A Medium Voltage CHB Inverter with a Modified THPWM for Step-Up-Transformer-Less and Line-Filter-Less Grid Integration

A simple traditional inverter which generates a square wave is not satisfactory for grid integration. A pure sinusoidal wave is highly desired for grid tied inverter. Multilevel inverter (MLI) has emerged a key technological development in the field of energy control for high-power medium-voltage (6–36 kV) by generating sinusoidal output waveform without using large and bulky line filter. The cascaded H-bridge (CHB) inverters produce more output voltage levels (e.g., more sinusoidal) in the medium-voltage range, hence minimize the harmonic components. In this paper, a fifty-five level (55L) CHB converter is designed, simulated, and analyzed for 11kV system using a new modified third harmonic injected pulse width modulation-based (MTHPWM) switching technique. Performance of existing switching techniques and proposed switching technique with a 55L, 3- $\phi$ , 11kV CHB inverter is evaluated in terms of total harmonic distortion (THD) and inverter loss. The proposed modulation scheme results very promising THD profile (3.41%) and reduces switching losses over other conventional modulation techniques. All the simulated results are carried out in the MATLAB/Simulink environment.