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Control, Modulation and Implementation of Modular Multilevel Converters
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [sv]

Denna avhandling behandlar analys och styrning av den modulära multinivå omvandlaren (M2C). M2C är en lovande omvandlarteknologi för högspända högeffekttillämpningar. Anledningen till detta är låg distorsion i utstorheterna kan uppnås med låg  medelswitchfrekvens per switch och utan utgångsfilter. Med M2C har utspänningen så lågt övertonsinnehåll att drift av högeffektmotorer är möjlig utan reduktion av märkeffekten. Emellertid innebär det stora antalet styrda switchar att styrningen blir mer komplex än för motsvarande tvånivåomvandlare. Styrningen av M2C måste måste konstrueras så att submodulernas kondensatorspänningar balanseras och är stabila oberoende av driftfall. En aktiv mekanism för val av submoduler, som är integrerad i modulatorn, har visat sig vara effektiv för att ombesörja den interna balanseringen av omvandlararmarna. Utöver balanseringen av de individuella kondensatorerna krävs en strategi för styrning av den totalt upplagrade energin i omvandlaren. Med utgångspunkt i en analytisk beskrivning av omvandlaren föreslås styrlagar för både öppen styrning och sluten reglering, vilka genom både simuleringar och med hjälp av experiment har visat sig vara stabila i hela arbetsområdet. Den potentiella växelverkan mellan den inre omvandlarstyrningen och en yttre strömreglering undersöks också. Både simuleringar och experiment bekräftar att eventuell interaktion inte innebär några avsevärda problem vare sig för omvandlaren eller motorn. En  hårdvaruimplementering av en nedskalad trefasig 10kVA-omvandlare har genomförts för att verifiera modellering och styrning. Implementeringen av styrningen beskrivs i detalj. Styrningen är anmärkningsvärt snabb och kan utökas till godtyckligt antal nivåer. Den kan därför användas för en fullskaleimplementering i MW-klassen.

 

Abstract [en]

This thesis deals with the analysis and control of the modular multilevel converter (M2C). The M2C is a promising converter technology for various high-voltage high-power applications. The reason to this is that low-distortion output quantities can be achieved with low average switching frequencies per switch and without output filters. With the M2C the output voltage has such a low harmonic content that high-power motors can be operated without any derating. However, the apparent large number of devices, requires more complex converter control techniques than a two-level counterpart. The internal control of an M2C must be designed so that the submodule capacitor voltages are equalized and stable independent of the loading conditions. An active submodule selection mechanism, included in the modulator, has been shown able to provide voltage sharing inside the converter arm. Apart from the individual capacitor voltage sharing, a strategy has to be designed to ensure that the total amount of energy stored inside the converter will always be controlled. Based on an analytical description of the converter, both feedback and open-loop control methods are suggested, simulated and experimentally evaluated, which will ensure stable operation in the whole operation range. The potential interaction of the internal controllers with an external motor current controller is also investigated. Both simulation and experimental results show that any interaction will not result in any problems neither for the converter nor for the motor control itself. A hardware implementation of a down-scaled 10 kVA three-phase laboratory prototype converter is performed, in order to evaluate the modeling and the controllers developed. The controller implementation is described in detail, as it exhibits remarkably fast response, and can be expanded up to an arbitrary number of levels. Therefore it can be used even by a full-scale converter implementation in the MW range.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 126 p.
Series
Trita-EE, ISSN 1653-5146 ; 2011:047
Keyword [en]
Modular Multilevel Converter, Modulation, Feedback Control, Open-Loop Control, Implementation, Prototype, High-Performance Motor Drives
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-34188ISBN: 978-91-7501-050-2 (print)OAI: oai:DiVA.org:kth-34188DiVA: diva2:419747
Presentation
2011-06-13, D3, KTH, Lindstedtsvägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110628Available from: 2011-06-28 Created: 2011-05-27 Last updated: 2011-06-29Bibliographically approved
List of papers
1. On Dynamics and Voltage Control of the Modular Multilevel Converter
Open this publication in new window or tab >>On Dynamics and Voltage Control of the Modular Multilevel Converter
2009 (English)In: 2009 13th European Conference on Power Electronics and Applications, EPE '09, IEEE , 2009, 3353-3362 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper discusses the impact of modulation on stability issues of the Modular Multilevel Converter (M2C). The main idea is to describe the operation of this converter system mathematically, and suggest a control method that offers stable operation in the whole operation range. A possible approach is to assume a continuous model, where all the modules in each arm are represented by variable voltage sources. and as a result, all pulse width modulation effects are disregarded. After simulating this model and testing different control methods, useful conclusions on the operation of the M2C have been extracted. The control methods are then implemented on a model with discrete half-bridge modules, in order to compare the results and to validate continuous model approach. When assuring that this model functions as expected, the goal of this paper is to conclude into a self-stabilizing voltage controller. A controller is proposed, which eliminates circulating currents between the phase legs and balances the arm voltages regardless of the imposed alteranting current.

