Fred C. Lee, Chair
Tuesday, April 11, 2017
Fred C. Lee
A high efficiency and high power density sigma converter for 48/1V voltage regulator module (VRM) is proposed in this paper. The Sigma converter is a quasi-parallel converter that uses a high efficiency unregulated converter to deliver most power to the load with small power flowing through buck converter responsible for regulating the output voltage. The unregulated isolated converter is LLC converter designed with matrix transformer structure integrating 4 transformers in one core structure with integrating the Synchronous Rectifiers (SRs) with the winding to minimize the termination losses of the transformer so a high efficiency can be achieved. The buck converter is designed with discrete GaN devices and PCB winding inductor to regulate the output voltage. The designed Sigma converter is 48/1V-80A achieving a power density of 420W/in3 and maximum efficiency of 93.4%.
Fred C. Lee
A wide-band-gap based bidirectional on-board charger (OBC) has been proposed with a variable DC-link voltage, which tracks the battery voltage fluctuation. Although this approach is deemed most efficient for the resonant DC/DC stage, it posts significant challenges for the rectifier/inverter stage which operates in the critical mode to realize ZVS, while subjecting to the large variations of input and output voltages. Design considerations of the AC/DC stage are presented in this paper, including the evaluation of 1.2 kV SiC MOSFETs; the zero-voltage-switching (ZVS) extension techniques to realize ZVS under all input/output variations; a novel universal control strategy for both the rectifier mode and the inverter mode. A prototype is built which achieves 98.5% efficiency at a switching frequency higher than 300 kHz. Furthermore, a 6.6 kW OBC system is demonstrated, using both SiC and GaN devices with 43 W/in3 power density and above 96% efficiency.
A notable feature of silicon carbide (SiC) is its high breakdown electric field, which is ten times greater than that of silicon. This characteristic allows for the fabrication of high-voltage (≥ 10 kV) power devices. At present the performance of these unique devices is limited by the package. This work aims to fabricate an optimal package for 10 kV SiC MOSFETs that would have minimal parasitic elements to allow for good transient performance, low thermal impedance to effectively remove the heat from the module, and a small footprint to achieve high power density. The 10 kV rating of these MOSFETs means that high electric fields will be present within the module. Accordingly, care must be taken to design a layout that will avoid the concentration of these electric fields. A proper package design will also consider the system integration. For instance, when designing the power module, the interface to the gate driver, dc bus bar, and phase output (for a half-bridge) must also be considered. Improper designs could result in partial discharge, coupling between the power and signal loops, or introduce undesirable parasitics into the power and signal paths. These considerations will be addressed in this work.