Design of Model Predictive Control for 7-Level Packed U-Cell Grid Connected Multilevel Inverter /

Abstract

As the penetration of renewable energy sources (RES) into power grids continues to rise, the reliance on power electronics-based systems has become more pronounced. Inverters that convert DC to AC play a vital role in harvesting green energy from the renewable sources and feeding into the power grid. This research thesis explains an on-grid (grid connected) 7-Level Packed U-cell (PUC7) inverter topology employing Model Predictive Control (MPC) technique. The primary objective is to minimize the number of active and passive elements from the circuitry to make inverter size compact, less complex and less costly. In this specific research work it is aimed to eliminate the need of DC-to-DC boost converter specifically when used for on-grid applications employed with solar photovoltaic (PV). The proposed approach is a single phase/stage multilevel inverter (MLI), comprising of three pairs of switches operating in a complementary fashion, One PV source (DC) and one flying capacitor that connects with grid via filtering inductor. Mainly, a DC-to-DC converter stage is necessarily requested between the Photovoltaic (PV) array and the inverter. Previously, boost converters were used to get maximum power when energizing the inverter with PV Source. This topology, compared to conventional multilevel inverter topologies generates seven different voltage levels (7-level) while utilizing less count of active and passive elements also performing Maximum Power Point Tracking (MPPT) by itself. The MPC technique objective is to reduce the THD of the injected current to grid while regulating the flying capacitor voltage at one by third (1/3rd) level as compared to PV voltages. The main goals of MPC controller are to control the injection of current into grid and regulate the flying capacitor voltage at reference to generate 7-level inverter voltage output. Theoretical analysis, mathematical modeling, and simulation were done in MATLAB/SIMULINK software. The proposed system is tested and verified on the Hardware-In-Loop (HIL) system. Finally, Experimental setup for proposed topology is designed and implemented in real time with grid-connected pattern to test the functionality and performance of inverter.