High Voltage High Power DC/DC Modular Multilevel Converter for Offshore Windfarm DC Collection Point

2016 ◽  
Author(s):  
He Liu ◽  
M. Armstrong ◽  
R.T. Naayagi ◽  
M. Dahidah
Keyword(s):  
High Voltage ◽  
High Power ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Collection Point

scholarly journals Energy balancing in modular multilevel converter systems

2017 ◽  
Vol 65 (5) ◽  
pp. 685-694
Author(s):  
P. Blaszczyk ◽  
K. Koska ◽  
P. Klimczak
Keyword(s):  
Control System ◽  
High Voltage ◽  
High Power ◽  
Power Converter ◽  
Modular Multilevel Converter ◽  
Energy Balancing ◽  
Multilevel Converter ◽  
Test Setup ◽  
Clear View ◽  
Hierarchical Levels

Abstract The modular multilevel converter (MMC) is a well-known solution for medium and high voltage high power converter systems. This paper deals with energy balancing of MMCs. The analysis includes multi-converter systems. In order to provide clear view, the MMC control system is divided into hierarchical levels. Details of control and balancing methods are discussed for each level separately. Finally, experimental results, based on multi-converter test setup, are presented.

scholarly journals New AC–AC Modular Multilevel Converter Solution for Medium-Voltage Machine-Drive Applications: Modular Multilevel Series Converter

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3664
Author(s):  
Gustavo Gontijo ◽  
Songda Wang ◽  
Tamas Kerekes ◽  
Remus Teodorescu
Keyword(s):  
High Voltage ◽  
Internal Control ◽  
High Power ◽  
High Performance ◽  
Offshore Wind ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Low Frequencies ◽  
Control Loops ◽  
Machine Drive

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.

scholarly journals Performance Analysis of Modular Multilevel Converter and Modular Multilevel Series Converter under Variable-Frequency Operation Regarding Submodule-Capacitor Voltage Ripple

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 776
Author(s):  
Gustavo Gontijo ◽  
Songda Wang ◽  
Tamas Kerekes ◽  
Remus Teodorescu
Keyword(s):  
High Voltage ◽  
High Power ◽  
Variable Frequency ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Low Frequencies ◽  
Machine Drive ◽  
Voltage Ripple ◽  
Start Up ◽  
Capacitor Voltage

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.

scholarly journals Novel Enhanced Modular Multilevel Converter for High-Voltage Direct Current Transmission Systems

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2257
Author(s):  
Dimitrios Vozikis ◽  
Fahad Alsokhiry ◽  
Grain Philip Adam ◽  
Yusuf Al-Turki
Keyword(s):  
High Voltage ◽  
Low Voltage ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Medium Voltage ◽  
High Voltage Direct Current ◽  
Current Transmission ◽  
The Cost ◽  
Voltage Harmonics ◽  
Chain Links

This paper proposes an enhanced modular multilevel converter as an alternative to the conventional half-bridge modular multilevel converter that employs a reduced number of medium-voltage cells, with the aim of improving waveforms quality in its AC and DC sides. Each enhanced modular multilevel converter arm consists of high-voltage and low-voltage chain-links. The enhanced modular multilevel converter uses the high-voltage chain-links based on medium-voltage half-bridge cells to synthesize the fundamental voltage using nearest level modulation. Although the low-voltage chain-links filter out the voltage harmonics from the voltage generated by the high-voltage chain-links, which are rough and stepped approximations of the fundamental voltage, the enhanced modular multilevel converter uses the nested multilevel concept to dramatically increase the number of voltage levels per phase compared to half-bridge modular multilevel converter. The aforementioned improvements are achieved at the cost of a small increase in semiconductor losses. Detailed simulations conducted in EMPT-RV and experimental results confirm the validity of the proposed converter.

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