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Receiver-Position-Controlled Field Focusing for Dynamic Inductive Power Transfer Systems

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Background:Wireless power transfer (WPT) based on magnetic coupling is becoming widely accepted as a means of transferring power over small to medium distances. WPT systems show promise for charging electric vehicle batteries electronic devices and other technologies. Stationary wireless charging systems have relatively high efficiencies (>90%) if the source and receiver coils are well aligned. However in dynamic charging systems (say when powering a vehicle while driving along a roadway powering a swarm of robots moving on a flat surface powering factory automated guided vehicles or overhead conveyers) the issue of alignment becomes more challenging. This leads to power transfer inefficiencies and potential non-adherence to electromagnetic field emission standards. One approach to dynamic WPT is to have an elongated source coil coupled with a small receiver. This system results in low coupling coefficient (and therefore low efficiency) due to the relatively large self-inductance of the elongated source coil. Another issue is that the field emitted in the uncoupled sections of the track needs to be contained to ensure that emissions standards are met. The issue of low coupling is solved by segmenting the source coil so that only the sections coupled with the receiver can be selectively turned on. The challenge becomes implementing a method to control the power delivery to each section of the source coil as the function of the receiver position. State of the art solutions use receiver position sensor communication links and complex relays or switches and compensation circuits to achieve the power flow control. Technology Description:Researchers in the Department of Electrical and Computer Engineering have developed a system for transferring power between a sectionalized source and a one or more dynamically moving receivers. The proposed system uses the reflected reactance from the receiver to automatically limit the field strength in uncoupled portions of the source-receiver system thus allowing the system to more easily meet the electromagnetic field emission standards without complex shielding circuits switches electronics and communication requirements. The power transfer is at its peak when the source and receiver coils are close to their maximum allowable coupling resulting in improved system-level efficiency. Applications:Dynamic Inductive Power Transfer Systems

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