Design, Analysis, and Experimental Verification of Arm Link Enhanced Modular Multilevel Converter

Abstract

The modular multilevel converter (MMC) has gained attention in high- and medium-voltage dc-ac conversion due to its modularity, scalability, and excellent results in power quality and efficiency. However, its complexity, multiple control loops, and extensive measurements make it unsuitable for low-voltage (LV) applications. Additionally, the power ripple in submodules (SMs) poses challenges in LV scenarios. To overcome the disadvantages of the MMC at low voltage and operate it from zero frequency to high output frequency, the arm link enhanced modular multilevel converter (ALE-MMC) was proposed, which employs dual active bridges (DABs) to transfer power ripple between the upper and lower SMs, substantially reducing its capacitance and eliminating all voltage measurements from the SMs. This work analyzes and tests the ALE-MMC in the entire operating range, giving design insights, and highlighting the various benefits, the proposed topology can obtain in low-voltage drives applications in terms of circulating currents control, DAB requirements, and efficiency. Simulation results are presented in a three-phase converter to verify its operation at high power, and the experimental results of a low-scale single-phase prototype are used to assess the operation under different scenarios.