Cooling Structure for Large Capacity H-shaped Core Contactless Power Transformers for Electric Vehicles

Abstract

Contactless power transfer systems for charging electric vehicles require a high efficiency, a large air gap, and a good tolerance to lateral misalignment and need to be compact and lightweight. Contactless power transformers have two types of structures: a single-sided transformer with a circular core and a double-sided transformer with a rectangular core. Past studies showed that H-shaped rectangular core transformers are more suitable for vehicles than circular core transformers.
However, the cooling of cores located between two magnetic poles is a major challenge for double-sided transformers. In particular, this problem is serious for large capacity transformers such as fast chargers because the loss density is higher than for normal charge transformers. If the radiator interrupts the magnetic flux, not only are eddy current losses created but a coupling is also prevented.
This paper proposes a novel cooling structure based on H-shaped core transformers. In the novel structure, radiator metal bars are inserted parallel to the main magnetic flux. As a result, the cooling performance is improved without compromising efficiency.