Research On Characteristic And Design Of Inductively Coupled Power Transfer System

As an emerging research field, Inductively Coupled Power Transfer (ICPT) technology has attracted wide spread attention recently. In ICPT system, power could be transferred from a stable primary source to one or more movable secondary loads through magnetic field. As no wires are needed to transfer power in the system, dangers from contact such as spark, non-reliable connect could be avoided. At the same time, connectors are maintenance free, and free from bad weather or other poor environmental conditions. Besides convenient charging for consumer electronic devices and electrical vehicles, ICPT can be widely used for charging in special conditions, such as underwater, mining wells, etc. As there are more and more demands of non-contact power transfer in various fields, ICPT technology has been a popular research project.The dissertation mainly focuses on the basic characteristics and the parameter design method of ICPT system based on the model of loosely coupled transformer, including following aspects:1. Modeling of loosely coupled transformerIn ICPT system, there are large leakage inductances in the transformer due to the non-compact coupling, which results in a fairly low coupling coefficient, and the characteristics are much different from conventional transformers. Loosely coupled transformer model is built in this dissertation based on conventional transformer models; the equivalence of flux and electrical parameters between leakage inductance model and mutual inductance model is clarified. Based on the built model, the effect of coupling coefficient, load resistance and wire resistance to the transformer voltage and current transfer characteristic is analyzed in detail. Theoretical analysis and experimental results are given to elaborate different measure methods of transformer parameters and to clarify the differences during measurement in each method. And suggestions on how to appropriately choose the measure method are given.2. Multi-resonant compensation design method of ICPTTo improve the power transfer capability, series or parallel capacitors are usually used in either side of the transformer as compensation, which can help to constitute resonant circuit. Different compensation topologies are discussed in detail, including single-resonant compensation, which compensate on only one side of the transformer (including primary series compensation, primary parallel compensation, secondary series compensation and secondary parallel compensation), and multi-resonant compensation, which compensate on both sides of the transformer (including primary series secondary series compensation, primary series secondary parallel compensation, primary parallel secondary series compensation and primary parallel secondary parallel compensation, etc.). Analyses are focused on the power factor, voltage gain and current gain in each topology; the results show that compared with single-resonant compensation, multi-resonant compensation can greatly improve the power factor. As a result, the circuit components and the power source can be selected at a lower power rate. According to the analysis, a general design method based on power factor is proposed to perform circuit parameter design, with which the system can be effectively compensated, and a high power factor can be achieved under different load condition.3. Steady state and small-signal model of a current source ICPT systemBased on theoretical and experiment analysis, steady state model of the linear and rectifier load is built, respectively. Core loss of the circuit is discussed briefly. An optimization principal for ICPT system parameter design is proposed. Resonant frequencies of different stages in this circuit are discussed in detail based on the analysis of dynamic circuit equations. Several simplification conditions are obtained, and experimental results verified the analysis. Small signal model of the circuit is given based on the steady state operation point obtained from general average method.4. Non-contact charging platform designAs a practical application of ICPT, a non-contact charging platform for portable electronic devices is built through simulations and experiments. The charging platform uses coreless planar transformer to realize non-contact power transfer. An optimized primary winding structure design technique is proposed by Ansoft FEA simulation. Based on multi-winding transformer model, circuit analysis of charging for multi-loads is presented. Finally a parameter design procedure in light of maximizing the power factor is proposed, by which the power factor can achieve a high value at different load numbers, and the voltage on each load remains constant. Compared with other methods, the proposed method can lower the voltage and current stress of circuit components at the same power rate, and help to achieve efficient components utilization.