Developed single-phase OMTHD technique for cascaded multi-level inverter by considering adjustable DC sources

There exists an effective method for reduction of multilevel inverter´s harmonics which is called the optimal minimization of the total harmonic distortion (OMTHD) technique. OMTHD technique is applied only for THD minimization with no constraint on the value of fundamental component; whereas, the primary objective in any method of inverter control is adjustment of the fundamental component to the desired value. For solving this problem, the new fitness function is proposed and fundamental component as a constraint is separately added to fitness function and genetic algorithm is applied to minimize this new fitness function. Most control methods used in cascaded multi-level inverters are based on the assumption that the DC sources all have the constant and equal value whereas employing adjustable DC sources if it is possible can improve the total harmonic distortion (THD) in OMTHD technique. First, the structure of cascaded multi-level inverter is explained. Then, the switching algorithm for the inverter based on developed OMTHD technique is proposed. Afterwards, the proposed technique is applied to the multi-level inverter with adjustable DC sources and constant DC sources. Ultimately, an accurate comparison of THD between multi-level inverter with constant and adjustable DC sources is performed. Comparisons show that employing adjustable DC sources which can be controlled results in substantial improvement in the harmonic minimization.