DETAILED EXPLANATION OF IGBT MODULE PARAMETERS-NTC THERMISTOR
IGBT junction temperature is one of the most important parameters of power electronic devices. It is very difficult to measure this temperature during operation of the device. One method is to approximately estimate the temperature of the chip in its stable operating state by using the NTC (thermistor) inside the IGBT module. This method is not suitable for measuring rapidly changing IGBT temperatures.
The chip temperature can be calculated by establishing a thermal model and measuring the temperature of the NTC. The NTC resistance value at the temperature T2 can be calculated by the following formula
The value of resistor R25 when temperature T1=298.15K is as shown below
According to the actual measured value of NTC resistor R2, the value of temperature T2 can be calculated by the following formula
The maximum relative deviation of resistance is represented by the ΔR/R value defined at 100 degrees. In order to avoid self-heating of NTC, the power consumption of NTC itself needs to be limited. In order to limit the temperature rise of the NTC to not exceed the maximum allowable value of 1K, the current passing through the NTC can be calculated by the following formula.
In order to more accurately calculate the resistance and temperature values of NTC, different B values are required. The B value depends on the temperature range considered. 25 degrees to 100 degrees is the most common temperature range, so the value of B25/100 will be used. In the lower temperature range, the value of B25/80 or B25/50 can be used, which will give a more accurate calculated resistance value in the lower temperature range.
The temperature measurement method using NTC is not suitable for short circuit detection or short-term overload detection. It can be used to protect the module when operating under long-term overload conditions or when the cooling system fails.
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