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Title: Rectifier design for optimisation of multi-MHz inductive power transfer systems
Author: Kkelis, George
ISNI:       0000 0004 7657 9813
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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This thesis presents the optimisation of multi-MHz inductive power transfer (IPT) systems through rectifier analysis and design. IPT systems operating in the multi-MHz frequency range utilise air core coils which allow greater mobility between transmitter and receiver than systems utilising ferrite in their coils. While high through-air efficiencies can be achieved with both air core and ferrite core coils, the power electronic topologies used in air core IPT systems tend to be more sensitive to variations in output load and coupling between the coils. Therefore, while good system efficiencies can be achieved with multi-MHz IPT systems the spectrum of operating conditions can be limited. The work presented in this thesis identified rectifier properties that overcome the aforementioned limitations allowing operation over a broad range of IPT conditions. From IPT theory the requirements for rectifier integration in multi-MHz systems were defined and a rectifier design method was developed. Rectifier topologies capable of operation in the multi-MHz frequency range, namely Class-D and Class-E topologies, were studied in detail and a generalised analysis for Class-E topologies is presented. A hybrid Class-E half wave low dv/dt topology is introduced and compared with the conventional Class-D and Class-E rectifier topologies. From the analysis, it is shown that the hybrid Class-E rectifier provides an extra degree of design freedom which enables optimal IPT operation over a wider range of operating conditions. Furthermore, it is shown that by designing both the hybrid and the current driven Class-E rectifiers to operate below resonance provides a low deviation input reactance and inherent output voltage regulation with output load allowing efficient IPT operation over wider dc load range than would otherwise be achieved. The results of the rectifier analysis were verified through comparative and application led case studies. The highlight of the comparative case studies was the achievement of a receiving end efficiency of 94% when utilising the hybrid Class-E rectifier. The application led case studies demonstrated a dc/dc converter with inherent output voltage regulation operating at 6.78 MHz and the development of a hybrid Class-E rectifier in a 13.56 MHz wireless quadcopter powering system capable of operating with large variations in coupling between transmitting and receiving coils.
Supervisor: Mitcheson, Paul D. Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral