Transistor Junction Temperature Estimation Using Switching di/dt
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Solution Overview
Problem
Existing methods for estimating semiconductor junction temperatures in power electronics converters are inaccurate and not capable of providing real-time measurements, leading to suboptimal operation and potential safety issues due to the inherent time lag in thermistor-based approaches and the inability of indirect methods to accurately predict instantaneous temperatures.
Innovation Solution
A method involving the measurement of the rate of change of current through a transistor during a switching period, while the gate voltage is above a threshold and the drain-source voltage is above a predetermined fraction of the supply voltage, using a Rogowski coil and processing this data to estimate the junction temperature, thereby minimizing the influence of external factors like stray inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTC thermistor is used to measure junction temperature, then temperature measurement is possible, but time lag occurs and real-time measurement is not achieved
Solution Approach 1:
The patent replaces the thermal-based NTC thermistor measurement system with an electrical measurement system that monitors the rate of change of current (di/dt) during transistor switching. This substitution eliminates the inherent thermal time lag by using electrical parameters that respond instantaneously to temperature changes, achieving real-time junction temperature estimation without the delays associated with thermal conduction to a separate sensor.
2Loss of time
If indirect methods using computer models are used to estimate junction temperature, then real-time estimation is attempted, but accuracy is insufficient
Solution Approach 1:
The patent employs a feedback mechanism where the measured di/dt rate is continuously correlated with junction temperature through a pre-established relationship (lookup table or calibration curve). This feedback loop enables real-time temperature estimation by using the instantaneous electrical measurement to infer the current thermal state, achieving both real-time capability and improved accuracy compared to open-loop computer models.
Solution Approach 2:
The patent introduces the rate of change of current (di/dt) as an intermediary parameter that links the electrical switching behavior to the thermal state of the junction. By measuring this intermediate electrical parameter and using it to infer temperature, the system achieves accurate real-time temperature estimation without requiring direct thermal measurement, bridging the gap between electrical operation and thermal state.
3Productivity
If converters are operated closer to thermal limits to increase power output, then productivity increases, but safety and reliability risks increase
Solution Approach 1:
The patent implements real-time junction temperature monitoring through di/dt measurement, providing continuous feedback on the actual thermal state of the transistor. This enables the control system to operate the converter close to thermal limits with confidence, dynamically adjusting operation based on actual temperature conditions rather than conservative static limits, thereby maximizing power output while maintaining safety through active monitoring.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a more accurate and real-time estimation of junction temperatures, allowing for safer and more efficient operation of power electronics converters by enabling them to be operated closer to their thermal limits and facilitating quicker response to fault conditions.
Implementation Method 1
measuring a rate of change of current through the converter during a switching period of the transistor
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The disclosure relates to estimation of junction temperatures of transistors in a power electronics converter. Example embodiments include a method of estimating a junction temperature of a transistor (S1-6) in a power electronics converter (304) configured to convert between first and second supply voltages, the method comprising: providing a gate switching signal to the transistor (S2); measuring a rate of change of current through the converter (304) during a switching period of the transistor (S1-6); and outputting an estimated junction temperature (Tj1-6) of the transistor based on the measured rate of change of current, wherein the rate of change of current is measured while a gate voltage of the transistor (S2) is above a gate threshold voltage and a drain-source voltage across the transistor is above a predetermined fraction of the first or second supply voltage whereby the rate of change of current is measured in a linear region (605).