Unveiling Aliasing Effect on Resonant Pole Locations in Wireless Battery Chargers

Resonance frequency bifurcation is a common phenomenon in resonant tank circuits used in wireless battery chargers, leading to a drift between the transmitter and receiver frequencies. Studying this drift helps to define the acceptable operating frequency range to ensure efficient power transfer and maintain soft switching conditions. While this understanding aids in improving steady-state performance and efficiency, the control dynamics depend on the small-signal model and the resonant pole locations of the system under control. State-of-the-art literature, based on the discrete-time (DT) model, indicates that the plant resonant poles show up at frequencies much below the coil resonance frequencies. However, the qualitative origin of the poles at the lower frequency range is not apparent. It is also unclear how the resonant poles and the tank resonance frequencies are correlated. In this work, the origin of the resonant poles is investigated and a method is suggested for the quick approximations of the pole locations without numerically solving the discrete-time model. The analysis leads to understanding the relation between the pole locations and the sampling and tank resonance frequencies. A series-series LC resonant converter-based battery charger is considered for the study and experimental validation. The derived conclusions are verified with the results available in the literature. Though the analysis evolves based on a full-bridge converter, the formulation lends itself to complex resonant converter topologies.