This paper proposes a new methodology of firing to increase the number of levels in the output voltage of a conventional seven-level inverter. In a conventional 7-level cascaded H bridge (CHB), by employing a new firing scheme with unequal DC sources, an output waveform of 21-levels has been generated. Thus near sinusoidal waveform has been achieved with the same number of switches. The simulation results and the harmonic analysis for the proposed technique are included to show its effectiveness in reducing the total harmonic distortion. The proposed strategy has also been applied to a Photovoltaic(PV) system to portray its robustness, when subjected to varying voltages produced by the PV panels.