Power Device Bonding Line In Buck Converter Research On Condition Monitoring Method

DC/DC converters are widely used in many high-tech industrial fields at home and abroad,such as aerospace,Marine,electric vehicles and renewable energy power systems.The power device plays an important role in power conversion and control in DC/DC converter.Data show that the power device is one of the components with the highest frequency of failure in the converter system,so its high reliability is an important condition to ensure efficient and stable operation of DC/DC converter.At the same time,the Insulated Gate Bipolar Transistor（IGBT）with its excellent and efficient switching characteristics and low switching loss,the insulated gate bipolar transistor（IGBT）,It is the most widely used and reliable full-control power device in the power switching converter control circuit structure.During the operation of the converter,the IGBT module circuit will continue to suffer from internal and external thermal stress,which will cause irreversible fatigue damage,and eventually lead to bonding line loss and solder layer aging package reliability problems.In order to avoid the huge loss caused by the aging failure of power components,it is of great significance to monitor the health status of power components,discover and replace the aging failure of power components in time,and improve the reliability of the converter.As one of the typical DC/DC converters,it is very necessary to study the aging monitoring method of the power device bond line.In this paper,according to the system model and topological structure characteristics of Buck converter,a monitoring method of power device bond line aging based on duty ratio and a monitoring method of power device bond line aging based on terminal voltage calculation of saturation on-voltage drop are proposed respectively.The main work is as follows:（1）The aging failure mechanism of the IGBT module bond line and the components of the equivalent parasitic resistance are analyzed,and the expression of the emitter pole pressure drop of the IGBT module is obtained.According to the expression of emitter voltage drop,the emitter saturation on-off voltage drop VCE and sat can be used as the characteristic values for monitoring the aging state of the bond line.The physical model of the non-ideal Buck converter is established and the relation between the parasitic resistance of the power device and the duty cycle signal of the system is obtained.The structure of Buck converter closed-loop control system and the working principle of DSP controller are analyzed.（2）A method is proposed to monitor the aging state of the bond line of power devices by identifying the change of the output duty ratio in the closed-loop control mode.Firstly,the influence mechanism of power device aging on its internal parasitic parameters is analyzed.When the bonding line is aging,its equivalent impedance increases,resulting in the change of inductance current in the loop.Secondly,in the open-loop control mode,the aging state of the power components can be monitored by the change of inductance current in the Buck converter.However,in the closed-loop mode,the Buck converter can not directly monitor the aging state of the power device with the change of current,but can obtain the change of current after aging of the power device by monitoring the change of duty ratio,and then identify the aging degree of the power device.Finally,the experiment verifies that the current variation of the aging power device in the open-loop state is consistent with that obtained by the duty ratio in the closed-loop state,which indicates the feasibility of the proposed method.（3）The aging monitoring method of bond line based on terminal voltage calculation of emitter saturation on-off voltage drop is proposed.Firstly,the calculation formula of collector saturation on-voltage drop V_CE,satand sat is obtained by IGBT model.The coupling relationship between V_CE,sat,sat and chip junction temperature is analyzed.The coupling effect of chip junction temperature is removed by using protection in specific collector current environment.Secondly,according to the characteristics of the topological structure of Buck converter,the input voltage and endpoint voltage are used to calculate the V_CE,satand sat of the power device,so as to identify the aging state of the bond line of the power device.Finally,an experimental platform was set up to simulate bonding line aging by increasing the parasitic resistance of the emitter to verify the feasibility of this method.