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Challenges in the Z-Class Compatible Inductive Power Transfer System Considering the Wide Varying Range of the Coupling Coefficient

This paper investigates the design of the Z-class compatible inductive power transfer system defined by the SAE-J2954 standard for the light-duty plug-in and electric vehicles. There are mainly three challenges in the practical applications. First, the variation of misalignment and airgap distance can induce a wide varying range of the coupling coefficient, which significantly affects the system power. Second, the tuning of the system power requires a wide range of the input dc voltage, which induces more difficulties in the power electronics converter design. Third, the wide range of the operation voltages, including the input dc voltage and the output battery voltage, can induce the discontinuous current mode, which causes significant waveform distortion and harmonics that affect the system efficiency and stability. A prototype is implemented to validate the analysis, and the experiments achieve 2.75 kW power transfer with 92.7% dc-dc efficiency at 170mm ground clearance. When the clearance increases to 250mm with 75mm x-direction and 100mm y-direction misalignment, it still maintains 1.16 kW power with 89.7% efficiency.