Soft-Switching and Efficient Power Transfer in Capacitive Wireless Systems with LCLC Compensation Networks

This study delineates the conditions for soft-switching in capacitively-coupled resonant converters that are compensated with LCLC matching networks. Such converters' setups are extremely popular in wireless capacitive power transfer (CPT) technology. The detailed analysis explores the intricate relationships between the parameters, operating conditions, and transfer characteristics. It reveals that by design of the compensation networks' parameters according to the highest expected coupling capacitance, then zero-voltage switching (ZVS) conditions are achieved over the entire operation range. The results of the analysis further outline the necessary conditions for zero-current switching (ZCS) at turn off. Consequently, the system maintains soft-switching both at turn on and turn off, for all switches. This provides a significant potential enhancement of the power transfer and processing efficiency, in particular for applications of wireless energy where the operating frequency is very high. The theoretical analysis and predictions have been verified by simulations and experimentally. The simulation platform incorporates a simple and flexible cross-coupled model, also developed in this study, which is used to evaluate the results under various conditions. The experiments have been carried out on a LCLC capacitive-based WPT prototype operated in the MHz range, and examined through several air-gaps up to 120 mm. An excellent agreement has been obtained between the theoretical work, simulations and the experimental evidence.