Total Harmonic Distortion (THD) Analysis of 5-Level and 7-Level Cascaded Multilevel Inverters at Different Switching Frequencies

Multilevel inverters convert DC voltage to AC voltage by using lower DC voltage at the input, with the help of an electronically controlled device. One of the primary challenges linked to these devices is the Total Harmonic Distortion (THD) present in the output waveforms. In this research paper, concise overview of Total Harmonic Distortion (THD) is presented for different cascaded H-bridge multilevel inverter topologies, in particular, the five-level and seven-level inverters illustrate this concept well. The five-level inverter employs eight switches, whereas the seven-level inverter uses twelve switches. Each H-bridge inverter circuit operates with separate DC sources. The inverter employs an Insulated Gate Bipolar Transistor (IGBT) serves as the switching component and a gating block to regulate the operation of the IGBT switching. Simulation results and waveform analysis are provided to confirm the research findings. The study also explores the effect of varying the switching frequency of the carrier wave on the total harmonic distortion of the output waveforms. The paper highlights the significance of choosing the right switching frequency according to application requirements to enhance the performance and efficiency of cascaded multilevel inverters.