About this Research Topic
Modular multilevel converters (MMCs) have been receiving increasing attention in recent years due to the demands of high power in industrial applications. The MMC was first proposed by Marquardt and Lesnicar in the 2000s and is regarded as one of the next-generation high-voltage multilevel converters. The MMC is composed of a number of submodules, which offers redundancy possibilities for greater reliability. The high number of modules can also produce greater levels of energy and enable a significant reduction in average switching frequency without compromising the power quality. In addition, the series-connected buffer inductor in each arm can limit the current and protect the system during faults. Due to ease of construction, assembly and flexibility in the converter design, the MMC is an attractive source for applications such as in high-voltage direct-current transmission, medium-voltage drives, electric railway supplies and microgrid.
This Research Topic aims to highlight advances and emerging applications of MMCs, as well as the challenges and limitations of the MMC system. Reliability of MMCs is a key challenge, due to the large number of power semiconductors and electrolytic capacitors. As a result, a number of topics should be further studied including MMC topologies, control strategies, lifetime prediction, health monitor and fault tolerance capability. Moreover, the challenges of the MMC DC-side fault protection, resonance and stability also need to be considered. On the other hand, due to the control capability of the converters, MMCs are expected to provide many advantages to advanced ancillary for electric grid e.g. faster frequency support, reactive power support and voltage regulation.
Topics of interest include, but are not limited to:
• New topology and advanced control strategies for the MMC
• Reliability and lifetime prediction for the MMC
• Advanced ancillary services for AC grid support
• Circuit/component parameters selection and optimization
• Efficiency improvement and losses balancing techniques for MMCs
• Advanced analysis and modelling techniques for MMCs
• Advanced modulation and control techniques of MMCs
• Fault diagnosis and tolerant operation of MMCs
• DC-side fault protection of MMCs
• Integration of new power devices in MMCs
• Integration of renewable energy and energy storage with MMCs
• Applications in HVDC, MTDC, FACTS, motor drives, power electronic transformers, smart grid, etc.
Prof. Fujin Deng holds a patent for Protection Circuit and Method for MMCs. This patent describes the protection of the MMC under diode open-circuit fault. The diode open-circuit fault would cause high voltage in the MMC and affect the performance of the MMC. In the patent, the varistor is adopted to be parallel with the switch to eliminate the overvoltage and protect the MMC under diode open-circuit fault. The other Topic Editors declare no competing interests with the Research Topic theme.
Keywords: Control, power converter, modeling, multilevel converter, topology
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