Power density has become increasingly important for applications where weight and space are limited. Power density is a unique challenge requiring the latest transistor technology to push switching frequency to shrink passive filter size. Furthermore, while high efficiency is an important thermal handling strategy, it must be weighed against increases in component size. Google's Little Box Challenge shone light on these challenges in pushing the power density of a 2kW inverter. The rise in electric vehicle infrastructure and demand represents a unique application for power electronics: pushing the power handling capability and functionality of bi-directional, on-board electric vehicle chargers for faster charging while simultaneously shrinking them in size.
New wide-bandgap (WBG) devices, combined with soft-switching, now allow inverters to shrink in size by pushing to higher switching frequencies while maintaining efficiency. Classic H-Bridge topologies have limited switching frequency due to hard switching. Soft switching allows inverters to operate at higher frequency while minimizing switching loss. Concurrently, interleaving can reduce current handling stress and conduction loss better than simply paralleling two transistors.
A novel interleaved auxiliary resonant snubber for high-frequency soft-switching is introduced. The design of an auxiliary resonant snubber is discussed; this allows the main GaN MOSFETs to achieve zero voltage switching (ZVS). The auxiliary switches and SiC diodes achieve zero current switching (ZCS). This soft-switching strategy can be applied to any modulation scheme. Here, it is applied to an asymmetrical unipolar H-bridge with two high frequency legs interleaved. While soft-switching minimizes switching loss, conduction loss is simultaneously reduced for high-power applications by interleaving two high frequency legs. This topology is chosen for its conduction loss reduction and bi-directional capability. / Master of Science / Electric vehicles have become a unique application for power electronics where battery chargers must both handle higher power and shrink in size and weight. The latest transistor technology allows the designer to push switching frequency, shrinking the size of components and increasing the power density. In 2014, Google’s Little Box Challenge shone light on the design trade-offs of high power density design with new transistor technology for a 2kW inverter.
New semi-conductor materials now allow transistors to switch at higher frequency with less loss. To take advantage of these features, a new switching method is developed. The main power transistors are brought to zero voltage before turn-on with auxiliary switches and resonant current. Interleaving is added for better efficiency and power handling. With further control, this method could prove attractive for new, high-density power electronic designs. Applications for this include bi-directional chargers for electric vehicles in the 6kW range
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/73584 |
| Date | 06 December 2016 |
| Creators | Born, Rachael Grace |
| Contributors | Electrical and Computer Engineering, Lai, Jih-Sheng, Li, Qiang, Sable, Daniel M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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