High-Frequency Voltage and Current Sense Circuits for Inductive Power Transfer Systems

This article proposes a voltage sense circuit and a current sense circuit for extracting the fundamental ac voltage and current in variable-frequency inductive power transfer systems. Particularly, the proposed circuits are designed for an electric vehicle (EV) wireless charger. A current source is generated via a high resistance and a current transformer in these two sense circuits, respectively. The main part of both sense circuits uses the "double resonance" and "critical damping" principles to gain a stable voltage gain and a linear phase response in the operating frequency band. The ac output voltage is processed by a rectifier for amplitude measurement and by a comparator for phase detection. Meanwhile, the harmonic components are effectively filtered due to the band-pass property of the sense circuits, hence their impact on the ac output voltage is negligible. The operating principle, parameter design method and parameter sensitivity analysis are discussed in detail. The feasibility of the proposed sense circuits is verified by calculations and experiments. (This article is accompanied by two videos demonstrating the performance of the voltage sense circuit.)