Turboshaft Load Control with Feedforward–Feedback Speed Stabilization
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Solution Overview
Problem
Existing gas turbine engines struggle to effectively control fuel flow in response to disturbances or changes in desired power from the load, particularly in turboshaft engines like those used in helicopters, where maintaining constant power turbine speed is challenging due to varying rotor loads.
Innovation Solution
A control logic system utilizing both feedforward and feedback control mechanisms to stabilize power turbine speed, incorporating a feedforward governing module that translates aircraft input rates into fuel flow demand and a feedback governing module that adjusts based on power turbine speed errors, with an aggressive control module for rapid responses to large disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional feedback control is used to maintain power turbine speed, then the system responds to speed errors, but the response is too slow for large disturbances and causes oscillations
Solution Approach 1:
The feedforward control module predicts future fuel flow requirements based on the rate of change of aircraft inputs (collective pitch rate) and applies corrections before speed errors develop. This preliminary action prevents disturbances from causing significant speed deviations, enabling quick acceleration or deceleration without waiting for feedback errors to accumulate.
Solution Approach 2:
The control system dynamically switches between aggressive control mode (for large disturbances) and stable control mode (for small disturbances). The aggressive mode provides rapid response to large speed errors, while the stable mode prevents oscillations during normal operation. This dynamic adaptation resolves the contradiction between fast response and stability.
2Speed
If aggressive control is applied to large disturbances, then quick response is achieved, but transitions between control modes cause oscillations
Solution Approach 1:
The control system dynamically adjusts its aggressiveness based on the magnitude of speed errors. For large errors, aggressive control provides rapid correction; for small errors, stable control prevents oscillations. The smooth transition between modes is managed by comparing error magnitude against thresholds, ensuring stability while maintaining fast response capability.
Solution Approach 2:
Different control strategies are applied to different operating conditions: aggressive control for large disturbances and stable control for small disturbances. This localized approach ensures that each control mode operates in its optimal performance region, achieving both fast response and stability without harmful transitions.
3Productivity
If feedforward control is used to predict fuel flow demand, then response to load changes is improved, but processing time increases due to complex calculations
Solution Approach 1:
The feedforward control extracts only the essential information needed for prediction: the rate of change of aircraft inputs (collective pitch rate). By focusing on this single critical parameter rather than computing full thermodynamic models in real-time, the system achieves effective load change response with minimal processing time.
4Speed
If the control system responds aggressively to all disturbances, then quick acceleration is achieved, but small disturbances cause unnecessary oscillations
Solution Approach 1:
The control system dynamically adapts its response characteristics based on disturbance magnitude. For large speed errors, aggressive control provides rapid acceleration or deceleration. For small speed errors, stable control maintains smooth operation without unnecessary oscillations. This dynamic adaptation resolves the contradiction between fast response and stability.
Data Source
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AI summary
Control schemes for controlling a gas turbine engine (100) in response to disturbances associated with a load (40) mechanically coupled with the gas turbine engine (100) are provided. In one aspect, a gas turbine engine (100) mechanically coupled with a load (40) has a controller (200) that includes executable control logic. The control logic includes a feedforward module (310), an aggressive control module (320), and a power turbine governor module (330). By executing the modules (310, 320, 330), the controller (200) seeks to maintain a constant power turbine speed stably and subtly in response to small disturbances associated with the load (40) and aggressively in response to large disturbances associated with the load (40), as well as smooth transitions between the responses.