Sensorless BLDC Motor Speed Control Without Coil Floating

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Solution Overview

Problem

Brushless direct current (BLDC) motors experience acoustic noise and degraded response characteristics due to the floating process of unused coils for back electromotive force signal detection.

Innovation Solution

A motor driving device and control method that utilizes a back electromotive force signal to control motor speed by loading data based on duty, extracting motor speed through linear interpolation, and generating driving signals using a controller with a PI controller and PWM signal generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a coil is floated to obtain the back electromotive force signal, then the motor position can be detected, but acoustic noise is generated and response characteristic is degraded

Engineering Contradiction:

Improvemotor position detectionVSAvoidacoustic noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary signal processing mechanism where the back electromotive force signal is detected through voltage sensing during PWM off-periods rather than by floating the coil. This intermediary approach allows position detection without the harmful floating process, eliminating acoustic noise while maintaining measurement capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the traditional mechanical coil floating method with an electrical signal sensing approach. Instead of physically disconnecting and floating the coil, the system senses voltage across the coil during PWM off-periods, substituting a mechanical/electrical operation with a purely electrical measurement that avoids acoustic noise generation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If a coil is floated to obtain the back electromotive force signal, then the motor position can be detected, but response characteristic is degraded

Engineering Contradiction:

Improvemotor position detectionVSAvoidresponse characteristic

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent enables continuous position detection by sensing the back electromotive force signal during every PWM off-period without interrupting the motor driving cycle. This continuous sensing approach eliminates the response delays associated with periodic coil floating, maintaining fast response characteristics while enabling accurate position detection.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The patent uses voltage sensing during PWM off-periods as an intermediary method to detect the back electromotive force signal. This intermediary approach allows position detection to occur continuously without interrupting the motor drive, thereby maintaining fast response characteristics while achieving accurate position measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If a separate detection device such as a Hall sensor is used, then the motor position can be detected accurately, but the device complexity increases

Engineering Contradiction:

Improvemotor position detectionVSAvoiddetection device

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent makes the existing coil serve multiple functions: it acts as both the driving element and the sensing element for position detection. By detecting the back electromotive force signal across the same coil used for motor driving, the system eliminates the need for separate Hall sensors, reducing device complexity while maintaining position detection accuracy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent enables the motor system to detect its own position using its own coils and the back electromotive force they generate during normal operation. This self-service approach eliminates the need for external detection devices, simplifying the overall system while maintaining accurate position detection capability.

Inventive Principle:

Principle #25Self-service

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

The method enables fast response characteristics and eliminates acoustic noise by controlling the motor without the need for floating processes.

Implementation Method 1

a sensorless BLDC motor driving circuit, which does not use a separate detection device such as a Hall sensor for a position detection of the rotor, may detect a position of a permanent magnet of the rotor by detecting a back electromotive force formed in coils of the motor

Methodology Applied

Scientific EffectBack electromotive force: Electromagnetic Induction

Data Source

PatentEP4625806A1Motor driving device, control method therefor, and electronic device driven by motor

Publication Date: 2025.10.01 LX SEMICON CO LTD

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AI summary

The present invention relates to: a device applicable to a motor driving device, for example, a device for driving a direct current motor (DC motor); a control method therefor; and a device (electronic device) driven by a motor. The method for controlling a BLDC motor, according to the present invention, may comprise the steps of: extracting a stabilized motor speed according to duty so as to import stored data by means of a counter electromotive force signal received from a motor; receiving a set duty by means of a command of a user; extracting, from the data, a motor speed according to the set duty; and generating a driving signal according to the extracted motor speed.