Modeling and Analysis of Polarized Couplers Under Misalignment for Electric Vehicle Wireless Charging Systems

Wireless power transfer (WPT) is becoming popular increasingly in stationary electric vehicle (EV) charging. Various coil structures were proposed to improve the coupling characteristics, and polarized couplers have been proven to have better performance. Considering the varying spatial scales of transmitting and receiving, coils will alter the mutual inductance, further affecting the output power and transmission efficiency; therefore, it is crucial to calculate the mutual inductance of polarized couplers with variable offset for WPT system design. However, given the complex structure and the various excitation conditions of polarized couplers, the solving process based on the finite element model is time-consuming and resource intensive, therefore it is necessary to develop analytical models of mutual inductance for polarized couplers under misalignment. In this paper, the analytical models of the two commonly used polarized couplers with a Double-D polarized coil (DDP) or a Bipolar polarized coil (BP) on both sides under misalignment along any direction under different excitation conditions are proposed based on dual Fourier transformation. The mutual inductance characteristics of the two polarized couplers under misalignment can be investigated based on the proposed analytical models and finite element models, respectively. The results show that the mutual inductance of BP-BP coupler with in-phase current excitation mode is greater and more stable, and the method based on the analytical model is timesaving. Finally, the prototype of the WPT system with the two polarized couplers has been built, and experiments have also been carried out to verify the accuracy of the analytical models.