Study of the design and control of a three-phase multilevel active filter

Abstract

This thesis addresses the issues of filtering the harmonics in electrical grids using active power filters. Power converters are the main element of an active power filter. The performance of the filter greatly depends on the type of the converter, on the control system and on the modulation technique used to command the converter. This thesis focuses in three-level neutral point clamped converters which work as shunt active power filters to compensate the current harmonics. Firstly, this thesis makes an introduction about what is the grid quality and why is important to not have currents and voltages with significant harmonics. Secondly, we describe several converter topologies which can work as an active power filter. This description includes the well-known two-level converter and also different topologies of multilevel converters. Thirdly, we present the control system used in the studied converter. The control system includes the grid synchronization, the voltage and current loops and how we detect the current harmonics to compensate. Finally, we present some modulation techniques used in multilevel converters and the modulation used in the proposed active power filter. All the simulations included in this these have been performed using the software MATLAB SIMULINK and PLECS