Rotor Bending Mode Control via Coast-Down Measurement
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Solution Overview
Problem
Integrated motor-driven gas compressors face destructive forces due to uncontrolled bending modes in their rotating parts, which can damage both the electric motor and the rotary machine if left unchecked.
Innovation Solution
A method and device for controlling bending modes by accelerating and decelerating the rotor assembly through torsional forces, obtaining measurements during coast-down periods, and using a control system to adjust magnetic bearings based on these measurements to manage rotational speed and frequency, thereby anticipating and mitigating damage from bending modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotor assembly operates at high rotational speeds, then productivity is improved, but bending mode vibrations increase causing harmful forces to components
Solution Approach 1:
The system performs preliminary identification of bending mode frequencies during coast-down periods before normal operation. By measuring vibrations during the coast-down phase when the rotor is naturally decelerating, the system obtains bending mode frequency data in advance, allowing the control system to prepare appropriate control actions to suppress vibrations during subsequent high-speed operation.
Solution Approach 2:
The system continuously monitors rotor vibrations using sensors and feeds this information back to the control system. The control system compares measured vibrations against identified bending mode frequencies and adjusts bearing control forces in real-time to actively suppress resonant vibrations, creating a closed-loop feedback control mechanism that maintains stability at high speeds.
2Reliability
If magnetic bearings are used to support the rotor assembly, then reliability is improved, but device complexity increases due to the need for active control systems
Solution Approach 1:
The system utilizes the rotor's own coast-down motion to generate the excitation needed for identifying bending mode frequencies. By allowing the rotor to naturally decelerate and measuring the resulting vibrations, the system performs self-diagnosis without requiring external test equipment or complex identification procedures, simplifying the overall system while maintaining reliability.
Solution Approach 2:
The magnetic bearing control system serves multiple functions: it provides continuous rotor support during operation, actively suppresses bending mode vibrations during high-speed operation, and enables bending mode frequency identification during coast-down periods. This multi-functionality reduces the need for separate dedicated systems, thereby managing complexity while enhancing reliability.
3Measurement precision
If bending mode frequencies are measured during coast-down periods, then measurement precision is improved, but loss of time occurs due to deceleration cycles
Solution Approach 1:
The system performs bending mode frequency identification during the coast-down period that naturally occurs during normal operation cycles. Rather than requiring separate dedicated measurement periods, the system utilizes the existing deceleration phase to gather measurement data, ensuring that the useful action of frequency identification continues without interrupting the overall operational cycle, thus minimizing time loss while maintaining measurement precision.
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 controls bending modes, reducing the risk of damage to components by providing accurate measurements and adaptive control of magnetic bearings, ensuring stable operation and extending the operational life of the compressor.
Implementation Method 1
one or more magnetic bearings
Implementation Method 2
a first torsional force applied to the drive shaft by the motor
Implementation Method 3
The rotating parts of any rotary machine have resonance frequencies, where such rotating parts, for example, a drive shaft, can physically bend
Data Source
AI summary
A system and method for controlling bending modes of a rotor assembly is disclosed. The rotor assembly can be supported by one or more bearings in an integrated machine. The method can include accelerating the rotor assembly to a first rotational speed via a first torsional force applied to the drive shaft and then removing the first torsional force. The method can also include obtaining first measurements of the rotational speed and frequency of one or more bending modes of the rotor assembly during a first rotary machine coast down period from the first rotational speed. The process can be repeated to determine a relationship between rotational speed, bending mode frequency, and gain. The one or more bearings can then be controlled based on the measurements and the relationship. The system can have one or more processors or controllers to implement the method.