A Case Study: Influence of Circuit Impedance on the Performance of Class-E2 Resonant Power Converter for Capacitive Wireless Power Transfer

The evolution of power electronics led to rapid development in wireless charging technology; as a result, a single active switch topology was introduced. The present market utilizes inductive wireless power transfer (IPT); because of the disadvantages of cost, size, and safety concerns, research on wireless power transfer was diverted towards capacitive wireless power transfer (CPT). This paper studies the optimal impedance tracking of the capacitive wireless power transfer system for maximum power transfer. Compared to prior methods developed for maximum power point tracking in power control, this paper proposes a new approach by means of finding impedance characteristics of the CPT system for a certain range of frequencies. Considering the drone battery as an application, a single active switch Class-E-2 resonant converter with circular coupling plates is utilized. Impedance characteristics are identified with the help of equations related to the input and resonant impedance. The impedance tracking is laid out for various resonant inductors, and the difference in current peak is observed for each case. Simulations verify and provide additional information on the reactive type. Additionally, hardware tests provide the variation of input current and output voltage for a range of frequencies from 70 kHz to 300 kHz. Efficiency at the optimal impedance points for a resonant inductor with 50 mu H and 100 mu H are tested and analyzed. It is noted that the efficiency for a resonant inductor with 50 mu H is 8% higher compared to the CPT with a 100 mu H resonant inductor. Further hardware tests were performed to investigate the impact of frequency and duty cycle variation. Zero-voltage-switching (ZVS) limits have been discussed with respect to both frequency and duty cycle.

Automated summary

The paper investigates optimal impedance tracking for capacitive wireless power transfer system to achieve maximum power transfer, proposing a new approach of finding impedance characteristics of the CPT system at certain frequencies. Simulations and hardware tests were conducted using a single active switch Class-E-2 resonant converter to study efficiency with different resonant inductors, frequency ranges, and duty cycles. Discussions on zero-voltage-switching (ZVS) limits with regards to frequency and duty cycle were also included.