Impact of hybrid multilevel modulation strategy on input and output harmonic performances

This paper develops a detailed analysis about the impact of hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are firstly discussed from the load point of view. After, this paper proposes a new modulation strategy for hybrid multilevel inverters, which can be used with asymmetrical multipulse connection of uncontrolled rectifiers to improve the input harmonic performance of adjustable-speed drives for any operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes possible to eliminate undesired low-frequency harmonics from input currents in all operating range, even when the series-connected cells process distinct active power levels.