Torque Ripple Compensation in MDPS Using Pre-Calculated Lookup Tables
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Solution Overview
Problem
Existing torque ripple compensation methods for Motor Driven Power Steering (MDPS) systems face challenges such as requiring separate test times, performance deviations due to system distribution, magnitude reduction, phase delay, and difficulty in recovering original signals, especially when using lookup tables or active disturbance compensation methods.
Innovation Solution
A torque ripple compensation apparatus and method that includes a torque measurement unit, motor speed measurement unit, control unit, and torque ripple compensation unit to synthesize and output a torque ripple compensation signal, using a torque signal model to estimate and correct torque ripple signals, and applying a gain to generate a corrected estimated signal for motor control, without the need for separate parameter extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lookup table-based control method is used to compensate for torque ripple, then the control can be easily applied to the MDPS motor, but a separate test time is required for parameter extraction and performance deviation occurs due to system distribution
Solution Approach 1:
The patent pre-calculates torque ripple compensation values for various operating conditions and stores them in a lookup table during the manufacturing phase. This preliminary action eliminates the need for separate field testing and parameter extraction, as all compensation parameters are prepared in advance based on typical system characteristics.
Solution Approach 2:
The patent uses a distribution-based parameter generation method that creates compensation parameters considering system distribution characteristics. By generating parameters that account for manufacturing tolerances and variations, the system achieves consistent performance across different units without requiring individual testing and calibration.
2Measurement precision
If a low-pass filter is used in the disturbance observer to estimate torque ripple, then the torque ripple can be estimated, but magnitude reduction and phase delay occur
Solution Approach 1:
The patent segments the torque ripple compensation into multiple frequency components, each handled by dedicated compensation values in the lookup table. By separating different frequency components rather than using a single filtered estimate, the system avoids magnitude reduction and phase delay while maintaining accurate torque ripple compensation for each component.
Solution Approach 2:
The patent creates a detailed copy of the torque ripple characteristics across various operating conditions and stores them in the lookup table. This comprehensive copying of ripple patterns for different speeds and loads eliminates the need for filtering during operation, preserving the original magnitude and phase of torque ripple components.
3Measurement precision
If a high-pass filter is used to remove offset of the torque sensor, then the offset can be removed, but additional operation is required to correct distortion of high frequency signal and it is difficult to recover the original signal
Solution Approach 1:
The patent extracts and removes the offset component from torque sensor signals during the parameter extraction phase, storing offset-compensated values in the lookup table. By taking out the offset beforehand, the system avoids the need for high-pass filtering and subsequent signal correction operations during real-time control, simplifying the overall signal processing.
4Measurement precision
If parameter estimation through integration is used, then torque ripple can be estimated, but a long convergence time is required and additional algorithm is required to block divergence of integration signal
Solution Approach 1:
The patent performs parameter estimation and torque ripple characterization during the manufacturing and testing phase, storing the results in the lookup table before deployment. By completing the estimation process preliminarily, the system eliminates the need for time-consuming convergence during actual operation, achieving immediate torque ripple compensation from startup.
Data Source
AI summary
A torque ripple compensation apparatus including a torque measurement unit configured to output torque measured through a torque sensor of an MDPS system; a motor speed measurement unit configured to output motor speed measured through a position sensor of an MDPS motor; a control unit configured to separately output an offset signal and a torque ripple signal based on the motor speed information and the measured torque information; and a torque ripple compensation unit configured to synthesize a plurality of torque ripple signals outputted from the control unit, and output a torque ripple compensation signal as a motor control signal to the MDPS motor, the torque ripple compensation signal being used to compensate for the synthesized torque ripple signal.