Output Voltage Range of a Power-Loaded Series-Series Compensated Inductive Wireless Power Transfer Link Operating in Load-Independent Regime

The article proposes an in-depth analysis of a series-series compensated resonant inductive wireless power transfer (WPT) link, operating at load-independent frequency while feeding a power load. It is shown that due to the presence of equivalent series resistances in practical systems, a load-independent operation point is only an approximation. The output voltage is still affected by the load, obtaining minimum and maximum values under rated load and no-load operation, respectively. While the output voltage value under rated load is typically well predicted by the commonly used first-harmonic-approximation-based equivalent circuit, the latter is unsuitable for obtaining the output voltage value under light loading due to nonlinearity caused by the discontinuous conduction mode of the secondary. Time-domain analysis is, therefore, used to accurately predict the WPT output voltage value under zero-load operation and accurately derive the expected WPT output voltage range in the load-independent regime. Simulations and experiments based on a 400-V 1-kW WPT link demonstrate excellent matching, validating the proposed analysis.