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Modeling and Design of Modular Multilevel Converters for Grid Applications
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis aims to bring clarity to the dimensioning aspects and limiting factors of the modular multilevel converter (MMC). Special consideration is given to the dc capacitors in the submodules as they are a driving factor for the size and weight of the converter. It is found that if the capacitor voltages are allowed to increase by 10% the stored energy must be 21 kJ/MW in order to compensate the capacitor voltage ripple. The maximum possible output power can, however, be increased by injecting a second-order harmonic in the circulating current.

A great advantage of cascaded converters is the possibility to achieve excellent harmonic performance at low switching frequencies. Therefore, this thesis also considers the relation between switching harmonics, capacitor voltage ripple, and arm quantities. It is shown that despite subharmonics in the capacitor voltages, it is still possible to achieve periodic arm quantities. The balancing of the capacitor voltages is also considered in further detail. It is found that it is possible to balance the capacitor voltages even at fundamental switching frequency although this will lead to a comparably large capacitor voltage ripple. Therefore, in order to limit the peak-to-peak voltage ripple, it is shown that a predictive algorithm can be used in which the resulting switching frequency is approximately 2–3 times the fundamental frequency.

This thesis also presents two new submodule concepts. The first submodule simply improves the trade-off between the switching frequency and capacitor voltage balancing. The second submodule includes the possibility to insert negative voltages which allows higher modulation indices compared to half-bridge submodules.

A brief comparison of cascaded converters for ac-ac applications is also presented. It is concluded that the MMC appears to be well suited for ac-ac applications where input and output frequencies are close or equal, such as in interconnection of ac grids. In low-frequency applications such as low-speed drives, however, the difficulties with handling the energy variations in the converter arms are much more severe in the MMC compared to the other considered topologies.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , x, 55 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2014:045
Keyword [en]
Modular multilevel converter, feed-forward control, modulation, switching frequency, energy storage
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-153762ISBN: 978-91-7595-293-2 (print)OAI: oai:DiVA.org:kth-153762DiVA: diva2:753599
Public defence
2014-11-03, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141010

Available from: 2014-10-10 Created: 2014-10-08 Last updated: 2016-02-26Bibliographically approved
List of papers
1. Steady-State Analysis of Interaction Between Harmonic Components of Arm and Line Quantities of Modular Multilevel Converters
Open this publication in new window or tab >>Steady-State Analysis of Interaction Between Harmonic Components of Arm and Line Quantities of Modular Multilevel Converters
2012 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 1, 57-68 p.Article in journal (Refereed) Published
Abstract [en]

The fundamental frequency component in the arm currents of a modular multilevel converter is a necessity for the operation of the converter, as is the connection and bypassing of the submodules. Inevitably, this will cause alternating components in the capacitor voltages. This paper investigates how the arm currents and capacitor voltages interact when the submodules are connected and bypassed in a sinusoidal manner. Equations that describe the circulating current that is caused by the variations in the total inserted voltage are derived. Resonant frequencies are identified and the resonant behaviour is verified by experimental results. It is also found that the effective values of the arm resistance and submodule capacitances can be extracted from the measurements by least square fitting of the analytical expressions to the measured values. Finally, the analytical expression for the arm currents is verified by experimental results.

Place, publisher, year, edition, pages
IEEE: , 2012
Keyword
Analytical steady-state model, arm currents, experimental results, modular multilevel converter, phase-leg resonance
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-55863 (URN)10.1109/TPEL.2011.2159809 (DOI)000298048500004 ()2-s2.0-83755187987 (Scopus ID)
Funder
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QC 20150626

Available from: 2012-01-03 Created: 2012-01-03 Last updated: 2017-12-08Bibliographically approved
2. Analysis of arm current harmonics in modular multilevel converters with main-circuit filters
Open this publication in new window or tab >>Analysis of arm current harmonics in modular multilevel converters with main-circuit filters
2012 (English)In: International Multi-Conference on Systems, Signals and Devices, SSD 2012 - Summary Proceedings, IEEE , 2012Conference paper, Published paper (Refereed)
Abstract [en]

