MODELLING AND COMPARATIVE ANALYSIS OF INDUCTIVELY COUPLED CIRCULAR AND SQUARE LOOP WIRELESS POWER TRANSFER AT UHF BAND FOR AUTOMOBILE CHARGING

Adebayo Olusakin, Adeniran,; Olusegun, Olabisi,; Akankpo, Akankpo; Okon, Akaninyene; Emmanuel Bassey, Umoren,; Kufre Israel, Udo,; Odira Anyanor, Oliver; Ebuka Okechukwu, Agbasi, · 2023 · Crossref

DOI: 10.26480/aem.01.2023.08.14

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Summary

This study addresses the need for efficient wireless power transfer (WPT) systems for electric vehicles (EVs) to reduce reliance on fossil fuels and minimize environmental pollution. The research specifically investigates and compares the performance of inductively coupled circular and square loop antennas operating at the Ultra-High Frequency (UHF) band. The primary objective is to determine which loop geometry offers superior coupling efficiency and stability under varying orientation and alignment conditions, which are critical factors in practical automobile charging scenarios. The researchers employed COMSOL Multiphysics 5.5 software to simulate and model the electromagnetic behavior of both loop types. The simulations were conducted in the frequency domain at a resonant frequency of 1.8 MHz. The antenna models consisted of printed loops on a 2 mm polytetrafluoroethylene (PTFE) substrate with a copper layer modeled as a perfect electric conductor (PEC). The study analyzed the effects of loop orientation by rotating the receiving antenna relative to a fixed transmitting antenna at angles of 0, 22.5, 45, 67.5, and 90 degrees. Key performance metrics included S-parameters (reflection coefficient $S_{11}$ and mutual coupling $S_{21}$), electromagnetic power flow, and directivity. Theoretical foundations were established using Faraday’s law of induction, Ampere’s circuital law, and equations for mutual inductance and radiation resistance. The results demonstrated distinct performance differences between the two geometries. The square loop exhibited strong coupling at 0 degrees but suffered significant coupling losses and heat generation around the receiving antenna at 90 degrees, with the mutual coupling parameter ($S_{21}$) dropping to -39.50 dB at this angle. In contrast, the circular loop maintained consistent and "perfect" coupling across all tested angles, with $S_{21}$ reaching -39.01 dB at 90 degrees. The average electromagnetic wave energy/power flow ranged from 3.4433 W/m² for the square loop to 12.308 W/m² for the circular loop. Additionally, the circular loop showed a directivity of 6.7502 dB compared to 1.3018 dB for the square loop. Both designs maintained reflection coefficients ($S_{11}$) below -20 dB, indicating good impedance matching regardless of orientation. The study concludes that while square loops are suitable for direct, aligned charging, circular loops are superior for general EV charging applications due to their ability to maintain efficient power transfer despite misalignment or indirect positioning. The circular geometry’s consistent performance across varying angles makes it more acceptable and robust for real-world automotive WPT systems, where precise alignment between the vehicle and charging pad cannot always be guaranteed. This finding supports the adoption of circular loop designs in future UHF-band wireless charging infrastructure for electric vehicles.

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• v2x connected vehicle