Abstract
Wireless power transfer (WPT) based on magnetic resonant coupling is a promising technology in many industrial applications. Efficiency of the WPT system usually depends on the tilt angle of the transmitter or the receiver coil. This work analyzes the effect of the tilt angle on the efficiency of the WPT system with horizontal misalignment. The mutual inductance between two coils located at arbitrary positions with tilt angles is calculated using a numerical analysis based on the Neumann formula. The efficiency of the WPT system with a tilted coil is extracted using an equivalent circuit model with extracted mutual inductance. By analyzing the results, we propose an optimal tilt angle to maximize the efficiency of the WPT system. The best angle to maximize the efficiency depends on the radii of the two coils and their relative position. The calculated efficiencies versus the tilt angle for various WPT cases, which change the radius of RX (r2 =0.075 m, 0.1 m, 0.15 m) and the horizontal distance (y=0 m, 0.05 m, 0.1 m), are compared with the experimental results. The analytically extracted efficiencies and the extracted optimal tilt angles agree well with those of the experimental results.
I. INTRODUCTION
Wireless power transfer (WPT) based on the magnetic resonant coupling scheme has recently become widely used in many applications, such as electric vehicles, robotics, and medical devices [1, 2]. The WPT using magnetic resonant coupling can improve the power transfer efficiency (PTE) or extend the service range compared with inductively coupled systems. To improve the PTE, researchers have used various methods, such as impedance matching [3, 4], adjusting the coupling among multiple transmitters (TXs) or multiple receivers (RXs) [5], and applying the optimum condition of the values of phase difference and amplitude ratio between two adjacent TXs [6], among others.
IV. CONCLUSION
We analyze the effect of the tilt angle of the coil on the PTE of the WPT system. Based on our analysis results, the PTE of a WPT with two circular coils can be optimized by changing the tilt angle, relative position, and radii of coils. To archive the optimized PTE, we propose a method to calculate the mutual inductance between the two coils with the tilt angle located at an arbitrary position in a 3D coordinate through the Neumann equation. Using the extracted mutual inductance and the equivalent circuit model of the WPT system, the coupling coefficient and the PTE depending on the tilt angle are extracted. We propose an analytical scheme to extract the optimal tilt angle that maximizes efficiency. To demonstrate our proposed theoretical method, we design experiments using a WPT with two circular coils. By changing the position, radius, and the tilt angle of the RX coils, we compare the transmission efficiency of the different cases. The suggested analysis effectively predicts the optimum tilt angle of the RX coil and the PTE for the various cases.
