Analytical Determination of Conduction and Switching Power Losses in Flying-Capacitor-Based Active Neutral-Point-Clamped Multilevel Converter

Abstract

Multilevel converters are mainly used in medium-voltage high-power applications. Active neutral-point-clamped (ANPC) flying capacitor multicell (FCM) converter is a well-known type of multilevel converters which is commercially available in high-power medium-voltage motor drive market. Since power loss investigation can be very advantageous in the design phase of multilevel converters, this paper presents an analytical approach to calculate and investigate the conduction and switching power loss in ANPC-FCM converter. First, the RMS and average currents of insulated-gate bipolar transistors (IGBTs) and antiparallel diodes are analytically calculated by considering the associated duty cycle of each IGBT and diode, converter modulation index, load current, and load power factor. Numerical results of the derived closed-form equations to calculate the RMS and average currents of IGBTs/diodes are compared with simulation results and experimental measurements. Numerical results match the simulation results and experimental measurements which validates the derived closed-form equations. Afterward, the obtained equations for RMS and average current computations are utilized to calculate the conduction power losses in a 12.1-MVA 6.6-kV nine-level (line-to-line) ANPC-FCM multilevel converter. For this purpose, a 4.5-kV 1.2-kA IGBT module from ABB is considered as a power switch and its parameters are employed in analytical computations and simulation of the ANPC-FCM multilevel converter for conduction power loss determination. Moreover, closed-form equations are derived for analytical determination of switching power losses for ANPC-FCM converter using Kapteyn (Fourier-Bessel) series. Based on the derived closed-form equations for conduction loss and switching loss calculation, a method is presented to determine the junction temperature in IGBTs and diodes for ANPC-FCM converter.