A New Multilevel Inductive Power Transfer System

Conventional on-line inductive power transfer (IPT) systems use a 60-Hz transformer and a rectifier at their front-ends to step down a medium-level input voltage (22.9 kV or 25 kV) to a low voltage of 0.1 - 3 kV(rms), so it is compatible with voltage ratings of commercial power switches. To achieve high output power level, multiple inverters and high-frequency transformers can be tied in parallel to the rectified DC bus. However, the 60-Hz transformer and the output high-frequency transformers are the main impediments that make the system bulky and expensive. This paper proposes a new on-line IPT system that utilizes multilevel inverters and excitation coils instead of the input and output transformers. Instead of the line frequency step-down transformer, series-connected active rectifiers and DC/AC inverters are used to convert the medium-level input voltage to multiple low-level voltage outputs. The excitation coils have strong magnetic coupling with the transmitter coil. Its magnetic field induces voltage and eddy-current in the transmitter coil and then, the transmitter coil induces a load current to a receiver coil via a loose coupling between the transmitter and the receiver. A theoretical analysis using an equivalent circuit model is presented. The frequency response of the input impedance and efficiency of the proposed IPT system are investigated. Also, an example design for the excitation coil is demonstrated. The feasibility of the proposed system is evaluated using a circuit analysis of a 4-level IPT system. The simulated efficiency of the proposed system was 88 % over a 7-cm air-gap.