Comparative Optimization Design of a Modular Multilevel Converter Tapping Cells and a 2L-VSC for Hybrid LV ac/dc Microgrids

Abstract

The paper presents the performance of the modular multilevel converter tapping cells associated with an ac filter in term of efficiency and power density in a hybrid LV ac/dc microgrid application and compares it to the performance of the conventional topology used in LV application, i.e., the Two-Level voltage source converter (2L VSC). A bi-objective optimization based on the Genetic Algorithm is hence developed, providing details on designing the components of the LCL filter, the MMC and the 2L VSC. The MMC reaches an efficiency of 99.4% when the main dcgrid is left floating. However, due to its modularity and scalability, offering multiport connections option, the MMC tapping cells has the disadvantage of low power density. Exploring the filtering capability of the equivalent arm inductance of the MMC seen from the ac grid side, optimization design results show that higher switching frequencies allow a significant volume reduction of the inductive components of the MMC/LCL filter while higher switching frequencies have little impact on the switching losses of the MMC. This has the benefit of reducing the overall footprint of the converter and encouraging the use of the MMC in LV application. Index Terms-Hybrid ac/dc microgrid, interlink converter, MMC, GA based optimization, tapping cells, two-level VSC.

On the Roles and Interactions of the MMC Internal Energy Balancing Degrees of Freedom for Three-Wire Three-Phase Connections

“…T he modular multilevel converter (MMC) has been attracting the interest of the industrial community in the past decades due to its easy scalability to higher voltages, standardized components assembly, superior efficiency and inherent redundancy [1]. In low and medium voltage operations, the converter can be employed in several scenarios such as AC motor drives [2], in STATCOM applications [3], microgrids [4] and electric vehicles [5]. Nevertheless, the MMC has been established as the preferred converter choice for High Voltage Direct Current (HVDC) applications [6], [7].…”

Scalable Multiport Converter Structure for Easy Grid Integration of Alternate Energy Sources for Generation of Isolated Voltage Sources for MMC

“…The application of IGCT based MMC is also presented in the literature [15]. The application of MMCs for power flow management in hybrid microgrids is also discussed [16][17][18][19]. In all of these applications, although significant performance benefits are obtained, balancing each submodule capacitor poses a significant challenge.…”

Performance Comparison of 2L-VSC, 3L-NPC, and 3L-MMC Converter Topologies for Interfacing Grid-Connected Systems

“…Currently, there is a real concern with the impacts of the use of various power converter topologies in several applications. In Lachichi et al (2019), a performance comparison is performed between a multiport 9 level MMC and a 2L-VSC when associated with a grid-connected AC filter, in terms of efficiency and power in a low voltage hybrid microgrid. The results show that the use of MMC compared to 2L-VSC enables an increase in efficiency as well as a significant reduction in size of the filter.…”