Design Methodology for A Transformerless Multilevel Inductive Power Transfer System

A transformerless multilevel inductive power transfer (IPT) system employs multilevel AC/DC and DC/AC converters, and multiple excitation coils to build a medium voltage (MV, 22.9 kV(rms) or 25 kV(rms)) grid-tied system. A conventional IPT system has a line-frequency (LF) and high-frequency (HF) transformers to increase its power level. However, the transformers result the conventional IPT system bulky and expensive. Instead of the LF and HF transformers, multiple excitation coils are used in the transformerless multilevel IPT systems. The excitation coils deliver power to a transmitter coil by strong magnetic coupling between them. Then, the transmitter coil transfer power to a receiver coil via a weak magnetic coupling between the transmitter and the receiver coils. This 3-stage (excitation coils - a transmitter coil - a receiver coil) configuration has advantages in efficiency, power density, and isolation. However, the high complexity of the transformerless multilevel IPT system makes it difficult to design the system. In this paper, a design methodology for a transformerless, 25 kV, 60-level, 200 kW multilevel IPT system using a multi-objective optimization technique (Pareto optimality) is presented. Its design variables and constraints are identified in the initial stage. The design variables include AC/DC and DC/AC converter topologies, impedance matching network topologies, self- and mutual-inductances of the coils, resonant tuning methods, and power switches. A new systematic design flow is proposed to select the optimal design. Using simulation results, the feasibility of the proposed design methodology is evaluated.