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Energies
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Grid Connected Modular Multilevel Converters (MMC) and New Applications
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Grid Connected Modular Multilevel Converters (MMC) and New Applications

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "F: Electrical Engineering".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 11053

Special Issue Editors

Prof. Dr. Dionisio Ramírez Prieto

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Guest Editor
Department of Automation, Electrical and Electronic Engineering and Industrial Computing, Higher Technical School of Industrial Engineering, Technical University of Madrid (UPM), Madrid, Spain
Interests: Control Systems, Power Systems, Renewable Energy Technologies, Electrical Power Engineering, Energy Conversion, Distributed Generation, Power Converters, Inverters Photovoltaics, Grid Integration, Electric control of renewable energy and DSP based control systems
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Fernando Martinez-Rodrigo

E-Mail Website
Guest Editor
Department of Electronics Technology, University of Valladolid, Valladolid, Spain
Interests: power converters; electric drives; HVDC; wind energy
Prof. Dr. Giri Venkataramanan

E-Mail Website
Guest Editor
WEMPEC, University of Wisconsin-Madison, Madison, WI, USA
Interests: power converter topologies; microgrids; wind power systems; utility-scale power electronic systems

Special Issue Information

Dear Colleagues,

Modular multilevel converters (MMC) are a sophisticated technology that was originally designed for very high-power applications. Over time, the scientific community has contributed with new solutions to solve some of its weak points, such as reducing the circulating currents, balancing the capacitor voltages, reducing the computing burden of the control, etc. Further, new control techniques have been developed for MMC, for example, to make the converter work as a current source, or others based on model predictive control, either applied to the internal operation or to the operation of the grid connection. Lately, medium power versions of MMCs are being applied to wind generation, STATCOMs, etc. In addition, new topologies have been investigated to reduce the number of semiconductors or to keep the MMC working under certain types of internal and external faults.

Any contribution within the aforementioned topics, and many other related ones, is welcome to this special issue.

As Guest-Editors, we cordially invite you to send a proposal for consideration, and possible publication, in the Special Issue “Grid-Connected Modular Multilevel Converters (MMC) and New Applications” that we are organizing for the journal Energies.

Energies (https://www.mdpi.com/journal/energies) is an open access journal publishing related scientific research and studies, published by MDPI online monthly. Since its launch in 2008, the journal has been indexed by Science Citation Index Expanded, COMPENDEX, and other large databases. The latest Impact Factor for 2018 is 2.707; 5-year Impact Factor: 2.990 (2018).

Prof. Dr. Dionisio Ramirez
Prof. Dr. Fernando Martinez-Rodrigo
Prof. Dr. Giri Venkataramanan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Fault tolerance 
  • Distributed control 
  • Model-predictive control 
  • Grid forming 
  • Medium voltage wind turbines and motor drives 
  • Models to speed up simulations 
  • Unbalanced grids and distorted grids 
  • Renewable energies

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Published Papers (4 papers)

