Sensorless Induction Motor Speed Measurement via Back-EMF
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Solution Overview
Problem
Existing methods for determining the electric angular speed of an induction motor without speed sensors are complex, prone to failure due to low saliency in magnetic cores, and generate harmonics and torque ripple, making them less effective for induction motors compared to Brushless Permanent Magnet motors.
Innovation Solution
A method that switches off the electric power supply to the stator phases for a short period, allowing stator currents to decay, and then picks up signals to determine the electric angular speed of the rotor, eliminating the need for saliency detection and reducing harmonic generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal injection methods are used to detect rotor speed without sensors, then speed measurement capability is achieved, but device complexity increases and reliability decreases due to low saliency in induction motors
Solution Approach 1:
The patent extracts the speed measurement capability from complex signal injection methods by utilizing the natural back-EMF signals generated during motor operation. Instead of injecting test signals to provoke saliency effects, the method directly measures the back-EMF voltages that naturally occur during normal motor operation, thereby achieving speed measurement without adding complexity to the control system.
Solution Approach 2:
The motor itself provides the measurement signal through its natural back-EMF generation during operation. The rotating rotor automatically generates voltages in the stator windings that contain speed information, eliminating the need for external test signal injection and making the motor self-sufficient for speed measurement.
2Loss of information
If signal injection methods are used for sensorless control, then speed and position detection is enabled, but harmful factors increase due to generated harmonics and torque ripple
Solution Approach 1:
The patent converts the harmful effect of low saliency in induction motors into a beneficial feature. Instead of trying to overcome the low saliency through complex signal injection, the method exploits the natural back-EMF signals that are generated during normal operation, which are present regardless of saliency magnitude. This approach turns the motor's inherent characteristics into an advantage for speed measurement.
Solution Approach 2:
The method utilizes the periodic nature of back-EMF generation during motor operation. By sampling the back-EMF voltages at appropriate intervals and analyzing their frequency content, the system can extract speed information without introducing additional periodic disturbances through signal injection.
3Loss of information
If saliency-based methods are used for induction motor control, then rotor position detection is achieved, but measurement precision decreases due to low saliency in magnetic cores
Solution Approach 1:
The patent replaces mechanical/saliency-based detection methods with an electromagnetic field-based approach. Instead of relying on magnetic saliency effects, the method uses the electromagnetic induction principle to generate and measure back-EMF voltages, which provide speed information independent of the magnetic core's saliency characteristics.
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 provides a simple and effective way to determine the electric angular speed of an induction motor without sensors, reducing complexity and noise, and is applicable even when saliency is low, ensuring stable motor control.
Implementation Method 1
the rotor is rotating, voltages are induced in the stator phases
Data Source
AI summary
The invention relates to a method for determining the electric angular speed of a rotor of an induction motor, wherein electric power supplied to phases of a stator of the induction motor affects the rotor, comprising the steps of: switching off the electric power supply to the phases of the stator during a particular period of time, picking-up signals corresponding to voltages at the stator phases within the particular period of time, and determining the electric angular speed of the rotor based on the picked-up signals.