| Wireless power transfer is an emerging technology that provides convenience, reliability, and safety enhancements in numerous applications by the elimination of galvanic connections between sources and loads. Electric power can be transferred wirelessly by using a variety of approaches, but the two dominant methods that generally operate with high efficiency are near field inductive power transfer (IPT) and capacitive power transfer (CPT). The thesis begins with a generalized comparison of IPT and CPT to determine general operating tradeoffs. Compared with IPT, CPT is more suitable for small gap wireless power transfer (WPT) applications such as brush-slipring replacement and sliding surfaces in industrial automation. Small gap CPT has advantages of a simple coupling structure, low cost materials, and less radiation due to gap confinement. It is also shown that there is no fundamental power advantage of one approach verses another, only more appropriate situations for deployment.;Following the comparison study, the bulk of the research focuses on suitable power electronics designs for CPT systems, ultimately to maximize throughput power while minding cost. Different switch mode and resonant power electronics topologies are reviewed and tested for CPT. Analysis was carried out on: 1.) Canonical dc-dc converters operating with quasi-resonant switching in the 100s of kHz, 2.) Class E converters with resonant tanks operating at integer MHz, and 3.) Polyphase Class D amplifiers driving resonant tanks. The strengths and weaknesses of these circuits have been ranked in active and passive component utilization, switching frequency, power level, load sensitivity and efficiency to create a roadmap for scalability. The analysis of these circuits was verified experimentally. A quasi-resonant dc-dc converter and Class E resonant converter were tested on a kilowatt scale CPT charging system for an electric vehicle (EV) in addition to a wound field synchronous machine (WFSM) slip-ring replacement. A Class D resonant converter was tested on a linear motion system, in which power is transferred through capacitive coupled sliding journal bearings. For both applications and circuits, a generalized control approach was developed and demonstrated load regulation. |
