Performance Evaluation of a Reduced-Switch Nine-Level Multilevel Inverter for Medium-Power Applications

Recent trends in multilevel inverter (MLI) technology stress few-number components and higher efficiency and lower total harmonic distortion (THD) to satisfy the energy demands of renewable energy generation, electric mobility, and medium-power industrial systems. Traditional cascaded H-bridge (CHB) inverters, however, do not account for modularity scalability and result in a higher switch count, higher conduction and switching losses, complex gate-drive circuits, and lower reliability with increasing voltage levels. High-voltage levels with lower power device counts and minimal harmonic distortion/high-efficiency operation under both resistive and inductive load scenarios is an area little explored in research. The issue was identified to be the exponential growth in switch count and the corresponding losses in traditional nine-level CHB topologies, which hinders their compact and cost-effective deployment. By this intermediate, only ten IGBT switches and four isolated DC sources are utilized to develop a modified reduced-switch nine-level multilevel inverter topology to obtain nine voltage levels that range from$+ 4$ V_{\text{dc}}$to$-4 \mathrm{V}_{\text{dc}}$. SPWM (Sinusoidal Pulse Width Modulation) is used for harmonic suppression and available control complexity. The detailed modeling and performance evaluation is done using MATLAB/Simulink. For input DC voltage of 75 V per source, switching frequency of 5 kHz, and output power rating of 1 kW, the topology results in a minimum voltage THD of 2.9% at a unity modulation index, which is superior to the conventional CHB inverter result of 3.1%. However, low power losses were achieved at a modulation index of 1, as well as a minimum loss for a modulation index below one, which is still very low: 11.8 W at a modulation index down to 0.5. The efficiency increases gradually with load and reaches a peak value of 97.4% at 1 kW, higher than the CHB inverter maximum value of 96.6%. For resistive$(\mathrm{R})$and resistive-inductive (RL) loads, the results of harmonic spectra verified the enhanced quality of waveforms and lower circuit distortion. With fewer switches in the primary current path, this topology offers lower conduction losses and shorter current paths, leading to a more reliable system. Scientific novelty lies in achieving nine voltage levels using only ten IGBT switches with optimized switching states while maintaining lower THD and improved efficiency compared with conventional CHB topology. This topology is suitable for photovoltaic interfacing, electric vehicle power converters, stand-alone renewable technologies, and medium-power industrial applications.