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

Abstract

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-E2 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 μH and 100 μH are tested and analyzed. It is noted that the efficiency for a resonant inductor with 50 μH is 8% higher compared to the CPT with a 100 μH 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.

8-Plate Multi-Resonant Coupling Using a Class-E2 Power Converter for Misalignments in Capacitive Wireless Power Transfer

“…The hardware tests are performed for different operating frequencies with an input of 20 V as the input impedance varies with respect to the operating frequency, resulting in the variation of input power. Using the formulas from [21], the parameters of the circuit are presented in Table 2. The maximum output power of 20.8 W is generated at the frequency of 470 kHz using the class-E 2 8-plate multi-resonant coupling structure.…”

“…To maintain ZVS for parameter variation such as coupling capacitance or load, [30] uses a control strategy by selecting a proper shunt capacitor. Some papers [21,31] also focused on maintaining ZVS without a control strategy by designing the appropriate impedance matching network. This paper follows the same approach of designing the proper impedance matching network and a shunt capacitor to achieve ZVS for the parameter variations.…”

“…This method follows a unique approach that uses a simple coupling structure with multiple series LC compensation networks connected in parallel. In [21], an impedance analysis of the class-E converter was presented. It was concluded that the optimal impedance points for each resonant inductor overlap with a resonant point for the maximum power point tracking (MPPT).…”

Application-Oriented Review of the LLC-Based Resonant Converters

“…3(b), which offers improved safety, affordability, and reliability [22]. Furthermore, other converters based on the CCWPT technique have been proposed in [23][24][25][26][27][28][29][30][31]. However, the LLC resonant converter outperforms these alternatives in terms of efficiency, reliability, and power density.…”