Revised Optimal design of power electronic transformer based on hybrid MMC under over-modulation operation

TL;DR

This paper proposes an optimized design approach for power electronic transformers using a hybrid MMC that operates in boost-AC mode, enhancing system flexibility, reducing costs, and improving performance.

Contribution

It introduces a method to utilize the additional modulation index in hybrid MMCs for optimizing power electronic transformer design.

Findings

Optimal modulation index schemes for different objectives

Reduced system cost and volume

Enhanced design flexibility

Abstract

The bridge arm of the hybrid modular multilevel converter (MMC) is composed of half-bridge and full-bridge sub-modules cascaded together. Compared with the half-bridge MMC, it can operate in the boost-AC mode, where the modulation index can be higher than 1, and the DC voltage and the AC voltage level are no longer mutually constrained; compared with the full-bridge MMC, it has lower switching device costs and losses. When the hybrid MMC boost-AC mode is used in the power electronic transformer, the degree of freedom in system design is improved, and the cost and volume of the power electronic transformer system can be further reduced. This paper analyzes how to make full use of the newly added modulation index of freedom introduced by the boost-AC hybrid MMC to optimize the power electronic transformer system, and finally gives the optimal modulation index selection scheme of the hybrid MMC for different optimization objectives.