In a modular multilevel converter the circulating current that flows through each phase leg can affect the performance and efficiency of the converter. If measures are not taken to control the circulating current, it will inevitably contain a second-order harmonic. There are various solutions for eliminating this second-order harmonic. One of the proposed solutions includes a main-circuit filter that is tuned to block the second-order harmonic in the circulating current. This paper presents an analytical relation between the ac-side current and the higher-order harmonics in the circulating current when such a filter is used. It is found that when third-order harmonic injection is used, a large fourth-order harmonic component may appear in the circulating current. This is verified by simulating a 32-MVA converter designed for grid connected applications. The simulation results support the conclusion that it is essential to take this effect into consideration when designing the main-circuit filter.

Place, publisher, year, edition, pages
IEEE, 2012
Keyword
AC-side, Analytical relations, Circulating current, Current harmonics, Fourth-order, Grid-connected, Harmonic components, Harmonic injection, Higher order harmonics, Modular multilevel converters, Second orders, Third-order
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-92265 (URN)10.1109/SSD.2012.6197915 (DOI)2-s2.0-84861630463 (Scopus ID)978-146731590-6 (ISBN)
Conference
9th International Multi-Conference on Systems, Signals and Devices, SSD 2012;Chemnitz;20 March 2012 through 23 March 2012
Funder
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QC 20120802

Available from: 2012-03-30 Created: 2012-03-30 Last updated: 2016-04-21Bibliographically approved
3. Controlling the ac-side voltage waveform in a modular multilevel converter with low energy-storage capability
Open this publication in new window or tab >>Controlling the ac-side voltage waveform in a modular multilevel converter with low energy-storage capability
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2011 (English)In: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) / [ed] EPE Association, 2011, 1-8 p.Conference paper, Published paper (Refereed)
Abstract [en]

During nominal operation of a modular multilevel converter the stored energy in the submodule capacitors will vary with time. If the energy storage capability of the capacitors is relatively small compared to the energy variations, this will give large variations in the capacitor voltages. These voltage variations will distort the ac-side voltage waveform and induce harmonic components in the current that is circulating between the dc terminals. The adverse effects on the ac-side voltage can be compensated for by identifying the factors that cause the distortion. It is shown that the compensation can be done by means of feed forward control while maintaining stable operating conditions and thus eliminating the need of additional stabilizing controllers. It is also shown that the voltage controller can be combined with a circulating current controller that removes the harmonics in the current that is circulating between the dc terminals. The functionality of the proposed controller is verified by both simulations and experimental results from a 10 kVA laboratory prototype. The simulations illustrate how the proposed controller successfully removes the distortion from the ac-side voltage waveform. The experimental results demonstrate stable operation during a step transient when the output power is increased by 125%.

Keyword
Converter control, Modulation strategy, Multilevel converters
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-40866 (URN)000308003502053 ()2-s2.0-80053483246 (Scopus ID)978-1-61284-167-0 (ISBN)E-ISBN: 978-90-75815-15-3 (ISBN)
Conference
EPE 2011
Funder
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QC 20110930

Available from: 2011-09-21 Created: 2011-09-21 Last updated: 2014-10-10Bibliographically approved
4. On Energy Storage Requirements in Modular Multilevel Converters
Open this publication in new window or tab >>On Energy Storage Requirements in Modular Multilevel Converters
2014 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 29, no 1, 77-88 p.Article in journal (Refereed) Published
Abstract [en]

