Motor Driven Power Steering Disturbance Compensation
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Solution Overview
Problem
Existing motor driven power steering systems face instability due to back electromotive force (EMF) disturbances, particularly when motor speed changes rapidly, leading to inadequate compensation and control issues.
Innovation Solution
A closed-loop based input value prediction model unit predicts the input voltage value separately from a feedback controller, and a disturbance compensating unit adjusts the compensation based on the difference between predicted and actual values to effectively compensate for disturbances across desired frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feed-forward and feed-back control method is used to compensate for back electromotive force, then disturbance compensation is achieved when motor speed is constant, but control stability deteriorates when motor speed changes rapidly
Solution Approach 1:
The invention predicts the input voltage value in advance using a closed-loop based input prediction model before the actual control action is taken. This prediction allows the system to prepare for upcoming disturbances caused by motor speed changes, enabling proactive compensation rather than reactive correction, thus maintaining control stability during rapid speed transitions.
Solution Approach 2:
The invention implements a closed-loop feedback mechanism where the predicted input voltage is compared with the actual input voltage, and the difference (error) is used to adjust the disturbance compensation. This feedback loop continuously refines the compensation accuracy, ensuring reliable disturbance compensation while adapting to changing motor operating conditions.
2Device complexity
If PI controller and linear feedback control are used for torque control, then current control is simplified, but control stability deteriorates due to back electromotive force disturbance
Solution Approach 1:
The invention segments the control system into distinct functional blocks: a PI controller for basic current control, a closed-loop based input prediction model for disturbance prediction, and a disturbance compensating unit for stability enhancement. This segmentation allows each component to perform its specialized function while maintaining overall system simplicity and stability.
Solution Approach 2:
The closed-loop based input prediction model acts as an intermediary between the PI controller and the motor. It processes the command current and predicted motor state to generate a predicted input voltage, which then informs the disturbance compensation. This intermediary layer isolates the simple PI controller from the complexity of back electromotive force compensation while maintaining control stability.
3Reliability
If existing disturbance compensation method is used, then compensation is adequate when motor speed is constant, but compensation fails when motor speed changes rapidly
Solution Approach 1:
The invention transitions from a static disturbance compensation approach to a dynamic one by implementing a closed-loop based input prediction model. This model continuously updates the predicted input voltage based on current motor state and command inputs, allowing the disturbance compensation to adapt dynamically to rapid speed changes while maintaining accuracy during constant speed operation.
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 allows for precise disturbance compensation, enabling tuning of the compensation function according to frequency bands without requiring low-frequency filters, effectively stabilizing motor control across varying speed conditions.
Implementation Method 1
When a permanent magnet is rotated, a change in magnetic flux induced in a stator and a current of the stator interact with each other, so that non-linearity is generated by back electromotive force
Data Source
AI summary
A system for compensating for disturbance of a motor for motor driven power steering is provided. The system for compensating for disturbance of a motor for motor driven power steering compensates for the disturbance based on a closed loop based input value prediction model unit, separately predicts an input value from a command by a closed loop based input value prediction model unit, and compensates for disturbance in accordance with a desired disturbance frequency band when there is a difference between the predicted input value and an input value error-compensated by a feedback controller.