This paper presents the design, simulation, and hardware implementation of a single-phase seven-level cascaded H-bridge multilevel inverter (CHBMLI) for medium-power applications. The proposed topology utilizes three H-bridge cells with isolated DC sources of 76V, 152V, and 230V derived from a multi-tap transformer through bridge rectifiers, synthesizing a seven-level stepped AC output waveform. A fundamental frequency switching scheme based on the equal area criteria (EAC) is employed to determine optimal switching angles (α₁ = 25.71°, α₂ = 51.42°, α₃ = 77.14°), which significantly reduces low-order harmonics and total harmonic distortion (THD). An Arduino Nano microcontroller generates the switching signals, which are amplified by TLP350 optocoupler-based gate driver circuits to control twelve IGBT switches (GW38IH130D). The hardware prototype delivers 230V AC output at 1.5A (345W) with a measured THD of [X]%, substantially lower than conventional two-level inverters. Simulation studies conducted in MATLAB/Simulink validate the theoretical analysis and show good agreement with experimental results. The modular topology offers several advantages including reduced voltage stress on power switches, lower electromagnetic interference, improved power quality, and scalability for higher voltage levels. A detailed comparative analysis demonstrates the superiority of the proposed design over conventional topologies in terms of harmonic performance and efficiency. Potential applications include renewable energy systems (solar PV and wind power integration), variable frequency motor drives, uninterruptible power supplies, and grid-connected systems. This work demonstrates that the seven-level CHBMLI provides an effective, low-cost solution for high-quality power conversion with minimal harmonic distortion, making it suitable for both educational and small-scale industrial applications.

This paper presented the design, simulation, and hardware implementation of a 7-level cascaded H- bridge multilevel inverter. The proposed topology successfully generates a seven-level output voltage using three H-bridge cells with isolated DC sources of 76V, 152V, and 230V. The equal area criteria switching technique with optimal angles (α₁=25.71°, α₂=51.42°, α₃=77.14°) significantly reduces total harmonic distortion. Simulation results validate the theoretical analysis, and hardware implementation confirms the generation of 230V AC output at 345W with substantially lower THD compared to conventional inverters. The modular design offers reduced voltage stress on switches, lower electromagnetic interference, and improved power quality. This work demonstrates that the 7-level CHB inverter provides an effective, low-cost solution for renewable energy systems, motor drives, and industrial applications requiring high- quality power conversion.

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