Sensorless Brush Motor Rotor Position Detection via Ripple Filtering

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing methods for detecting the angular position and speed of DC brush motors without sensors face challenges due to noise and irregularities in the armature current signal, caused by wear, physical phenomena, and power line disturbances, leading to inaccurate counting of peaks and synchronization issues.

Innovation Solution

A self-synchronized time-domain filtering method that transforms the discrete angular position into a continuous function by validating leading edges of a square wave pulse signal within a time window, integrating the ripple frequency, and resetting the integration ramp to accurately discriminate ripple peaks from disturbances, thereby reducing estimation errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If Hall sensors or encoders are used to detect rotation speed, then measurement precision is improved, but device complexity and cabling requirements increase

Engineering Contradiction:

Improverotation speed detection precisionVSAvoidcabling complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention extracts the useful signal (brush switching ripple) from the armature current and separates it from harmful components (noise, BEMF, disturbances) through signal processing. By focusing only on the ripple component generated during brush switchings, the system achieves accurate rotation speed detection without requiring additional sensors or cabling

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the mechanical sensor-based detection system (Hall sensors, encoders requiring physical mounting and cabling) with an electronic signal processing approach that analyzes existing electrical signals in the armature current, eliminating the need for additional mechanical components and their associated cabling

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If frequency-based filtering is used to discriminate ripple peaks, then noise reduction is improved, but reliability deteriorates when main ripple frequency components are missing

Engineering Contradiction:

Improvenoise discrimination capabilityVSAvoidpeak detection reliability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The invention uses a dynamic time window that adapts to the current estimated ripple frequency, allowing the validation window to automatically adjust its duration based on real-time frequency estimates. This dynamic approach ensures reliable peak detection even when frequency components vary or are temporarily missing

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system implements feedback by continuously updating the ripple frequency estimate based on detected peaks and using this updated estimate to adjust the validation time window for subsequent peaks. This closed-loop approach maintains detection reliability even when frequency components are missing or distorted

Inventive Principle:

Principle #23Feedback

3Productivity

If peak counting is performed during relay switching, then productivity is improved, but measurement precision deteriorates due to signal absence

Engineering Contradiction:

Improvedetection speedVSAvoidpeak counting accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The system performs preliminary action by predicting when the next ripple peak should occur based on the current frequency estimate and establishing a validation time window in advance. This allows the system to be prepared for peak detection even during transient events like relay switching, maintaining accuracy without sacrificing detection speed

Inventive Principle:

Principle #10Preliminary action

4Device complexity

If brush motors with reduced number of brushes are used, then device complexity is reduced, but measurement precision deteriorates due to fewer switching events

Engineering Contradiction:

Improvebrush motor simplicityVSAvoidangular position detection precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The invention transitions from discrete peak counting to continuous function representation by using the integration ramp to estimate intermediate angular positions between brush switchings. This dimensional transformation from discrete to continuous provides sufficient precision even with fewer brush switching events

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS8169178B2Detection of the angular position of the rotor of a brush motor without using sensors

Publication Date: 2012.05.01 STMICROELECTRONICS SRL

AI summary

A method of detecting an angular position of a rotor of a motor includes detecting switching ripple peaks and armature current disturbance peaks using a peak detector configured to generate a square wave having edges coinciding with detected peaks. The method further includes filtering the square wave in a time domain by generating an integration ramp, toward a set value, of an estimated ripple frequency for an interval of time based on the estimated ripple frequency. An enablement range is established to reset the integration ramp by setting a threshold below and above the set value and a time window centered on an end time of each period of the estimated ripple frequency. The method further includes resetting the integration ramp, and updating the estimated ripple frequency based upon a period determined by a time of the resetting, if an edge of the square wave is within the time window.