Analytical Loss Model of Modular Multilevel Converter with Reduced Switching Topology

Multilevel converters present great advantages compared to the conventional two-level converters for step-up transformer-less direct medium voltage (0.6-66 kV) grid connected renewable power generation systems. Modular multilevel converter (MLC) with high frequency magnetic link is considered as the best alternative for such kind of application. But in high power application, higher switching frequency generate significant amount of switching and conduction losses, harmonic components and as a result high junction temperature. The initialization of failure mechanism owing to the overheating may cause serious damage of the converter, which results in the high cost of replacement at a very limited space of installation. Hence the conduction and switching power losses of the multilevel converter are needed to be precisely designed, calculated, analyzed, and minimized. In this paper, an analytical method has been proposed to calculate the conduction power losses in MLCs with reduced number of switching of bus-clamping pulse width modulation (BCPWM) technique. Numerical results of the continuous conduction power loss function representing the discrete loss profile of the switching devices are compared with the outcomes of circuit level simulation in MATLAB/Simulink environment.