Active Disturbance Rejection for EPS Steering Feel
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Solution Overview
Problem
Existing electrical power steering (EPS) systems face challenges in achieving 100% disturbance rejection without affecting steering feel, as they often require complex calibration, are sensitive to parameter uncertainties, and consume significant computational resources, especially when dealing with non-periodic or random disturbances like brake pulsations.
Innovation Solution
A generalized active disturbance rejection (ADR) system using a combined feedback and feed-forward compensator structure that isolates disturbances from the column torque, allowing for minimal impact on steering feel and stability, with the ability to reject disturbances in specific frequency ranges without requiring wheel frequency information, and enabling 100% disturbance reduction capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resonant filters are used to detect and counteract disturbances, then disturbance rejection capability is improved, but steering feel is degraded and complex calibration is required
Solution Approach 1:
The patent introduces an intermediary disturbance observer that estimates disturbances without directly filtering the motor torque signal. This observer acts as a mediator between the system output and the disturbance rejection control, avoiding the need to filter out disturbance frequencies from the motor torque, thereby preserving steering feel while achieving disturbance rejection
Solution Approach 2:
The patent implements a feedback mechanism where the estimated disturbance from the disturbance observer is fed back to the control input to counteract the disturbance. This feedback approach allows 100% disturbance rejection without requiring resonant filters that would degrade steering feel, as the disturbance estimation is performed separately from the torque signal processing
2Reliability
If high gain is used in proportional or integral methods to increase disturbance rejection, then disturbance rejection capability is improved, but system stability is degraded and sensitivity to parameter uncertainties increases
Solution Approach 1:
The patent replaces the traditional mechanical control approach (proportional-integral controllers with high gain) with a disturbance observer-based approach. This substitution allows the system to achieve disturbance rejection by estimating and compensating for disturbances directly, rather than relying on high-gain feedback that compromises stability
Solution Approach 2:
The patent changes the control parameter from high gain values in PI controllers to disturbance estimation parameters in the disturbance observer. This parameter transformation enables effective disturbance rejection without the stability issues associated with high gain, as the observer parameters can be tuned independently of the stability-critical feedback gain
3Measurement precision
If disturbance detection relies on transient time for accurate detection, then measurement precision is improved, but response speed is degraded making it unsuitable for dynamic disturbances
Solution Approach 1:
The patent performs preliminary action by continuously estimating the disturbance through the disturbance observer before it significantly affects the system. The observer proactively tracks disturbance trends and provides early compensation, eliminating the need to wait for transient time to accumulate sufficient data for accurate detection
4Measurement precision
If standard feed-forward approach with column torque sensor is used to measure disturbance indirectly, then disturbance measurement is achieved, but 100% disturbance rejection cannot be achieved due to feedback mechanism in the loop
Solution Approach 1:
The patent segments the control system into distinct functional blocks: the disturbance observer that estimates disturbances independently, and the control input that compensates for estimated disturbances. This segmentation separates the disturbance measurement function from the feedback control loop, enabling 100% disturbance rejection by preventing the disturbance from entering the feedback path in the first place
Data Source
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AI summary
A method of controlling disturbances associated with electric power steering (EPS) systems maintains an original assist torque to feedback signal in the EPS, such as a column torque, and further minimizes the impact from the disturbance source to the feedback signal so that the disturbance is rejected while the original steering feel is maintained. The method further considers interaction of the rejection feature with other functions of the EPS. In one embodiment, relationships for isolating the disturbance are achieved by utilizing a combined feedback and feed-forward compensator.