Maximising Inductive Power Transmission using a Novel Analytical Coil Design Approach

Abstract

Maximising power transfer efficiency (PTE) in resonant inductive power transfer (IPT) systems requires strong coupling between transmitter and receiver coils. In applications where system constraints yield a weak inductive link (e.g.: significant distance between coils.) or there is a requirement for a specific power level, then geometrically optimising the coils can enhance inductive linkage. To achieve this, a novel coil design method has been presented which provides maximum efficiency for both strongly-and loosely-coupled inductive links. A parameter (i.e.: Strong Coupling Factor.) has been introduced to assist the design procedure. Discussed results from a practical 1.06 MHz inductive link, developed using the proposed design method, show that with proper selection of strong coupling factor (e.g.: C = 220.) the designed coil geometry can provide maximum PTE of 86%, which is in close correlation (≈ 3%) with theoretical analysis using MATLAB. Index Terms-Wireless power transfer (WPT), inductive power transfer (IPT), resonant coupling, electromagnetic induction, near-field communication.

A Design Technique for Optimizing Resonant Coils and the Energy Transfer of Inductive Links

“…In selecting a suitable coil ac ohmic resistance, an FoM parameter (P scf ) has been introduced, in [31] and [32], such that its value indicates how strongly the Tx and Rx coils are linked together. The constant parameter P scf (P scf 1) has been named as strong coupling factor and provides a guideline for designing a geometrically optimized coil.…”

“…Much work has been devoted to maximizing PTE with regards to the mentioned three impacting factors (i.e., K , Q i -, and Q L -factors). This article focuses on geometric optimization of Tx/Rx coil pairs as a means of improving inductive linkage [1], [5]- [9], [14], [15], [23]- [32], which can additionally reduce the IPT system's physical size. One of the methods for geometric optimization of inductive coils is through increasing Q i -factor of the Tx/Rx coil pairs which has been considered by many researchers including [24]- [27].…”

“…To maximize the system's overall PTE through coil geometry optimization, different iterative design algorithms have been proposed over the last few decades [1], [5]- [7], [9], [14], [15], [28]- [32]. As a common approach to cancel out the loading effect of Tx/Rx terminating circuitry, Jow and Ghovanloo [1], Ibrahim and Kiani [5], Sallan et al [9], Hwang and Jang [15], Ko et al [29], and Donaldson and Perkins [30] have found equations for PTE based on the system parameters (e.g., K , R s , R L , etc.).…”

“…The theoretical method in [31] was practically exemplified by the design of an optimized Tx/Rx solenoid pair geometry for an inductive link with a transmission distance of 9.5 mm (K = 0.215) at f o = 1 MHz [32]: a PTE of 86% was measured thus showing merit in the design approach. However, a proper selection method for identifying a numerical value to represent the FoM parameter (i.e., P scf ) used in [31] and [32] still requires in-depth analysis.…”

“…Building upon the proposed coil optimization technique used in [31] and [32], this article introduces a method to assist selecting the most favorable numerical value for the strong coupling factor which can maximize PTE for the designed optimum coil geometry. The proposed method will be developed through geometrical optimization of a helical coil (i.e., solenoid).…”