Aspects of Foreign Object Detection in a Wireless Charging System for Electric Vehicles Using Passive Inductive Sensors

Abstract

If the energy transfer for charging the traction battery of an electric vehicle takes place wirelessly and with inductive components, the active area of the charging system must be monitored for safety reasons for the presence or intrusion of metallic objects that do not belong to the charging system. In the past, different concepts for such monitoring have been described. In this paper, passive inductive sensors are used and characterized based on practical measurements. With this type of sensor, the detectability of metallic foreign objects is very closely related to the characteristics of the magnetic field of the charging system. By optimizing the geometry of the sensor coils, the authors show how foreign object detection can be improved even in areas with low excitation of the foreign objects and the sensor coils by the magnetic field. For this purpose, a charging system, with which charging powers of up to 10 kW have been realized in the past, and standardized test objects are used. Furthermore, the thermal behavior of the metallic test objects was documented, which in some cases heated up to about 300 °C and above in a few minutes in the magnetic field of the charging system. The results show the capability of passive inductive sensors to detect metallic foreign objects. Based on the measurements shown here, the next step will be to simulate the charging system and the foreign object detection in order to establish the basis for a virtual development and validation of such systems.

Simulation of Foreign Object Detection Using Passive Inductive Sensors in a Wireless Charging System for Electric Vehicles

“…During the simulation, the coil geometry and the magnetic field of the current-carrying coil were analyzed at a frequency of 80 kHz. This way, the simulation results are comparable to the measurements from [7], where a switching frequency of 80 kHz was also used. The results of the coil geometry analysis are shown for the three parallel subcoils and the entire ground assembly coil in Table 1.…”

“…Therefore, this was simulated separately in the first step and validated with the values determined during practical measurements. The magnetic field probe used in [7] for the measurements on the ground assembly of the charging system has a nearly square housing (height: 27 mm) and was moved over the coil at a height of z = 13 mm. Therefore, the magnetic flux density was extracted from the simulation at three different heights: z = 13 mm (bottom of the probe), z = 26.5 mm (center of the probe), and z = 40 mm (top of the probe).…”

“…The work on the detection of metallic foreign objects in the ArchitectECA2030 project is organized into two main parts-the measurements on a real wireless charging system and the simulation of this system. The results of the practical measurements were published in [7]. In this paper, simulations related to foreign object detection are presented.The simulations were performed using the COMSOL Multiphysics ® software including the AC/DC module [8].…”

“…Section 2 of the paper presents the basic structure of the simulation environment. This represents the measurement setup, which was described in detail in [7]. Subsequently, in Section 3, the results of the simulation of the magnetic field of the ground assembly coil of the charging system are shown and compared with the values determined by measurement.…”

Numerical and Experimental Investigation of Time-Domain-Reflectometry-Based Sensors for Foreign Object Detection in Wireless Power Transfer Systems

“…Any electrically or magnetically conductive material (i.e., materials with a sufficient deviation in magnetic permeability or electric conductivity relative to air) changes the local magnetic field distribution of the GA coil or of a separate excitation coil, which can be detected as a change in induction voltage of a local sensor loop. Several monitoring device designs based on the field-based detection method have been proposed in the past [17][18][19][20][21][22][23][24][25]. However, these designs require multiple sensor coils to cover the entire surface area of the GA, which need to be interconnected in pairs to cancel out both the GA induction voltage as well as the external noise and have to be multiplexed to a detection circuit.…”