Middle-Level SHE Pulse-Amplitude Modulation for Cascaded Multilevel Inverters

This letter presents a novel middle-level selective harmonic elimination-pulse-amplitude modulation (SHE-PAM) method to calculate switching angles and to synthesize reference voltage for variable dc voltage sources connected to multilevel inverter. Instead of conventional multivariable nonlinear transcendental SHE-pulse-width modulation (SHE-PWM) equations or polynomial equations derived from them, the proposed method works on univariate linear equations. Due to reduced computational complexities, it can be implemented in real-time for the inverter having a large number of levels. Without amplifying the magnitude of higher order harmonics, proposed method eliminates a significant number of harmonics as compared to SHE-PWM and conventional SHE-PAM methods. The total harmonic distortion (THD) of the output voltage is a function of only number of voltage levels and remains constant for a whole range of modulation index. The theoretical analysis and working characteristics of suggested method are validated by simulation and experimental studies.