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A novel wire bonded GaN rectifier for high-power wireless power transfer (WPT) applications is proposed. The low breakdown voltage in silicon Schottky diodes limits the high-power operations of microwave rectifier. The proposed microwave rectifier consists of a high breakdown voltage GaN rectifying element for high-power operation and a novel low loss impedance matching technique for high efficiency performance. Wire bonding method is adopted to provide electrical connection between GaN chip and board which induces undesirable inductance. In order to realize high efficiency performance, an impedance matching network is proposed to exploit the unavoidable inductance along with a single shunt capacitor, resulting in a low loss matching circuit to achieve a compact high-power rectifier. The fabricated GaN rectifier exhibits a good performance in the high-power region and can withstand up to 39 dBm input power before reaching the breakdown limit at the operating frequency of 0.915 GHz and load resistance of 100 Ω. It has a compact size and exhibits high efficiency performance in high-power region (achieved a maximum efficiency of 61.2% at 39 dBm), making it suitable for high-power applications like future unmanned intelligent devices and WPT in space applications.

This work presents design, fabrication, and analysis of GaN Schottky barrier diodes with multi-finger structure on the silicon substrate using various layout parameters, aiming for RF energy harvesting applications. The measured results demonstrate a low turn-on voltage (Von) and a high breakdown voltage (VBK) of 0.56 V and 47 V, respectively. A high cut-off frequency (fc) of 360.9 GHz under reverse bias of -10 V is also obtained for a two-finger device with each finger of W = 12.5 μm and L = 0.2 μm.

In a doubly-fed induction generator (DFIG) wind turbine (WT), large thermal and mechanical oscillations occur around synchronous speed due to the nearly zero-frequency current circulating between rotor windings and rotor-side converter (RSC). A switching frequency dynamic control technique is proposed in this paper to overcome the problem. The basic idea is to dynamically reduce the switching frequency during operation so that both the switching losses and dead-time effect of RSC can be reduced around synchronous speed. According to the characteristic that high-frequency pulse width modulation (PWM) harmonics in DFIG decrease significantly with rotor slip, there would be a new space for switching frequency reduction especially around synchronous speed. The reduced of switching frequency is actually determined by a tradeoff between the increase of both the stator current PWM harmonics and speed PWM ripples and the decrease of insulated-gate bipolar transistor temperature. Compared with the conventional technique with constant switching frequency, the new technique can effectively improve the system performance around synchronous speed including not only better thermal behavior and efficiency of RSC but also smaller current total harmonics and speed total ripples in generator. To clarify the method, first, the effects of switching frequency reduction on a DFIG WT system are investigated. Second, the criteria, control scheme, and procedure of the method are presented. Finally, experimental and simulation studies were carried out, and the results validate its feasibility and effectiveness.