| As more and more countries put emphasis on energy conservation and environmental protection,the renewable energy industry represented by photovoltaic power generation,wind power generation and EVs has developed rapidly in recent years.Power converter based on power semiconductor module is not only important to the quality of renewable energy power generation and the stability of its connection to the grid,it is also a key component that determines the startup,operation and acceleration performance of EVs.Currently,power converters are designed with an overload capacity of 1.1-1.2 times of the rated capacity.Studies have shown that power converters' lack of overload capacity will seriously affect the grid support capacity of renewable energy power generation and the performance of EVs.The power semiconductor module is therefore essential to the power converter,as its short-term overload capability will directly determine the overload performance of the power converter.This thesis takes multi-chip parallel power modules as the research object,and aims to improve their short-term overload capacity.Relevant theories and methods to improve the overload capability is studied thouroughly,from the aspects of current sharing of the multi-chip power module and the regulation of the power module junction temperature.A novel multi-chip power module current sharing design,active current sharing method and junction temperature control design based on phase change materials is further proposed.The main work of the paper concludes as follows:(1)It is firltly pointed out that the short-term overload capability of the power module is a key factor that determines the performance of the power converter,from the application background of power module.Then,according to domestic and foreign research status,two solutions that can effectively improve the short-term overload capacity of the power module are proposed,which are current sharing and junction temperature regulation method.Finally,the shortcomings of existing research results are elaborated,and the research contents and goals of this thesis are proposed.(2)The uneven current distribution inside the multi-chip module leads to current stress on a specific chip,forming weak points as a result,which is not beneficial to the utilization of the chip rated current and the improvement of the overload capacity of power modules.To address this problem,the dynamic characteristics of a typical multi-chip parallelled power module is firstly studied,key factors that affect the dynamic and static current sharing of the power module are deeply analyzed.Following that,the influence of the parasitic inductances,brought about by the drive circuit and power circuit,on the dynamic current sharing is studied,and a current sharing theoretical model is established.Finally,the stray parameter model of the power module is established,the calculation method of the stray inductance of the power module is proposed,which provides an important theoretical basis and method foundation for the design of the power module under study.(3)To solve the current sharing problem of multi-chip paralleled power module,a novel power module design and active current sharing method are proposed.Firstly,the stray inductance distribution and current distribution characteristics of several DBC layouts commonly used in existing commercial power modules are analyzed.Then,the stray parameters fast calculation model is used to realize the rapid iteration of the power module design.With the goal of uniform current distribution,the paper proposes a DBC layout with symmetrical parasitic inductance,which is compared with the existing layouts.The current sharing capability of the designed power module is verified through simulation and dynamic characteristic experiments.Finally,an active current sharing scheme based on magnetic coupling is proposed,due to the chip parameter drift caused by the long-term operation of the power module causes an ununiform static current distribution.The active current sharing mechanism of the magnetic coupling and the design method of the coupling inductance are analyzed in detail,and the magnetic coupling effect on balancing current in parallelled branches is verified through a comparative experiment.(4)To address the problem that the traditional packaging materials,heat dissipation methods and power module structure do not provide enough short-term overload capacity support.Firstly,the instantaneous junction temperature control method based on phase-change materials is studied,and the instantaneous junction temperature control method for short-term overload power modules is proposed.Secondly,on the basis of study of different phase-change materials and heat conduction enhancement methods on short-term overload capacity enhancement of power modules,a detailed study was carried out to analyze the most suitable placement position of the phase change material in the power module,and a thermal model of the power module considering the phase change effect was established;on this basis,theoretical simulation study of different thermal conductivity enhancement frame structures,opening positions and opening shapes on the short-term overload capability of power modules were developed,and a novel structure with enhanced short-term overload capability power modules is proposed.Finally,the temperature distribution characteristics of the new power module are obtained using the finite element method,verifying the effectiveness of the proposed method in limiting the junction temperature in a short time.(5)In order to accurately evaluate the effect of the instantaneous junction temperature control method using phase change material on power modules' short-term overload capacity improvement.Firstly,a power module integrated with phase change materials was fabricated based on the power module packaging process.Secondly,a short-term over current experimental test rig was built using the power module fabricated,and the power module junction temperature test and the temperature change rule of the phase change material during the phase change process under overload conditions was deeply developed using the test platform.The experimental results verify the feasibility of integrating the phase change material inside the power module and the effectiveness of the phase change material in limiting the temperature rise during the power module overload period.Finally,feasibility and effectiveness of the internal current sharing and instantaneous junction temperature control method proposed by this thesis in limitting the power module's short-term overload is furtherly verified,through the experimental analysis of the presence or absence of phase change materials,the amount of phase change materials and the effect of overload current on the phase change time.The experimental results show that the power module designed in this study achieves uniform current sharing and instantaneous regulation of junction temperature between multiple chips,and can withstand 3 times overload for more than 3seconds.The research results of this paper have important academic value and technical support for the reliability design of power modules and the enhancement mechanism and method of short-term overload capability.They have improtant reference significance for the design of power modules with special needs such as low inductance,high voltage,and high temperature. |
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