Dissertation Defence: Impedance Compensation Methods in Wireless Power Transfer Systems Under Variable Coupling Conditions

Masoud Ahmadi, supervised by Dr. Thomas Johnson and Dr. Loic Markley, will defend their dissertation titled “Impedance Compensation Methods in Wireless Power Transfer Systems Under Variable Coupling Conditions” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering.

An abstract for Masoud Ahmadi’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Please email thomas.johnson@ubc.ca or loic.markley@ubc.ca to receive the Zoom link for this defence.

---

ABSTRACT

Wireless power transfer (WPT) systems use resonators that are carefully matched to
deliver power at a particular transmission distance and operating frequency. Spatial variations in the position of the coupled resonators can significantly alter the input impedance of the system, leading to a direct impact on system efficiency and output power. The objective of this work is to investigate methods that can be used to maintain a constant
input impedance in WPT systems with variable coupling conditions.

The canonical filter theory approach serves as the central method for our investigation. We first highlight the the benefits of canonical filter prototypes in the systematic synthesis of matched inductive (IPT) and capacitive (CPT) power transfer systems with series-series and shunt-shunt resonator topologies.

In the filter theory approach, impedance inverters are used to model the mutual coupling between coupled resonators. Using the inverter model, various impedance compensation methods can be derived. We first explore the application of an adaptive load resistance method in series and shunt CPT and IPT systems. Experimental examples of CPT and IPT systems are provided to explain how modifications to the load resistance can compensate for spatial variations. The results show that except for series IPT systems, the efficacy of the adaptive load method is constrained to a limited distance range.

We then show how an adaptive load can be combined with frequency band switching. The method is then experimentally tested on a CPT system comprised of a class-E inverter, a six-plate CPT transmission link, and a class-E dual rectifier. We also explore adding frequency tracking and adaptive reactive matching elements to the adaptive load method to further extend the range of compensation.

Our final study investigates using the filter theory approach for the synthesis of both singly- and doubly-terminated WPT networks. Since both models have been widely used for WPT systems, our study compares the spatial robustness of singly- and doubly-terminated capacitively-coupled WPT systems to evaluate whether one network has spatial advantages over the other.