Motor Controller Angle Error Correction for Torque Fluctuation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor controllers with low angle detection resolution experience torque fluctuation issues due to errors in rotational speed calculation, especially at low speeds, and require complex calculations for induced voltage and inductance estimation, leading to increased arithmetic load and potential torque fluctuations.
Innovation Solution
A motor controller with an angle detection unit that changes detection values stepwise, a current detection unit, a rotation state detection unit, a current command calculation unit, a current control unit, and an angle error correction unit that estimates and corrects angle errors based on current command values, reducing torque fluctuations without needing induced voltage and inductance estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rotational speed is calculated from angle sensor output signal, then angle detection value can be corrected, but calculation precision deteriorates at low rotational speeds
Solution Approach 1:
The patent changes the parameter used for angle error correction from rotational speed to current command value. By using current command value instead of rotational speed to determine the angle error correlation value, the system avoids the calculation precision deterioration that occurs at low rotational speeds, thereby maintaining accurate angle detection value correction across all speed ranges.
2Measurement precision
If induced voltage and inductance are estimated to improve angle detection accuracy, then torque fluctuation is suppressed, but arithmetic load increases
Solution Approach 1:
The patent extracts and uses only the current command value from the available system parameters to determine the angle error correlation value, eliminating the need for complex induced voltage and inductance estimations. This simplification reduces the arithmetic load while still achieving effective angle detection value correction and torque fluctuation suppression.
3Stability of the object's composition
If change rate of current command value is limited to suppress torque fluctuation, then torque stability improves, but torque drops due to excessive limitation
Solution Approach 1:
The patent applies preliminary correction to the angle detection value before current control, by determining an angle error correlation value based on the current command value and correcting the angle detection value in advance. This preliminary action eliminates the need for restrictive limitation on current command value change rate, thereby maintaining both torque stability and adequate torque output.
Data Source
AI summary
To provide a motor controller and an electric power steering apparatus which can suppress torque fluctuation resulting from low detection resolution of angle, with simple calculation, even in condition where the rotational speed of motor is low. A motor controller estimates an angle error correlation value correlated with the angle detection error based on the current command value when a change frequency of the angle detection value is lower than a cutoff frequency of feedback control system which controls a rotation state; corrects the current command value or the angle detection value based on the estimation value of angle error correlation value; and changes the estimation value of angle error correlation value so that the absolute value of angle detection error increases with respect to increase in the current command value, and the absolute value of angle detection error decreases with respect to decrease in the current command value.