IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS

This paper presents a hybrid SHM-SHE switching technique based on pulse amplitude modulation (PAM) concept. It has been applied on a 4-leg NPC inverter to eliminate and mitigate more harmonic orders than recently proposed hybrid SHM-SHE-PWM method while generating switching pulses at the same frequency. In conventional SHE and SHM techniques, equations are solved to attain the switching angles. Regarding the PAM, value of inverter DC voltage can be considered as an additional degree of freedom by which the flexibility of such techniques would be increased maintaining the switching frequency. In the proposed SHM-SHE-PAM, the conventional equations are reformulated to obtain constant switching angles for a vast range of modulation index (ma) applied on a 4-leg NPC inverter. Switching pulses of the 3 phase legs and the 4 leg are calculated to mitigate the non-triplen harmonics and eliminate the triplen ones, respectively. Due to the unique switching angles valid in the whole range for ma, the calculation time and volume (storage capacity) are significantly reduced leading to a simpler controller implementable on a low risk and cheap AVR Chip. Experimental tests results of a 4-leg NPC inverter as UPS application prove the good dynamic performance and accuracy of the proposed implemented switching technique in producing associated pulses for the inverter switches at very low frequency to mitigate/eliminate undesired harmonic orders from the output phase/line voltage waveforms without using bulky filters.