An Analytical Essential Switching Loss Estimation Method for Modular Multilevel Converters with Nearest Level Modulation

A novel switching power loss estimation method for modular multilevel converters (MMCs) with the nearest level modulation (NLM) is introduced in this paper. It focuses on the switching actions caused only by change of the inserted submodule (SM) number per arm, named as the essential switching transitions. Every essential switching action can be identified under the assumption of ideal sinusoidal arm voltage reference. The corresponding arm current value determining the switching energy can be obtained with the exclusive use of the exact time of the switching action. Effects of the modulation index and the power factor on the power loss are also taken into account. Simulations have been performed on a 30-MVA threephase grid-connected MMC system with 20 SMs per arm. The results have confirmed the effectiveness of the proposed method, where high estimation accuracy can be achieved under a range of operating conditions.