A Four-Quadrant Modulation Technique to Extend Modulation Index Range for Multilevel Selective Harmonic Elimination/Compensation Using Staircase Waveforms

One critical drawback of staircase multilevel selective harmonic elimination and compensation is that the modulation index range is very narrow. As a result, its application is limited. This paper presents a technique to transform the transcendental equations to geometry-based voltage phasor diagrams to explore the reason for the limited solution range and proposes a four-quadrant modulation technique to extend the modulation index range. Moreover, this paper investigates the inductor design considering both compensation capacity and undesired harmonic injection. Finally, the simulation and experimental results verify that the proposed modulation technique can greatly extend the modulation index range so it can be implemented in a wide range of applications.