Operation, Control, and Applications of the Modular Multilevel Converter: A Review

ABSTRACT:

 The modular multilevel converter (MMC) has been a subject of increasing importance for medium/high power energy conversion systems. Over the past few years, significant research has been done to address the technical challenges associated with the operation and control of the MMC. In this paper, a general overview of the basics of operation of the MMC along with its control challenges are discussed, and a review of state of-the-art control strategies and trends is presented. Finally, the applications of the MMC and their challenges are highlighted.

KEYWORDS:

1.      Capacitor Voltage Balancing

2.      Circulating Current Control

3.      High-Voltage Direct Current (HVDC) Transmission

4.      Modular Multilevel Converter (MMC)

5.      Modulation Techniques

6.      Redundancy

7.      Variable-Speed Drive Systems

SOFTWARE: MATLAB/SIMULINK

CONCLUSION:  

The salient features of the MMC, i.e., its modularity and scalability enable it to conceptually meet any voltage level requirements with superior harmonic performance, reduced rating values of the converter components and improved efficiency. Over the past few years, the MMC has become a subject of interest for various medium to high voltage/power system and industrial applications including HVDC transmission systems, FACTS, medium-voltage variable-speed drives, and medium/high voltage dc-dc converters.

For power system applications, e.g., HVDC systems and FACTS, the MMC has reached a certain level of maturity and seems to stand as the most promising technology as a number of MMC-HVDC systems and STATCOMs has been successfully implemented and installed. For medium-voltage variable-speed drives, there is still a plenty of room for further development and to address the operational and control issues of the MMC, specifically under constant-torque low-speed operation. One major problem that needs to be addressed is to minimize the magnitude of the capacitor voltage ripple of the converter SMs at low frequencies without sacrificing the converter efficiency, thereby making a reasonable tradeoff between the converter size/volume/cost and efficiency.

The introduction of a family of modular multilevel dc-dc converters, originated from the MMC topology, has opened up a new avenue on research and development of medium/high voltage dc-dc converters. To take the full advantage of these converters for various applications, advanced modulation strategies that enable high voltage conversion ratio, high efficiency and reduced component stresses are required. With a significant amount of MMC-derived converter topologies and applications, it is concluded that development of novel modulation and control strategies will be a major driving factor to shape the future of MMC applications.

REFERENCES:

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