Dynamic Junction Temperature Calculation And Life Prediction Of IGBT Power Module For Doubly-fed Wind Power Converters

As the hub of wind energy conversion system,power converters are an important part influencing the stability of wind turbines accessing to the grid.With the large-scale investment of wind farms,the reliability of the power converters has been paid more and more attention.The continuous fluctuation of the junction temperature of Insulation Gate Bipolar thyristor(IGBT)with the power output is the main reason for the high failure rate of the power converter.Therefore,obtaining an accurate IGBT junction temperature is the basis for achieving its condition monitoring and life prediction.This paper takes the actual IGBT power module of DFIG power converter as the research object,aiming at the impact of module package stray parameters on the dynamic characteristics of the switch-on,focusing on the internal temperature distribution rule of the module and studying on the effect of abnormal operating conditions(the grid fault.)on the life of the power module.The main contents of this thesis are followings:(1)Considering the difficulty of extracting spurious parameters from the internal package of the power module,it is difficult to evaluate the effect rules of the stray inductance efficiently and accurately on the dynamic current distribution for parallel chips in the module.First of all,based on the physical structure of the IGBT power module,a stray inductance model of the internal package of the module is established.Second,based on the stray inductance model and IGBT turn-on characteristics,the influence of stray inductance on the current distribution of each parallel chip is analyzed.Finally,based on the finite element method,the stray inductance of the module package is extracted,and a detailed equivalent circuit model is established to simulate and verify the phenomenon of switch-on dynamic non-uniform current.(2)Considering the problem that the traditional junction temperature calculation model does not consider the losses difference between parallel chips caused by turn-on dynamic non-uniform current leading to inaccuracy in calculating the junction temperature at the weak link,a calculation method for the junction temperature of the IGBT power module is proposed taking into account the influence of the dynamic current sharing between the chips.First,a theoretical derivation of the quantitative relationship between stray inductance parameters and turn-on losses is done.Second,a thermal network model considering the internal coupling of the module is established,and a method for calculating the internal dynamic junction temperature of the IGBT module based on the electro-thermal coupling theory is proposed with verified through experiments.Finally,taking a 1.5MW doubly-fed wind turbine as an example,the internal heat distribution of the IGBT power module under actual operating conditions is analyzed and compared with the results of the traditional junction temperature calculation model.(3)In order to accurately assess the thermal distribution of and reliability of doubly-fed wind power converter power modules under Grid fault crossing condition,a power module life prediction model is proposed that takes into account the cumulative effects of fault traversing fatigue.Firstly,a simulation model of DFIG with the control strategy of low-voltage ride-through is established and the rule influenced by junction temperature distribution of converter power module under different grid fault conditions and different wind speed operating conditions is analyzed.Secondly,the temperature fluctuations on different time scales are divided.Taking into account the complex operating conditions such as grid faults and wind speed operating conditions,a multi-time scale life assessment model of the converter power module that takes into account the cumulative effects of grid fault crossing is proposed.Finally,taking the actual annual wind speed data of a wind farm as an example,the life distribution rules of the wind power converter power modules are obtained considering the distribution scene of grid faultsThe research results of this dissertation have important academic value and technical support meaning for the reliability design of converter power modules and the condition monitoring based on reliability.It also has important reference significance for optimization of operation and maintenance of wind power converters.