Analysis and design of an S/SP compensated IPT system to minimize output voltage fluctuation versus coupling coefficient and load variation

The capability of misalignment tolerance is vital for inductive power transfer (IPT) systems. S/SP compensation topology can provide a strong capability of misalignment tolerance if it is properly designed. This paper presents a detailed deduction process to acquire the optimal coupling coefficient, tuned at which the system can achieve minimum output voltage fluctuation. The impact of primary and secondary coupling inductance on output voltage fluctuation versus load variation was also analyzed. The output voltage fluctuation is not affected by the primary coupling inductance, but it decreases when the secondary coupling inductance is increased. Theoretical analysis was validated by both simulation and experiment. Three 200-W IPT prototypes were built. An overall efficiency of 94.1% was achieved when the coupling coefficient was 0.1733. The output voltage fluctuation was as low as 1.5% when the coupling coefficient increased by 34.5%, from 0.1288 to 0.1733. With a 900% rise in load resistance (from 80 to 800 Ω), the output voltage fluctuation decreased from 5.8% to 4.0% when the secondary coupling inductance increased from 136.3 to 250.0 μH.