Sensorless Motor Initial Position Estimation via Phase Current Correction

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Solution Overview

Problem

Sensorless-type brushless DC motors face challenges in accurately estimating the initial position of the magnetic pole due to variations in electrical and magnetic properties among phases, leading to errors in peak current detection and rotor positioning, which can cause vibration and paper jam issues in applications like electrophotographic image forming apparatuses.

Innovation Solution

A motor control device that applies voltages to multiple phases of the stator winding at various energization angles, converts peak currents into components with specific electrical angles, and corrects these components to accurately estimate the magnetic pole position, ensuring precise rotor positioning without rotation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the rotor is pulled to estimate the initial position of the magnetic pole, then the magnetic pole position can be estimated, but the rotor may vibrate greatly and paper jamming may occur

Engineering Contradiction:

Improvemagnetic pole position estimationVSAvoid rotor vibration and paper jamming

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical rotor pulling method with an inductive sensing method that uses electrical measurements. By applying voltages at different energization angles and detecting current values, the initial magnetic pole position is estimated without mechanical movement, thus avoiding vibration and paper jamming while achieving accurate position estimation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If the inductive sensing method is used to estimate the initial position, then the rotor does not need to move, but errors occur in the estimation result due to differences in electrical and magnetic properties among phases

Engineering Contradiction:

Improve rotor vibration and paper jammingVSAvoidmagnetic pole position estimation accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent changes the approach from directly using peak current values to using current values at specific timing (when the current reaches its maximum in the energization period). It also introduces correction mechanisms by comparing current values at different energization angles and using the relationship between current values to determine the magnetic pole position, thereby compensating for phase differences in electrical and magnetic properties

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a feedback mechanism where the current values detected at different energization angles are analyzed to identify the magnetic pole position. The system uses the relationship between current values at different angles to correct estimation errors, effectively compensating for phase differences through iterative comparison and determination

Inventive Principle:

Principle #23Feedback

3Measurement precision

If voltages are applied at multiple energization angles to improve estimation accuracy, then the magnetic pole position can be estimated more accurately, but the control device complexity increases

Engineering Contradiction:

Improvemagnetic pole position estimation accuracyVSAvoidcontrol device complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the estimation process into discrete steps: applying voltage at multiple predetermined energization angles, detecting current values at each angle, comparing the current values, and determining the magnetic pole position based on the comparison results. This segmented approach manages complexity by breaking down the estimation process into manageable stages

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method enhances the accuracy of magnetic pole position estimation, reduces motor vibration, and prevents paper jams by correcting peak current values based on phase differences, allowing for reliable operation in applications where rotor movement before startup is not feasible.

Implementation Method 1

a stator is energized at a prescribed electrical angle so as to pull the magnetic pole of the rotor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

start the rotation of the motor

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Data Source

PatentUS11223309B2Motor control device, method of estimating initial position of magnetic pole of rotor, and image forming apparatus

Publication Date: 2022.01.11 KONICA MINOLTA INC

AI summary

In a motor control device that controls a sensorless-type motor, a controller estimates an initial magnetic pole position of a rotor of a motor by an inductive sensing scheme while sequentially setting a plurality of energization angles. At each of the set energization angles, the controller converts peak values of currents flowing through a plurality of phases of a stator winding into a first current component having an electrical angle that is equal to a corresponding one of the set energization angles and a second current component that is different in electrical angle by 90 degrees from the first current component, to correct the first current component based on the second current component. The controller estimates the initial magnetic pole position of the rotor based on the corrected first current component that is obtained at each of the set energization angles.