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Modular Multilevel Converters MMC
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Modular Multilevel Converters MMC

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A1: Smart Grids and Microgrids".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 16808

Special Issue Editor

Dr. Sanjay K Chaudhary

E-Mail Website
Guest Editor
Department of Energy Technology, Aalborg University, 9220 Aalborg Ø, Denmark
Interests: modular multilevel converter (MMC); grid integration of renewable energy sources (wind and photovoltaic); black start service; power converter applications in power systems

Special Issue Information

Dear Colleagues,

Since their invention in 2003 and first deployment in 2010, modular multilevel converters (MMC) have been very successful in high voltage DC transmission systems. Further, they have been applied or at least proposed for several other high voltage and medium voltage applications like static compensators (STATCOM), drives, traction, active power filters, grid connection of renewable energy sources, etc. A lot of work has been done in identifying new topologies, advanced control methods, design optimization, etc.

Therefore, in order to bring together the latest research and developments in the field of MMC, its control and modulation and different application aspects, including dynamic and harmonic characteristics, this Special Issue, entitled “Modular Multilevel Converters (MMC)”, has been proposed for the international journal Energies, which is an SSCI and SCIE journal (2018 IF = 2.707). This Special Issue mainly covers original research and studies related to the abovementioned topics, including but not limited to the control, dynamics, and performance of MMC in selected applications.

Prospective authors are invited to submit original contributions for publication in this Special Issue. Topics of interest include but are not limited to:

  • Control for different applications of MMC—HVDC, FACTS, drives, renewable energy sources, etc.;
  • Optimal design and selection of components for the selected application;
  • Control, dynamics and performance of MMC in the selected application;
  • Advances in the control and modulation techniques;
  • Operation of MMC under unbalanced grid conditions;
  • Fault tolerant control and operation of MMC;
  • Stability analysis of MMC;
  • Harmonic impedance characteristic and frequency response of MMC.

Assoc. Prof. Dr. Sanjay K Chaudhary
Guest Editor

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Keywords

  • Dynamics, control, and stability
  • Fault-tolerant control
  • Flexible AC transmission system (FACTS) devices, STATCOM
  • High-voltage DC (HVDC) transmission
  • Modeling and simulation
  • Modular multilevel converters (MMC)

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Published Papers (5 papers)

