Analysis and Introduction of Effective Permeability with Additional Air-Gaps on Wireless Power Transfer Coils for Electric Vehicle Based on SAE J2954 Recommended Practice

Abstract

The wireless power transfer (WPT) method for electric vehicles (EVs) is becoming more popular, and to ensure the interoperability of WPT systems, the Society of Automotive Engineers (SAE) established the J2954 recommended practice (RP). It includes powering frequency, electrical parameters, specifications, testing procedures, and other contents for EV WPT. Specifically, it describes the ranges of self-inductances of the transmitting coil, the receiving coil, and coupling coefficient (k), as well as the impedance matching values of the WPT system. Following the electrical parameters listed in SAE J2954 RP is crucial to ensure the EV wireless charging system is interoperable. This paper introduces a method for adjusting the effective permeability of the ferrite blocks in the standard model, to tune the self-inductance of the coils as well as the coupling coefficient. To guarantee the given values of the self-inductance of the coil and coupling coefficient matched those in the standard, we slightly modified the air-gap between the ferrite tiles in a specific region. Based on this method, it was possible to successfully tune the self-inductance of the transmitting coil and receiving coil as well as the coupling coefficient. The proposed method was verified by simulation and experimental measurements.

Design Considerations for Adding Series Inductors to Reduce Electromagnetic Field Interference in an Over-Coupled WPT System

“…In most cases, the load resistance is much larger than that of the Rx coil, so the Rx coil should be included in the load resistance (R + R ≃ R ). Based on this assumption, the input impedance of the WPT system with the SS topology viewed from the power source is as shown in Equation (2) under the conditions of Equations ( 3) and (4).…”

“…The solution in Equation ( 5) is the same as in Equations ( 6) and ( 7) under the condition of Equation ( 8) if the values of electrical constants on Tx and Rx sides are identical [20]. In the process of calculating the frequency with the reactance component of Equation (2) as zero, Equation ( 6) is the solution to make all reactance on the Tx and Rx sides 0, so it is not related to the resistance values of the coils. However, the solutions in Equation ( 7) depend on the resistance of coils, load resistance, and coupling coefficient of the coil.…”

“…Wireless power transfer (WPT) systems are good candidates to replace conventional wired power transfer methods in the future, because of their convenience and safety [1][2][3]. WPT systems have already been commercialized and applied to mobile applications, and an international standard has been established [4][5][6].…”

“…WPT systems have already been commercialized and applied to mobile applications, and an international standard has been established [4][5][6]. Research is also being actively conducted on how to apply a wireless charging system to electric vehicles (EVs), which is the current automobile trend [2,3,7]. The WPT system is not limited to simply transferring power, and a variety of methods to help automation of vehicles, which is another electric vehicle trend, are being studied [7,8].…”

Thin, stretchable, universal wireless power transfer system for electric vehicle charging

“…[20][21][22][23] The distance between the vehicle's chassis and ground is long, resulting in the leakage magnetic ux and low charging efficient, and the different distances between the chassis of different vehicles and the ground cause unstable charging efficient. [24][25][26] In addition, it is difficult for most drivers to park at the accurate location to satisfy a good alignment of the two coils, and hence, this human factor decrease the charging efficiency. [27][28][29] Moreover, some debris around the charging pad such as metal objects, cigarette packs, and gum wrappers could result in lower charging efficiency and even re accidents due to eddy current.…”