Determination of Compensation Capacitor Considering the Dead-Time Characteristics for ZVS in Wireless Power Transfer System

In the wireless power transfer (WPT) system, the input impedance characteristics change depending on the load and the air gap between the coils. Changes in input impedance affect zero-voltage switching (ZVS) and dead time related to stability, efficiency, and electromagnetic interference. Existing studies lack the dead-time analysis according to operating conditions. In addition, this resulted in unnecessary power dissipation as it cannot determine an appropriate compensation capacitance. Thus, it is important to analyze dead time and determine the compensation capacitance accordingly for ZVS. This article presents a compensation capacitor selection method for ZVS in a WPT system with various operating conditions based on dead-time analysis. The compensation capacitor that should be adjusted is identified, and its value is calculated considering dead time, output power, and efficiency. Therefore, the proposed method can stably implement the WPT system and improve the power and overall system efficiency. A 500-W WPT system is designed to validate the theoretical analysis. The designed WPT system is measured under various coupling coefficients and load conditions. It is confirmed that the proposed method implements ZVS under various conditions of the WPT system. Experiments show that the proposed method improves the overall system efficiency by up to 3.75% and reduces the dead time by 77%.