Performance Analysis and Design of Frequency Controlled Series-Series Compensated Inductive Power Transfer System for Electric Vehicle Battery Charging

This article presents a new method to design the coils of a series-series inductive power transfer system taking into consideration the compensation network, the battery charging profile and the efficiency of the system. Harmonic balance technique is used to derive the transient and steady-state model of the coil. Equations defining the possible frequency trajectories for the entire charging profile are derived. A design algorithm for the coil and selection of the compensation network capacitance is presented. To prevent the frequency splitting phenomenon a reduction of the secondary (receiver coil) inductance value is required. To this end the condition under which frequency splitting occurs is derived, without any simplifying assumptions, and used to guide the selection of the new secondary inductor value. An analysis for the redesigned system with the reduced secondary inductance is presented. It is observed that operating the system close to the transmitter coil resonant frequency results in both zero voltage switching and optimum efficiency. For the redesigned system, the upper frequency trajectory of the system operates close to the resonant frequency of the transmitter coil and hence ensuring high efficiency and zero voltage switching.