IGBT Junction Temperature Estimation Using VCE(ON) and Kalman Filter
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Solution Overview
Problem
Existing methods for estimating the junction temperature of IGBT power modules are prone to measurement errors and are affected by changes in operating conditions, particularly due to high failure rates of thermocouples and difficulty in maintaining them, which compromises the accuracy and reliability of thermal analysis.
Innovation Solution
A method utilizing a full-bridge inverter circuit and a VCE(ON) on-line measuring circuit, combined with a Kalman filter, to estimate junction temperature by simulating the IGBT power module's behavior and thermal model, incorporating the coupling effect between the IGBT and diode, and using the temperature-sensitive electrical parameter method to improve measurement accuracy and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermocouple method is used to measure junction temperature, then temperature measurement can be achieved, but measurement error increases and failure rate becomes high
Solution Approach 1:
The patent replaces the mechanical thermocouple measurement system with an electrical parameter-based measurement system. Specifically, it uses the temperature-sensitive electrical parameter method by measuring the collector-emitter voltage VCE(ON) of the IGBT, which varies with junction temperature. This substitution eliminates the need for physical thermocouple contact, thereby reducing measurement errors and thermocouple failures while maintaining temperature measurement capability.
Solution Approach 2:
The patent introduces an intermediary electrical parameter (VCE(ON) voltage) that correlates with junction temperature. Instead of directly measuring temperature with a thermocouple, the system measures the electrical voltage across the IGBT collector-emitter terminals, which serves as an indirect but more reliable indicator of junction temperature. This intermediary measurement approach improves both accuracy and reliability.
2Device complexity
If fixed thermal model is used for temperature prediction, then calculation is simplified, but compensation for thermal path degradation is lost
Solution Approach 1:
The patent transforms the static fixed thermal model into a dynamic adaptive model. The thermal model parameters are continuously updated based on real-time measurements of VCE(ON) voltage and actual junction temperature observations. This dynamic adjustment allows the system to compensate for thermal path degradation caused by aging and changing cooling conditions, maintaining accurate temperature estimation without requiring excessively complex modeling.
Solution Approach 2:
The patent implements a feedback mechanism where the measured VCE(ON) voltage and observed junction temperature are continuously fed back to update the thermal model parameters. This closed-loop approach enables the system to adapt to changing thermal conditions and compensate for degradation over time, improving temperature estimation accuracy while keeping the model structure manageable through iterative parameter refinement.
3Productivity
If voltage measurement is performed during switching operations, then real-time temperature data is obtained, but intermittent effects and noise increase
Solution Approach 1:
The patent employs periodic sampling of the VCE(ON) voltage at specific intervals during the IGBT conduction period. By measuring voltage only during stable conduction phases rather than during switching transitions, the system obtains real-time temperature data while avoiding the intermittent effects and noise associated with switching operations. This selective periodic measurement strategy maintains productivity while improving measurement precision.
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 enhances the accuracy of junction temperature estimation, reduces noise, and allows for real-time monitoring without altering the power converter's control strategy, improving the reliability of IGBT power modules by effectively accounting for self-heating and diode coupling.
Implementation Method 1
obtaining IGBT conduction voltage drop VCE(ON) for the connected full-bridge inverter circuit and the VCE(ON) on-line measuring circuit, using the temperature sensitive electrical parameter method to obtain the calibration curve and fitting relationship of IGBT conduction voltage drop VCE(ON) and an IGBT power module junction temperature Tj
Implementation Method 2
setting a system model of the Kalman filter (i.e., the Kalman filter), the IGBT power module junction temperature obtained in the step 2, the switching loss and conduction loss of the IGBT obtained in the step 3, the reverse recovery loss and conduction loss of the diode obtained in the step 3 are used as filter inputs to calculate the optimal estimated value of junction temperature
Implementation Method 3
calculate the switching loss and conduction loss of the IGBT, reverse recovery loss and conduction loss of the diode
Implementation Method 4
setting a thermal model of extended state space of the IGBT power module
Data Source
AI summary
A method for estimating the junction temperature on-line on an insulated gate bipolar transistor (IGBT) power module, including the following steps. Estimate the junction temperature by the temperature sensitive electrical parameter method, set the space thermal model of the extended state, and apply the Kalman filter to the junction temperature estimation. The temperature sensitive electrical parameter method estimates the junction temperature of the IGBT power module in real time, selects the IGBT conduction voltage drop VCE(ON) as the temperature sensitive electrical parameter, and provides a VCE(ON) on-line measuring circuit. The power loss of the diode and IGBT and the estimated value of junction temperature obtained by the temperature sensitive electrical parameter method are taken as the input of the Kalman filter, and measurement noise and process noise are considered to obtain an optimal estimated value of junction temperature.