Modeling and Analysis of AC Output Power Factor for Wireless Chargers in Electric Vehicles

This paper presents a general mathematical expression and characteristic analysis of the output power factor before rectification on the receiver side for wireless chargers in electric vehicles. This power factor is usually regarded as unity (i.e., the ac output voltage is in phase with the current), based on fundamental harmonic approximation. However, the default unity power factor assumption is not accurate for output power derivation even at resonance frequency. This study explores not only output power factor characteristics for different frequencies or power levels, but also the phase relationships of the input and output ac voltages. The continuous conduction mode and discontinuous conduction mode are both analyzed. An integrated LCC compensation topology is selected as the research object, and its analysis process can be readily extended to other common topologies. Furthermore, this study is beneficial for the implementation of some control strategies requiring precise power computation/estimation, e.g., feedforward control or model prediction control. Finally, a comparison of numerical and experimental results with various misalignment cases validates correctness of the proposed theoretical derivation and analysis methodology.