Model Predictive Control for Three-Level Four-Leg Flying Capacitor Converter Operating as Shunt Active Power Filter

This paper presents the new implementation of the finite control states set model predictive control (FS-MPC) applied to three-level four-leg flying capacitor converter (FCC) operating as a shunt active power filter (SAPF). The three main issues regarding the algorithm development are described and the solutions are proposed. The first is addressed to modeling of the four-wire system, which for simplification is based on wire-to-wire voltage equations. The second relates to the control of FCC by MPC, i.e., a proper interpretation of the FCC switching states and control of flying capacitor (FC) voltages, which was moved from the prediction loop. Finally, the system restriction regarding undesirable switching states' transitions is explained and the solution is presented. The control performance was tested in the simulation model in MATLAB-Simulink and validated experimentally by measurements on the 10-kVA FCC laboratory setup.

I. Introduction

The energy quality aspect becomes more and more important with a fast growth of the electrical energy consumption. Nonlinear loads cause significant distortions in the grid currents which also lead to voltages distortion in high impedance grid. Shunt active power filters (SAPFs) are designed to deal with those issues by generation of properly shaped compensation currents, which can significantly reduce grid currents THDs and cover reactive power demand. According to the system topology (three- or four-wire network), SAPFs are based on three- or four-leg power converters [1], [2].