Power Inverter Module Junction Temperature Estimation
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Solution Overview
Problem
Conventional derating techniques for power inverter modules in hybrid electric vehicles and battery electric vehicles are inadequate in accurately determining the junction temperature of semiconductor switches, leading to overprotection and reduced motor torque output due to the reliance on inaccurate and dynamically slow thermistor measurements.
Innovation Solution
A system and method that utilize a controller to estimate the junction temperature of semiconductor switches based on coolant and module temperatures, along with electrical values, to selectively derate the power inverter module by adjusting torque, switching methods, and frequency, while also considering the age and thermal impedance of the switches, and monitoring coolant health.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional derating techniques using thermistor measurements are used, then semiconductor switches are protected from overheating, but motor torque output is reduced due to overprotection and inaccurate temperature determination
Solution Approach 1:
The patent changes the parameters used for temperature estimation from static thermistor measurements to dynamic parameters including coolant temperature, module temperature, and electrical values (phase currents, switching frequencies). This allows more accurate real-time estimation of junction temperature, enabling better derating decisions that protect switches while maintaining torque output.
Solution Approach 2:
The patent replaces the mechanical/physical thermistor measurement system with a computational estimation system that uses mathematical models and multiple sensor inputs. This substitution enables more accurate and responsive temperature determination without the limitations of physical thermistor placement and response time.
2Measurement precision
If thermistor measurements are used for temperature monitoring, then junction temperature can be determined, but the measurements are inaccurate and dynamically slow
Solution Approach 1:
The patent uses coolant temperature and module temperature as intermediary measurements that can be obtained rapidly and accurately. These intermediaries serve as proxies for the difficult-to-measure junction temperature, providing timely data for derating decisions without the response delays of direct thermistor measurements at the junction.
Solution Approach 2:
The patent replaces the slow thermistor measurement system with a computational model that processes multiple fast-response sensor inputs (coolant temperature, module temperature, electrical parameters) to estimate junction temperature. This computational approach provides both higher accuracy and faster response than physical thermistor measurements.
3Object-affected harmful factors
If derating is applied to protect semiconductor switches, then overheating risk is reduced, but power output from the PIM is reduced
Solution Approach 1:
The patent implements dynamic derating control that continuously adjusts power output based on real-time estimated junction temperature. Unlike static derating thresholds, this dynamic approach allows the PIM to operate at full power when temperatures are acceptable and applies derating only when necessary, optimizing the balance between protection and power output.
Solution Approach 2:
The patent uses feedback from multiple temperature sensors and electrical measurements to continuously update the junction temperature estimate and adjust derating decisions. This closed-loop control ensures that power output is reduced only to the extent necessary for protection, maintaining maximum possible power delivery when conditions permit.
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 effectively reduces the risk of overheating while maintaining motor torque output, avoiding overprotection and allowing for a wider operating region by accurately estimating junction temperatures and adjusting power delivery accordingly.
Implementation Method 1
an inverter coolant loop configured to receive coolant from a source, circulate the coolant through the power inverter module, and discharge the coolant to a sink
Implementation Method 2
circulate the coolant through the power inverter module
Data Source
AI summary
A system includes a DC battery pack, an inverter coolant loop, first and second temperature sensors, a polyphase electric machine, and a power inverter module (PIM) connected to the battery pack and electric machine. The PIM includes a plurality of semiconductor switches. The controller is operable to selectively derate the PIM and thus reduce a commanded torque to the electric machine. The controller is programmed to execute a method and thereby receive a coolant temperature from the first temperature sensor and a PIM temperature from the second temperature sensor, and to determine a set of electrical values of the electric machine. The controller estimates a junction temperature of the semiconductor switches using the temperature of the coolant, the temperature of the PIM, and the set of electrical values. The controller selectively derates the PIM using the estimated junction temperature when the temperature of the PIM exceeds a calibrated maximum temperature.