Design and Implementation of Wireless Power Transfer Systems With Improved Capacitor Error Tolerance
Yi Wang, Zhongping Yang, Fei Lin
Abstract
Owing to manufacturing defects and aging, compensation capacitors are inevitably prone to errors, leading to the performance deprecation in a wireless power transfer (WPT) system. This article focuses on the sensitivity analysis of system characteristics to capacitor errors and design methods to improve detuning tolerance. First, the output voltage, power factor, transfer efficiency, and capacitor voltages are derived for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> -S compensated WPT systems. The worst-case scenarios (i.e., the maximum and minimum values of these indicators) are used to evaluate the effect of capacitor errors. They are calculated under detuned conditions with different inverter quality factors, load quality factors, and the ratios of the primary coil's self-inductance to the compensation inductance. Then, the design constraints are summarized to meet the system requirements considering ±10% capacitor errors. A simplified and easy-to-follow system design process is proposed and a 22-kW wireless charger for an electric bus is designed. Experimental results show that, compared with the traditional design, the change ratio of the output voltage of the proposed design is reduced from between −40.9% and 13.1% to between −21.5% and 12.4%. The lowest power factor is increased from 0.64 to 0.78, and the maximum drop in transfer efficiency is reduced from 9.9 to 5.9%.