Sensorless Induction Motor Speed Estimation via Slip Frequency Over-estimation
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Solution Overview
Problem
Existing sensorless induction motor control solutions lack accuracy in estimating mechanical parameters like speed and torque, especially under varying operating conditions, which affects functional safety by potentially exceeding safety references.
Innovation Solution
A method that determines the amplitude, phase, and frequency of stator voltage, estimates current components, torque, and speed, and calculates an over-estimation of speed considering slip frequency, enabling more accurate control of induction motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sensorless induction motor control solutions are used to eliminate speed sensors, then cost is reduced, but measurement precision of motor speed deteriorates
Solution Approach 1:
The patent introduces an intermediary calculation process that uses measured electrical quantities (stator voltage and current) combined with motor model parameters to derive mechanical quantities (speed and torque). Instead of directly measuring speed with a sensor, the system uses electrical measurements as intermediaries to estimate mechanical parameters through mathematical relationships, thereby avoiding the need for physical speed sensors while maintaining functional capability.
Solution Approach 2:
The patent replaces the mechanical speed sensing system with an electrical measurement and calculation system. Rather than using mechanical tachometers or encoders that physically interact with the motor shaft, the invention substitutes these with electrical sensors measuring voltage and current, combined with computational algorithms based on motor equations, thereby eliminating mechanical sensing components while achieving speed estimation.
2Device complexity
If sensorless speed estimation is used, then device complexity is reduced, but reliability for functional safety control deteriorates
Solution Approach 1:
The patent implements feedback mechanisms where the estimated speed and torque are continuously monitored and used to adjust control parameters. The system compares estimated mechanical parameters against safety thresholds and provides feedback control to ensure functional safety requirements are met, thereby compensating for the lack of direct mechanical sensing through continuous electrical measurement and computational correction.
Solution Approach 2:
The patent performs preliminary calculations of speed and torque estimates using measured electrical quantities before actual control decisions are made. By pre-calculating these mechanical parameters from electrical measurements using motor models, the system prepares safety-relevant information in advance, allowing for proactive safety control rather than reactive responses.
Data Source
AI summary
A method for controlling an electrical motor taking in account slip frequency. The method including determining amplitude, phase and frequency of the stator voltage from voltage measurements, determining estimates for current components from current measurement and stator voltage phase, determining estimate for torque from voltage amplitude, frequency, current amplitude and motor data, determining estimate for speed from torque, frequency and motor data, and determining over-estimation of speed from speed estimate, torque estimate and slip frequency. The over-estimation may be used to improve functional safety of the motor.