Asynchronous Motor Speed Control Using Fixed-Frequency PWM

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Solution Overview

Problem

Existing methods for controlling asynchronous motors with speed variations require complex computations and high computing resources, making them inefficient and resource-intensive.

Innovation Solution

A method for controlling a polyphase asynchronous motor using a fixed control frequency and adjusting the duty cycle of control signals based on measured rotational speed, eliminating the need for complex frequency calculations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If U/f control method with variable control frequency is used to control motor speed variations, then motor speed control is achieved, but control complexity and computing resource requirements increase

Engineering Contradiction:

Improvemotor speed controlVSAvoidcontrol complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent changes the control parameter from variable frequency to variable duty cycle while keeping the control frequency fixed. This parameter substitution simplifies the control algorithm and reduces computing resource requirements while maintaining speed control capability through pulse-width modulation of the inverter output

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of varying the control frequency to control motor speed (conventional approach), the patent inverts the approach by keeping frequency fixed and varying the duty cycle of the control signals. This inversion simplifies the control system architecture and reduces computational complexity

Inventive Principle:

Principle #13The other way round (Inversion)

2Speed

If U/f control method with variable control frequency is used to control motor speed variations, then motor speed control is achieved, but computing resource requirements increase

Engineering Contradiction:

Improvemotor speed controlVSAvoidcomputing resource consumption

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The patent substitutes the computationally intensive frequency variation approach with a simpler duty cycle modulation approach. This parameter change significantly reduces the computing power required for real-time control calculations while maintaining effective speed control through PWM technique

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If fixed control frequency with duty cycle adjustment is used, then control simplicity and computing resource reduction are achieved, but motor performance may be limited

Engineering Contradiction:

Improvecontrol simplicityVSAvoidmotor performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the actual motor speed is measured and compared with the reference speed, and the duty cycle is continuously adjusted based on the speed error. This closed-loop control ensures that motor performance requirements are met while maintaining the simplicity of fixed-frequency control

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Although the control frequency is fixed, the system achieves dynamic speed control through real-time adjustment of the duty cycle parameter. This dynamic modulation of the PWM duty cycle allows the motor to adapt to varying load conditions and maintain optimal performance across different operating points

Inventive Principle:

Principle #15Dynamics

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

Simplifies motor speed control by reducing computational requirements while maintaining motor performance, without the need for bulky phase-shifting capacitors.

Implementation Method 1

supply by the inverter of electrical supply currents, according to the control signals, to power the motor, the electrical supply currents powering the motor windings in order to rotate the motor at a rotational speed

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

measurement of the motor's rotational speed, by a speed sensor

Methodology Applied

Scientific EffectSpeed sensing:

Implementation Method 3

generation of control signals for an inverter, by the control device; supply by the inverter of electrical supply currents, according to the control signals

Methodology Applied

Scientific EffectPulse-width modulation:

Data Source

PatentEP4657747A1Method for controlling an electromechanical actuator, associated electromechanical actuator and concealment device

Publication Date: 2025.12.03 SOMFY ACTIVITES SA

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AI summary

The present invention relates to a method for controlling an electromechanical actuator comprising a motor, the method comprising: - determining (102) a setpoint speed (Vc) of the motor; - generating (106) control signals from an inverter; - supplying (108) by the inverter electrical supply currents, according to the control signals, in order to rotate the motor at a rotational speed (Vm); and - measuring (110) the rotational speed (Vm) of the motor by a speed sensor. A frequency of the generated control signals is fixed and determined according to the setpoint speed (Vc), and a duty cycle of the control signals is adjusted according to the rotational speed (Vm) of the motor, measured by the speed sensor, so that the rotational speed (Vm) of the motor corresponds to the setpoint speed (Vc).