Mersche, Stefan , Bernet, Daniel , Hiller, Marc        

2019 IEEE Energy Conversion Congress and Exposition (ECCE)

Abstract:

Medium voltage converters are becoming more relevant in future grid applications. Especially more wind and PV generation systems will be have to added and integrated into the grid in order to achieve the required reduction in CO2 emissions. High power generation units will be integrated into the grid at medium voltage level. Furthermore meshed MV grids will require interties based on MV converter technology. Today's standard medium voltage converters are either based on the MMC technology or us 3L/5L approaches operated at low switching frequencies and containing bulky filters. Both concepts still lead to relatively high costs and low efficiencies which are major reasons for the slow spread of power converters in medium voltage grid applications.. Future grid applications demand less distortion, higher reliability and lower costs for converter systems at each voltage level. The Quasi-Two-Level operation of the flying capacitor multilevel converter with silicone-carbide (SiC) based semiconductors is a method for achieving these requirements for medium voltage converters. This paper presents a new concept for minimizing capacitance and balancing the capacitors with fast switching semiconductors. Moreover, a novel approach for limiting the overvoltage stress caused by the Quasi-Two-Level modulation of a flying capacitor converter is presented.

Braeckle, D.; Himmelmann, P.; Mersche, S.; Stefanski, L.; Hiller, M.

2021. 23rd European Conference on Power Electronics and Applications (EPE’21 ECCE Europe), 06.09.2021 – 10.09.2021, Seite 1–10, IEEEXplore

Abstract:

A highly robust and dynamic control of the MMC grid currents is necessary to ensure grid stability. Based on a state space modelling of the MMC, a real time capable indirect modelbased control is presented. Measurements with a laboratory setup show the reliability even under disturbed grid conditions.

Stefan Mersche; Robert Schreier; Patrick Himmelmann; Marc Hiller

2021 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE Europe)

Abstract:

Today’s standard medium voltage converters are operated at low switching frequencies and contain bulky line filters. One concept to change this is the Quasi-Two-Level operation of multilevel converters with fast switching semiconductors to minimize passive components. This paper presents the hardware of a full-scale medium voltage SiC-based flying capacitor converter for quasi-two-level operation with up to 10kV DC voltage and 150A line current. This hardware enables studies on the influence of components, modulation principles and control algorithms on the needed filters and the operation of the converter.