Induction Motor Inductance Estimation Without Speed Sensors
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Solution Overview
Problem
Existing methods for estimating inductance parameters of line-connected squirrel-cage induction motors are impractical due to the need for speed sensors and electronic injection circuits, which are costly and difficult to install, especially for motors under dynamic operations like time-varying loads.
Innovation Solution
A method that estimates inductance parameters using motor nameplate data and instantaneous reactive power derived from voltage and current measurements, eliminating the need for speed sensors and electronic injection circuits, by synthesizing complex voltage and current signals and employing linear-phase band-pass filters and least-squares solvers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If speed sensors and electronic injection circuits are used for inductance parameter estimation, then measurement precision is improved, but device complexity and installation difficulty increase
Solution Approach 1:
The patent extracts and eliminates the speed sensor and electronic injection circuit from the system, achieving inductance parameter estimation using only voltage and current measurements already available at the motor terminals. This removes the complex hardware while maintaining estimation capability through alternative signal processing methods.
Solution Approach 2:
The system uses the motor's own operational voltage and current signals to estimate inductance parameters, without requiring external injection circuits or speed sensors. The motor's normal operation provides sufficient information for parameter estimation through the proposed signal processing approach.
2Device complexity
If steady-state equivalent circuit model is used for parameter estimation, then device complexity is reduced, but adaptability to dynamic operations deteriorates
Solution Approach 1:
The patent transitions from static steady-state models to a dynamic estimation approach that works during motor operation. By using instantaneous voltage and current measurements with signal processing techniques, the method adapts to changing load conditions and dynamic operations while maintaining practical implementation complexity.
Solution Approach 2:
The approach changes the estimation parameters from requiring multiple steady-state operating points to using instantaneous measurements during normal operation. This allows continuous parameter estimation across varying load conditions without requiring the motor to be stopped or operated at specific steady-state points.
3Measurement precision
If dynamic equivalent circuit model with least-squares solution is used, then measurement precision is improved, but device complexity increases due to speed sensor requirement
Solution Approach 1:
The patent removes the speed sensor requirement from the dynamic estimation approach by extracting rotor speed information indirectly from the voltage and current measurements through signal processing, eliminating the need for external speed sensing hardware while maintaining dynamic operation capability.
Solution Approach 2:
The system uses signal processing techniques as an intermediary to obtain rotor speed information indirectly from electrical measurements rather than direct mechanical sensing. This mediator approach allows dynamic parameter estimation without physical speed sensors.
Data Source
AI summary
Methods and devices are presented herein for estimating induction motor inductance parameters based on instantaneous reactive power. The induction motor inductance parameters, e.g., the stator inductance and the total leakage factor, can be estimated from motor nameplate data and instantaneous reactive power without involving speed sensors or electronic injection circuits. In one embodiment, the method includes: measuring voltages and currents; converting the measured voltages and currents into discrete-time voltage and current samples by analog-to-digital converters; synthesizing a complex voltage from the discrete-time voltage samples; synthesizing a complex current from the discrete-time current samples; acquiring and storing motor nameplate data; detecting instantaneous rotor speed by calculating an instantaneous rotor slot harmonic frequency with respect to an instantaneous fundamental frequency; calculating, via an induction motor inductance estimator, the motor's instantaneous reactive power and other intermediate quantities; and outputting the stator inductance and the total leakage factor.