The modular multilevel converter is a promising topology for high-voltage and high-power applications. By using submodules equipped with dc-capacitors excellent output voltage waveforms can be obtained at low switching frequencies. The rated energy storage of the submodule capacitors is a driving factor of the size, cost, and weight of the submodules. Although the modular multilevel converter has been thoroughly investigated in the literature, a more detailed analysis of the energy-storage requirements will provide an important contribution for dimensioning and analysis of modular multilevel converters. Such an analysis is presented in this paper. The analysis relates the power transfer capability to the stored energy in the converter and the findings are validated by both simulations and experimental results. The required size of the submodule capacitors in a 4.5 MW grid-connected converter is first calculated and the calculated operating range is then compared with simulation results. The experimental results show that if the average capacitor voltage is allowed to increase 10% above the nominal value an energy storage to power transfer ratio of 21 J/kW can be achieved. It is concluded that the presented theory can relate the power transfer capability to the energy storage in the converter and is thus a valuable tool in the design and analysis of modular multilevel converters.

Keyword
AC-DC power converters, energy storage, HVDC transmission
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-105771 (URN)10.1109/TPEL.2013.2254129 (DOI)000324020500012 ()2-s2.0-84880863213 (Scopus ID)
Funder
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QC 20131004

Available from: 2012-11-26 Created: 2012-11-26 Last updated: 2017-12-07Bibliographically approved
5. Capacitor Voltage Ripple Shaping in Modular Multilevel Converters Allowing for Operating Region Extension
Open this publication in new window or tab >>Capacitor Voltage Ripple Shaping in Modular Multilevel Converters Allowing for Operating Region Extension
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2011 (English)In: IECON 2011: 37TH ANNUAL CONFERENCE ON IEEE INDUSTRIAL ELECTRONICS SOCIETY, New York: IEEE , 2011, 4403-4408 p.Conference paper, Published paper (Refereed)
Abstract [en]

The second-order harmonic in the circulating current of a modular multilevel converter (M2C) influences the capacitor voltage ripple. If no measures are taken to control it, it is not possible to operate the converter with unity modulation index. An open-loop method that precalculates the instantaneous values of the circulating current and the capacitor voltages is used, in order to control the circulating current. A desired second-order harmonic is intentionally induced in the circulating current in order to make the peak of the capacitor voltage coincide with the maximum requested voltage, aiming either to extend the limits of the instantaneous available voltage or avoid unnecessarily high capacitor voltages. A method for numerical estimation of the appropriate amplitude and phase of the induced second-order harmonic is described. The method is experimentally evaluated on a three-phase down-scaled laboratory prototype. From the experiments it was found that significantly improved operating conditions could be obtained.

Place, publisher, year, edition, pages
New York: IEEE, 2011
Series
IEEE Industrial Electronics Society. Annual Conference. Proceedings, ISSN 1553-572X
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-61342 (URN)000299032404116 ()2-s2.0-84856515329 (Scopus ID)978-1-61284-972-0 (ISBN)
Conference
37th Annual Conference of the IEEE Industrial Electronics Society, IECON 2011; Melbourne, VIC; 7 November 2011 through 10 November 2011
Funder
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QC 20120117

Available from: 2012-01-17 Created: 2012-01-17 Last updated: 2016-04-26Bibliographically approved
6. Analysis and Operation of Modular Multilevel Converters With Phase-Shifted Carrier PWM
Open this publication in new window or tab >>Analysis and Operation of Modular Multilevel Converters With Phase-Shifted Carrier PWM
2015 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, 268-283 p.Article in journal (Refereed) Published
Abstract [en]

Many publications have been presented on the modulation and control of the modular multilevel converter, some of which are based on phase-shifted carrier modulation. This paper presents an analysis of how the switching frequency affects the capacitor voltages, circulating currents, and alternating voltages using phase-shifted carrier modulation. It is found that switching frequencies that are integer multiples of the fundamental frequency should be avoided as they can cause the capacitor voltages to diverge. Suitable switching frequencies are derived for which the arm and line quantities will be periodic with symmetric operating conditions in the upper and lower arms. Thus, the practical outcome of this paper is a detailed description of how the switching frequency should be chosen in order to achieve advantageous operating conditions. The theoretical results from the analysis are validated by both simulations and experimental results.

