Design and Implementation of a Radiation Hardened GaN Based Isolated DC-DC Converter for Space Applications Victor Turriate-Gastulo Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Electrical Engineering
ABSTRACT
Power converters used in high reliability radiation hardened space applications trail their commercial counterparts in terms of power density and efficiency. This is due to the additional challenges that arise in the design of space rated power converters from the harsh environment they need to operate in, to the limited availability of space qualified components and field demonstrated power converter topologies. Recently released radiation hardened Gallium Nitride (GaN) Field Effect Transistors (FETs) with their inherent radiation tolerance and superior performance over Silicon Power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), however, offer a promising alternative to improve power density and performance of space power converters.
This thesis presents a practical implementation of the Phase Shifted Full Bridge DC-DC Isolated converter with synchronous rectification for space applications using newly released radiation hardened GaN FETs. A survey outlining the benefits of new radiation hardened GaN FETs for space power applications compared to existing radiation hardened power MOSFETs is included. In addition, this work summarizes the main design considerations to implement the selected converter topology for space applications. Furthermore, the overall design process followed to design the DC-DC converter power stage, as well as a comprehensive power loss analysis are included.
This work also includes details to implement a conventional hard-switched Full Bridge DC-DC converter using radiation hardened GaN FETs for this application. An
efficiency and component stress comparison was performed between the hard-switched Full Bridge design and the Phase Shifted Full Bridge DC-DC converter design. This comparison highlights the benefits of phase shift modulation (PSM) and zero voltage switching (ZVS) for GaN FET applications. Furthermore, different magnetic designs were characterized and compared for efficiency in both converters. The DC-DC converters implemented in this work regulate their outputs to a nominal 20 V, delivering 500 W from a nominal 100 V DC Bus input. Failure mode and effects analysis (FMEA) and protection circuitry required for complete radiation qualification of the Phase Shifted Full Bridge DC-DC converter topology are not addressed by this work.
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