Impact of Hybrid Multilevel Modulation Strategies on Input and Output Harmonic Performances

This paper presents a detailed analysis of the impact of a hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are first discussed from the load point of view. This paper also 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 at every operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes it possible to eliminate undesirable low-frequency harmonics from input currents in all operating ranges, even when the series-connected cells process distinct active power levels