Abstract
Research and/or Engineering Questions/Objective
This study is aimed at exploration of phase relationships of input and output AC voltages and currents in a wireless power transfer (WPT) system for battery charging in an electric vehicle. The AC output voltage is usually regarded as in phase with current (i.e. power factor equals unit), which however causes imprecise power calculation in some control strategies, e.g., model prediction control or feedforward control. Meanwhile analysis of a new compensation network will be negatively influenced by imprecise phase relationships. Therefore this study is beneficial for improvement of these control strategies and initial design of novel WPT topologies as well.
Methodology
Due to different combinations of three resonant stages including the open stage, negative clamped stage and positive clamped stage, two operation modes, i.e., continuous conduction mode (CCM) and discontinuous conduction mode (DCM) will be both discussed in detail. An equivalent output voltage curve is introduced to decrease the calculation complexity in DCM. The analysis transformation for various common WPT compensation network topologies is provided. MATLAB is employed as a tool for processing and plotting numerical results compared with experimental results, and a 5kW experimental prototype of the WPT system is established for verification of the proposed theoretical derivation.
Results
In the paper, the numerical and experimental results of phase differences between the AC input and output voltages and currents will be presented. Additionally, the experimental results and calculations with/without power factor consideration for the WPT output power are also given. Three cases of X- or Y-misalignments are considered for the measurements of mutual inductances and derivation of voltage and current waveforms. The comparison between the calculations and experimental results will be presented to validate the correctness of the proposed theoretical derivation and relevant analysis.
Limitations of this study
A limitation of this study is the limited experimental power level and operating frequencies of a WPT system for an electric vehicles (EV). Future work will focus on increasing the output power capability and inverter switching frequency (i.e., operating frequency), covering broader application situations of EV battery wireless chargers.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The modeling and analysis in a wide operating frequency range is new for WPT systems since other authors only analyzed the situation at resonance frequency. Meanwhile design of an equivalent output voltage curve is introduced for the first time to decrease calculation complexity in operation modes of the WPT system.
Conclusions
The proposal of the modeling and analysis methodology in this paper contributes new WPT topology design and performance improvement of some advanced control strategies for WPT systems with precise power calculation required. The comparison of experimental and calculated results proves the correctness and validity of the proposed strategy.
Key Words : Phase Relationship; Wireless Power Transfer; Electric Vehicle Research