Research On Gallium Nitride Totem-Pole Bridgeless PFC Converter Crosstalk And Harmonic Suppression

Energy saving and carbon reduction is an important trend in the development of electric power conversion systems.System efficiency and power density have become the key issues of electric power conversion systems.The traditional Boost power factor correction(PFC)converter is used to solve the problem of harmonic pollution in the power grid.However,the losses of the rectifier bridge and the boost circuit restrict the further improvement of the system efficiency.Compared with conventional boost PFC converter,the totem-pole bridgeless PFC converter has the advantages of high device utilization and low conduction losses.Since gallium nitride(GaN)power devices have a higher switching speed and lower switching loss,and there is no reverse recovery problem,using the totem-pole bridgeless PFC converter based on GaN devices can effectively improve the efficiency and power density of the system.At present,the totem-pole bridgeless PFC converter based on GaN devices has become a research hotspot,and the dynamic characteristics of GaN devices,reliable driving under high voltage conditions,grid-side current phase shift,and current harmonics suppression of converters need to be further solved.This thesis studies the above key issues and proposes corresponding solutions according to the engineering application requirements.Due to the fast switching speed and low gate-source threshold voltage of the GaN power devices,the bridge-leg crosstalk problem caused by high dv/dt is significant.Therefore,a bridge-leg configuration analytical model considering the nonlinear junction capacitances of GaN device is proposed to investigate the crosstalk problem.The nonlinear junction capacitance model of GaN device is built by curve fitting and parameter extraction.The nonlinear junction capacitances and parasitic parameters are taken into account to improve the accuracy of the model.In order to reduce the complexity of the model,the channel current is ignored and the control transistor is equivalent with the ramp voltage source.Thus,the equivalent circuit diagrams and equivalent equations are constructed,which contain four state variables.Besides,the analytical model is obtained by solving the nonlinear state equation and the influences of circuit parameters on the amplitude and oscillation of crosstalk voltage are revealed.The simulation and experimental results show that the crosstalk voltages obtained by the analytical model are in good agreement with those obtained by the experiments under different conditions.The proposed model can be used to analyze and predict the crosstalk phenomenon in the switching process of GaN devices and lays a foundation for the optimization design of the crosstalk prevention high-speed drive of GaN devices.In order to suppress the crosstalk phenomenon in GaN-based bridge-leg configuration,a negative voltage self-recovery gate drive(NVSRGD)is proposed to suppress the crosstalk based on the analysis of the crosstalk generation mechanism and the sensitivity of driving parameters.In this study,the drive realizes impedance decoupling by separating the turn-on and turn-off circuits.A voltage divider composed of resistors,capacitors,and diodes produces the negative gate-source voltage to suppress positive crosstalk.Besides,the antiparallel diode is used to establish a low-impedance Miller current path from the driver chip to the GaN device.It works together with the self-recovery gate-source voltage to suppress the negative crosstalk,which prevents the negative overstress of the GaN device.The negative voltage level and recovery time of the drive can be determined by matching the parameters of capacitors and resistors.What’s more,no additional negative voltage power supply or active device is required in this method.The results show that the proposed method can reduce the reverse conduction losses in dead time and has the advantages of low cost and simple control.Influenced by the current loop bandwidth and the electromagnetic interference(EMI)filter in the compressor drive system,the GaN totem-pole bridgeless PFC converter has the phenomenon of grid-side current phase shift.By establishing the input admittance model of the GaN totem-pole bridgeless PFC converter considering EMI filter and current loop,the mechanism of grid-side current phase shift caused by the EMI filter and the current loop is revealed.In order to compensate the grid-side current phase shift,a current phase shift compensation strategy based on virtual admittance reshaping of the converter is proposed.According to the extracted input voltage phase,the virtual admittance is constructed by this strategy,and then the equivalent virtual admittance current is obtained by designing the inductor current reference value and the modulation voltage value.The proposed method is less sensitive to the converter parameters,and the effect of phase shift compensation is hardly affected when the differential mode capacitance and PFC inductance vary.The experimental results show that the proposed method can effectively compensate the grid-side current phase shift and solve the problem of power factor decrease caused by EMI filters in GaN totem-pole bridgeless PFC converters.Aiming at the grid-side current harmonics caused by the resonance of differential mode capacitor and inductor of EMI filter in GaN totem-pole bridgeless PFC converters,this thesis proposes an input voltage feedforward active damping based grid-side current harmonic suppression method.Firstly,the current harmonic generation mechanism is revealed via the analysis of the LC resonance characteristics of the system.Based on establishing the converter input admittance model,the non-ideal characteristics of the converter system are taken into account to further improve the accuracy of the model.In order to suppress the current harmonics,a virtual admittance is constructed at the target harmonic frequency,and the system impedance at this frequency is changed.The corresponding input voltage is extracted by a filter,and the equivalent current is obtained according to the virtual admittance,which is then transformed into the converter current reference and the modulating voltage instructions.Thus,active damping is achieved.In addition,the sensitivity of the active damping to load variation conditions is analyzed to realize the accurate matching of virtual admittance.The results show that the harmonic current can be reduced in a wide load range by using the proposed current harmonic suppression method.Finally,a GaN device based half-bridge power module is designed.A prototype of high-efficiency compressor drive system based on the GaN power device is developed and the software architecture of the drive system is designed,the proposed current phase shift compensation and current harmonic suppression digital algorithms are realized in the prototype.The experimental verification is carried out through the air conditioning compressor system.The grid side power quality,dynamic performance,and efficiency of the prototype are tested.The results show that the grid-side power quality of the prototype can satisfy the harmonic standard,and the efficiency is significantly improved.The general performance of the prototype can meet the practical application requirements of the air conditioning compressor load.