Transistor Junction Temperature Estimation from 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 information can be obtained, but there is inherent time lag and cannot provide instantaneous temperature during operation
Solution Approach 1:
The patent replaces the physical NTC thermistor measurement system with an electrical measurement system that uses current rate of change (di/dt) during transistor switching to infer junction temperature. This substitution eliminates the thermal mass and response time limitations of physical temperature sensors, providing instantaneous temperature information through electrical characteristics that directly reflect the semiconductor junction state.
2Measurement precision
If indirect methods using computer models are used to estimate junction temperature, then temperature prediction is possible, but accuracy and reliability for instantaneous temperature is insufficient
Solution Approach 1:
The patent utilizes the transistor's own switching characteristics and electrical behavior during normal operation to self-diagnose its junction temperature. By measuring the di/dt during switching events and comparing it against pre-stored reference values obtained from simulations, the system enables the device to provide accurate instantaneous temperature information without requiring external sensors or complex real-time computational models.
3Measurement precision
If measurement is performed in non-linear region, then current change can be detected, but external influences like stray inductance affect measurement accuracy
Solution Approach 1:
The patent identifies and utilizes a specific local operating condition - the linear region during transistor switching where the collector-emitter voltage is above a predetermined fraction of the supply voltage. In this localized voltage range, the transistor exhibits linear current characteristics that are dominated by the transistor's intrinsic behavior rather than external parasitic elements. By confining measurements to this specific operational window, the method achieves high measurement precision while minimizing the impact of stray inductance and other external harmful factors.
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, enabling them to be operated closer to their thermal limits and facilitating better fault detection and maintenance scheduling.
Implementation Method 1
measuring a rate of change of current through the converter during a switching period of the transistor
Data Source
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 in a power electronics converter configured to convert between first and second supply voltages, the method comprising: providing a gate switching signal to the transistor; measuring a rate of change of current through the converter during a switching period of the transistor; and outputting an estimated junction temperature 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 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.