Passivity-based Control Strategy of MMC-SMES Based on PCHD Model

Abstract

Compared with conventional two/three-level converters, module multilevel converter (MMC) has the advantages of high power, small harmonic distortion and low switching loss because of its modularity and flexibility. Therefore, MMC has a broad application prospect in superconducting magnetic energy storage (SMES) system with high power density. In this paper, a novel topology of SMES based on MMC and its passivity-based control strategy are proposed to effectively improve power quality and robustness of the controlled system. Firstly, a mathematical model and a port-controlled Hamiltonian-with-dissipation (PCHD) model of MMC-SMES are established. Secondly, in order to solve the nonlinearity in operation of MMC-SMES, the passivity-based control strategy is designed considering the internal-external interaction structure of the controlled system. Then, in order to solve the problems of voltage balancing and circulating current of MMC, sub-module capacitor voltage classification balancing control and inter-phase decoupling control under negative-sequence double-frequency coordinate transformation are adopted. Finally, effectiveness of the proposed topology of SMES and its control strategy are verified through simulation studies.