A New IGBT Junction Temperature Online Monitoring Method And Its Applications In The Electrical Vehicles Traction

As an important part of new energy vehicles,the reliability of power converters has become one of research hotspots.Therefore,as an important parameter about reliability,IGBT junction temperature monitoring naturally becomes the focus of academic and industry research.In this paper,the correlation between IGBT junction temperature and turn-off delay time and the real-time monitoring of IGBT junction temperature are carried out from the industrial application requirements of IGBT module.Through the analysis of the IGBT short circuit protection circuit,it is found that the diode in the short circuit protection circuit generates the reverse recovery current during the IGBT turn-off process,and there are some relations between the current and the turn-off voltage.Based on the discoveries,a simple,high-precision,highly integrated driver board that can extract the IGBT turn-off delay time is designed.On the basis of this drive board,the experimental platform is built to study the correlation between IGBT junction temperature and turn-off delay time and achieve real-time monitoring of junction temperature.This paper first summarizes the one-to-one relationship between IGBT junction temperature and a variety of thermal sensitive electrical parameters.Through the study of the turn-off process,it is revealed that there are some internal relations between the turn-off delay time and the multiple variables,that is,the DC bus voltage,the load current,the junction temperature and the turn-off delay time have independent and monotonous changing laws.Based on this analysis,the turn-off delay time is proposed as the heat-sensitive electrical parameters to study the junction temperature of the IGBT,and the reverse recovery current of the diode in the short circuit protection circuit is used to capture the IGBT turn-off voltage,then the measurement of the turn-off delay time is converted to the diode reverse recovery current monitoring,which prevents direct measurement of the turn-off delay time.The experimental results confirm the feasibility of extracting the off delay time based on the short circuit protection circuit.Secondly,in the calibration process of IGBT junction temperature and turn-off delay time,the traditional double-pulse or single-pulse turn-off time extracting method has a large error due to the self-heating effect caused by the large current flowing through the IGBT.In this paper,the three-phase motor drive system cleverly utilize the inverter topology,a constant current flows through the calibrated IGBT,DC loss generates a constant temperature rise after the heat balance.Heating the water to the plate until the IGBT junction temperature reaches the reference value,turn off the IGBT and extract the off delay time.This process makes reasonable use of the IGBT self-heating effect in the high current,and reduces the measurement error.The experimental results show that the IGBT junction temperature is positively correlated with the turn-off delay time at the specific DC voltage and load current,that is,the higher the junction temperature is,the longer the turn-off delay time is.Finally,the dynamic model of the vehicle,the mathematical model of the permanent magnet synchronous motor,the IGBT loss and the junction temperature calculation model are put forward,the temperature variation of the IGBT under NEDC condition is simulated by MATLAB software.Based on the laboratory existing electric drive test platform,the IGBT junction temperature on-line monitoring system is built.The instantaneous junction temperature fluctuation law of the IGBT and the changing law of the IGBT junction temperature under the NEDC condition are obtained,the experimental data are basically consistent with the results of the modeling and simulation,and it is proved feasible to monitor the IGBT junction temperature in real time based on the turn-off delay time.