Control of the DC link capacitor voltage on a new four-level SMC based topology

Abstract

The multilevel topologies allow the power transfer for applications in the range of medium voltage with switching frequencies less than one kHz. For many years, many structures were proposed to increase the number of levels. A new three-phases topology with 4 levels is proposed in this paper using the concept of both SMC (Stacked Multicell Converter) and ANPC (Active Neutral Point Clamp). To increase the number of output level voltage it's possible to split the DC link capacitor. When having more than 2 capacitors in series, it is difficult to guarantee the balanced of the capacitor voltages. Some solutions are available to solve this problem and in this paper we propose to use a Space Modulation Vector (SVM) using the different redundancies of the system to balance these capacitor voltages. The strategy is mainly based on a minimisation of the stored energy in the DC link capacitors. This solution allows balancing of the capacitor voltages for a wide range of the modulation index.