A Contactless Single-Wire CPT (Capacitive Power Transfer) Power Supply for Driving a Variable Message Sign

This paper proposes a single-wire Capacitive Power Transfer (CPT) system based on electric field coupling. The aim is to provide a contactless power supply for a Variable Message Sign (VMS) with a metallic back cover to improve its safety and reliability. As Inductive Power Transfer (IPT) is not suited to transferring power across metal barriers, the CPT technology is developed to provide a new solution for driving VMS displays, and potentially offers low electromagnetic interference (EMI). The proposed single-wire CPT system requires only a single pair of electric coupling plates without a current return path, which enables power transfer across metal barriers, and allows a large coupling tolerance compared to the traditional CPT systems with two pairs of coupling plates. This paper covers system design of the primary power converter, two coupling plates, as well as the secondary receiver. A practical prototype CPT power supply has been built, and it has demonstrated that about 5 watts of power can be transferred across the metal back cover of the VMS. Moreover, such a single-wire CPT system also has a large coupling tolerance against misalignment between the coupled plates.