Motor Control Unit Suppressing Torque Ripple via Back-EMF Harmonic Extraction
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in accurately compensating for torque ripple due to higher harmonic components in back-EMFs, especially at high motor speeds, as existing feed-forward control methods are sensitive to motor resistance and inductance errors and do not effectively address the relationship between higher harmonics and compensation values.
Innovation Solution
A motor control unit that employs Taylor expansion (Maclaurin expansion) to extract higher harmonic components from back-EMFs in the dq-axis control system, allowing for precise correction of gain and phase adjustments for the q-axis current command value, thereby suppressing torque variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional feed-forward control methods are used to compensate for torque ripple, then the control system is simple to implement, but the compensation accuracy deteriorates due to sensitivity to motor resistance and inductance errors
Solution Approach 1:
The invention changes the control parameters by extracting higher harmonic components from back-EMF waveforms and using them to generate compensation values. This approach replaces conventional methods that are sensitive to motor parameter errors with a method that directly measures the actual back-EMF harmonics, thereby improving compensation accuracy without significantly increasing system complexity
Solution Approach 2:
The invention substitutes the conventional feed-forward control mechanism with a new approach that extracts harmonic components from measured back-EMF signals. By using actual measured data instead of theoretical calculations based on motor parameters, the system achieves higher precision while maintaining implementation feasibility
2Object-generated harmful factors
If higher harmonic components are extracted and compensated, then torque variation is suppressed, but the device complexity increases due to additional processing requirements
Solution Approach 1:
The invention extracts only the relevant higher harmonic components from the back-EMF waveform that contribute to torque ripple. By selectively extracting and compensating for specific harmonic frequencies rather than processing the entire signal spectrum, the system effectively suppresses torque variation while limiting the increase in processing complexity
Solution Approach 2:
The invention performs preliminary extraction of higher harmonic components from the back-EMF waveform before the main control processing. By pre-processing the signal to isolate harmonic components and store them for compensation, the system achieves torque ripple suppression while organizing the complexity into manageable preprocessing and compensation stages
3Stability of the object's composition
If conventional current feedback control is used, then the control system is stable, but torque ripple increases at high motor speeds due to insufficient compensation
Solution Approach 1:
The invention introduces higher harmonic components extracted from back-EMF as an intermediary element between the current feedback control and the motor drive. This intermediary compensation signal specifically addresses the torque ripple issue at high speeds while the underlying feedback control maintains system stability, allowing both objectives to coexist
Data Source
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AI summary
[Problem] An object of the present invention is to provide a motor control unit that extracts a higher harmonic component, which is contained in back-EMFs of the dq-axis control system, by means of Taylor expansion (Maclaurin expansion), and suppresses a torque variation by precisely correcting a gain and a phase of the higher harmonic component for a q-axis current command value and the electric power steering apparatus equipped with the same. [Means for solving the problem] The present invention is the motor control unit that drives a brushless motor having three or more phases by using a vector control on a dq-axis rotary coordinate system, comprising: a current command value calculating section to calculate a d-axis current command value id and a q-axis current command value iq based on a torque command value τc for the brushless motor, a rotational angle θe and a motor angular speed ω of the brushless motor, wherein the current command value calculating section extracts a higher harmonic component, which is contained in dq-axis back-EMFs of the brushless motor, by means of Taylor expansion, and corrects a gain and a phase of the higher harmonic component with a gain increasing and a phase lead, respectively, so as to compensate an attenuation due to a current control bandwidth.