Line Voltage THD Minimization in Multilevel Inverter using Particle Swarm Optimization

THD minimization is a powerful technique for lowering the harmonic content of an inverter's output voltage. In most three-phase multilevel inverters, the optimization algorithm is applied to the inverter's phase voltage, and then line voltage THD is calculated. As a result, although it achieves the lowest THD in phase voltage, it does not always have the lowest THD in line voltage. Line voltage harmonics play an important role in terms of load. In this paper, the Particle Swarm Optimization (PSO) technique is applied to a multilevel inverter to determine the optimal switching angles using the direct formula of Line voltage Total Harmonic Distortion (LVTHD) as the objective function. The simulation was performed in MATLAB for a 7-level cascaded H bridge multilevel inverter using both the Minimization of Phase Voltage Total Harmonic Distortion (MPVTHD) and Minimization of Line Voltage Total harmonic distortion (MLVTHD) approaches and comparison was done. The result indicates that phase voltage THD minimisation approach produces line THD of 8.36% whereas line voltage THD approach provides better results with line THD value of 6.87% without using filter circuits. Thus, THD optimization applied directly to line voltage provides significant reduction in harmonics with that of phase THD minimization approach.