Analysis and Demonstration of a Dynamic ZVS Angle Control Using a Tuning Capacitor in a Wireless Power Transfer System

In this article, a dynamic zero-voltage switching (ZVS) angle control scheme on the wireless power transfer (WPT) system inverter is proposed by implementing a tuning capacitor. High-frequency (HF) and high-power WPT systems are desired in battery charging applications to reduce the battery charging time. Consequently, the power semiconductor devices are subjected to increased voltage, current, and thermal stresses. In this article, the switching losses in the primary-side inverter of a WPT system are suppressed by realizing the ZVS operation during the battery charging process. A dual-loop control strategy is proposed, which involves traditional phase shift control between the inverter phase legs to maintain constant-current (CC)/constant-voltage (CV) at the output and a tuning capacitor to dynamically tune the ZVS angle. The dynamic tuning of the ZVS angle ensures a minimum reactive power requirement from the input source and, therefore, helps to improve the overall efficiency of the system. Closed-loop simulations of the proposed control strategy are carried out using the piecewise linear electrical circuit simulation (PLECS) simulation software. The proposed control strategy is verified on a 10-W WPT prototype by performing the open-loop experimental validations. The maximum efficiency of the proposed control strategy is found to be ~ 87 % during the CC/CV charging modes. The improvement of ~ 10 % in the dc-dc efficiency is achieved with the proposed ZVS control strategy.