Novel Transformerless Multilevel Inductive Power Transfer System

Previous high power on-line inductive power transfer (IPT) systems use line-frequency (LF) transformers and high-frequency (HF) transformers to be compatible with the ratings of commercial power switches. However, LF and HF transformers make the IPT systems bulky and expensive. This study proposes a new transformerless multilevel on-line IPT system using multilevel rectifiers, inverters, and excitation coils. Instead of the LF transformers, a series-connected multilevel rectifier and inverter are used. Instead of the HF transformers, excitation coils, which have strong magnetic couplings with a transmitter coil, is connected to each of the output terminals of the multilevel inverter. The magnetic fields generated by the multiple excitation coils induce a high voltage and current in the transmitter coil. The induced current generates the augmented magnetic field in the transmitter; therefore, a receiver coil that is loosely coupled with the transmitter can collect power from the mains. The input impedance, voltage and current gains, and efficiency of the proposed IPT system are investigated using an equivalent circuit model. The impact of the excitation coil shape on the magnetic couplings is explored using finite element analysis. Based on the investigation, a design for the excitation coil is presented. The feasibility of the proposed system is evaluated using a 4-level experimental test-bed. Measured coil-to-coil and DC-to-load efficiencies of the proposed system are observed to be 88% and 84%, respectively, over a 7 cm air-gap.