Single Stage Wireless Power Transfer Battery Charger for Electric Vehicles

This paper analyzes the feasibility of a wireless charging system for electric vehicles controlled with variable frequency. The design of the battery charger is based on the load requirements, that have been defined with a complete characterization of the battery pack. The coupling system and compensation networks have been sized to guarantee the voltage gain requested by the load and to allow soft-switching operations of the inverter MOSFETs. In particular, with a parallel secondary compensation, the vehicle assembly inductance is reduced when compared with a series compensation, allowing space and weight on the vehicle to be saved. The control system is designed to generate a variable inverter output voltage in the range of variation demanded by the direct supply of a Li-Ion battery pack connected to the WPT output. The paper demonstrates that the output voltage range is obtained with a switching frequency that falls into the range recommended by the SAE J2954:2020 standard.

I. Introduction

In recent years, electric mobility has received a growing attention due to the increasing public awareness for environmental issues and technology improvements. Indeed, recent developments of power electronics and modern batteries have made battery electric vehicles (BEV) an efficient and reliable alternative to the traditional fossil fuel-powered ones, as it is also testified by the positive trend of the sales market [1]. In this frame, the transition from conventional to electric vehicles can also be accelerated by the possibility of wireless charging, being a more practical and robust solution with respect to the wired one, especially when operating in difficult environments [2]–[4]. Wireless power transfer (WPT) systems of practical interest are based on inductively coupled transmission coils, which are fed by a (relatively) high frequency current which generates the magnetic fields that allows the power transfer.