Switching loss analysis of modulation methods used in cascaded H-bridge multilevel converters

Multilevel converters are used mainly in medium- voltage high-power applications. In this field, switching losses are an important issue due to long term operation costs and cooling system design. Previous works have centered the analysis in comparing different topologies and semiconductors in relation to switching losses. However, switching losses are also closely related to the modulation method used to control the converter, since they are responsible of producing the commutations. This paper presents an in depth evaluation of switching losses produced by the most representative modulation schemes used for cascaded H-bridge topologies. To perform this analysis, a switching loss estimation model is developed based on experimental measurements and semiconductors datasheets. Then, each modulation method is simulated and evaluated with the switching loss model, to compute the energy loss of each commutation. The losses are obtained for a full representative fundamental cycle, and then expressed in terms of normalized energy loss in relation to the rated values. The aim of the paper is to provide quantitative results to compare the different modulation schemes in terms of efficiency and performance. Some comments regarding the application scope for each method based on the results are included.