Comparative study between three and seven multilevel inverter for grid-connected photovoltaic (PV) system controlled by PI regulator

Power quality is a good indicator of the health of a three-phase industrial electrical system. It can cause many problems, including damaging equipment and wasting energy if its use is not optimized. Harmonics, i.e. distortions caused by variations in the voltage or current waveform, are one of the main problems to be solved to ensure maximum efficiency of electrical power systems. A larger number of levels in a multi-level inverter leads to better power quality. The main problem lies in the optimal number of levels for a multi-level inverter in order to obtain the best performance. To achieve this objective, this manuscript proposes a comparative study between two inverters (NPC) with 3 and 7 levels for grid-connected photovoltaic (PV) production systems, where the performance will be evaluated in terms of reduction of total harmonic distortion (THD). The output voltage of each inverter must be maintained for grid connection, although the output voltage of solar power varies significantly depending on solar radiation. To achieve this, three PI controllers were used to control the inverter output voltage (Vdc), direct current (Id) and quadratic current (Iq) around the reference values. The proposed system is simulated using Matlab-Simulink.