A generalized formulation of SHM-PAM for cascaded H-bridge inverters with non-equal DC sources

In this paper a generalized formulation for Selective Harmonic Mitigation Pulse Amplitude Modulation (SHM-PAM) has been presented to control Cascaded H-bridge (CHB) inverter with non-equal DC sources. Consistent with the proposed SHM-PAM technique, switching angles are attained constant while the calculated magnitudes of DC sources vary linearly for all modulation indexes (ma). In fact, in the SHM-PAM, the pulse width of the output staircase voltage waveform is remained constant while the pulse amplitude is changed with respect to ma. Moreover, the new general formula simplifies and reduces calculations of the conventional SHM's nonlinear equations through omitting ma. Furthermore, in order to calculate angles and magnitude of DC voltage, it is enough that the equations in the SHM-PAM being solved only for one time. The SHM-PAM calculations are carried out for the 5, 7, 9 and 11-level low switching frequency voltage waveforms. Simulation results of a 5 level CHB inverter verify the practicability of the proposed modulation technique to mitigate the desired harmonics of the output voltage waveform.