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.
