Load Effect Analysis and Maximum Power Transfer Tracking of CPT System

Owing to the flexibility of coupling structure, low standing losses and low Electromagnetic Interference (EMI), capacitive power transfer (CPT) has drawn much attention as one of the new wireless power transfer (WPT) technologies. However, to date, the load effect on the system performance has not been analyzed comprehensively, and the CPT system is usually fully tuned (tank network resonant frequency fully tuned to the fundamental components of the nominal switching frequency), which is challenging to maintain practically. Based on these considerations, this paper first provides a detailed analysis of how the load can affect the performance of a CPT system. An optimal load resistance is shown to exist for a CPT system with a non-fully/partially tuned LCC tank (tank network resonant frequency is designed to be lower than the fundamental components of the switching frequency). By dynamically transforming the load to its optimal value, the system can transfer maximum power to the load while maintaining zero voltage switching (ZVS) operation. Then, a controlled buck-boost converter based on perturbation and observation algorithm is introduced to the system to obtain the optimal equivalent resistance against the actual load variations via tracking the maximum power transfer point. The final prototype has demonstrated that a maximum power of 10 W is obtained, with an end-to-end power efficiency of about 70% over a wide range of load variations from $5~\Omega $ to 1 $\text{k}\Omega $ .