Abstract:
Inductively coupled power transfer (ICPT) systems use electromagnetic fields to transfer electric power from a primary source (power supply) to one or more secondary loads (pickups). Because there is no physical contact between the primary and secondary, ICPT systems are intrinsically safe and reliable. This technology has been significantly commercialised for around a decade. Present applications include material handling, public transport, and battery charging. This thesis focuses on the design of ICPT systems for high power applications where both the primary and secondary coils are compensated by capacitors. The main aim is to develop systems with smaller size, less weight, lower cost, greater power and better efficiency. Previous work in this field has concentrated on either the power supply or the pickup. This thesis instead focuses on the interactions between the power supply and the pickup. When power is transferred from the primary to the secondary, the primary is affected by the secondary loading. This can result in poor displacement power factor (DPF), reduced power transfer capability, and a loss of controllability. First, steady state linear mathematical models are developed to represent the load seen by the power supply that includes the primary compensation capacitor, the electromagnetic structure, the secondary compensation capacitor, and the pickup load. These models quantify the system behaviour in terms of the fundamental design parameters, and are used to evaluate a design procedure for ICPT systems. This evaluation provides an insight into the system, enabling suitable design decisions as well as quantification of frequency bifurcation boundaries in variable-frequency systems. Several new primary tuning schemes are also proposed, taking into account the secondary loading effects. In loosely coupled systems, the primary and secondary resonant circuits can be tuned independently as the secondary loading effect on the primary are negligible. In well-coupled systems, the secondary loading affects the primary resonance significantly, and the proposed new tuning schemes greatly improve the DPF and power transfer capability. Various sensitivity analyses to variations in the primary and secondary compensation capacitances as well as misalignment of the electromagnetic structure show that systems designed using the proposed new tuning schemes have similar sensitivities compared with the original tuning. Throughout the thesis work, an LCL resonant inverter driving a contact-less electric vehicle battery charger was used to verify the proposed theory. The operation of this inverter under discontinuous current mode is also investigated. A novel design procedure is detailed and verified that enables this inverter to deliver maximum power to the load.