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Research

17 pages, 2819 KiB  
Article
Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple
by Gustavo Gontijo, Songda Wang, Tamas Kerekes and Remus Teodorescu
Energies 2021, 14(3), 776; https://doi.org/10.3390/en14030776 - 2 Feb 2021
Cited by 8 | Viewed by 2515
Abstract
The modular multilevel converter is capable to reach high-voltage levels with high flexibility, high reliability, and high power quality as it became the standard solution for high-power high-voltage applications that operate with fixed frequency. However, in machine-drive applications, the modular multilevel converter shows [...] Read more.
The modular multilevel converter is capable to reach high-voltage levels with high flexibility, high reliability, and high power quality as it became the standard solution for high-power high-voltage applications that operate with fixed frequency. However, in machine-drive applications, the modular multilevel converter shows critical problems since an extremely high submodule-capacitor voltage ripple occurs in the machine start-up and at low-speed operation, which can damage the converter. Recently, a new converter solution named modular multilevel series converter was proposed as a promising alternative for high-power machine-drive applications since it presented many important structural and operational advantages in relation to the modular multilevel converter such as the reduced number of submodule capacitors and the low submodule-capacitor voltage ripple at low frequencies. Even though the modular multilevel series converter presented a reduced number of capacitors, the size of these capacitors was not analyzed. This paper presents a detailed comparison analysis of the performance of the modular multilevel converter and the modular multilevel series converter at variable-frequency operation, which is based on the proposed analytical description of the submodule-capacitor voltage ripple in such topologies. This analysis concludes that the new modular multilevel series converter can be designed with smaller capacitors in comparison to the modular multilevel converter if these converters are used to drive electrical machines that operate within a range of low-frequency values. In other words, the modular multilevel series converter experiences extremely low submodule-capacitor voltage ripple at very low frequencies, which means that this converter solution presents high performance in the electrical machine start-up and at low-speed operation. Full article
(This article belongs to the Special Issue Modular Multilevel Converters MMC)
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17 pages, 10813 KiB  
Article
Modeling and Mitigation Control of the Submodule-Capacitor Voltage Ripple of a Modular Multilevel Converter under Unbalanced Grid Conditions
by Songda Wang, Danyang Bao, Gustavo Gontijo, Sanjay Chaudhary and Remus Teodorescu
Energies 2021, 14(3), 651; https://doi.org/10.3390/en14030651 - 28 Jan 2021
Cited by 14 | Viewed by 2204
Abstract
A modular multilevel converter’s (MMC’s) submodule (SM)-capacitor voltage will increase under unbalanced grid conditions. Depending on the imbalance level, the voltage ripple can be considerably high, and it can exceed the pre-defined safe limits. If this occurs, the converter will trip, which can [...] Read more.
A modular multilevel converter’s (MMC’s) submodule (SM)-capacitor voltage will increase under unbalanced grid conditions. Depending on the imbalance level, the voltage ripple can be considerably high, and it can exceed the pre-defined safe limits. If this occurs, the converter will trip, which can lead to serious stability problems for the grid. This paper first proposes an analytical solution for deriving the three-phase imbalanced SM ripple of an MMC under an unbalanced grid. With this analytical tool, the imbalance mechanism of the SM voltage ripple can be easily understood. What is more, the symmetrical component method is first applied to analyze the three-phase SM capacitor ripple, and the positive-/negative-/zero-sequence components of the three-phase SM voltage ripple are easily identified by the proposed analytical method. Then, based on this powerful analytical tool, the proper circulating-current profile to be injected can be obtained, allowing for the right compensation of the voltage ripple. Based on this approach, two new voltage ripple compensation methods are proposed in this paper. Simulations were carried out to validate the analytical description of the submodule-capacitor voltage ripple proposed in this paper. Moreover, simulation and experimental results are provided to validate the new compensation techniques introduced in this paper. Full article
(This article belongs to the Special Issue Modular Multilevel Converters MMC)
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48 pages, 6275 KiB  
Article
New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter
by Gustavo Gontijo, Songda Wang, Tamas Kerekes and Remus Teodorescu
Energies 2020, 13(14), 3664; https://doi.org/10.3390/en13143664 - 16 Jul 2020
Cited by 11 | Viewed by 3336
Abstract
Due to its scalability, reliability, high power quality and flexibility, the modular multilevel converter is the standard solution for high-power high-voltage applications in which an AC–DC–AC connection is required such as high-voltage direct-current transmission systems. However, this converter presents some undesired features from [...] Read more.
Due to its scalability, reliability, high power quality and flexibility, the modular multilevel converter is the standard solution for high-power high-voltage applications in which an AC–DC–AC connection is required such as high-voltage direct-current transmission systems. However, this converter presents some undesired features from both structural and operational perspectives. For example, it presents a high number of components, which results in high costs, size, weight and conduction losses. Moreover, the modular multilevel converter presents problems dealing with DC-side faults, with unbalanced grid conditions, and many internal control loops are required for its proper operation. In variable-frequency operation, the modular multilevel converter presents some serious limitations. The most critical are the high-voltage ripples, in the submodule capacitors, at low frequencies. Thus, many different AC–AC converter solutions, with modular multilevel structure, have been proposed as alternatives for high-power machine-drive applications such as offshore wind turbines, pumped-hydro-storage systems and