Keyword
Capacitor voltages, circulating current, modular multilevel converter (M2C), phase-shifted PWM, switching harmonics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-153755 (URN)10.1109/TPEL.2014.2321049 (DOI)000341624200023 ()2-s2.0-84906810276 (Scopus ID)
Funder
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QC 20150622

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
7. A New Modulation Method for the Modular Multilevel Converter Allowing Fundamental Switching Frequency
Open this publication in new window or tab >>A New Modulation Method for the Modular Multilevel Converter Allowing Fundamental Switching Frequency
2012 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 27, no 8, 3482-3494 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a new modulation method for the modular multilevel converter. The proposed method is based on a fixed pulse pattern where harmonic elimination methods can be applied. In the proposed modulation method, the pulse pattern is chosen in such a way that the stored energy in each submodule remains stable. It is shown that this can be done at the fundamental switching frequency without measuring the capacitor voltages or using any other form of feedback control. Such a modulation scheme has not been presented before. The theoretical results are verified by both simulations and experimental results. The simulation results show successful operation at the fundamental switching frequency with a larger number of submodules. When a smaller number of submodules are used, harmonic elimination methods may be applied. This is verified experimentally on a converter with eight submodules per phase leg. The experimental results verify that stable operation can be maintained at the fundamental switching frequency while successfully eliminating the fifth harmonic in the ac-side voltage.

Keyword
Fixed pulse pattern, modular multilevel converter (M2C), switching frequency, voltage balancing
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-95223 (URN)10.1109/TPEL.2012.2185832 (DOI)000303204100003 ()2-s2.0-84860283132 (Scopus ID)
Funder
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QC 20150624

Available from: 2012-05-22 Created: 2012-05-21 Last updated: 2017-12-07Bibliographically approved
8. Circulating current control in modular multilevel converters with fundamental switching frequency
Open this publication in new window or tab >>Circulating current control in modular multilevel converters with fundamental switching frequency
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2012 (English)In: Conference Proceedings - 2012 IEEE 7th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2012, IEEE , 2012, 249-256 p.Conference paper, Published paper (Refereed)
Abstract [en]

The modular multilevel converter is a suitable topology for high-voltage applications as it combines very low switching frequency and excellent harmonic performance. In fact, it has been shown that the modular multilevel converter can even be operated at the fundamental switching frequency. If the circulating current is not controlled, a second-order harmonic component will appear. This component increases the resistive losses and the capacitor voltage ripple. Different control methods have been developed for eliminating this component in the circulating current. These are, however, based on continuous representations of the system and no control method suitable for fundamental switching frequency have yet been proposed. This paper presents a control method that combines a fundamental switching frequency scheme with an active control of the circulating current. The controller is verified experimentally on a 10-kVA laboratory prototype with five submodules per arm. The experimental validation is performed in both inverter and rectifier modes.

Place, publisher, year, edition, pages
IEEE, 2012
Keyword
Electric converters, Motion control, Power electronics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-100853 (URN)10.1109/IPEMC.2012.6258844 (DOI)2-s2.0-84866782674 (Scopus ID)978-145772086-4 (ISBN)
Conference
2012 IEEE 7th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2012; Harbin; 2 June 2012 through 5 June 2012
Funder
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QC 20121121

Available from: 2012-08-20 Created: 2012-08-20 Last updated: 2016-04-21Bibliographically approved
9. Predictive Sorting Algorithm for Modular Multilevel Converters Minimizing the Spread in the Submodule Capacitor Voltages
Open this publication in new window or tab >>Predictive Sorting Algorithm for Modular Multilevel Converters Minimizing the Spread in the Submodule Capacitor Voltages
2015 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 1, 440-449 p.Article in journal (Refereed) Published
Abstract [en]

