Electric Machine Torque Control via Segmented Aging Parameters
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Solution Overview
Problem
Existing motor control approaches for electric machines in powertrain systems rely solely on motor temperature as a control parameter, leading to inefficient torque derating and potential reduced service life, as they prohibit short-duration high temperature excursions and operate indefinitely at temperatures below the derating threshold, affecting service life.
Innovation Solution
A method for dynamically controlling electric machines by periodically determining aging parameters, short-term, and long-term aging effects, and adjusting temperatures to determine derated motor torque, allowing for temperature-based torque derating that extends service life and improves intermittent performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor temperature is used as a single control parameter for torque derating, then the electric machine can avoid reduced service life through temperature-based derating, but it prohibits short-duration high temperature excursions and operates indefinitely at temperatures below the derating threshold, affecting service life
Solution Approach 1:
The patent segments the temperature control into two independent components: a long-term aging counter that tracks cumulative thermal exposure over the motor's operational life, and a short-term aging counter that captures transient temperature excursions. This segmentation allows each counter to be optimized independently - the long-term counter protects service life through gradual derating, while the short-term counter permits brief high-temperature excursions that do not significantly impact aging, thereby resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The patent implements dynamic torque derating by continuously updating both long-term and short-term aging counters based on real-time temperature measurements. The derated torque is dynamically adjusted as the sum of deratings from both counters, allowing the system to adapt to changing thermal conditions. This dynamic approach enables the motor to operate at higher temperatures during short-duration excursions while maintaining service life protection through cumulative aging tracking, resolving the contradiction between temperature flexibility and service life.
2Reliability
If motor torque is linearly derated as motor temperature increases from 170°C to 190°C, then the electric machine protects against overheating, but it reduces productivity during transient high-load conditions that may not affect service life
Solution Approach 1:
The patent applies partial derating action by separating the total torque reduction into two components: a long-term derating component that provides sustained protection against overheating, and a short-term derating component that addresses transient excursions. During brief high-temperature events, the short-term counter captures the excursion while the long-term counter remains relatively unchanged, allowing the motor to maintain higher torque output during transient conditions while still providing overheating protection through the long-term mechanism, thus resolving the contradiction between reliability and productivity.
3Productivity
If the electric machine operates indefinitely at motor temperatures slightly below the minimum temperature for derating, then it maintains maximum torque output, but it accumulates thermal aging that affects service life
Solution Approach 1:
The patent implements feedback through the long-term aging counter that continuously accumulates thermal exposure data and feeds this information back to the torque derating mechanism. Even when the motor operates below the immediate derating threshold, the long-term counter gradually accumulates aging information, which eventually triggers torque derating to protect service life. This feedback mechanism resolves the contradiction by allowing maximum torque during short-term operation while preventing cumulative thermal damage over the motor's operational life.
Data Source
AI summary
A method for operating an electric machine of a ground vehicle includes periodically determining an aging parameter based upon a temperature of the electric machine and periodically determining a short-term aging effect based upon the periodically determined aging parameter. A long-term aging effect is determined based upon the short-term aging effect. A short-term temperature adjustment is determined based upon the short-term aging effect and a long-term temperature adjustment is determined based upon the long-term aging effect. A temperature-based derated motor torque is determined based upon the long-term temperature adjustment and the short-term temperature adjustment. Operation of the electric machine is controlled responsive to an operator command for torque based upon the temperature-based derated motor torque.