Investigation of Highly Efficient Five Level Asymmetrical Inverter Family With Embedded Buck-Boost Converter

In recent years, focus is given to the increment of the power conversion efficiency of multilevel inverters with integrated voltage boosting characteristics. This can be accomplished by integrating DC/DC converters, featuring partial processing characteristics. In this paper the optimal configuration of the front-end DC/DC converter is proposed considering the lowest power processed by the integrated DC/DC converter for a given asymmetrical five-level topology. It is shown that the Buck-Boost converter is the best candidate solution if the proper configuration is adopted. The operation with asymmetrical output voltage levels offers the ability for variable voltage gain and extension of the input voltage range. However, to avoid low order harmonics due to the asymmetrical levels a modified modulation scheme is proposed. Furthermore, it is proven through rigorous mathematical analysis that efficiency and power density increment can be achieved only if the appropriate mode of operation of the Buck-Boost converter is chosen. The previous statement is supported through an analytical comparison considering the three possible operating modes, proving that DCM operation is the optimal solution. Concluding, a 1.5kVA laboratory prototype is designed with a peak efficiency of 98.7% and experimental results are provided, denoting the converter performance and the accuracy of the preceded analysis.