Passive Reactance Compensation for Shape-Reconfigurable Wireless Power Transfer Surfaces

TL;DR

This paper addresses the problem of dead zones and impedance detuning in shape-reconfigurable wireless power transfer surfaces composed of 2-D relay resonator arrays. It introduces a passive reactance compensation scheme that attaches capacitive elements between neighboring resonators to neutralize inductive coupling, enabling simultaneous activation of all resonators at a fixed operating frequency regardless of array shape. The method derives an impedance condition and static capacitor values, and demonstrates through simulations and experiments at 13.56 MHz that dead zones are eliminated and the minimum power-transfer efficiency improves dramatically (from 0.5–3.0% to 46.7–56.8% in various configurations). The work enables readily deployable deformable WPT surfaces suitable for dynamic devices without receiver tracking or active control, with potential for large-scale implementations.

Abstract

The powering range of wireless power transfer (WPT) systems is typically confined to areas close to the transmitter. Shape-reconfigurable two-dimensional (2-D) relay resonator arrays have been developed to extend this range, offering greater deployment flexibility. However, these arrays encounter challenges due to cross-coupling among adjacent resonators, which detune system impedance and create power dead zones. This issue often necessitates active components such as receiver position tracking, increasing system overhead. This study introduces a passive reactance compensation mechanism that counteracts detuning effects, enabling the simultaneous activation of all resonators at a fixed operating frequency, regardless of the array's shape, thus providing a consistent charging area. The key innovation involves mechanically appending reactance elements to neutralize detuning caused by inductive coupling, facilitating hassle-free resonator reconfiguration without requiring prior knowledge. Our experiments demonstrate the elimination of dead zones with multiple configurations, boosting the minimum power transfer efficiency from 3.0% to 56.8%.

Figures (4)

• Figure 1: Concept and principle of the proposed compensation mechanism: (a) Simply arranging $LC$ resonators in a 2-D array leads to dead zones due to inductive coupling between resonators. (b) The proposed approach compensates for detuning caused by coupling via mechanical connections, enabling a consistent charging range across the array. (c) Basic schematic of the proposed passive reactance compensation mechanism, where $L_{\rm array}$ represents the inductance, $C_{\rm def}$ is the series capacitance, $C_{\rm comp}$ is the compensation capacitance, and $Z_{\rm other}$ denotes the remaining circuit impedance. (d) Inductive coupling between adjacent resonators, characterized by mutual inductance $M_{\rm adj}$, is offset by a capacitor attached by the neighboring unit.
• Figure 2: Overview of the proposed reactance compensation method. (a-c) Operating principles of the deformable resonator coil array are illustrated. The colored traces indicate the current loop forming the resonator, while $n$ denotes the number of adjacent resonators for each unit. Note that inductance symbols are omitted. (a) Schematic of a single resonator array unit, displaying each edge with a default capacitor $C_{\rm def}$ and a compensation capacitor $C_{\rm comp}$, which offsets the reactance of adjacent resonators. (b) When two resonator units are connected, impedance detuning from inductive coupling with mutual inductance $M_{\rm adj}$ is compensated via the attached compensation capacitance. (c) This principle extends to configurations with more resonator units, as the number of inductive couplings and connected compensation capacitors naturally align. (d) Implemented prototype of the resonator unit employing the proposed reactance compensation method.
• Figure 3: Frequency response measurements of the proposed deformable resonator array. (a-c) resonator array shapes used for measuring frequency response, with the black circle indicating the external measurement coil. The measured frequency response is shown (d) without compensation and (e) with the proposed compensation method. The resonant frequency of a single transmitter resonator is 13.56 MHz.
• Figure 4: Simulated and measured power transfer efficiency using the proposed shape-reconfigurable wireless power transfer surface. Results are presented with and without the proposed compensation method to illustrate its impact. "TX" indicates the resonator connected to the power source. (a) Simulation results without compensation. (b) Simulation results with the proposed compensation. (c) Measurement results without compensation. (d) Measurement results with the proposed compensation method.