Sensorless DC Motor Position Determination via Ripple Frequency Correction
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Solution Overview
Problem
Existing methods for determining the rotational position of a rotating element driven by an electric motor, such as a commutated DC motor, are prone to measurement errors due to distorted current ripples and false ripples, especially under load conditions, which can lead to erroneous position determination, particularly in sensorless systems.
Innovation Solution
The method involves continuously measuring the time duration between consecutive current ripples to detect errors and correct the frequency signal based on a probable waveform, ensuring the frequency profile remains consistent with expected inertia characteristics, thereby accurately determining the number of revolutions and rotational position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If current ripple detection is used for sensorless position determination, then device complexity is reduced, but measurement precision deteriorates due to distorted ripples and false ripples under load
Solution Approach 1:
The patent applies feedback by continuously monitoring the frequency signal and comparing it against expected frequency ranges. When the detected frequency deviates from the expected range, the system identifies this as an error condition and corrects the ripple count accordingly. This feedback mechanism allows the sensorless system to maintain measurement precision despite the presence of distorted or false ripples during motor operation
Solution Approach 2:
The patent changes the parameter being monitored from raw current ripple amplitude to ripple frequency. By converting the time duration between ripples into a frequency signal and comparing it against expected frequency ranges, the system can distinguish between valid ripples and false ripples. This parameter transformation enables accurate position determination even when ripple morphology changes under load conditions
2Productivity
If current ripple counting is performed without frequency validation, then productivity is improved through direct position determination, but reliability deteriorates due to erroneous position determination from distorted ripples
Solution Approach 1:
The patent performs preliminary validation of the frequency signal before using it for position determination. By checking whether the detected frequency falls within the expected range before counting ripples, the system prevents erroneous position measurements from distorted or false ripples. This preliminary check ensures reliability without significantly impacting productivity
Solution Approach 2:
The system continuously monitors frequency and provides feedback to validate whether detected ripples are genuine. When frequency falls outside expected ranges, the system identifies measurement errors and corrects them, ensuring reliable position determination while maintaining efficient operation
3Measurement precision
If frequency signal correction is applied based on expected waveform, then measurement precision is improved, but device complexity increases due to additional correction mechanisms
Solution Approach 1:
The patent corrects measurement precision by transforming the ripple detection parameter from time duration to frequency and comparing it against expected frequency ranges. This parameter change enables simple threshold-based correction logic that maintains low device complexity while significantly improving measurement precision by filtering out false ripples and correcting distorted measurements
Data Source
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AI summary
The method involves measuring time period between two current ripples for detecting errors during the current ripple detection. The frequency of the detected current ripple is defined by the reciprocal value. The wave form of the frequency signal is adjusted in the area of the detected changes particularly by a probable wave form resulting from the remaining measuring data. The multiple rotations of the rotating elements are defined by the adjusted frequency signal. An independent claim is included for a device for determining the rotational position of a rotating element that actuates an electric motor like a commuted direct current motor.