Small-Signal State-Space Analysis of Inductive Battery Charging System in Off-Resonant Operation
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This paper analyses the small-signal dynamics of a series-series compensated inductive charging system with a passive diode rectifier interfaced directly to a battery on the receiving side. The analyzed system is designed for utilizing the constant voltage load (CVL) characteristics of the battery to enable power flow control at constant input/output voltages by changing the frequency in response to variations in coupling conditions. A linearizable state-space model, including the nonlinear CVL characteristics, is presented and utilized to evaluate the small-signal dynamics of the studied system. Eigenvalue trajectories and frequency characteristics are presented to show how the small-signal dynamics vary with the coupling conditions and how this will influence controller tuning requirements. Time-domain simulations are presented to verify the validity of the small-signal modelling and to demonstrate the performance of sub-resonant frequency control by a simple PI-controller regulating the power flow in response to variations in the coupling conditions.