Ground Assembly Research Articles

Resonant coil matrix shielding for dynamic WPT systems

In this article, a magnetic shield for automotive Wireless Power Transfer (WPT) systems is proposed. Its innovative feature consists in the positioning of the shield, that is part of the Ground Assembly (GA) of the WPT system. Passive coils, assembled in an array-like structure to build the shields properly located near the transmitting coils are investigated. Currently, there are a variety of shielding methods, each of them with its peculiar feature. The proposed method is simple and does not increase the transmitting and the receiving coil sizes, a constraint that is often critical from a practical and an economical point of view. The main characteristic of the proposed shielding method is the location of the shielding coils on the same level as the GA. The results here presented are validated by Finite Element (FE) based simulations and are referred to an experimental prototype of wireless charging systems for electric vehicles operating at 85 kHz with a transmitted nominal power of 3.3 kW. The results show that the proposed shield reduces the leakage magnetic flux density in the system up to 37% with a marginal impact on the transmission efficiency, complying the SAE J2954 international standard.

Metal Object and Vehicle Position Detections Integrated With Near-Field Communication for Wireless EV Charging

To commercialize wirelesselectric vehicle charging (WEVC), three critical issues must be resolved: communication between the vehicle assembly (VA) and the ground assembly (GA), metal object detection (MOD) on the GA coil, and position detection (PD) of the VA. This paper proposes a comprehensive system that integrates MOD and PD with VA-GA near-field communication (NFC). A common high-frequency aided carrier is used not only for NFC, but also for MOD and PD. In addition, an array of dual-purpose detection coils is proposed as a sensor for MOD and PD. As a result, the three functions listed above share numerous components and circuits, greatly simplifying the system structure. Furthermore, because the high-frequency aided carrier can operate with or without a power carrier, the preceding three functions are independent of system power status. The proposed method has been validated using a 3.3 kW WEVC prototype operating at 85 kHz. The experimental results show that the proposed system is capable of performing both online and offline NFC, MOD, and PD with high sensitivity while having no impact on wireless charging efficiency.

Cost-Efficiency Optimization of Ground Assemblies for Dynamic Wireless Charging of Electric Vehicles

Dynamic wireless power transfer (DWPT) allows electric vehicles (EVs) to be charged while in motion. However, high cost and efficiency concerns limit the widespread adoption of DWPT. A ground assembly (GA) accounts for most of the system cost since it is implemented on a significant portion of the road. This article proposes a cost-efficiency optimization algorithm to determine the optimum design of a DWPT transmitter (Tx) pad. Elongated rectangular pads are considered a compromise between cost and efficiency. An optimization methodology is put forward to maximize Tx pad efficiency while minimizing GA cost over a selected road. The optimum design allows constant power transfer inside a selected rated power zone while considering EV lateral misalignment as a random variable. Main cost factors are accounted for, including the cost of the pad coil Litz wire and ferrite material and Tx power electronics and compensation network. Particle swarm optimization allowed the number of finite element analysis simulations to be reduced by intelligently selecting test designs. Statistical analysis is applied to understand the impact of different variables on the final design and the interdependence between variables. Additional analyses are conducted to evaluate the impact of different DWPT aspects, including the wire gauge, probability density of the misalignment variable, multilayer coil design, and capacitor cost modeling. The algorithm is used to design a 3.7-kVA Tx pad with respect to the SAE J2954 receiver test stand VA WPT1/Z1. The optimization Pareto fronts illustrate the family of optimum designs, while the chosen 3.7-kVA pad offers the statistical expected value of pad efficiency as 96%, GA per meter cost of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\$ $ </tex-math></inline-formula> 1004, and an optimum pad length of 1.75 m. The 3.7-kVA optimized pad is manufactured and tested for several operating conditions verifying the simulation results.

Power loss analysis and thermal assessment on wireless electric vehicle charging technology: The over-temperature risk of ground assembly needs attention

To support e-mobility, wireless electric vehicle charging (WEVC) emerges as a promising technology by virtue of convenience characteristics and the mitigation of range anxiety. Recently, the safety issues on WEVC systems have drawn considerable attention. In light of thermal safety, the most critical part of WEVC systems is the surface of ground assembly (GA). During the charging process, its temperature increases due to the power losses, possibly resulting in cutaneous injury to living bodies and the ignition of foreign objects. Especially when there are evitable misalignments between the GA and vehicle assembly, its temperature rise will be higher as a penalty of efficiency deterioration of WEVC systems. Unfortunately, it has rarely been deemed as a safety hazard yet. Taking a commercialized WEVC system rated at 6.6 kW as an example, this paper focuses on the safety assessment of GA surface. The overtemperature-related losses, including core loss, ohm loss and eddy-current loss, are calculated. The thermal analysis is conducted based on the heat transfer theory. The temperature distribution of GA surface is obtained using transient-state FEM simulations. Based on IEC standards, four hazard levels are proposed as evaluation criteria. Finally, the calculated accuracy is validated experimentally. The results reveal direct influence of misalignments on the temperature rise. The sensitivity of different misalignments to the temperature rise is also analyzed. When the horizontal displacement exceeds 98.86 mm or the angular offset (type II) exceeds 9.91 deg., the highest hazard level could be reached, which highlights severe over-temperature risks of GA surface.