Electric Machine Stall Torque Derating for Winding Heat Control
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Solution Overview
Problem
Electric machines in vehicles can experience excessive heating during stall states, leading to potential degradation, as the windings generate higher temperatures than desired, even with cooling systems in place.
Innovation Solution
A method is developed where a controller adjusts the torque output of the electric machine based on the time it has been in a stall state and the torque delivered, generating a variable to determine when to limit output and perform mitigating actions, such as applying brakes or starting an internal combustion engine, to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the electric machine operates in a stall state to deliver high torque, then the vehicle can overcome obstacles or start moving from stationary position, but the windings generate excessive heat leading to potential degradation
Solution Approach 1:
The controller performs preliminary monitoring of stall duration and torque levels before critical overheating occurs. By tracking the cumulative stall time and torque product, the system proactively identifies when the electric machine is approaching dangerous temperature thresholds and takes preventive torque reduction actions before degradation occurs.
Solution Approach 2:
The system continuously monitors operating conditions (stall duration, torque levels) and uses this feedback to dynamically adjust torque output. The controller calculates a thermal stress metric based on accumulated stall conditions and responds by modulating torque delivery, creating a closed-loop control system that prevents overheating while maximizing usable torque.
2Temperature
If the controller limits torque output during stall states to prevent overheating, then the electric machine temperature is controlled, but the vehicle performance and driving experience are reduced
Solution Approach 1:
The controller applies partial torque limitation only when necessary based on accumulated stall conditions. Rather than continuously limiting torque, the system allows full torque delivery during brief or low-intensity stall events, and only reduces torque when the cumulative thermal stress metric exceeds thresholds, thereby maintaining performance during acceptable operating conditions.
Solution Approach 2:
The torque limitation strategy is dynamic rather than static. The controller continuously adjusts torque output based on real-time monitoring of stall duration and intensity, allowing the system to adapt to varying operating conditions. This dynamic approach enables maximum performance during safe operating windows while preventing damage during excessive thermal stress conditions.
3Temperature
If the electric machine is continuously cooled, then the temperature is reduced, but the cooling system complexity and energy consumption increase
Solution Approach 1:
The electric machine control system monitors its own thermal stress conditions and self-regulates torque output to prevent overheating. By using the cumulative stall metric to trigger torque reductions, the system serves its own thermal management needs without requiring additional temperature sensors or complex active cooling control mechanisms.
Solution Approach 2:
The system converts the harmful effect of stall-induced heating into a useful control signal. The cumulative stall time and torque product, which represents thermal stress, is used as a trigger for torque reduction. This transforms the heating problem into a beneficial feedback mechanism that automatically protects the machine without additional cooling infrastructure.
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 reduces the risk of electric machine degradation by limiting torque output when necessary, improving the vehicle driving experience and extending the machine's operational life without unnecessarily reducing operating time.
Implementation Method 1
The electric machine may generate heat while it operates and the heat may be carried away via a cooling system
Data Source
AI summary
Methods and systems are provided for operating a vehicle that includes an electric machine as a propulsion source. In one example, a motor stall assessment level is generated based on an amount of time that the motor is stalled and an amount of torque that is generated by the motor. Mitigating actions may be performed if the motor stall assessment level exceeds a threshold level or value.