Current Sensor Fault Mitigation in PMDC Steering Systems
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Solution Overview
Problem
Current electric power steering (EPS) systems using Permanent Magnet DC (PMDC) motors face challenges in maintaining stable torque control and disturbance rejection due to the loss of current sensors, leading to system shutdown and loss of assist to the driver.
Innovation Solution
A fault mitigation system is implemented, which includes a current sensor fault detector, a velocity observer, and a feedforward controller to estimate motor velocity and generate torque commands, allowing the system to transition smoothly into a post-fault operation mode without relying on current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback current control is used for torque regulation, then current control bandwidth and disturbance rejection are improved, but the system becomes vulnerable to current sensor faults causing shutdown
Solution Approach 1:
The patent introduces a velocity observer as an intermediary component that estimates motor velocity without requiring current sensors during fault conditions. This mediator enables the system to bypass the faulty current measurement path while maintaining control functionality through estimated velocity feedback, thus resolving the contradiction between reliable operation and sensor fault vulnerability.
Solution Approach 2:
The system implements preliminary fault detection and mitigation strategies by continuously monitoring current sensor health and pre-configuring alternative control paths. When a sensor fault is detected, the system has already prepared the observer-based control mode to take over, preventing shutdown before it occurs and maintaining operational reliability.
2Measurement precision
If current sensors are used for observer-based velocity estimation, then velocity estimation accuracy is improved, but the system loses fault tolerance when current sensors fail
Solution Approach 1:
The patent implements a dynamic control architecture that can switch between different operational modes depending on sensor health status. The system dynamically transitions from sensor-based velocity estimation to observer-based estimation when faults occur, making the system adaptable to changing conditions and resolving the contradiction between measurement precision and fault tolerance.
3Reliability
If feedforward current control is used without current sensors, then fault tolerance is improved, but current control bandwidth and disturbance rejection deteriorate
Solution Approach 1:
The patent merges the advantages of both feedback and feedforward control approaches by combining observer-based velocity estimation with feedforward current control. This hybrid approach integrates the fault tolerance of sensorless operation with the improved control bandwidth achieved through velocity feedback, resolving the contradiction between reliability and control speed.
Data Source
AI summary
Technical solutions are described for current sensor fault mitigation for systems with permanent magnet DC drives. An example power steering system includes a brush motor, and a motor control system that generates an amount of torque using the brush motor, the amount of torque corresponding to a torque command. The motor control system includes a current sensor fault detector that detects a current sensor fault associated with a current sensor used to measure a current across the brush motor. The motor control system further includes a velocity observer that computes an estimated motor velocity in response to the current sensor fault. The motor control system further includes a feedforward controller that generates a current command for generating the amount of torque using the brush motor, the current command generated using the estimated motor velocity.