Study On Model Analysis And Oscillation Suppression Of GaN HEMT Devices

Gallium nitride high electron mobility transistor(GaN HEMT)devices have been widely used in consumer electronics,aerospace,5G communications and other fields due to their advantages of high switching frequency,low switching loss,and fast switching speed.However,serious switching oscillation problems may occur in the above-mentioned applications,which will threaten the safe and reliable operation of the system.At present,there are only some qualitative oscillation suppression methods,and it is difficult to guarantee the oscillation suppression effect.In response to the above problems,this article starts with the analytical model of the GaN HEMT devices,and on the basis of clarifying the mechanism and negative effects of the oscillation,has carried out a systematic research on the oscillation suppression method,achieved quantitative suppression and ensured the effect of oscillation suppression.(1)In terms of the analytical model of the GaN HEMT devices,this article has determined all the parasitic parameters through curve fitting and parameter extraction,and established for the first time the equivalent circuit model of the turn-on and turn-off transitions of the GaN HEMT devices including the reverse conduction model.The accurate switching analytical model of the GaN HEMT devices is obtained through the numerical solution of the state equation.Simulation and experimental results show that during the turn-on and turn-off transitions,the switching drain-source voltage and drain current waveforms obtained according to the analytical model are in good agreement with the simulation and experimental results.On the one hand,an accurate switching analysis model can be used for loss analysis and to explore the effects of different circuit parameter changes on switching characteristics and switching losses,which will achieve the purpose of improving conversion efficiency.On the other hand,it also lays the foundation for establishing the switching high-frequency oscillation model to achieve effective suppression.(2)In terms of the false triggering oscillation of the gate-source voltage of the GaN HEMT devices,due to the high dv/dt and di/dt after the device is turned off,the gate-source voltage will always exceed the threshold voltage under certain conditions,the false triggering oscillation will occur.If this oscillation is not effectively suppressed,it will cause serious consequences including additional power loss and even device damage.For this reason,this article establishes a high-frequency equivalent model of false triggering oscillation of GaN HEMT devices,and proposes to add a passive snubber circuit between the gate and source terminals to suppress it.Through the analysis of the root locus of the system pole,the design region of the passive snubber circuit parameters is quantitatively described,and the false triggering oscillation is better suppressed.Simulation and experimental results show that in the determined design region,the system damping ratio can be ensured to be greater than 0.4,which has a shorter oscillation duration and smaller amplitude than outside the design region,thus proves the accuracy of the design region.The above-mentioned quantitative design method of passive snubber circuit makes up for the shortcoming that the existing method can only be applied to the third-order and below systems,and provides a solution for the oscillation suppression of high-order systems.(3)In terms of the sustained oscillation of the drain-source voltage of GaN HEMT devices,due to the reverse conduction characteristics of GaN HEMT devices different from Si and Si C devices,when the gate-source voltage does not exceed the threshold voltage,the drain-source voltage may occur sustained oscillation under certain conditions.This will cause serious voltage and current overshoots,electromagnetic interference and other negative effects.To this end,this article establishes a high-frequency equivalent model of sustained oscillation of GaN HEMT devices,and proposes to add a passive snubber circuit between the drain and source terminals to suppress this oscillation.By analyzing the root locus of the characteristic equation and the zero point equation,the dipole elimination method is adopted to eliminate the influence of one pair of dominant poles.Thus,the design region of passive snubber circuit parameters is quantitatively described,which achieves well and full suppression of sustained oscillation.In addition,the influence of passive snubber circuit on switching speed and switching loss is also explored.Simulation and experimental results show that in the determined well design region,the system damping ratio can be ensured to be greater than 0.4,and the oscillation can be well suppressed.In the full suppression region,the system damping ratio can be ensured to be equal to 1,and the sustained oscillation can be fully eliminated.By reasonably selecting the magnitude of the passive snubber circuit parameters in the design region,the switching speed and switching loss will hardly be affected.The above analysis and design ideas that combine the characteristics of the pole root locus and eliminate the influence of the dominant pole through the dipole are very enlightening for the oscillation suppression of the high-order system.(4)Based on the previous research on the analytical model and oscillation suppression of GaN HEMT devices,combined with existing literature,we hope to form a comprehensive and profound understanding of switching oscillations of wide bandgap devices,and provide a reference for oscillation suppression in practical engineering applications.For this reason,this article has conducted a comprehensive and systematic analysis of the possible switching oscillation types of wide bandgap devices,the generation mechanism of these oscillations,the possible negative effects,and the influence of different parasitic parameters on switching oscillations.On this basis,a qualitative comparative analysis of the existing oscillation suppression methods is carried out.The results show that quantitative oscillation suppression method of the proposed passive snubber circuit is simple to implement,low in cost,and can guarantee the effect of oscillation suppression.Therefore,it has good engineering practical value.