Negative Conductance Modeling and Stability Analysis of High-Frequency Oscillation Based on Cascode GaN Circuits

Abstract

GaN devices are developed rapidly in recent years, which makes it possible to produce power electronic converters with higher efficiency and higher power density. However, with the circuit parasitic parameters, large di/dt and dv/dt caused by the GaN devices' extremely fast switching can easily lead to voltage and current oscillations. This problem affects circuit stabilities and increases the difficulty of application with GaN devices. In this paper, oscillation problems will be explained by oscillator theory and an oscillation suppression method will be introduced. All the researches here are based on Cascode GaN devices. Considering all circuit parasitic parameters, negative conductance models of the GaN devices in the switching-on and switching-off process have been established according to oscillation mechanism analysis. And stability criteria of the GaN-based circuit have been derived which can well predict that whether the oscillations will happen and how will the oscillations last. Besides, the suppression method that placing a ferrite bead in power loop in series has been introduced based on the established model. Selection method is provided quantitively and suppression effect can be calculated. All the achievements of this research have been verified by simulations and experiments.

Keywords

• GaN
• stability criteria
• modeling
• high-frequency oscillation
• oscillation suppression