Improved VSG and its seamless transfer control for multilevel converter based energy storage system

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Why is it important?

in this work, we studied a transformerless energy storage system (ESS) based on cascaded H-bridge Converter (CHB) with virtual synchronous generator (VSG) control. The coupling problem between the primary frequency regulation (PFR) of ESS and the damping link in VSG is presented and analyzed. In order to solve this, the transient damping link based VSG control is proposed, which will not affect the PFR characteristic of ESS and keep the advantages of traditional VSG control. In addition, the seamless transfer of VSG controlled ESS from islanded mode to grid-connected mode is very essential. In this work, according to the special structure of VSG control, a novel direct voltage-phase discrimination based pre-synchronizing control strategy is presented. Moreover, this method utilizes voltage information only and is easy to realize.