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This paper identifies extra junction capacitances and switching commutation loops introduced by line-frequency devices (i.e., non-active every other half line cycle) in three-level ac/dc converters and investigates the corresponding effects. Junction capacitances and power loops are well known as the key factors that impact converter switching loss and device stress, thus influence device selection, power stage layout, and thermal design. By examining switching transients of the commonly used T-shaped and I-shaped three-level converters, the cause and mechanism of the extra junction capacitances and power loops are presented. The impacts on switching loss, device voltage stress, and ac-side voltage/current distortion are respectively reported and analyzed. A loss calculation scheme for the three-level converter to include that extra loss is proposed. A power layout scheme to mitigate the device voltage stress is provided. Compensation and modeling of the voltage and current distortion are also proposed. Experimental results conducted on several types of three-level converter prototypes including a gallium nitride based 115 $V_{{\text{ac}}}{\text{/650}}$ Vdc/1.5-kW/450-kHz Vienna-type rectifier and a SiC mosfet based 1-kV/10-kW/280-kHz three-level active neutral-point-clamped inverter confirm the presented effects and verify the associated analysis and solutions. [ABSTRACT FROM AUTHOR]

Three-phase three-level Vienna rectifier using powder core inductors has been widely used for power conversion. Inductor current ripple analysis of rectifier is essential for pulsewidth modulation method optimization, loss estimation, filter inductor design, etc. However, it is hard to analyze the current ripple of Vienna rectifier. Moreover, the inductance of powder core inductor varies with sinusoidal input current, which makes it even more complicated. In this article, a current ripple analysis method for three-phase Vienna rectifier considering the inductance variation of the powder core inductor is presented. The current ripple distribution of Vienna rectifier with constant inductance is studied based on the space vector approach. To determine the current ripple of Vienna rectifier with powder core inductors, an inductor voltage calculation method considering inductance variation is proposed. The compensation voltage is introduced to compensate for the effect of inductance variation on current ripple. Then, the analytical expression of the peak-to-peak current ripple with powder core inductor is derived. In addition, a design method of powder core inductor is proposed based on the analytical expression. At last, the correctness of the analytical result is verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]