Reducing Harmonic Distortions in Multilevel Inverter Based on PSO

A single-phase multilevel inverter (MLI) capable of generating multiple voltage levels is used as an AC power source at a frequency of 50Hz with minimal total harmonic distortion (THD%). The key factor in reducing THD is determining the optimal switching angles of the inverter, as optimization algorithms provide the best solutions to eliminate or minimize many harmonics associated with inverter voltages, thereby significantly enhancing inverter efficiency. For this purpose, these optimal angles are derived by solving the trigonometric equations for the inverter's output voltage, obtained through Fourier analysis, aiming to reduce the total harmonic distortion (THD%). Objective function equations are introduced into MATLAB software, utilizing the PSO algorithm, and the best results are selected by developing a MATLAB program to calculate the THD% value over a wide range of modulation index ($0<m<1$). Performance analysis and validation are conducted through simulation models and an experimental prototype. The selective harmonic elimination technique (SHE) is incorporated to ensure the elimination of third-order harmonics that negatively affect the inverter's efficiency. The results demonstrate that the multilevel inverter can effectively generate multiple voltage levels while maintaining low THD%. Voltage and current measurements, along with frequency analysis results, indicate the cancellation of selected harmful harmonics, leading to a noticeable improvement in system efficiency.