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23 pages, 2427 KiB  
Article
Detailed Assessment of Modulation Strategies for Hexverter–Based Modular Multilevel Converters
by Héctor R. Robles-Campos and Fernando Mancilla-David
Energies 2022, 15(6), 2132; https://doi.org/10.3390/en15062132 - 15 Mar 2022
Cited by 4 | Viewed by 2313
Abstract
Modular multilevel converters are playing a key role in the present and future development of topologies for medium–to–high–power applications. Among this category of power converters, there is a direct AC–AC modular multilevel converter called “Hexverter”, which is well suited to connect three–phase AC [...] Read more.
Modular multilevel converters are playing a key role in the present and future development of topologies for medium–to–high–power applications. Among this category of power converters, there is a direct AC–AC modular multilevel converter called “Hexverter”, which is well suited to connect three–phase AC systems operating at different frequencies. This topology is the subject of study in this manuscript. The complete Hexverter system is composed of an Hexverter power converter and several control layers, namely, a “virtual VC2 controller”, a branch current controller in a two–frequency dq reference frame, a modulator, and a voltage balancing algorithm. The paper presents a thorough description and analysis of the entire Hexverter system, providing research contributions in three key aspects: (i) modeling and control in a unified two–frequency dq framework; (ii) developing a “virtual VC2 controller” to dynamically account for Hexverter’s active power losses allowing to achieve active power balance on the fly; and (iii) a comparative evaluation of modulation strategies (nearest level control and phase disposition–sinusoidal pulse width modulation). To this end, a detailed switched simulation was implemented in the PSCAD/EMTDC software platform. The proposed “virtual VC2 controller” is evaluated through the measurement of its settling time and calculation of active power losses. Each modulation technique is assessed through total harmonic distortion and frequency spectrum of the synthesized three–phase voltages and currents. The results obtained suggest that the control scheme is able to properly regulate the Hexverter system under both modulation strategies. Furthermore, the “virtual VC2 controller” is able to accurately determine the active power loss, which allows the assessment of the efficiency of the modulation strategies. The nearest level control technique yielded superior efficiency. Full article
(This article belongs to the Special Issue Grid Connected Modular Multilevel Converters (MMC) and New Applications)
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23 pages, 4838 KiB  
Article
Effect of Frequency Coupling on Stability Analysis of a Grid-Connected Modular Multilevel Converter System
by Yixing Wang, Qianming Xu and Josep M. Guerrero
Energies 2021, 14(20), 6580; https://doi.org/10.3390/en14206580 - 13 Oct 2021
Cited by 9 | Viewed by 2289
Abstract
Due to the internal dynamics of the modular multilevel converter (MMC), the coupling between the positive and negative sequences in impedance, which is defined as frequency coupling, inherently exists in MMC. Ignoring the frequency coupling of the MMC impedance model may lead to [...] Read more.
Due to the internal dynamics of the modular multilevel converter (MMC), the coupling between the positive and negative sequences in impedance, which is defined as frequency coupling, inherently exists in MMC. Ignoring the frequency coupling of the MMC impedance model may lead to inaccurate stability assessment, and thus the multi-input multi-output (MIMO) impedance model has been developed to consider the frequency coupling effect. However, the generalized Nyquist criterion (GNC), which is used for the stability analysis of an MIMO model, is more complicated than the stability analysis method applied on single-input-single-output (SISO) models. Meanwhile, it is not always the case that the SISO model fails in the stability assessment. Therefore, the conditions when the MIMO impedance model needs to be considered in the stability analysis of an MMC system should be analyzed. This paper quantitatively analyzes the effect of frequency coupling on the stability analysis of grid-connected MMC, and clarifies the frequency range and grid conditions that the coupling effect required to be considered in the stability analysis. Based on the quantitative relations between the frequency coupling and the stability analysis of the grid-connected MMC system, a simple and accurate stability analysis method for the grid-connected MMC system is proposed, where the MIMO impedance model is applied when the frequency coupling has a significant effect and the SISO impedance model is used if the frequency coupling is insignificant. Full article
(This article belongs to the Special Issue Grid Connected Modular Multilevel Converters (MMC) and New Applications)
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12 pages, 5420 KiB  
Article
Modular Multilevel Converter for Low-Voltage Ride-Through Support in AC Networks
by Victor Ramon França Bezerra de Souza, Luciano Sales Barros and Flavio Bezerra Costa
Energies 2021, 14(17), 5314; https://doi.org/10.3390/en14175314 - 27 Aug 2021
Cited by 6 | Viewed by 2954
Abstract
New grid-connected systems have imposed additional requirements regarding reliability, power quality, high levels of power processing capacity, and fault support, where power converters have a crucial role in fulfilling these requirements. Overcoming one of these challenges, this paper proposes a new alternative application [...] Read more.
New grid-connected systems have imposed additional requirements regarding reliability, power quality, high levels of power processing capacity, and fault support, where power converters have a crucial role in fulfilling these requirements. Overcoming one of these challenges, this paper proposes a new alternative application to improve the low-voltage ride-through (LVRT) support based on the arm impedance employment of the modular multilevel converter (MMC) by attenuating the fault impacts, avoiding overcurrents and overvoltages. This proposal does not require additional hardware or control loops for LVRT support, only using PI controllers. This paper evaluates symmetrical and asymmetrical grid fault impacts on the converter DC side of four converter topologies: two-level voltage source converter topology (2L-VSC), neutral point clamped (NPC), MMC, and 2L-VSC equipped with a DC-chopper, employing the same control structure for the four topologies, highlighting that the MMC contributed better to LVRT improvement under severe grid conditions. Full article
(This article belongs to the Special Issue Grid Connected Modular Multilevel Converters (MMC) and New Applications)
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21 pages, 3471 KiB  
Article
Connection System for Small and Medium-Size Wind Generators through the Integration in an MMC and NLC Modulation
by Fernando Martinez-Rodrigo, Dionisio Ramirez, Santiago de Pablo and Luis Carlos Herrero-de Lucas
Energies 2021, 14(9), 2681; https://doi.org/10.3390/en14092681 - 7 May 2021
Cited by 1 | Viewed by 1915
Abstract
This paper presents a new way of organizing a wind farm with a large number of small to medium-sized turbines. Each wind generator has been included in a switching module of a modular multilevel converter (MMC), which generates the output voltage by near [...] Read more.
This paper presents a new way of organizing a wind farm with a large number of small to medium-sized turbines. Each wind generator has been included in a switching module of a modular multilevel converter (MMC), which generates the output voltage by near level control (NLC). The proposed topology reduces the number of semiconductors required, switching losses, and voltage filtering requirements. This topology replaces the usual configuration where each wind turbine is connected to a three-phase two-level back-to-back converter plus a filter and then connected in parallel with the other wind generators. To test the topology and its control performance, a case has been developed and simulated for generator configurations producing the same power, for generation imbalances between phases and for imbalances between arms. The analysis of the data shows that the converter works correctly and that it can deliver power to the grid in a balanced way even if the generation has imbalances. The generation imbalances between phases are compensated through the average value of the circulating current, while the imbalances between arms are compensated through the 50 Hz circulating current. Full article
(This article belongs to the Special Issue Grid Connected Modular Multilevel Converters (MMC) and New Applications)
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