Study On Health Assessment Based On Magnetic Flux Density For Multi-chips Parallel IGBT Module

Power semiconductor devices are the key but most vulnerable component in the fields of new energy generation and grid connection,flexible AC/DC power transmission,electric vehicles and charging devices,electric traction of rail transit,etc.,their operation condition monitoring and health status evaluation are of great significance to reduce the whole life cycle cost and improve the overall performance of the system.With the increasing demand for power converters in high-voltage and high-current applications,the IGBT-based semiconductor devices are developing in the direction of large-capacity and standard modularization,and power density requirements are being met in the form of multi-chips parallel modules.Due to the complex spatial structure of the multi-chips parallel module,there are electrothermal characteristics such as uneven current distribution and uneven temperature distribution,resulting in uneven aging.Since the parallel chips are connected to the same terminal,the condition monitoring method based on the electrical and thermal characteristics of the module ends cannot the uneven aging inside the module,at the same time,the aging failure of some parallel chips in the module has a nonlinear relationship with the overall aging failure of the module.Therefore,the condition monitoring and health assessment of multi-chips parallel IGBT modules are facing more challenges.Focusing on the evaluation of the uneven aging of multi-chips parallel modules,this thesis takes the most widely used multi-chips parallel IGBT modules as the research object,based on the multi-physics field finite element simulation,combined with the failure mechanism of power modules,the degradation of electro-thermal-magnetic characteristics parameters of multi-chips parallel IGBT modules during the aging process are studied,and the suitable aging state monitoring parameter for multi-chips parallel IGBT module is selected,and the health assessment model is established for the two main failure modes of bond wires lift-off and solder layer aging to achieve failure mode identification,quantitative health assessment and aging chip location of the multi-chips parallel IGBT modules.The main contents of this thesis include the following aspects:(1)Based on the steady-state equivalent circuit model of multi-chips parallel IGBT module,the degradation of its electro-thermal-magnetic properties in the aging process is qualitatively analyzed.Based on the multi-physics finite element simulation software COMSOL,a high fidelity electric-thermal-magnetic multi-physics coupling finite element model of multi-chips parallel IGBT module is established,in which the output characteristic curve is used to calculate the equivalent resistance of the IGBT chip and the temperature dependence is taken into account to accurately simulate the IGBT conduction characteristic,and the model excitation and boundary conditions are set up according to the operation condition.The validity of the finite element model is verified by comparing the simulation results with the datasheet and the steady-state experiment results.It provides a research foundation for the study of the degradation of the electro-thermal-magnetic characteristic parameters of the module during the aging failure process.(2)Based on the electro-thermal-magnetic finite element model,the degradation of the electro-thermal-magnetic characteristic parameters of the module during the aging process of bond wires lift-off is analyzed.The sensitivity of different characteristic parameters to the bond wires lift-off is compared,and the characteristic parameter with high sensitivity and easy to monitor is selected as the condition monitoring parameters for uneven aging of multi-chips parallel modules.The results show that the magnetic flux density is more sensitive to bond wires lift-off and is not affected by changes in ambient temperature,at the same time,since the conduction current and magnetic flux density have a linear relationship,the magnetic flux density under different conduction current can be converted to the same current for comparison.Therefore,the health condtion assessment model of the multi-chips parallel IGBT module based on the change of the magnetic flux density is established.According to the mapping relationship between the aging characteristic parameter and the number of bond wires lift-off,the evaluation indicator is determined and the health status interval is divided.The chips with bond wires lift-off are located and and the unreliability of the chip is quantified,and the overall health status of the module is evaluated with the fault tree analysis method.The accuracy of the health condition assessment model is verified by experiments,and the condition monitoring method does not need to change or touch the internal circuit of the module.(3)In view of the aging of the solder layer,the degradation of the electro-thermal magnetic characteristic parameters of the modules during the aging failure process is analyzed.By comparing and analyzing the sensitivity of different characteristic parameters to solder layer aging,it is found that the change of the magnetic flux density is consistent with the change of the chip current,both of them have high sensitivity and are not affected by the change of ambient temperature,while the magnetic flux density is easier to monitor because it does not need to change or touch the circuit inside the module.For uneven aging of chip solder layers,the ratio of magnetic flux density corresponding to the aging chip and the healthy chip can independently quantify the aging degree of the solder layer of the aging chip.Therefore,the health condition assessment model of the multi-chips parallel IGBT module based on the magnetic flux density ratio is established.The aging chip is located according to the change of the magnetic flux density and the unreliability of the chip is quantified by the magnetic flux density ratio,and the overall health status of the module is evaluated with the fault tree analysis method.The accuracy of the health condition assessment model is verified by experiments.Finally,a method for discriminating the aging failure mode based on the change of the total magnetic flux density is proposed to realize the determination of the aging failure mode of the multi-chips parallel IGBT module and the quantitative evaluation of the module health status.