Wei Liang

PhD 2018

Arity Email Dissertation

Doctoral Dissertation

High frequency power converters with printed air core inductors for emerging applications

In the past few decades, power electronics has advanced greatly in part thanks to newer generations of power semiconductors. As faster and more efficient power semiconductors become commercially available, for example, Wide Bandgap (WBG) devices such as Silicon Carbide (SiC) and Gallium Nitride (GaN), a direct replacement of Silicon semiconductors for their WBG counterpart is often regarded as an obvious way to continue improving performance of the power electronics system. However, not much has changed on the design of passive components (inductors, transformer, capacitors). This is especially true for magnetic components, inductors and transformers, which often contribute to a large portion of volume and weight in today’s power converters. As the demand for smaller and lighter power converters continues to grow, the development of smaller, lighter and more efficient magnetic components has not been able to keep up with semiconductors development. Advancing performance of magnetic components usually relies on researching novel magnetic materials with distinct ferromagnetic properties, which is a slow process that may span over decades. A more fundamental approach to miniaturize passive components is to increase the frequency of switching mode power converters. Increasing switching frequency enables reductions in the numerical values and energy storage of the passive components. But at frequencies of 100s kHz where majority of today’s conventional power converters design lies, performance and volume reduction gains with increasing frequency reach a point of diminishing returns that comes as a result of increases in frequency dependent losses, such as semiconductor device switching, gating, and magnetic core losses. The added losses require additional necessary elements such as larger heatsinks, snubbers and complex gate drive circuitry to prevent overheating of the semiconductor devices. Recent developments of novel power converter topologies, resonant gate drive circuits, as well as the use of air core inductors to mitigate above mentioned frequency dependent losses, have pushed the switching frequency well into 10s MHz and even above 100 MHz. These techniques have potential to achieve significant reductions in volume and weight, much faster transient response, and the ability to operate at harsh environment (e.g. strong magnetic field) due to the absenceof magnetic material. To pursue the goal of developing smaller, lighter and better performance power converters that can become the enabling technology for many exciting emerging applications, this Dissertation presents new methods of designing and fabricating air core inductors for use in high frequency (above 10 MHz) switched mode power converters. Modern fabrication techniques such as PCB embedding and 3D printing are leveraged to design and implement air core toroidal inductors that can be incorporated into high frequency power converters, achieving better electrical, mechanical and/or thermal performance while providing greater design exibility than conventional wire wound air core inductors. Conventional power converter design and implementation usually involve fabrication of Printed Circuit Boards (PCBs) to serves as a substrate that components can be soldered to, as well as to connect the components in a designed pattern. This Dissertation also describes power converter designs that employ the PCB not only as a connection substrate, but as functional electrical component. Copper traces, vias, dielectric materials, and cavities within the PCB are designed to make inductors, capacitors, Electro-Magnetic Interference (EMI) shields, etc. Moreover, this concept is extended to the fabrication of 3D printed air core inductors.

Publications

Patents