A constant resistance analysis and control of cascaded buck and boost converter for wireless EV chargers

This paper presents a new constant resistance control technique for a cascaded buck and boost converter, which is suitable for wireless energy transfer pickup systems in variable load applications such as battery or ultra-capacitor charging. In order to achieve high efficiency, an impedance matching network is commonly used in the contactless energy transfer systems especially for low coupling coefficient circuits. The proposed control technique avoids a divergence of the designed impedance matching system considering the load variation. This is important to secure high wireless energy transfer efficiency under voltage and current changes at the load terminals. The transfer function of the converter is presented with theoretical calculations describing the small-signal model. The system model is used to control the resistance in the cascaded buck and boost converter for electric vehicle (EV) charging applications in a 2 kW prototype.