Design of Accurate Position Detection System Applied to Large Misalignment Range for Electric Vehicle Wireless Charging System
Sun Tian1,2, Song Beibei1,2, Cui Shumei1,2, Zhu Chunbo1, Dong Shuai1,2
1. School of Electrical Engineering and Automation Harbin Institute of Technology Harbin 150001 China; 2. Zhengzhou Research Institute of Harbin Institute of Technology Zhengzhou 450001 China
Abstract In the practical application of an electric vehicle (EV) wireless charging system, quite a few human-driven or driverless electric vehicles cannot accurately stop in the effective charging area without parking guidance. During charging process, the receiver misalignment beyond an acceptable range will cause severe problems such as low charging efficiency, excess electromagnetic radiation and rapid temperature rise of the system components. Since the beginning of industrialization of EV wireless charging technology, position detection (PD), as one of the three main auxiliary functions for wireless power transfer (WPT), has been widely researched by several researchers and institutes for years. By far, hundreds of PD methods have been proposed, but there are still many problems to positioning accurately within a wide range. Based on electromagnetic (EM) position detection method, this paper proposed an accurate PD system applied to large misalignment range for EV wireless charging system. By reasonable design of the positioning coil array and optimized calculation of the induced voltages, it gets the position coordinates of the receiver in widediscrete two-dimensional space accurately and effectively. Difficulties for the application of EM position detection to a large range stem from the low magnitude and symmetric spatial distribution of the magnetic field. To address the problem, a PD device using a triple coil array was proposed. The coil array was fixed on board, quite under the receiver coil, with the outer contour the same as the vehicle assembly (VA) for making full use of the installation space. Small quantities of the PD coils together with the design of coil geometric parameters based on effective magnetic flux area achieve a sufficient induced voltage magnitude. Non-centrosymmetric arrangement of the PD coils and the asymmetric spatial mapping relationship from each PD coil to VA guarantee the one-to-one correspondence between the VA position and the induced voltage vector. During positioning process, low power excitation was added to the coil of the ground assembly (GA), and the PD coil array moves with VA. Before positioning, fingerprint database should be set up, so that the fitted induced voltage curves can be obtained. Position detection is a process of finding the space coordinates corresponding to the real-time obtained voltages on the fitted curves based on one-to-one correspondence relationship. In fact, those fitted curves are non-monotonic and therefore have no inverse functions. As the car moves in a straight line, the real-time voltages are regarded as three straight lines in coordinate system. By intersecting them with three corresponding fitted curves, three spatial coordinate sets can be obtained, and the final result lies in the intersection set of the three. As the car moves in a two-dimensional area, the first step is the same as the car going straight. What's more, induced voltages at a previous sampling time should be used to calculate the voltage variation rates. Taking the fingerprint database as reference, the calculated voltage variation rates can help to obtain the spatial coordinate of another dimension. Based on WPT3 Z2 system, a PD system prototype was established and integrated. 400 points were tested within ±800 mm at the center of the GA. The single detection process delay is less than 5 ms. The positioning precision is 20 mm within ±600 mm and 50 mm between ±600 mm to ±800 mm, with the positioning accuracy rate more than 96%. From the result, it is feasible for integration of EM detection with other PD methods by data fusion technology to achieve a continuous accurate position detection at multiple spatial scales.
Sun Tian,Song Beibei,Cui Shumei等. Design of Accurate Position Detection System Applied to Large Misalignment Range for Electric Vehicle Wireless Charging System[J]. Transactions of China Electrotechnical Society, 2024, 39(21): 6626-6635.
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2024, Vol. 39 
