Small-Signal Modeling of an S-S Compensated IPT System Under Frequency Modulation

Frequency modulation is widely utilized in inductive power transfer systems and is also included in the Qi standard for low-power chargers. This brief examines small-signal modeling and simplification methods using an example of an S-S compensated system under frequency modulation. Initially, it develop models for the resonant components under frequency perturbation, which subsequently help in constructing the model of the resonant tank. By incorporating the models of the inverter and rectifier, it derives a sixth-order model for the entire system. The pole-zero analysis helps simplify this sixth-order model to a third-order and a first-order model. Experimental results show that these models can accurately predict the system’s control-to-output gain up to 1/2, 2/5, and 1/10 of the switching frequency. These models effectively illustrate the impacts of circuit parameters and the trade-offs between accuracy and complexity.