Development of A Medium-Voltage Isolated Excitation Coil for A Transformerless Multilevel Inductive Power Transfer System

A transformerless multilevel inductive power transfer (IPT) system converts a medium-voltage (MV, 22.9 kVrms to low-voltage (LV, 1 kV) using a multilevel active rectifier and resonant inverters. Excitation coils are connected to the output terminals of the inverters and generate magnetic fields to excite voltages and currents on a transmitter coil. Then, the transmitter coil generates augmented magnetic field to induce load voltages on receiver coils via loose couplings between them. However, high voltage isolation is the key challenge of the MV multilevel system. An MV isolation between the excitation and transmitter coils should be guaranteed for safe operation. In this paper, a novel insulation concept of the excitation coil is proposed. An analytic model calculating the proposed structure's E-field intensity is also derived. The MV insulation performance is verified by finite-element-analysis simulation and over-voltage (OV) test. The achieved insulation level was 55 kV, and a dielectric breakdown was observed during a 60 kV potential difference between the excitation and transmitter coils. In addition, magnetic flux density, core loss, and cross-couplings between the excitation coils are discussed. An example design of 22.9 kV, 1 MW, 85 kHz, 42-level IPT system is evaluated using PLECS circuit simulation results.