Variable Gain Control System for Turbofan Stability
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Solution Overview
Problem
Existing engine fuel control systems, particularly for high bypass ratio turbofans, face inadequate control loop stability and phase margins when tuned for desired bandwidth, and turbine tip clearance control systems experience performance degradation due to radial clearance issues between rotor and stator assemblies.
Innovation Solution
The Modified Rolls-Royce Inverse Model (MRIM) control system introduces additional variable gains to adjust the integration time of the control system, allowing for improved trade-offs between bandwidth and stability, and applies a similar approach to engine-casing cooling air control systems to manage valve position dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the control system is tuned for desired bandwidth, then the response speed is improved, but the phase margins and stability deteriorate
Solution Approach 1:
The patent applies dynamics by making the integration time variable rather than fixed. The control system dynamically adjusts the integration time based on operating conditions, allowing the system to achieve fast response when needed while maintaining stability when required. This is accomplished through a variable gain element that modifies the integration time constant, enabling the controller to adapt its behavior to different operational states and resolve the trade-off between speed and stability.
Solution Approach 2:
The patent changes the parameter of integration time from a fixed value to a variable parameter. By introducing a variable gain element that adjusts the integration time constant based on system state, the control system can optimize performance across different operating conditions. This parameter change allows the system to achieve desired bandwidth and fast response while maintaining adequate phase margins and stability through adaptive tuning.
2Stability of the object's composition
If additional variable gains are added to adjust integration time, then the stability and phase margins are improved, but the device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by designing a control structure where a single variable gain element serves multiple purposes. The same gain adjustment mechanism that modifies integration time also simultaneously optimizes phase margins and maintains stability across different operating conditions. This universal approach avoids the need for separate complexity-intensive mechanisms for each control objective, resolving the contradiction between improved stability and increased device complexity.
3Stability of the object's composition
If the integration time is increased to improve stability, then the phase margins are improved, but the response time deteriorates
Solution Approach 1:
The patent resolves this contradiction by making the integration time dynamic rather than static. The variable gain element allows the integration time to be extended when stability is needed (improving phase margins) while being reduced when fast response is required. This dynamic adjustment eliminates the need to permanently increase integration time for stability, thereby preventing response time degradation while maintaining phase margins when needed.
Data Source
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AI summary
A control system provides an aggregate driven quantity demand signal for controlling an actuatable component. The system has a summing junction which generates the aggregate driven quantity demand signal by summing a first output signal, which converges on a steady state driven quantity requirement value, and a change in driven quantity demand signal. The system further has a feedback loop which generates the first output signal in response to the aggregate driven quantity demand signal. The system also has a first variable gain which tunes the change in driven quantity demand signal in response to a reference demand signal. The feedback loop includes a second variable gain which tunes the rate at which the first output signal converges on the steady state driven quantity requirement value. Typically, the reference demand signal corresponds to a desired value or desired change in value of a parameter which is itself varied or controlled by actuation of the actuatable component.