Enhancing the Performance of Pre-Charging Strategy of a Modular Multilevel Static Synchronous Compensator

Abstract

This paper presents an improvement in an energizing strategy for a three-phase four-wire modular multilevel converter connected to an electric network as a static synchronous compensator. The new procedure comprises three stages. During the first stage, two thyristors control the current drained from the grid in order to charge the capacitors of the submodules of the positive and negative arms of two phases of the converter. After that, the energy stored in these capacitors is shared with the others submodule capacitors by firing the semiconductor switches of the converter in a strategic way. In addition of limiting the current drained from the grid during all the energizing procedure, the proposed strategy does not produce overvoltage at the converter dc terminals. The results of digital simulations are presented to validate the mathematical analysis and to demonstrate the performance of the proposed energizing strategy.