Optimization-based reference calculation for Modular Multilevel Converters in balanced and unbalanced network conditions

Abstract

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

The paper addresses an optimization-based algorithm to calculate the references of the Modular Multilevel Converter (MMC) during normal and constrained scenarios (when the prioritization of quantities is required). The optimization problem prioritizes to satisfy the positive- and negative-sequence active and reactive current set-points demanded by the Transmission System Operator (TSO) through the corresponding grid code. If the TSO’s requirements are achieved, the algorithm minimizes the arm impedances losses. Otherwise, it attempts to reduce the error between the current components and the TSO’s current set-points. The optimization-based current reference calculation is derived based on the steady-state equations of the MMC, considering the maximum currents that can flow through the MMC’s arms, the maximum and minimum arm applied voltages and the maximum sub-module capacitor’s voltage. Simulation in the time-domain have been conducted and the results indicate that this method can be potentially employed to calculate the converter’s references during both normal and faulted conditions.

Peer Reviewed

Postprint (author's final draft)