Comprehensive Analysis and Wide Range Operation of ZVS and Quasi-ZPA in Wireless Power Transfer System

To reduce switching loss and minimize backflow power, zero voltage switching (ZVS) and zero phase angle (ZPA) technology are normally implemented in wireless power transfer (WPT) systems. However, traditional concepts of ZPA and ZVS are usually independent and misleading, lacking clear and strict theoretical explanations. More importantly, the design of ZPA circuit parameters is usually based on fundamental harmonic analysis in the frequency domain. To tackle this problem, first, comprehensive analysis of the relationships among ZVS, ZPA, and quasi-ZPA (time-domain) are discussed in detail. Second, an impedance factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula> based on multiharmonic analysis is proposed to evaluate the input current characteristics of WPT systems under different topologies and load conditions. Third, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula> is associated with quasi-ZPA, and the boundary value <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta _{\mathrm{th}}$</tex-math></inline-formula> required to achieve quasi-ZPA is defined. Finally, an experimental prototype with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1 \,\mathrm{\text{kW}}/85 \,\mathrm{\text{kHz}}$</tex-math></inline-formula> is built to verify the analysis. Experimental results demonstrate that the impedance factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\delta$</tex-math></inline-formula> proposed is consistent with the theoretical analysis regarding its influence on the input current waveform characteristics of the WPT system. In addition, phase shift control enables constant power output and ZVS across a wide load range.