In inductive power transfer (IPT) systems for electric vehicle applications, the coupling coefficient k and self-inductances of the pads can vary depending on the misalignment and vertical distance due to the presence of loosely coupled pads. Furthermore, the operating frequencies of IPT systems are restricted by a Society of Automotive Engineers standard. These frequencies lead to increases in volt-ampere rating and switching losses. Therefore, this paper proposes a control method for operation in a zero voltage switching region close to the zero phase angle frequency for a low volt-ampere rating considering k and the self-inductance variation in a limited operating frequency range. A mathematical analysis is performed, and the critical coupling coefficients of the proposed control are derived. Simulation and experimental results using a 3.3 kW IPT prototype are presented so as to verify the numerical analysis.
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