Motor Driving Apparatus Current Sensor Offset Correction
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Solution Overview
Problem
Existing methods for correcting current sensor offset errors in three-phase alternating current motor driving apparatuses are inadequate, particularly in NC machine tools, as they are prone to noise and strain, leading to torque ripples and position errors that degrade machining precision.
Innovation Solution
A motor driving apparatus that employs a computation device to calculate a power spectrum of position errors at constant motor speed, using a gradient method to update offset correction amounts for the current sensor, thereby reducing torque ripples and position errors without requiring extensive learning or motor operation under various conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the detection value of the current sensor during a period in which no current is applied to the motor is used as an offset correction amount, then the offset error can be corrected, but the detected current value is affected by noise and strain, making the correction insufficient for suppressing torque ripple and position error
Solution Approach 1:
The patent applies preliminary action by performing offset correction during a coasting period (when no current is applied) before the motor enters the next operation phase. The computation device calculates the offset correction amount based on detection values obtained during this preliminary coasting period, ensuring the correction is ready before actual motor operation begins, thereby improving correction precision while avoiding noise interference during active operation.
2Manufacturing precision
If feedback gains for speed and position of a closed loop control system are increased to suppress position error due to torque ripple, then position error can be reduced, but the implementation is not easy and depends on characteristics of the control target
Solution Approach 1:
The patent extracts the torque ripple problem from the overall control system by specifically targeting the current sensor offset error as the root cause. Instead of increasing feedback gains across the entire control system, the invention isolates and corrects the offset error through a dedicated offset correction computation, thereby reducing torque ripple and position error without complicating the overall control system architecture.
3Measurement precision
If machine learning is used to learn current offset compensator with multiple inputs including temperature, voltages, and position error, then offset correction can be improved, but the learning process requires a very long period of time
Solution Approach 1:
The patent extracts only the essential element for offset correction - the detection value during the coasting period - and discards unnecessary complex inputs. By focusing solely on the current sensor detection value when no current is applied, the invention achieves accurate offset correction without requiring lengthy machine learning processes involving multiple parameters such as temperature, voltages, and position errors.
Data Source
AI summary
A torque ripple and a position error caused by an offset error of the current sensor affects an electrical angle frequency of a motor. In an apparatus of the present disclosure, a computation device executes a power spectrum computing process when a three-phase alternating current motor is at a constant speed, and a value obtained by subtracting a position command value from a position detected by a position detector is fast Fourier transformed, to compute a power spectrum of a position error signal at the electrical angle frequency. Then, the computation device executes an offset correction computing process, to evaluate the power spectrum and to update an offset correction amount. By repeatedly executing these processes when the three-phase alternating current motor is driven at a constant speed, the torque ripple and position error caused by the offset error are reduced.