Jun 5, 2020

Assessment of Exposure to Electric Vehicle Inductive Power Transfer Systems: Experimental Measurements and Numerical Dosimetry

Ilaria Liorni, Oriano Bottauscio, Roberta Guilizzoni, Peter Ankarson, Jorge Bruna, Arya Fallahi, Stuart Harmon and Mauro Zucca, Sustainability 2020, Volume 12, Issue 11, 4573, online 03 June 2020; doi: 10.3390/su12114573

High-power inductive power transfer (IPT) systems for charging light and heavy electric vehicles (EV) pose safety concerns if they are installed in uncontrolled environments. Within the framework of the European Project EMPIR-16ENG08 MICEV, a wide experimental and numerical study was conducted to assess the exposure of the general public to IPT stray magnetic fields for two different exposure scenarios: (i) for an IPT model system derived from the SAE J2954 standard operating at 85 kHz for a light EV coupled with the model of a realistic car-body model; and (ii) for an IPT model system with a maximum rated power of 50 kW at 27.8 kHz for a real minibus that was reproduced with some simplifications in two different 3D finite element method (FEM) simulation tools (Opera 3D and CST software). An ad hoc measurement survey was carried out at the minibus charging station to validate the simulations of the real bus station for both aligned and misaligned IPT coils. Based on this preliminary study, a safety factor was chosen to ensure a conservative dosimetric analysis with respect to the model approximations. As highlighted in this study, the vehicle-body serves as an efficient screen to reduce the magnetic field by at least three orders of magnitude close to the coils. By applying FEM, and obtaining computed spatial distribution with the Sim4Life software, the exposure of three Virtual Population human anatomical phantoms (one adult, one child, and a newborn) was assessed. The three phantoms were placed in different postures and locations for both exposure scenarios. The basic restriction limits, established by the current guidelines, were never exceeded within the vehicles; however, the basic restrictions were exceeded when an adult crouched outside the minibus, i.e., near the coils, or when a newborn was placed in the same location. Borderline values were observed in the light car. In the case of the bus, limits coming from the Institute of Electrical and Electronics Engineers (IEEE) guidelines are never exceeded, while basic restrictions coming from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines are exceeded up to 12% for an adult and up to 38% for a newborn. This paper presents novel dosimetric data generated in an IPT system for heavy vehicles and confirms some of the literature data on light vehicles.

The scientific and technical impact of the study can be summarized as:

  • IPT charging technology for electric cars can be intrinsically safe
  • The use of metal vehicle-bodies with a relative magnetic permeability higher than 300, and electrical conductivity of at least 1 MS/m reduces the magnetic induction values inside the vehicle to close to the environmental noise and the exposure levels at least one order of magnitude lower than the basic restrictions
  • In order not to increase the driver’s/passenger’s exposure during charging, glass surfaces of the vehicles (i.e., windows) must be limited, the doors should not be opened when charging, and a fiberglass body should not be used
  • Basic exposure restrictions are exceeded in the event of a driver or passenger crouching or sitting outside the EV, specifically at the side of the EV closest to the coils