An on-line approach for calculating of conducting angles for a multilevel cascaded inverter is presented. The proposed method is a combination of equal voltage-second area and superposition principles. The conducting angle for each voltage level can be determined so that the fundamental component of the output voltage waveform of each H-bridge inverter unit musts accord with each voltage-second area of the reference voltage waveform. This approach can be suitable for calculating of switching angles for any level of multilevel inverter, particularly in case of unequal DC sources. To demonstrate the validity of the proposed method, a simulation study has been done using Matlab/Simulink.