Sensorless Motor Speed Control via Back EMF Measurement

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Solution Overview

Problem

Conventional motor control systems are costly due to the need for Hall effect sensors and two-speed motors, and they often generate noise, while also increasing manufacturing costs and complexity.

Innovation Solution

A sensorless motor controller that uses electromotive force (EMF) conditions to control and monitor the speed of AC inductive motors, eliminating the need for Hall effect sensors and reducing noise by implementing periodic motor control instead of continuous control, thereby reducing costs and simplifying manufacturing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If Hall effect sensors are used to monitor motor speed, then speed detection accuracy is improved, but manufacturing cost increases

Engineering Contradiction:

Improvespeed detection accuracyVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The motor itself generates the speed detection signal through its back EMF characteristics. The controller measures the motor's own electrical characteristics (current, voltage, frequency) to determine speed, eliminating the need for external sensors. This self-service approach resolves the contradiction by using the motor's inherent properties for measurement without adding costly Hall effect sensors.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces mechanical/sensor-based speed detection (Hall effect sensors) with electrical field-based detection by measuring back EMF and current characteristics. This substitution eliminates physical sensors while maintaining speed detection capability, thereby reducing manufacturing cost while preserving measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If two-speed motors are used, then motor speed control capability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvemotor speed control capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent implements dynamic speed control of a single-speed motor by continuously adjusting the RMS voltage applied to the motor based on real-time back EMF measurements. This dynamic control approach provides multi-speed operation capability without requiring a physically complex two-speed motor, thereby maintaining adaptability while reducing manufacturing cost.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the electrical parameters (voltage magnitude, frequency) applied to the motor to achieve different operating speeds. By controlling the RMS voltage and switching between different voltage levels based on measured conditions, the system provides speed control capability equivalent to a two-speed motor while using a simpler single-speed motor design.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If continuous motor control is implemented, then speed control precision is improved, but noise generation increases

Engineering Contradiction:

Improvespeed control precisionVSAvoidnoise generation

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The controller implements periodic measurement of back EMF and RMS voltage at specific intervals during motor operation. Rather than continuous control, the system samples motor conditions periodically and adjusts speed at discrete moments, maintaining control precision while reducing the noise associated with continuous switching and control adjustments.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary measurements of back EMF and motor conditions before making control adjustments. By measuring and evaluating motor state in advance and only making necessary speed changes when needed, the system maintains precise speed control while avoiding unnecessary control actions that would generate noise.

Inventive Principle:

Principle #9Preliminary anti-action

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 solution provides an inexpensive, efficient, and safe method for monitoring and controlling motor speed, reducing noise and manufacturing costs, while ensuring proper motor operation by dynamically adjusting speed settings and improving safety features.

Implementation Method 1

The present invention provides a sensorless motor controller for controlling an AC inductive motor using the electromotive force (EMF) conditions within the motor

Methodology Applied

Scientific EffectElectromotive force (EMF): Electromagnetic Induction

Implementation Method 2

each time the motor is cut off (i.e., power is cut off), an inductive spike results. The present invention further recognizes that the EMF is dependent on the speed of the motor at the time the motor is cut off

Methodology Applied

Scientific EffectBack EMF: Electromagnetic Induction

Data Source

PatentUS8198853B2Motor speed controller

Publication Date: 2012.06.12 BSH HOME APPLIANCES CORP

AI summary

A motor speed controller and a method of controller a speed of a motor are provided. The system and method include a motor and a motor controller that monitors operation of the motor based on electromotive force (EMF) conditions of the motor. The motor controller cuts a voltage to the motor, measures an electromotive force (EMF) of the motor at a predetermined time after the cutting of the voltage to the motor, and compares the measured electromotive force (EMF) to a table.