Optimized Duty Cycle Control to Reduce the Reverse Conduction Loss of GaN HEMTs in a Very High Frequency Class Φ2 inverter

This paper presents an optimized duty cycle control to reduce the reverse conduction loss of GaN HEMTs in very high frequency (VHF) class Φ2 inverter. VHF class Φ2 inverters are widely used in wireless power transfer systems and DC-DC power converters due to its high power density and fast dynamic response. However, the overall efficiency can be easily degraded by the reverse conduction loss of GaN HEMTs, which is high in conventional fixed duty cycle control. To address this issue, this paper proposes an optimized duty cycle control to reduce the reverse conduction time and loss. Firstly, current of the power switch is derived by resolving the analytical expression of inductor current. Secondly, by exploring the spectrum of switching current and the switching node impedance characteristics, the drain voltage under different load resistance is derived. Through the derived drain voltage, the optimized duty cycle under different load is calculated, which significantly reduces the reverse conduction time. Thirdly, the optimized duty cycle control is realized through an analog circuit. By measuring the average input current, the load resistance is estimated and the duty cycle is adjusted to the optimized value accordingly. Finally, a 27.12MHz class Φ
₂
inverter prototype is built to verify the proposed control strategy. Experimental results show that the proposed strategy improves the power efficiency over the whole load range, and achieves a peak efficiency of 93.6% at full load.