Multi-Winding Planar Transformer-based On-Board Charger for Small Mobility Applications

The lack of onboard charging capability is one of the major challenges for the widespread adaptation of small mobility vehicles such as electric scooters, which arises due to the limited space for power electronics units on the chassis of the e-scooters. Magnetics design is the bottleneck for increasing the power density, and it’s also the reason that the e-scooters come with a separate off-board charger as an off-the-shelf planar flyback transformer with the required center airgap and power rating is readily not available in the market. This research solves this problem by designing a very low-footprint multi-winding flyback planar transformer, operating in discontinuous conduction mode with an interleaved arrangement of windings, resulting in a height of only 12mm and improved current density distribution. This led to the realization of a high power-density power electronics unit integrating both the onboard charger and motor drive. A benchmark comparison in terms of power density was made to evaluate the achieved benefits. This enables the user to charge anywhere without carrying a separate off-board charger, contributing to the rapid adaption of electrified transportation. The paper explains the design process, key parametric calculations and considerations, and electrostatic and magnetostatic analysis.