Zero-Phase-Angle Controlled Bidirectional Wireless EV Charging Systems for Large Coil Misalignments

Abstract

Misalignment between charging coils is an unavoidable problem in all electric vehicle (EV) charging systems that are based on wireless power transfer (WPT) technology. This is because variations in both self- and mutual inductances of charging coils due to coil misalignments significantly affect the charging rate and efficiency of the EV charger. As a solution, this article proposes a new control technique that maintains the rated charging power level at optimum efficiency in spite of large coil misalignments. To compensate for the variations in inductances, the technique uses the information extracted from input impedance to operate the system essentially at unique converter voltages with zero phase angle, ensuring that charging will take place at rated power with optimal efficiency despite any pad misalignments. The article presents a comprehensive mathematical model, describing the theoretical basis of the proposed control philosophy. To demonstrate the validity of the proposed control concept, a 1-kW bidirectional WPT EV charging system is built and results are presented under misaligned coil conditions. Results convincingly indicate that the proposed controller is efficient and capable of maintaining the rated charging rate despite large coil misalignments and without any dedicated wireless communication.