Technologies to improve power density of power electronic systems

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Liu, Wenbo
Power electronics, power density, thermal performance
Advanced power electronic supplies with high power density are strongly demanded in a wide range of power levels. This thesis proposes high power density and thermal management solutions for three levels of power system integration: chip level for low power converters with 5W to 30W power ratings; power device level to decrease the component size; and power converter level including DC-DC converters and AC-DC converters range from 1kW to 6.6kW. High performance point of load converter structure is investigated for low power level compact module applications based on the power supply in inductor (PSI2) technology. This thesis proposes a 3D PSI2 integrated power module at 5V/8A output which reduces the size of POL module while maintaining a low junction temperature. Improved thermal modeling methodology is developed for integrated modules to achieve more accurate thermal analysis. In device level, a novel micro electromechanical system (MEMS) power relay which uses tiny MEMS switches is designed. The MEMS switch is used to replace the bulky magnetic – metal contact structure in traditional power relay solutions. Much lower on state resistance than solid state relay (SSR) is achieved, therefore less thermal issue is address due to lower conduction loss. Power density improvement and thermal design for discrete mid-level power converters from 1 to 20kW are studied and two high power density converters are proposed. The first implementation is a high current low voltage converter (with 14V/270A load) for electric vehicles (EVs). By building a multi-PCB cooling (MPC) cooling structure, the volume of converter is reduced by 31% while achieving the best heat dissipation performance. The second research is a single stage LLC AC-DC converter with PFC for on board charger (OBC) application. The LLC converter is proposed which combines the functions of power factor correction (PFC), DC-DC voltage regulation and galvanic isolation in only one stage. Bulky magnetic components are saved, and high power density is achieved by the proposed converter. In this thesis, multiple research methodologies including mathematical modeling, finite element analysis (FEA), SPICE based simulation and experimental test are employed to verify the proposals and theories.
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