Research on Impedance Boundary and Tolerance Zone for Improving Wireless Charging Interoperability Evaluation of Electric Vehicles

The impedance-based interoperability evaluation is a commonly used testing method to guarantee interconnection and interoperability among different wireless charging devices. Its advantage lies in using reference devices to avoid extensive cross testing. However, the manufacturing tolerances and the parameter drift of the reference devices often result in deviations of the tested values from the standard, increasing misjudgment rates. This incurs in the need of determining boundaries and tolerance zones to characterize the uncertainty of test results, which still lacks clear methods. To solve this problem, this letter introduces a characterization model for the correlation between port impedance and interoperability according to volt-ampere requirements for coils and power electronics. Then, a method for determining tolerance zones through error transfer functions is proposed. Finally, the effectiveness of the proposed tolerance zones in identifying the uncertainty propagation from parameter drift to test results is verified by the designed experiment. Given a manufacturing tolerance or parameter drift of +/- 2%, the interoperability evaluation indicated by the proposed tolerance zones can provide a more precise classification assessment for 20% of interoperable devices.