Analysis of asymmetrical cascaded multilevel inverter for traction systems

Multilevel inverters when supplied from equal and constant DC sources does not have a practical sense of applications. For each of the specific harmonic profiles the variation of the DC sources affects the values of the switching angles. This increases the difficulty of the harmonic elimination´s equations. This paper presents the application of the cascaded asymmetrical multilevel inverter in the railway traction drive. The total harmonic distortion (THD) reduces with the increase in the voltage level. Various modulation techniques such as Phase Shifted Modulation (PSM), Level Shifted Modulation (LSM) and Selective Harmonic Elimination Techniques (SHE) were implemented in order to find the best modulation techniques among them. Also it is shown that SHE technique resulted in low THD. Thus, an IGBT based-cascaded five level asymmetrical inverters with SHE method has been modelled to lower the supply voltage to a level convenient for the traction induction motors.