Electric Machine Thermal Mitigation via Periodic Torque Modulation
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Solution Overview
Problem
Electric vehicles face challenges in maintaining a stationary position on an inclined surface without overheating their electric motors, as existing control systems often shut down the motor unexpectedly when a critical temperature is reached, leading to undesirable vehicle behavior.
Innovation Solution
A method and system for controlling the electric machine arrangement that implements a thermal mitigation strategy by adjusting the time between successive torque reductions and increases based on the motor's temperature, allowing for incremental redistribution of heat and extended stationary positioning before shutdown, using a frequency-based approach to manage motor torque and cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the electric machine is used exclusively to maintain vehicle position on an inclined surface, then the vehicle can be held stationary without friction brakes, but the electric machine overheats due to high current concentration in one or two phases
Solution Approach 1:
The control system implements periodic torque reductions at predetermined time intervals while maintaining the vehicle in a stationary position. This periodic action redistributes heat generation across different time periods, preventing continuous high current concentration in specific phases and allowing thermal mitigation without complete motor shutdown
Solution Approach 2:
The system dynamically adjusts the torque command to the electric machine by implementing temporary torque reductions at scheduled intervals. This dynamic modulation of torque allows the vehicle to remain stationary while preventing overheating through controlled, periodic changes in operational parameters
2Reliability
If a thermal mitigation strategy shuts down the motor upon reaching critical temperature, then overheating is prevented, but vehicle behavior becomes unexpected and undesirable for the operator
Solution Approach 1:
Instead of abrupt shutdown at critical temperature, the system employs periodic torque reductions at predetermined time intervals before critical temperature is reached. This approach maintains vehicle stationary positioning while proactively managing thermal buildup, providing predictable and smooth vehicle behavior that does not surprise the operator
Solution Approach 2:
The control system implements thermal mitigation through periodic torque reductions before the electric machine reaches critical temperature. This preliminary action prevents overheating from occurring in the first place, eliminating the need for reactive shutdown and maintaining predictable vehicle operation throughout the stationary period
3Duration of action of stationary object
If the electric machine operates continuously to maintain stationary position, then vehicle positioning is maintained, but the time before motor shutdown is limited due to thermal constraints
Solution Approach 1:
The control system implements periodic torque reductions at predetermined time intervals, allowing the electric machine to operate continuously while managing thermal accumulation. This periodic modulation extends the duration the vehicle can remain stationary by redistributing thermal load over time, preventing premature shutdown
Solution Approach 2:
The system maintains continuous stationary positioning of the vehicle while implementing periodic thermal mitigation through torque reductions. This approach ensures uninterrupted useful action (vehicle holding) while managing thermal constraints, extending operational duration before shutdown is necessary
Data Source
AI summary
A vehicle having an electric machine arrangement, including an electric machine operable to drive the vehicle includes a control system having at least one controller. The control system is configured to implement a method for thermal mitigation of the electric machine arrangement. The thermal mitigation strategy is controlled such that a time between successive implementations of the strategy is inversely related to a temperature of at least a portion of the electric machine arrangement, and the time between two successive implementations of the thermal mitigation strategy may decrease with each successive pair of implementations.