Sensitivity Analysis of a Polyphase Wireless Power Transfer System Under Off-Nominal Conditions

- Misaligned and/or variable coil air gaps cause coupling coefficient variation in wireless power transfer (WPT) systems, resulting in a decrease in the system's transmitted power and efficiency. This article presents sensitivity analyses of a threephase, Y-Y-connected, series-tuned WPT system in the frequency domain in terms of several different electric vehicle (EV) wireless charging off-nominal conditions (misalignments in Delta x- and Delta y-directions, change of air gap Delta z , and the roll Delta psi, pitch Delta Phi , and yaw Delta Phi angles) as specified in the Society of Automotive Engineers (SAE) J2954 Standard. Coil inductance matrices were obtained by measuring the self- and mutual inductances of the primary and secondary coil phase windings at variable air-gap classes (from 5 to 30 cm) for five different charging positions as identified in SAE J2954. These 6 x 6 inductance matrices were used in sensitivity and Plexim/PLECS simulation analyses. The sensitivity of the WPT system was analyzed analytically using the input impedance and phase angle, voltage gain, current gain, quality factor, and coupling coefficient parameters of the series- tuned WPT system. The results were confirmed experimentally on a 50-kW WPT system.