Place, publisher, year, edition, pages
IEEE, 2009
Keyword
Converter control, Multilevel converters, Modulation strategy, Emerging topology, VSC
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-30152 (URN)000275384101138 ()2-s2.0-72949122524 (Scopus ID)978-1-4244-4432-8 (ISBN)
Conference
2009 13th European Conference on Power Electronics and Applications, EPE '09; Barcelona; Spain; 8 September 2009 through 10 September 2009
Note

QC 20110304

Available from: 2011-03-04 Created: 2011-02-21 Last updated: 2014-12-01Bibliographically approved
2. Inner Control of Modular Multilevel Converters - An Approach using Open-loop Estimation of Stored Energy
Open this publication in new window or tab >>Inner Control of Modular Multilevel Converters - An Approach using Open-loop Estimation of Stored Energy
Show others...
2010 (English)In: Proc. Int. Power Electronics Conf. (IPEC), 2010, 1579-1585 p.Conference paper, Published paper (Refereed)
Keyword
modular multilevel converter, open-loop control, modulation, prototype, energy balance
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-34179 (URN)10.1109/IPEC.2010.5544607 (DOI)2-s2.0-77956500071 (Scopus ID)978-142445395-5 (ISBN)
Conference
International Power Electronics Conference (IPEC)
Note
QC 20110628Available from: 2011-06-28 Created: 2011-05-27 Last updated: 2011-06-28Bibliographically approved
3. Evaluation of Control and Modulation Methods forModular Multilevel Converters
Open this publication in new window or tab >>Evaluation of Control and Modulation Methods forModular Multilevel Converters
Show others...
2010 (English)In: Proc. Int. Power Electronics Conf. (IPEC), 2010, 746-753 p.Conference paper, Published paper (Refereed)
Abstract [en]

The modular multilevel converter is a promising converter technology for various high-voltage high-power applications. Despite the apparent simplicity of the circuit, the inherent dynamics of the converter and the balancing of the sub-module capacitor voltages impose high requirements on the control system, which can be implemented in quite different ways. To illustrate this, and to provide a guidance for future research on the subject, this paper presents an evaluation of four different control and modulation methods. The investigation is based on experiments on a down-scaled 10 kVA converter having 10 submodules per phase leg. The main items to be investigated are dynamics within the sub-modules, arm voltages and circulating currents. It is found that the suggested open-loop control method provides the fastest arm-voltage response and that the balancing approach based on a sorting algorithm is substantially faster and less complicated to implement than the method using a dedicated voltage controller for each sub-module.

 

 

Keyword
modular multilevel converter, controller evaluation, prototype, feedback control, open-loop control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-34180 (URN)10.1109/IPEC.2010.5544609 (DOI)2-s2.0-77956552410 (Scopus ID)978-142445395-5 (ISBN)
Conference
International Power Electronics Conference (IPEC)
Note
QC 20110628Available from: 2011-06-28 Created: 2011-05-27 Last updated: 2011-06-28Bibliographically approved
4. On Interaction between Internal Converter Dynamics and Current Control of High-Performance High-Power AC Motor Drives with Modular Multilevel Converters
Open this publication in new window or tab >>On Interaction between Internal Converter Dynamics and Current Control of High-Performance High-Power AC Motor Drives with Modular Multilevel Converters
2010 (English)In: Proc. IEEE Energy Conversion Congress and Exposition (ECCE), 2010, 4293-4298 p.Conference paper, Published paper (Refereed)
Abstract [en]

The modular multilevel converter (M2C) is a promising converter technology for various high-voltage highpower applications. The reason to this is that low-distortion output quantities can be achieved with low average switching frequencies per switch and without output filters. With the M2C the output voltage has such a low harmonic content that highpower motors can be operated without any derating. However, the apparent large number of devices, requires more complex converter control techniques than a two-level counterpart. Even though there have been several ways suggested to control the converter itself, it is still a challenge to investigate the interaction of these controllers with an external motor current controller. It is shown in the paper that the anticipated interaction will not result in any problems neither for the converter nor for the motor control itself.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-34181 (URN)10.1109/ECCE.2010.5618474 (DOI)2-s2.0-78650088280 (Scopus ID)978-142445286-6 (ISBN)
Conference
Energy Conversion Conference and Exposition (ECCE)
Note
QC 20110628Available from: 2011-06-28 Created: 2011-05-27 Last updated: 2014-12-01Bibliographically approved

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