Accurate Circulating Current Estimation of Modular Multilevel Converters with Coupled Inductors

The modular multilevel converters (MMCs) are considered the new generation of multilevel voltage source converter with an expecting prospect. This paper focuses on the MMCs with coupled inductors (CIs). An accurate circulating current estimation methodology is proposed. The application of equivalent decoupling method for different kinds of CI connections is deduced, and the influences of CIs on the harmonic components in circulating currents as well as submodule (SM) voltage fluctuations are discussed with emphasis on the fourth-order harmonic. The effectiveness and accuracy of the proposed estimation method was demonstrated by several test results.