Comprehensive Analysis of Bifurcation and Frequency Splitting Phenomena in Inductive Battery Charging Systems

This article identifies the critical conditions of bifurcation and frequency splitting phenomena in inductive power transfer (IPT) systems used for battery charging, considering a constant voltage load (CVL) model. While prior studies covered these phenomena for IPT systems with constant resistance loads, their application to battery-loaded systems is limited due to the variation of equivalent load resistance with the operating frequency. By using the CVL model and analyzing the output power peak points, this article calculates the critical conditions for the frequency splitting phenomenon. This enables determining the power's monotonic range and peak in the frequency-control system. Moreover, by analyzing the monotonicity of the system's input impedance angle, the critical condition for bifurcation can be identified for determining the operating region that achieves zero-voltage switching or designing zero-phase angle IPT systems. To avoid bifurcation and achieve zero-voltage switching across the entire operational range, boundary conditions for frequency detuning design in systems with resistance or voltage loads are identified. The proposed analysis is validated through experimental measurements, and an example illustrating the impact of critical conditions on IPT system design for battery charging is provided.