Automated Alignment with Respect to a Moving Inductive Wireless Charger
Abstract : Wireless charging is an attractive technology that often promises increased mobility for electrical devices. However, commonly-available wireless charging systems are generally intolerant to misalignment between the charger and the receiving device due to the need for inductive coupling between the two, defeating the promise of mobility. Many techniques have been studied to address this issue, including improved electrical circuits, novel charger coil designs, and the use of sensors for detecting misalignment. In this paper, a new arrangement of sensing coils is used to detect lateral misalignment between a moving wireless charger and a mobile robot. Data from the sensing coils are used in a dual-loop control of the robot. The inner loop controls the robot velocities and consists of a linear quadratic regulator with integral action. The outer loop provides reference velocities to the inner loop based on the readings of the sensing coils. Using this method, an experimental mobile robot maintains alignment within 2 cm with respect to a 5-W wireless charger that moves up to 0.145 m/s. This automated alignment method is a low-cost solution that enables mobile systems, such as autonomous vehicles, to wirelessly charge while the charger is moving.
? The magnetic alignment approach uses the existing coil and frequency tracking control electronics of wireless chargers to detect the distance between the two coils while using 4 small auxiliary coils for direction and fine adjustment, leading to a cost effective detection method for coil alignment in electric vehicle wireless charging (EVWC).
? It uses the existing coil to generate a weak magnetic field that is detected by magnetic sensors installed on the secondary side.
? The system utilizes the existing charging facility to generate a magnetic field and sense the relative distance between the two coil centers.
? A magnetic alignment system using existing charging electronics demonstrates that it can be a practical approach to address the misalignment issues in wireless EV charging.
? We develop a conditional gradient descent method to solve the problem, which performs gradient descent (or conditional gradient descent on the boundary of the search space) and projects out-of-boundary points back into the space.
? The key idea is that we propose to convert the nonconvex misalignment estimation problem to a problem with a convex objective of estimating the actual distances between the sensors.
? Another key aspect is to convert the nonconvex misalignment estimation to a more tractable problem with a convex objective.
? We develop a search algorithm to solve the problem (4), where we perform gradient descent (or sometimes conditional gradient descent, e.g., on the boundary of S), and then project the out-of-boundary points back into S.
• The switching frequency is assumed as 20 kHz which is the proposed switching frequency of the wireless EV charger.
• The charging facility reads the vehicle height and then calibrates and chooses the appropriate built-in data array for matching purposes.
• The distance between the two coils is transmitted to the user immediately for navigation purposes.
• The four auxiliary coils provide direction information and help the driver adjust the vehicle to ensure good alignment.
• Wireless charging is a competitive option to overcome the inconvenience of plug-in EV charging and the relatively low energy density stored in batteries by opportunity charging.
? In this paper, we consider a circular topology of magnetic core, because it is tolerant to angular misalignment and can also achieve high efficiency.
? Inductive charging can provide a high power transfer efficiency of over 90% , and will be crucial to autonomous EVs.
? Caused by an imprecise positioning manoeuvre or uneven ground surfaces, misalignments could significantly degrade the power transfer efficiency.
? The focus of this paper is the coil alignment, which is crucial to the power transfer efficiency.
? In this sense, the coil alignment is important for any charging mode or current/voltage control mechanism, and can help improve the power transfer efficiency of the mode or mechanism.
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