My work focuses on the redesign of the existing cell-design of the MMC (see below). The goal is to increase (roughly double) its voltage rating with similar current ratings, making it suitable for the new Direct-MMC prototype in the laboratory. To reach this goal -- while at the same time not increasing the cell size -- the well-known 1.2 kV IGBTs will be replaced by silicon carbinde MOSFETs with a maximum blockage voltage of 3.3 kV. This of course puts new constraints on insulation, but also other topics like auxiliary supply (due to the steep voltage slope, the coupling capacitance has to be extremely small), thermal design (the higher capacitance needed for the increase power rating basically requires the volume which is at the moment occupied by the heatsink, thus an idea is to use the case as heatsink) or protection.


The Modular-Multilevel-Converter (MMC) is a converter design suitable for medium and high voltage. To reach the required blocking voltage, several cells or submodules (in a full-bridge or half-bridge configuration) are connected in series, but can be switched independently. As the resulting voltage will be formed by many small steps of the individual cell, the resulting waveform is very nice. The price to pay is the large required energy storage in each cell, as they have to buffer the second harmonic.

The MMC can be configured in two ways:

• An Indirect-MMC, where -- like in classical converters -- one AC system will first be converted into DC, to then do another conversion into AC with independent voltage and frequency. This requires six branches each, thus twelve in total.
• A Direct-MMC, where each phase of the first grid is connected to each phase of the second grid in a matrix-alike way over a branch, resulting in a total of nine branches.If any of the above mentioned sounds interesting for you, or just if have some question, feel free to get in touch with me.