Research On Design Of Contactless Energy Transmission System

As a new electricity transfer method, contactless energy transfer(CET) has been focused on lately. Compare with traditional transfer ways, CET doesn't need wires and plugs, which avoids direct touch between electrical equipments and the power source, hence it has advantages in safety, reliability, service life, maintenance costs and so on. Recently, CET has been used and studied from power grade dozens mW to hundreds of kW, in applications like cellphone charging, artificial transplant, and mobile charging of EV. Nowadays, requirements like security, convenience make CET more and more popular, and became a hot research topic.However, the transfer efficiency is low, which is the main factor constraints the wide applications of CET, so designing an efficient contactless energy transfer system(CETS) is of great significance, but it is not easy as the calculation of separable transformer's model is really complicated. This thesis has researched on the characteristics and the design methods of CETS on the basis of mutual inductance model, including the following aspects:1, Discussed different compensated CETS's characteristics by using mutual inductance modelBuilt the mutual inductance model of separable transformer. Characteristics of four compensation model CETS, e.g., voltage gain versus frequency, loads, coupling coefficient et al., impedance characteristics were studied. Coupling coefficient k, secondary circuit's quality Qs and the self-inductance ratio of primary and secondary coils n were proposed as variables to describe the features mentioned above on condition that the resonance tank's quality was enough high to make the current flow through the primary coil sinusoidal.2, Design of frequency tracking CETS with coresThis thesis proposed using the CETS's stability condition constraint the self-inductance of secondary coil to avoid the frequency bifurcation. On premise of known load and frequency range, the only factor impacts the transfer efficiency is the primary coil's turns, and was made design variable, different groups of primary coils were wound, the one with maximum efficiency was adopted to finish the design of separable transformer, experiments of the prototype shows the efficiency is high. A further study was carried out, i.e., the design method of constant output system. The stability condition was used on a CETS with two stage, the first stage frequency tracking, and the second stage voltage regulation, the output voltage of the designed prototype is constant though the air gap varies in a large range.3, Design of CETS with general separable transformerAiming at the design of coreless CETS, the important characteristics of CETS, e.g., voltage gain, current gain, were first described by k, n, Qs, and the electrical parameters such as primary current, compensation capacitors'voltage as well. Then the output characteristics, the relation between transfer efficiency and voltage stress on compensation capacitors under different compensation types were compared, and the design of the system was simplified to choose Qs and n. When the input voltage, or the air gap, or loads change, the output can no longer be stable, hence, a Buck circuit was added after the secondary rectifier, a 48V/20AH battery charging system with high efficiency was realized according to the improved design method.4, Modeling and design of multiple loads CETSThe model of multiple loads system was simplified by the three factors k, n, Qs, combined with the ratio of coils'resistance and the equivalent load a,β. By converting the secondary circuits'parameters to the primary, a single circuit was deduced to replace all loops including both the primary and secondary circuits, thus the selection principle of compensation capacitors was proposed, and the transfer characteristics, methods to achieve stable output, factors affect transfer efficiency and devices'voltage stress were discussed. The characteristics of a primary series compensation, secondary parallel compensation(PSSP) multi-loads CETS was validated by experiments. The results show that when the transfer distance is fixed, by controlling the primary current constant, stable output current can be realized even the loads number changes. Finally, a multi-loads system was designed to realize the charging of four cellphones.