The balancing of the capacitor voltages in modular multilevel converters becomes increasingly difficult when the switching frequency is reduced. Typically, a reduced switching frequency will increase the spread in the capacitor voltages and, thus, the voltage ripple in the individual submodules. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor-voltage ripple. This is done by a predictive algorithm that controls the converter in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltages in the submodule capacitors at switching frequencies as low as 2-3 times the fundamental switching frequency. The proposed capacitor voltage balancing strategy is validated by both simulations and experimental results with 130-Hz and 140-Hz switching frequency. In the simulations, the capacitor voltage ripple was reduced by 24% compared to the case when a conventional sorting algorithm is used, and the experimental results show that it is possible to combine the proposed voltage balancing strategy with a circulating-current controller.

Keyword
Capacitor voltage balancing, modular multilevel converter (MMC), switching frequency
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-153752 (URN)10.1109/TPEL.2014.2308018 (DOI)000341624200037 ()2-s2.0-84906810329 (Scopus ID)
Funder
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QC 20150623

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
10. On energy variations in modular multilevel converters with full-bridge submodules for Ac-Dc and Ac-Ac applications
Open this publication in new window or tab >>On energy variations in modular multilevel converters with full-bridge submodules for Ac-Dc and Ac-Ac applications
2013 (English)In: Power Electronics and Applications (EPE), 2013 15th European Conference on, 2013Conference paper, Published paper (Refereed)
Abstract [en]

The modular multilevel converter is a promising topology for high-voltage high-power applications. By the series-connection of submodules it can generate high-quality voltage waveforms with low harmonic distortion at low switching frequencies. The submodules are low-voltage converters with capacitive energy storages. These capacitive energy storages are a driving factor of the size, weight, and cost of the converter. For this reason it is important to ensure that the stored energy in the converter is distributed as evenly among the submodules as possible. In this paper it is found that during nominal operating conditions, a large amount of energy is moved back and forth between the upper and lower arms in the converter. These energy oscillations can, however, be reduced or even eliminated if an appropriate modulation index or voltage ratio is used. It is also found that an appropriate modulation index or voltage ratio can reduce the power rating of the semiconductors as well. The theoretical findings are validated by simulating two systems with different voltage ratios for ac-ac conversion.

Keyword
AC-AC power convertors, AC-DC power convertors, energy storage, power capacitors, AC-AC power converter, AC-DC power converter, capacitive energy storages, energy oscillations, energy variations, full-bridge submodules, modular multilevel converters, modulation index, nominal operating conditions, semiconductor power rating reduction, voltage ratio, Bidirectional control, Capacitors, Energy storage, Inductors, Integrated circuits, Modulation, Topology, AC/AC converter, Energy storage, Multilevel converters, Traction application
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-134876 (URN)10.1109/EPE.2013.6634324 (DOI)2-s2.0-84890158232 (Scopus ID)
Conference
15th European Conference on Power Electronics and Applications (EPE) 2013
Funder
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QC 20140225

Available from: 2013-12-02 Created: 2013-12-01 Last updated: 2014-10-10Bibliographically approved
11. Comparison of Cascaded Multilevel Converter Topologies for AC/ AC Conversion
Open this publication in new window or tab >>Comparison of Cascaded Multilevel Converter Topologies for AC/ AC Conversion
2014 (English)In: 2014 International Power Electronics Conference, IPEC-Hiroshima - ECCE Asia 2014, IEEE Computer Society, 2014, 1087-1094 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a simplified qualitative comparison of previously presented cascaded multilevel converter topologies for ac-ac conversion with particular emphasis on motor drive applications. Performance criteria such as the pulsation of the stored energy in the cell capacitors and the total required semiconductor rating are derived by analytical methods. The main conclusion is that the back-to-back connected modular multilevel converter operates best at synchronous speed, whereas the modular matrix converter and Hexverter are better suited for low-frequency output. However, by injecting circulating currents in the phase arms the operating region can be extended for all of the studied topologies.

