Best practice guide for the assessment of EMF exposure from vehicle Wireless Power Transfer systems

This document is based on the experience gained by the partners involved in the EMPIR Project 16ENG08 "Metrology for inductive charging of electric vehicles (MICEV)" (www.micev.eu). The project addressed the electromagnetic metrology and human exposure problems related to inductive charging of electric vehicles, both from a modelling and a measurement point of view. The guidelines reported here are designed for people who approach the assessment of human exposure in vehicles and around inductive charging stations. These guidelines are intended to complement the published standards in use and those currently being developed by international technical organisations and bodies. This document concerns the charging of electric vehicles, for transmitted power up to 200 kW. The frequency range of interest is related to resonant coils that produce significant electromagnetic field (EMF) emissions from the charging station. Resonant coils operate in the frequency range between 20 kHz and 85 kHz. Their electric current, and thus the magnetic field and harmonic distortion, is very low and not significant in relation to human exposure guidelines. Consequently, the frequency range of interest for human exposure does not exceed 100 kHz. This guide seeks to assemble the experience gained in the field of human exposure assessment and to provide information for the assessment of exposure through experimental measurements and validated calculations. The calculation of the induced quantities, in particular the induced electric field and electric currents in the tissues, is of fundamental importance for the determination of human exposure. From the point of view of dosimetry, for obvious reasons of feasibility, the calculation replaces the measurement. Therefore, a whole chapter of this guide covers the choice of instruments and the description of the correct settings for both the magnetic field calculations and the dosimetric calculations. The document particularly focuses on the following challenges: • the testing framework, including the common layout of charging stations, with reference to the normative and EU Directive on magnetic field exposure (Sections 4 to 6); • means and methods to perform: o measurements of the magnetic flux density in and around a vehicle; o measurements of limb currents (Section 7); • means and methods to perform: o analytical calculation of magnetic flux density levels for EMF exposure assessment; o computation of the induced electric fields in human beings (Section 8). The guidelines contain some appendices, which include the following: a real example of a charging station; some tables with the exposure limits referred to in this guide; a brief comparison between two existing standards; a test case of a numerical code to calculate the sources; some results on the sensitivity of simulated exposure metrics to the variations in tissue properties and, finally, the measurement capabilities of European national metrological institutes concerning AC magnetic fields at the frequency range of interest for Wireless Power Transfer systems (WPTs). These guidelines do not intend to discuss the implementation of wireless charging systems, the design of their components or the optimisation of their performance, as they do not discuss the interoperability or the techniques for building the systems, or their classification. Risk analysis and mitigation measures are beyond the scope of this guide