Analysis of Coplanar Intermediate Coil Structures in Inductive Power Transfer Systems

Intermediate couplers have been shown to increase the coupling from primary to secondary pads in inductive power transfer (IPT) systems. This paper investigates embedding a coplanar intermediate coupler coil with the primary coil inside the primary pad to boost the coupling to the secondary pad and improve the efficiency of the system. Several coil designs are simulated and a mathematical model is developed to evaluate the efficiency of parallel-parallel and series-series tuned systems. As shown a coplanar, independently tuned intermediate coupler coil improves the efficiency of a series-series-tuned system since it reduces source losses. However, there appears to be no benefit to having an intermediate coupler with a parallel-parallel-tuned system. Furthermore, boosts in coupling are a result of adding extra current carrying windings to the primary pad and simulations show that operating the system as a traditional two coil IPT system may be simpler and more effective based on tuning topology. An experimental system was constructed to validate the simulations.