Identification of Coupling Coefficient and Load Resistance for Control of Wireless Power Transfer Systems

Inductive wireless power transfer has become one of the most important emerging technologies in electric-vehicle applications. Important parameters in such technology are the variable coupling coefficient and equivalent load resistance that depend on the relative position of the coils and the load power, respectively. These parameter values are needed to optimize the system performance. This work proposes a novel method to accurately estimate the values of coupling coefficient and load resistance dynamically without any receiver side measurements. The method is based on measuring the system input impedance seen from the transmitter side. A set of perturbation voltages with different frequencies are injected into the system, and the magnitude of the impedance obtained from measured voltage and current responses is then utilized to estimate the parameter values. The proposed method does not require communication between the transmitter and receiver subsystems, and therefore, the technique is well suited for applications in which the dynamics of the charged object are unknown. The effectiveness of the method is validated by experimental results.

I. Introduction

Employing resonant based inductive wireless power transfer (WPT) systems is an attractive solution in coping with the deficiencies of electric vehicle (EV) cable-based chargers. Thanks to the convenience and safety of the charging process, the accessibility to EV chargers is improved if wireless chargers are exploited. Thus, EV battery size, weight, and cost can be reduced [1].