THD Investigation of Hybrid Cascaded Multilevel Inverter

Hybrid cascaded multilevel (HCML) inverter is a modification of the cascaded H-bridge (CHB) inverter, where this inverter has overcome the main drawback of the CHB inverter, which is the connection of a separate DC source in each H-bridge (cell). The solution was connecting one DC source in the first cell, and capacitors in the rest of the cells. Therefore, by controlling the switches of the inverter, the voltages of the capacitors can be regulated at a certain level and the inverter can generate an alternating voltage. In this paper, two cells and three cells HCML inverters have been simulated with Plecs software and modulated with phase shift- pulse width modulation strategy (PS-PWM). This modulation scheme was implemented with C language. The modulation program considers the load current and the voltages of the capacitors as feedbacks. The two inverters have been investigated in terms of the total harmonic distortion (THD) of the voltage and current waveforms. Therefore, the effect of the load sizes and cells number was addressed. Several significant results have been obtained from this study.