State-of-the-art of Multi-Carrier Modulation Techniques for Seven Level Inverter: A Critical Evaluation and Novel Submissions based on Control Degree of Freedom

A detailed comparison and the correlation between all the existing multilevel carrier-based pulse width modulation (PWM) methods based on output voltage spectral quality is presented. This work also proposes an additional clew for the carrier-based PWM methods on control of multilevel inverters, which is based on the concept of combination of the control freedom degrees (CFD) and novel carrier/reference functions for multi-level cascaded inverter. The correctness and the guiding significance of the proposed CFD clew on multilevel PWM techniques are verified and well demonstrated by simulation for seven level output. The proposed novel carrier/reference based multilevel PWM methods take the advantage of multiple control degrees of freedom available in multilevel inverters.