Published
Abstract [en]

This paper presents a synchronous current control method for a three-level neutral point clamped inverter. Synchronous reference frame control based on two decoupled proportional-integral (PI) controllers is used to control the current in direct and quadrature axes. A phase disposition pulse width modulation (PDPWM) method in regular symmetrical sampling is used for generating the inverter switching signals. To eliminate the harmonic content with no phase errors, two first-order low pass filters (LPFs) are used for the dq currents. The simulation of closed-loop control is done in Matlab/Simulink. The Vertex-5 field programmable gate array (FPGA) in Labview/CompactRio is used for the implementation of the control algorithm. The control and switch pulse generation are done in independent parallel loops. The synchronization of both loops is achieved by controlling the length of waiting time for each loop. The simulation results are validated with experiments. The results show that the control action is reliable and efficient for the load current control.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-218168 (URN)10.1155/2014/620607 (DOI)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2014-02-09 Created: 2014-02-09 Last updated: 2017-11-01
8. DC-Link Stress Analysis for the Grid Connection of Point Absorber Type Wave Energy Converters
Open this publication in new window or tab >>DC-Link Stress Analysis for the Grid Connection of Point Absorber Type Wave Energy Converters
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.

Keyword
DC-link stress analysis; harmonic distortion; passive rectifier; wave energy converter
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-258208 (URN)10.1109/ICCEP.2015.7177601 (DOI)000380609800010 ()9781479987047 (ISBN)
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
9. Interconnection Strategies of Point Absorber Type Wave Energy Converters and Rectifier Units
Open this publication in new window or tab >>Interconnection Strategies of Point Absorber Type Wave Energy Converters and Rectifier Units
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-332728 (URN)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2017-11-01
10. Status Update of the Wave Energy Research at Uppsala University
Open this publication in new window or tab >>Status Update of the Wave Energy Research at Uppsala University
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2013 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Aalborg, Denmark: , 2013
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212701 (URN)
Conference
10th European Wave and Tidal Conference (EWTEC)
Available from: 2013-12-13 Created: 2013-12-13 Last updated: 2017-11-01
11. Development of Power Electronics Based Test Platform for Characterization and Testing of Magnetocaloric Materials
Open this publication in new window or tab >>Development of Power Electronics Based Test Platform for Characterization and Testing of Magnetocaloric Materials
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2015 (English)In: Advances in Electrical Engineering, ISSN 2356-6655, Vol. 2015, no 670624, 7- p.Article in journal (Refereed) Published
Abstract [en]

Magnetocaloric effects of various materials are getting more and more interesting for the future, as they can significantly contribute towards improving the efficiency of many energy intensive applications such as refrigeration, heating, and air conditioning. Accurate characterization of magnetocaloric effects, exhibited by various materials, is an important process for further studies and development of the suitable magnetocaloric heating and cooling solutions. The conventional test facilities have plenty of limitations, as they focus only on the thermodynamic side and use magnetic machines with moving bed of magnetocaloric material or magnet. In this work an entirely new approach for characterization of the magnetocaloric materials is presented, with the main focus on a flexible and efficient power electronic based excitation and a completely static test platform. It can generate a periodically varying magnetic field using superposition of an ac and a dc magnetic field. The scale down prototype uses a customized single phase H-bridge inverter with essential protections and an electromagnet load as actuator. The preliminary simulation and experimental results show good agreement and support the usage of the power electronic test platform for characterizing magnetocaloric materials.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-245221 (URN)10.1155/2015/670624 (DOI)
Projects
Magnetocaloric
Available from: 2015-02-25 Created: 2015-02-25 Last updated: 2017-11-01
12. Kalman Filter Based Grid Synchronization in Stationary Reference Frame
Open this publication in new window or tab >>Kalman Filter Based Grid Synchronization in Stationary Reference Frame
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-332729 (URN)
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2017-11-01

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