Analysis and design of a coaxial winding transformer interface for an electric vehicle charging system.

摘要

The design and analysis of an inductively coupled EV charging system suitable for all power levels and all foreseeable infrastructure equipment is described. The separable coaxial winding transformer (CWT) is used as the inductive interface due to its unique structure and magnetic leakage field. The novel universal CWT-based EV charging system has helped remove two major barriers to widespread EV commercialization: user-unfriendly charger connection and lack of fast charging capability.;Exact, closed-form solutions for current density and magnetic field intensity of the CWT, including the effects of finitely thick conductors and multiple layers, are presented for the first time. From these field equations, exact normalized power and normalized energy are determined. Minimum power loss and minimum energy storage are conflicting requirements. To get more turns, minimum power loss is achieved by adding layers rather than segmenting a layer. Conversely, minimum energy storage is achieved by first segmenting a layer.;When skin effect dominates, ac resistance of the first layer is confirmed to be approximately that of a conductor of the same mean radius, one skin depth thick and carrying dc current. Similarly, the ac inductance is the same as a conductor of the same mean radius, one skin depth thick and carrying dc current, while also in the same layer position of the winding. Each layer has an optimal thickness for minimum power loss, which depends on the mean radius. However, there is no optimal thickness for the first layer of the inner winding when the mean radius is less than about five skin depths.;A single universal inductive coupler and EV charging system has been designed for both low and high power charging systems. Only two dimensions need standardization to allow all EV's to couple to all chargers, regardless of power rating: the center-to-center distance of the core windows and the diameter of the core window. The power electronics and thermal issues are important considerations in designing the system, but hold no unexpected surprises.