Magnetic machines and power electronics for power MEMS applications

Abstract

This thesis presents the modeling, design, and characterization of microfabricated, surface-wound, permanent-magnet (PM) generators, and their power electronics, for use in Watt-level Power MEMS applications such as a microscale gas turbine engine. The generators are three-phase, axial-flux, synchronous machines, comprising a rotor with an annular PM and ferromagnetic core, and a stator with multi-turn surface windings on a soft magnetic substrate. The fabrication of the PM generators, as well as the development of their high-speed spinning rotor test stand, was carried out by collaborators at the Georgia Institute of Technology. The machines are modeled by analytically solving 2D magneto-quasistatic Maxwell's Equations as a function of radius and then integrating the field solutions over the radial span of the machine to determine the open-circuit voltage, torque and losses in the stator core. The model provides a computationally fast method to determine power and efficiency of an axial-air-gap PM machine as a function of geometry, speed and material properties. Both passive and active power electronics have been built and tested. The passive power electronics consist of a three-phase transformer and diode bridge rectifier.

(cont.) The active power electronics consist of a switch-mode rectifier based on the boost semi-bridge topology which is used to convert the unregulated AC generator voltages to a regulated 12 V DC without the need for rotor position/speed or stator terminal current/voltage sensing. At the rotational speed of 300,000 rpm, one generator converts 16.2 W of mechanical power to electrical power. Coupled to the transformer and diode bridge rectifier, it delivers 8 W DC to a resistive load. This is the highest output power ever delivered by a microscale electric generator to date. The corresponding power and current densities of 57.8 MW/m3 and 6x 108 A/m2, respectively, are much higher than those of a macroscale electric generator. At the rotational speed of 300,000 rpm, the generator and switch-mode rectifier delivered 5.5 W DC to a resistive load at a power density three times that of the passive electronics. This Watt-scale electrical power generation demonstrates the viability of scaled PM machines and power electronics for practical Power MEMS applications.