Place, publisher, year, edition, pages
IEEE Computer Society, 2014
Series
International Conference on Power Electronics, ISSN 2150-6078
Keyword
Matrix converters, Power converters, Topology, Cascaded multilevel converter, Circulating current, Modular matrix converters, Modular multilevel converters, Motor drive applications, Operating regions, Performance criterion, Synchronous speed
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-153758 (URN)10.1109/IPEC.2014.6869722 (DOI)000347109201005 ()2-s2.0-84906662220 (Scopus ID)978-1-4799-2705-0 (ISBN)
Conference
7th International Power Electronics Conference, IPEC-Hiroshima - ECCE Asia 2014, Hiroshima, Japan, 18 May 2014 through 21 May 2014
Funder
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QC 20141010

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2016-02-12Bibliographically approved
12. A Submodule Implementation for Parallel Connection of Capacitors in Modular Multilevel Converters
Open this publication in new window or tab >>A Submodule Implementation for Parallel Connection of Capacitors in Modular Multilevel Converters
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2015 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 7, 3518-3527 p.Article in journal (Refereed) Published
Abstract [en]

In modular multilevel converters there is a trade-off between the switching frequency and the voltage ripple in the submodule capacitors. The reason for this is that it becomes increasingly difficult to balance the capacitor voltages when the switching frequency is reduced. This paper presents a new submodule circuit which improves the balancing of the capacitor voltages at low switching frequencies. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current ratings of the switches can be chosen such that the combined power rating of the semiconductors is the same as for the equivalent solution with conventional half-bridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies and thus allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulations and experimental results. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.

Keyword
Capacitor voltages, modular multilevel converter (MMC), switching losses
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-153757 (URN)10.1109/TPEL.2014.2345460 (DOI)000353126300007 ()2-s2.0-84923933547 (Scopus ID)
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QC 20150622

Available from: 2014-10-08 Created: 2014-10-08 Last updated: 2017-12-05Bibliographically approved
13. Semi-full-bridge submodule for modular multilevel converters
Open this publication in new window or tab >>Semi-full-bridge submodule for modular multilevel converters
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2015 (English)In: Power Electronics and ECCE Asia (ICPE-ECCE Asia), 2015 9th International Conference on, IEEE conference proceedings, 2015, 1067-1074 p.Conference paper, Published paper (Refereed)
Abstract [en]

The energy variations in each arm of the modular multilevel converter comprises two components. The first component relates to the difference between the instantaneous input and output power of each phase-leg, and the second component relates to the energy which is moved back and forth between the two arms of the phase-leg. The latter component can be reduced or even eliminated if the peak-to-peak amplitude of the alternating voltage is greater than the pole-to-pole voltage of the dc link. This will, however, require submodules which can insert negative voltages. Therefore, a semi-full-bridge submodule which uses less semiconductors than the conventional full-bridge is proposed. Simulation results shows that by using the negative voltage-levels the capacitor voltage ripple can be reduced by up to 59%. Experimental results also shows that a 7-level voltage waveform can be generated using only one semi-full-bridge submodule with two capacitors per arm.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keyword
power convertors;7-level voltage waveform;capacitor voltage ripple;modular multilevel converters;negative voltage-levels;peak-to-peak amplitude;pole-to-pole voltage;semifull-bridge submodule;Capacitance;Capacitors;Converters;Energy storage;Modulation;Semiconductor diodes;Switches;energy ripple;full-bridge submodules;modular multilevel converter;modulation index
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-182750 (URN)10.1109/ICPE.2015.7167913 (DOI)000382948300156 ()2-s2.0-84961933336 (Scopus ID)
Conference
Power Electronics and ECCE Asia (ICPE-ECCE Asia), 2015 9th International Conference on
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QC 20160226

Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2016-10-24Bibliographically approved

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