Modelling and Design in Advanced Mega-Hertz Range Wireless Power Transfer Systems

The rapid development of power semiconductors and scientific computation are shaping the design methodologies and performance limitations for mega-hertz (MHz) range wireless power transfer (WPT) systems. Currently, the high-frequency performance of Gallium Nitride (GaN) power devices have been gradually revealed, and their superiority was validated by several high-frequency/very-high-frequency (HF/VHF) design references. Moreover, the improvement of scientific computation makes it possible to apply complicated optimization algorithms and precise finite-element-method (FEM) simulations during power electronics systems’ design and evaluation process. Hence, the wireless power transfer systems in MHz-range operational frequency are expected to be applied in much broader applications after intentional and strategical design and optimization, such as for autonomous mobile robots, inspection drones and implanted medical devices. With higher operational frequency, the substantial improvement of the WPT system comes from the increasing of the quality factor for all the resonant operations, which contributes to a higher power transfer efficiency and a higher volumetric power density. However, design challenges for the MHz-range systems emerge, which have been identified but not fully comprehended and are far away from being addressed. On the one hand, the trade-off between the precision and the complexity in the system’s mathematical modelling needs to be re-defined considering the high-frequency performance for both the semiconductors and the passive components. On the other
hand, modern optimization algorithms can be applied for performance improvement and function achievement in the design process. Nevertheless, many efforts are still required during the application-based implementations. The main focus of the thesis is thus, to propose, investigate and technically demonstrate novel solutions in advanced mega-hertz range wireless power transfer systems with mathematical modelling and optimization design. First, the novel class-E inverter/rectifier topologies are proposed and investigated to improve the system’s overall efficiency by performing a resistive impedance during the shifted load range. The proposed topologies can achieve the near-/pure- resistive impedance with passive-/activerectification during all load range under MHz-range operation. In addition, the modelling and design method for the inductive coupler is investigated, which dedicates to an improved position tolerance. Finally, the system design framework is proposed and demonstrated on a design case-study that applying the aforementioned topologies and the design algorithm for the inductive coupler. Particularly, an analytical eddy-current loss model for the air-core inductors and coils in the system is presented to be integrated into the Pareto-searching for the system’s performance estimation. The proposed topologies, derived circuit and power loss models, and the design methods are applied on MHz-range wireless power transfer systems. On the first prototype, a 6.78 MHz 300 W inductive power transfer system was built and tested. Both the passive- and active- rectification solutions perform with a resistive impedance. The genetic algorithm (GA) based design was applied for both the air-core and magnetic shielded transmitting coil on the next prototype. Consequently, the prototype obtained an excellent position tolerance on the inductive coupler. The operations of the inverter and the system’s output will not be interfered with as long as the receiving coil locates in the target range. Finally, an optimized system design was achieved using the full analytical loss model on the proposed circuit topologies and the transmitter coil design. The design trade-off was identified based on the proposed design framework regarding power conversion efficiency and power density. The results obtained, including the theoretical analysis and the technical demonstrations, fill the current knowledge gap for power converter design and validate the MHz-range WPT systems’ advanced performance for future industrial applications.