WiTricity (United States)

<div class="section abstract"><div class="htmlview paragraph">Notice of Concern: The Publisher has put a notice of caution and inquiry on this paper because of an expression of concern about the figures and so have temporarily withdrawn the article. We will update after our investigation. </div></div>

Designing an inductive power transfer system to deliver constant power over large ranges of lateral and vertical pad misalignment is challenging. Existing power electronic solutions to this problem include duty-cycle control, theta control, and the use of tunable matching networks (TMNs). The disadvantages of these solutions include switch stresses, pad losses, and control complexity. This article proposes a method of tuning and controlling the system known as active impedance control that emulates the behavior of a TMN using fewer components. The method utilizes a novel combination of deliberate mistuning of the secondary compensation network and relative phase angle control to deliver constant power while minimizing converter stresses over a large misalignment range. A mathematical model and search algorithm were developed in order to determine appropriate values for the relative phase angle and compensation elements. A 7-kW system was designed to validate the proposed method. Simulation and experimental results show that the system can deliver near constant power for a 100% change in mutual inductance with a constant battery voltage, and a maximum dc–dc efficiency of 92.7% was achieved.

Inductive charging of electric vehicles requires that the vehicle and ground systems work together for power transfer from grid to the vehicle battery. In order to qualify if the vehicle system is compatible with the ground system, the presented impedance of the vehicle to the ground system can be used for characterization. However, there are no commercially available systems existing that are able to measure the impedance precisely while power transfer. For this reason, we developed a device that can be applied to characterize the presented impedance of vehicle systems. We will present first measurement results that were obtained with the device and discuss the main challenges in impedance measurements during power transfer.

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