Abstract:
In most electrical and electronic systems, power is transferred by direct electrical contacts, which can cause inconvenience and electrical hazards, particularly in dirty and wet environments. Inductive power transfer (IPT) technology based on magnetic field coupling is proposed to transfer power across an air gap when direct wire connection is difficult or impossible. However, due to the nature of near magnetic field coupling, the power transfer capability of an IPT system decreases quickly with the distance between the primary transmitter and power pickup. One way to increase the power transfer capability is to use magnetic power repeaters to relay power. Power repeaters can be in form of a single coil or multiple coils in matrix forms that are known as matrix power repeaters. Although being effective, the operating mechanism and the actual effect of even a single coil passive power repeater on an IPT system is not clear, so the design of the power repeaters has been largely a trial and error exercise. As for matrix power repeaters, only recently they are introduced in near field IPT systems. Therefore little is known about their effects on magnetic field distribution and power transfer capability. This thesis presents a general study of single and multiple coil power repeaters for enhancing the power transfer capability of IPT systems. The effects of the tuning conditions of single coil passive power repeaters on the power transfer capability of IPT systems are investigated by mathematical analysis, computer simulations, and practical experiments. An active power repeater is also proposed to maintain the maximum power transfer condition of an IPT system with variable load conditions and pickup positions. Furthermore, the effects of matrix power repeaters on the magnetic field distribution at the power pickup of IPT systems are studied to understand the field enhancement and shielding effects. The relationship between the system operating frequency and power transfer capability of an IPT system with a matrix power repeater is further studied to determine the optimal system frequencies corresponding to maximum and minimum power transfer conditions. The theoretical optimal tuning condition of a single coil power repeater for maximum output power at a power pickup is determined, as together with the boundary between enhancing and reducing the power transfer capability of an IPT system. The results have been experimentally verified by passively tuning a power repeater. A controller is also proposed to actively tune the power repeater to the optimal condition which leads to an increase in the output power by 21.6%. The effective permeability of a 4 × 4 matrix power repeater is found to be negative when the operating frequency is above the nominal frequency. The critical system operating frequency corresponding to the boundary between enhancing and reducing the magnetic field at a power pickup of an IPT system has been determined by taking the coupling coefficients among the primary transmitter, the power pickup, and the power repeater into consideration. The system operating frequency corresponding to the maximum power transfer of an IPT system with a matrix power repeater is predicted with a maximum error of 2%. These results are helpful for understanding the performance of matrix power repeaters of IPT systems and guiding their optimal design.