Self-Oscillating Tuning Loops for Series Resonant Inductive Power Transfer Systems

This paper presents power and frequency tuning loops based on fundamental harmonic operation (FHO) and third harmonic operation (THO) for inductive power transfer (IPT) systems. THO is an effective solution for applications requiring high-frequency power supply with low voltage gains, e.g., low-voltage contactless battery chargers. Moreover, it can reduce the switching losses and increase the net efficiency of IPT systems in light-load conditions. Compared to conventional methods, such as phase-locked-loop (PLL) circuits, the proposed methods are less affected by misalignments and instantly track the resonant frequency. Hence, they can be utilized in self-switched capacitor and variable coupling applications. In addition, the new tuning systems can switch between THO and FHO modes for different loadings, voltage gains, and couplings conditions, e.g., dynamic powering of different moving pickups. To show the performance of the new tuning loops, laboratory prototypes with switching frequency of 20-50 kHz are implemented based on half-bridge and full-bridge inverters.