A Novel Method to Calculate the Efficiency of a Wireless Power Transfer System Using Modified Ferreira’s/Dowell’s Method

Abstract

Inductive power transfer has gained significant interest by researchers over the last decade. The technology is showing great potential for inclusion in home appliances, industrial devices, biomedical implants and automotive vehicles. The efficiency of a wireless power transfer system (WPTS) is of utmost interest and is proportional to the coupling factor and quality factor of the transmitter and receiver coils used. Existing methods to calculate the efficiency assume fundamental harmonic approximation (FHA) at the resonant frequency, use SPICE software, and rely on experimental results. The AC resistance of the coils increase exponentially with frequency and is a vital parameter for the analytical calculation of the efficiency. The best-known methods to calculate the AC losses of the coils are the Ferreira's method, Dowell's method, or a modified version of these methods. Approaches involving electromagnetic field solvers require high computational time, and are not practical if the wire consists of thousands of twisted strands. Due to that, the focus of this paper would be on 1D analytical calculations. Experimental results show that Dowell's and Ferreira's method overestimate the AC losses. Moreover, these methods are unable to approximate the AC resistance of litz wire accurately at high frequencies. Error could exceed 100%. This paper proposes a modified Ferreira's method to calculate the AC resistance of WPTS coils and a novel method to calculate the efficiency of a WPTS at any operational frequency considering higher order harmonics. Lastly, SiC and GaN converters are compared for an efficiency check for high power applications.