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.

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Standard medium-voltage converters are operated at low switching frequencies using bulky passive components. One concept to change this involves the quasi-two-level operation (Q2O) of multilevel converters that use fast-switching semiconductors to minimize the need for passive components. The flying capacitor converter (FCC) uses SiC semiconductors and operates with Q2O to minimize passive components. In this paper, two different quasi-two-level algorithms are analyzed. A medium-voltage prototype was built and low-voltage and medium-voltage measurements were used to validate the concept. A particular focus is on the overvoltage, the dv/dt behavior of the converter, as well as the dynamic behavior.

The design of a fully superconducting wind power generator is influenced by several factors. Among them, a low number of pole pairs is desirable to achieve low AC losses in the superconducting stator winding, which greatly influences the cooling system design and, consecutively, the efficiency of the entire wind power plant. However, it has been identified that a low number of pole pairs in a superconducting generator tends to greatly increase its output voltage, which in turn creates challenging conditions for the necessary power electronic converter. This study highlights the interdependencies between the design of a fully superconducting 10 MW wind power generator and the corresponding design of its power electronic converter.

Today's standard medium voltage converters are operated with low switching frequencies and contain bulky passive components. One concept to change this is the Quasi-Two-Level operation of a multilevel converter with SiC semiconductors. A three-phase hardware setup for a Quasi-Two-Level Flying Capacitor Converter with control and measurement results in a test setup are presented.