Hybrid inductive and capacitive wireless power transfer system for future transportation electrification
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The inductive link in wireless power transfer (WPT) fed by various high–frequency power converters is widely accepted for medium power (<50 kW) and medium power transfer distance (100 mm-200 mm) applications due to remarkable efficiencies (>90%) in stationary wireless charging scenarios. However, considering the dynamic or the on the move wireless charging, the inductive link implementation for millions of kilometers is quite expensive due to the need for sophisticated resources. Therefore, relatively inexpensive capacitive link, which initially focused on low power (<100 watts) and small distance (<10 mm) applications, has gained momentum and is explored for medium power (~3 kW) and medium distance (~100 mm) applications. It has achieved considerable DC-DC efficiencies (70%-90%), no induced eddy current loss in the nearby metal objects and low cost and weight implementation. First, the thesis identifies the significant roles played by inductive and capacitive AC link designs in static and dynamic expansion of wireless electric vehicle charging. Through a relative analysis, the thesis emphasizes the need for mutual promotion of these AC links as a hybrid system in order to boost wireless EV charging technology. Second, capacitive wireless power transfer system is analyzed under different link configurations and dielectric influences aiming to improve their performances. Third, a reduced capacitance model is derived from the existing six capacitance model of bipolar 2x2 matrix configuration which is suitable for large charging area applications like electric vehicle charging. Here, when the separation distance between the same side plate pair is large enough, the effect of cross-coupling capacitances diminishes and the analysis based on a reduced capacitance model can be carried out. The advantage of using this model is that it attains the unity gain and load-independent operation at designed resonant frequency instead of at dual resonant frequencies in the conventional model. Fourth, a novel hybrid inductive and capacitive wireless power transfer system is realized by combining both systems using a three-leg, mixed switching frequency inverter. The combination offered a choice of power management between two systems. The modular structure makes both systems independent and helps to achieve individual or combined wireless power transfer.