Authors: Margarita Norambuena ; Samir Kouro ; Sibylle Dieckerhoff ; Jose Rodriguez

Extended Abstract:
Multilevel converters have made a strong entrance in the low voltage market (typically below 690V), particularly for wind and photovoltaic energy conversion systems, UPS, and EV fast-charging stations. Since the device blocking voltage is not an issue in this voltage range, the main driver behind this trend is the more demanding grid codes, the filter size reduction, and the increased efficiency, which are directly or indirectly achieved by the more sinusoidal multilevel voltage waveforms. However since these applications are reaching quite high power levels (e.g. several wind turbines above 5MW, central PV inverters above 2MW), they require several converters operating in parallel, multichannel or interleaved mode. In fact, some PV inverters have up to 12 converters (four per phase) to reach 2MW. In these cases, a reduction in the number of active devices and capacitors for each individual converter could translate in cost reduction, higher power density and less failure probability (less gate drives and capacitors).

This paper proposes a new multilevel converter topology which reduces the number of power switches and capacitors to generate the same or more number of output voltage levels as traditional multilevel converters. The operating principle is based on a variable multilevel dc-link voltage which is shared by all the phases of an output inverter stage. The variable dc-link is generated by a multicell arrangement of DC-cells which have a controlled current path through a floating capacitor. Combinations of several DC-cells at the dclink can increase the number of voltage levels generated at the ac side, without increasing the number of active devices proportionally to the three phases, hence the name reduced multilevel converter (RMC).

2019 Best student paper award for IEEE Industrial Electronics Society
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