Motor Vibration Identification Using Reactive Torque Sweeps
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Solution Overview
Problem
Existing methods for reducing vibrations in electric motors, such as design modifications and frequency converter techniques, are costly, time-consuming, and can lead to instability issues due to the need for precise natural frequency measurement and compensation, especially during mechanical wear and dynamic changes.
Innovation Solution
A method involving sweeping the frequency of oscillating reactive torque to determine the natural frequency of the motor system, incrementally increasing the reactive torque magnitude, and obtaining gain and phase responses to adaptively control the reactive torque using an adaptive closed-loop strategy, eliminating the need for mechanical modifications and Phase Locked Loop synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If design modifications are made to the mechanical assembly to alter natural frequency modes, then vibrations at natural frequencies are reduced, but the cost and complexity of the machine increase
Solution Approach 1:
The patent replaces mechanical design modifications with an electrical control system. A frequency converter injects a compensation torque reference signal that generates counter forces in the air gap to suppress vibrations, eliminating the need for mechanical assembly modifications while achieving the same vibration reduction effect
Solution Approach 2:
The patent changes the operating parameters of the frequency converter to dynamically compensate for vibrations. By adjusting the compensation torque reference signal parameters (magnitude and phase) based on detected vibration levels, the system adapts to changing natural frequencies without mechanical modifications
2Object-affected harmful factors
If frequency skip functions are used to prohibit operation at critical speeds, then vibrations are avoided, but the operating speed range of the motor is reduced
Solution Approach 1:
The patent converts the harmful vibrations at critical speeds into useful information. By detecting vibrations and using them to generate a compensation torque reference signal, the system allows operation at previously prohibited critical speeds while actively suppressing vibrations rather than avoiding them
3Object-affected harmful factors
If PI-type or PR-type controllers are used to generate compensation torque, then machine vibrations are suppressed, but the controller output saturates due to small remaining vibrations, leading to dynamic stability issues
Solution Approach 1:
The patent implements a feedback mechanism where vibration sensors continuously monitor the motor assembly, and the detected vibration signal is used to dynamically adjust the compensation torque reference signal. This closed-loop feedback prevents controller saturation by continuously adapting the compensation level to actual vibration conditions
Solution Approach 2:
The patent makes the compensation system dynamic by continuously adjusting the compensation torque magnitude and phase based on real-time vibration measurements. This dynamic adaptation prevents the static controller output saturation that leads to instability
4Ease of operation
If Phase Locked Loop (PLL) is used for synchronization in the control system, then the reactive torque can be synchronized with the motor, but the delay caused by PLL synchronization leads to suboptimal vibration control and instability issues during dynamic speed changes
Solution Approach 1:
The patent replaces the PLL synchronization mechanism with a direct vibration-based phase detection method. By using the vibration signal itself to determine the phase for compensation torque injection, the system eliminates the PLL delay and its associated stability issues during dynamic speed changes
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 approach effectively reduces vibrations, increases the operating speed range of the motor, extends bearing lifetime, and minimizes structural noise without mechanical modifications, while improving dynamic stability and reducing the need for costly frequency skip functions.
Implementation Method 1
use a frequency converter to inject a compensation torque reference which is added to the torque reference generated by the frequency converter's speed controller. This additional torque generates counter forces in the air gap of the machine which leads to suppression of machine vibrations
Implementation Method 2
determining a natural frequency of the motor system, the natural frequency being the frequency at which the oscillating reactive torque produces a maximum amplitude of a vibration-related parameter
Data Source
AI summary
A method of identifying parameters of a motor system having an electric motor assembly and a control system, for vibration reduction in the electric motor assembly, the method including: a) sweeping a frequency of an oscillating reactive torque injected into the electric motor, b) determining a natural frequency of the motor system, the natural frequency being the frequency at which the oscillating reactive torque produces a maximum amplitude of a vibration-related parameter obtained based on vibration-related measurements by sensors mounted to the electric motor, c) incrementally increasing a magnitude of reactive torque oscillating at the natural frequency, injected to the electric motor, d) obtaining a magnitude of the vibration-related parameter for each magnitude of the reactive torque injected in step c), and e) determining, for each magnitude of the injected reactive torque, a gain and a phase response of the motor system, the gain being determined based on the magnitude of the injected reactive torque and the corresponding magnitude of the vibration-related parameter, and the phase response being determined based on a phase angle of the injected reactive torque and a phase angle of the corresponding vibration-related parameter.