Air-Core Resonant Converter Design With Reduced Secondary Reactance and Primary Current for Wide Voltage Range CC/CV and ZVS

This paper proposes an air core, minimum frequency variation, and wide output range resonant converter for lightweight aerial mobility with full zero-voltage switching (ZVS) region. Traditionally, an air-core transformer suffers from low magnetic coupling between primary and secondary windings, thereby increasing resonant current at primary winding. Meanwhile, even if wireless power transfer (WPT) has been successful with air-core magnetics, the parameter design and control strategies of air-core WPT cannot be directly used due to reduced ZVS region, lower power factor, and increased circuit components. Unlike conventional converters which resonate only with leakage inductance, the proposed converter's secondary winding resonates with total self-inductance (which includes both leakage and magnetizing inductances) of air-core transformer. In this way, lower amplitude of primary current is enough to output a given power. The proposed design also achieves a full-range ZVS and exhibits a natural constant-current (CC) characteristic with negligible frequency variation. The air-core magnetic is lightweight, low volume, and resistant to mechanical shock which are required by Aerial Drone. The measured peak efficiency is 96.9%. The output voltage range is 35-120V with 10.5A maximum current across the frequency variation of 380 kHz∼445 kHz.