Efficiency and Power Compatibility Visualization Methodology for Dynamic Wireless Power Transfer

In recent years, wireless power transfer has been attracting attention as a means of improving quality of life. In particular, Wireless Power Transfer to electric vehicles is important as part of efforts to solve environmental problems because it contributes to the widespread adoption of electric vehicles. Since electric vehicles need to be recharged more frequently than conventional gasoline-powered vehicles, there are problems such as charging while parked is not enough to cover a sufficient distance, and there is not enough space to install a lot of charging station. Therefore, wireless power transfer to running electric vehicles (DWPT) is important. In this study, the method, which can visualize the compatibility is proposed. The compatibility is visualized by mapping the transfer power and efficiency corresponding to the positional relationship between the transmitting and receiving coils in a DWPT system. Proposed method can be applied not only to sine waves, but also to square waves, which are closer to the real environment. By using this method changes in those coils’ positions can be taken considered easily when designing a WPT system. The proposed method is demonstrated by experiments.

I. Introduction

Research on Wireless Power Transfer (WPT), which is the transfer of power without cables, is gaining momentum [1]. In particular, WPT for running electric vehicles (DWPT) has advantages such as enabling long-distance driving and reducing the number of charging stations [2] -[9]. However, it is known that in DWPT, the positional relationship between the transmitting and receiving coils constantly changes, which also changes the transfer characteristics. The power transfer characteristics of a WPT can be obtained by some method such as solving the KVL equation based on the equivalent circuit of a WPT [10], but it is difficult to analyze and clearly understand the changing transfer characteristics of a DWPT. To solve this problem, there is research on a method to visualize the compatibility of transmittable power by mapping the magnitude of the power in response to changes in the positional relationship [11],[12]. However, the conventional method can only check the maximum power that can be transferred and does not correspond to the transfer efficiency. Therefore, this study proposes a method to visualize compatibility including efficiency. The compatibility is visualized by mapping the transfer power and efficiency corresponding to the positional relationship between the transmitting and receiving coils in a DWPT system. The proposed method can be applied not only to systems with sine wave inputs, but also to systems with square wave inputs that are similar to real-world environments. Chapter 2 shows the principle of the conventional impedance mapping method that visualizes only power, and Chapter 3 shows the principle of the new impedance mapping method that includes efficiency. In addition, the principle of the square wave input is also presented. Chapter 4 demonstrates the method through experiments, and Chapter 5 presents conclusions.