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Pulse delay Control for Capacitor VoltageBalancing in a Three Level Boost Neutral PointClamped Inverter
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave power)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2015 (English)In: IET Power Electronics, ISSN 1755-4535, E-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.

Place, publisher, year, edition, pages
2015. Vol. 8, no 2, 268-277 p.
Keyword [en]
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: urn:nbn:se:uu:diva-218163DOI: 10.1049/iet-pel.2014.0103ISI: 000349535400011OAI: oai:DiVA.org:uu-218163DiVA: diva2:694979
Available from: 2014-02-09 Created: 2014-02-09 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Grid Connected Three-Level Converters: Studies for Wave Energy Conversion
Open this publication in new window or tab >>Grid Connected Three-Level Converters: Studies for Wave Energy Conversion
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter.

To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation.

Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory. 

Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1123
Keyword
Wave energy, power converters, control strategies, grid connection
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-218219 (URN)978-91-554-8875-8 (ISBN)
Public defence
2014-03-26, Häggsalen, Lägerhyddsvägen 1, Angstrom laboratory, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2014-03-04 Created: 2014-02-10 Last updated: 2014-12-02Bibliographically approved
2. 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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Krishna, RemyaElamalayil Soman, DeepakLeijon, Mats

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