**5. Design guidelines**

spectrum ranges from 5 Hz to 100 kHz. Magnetic field values found in the car are low (in the order of a few µT), especially when compared to ICNIRP's reference levels, although it is not clear which method was used to account for multifrequency exposure (see Subsection 3.1). In average, highest magnetic field values were found at the rear left side of the hybrid car. The maximum levels of recorded magnetic field strength are emitted at 12 Hz, which is a very low frequency. About the study published in [34], it provides an example of how to deal with multifrequency exposure in accordance to ICNIRP's recommendations. This work focuses on electric vehicles exclusively, and the magnetic field values obtained are in line with those from [13], around 15–20% of ICNIRP's reference levels. The paper also presents simulation results

In 2015, two journal papers were published with measurement results from a wide variety of hybrid and electric cars [9, 10]. Some of their authors participated in the two publications from the previous paragraph. The study in [9] comprises a total of three conventional cars and eight electric vehicles, including some based on fuel cells instead of batteries. Both laboratory measurements and road measurements were taken and compared to INCIRP's reference levels with a wide‐frequency range, up to 10 MHz. The vehicle that showed highest values reached 18% of ICNIRP's levels. Unsurprisingly, the researchers found that magnetic field exposure was higher in EVs than in ICE‐based vehicles in average. However, the position of maximum exposure within each vehicle (front vs. rear part, foot vs. seat level) was different. This position is probably influenced by the configuration and topology of the vehicle, as described in Section 2. The main sources of magnetic field are identified in this study: at frequencies below 1 Hz, hundreds of µT are present (most likely due to battery current). Between a few Hz and 1 kHz, fields up to 2 µT were found, generated by most sources (combustion engine, steering pump, and wheels are mentioned in the paper, but probably fundamental currents in the inverter and in the electrical machine were also responsible). Finally, above 1 kHz, less than 100 nT was measured, and the authors identified the inverter as the only source (which makes sense, since

The open‐access study in Ref. [10] focuses on diesel, gasoline, and hybrid cars. Up to 10 vehicles are analyzed, and the results are consistent with previous investigations. Results are presented separately for different seats and for different engine types. In general, magnetic field exposure was higher in hybrid cars, and then in gasoline cars. The authors state that magnetic field exposure depends on the operating conditions (speed, acceleration, etc.), which is unsurpris‐

Other research projects take a different approach and analyze the problem by means of finite element method (FEM) simulations and even analytical approximations. FEM simulations are helpful to better understand the problem, to analyze magnetic field exposure dependence on certain parameters (for instance, by performing sensitivity analysis), and to develop a predic‐ tive methodology. Being able to estimate magnetic field exposure without actually having to perform measurements could prove extremely useful for EV designers. As proposed in Ref.

it is the only power electronics device in the traction drive).

**4.2. Magnetic field estimation by numeric simulations**

(see Subsection 4.2).

62 Modeling and Simulation for Electric Vehicle Applications

ing.

In this section, some design guidelines and recommendations to minimize magnetic field exposure in EVs are provided. Note that all these measures are of pure electric nature, and therefore they may not be applicable when considering other factors. They are based on the ALARP principle ("As Low As Reasonably Practicable"). In other words, the goal is to maintain exposure levels as low as reasonably possible with the available means, both in a technical and in an economic sense. This criterion allows the implementation of safety strategies at an acceptable cost, and it should preferably be applied during the first design stages of the EV and its components.

These guidelines are classified into two groups, depending on whether they involve major changes in the vehicle or not. The first group contains measures that do not change the topology nor the configuration of the vehicle, and that do not increase its weight nor its cost:


If further actions were necessary in order to reduce the magnetic field generated by the EV, these additional measures may prove helpful:


**•** A magnetic shield can be placed around the main devices responsible for the magnetic field in the interior of the car. Alternatively, the whole interior could be shielded, yielding higher protection at the expense of increased shield weight and cost. In both cases, the efficacy of the shield will be determined by its properties, and especially by its thickness. In the first case, a ferromagnetic alloy of high magnetic permeability, such as Mu‐metal or similar, could be used [66]. For shielding the whole interior, ferromagnetic sheets such as those used to shield hospital rooms and some laboratories are recommended instead [67]. Notice that if switching frequencies grow above 100 kHz (by using SiC power devices, for instance), Faraday shielding could become necessary. This consist in radiofrequency shields made of copper or similar [67], such as those found in microwave ovens.
