Fundamental Study on Capacitively Coupled Contactless Power Transfer Technology

Abstract

For decades, contactless power transfer technologies have been developed to supply power from a stationary power source to movable loads without direct electrical contact. Amongst these technologies, IPT (Inductive Power Transfer) has been widely accepted with successful implementations in materials handling systems, battery chargers, power supplies to electric vehicles, etc. However, IPT cannot be used to transfer power across metal barriers, and power losses are of concern when metal objects are present close to the magnetic field. Recently, a new technology named CCPT (Capacitively Coupled Power Transfer) has been proposed and investigated as an alternative to achieve contactless power transfer. Employing the electric field as the energy transfer medium, CCPT has the advantages of the confined electric field between the coupling plates, power transfer capability through metal barriers, very low eddy current power losses associated with metal surroundings, and low standing power losses under no-load conditions. In addition, it also has the potential to reduce the circuit size and cost. Currently, CCPT is mainly considered for low power applications such as contactless battery charging for robotics, mobile phones, laptops, sensors, and so on. In this thesis a fundamental study on CCPT technology is carried out using mathematical analysis, computer simulations and practical experiments. Firstly, a system level modelling and analysis is performed to obtain ZVS operating frequencies and steady-state system performance. Then, capacitive coupling is modelled and analysed using different coupling structures and dielectric materials. The analysis is verified through two CCPT prototypes, an E-puck robot charging platform and a contactless power supply to CPAP (Continuous Positive Airway Pressure) respiratory sensors. Next, the effect of tuning inductor positions on the system performance is analysed and verified through experimental results. Finally, two novel power flow control topologies are proposed and analysed. Applying the proposed control methods, a matrix type CCPT charging platform is developed to dynamically maintain the output voltage regardless of the positioning and alignments of the pickup. The results obtained from this research demonstrate the feasibility and potential of CCPT as an emerging contactless power transfer solution, and the theory and practical design methods established lay a solid foundation for future CCPT research and development.