Harmonics Minimization of Symmetric Five-Level Inverter Using Improved LSF Modulation Scheme

The use of multilevel inverters has gained popularity due to their ability to generate high-quality output voltage with reduced harmonic distortion. The performance of these multilevel inverters can be improved by using a low switching frequency modulation scheme as it enables precise amplitude and harmonic control in the output voltage. Determination of optimum switching angles for minimum total harmonic distortion generally requires complex algorithms with large number of iterations. This work presents a novel approach for calculating optimum switching angles at low frequencies that produces low total harmonic distortion in the output voltage. The calculation process uses only one controlling parameter that allows easy computation of optimum switching angles with a lesser number of iterations. The effectiveness of the calculated switching angles in producing lower total harmonic distortion is verified through simulation in MATLAB/Simulink platform as well as experimentally by developing a small-scale lab prototype of symmetric five-level inverter systems. For generalization, the proposed switching angle calculation technique is examined through different levels of inverter for minimum total harmonic distortions. The superiority of the proposed switching technique is verified through an extensive comparison with other popular low-frequency strategies which revealed that the proposed technique produces lower total harmonic distortions and higher fundamental voltage than those of the Equal Phase, Feed Forward, and Half Height methods. This feature of producing higher-quality fundamental voltage would make it a preferred choice for high power multi-level inverters.