Application of OHSW technique in cascaded multi-Level inverter with adjustable DC sources

The Optimized Harmonic Stepped Waveform (OHSW) technique is an effective method for reduction of multi-level inverter´s harmonics. This technique is very efficient for improving the quality of multi-level inverter output voltage. It is usually assumed that cascaded multi-level inverters have equal DC sources. In practice, however, this will not be happened even if the DC sources are nominally equal. In addition, in some applications the DC sources can be regulated. Employing adjustable DC sources can increase degree of freedom to eliminate more harmonics in OHSW technique and therefore can result in substantial improvement in the total harmonic distortion (THD). In this paper first, the 7-level cascaded inverter structure is briefly described. Then, the basic idea and concept of three-phase and single-phase OHSW technique is described. Ultimately, the results obtained by simulation for the OHSW technique are analyzed and the using OHSW in multi-level inverter with constant DC sources is compared with adjustable DC sources. Genetic Algorithm (GA) is used as a powerful tool to calculate optimal switching angles. Computer simulations show that more harmonics can be eliminated in OHSW technique by employing adjustable DC sources which can be controlled.