부산대학교 도서관

High-power (>50W) and high-efficiency (>90%) wireless-power-transfer (WPT) systems are becoming in demand for portable electronic applications. In Fig. 8.2.1, power efficiency and/or output power specifications in prior-art designs are much below the expected requirements [1-5]. Frequency tuning in [1,2] is simple, but the switching frequency (f SW ) deviates from 6.78MHz. Capacitor tuning [3,5] is the most intuitive approach, but the capacitor matrix occupies a large area, and the dynamically tuned compensation capacitor bank is limited by the digital-control resolution and compensation accuracy. In addition, the duty-cycle control in [4] leads to an unregulated output voltage at the RX side. Existing impedance-matching techniques for reducing power loss are not applicable to high-power impedance matching of a GaN-based WPT system in the case of timevariable charging distance, loading, operation voltage, and temperature variations that induce a wide range of inductive or capacitive loading effects. Inductive loading degrades the efficiency by 51% in a GaN power switch and induces serious coupling effects to the gate of the GaN device due to the hard-switching (HS) power loss. Likewise, capacitive loading results in the efficiency degradation of 14% due to the body-diode conduction (BDC) power loss. Such large dissipation easily breakdowns a GaN device and even seriously damages the wPt system, especially when transmitting high-power. Therefore, simultaneously achieving both (1) the minimized HS and BDC power loss by efficient impedance matching and (2) highly reliable operation of a GaN device over a wide range of loading effects is in urgent demand for high-power and high-efficiency WPT systems.