industrial motor drives. These converters present their own drawbacks mostly related to control complexity, operational limitations, size and weight. This paper introduces an entirely new medium-voltage AC–AC modular multilevel converter solution with many operational and structural advantages in comparison to the modular multilevel converter and other alternative topologies. The proposed converter presents high performance at low frequencies, regarding the amplitude of the voltage ripples in the submodule capacitors, which could make it very suitable for machine-drive applications. In this paper, an analytical description of the voltage ripples in the submodule capacitors is proposed, which proves the high performance of the converter under low-frequency operation. Moreover, the proposed converter presents high performance under unbalanced grid conditions. This important feature is demonstrated through simulation results. The converter solution introduced in this paper has a simple structure, with decoupled phases, which leads to the absence of undesired circulating currents and to a straightforward control, with very few internal control loops for its proper operation, and with simple modulation. Since the converter phases are decoupled, no arm inductors are required, which contributes to the weight and size reduction of the topology. In this paper, a detailed comparison analysis with the modular multilevel converter is presented based on number of components, conduction and switching losses. This analysis concludes that the proposed converter solution presents a reduction in costs and an expressive reduction in size and weight, in comparison to the modular multilevel converter. Thus, it should be a promising solution for high-power machine-drive applications that require compactness and lightness such as offshore wind turbines. In this paper, simulation results are presented explaining the behavior of the proposed converter, proving that it is capable of synthesizing a high-power-quality load voltage, with variable frequency, while exchanging power with the grid. Thus, this topology could be used to control the machine speed in a machine-drive application. Finally, experimental results are provided to validate the topology. Full article
(This article belongs to the Special Issue Modular Multilevel Converters MMC)
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22 pages, 1591 KiB  
Article
Benchmarking of Modular Multilevel Converter Topologies for ES-STATCOM Realization
by Sanjay K. Chaudhary, Allan F. Cupertino, Remus Teodorescu and Jan R. Svensson
Energies 2020, 13(13), 3384; https://doi.org/10.3390/en13133384 - 1 Jul 2020
Cited by 26 | Viewed by 4641
Abstract
In recent years, the integration of the high-power static synchronous compensator (STATCOM) and energy storage in the same device has gained interest. Such a system is referred to as ES-STATCOM. Modular multilevel converter (MMC) topologies constitute a promising converter family for ES-STATCOM realization, [...] Read more.
In recent years, the integration of the high-power static synchronous compensator (STATCOM) and energy storage in the same device has gained interest. Such a system is referred to as ES-STATCOM. Modular multilevel converter (MMC) topologies constitute a promising converter family for ES-STATCOM realization, providing a modular and scalable solution with a high efficiency that handles high-power and high-voltage ratings in grid applications. There is a gap in technical literature discussing the design and the comparison of MMC-based ES-STATCOMs while utilizing batteries to find the most suitable MMC topology for ES-STATCOMs. Therefore, this paper benchmarks MMC family members for ES-STATCOM realization. Both centralized and distributed energy storage approaches are investigated. The proposed design flowcharts can be employed for comparison and optimization purposes. In total, seven topologies are compared in terms of number of cells, required silicon area and total battery volume. Different semiconductor devices and battery types are analyzed. The result indicates that centralized energy storage systems are the most suitable due to their design flexibility, low volume and small silicon area. Moreover, the possibility of using over-modulation in MMC using bridge cells has an important role in the optimization of ES-STATCOM. The results for the adopted case study shows that the decentralized approach can lead to 55% higher silicon area and 30% higher volume than the centralized approach. The double-star bridge cell MMC with centralized energy storage is determined as the most suitable solution for ES-STATCOM systems. Full article
(This article belongs to the Special Issue Modular Multilevel Converters MMC)
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18 pages, 4426 KiB  
Article
Single Pole-to-Ground Fault Analysis of MMC-HVDC Transmission Lines Based on Capacitive Fuzzy Identification Algorithm
by Hongchun Shu, Na An, Bo Yang, Yue Dai and Yu Guo
Energies 2020, 13(2), 319; https://doi.org/10.3390/en13020319 - 9 Jan 2020
Cited by 10 | Viewed by 2893
Abstract
The probability of a single pole-to-ground fault in high voltage direct current (HVDC) transmission lines is relatively high. For the modular multilevel converter HVDC (MMC-HVDC) systems, when a single pole-to-ground fault occurs, the fault current is small, and it is difficult to identify [...] Read more.
The probability of a single pole-to-ground fault in high voltage direct current (HVDC) transmission lines is relatively high. For the modular multilevel converter HVDC (MMC-HVDC) systems, when a single pole-to-ground fault occurs, the fault current is small, and it is difficult to identify the fault quickly. Through a detailed analysis of the characteristics of the single pole-to-ground fault of the MMC-HVDC transmission line, it is found that the single pole-to-ground fault has obvious capacitance-related characteristics, and the transient process after the single pole-to-ground fault is the discharge process of the distributed capacitance of the line. However, other faults do not have such obvious capacitance-related characteristics. Based on such feature, this paper proposes a novel capacitive fuzzy identification method to identify the single pole-to-ground fault. This algorithm can effectively identify both the fault of single pole-to-ground and the fault pole, which can contribute to the large database of the future smart grid. Full article
(This article belongs to the Special Issue Modular Multilevel Converters MMC)
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