Analysis of Inductive Coupling Wireless Power Transfer Systems

Abstract

Inductive coupling wireless power transfer (WPT) technology is gaining increasing popularity in recent years, especially in the field of wireless charging of portable devices. Although the principles behind WPT systems can be explained using well known results from electromagnetic theory, many questions remain regarding the behavior of such systems. This thesis focuses on identifying and analyzing the most important parameters of such system, with emphasis on the coupling factor. Algorithms to calculate the coupling factor and other parameters based on mathematical models of physical phenomena are developed and presented. This algorithm development is also called the analytical approach. For the coupling factor part, a commercial electromagnetic simulation software (Ansys Maxwell) was selected to validate the results obtained from the corresponding algorithm and also evaluate the performance of general-purpose simulators suitable for use in this field. For other WPT system parameters, the algorithm was compared to the results from LTspice. The results obtained from the developed algorithms and simulations are compared to measurement results collected from real transmitter and receiver coils. The results show that both the analytical and simulation approaches can provide estimated parameter values of interest that are close to the empirical values, with percentage error being in the low single digits in most scenarios. However, the developed algorithms are more specialized, and hence easy to implement and computationally more efficient. Consequently, they can be used to generate larger amounts of data for detailed analysis and characterization of WPT systems with relative ease.

Popular Abstract

Wireless charging is a popular new feature for electronic devices such as smartphones and tablets. This technology eliminates the need of carrying multiple power adapters and cables. What’s more, wireless chargers can be embedded in furniture in places such as hotels, restaurants and libraries, and clients need only take out their devices and put them in a designated spot to charge them. The same wireless power transfer (WPT) technology has also been used in other applications such as powering kitchen appliances and charging electric vehicles. Due to the growing interest in this field, it is important to clearly understand the relationship between the different parts of WPT systems.

This thesis project focuses on identifying the most important parameters of WPT systems and studying how such systems respond to changes in any one of these parameters. The emphasis is on the coupling factor, which measures how much of the energy transmitted reaches the receiving device. The thesis work was commissioned by nok9 AB, a Swedish company with headquarters on Malmö that builds and sells the equipment used to verify if wireless chargers comply with the Qi Specification, which is the dominant wireless charging standard today. For this study, relatively simple algorithms are developed analytically based onmathematical models of WPT systems. Commercial simulators are also used for comparison. Simple real systems are also built, and the parameters under study are measured, to validate the analytical and simulation results.

The data collected are presented in graphical forms, to show how WPT systems respond to changes in parameters such as relative position of transmitter and receiver coils, input voltage, as well as receiver and transmitter coil geometries. Comparison with measurements shows that both simulations and the proposed analytical methods achieve acceptable accuracy on most occasions. This is important, because it demonstrates that the relatively simple algorithms of the analytical approach can be successfully used to study WPT systems. They could be used to decrease the cost associated to developing new devices, by reducing the reliance on building prototypes. Furthermore, the algorithms developed in this thesis project can be as accurate as commercial simulation software, and can be faster to run for the cases considered in this study. However, the current version of the algorithm for coil parameter calculation cannot take into account the presence of other objects. Similarly, the algorithm for calculating WPT system behavior assumes a simplified WPT system. These limitations present opportunities for future work in this field.

• author: Amaya Colina, Arianna Ginette
• supervisor: Buon Kiong Lau
• organization: Department of Electrical and Information Technology
• course: EITM01 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: wireless power transfer, inductive coupling, coil parameters, wireless charging
• report number: LU/LTH-EIT 2018-667
• language: English
• id: 8958849
• date added to LUP: 2018-09-17 15:47:56
• date last changed: 2020-03-11 10:21:22