Research On Power Module Junction Temperature Control Based On Drive Circuit Parameter Adjustment

Nowadays,converter is facing lager power level and more complex operation situation.Consequncely,the power fluctuation repeatedly put unbalanced electric-thermal stress impact on IGBT module,which makes it age and fail. The junction temperature fluctuation is a product and characterization of the power fluctuation.When the junction temperature is smoothed,the IGBT reliability can be improved largely.The main approath is changing the cooling situation or internal power loss.The former method establish two-dimensional thermal network model,and get the analytical expressions through which change the cooling situation.But the acuuracy of the model is not enough,and control has unacceptable time delay which makes the control result not satisfied.The latter method focus on switching frequency.Experiments show that changing the switching frequncy can multiply the change of the switching loss.When the proportion of the switching loss take advantage of the total loss, the effect is obvious. However, in certain conditions, when the converter design is completed,the switching frequency range is not so widely.The conduction loss and the switching loss based on drive resistor expression can be worked out through datasheet.When drive resistor range is worked out the total loss can be worked out by add the loss together.Tthe mathematical model established in Simulink, the loss calculated before can be transformed into a current source.After the current source go through the thermal network, the junction temperature.is worked out. By changing the values of the imput drive resistor,steady-state junction temperature can be got respectively,which prove that changing the drive resistor can change the junction temperature.The IGBT model can be established in saber through the information in the datasheet.Then the main circuit and the thermal network is also established.Firstly,to adjust the junction temperature by changing the driving resistance,the junction temperature variation with and without drive resistor control were compared.Then take the switching frequency and the collector-emitter voltage UCE into consideration, analysis is made of the impact of these two factors on the junction temperature control.Considering the impact of IGBT drive resistance changing, a BJT control circuit based on current controled characteristic take the palce of drive resistor regulation, after analysis of the theory, the BJT control circuit is established in saber, the feasibility of the junction temperature regulation of the method is verified through the simulation results.Finally, based on theoretical analysis and simulation, the main circuit and a control circuit is built, taking DSP as the control core, function of the the load current sampling, load current jump,junction temperature measurement, BJT control is realized. By Comparing the value of temperature fluctuation with and without control,the experimental results verify the correctness of the theoretical analysis and simulation mentioned before.