Analytical Modelling and Simulation of a Class-E π2b Resonant Inverter for Inductive Wireless Power Transfer

Abstract

High-efficiency power conversion is critical for Wireless Inductive Power Transfer (IPT) systems, especially at high operating frequencies where switching losses, impedance sensitivity, and load variations strongly affect overall performance. Conventional Class-E inverters typically exhibit efficiency degradation when operating outside their optimum load conditions due to impedance mismatch and the consequent loss of soft-switching. To address these limitations, this study investigates the design and performance analysis of a Class-E π2b resonant transmitter, a topology chosen for its capability to sustain zero voltage switching (ZVS) under appropriately matched conditions. The Class-E 2b transmitter is analytically designed for a 16 W power specification using standard Class-E design equations, and its performance is examined through detailed circuit-level simulations in PSIM. The resonant transmitter is evaluated under two operational scenarios: (i) direct operation without an impedance-matching network, and (ii) operation incorporating a π2b impedance-matching network. This comparative approach enables a controlled assessment of how impedance matching influences efficiency, switching behaviour, and output stability. Simulation results show that the Class-E π2b inverter operating without impedance matching achieves approximately 74% efficiency, primarily due to load-dependent mismatch and partial loss of soft-switching. In contrast, when integrated with a π2b matching network, the transmitter preserves ideal ZVS switching characteristics and delivers stable 16 W at 6.78 MHz ISM (Industrial, Scientific, and Medical) band, achieving a significantly improved overall efficiency of 98.2% when driving a 22 Ω load. These findings demonstrate that the Class-E π2b topology, when complemented with an appropriate impedance-matching network, provides a robust and highly efficient solution for high-frequency inductive wireless power transfer applications.