Electric Motor Reactive Torque Control for Critical-Speed Vibration
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Solution Overview
Problem
Electric motors experience severe vibrations at natural frequencies, which are costly and time-consuming to mitigate through design modifications or frequency skip functions, and can lead to operational halts due to mechanical wear and bearing degradation.
Innovation Solution
A method involving a frequency converter that injects a reactive torque reference to counteract mechanical vibrations, using sensors to generate a vibration-related signal and control the motor with both main and reactive torque references, allowing operation at natural frequencies while reducing structural noise and extending bearing lifetime without mechanical modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If design modifications are made to alter natural frequency modes, then vibration severity is reduced, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent replaces mechanical design modifications with an electrical control solution. A frequency converter generates a reactive torque reference signal that is injected into the motor control system, creating counter-forces in the air gap to suppress vibrations. This substitutes complex mechanical alterations with an electrical control approach, reducing device complexity while maintaining vibration reduction effectiveness.
Solution Approach 2:
The patent changes the operating parameters of the motor by injecting a reactive torque reference through the frequency converter. This allows dynamic adjustment of torque characteristics to counteract vibrations at natural frequencies without physically modifying the motor structure. The parameter change approach enables flexible vibration suppression while avoiding permanent design modifications.
2Object-affected harmful factors
If frequency skip functions are used to prohibit operation at critical speeds, then vibration is reduced, but productivity and operating speed range decrease
Solution Approach 1:
The patent converts the harmful vibration phenomenon into a beneficial control opportunity. Instead of avoiding critical speeds, the system actively counteracts vibrations at these speeds by injecting reactive torque references. This allows the motor to operate continuously through critical speeds without interruption, maintaining full productivity while eliminating the harmful vibration effects that would otherwise occur.
Solution Approach 2:
The patent employs periodic reactive torque injection synchronized with the motor's natural frequency vibrations. The frequency converter generates torque references that oscillate at the critical frequency, creating counter-forces that cancel out the harmful vibrations. This periodic action enables continuous operation at all speeds including critical speeds, unlike frequency skip functions that require interrupting operation.
3Object-affected harmful factors
If mechanical modifications are made to reduce vibrations, then vibration performance improves, but ease of manufacture and installation deteriorate
Solution Approach 1:
The patent replaces mechanical vibration reduction measures with an electrical control system. Instead of modifying the motor's mechanical structure, bearings, or mounting assembly, the solution uses a frequency converter to generate reactive torque references that are processed by a controller to produce counter-forces. This electrical approach maintains ease of manufacture and installation while achieving superior vibration performance.
4Object-affected harmful factors
If reactive torque reference injection is implemented, then vibration suppression is achieved without mechanical modifications, but device complexity increases due to additional control system
Solution Approach 1:
The patent makes the frequency converter perform multiple functions: it not only controls the motor's speed and torque but also generates reactive torque references for vibration suppression. The controller processes both the main torque reference and the reactive torque reference, combining them to achieve both motor control and vibration reduction. This multi-functionality approach avoids adding separate dedicated vibration control hardware, thereby limiting the increase in device complexity.
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 suppresses mechanical vibrations in both steady-state and dynamic conditions, increasing the operating speed range and extending the life of motor bearings, while avoiding the need for costly mechanical adjustments.
Implementation Method 1
use a frequency converter to inject a reactive 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.
Data Source
AI summary
A method of reducing mechanical vibrations of a motor system including an electric motor, the method including: a) receiving a vibration-related signal based on measurements by one or more sensors mounted on the electric motor, b) generating a reactive torque reference based on the vibration-related signal, and c) controlling the electric motor based on the reactive torque reference and a main torque reference to counteract the mechanical vibrations.