Analytical determination of conduction power loss and investigation of switching power loss for modified flying capacitor multicell converters

Considering advantages of modified flying capacitor multicell (MFCM) converter over conventional flying capacitor multicell converter, and noting that conduction loss investigation can be very advantageous in design phase of multilevel converters, this study presents an analytical approach to calculate and investigate conduction losses in MFCM converters. First, rms and average currents of insulated gate bipolar transistors (IGBTs) and anti-parallel diodes are analytically calculated by considering the associated duty cycle of each IGBT/diode in terms of the converter modulation index, load current, and load power factor. Numerical results of derived closed-form equations to calculate rms and average currents of IGBTs/diodes are compared with simulation results and experimental measurements. All simulation, analytic, and experimental results agree well with each other which validate derived closed-form equations. Afterwards, derived equations for rms and average current computations are utilised to calculate the conduction power losses in a 12.4 MVA, 3.3 kV, nine-level (line-to-line) MFCM converter. A 2.5 kV, 1.5 kA IGBT module from ABB is considered as a power switch in the performed case study for MFCM converter. In addition, switching power loss investigation is performed using numeric approach and curve-fitting method for aforementioned MFCM converter. Comparative analysis and evaluation of conduction and switching losses are presented.