Electric Motor Eccentricity Detection Using Apparent Inductance
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Solution Overview
Problem
Existing methods for detecting static and dynamic eccentricities in electric motors are inaccurate and costly, as they either require bulky equipment or fail to distinguish between different types of eccentricities, leading to unclear maintenance thresholds and potential mechanical failures.
Innovation Solution
A method and device that analyze electrical waveforms to determine static and dynamic eccentricities by calculating the apparent inductance of the motor, using voltage and current waveforms to identify average and oscillating components, and compensate for variations due to speed and torque, allowing for clear estimation of eccentricity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical micrometers are used to detect motor shaft movement with high precision, then measurement precision of eccentricity is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical/optical measurement system (optical micrometers) with an electrical measurement system. By analyzing motor current signals and calculating apparent inductance variations, the system achieves eccentricity detection without requiring external optical sensors or mechanical measurement devices.
Solution Approach 2:
The motor itself serves as the measurement tool. The patent utilizes the motor's own current consumption patterns and inductance characteristics to detect eccentricity, eliminating the need for separate measurement equipment. The motor's electrical parameters directly reveal the eccentricity condition.
2Measurement precision
If accelerometers and acoustic sensors are used to detect vibrations, then vibration level detection is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical vibration sensors (accelerometers, acoustic sensors) with electrical signal analysis. By examining variations in motor current and apparent inductance, the system detects eccentricity-induced vibrations through electrical parameters rather than mechanical sensing.
Solution Approach 2:
The patent uses electrical current signals as an intermediary to detect mechanical vibration effects. Instead of directly measuring mechanical vibrations, the system measures the electrical signature (current harmonics, inductance variations) that results from vibration-causing eccentricity.
3Measurement precision
If Motor Current Signal Analysis is used to detect fault signatures, then detection capability is improved, but ability to distinguish between static and dynamic eccentricity deteriorates
Solution Approach 1:
The patent segments the fault detection process into two distinct analyses: one for static eccentricity (using average apparent inductance) and one for dynamic eccentricity (using oscillating component at rotor frequency). This segmentation allows clear distinction between the two eccentricity types while maintaining detection sensitivity.
Solution Approach 2:
The patent adds a new dimension to fault analysis by introducing apparent inductance as a measurement parameter. By analyzing both the average value and the rotor-frequency oscillating component of apparent inductance, the system distinguishes between static and dynamic eccentricity in the frequency domain.
4Manufacturing precision
If closed loop current controller is used to produce perfect current sinewaves, then current quality is improved, but fault signal level deteriorates
Solution Approach 1:
The patent converts the harmful effect of closed-loop controllers (which mask fault signals by producing perfect sinewaves) into a benefit. By using apparent inductance analysis, the system can detect eccentricity even when current harmonics are suppressed, as the inductance variations remain present regardless of controller action.
Data Source
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AI summary
The present invention concerns a device and a method for determining static and dynamic eccentricities of an electric motor. The invention: - obtains voltage and current waveforms of the electric motor; - obtains a waveform representative of an apparent inductance of the motor from the obtained voltage and current waveforms; - determines an average value (LDC) and an oscillating component value (ΔL) of the apparent inductance of the motor from the obtained waveform representative of the apparent inductance of the motor; - determines a reference apparent inductance value (Lo) expected in absence of eccentricity; - determines static and dynamic eccentricities from the determined average value and the determined oscillating component value of the apparent inductance of the motor and from the determined reference apparent inductance of the motor.