Self-Oscillating Contactless Resonant Converter With Phase Detection Contactless Current Transformer

In this paper, a self-oscillating control strategy is proposed for a series-series type contactless resonant converter (CRC). By detecting the secondary current phase of a CRC to control the inverter, better output controllability, dynamic response, and self-adaptability can be achieved. While the realization of self-oscillating control strategy depends on phase detection of secondary current. To provide a passive solution, a current transformer with shorted secondary, called phase detection contactless current transformer (PDCCT) is proposed. The proposed PDCCT can detect the current phase from the secondary side of a CRC and feedback to the primary side rapidly and accurately despite the changes in air gap. To guarantee the accuracy of self-oscillating control strategy, the time delay in control circuitry is studied and compensated. A 60-W self-oscillating CRC with PDCCT is then fabricated to demonstrate the validity of both PDCCT and self-oscillating control strategy. Besides, a testing circuit is designed to emulate the changes in converter parameters, and the dynamic performance shows that self-oscillating control strategy can respond to parameter changes in a switching period.