Ss-type Self-oscillating Contactless Resonant Converter With Contactless Current Transformer

Contactless power transmission (CPT) is a power conversion technology which has been paidmuch attention to in recent years. By using a contactless transformer, a CPT system is able to transferpower by magnetic coupling. Since it is quite safe and convenient, it has been employed in manyapplications, such as implanted devices, mobile phones and electrical vehicles.In a CPT system, the load and converter parameters need to be changed, especially in somespecific applications such as implanted devices, the parameter changes are in real-time. Thus a CPTsystem with better adaptability to parameter changes will be more competitive. To achieve betteradaptability to parameter changes and favorable dynamic performance, this thesis studies theself-oscillating control strategy for a SS-type contactless resonant converters (CRC), and mainlyfocuses on the realization of the self-oacillating control strategy.Firstly, by taking winding resistances into consideration, the input-to-output voltage gain,transfer impedance, input impedance and power transfer efficiency characteristics of a SS-type CRCare analyzed based on the mutual inductance model. The analysis proves that by detecting thezero-crossing points of secondary current to control the inverter, self-oscillating control strategy canbe achieved, and the converter will be able to operate at voltage gain intersection. The control diagramof self-oscillating control strategy is also provided.Based on the analysis of the control diagram, the thesis specifies that the difficulty in therealization of self-oscillating control strategy is secondary current phase detection. Therefore, asecondary shorted current transformer called phase detection contactless current transformer (PDCCT)is proposed and analyzed. To guarantee the accuracy of the control strategy, the time delay in allcontrol blocks is studied and a RCR compensator is proposed, and nearly constant leading-timecompensation is achieved within the operation frequency range. Besides, a solution is also provided toovercome the starting problems in upper switch, and reliable starting is achieved.Finally, a60W prototype of a self-oscillating contactless resonant converter is then fabricatedand tested. The steady state experimental results demonstrate the validity of both PDCCT and theRCR compensator. With the self-oscillating control strategy, nearly constant output is obtained, andthe efficiency of the converter reaches89.2%at10mm air gap,84%at20mm air gap. Besides, toemulate the changes in converter parameters, a testing circuit is designed and the dynamicperformance shows that self-oscillating control strategy can respond to parameter changes in a switching period.