Physical Design Considerations for Three-Level Neutral-Point Clamped DC-DC Converters Using Discrete SiC MOSFETs

This article examines electrical, thermal, and packaging considerations for realizing DC-DC converters based on neutral-point clamped (NPC) phase legs. Four variations of a three-level NPC leg are contrasted. These variants cover different device packaging technologies, viz., surface mount, and through-hole devices. The scope of variants is limited to systems with liquid cooling and converters with a cuboid shape of a limited z-axis dimension. Each variant and gate driver are designed using Altium Designer, assuming certain converter specifications. Printed circuit board (PCB) parameters are extracted using finite-element analysis (FEA) in ANSYS Q3D. Electrical switching behavior of the MOSFETs under each variant is evaluated using double-pulse testing in LTSpice. Thermal interfacing and its associated consequences on device capability utilization, manufacturing challenges, and cost are also discussed. A comparison showing the merits and limitations of all four variations based on device technology usage—the basis of comparison being volume, thermal management, cost, parasitic circuit elements, and switching behavior is presented. Furthermore, the design consideration trade-offs for building a converter are listed to achieve the application priorities. The list, along with the comparison, aids in selecting one of the four variants or their derivatives for designing converters that fall under the defined scope.