Variable Pitch Fan Engine Control Decoupling
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Solution Overview
Problem
Current control systems for variable pitch fan engines and turbo-shaft, turbo-propeller engines lack a systematic method to coordinate propeller speed, power turbine shaft speed, and pitch angle while maintaining active constraints and rejecting disturbances, leading to inefficiencies in thrust control.
Innovation Solution
A control system that decouples the engine into two single-input single-output (SISO) control loops, using fuel flow and pitch change mechanism signals to manage propeller speed, power turbine shaft speed, engine core speed, and torque, while incorporating constraint decoupling to maintain core pressure, exhaust temperature, and torque within defined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a unified control system is used to manage propeller speed, power turbine shaft speed, and pitch angle, then coordination between these parameters is improved, but the system complexity increases and difficulty in controlling multiple constraints simultaneously worsens
Solution Approach 1:
The control system is segmented into two independent SISO control loops: one loop controls propeller speed (Nr) via the pitch change mechanism, and the other loop controls power turbine shaft speed (N1) via fuel flow. This segmentation simplifies the control architecture while maintaining coordination between the parameters, as each loop can be designed and tuned independently without affecting the other.
Solution Approach 2:
The patent introduces an intermediary decoupling control mechanism that separates the coupled multi-variable control problem into independent SISO loops. The decoupling control acts as a mediator that transforms the complex multi-input multi-output control system into simpler independent control loops, making it easier to manage multiple constraints simultaneously.
2Reliability
If multiple constraints (core pressure, exhaust temperature, core speed rate, torque) are controlled simultaneously in a unified system, then constraint satisfaction is improved, but the difficulty of detecting and measuring each constraint independently worsens
Solution Approach 1:
Each constraint (core pressure, exhaust temperature, core speed rate, torque) is assigned to and monitored within its respective SISO control loop. This segmentation allows each constraint to be detected and measured independently within its own control context, simplifying monitoring while ensuring all constraints are satisfied through coordinated control of the two loops.
Solution Approach 2:
The control system changes parameters dynamically within each SISO loop to satisfy constraints. For example, the pitch angle is adjusted to maintain core pressure within limits, while fuel flow is modified to control exhaust temperature and torque, allowing each constraint to be managed through appropriate parameter adjustments in its dedicated control loop.
3Measurement precision
If the pitch change mechanism is used to control propeller speed, then propeller speed control precision is improved, but the response time to disturbances worsens due to mechanical inertia
Solution Approach 1:
The patent merges the control of propeller speed through two mechanisms: the pitch change mechanism (for precision) and fuel flow adjustments (for rapid response). This combination allows the system to achieve both precise propeller speed control and fast response to disturbances by utilizing the strengths of both control mechanisms simultaneously.
Solution Approach 2:
The control system performs preliminary action by adjusting fuel flow in advance to anticipate disturbances, while the pitch change mechanism provides fine-tuned precision control. This preliminary adjustment of fuel flow prepares the system for upcoming disturbances, reducing the overall response time while maintaining precision through the pitch control loop.
Data Source
AI summary
A method and control system for an aircraft engine comprising a gas turbine driving a fan propeller with a mechanical gear-train and a dedicated pitch change mechanism for the fan propeller includes a fuel flow signal input; a pitch change mechanism signal input; a controlled plant for relating a pitch change mechanism pitch angle (BetaP) and a fuel flow (Wf) to at least two controlled outputs and a set of constraints. A decoupling control decoupling the controlled plant and/or the constraints into two separate single-input single-output (SISO) control loops for the first and second controlled outputs and a decoupling control decoupling the constraints from the decoupled controlled outputs and the constraints from one another provide gas turbine and fan propeller coordinate control while coordinately controlling constraints and outputs. A feedforward control can compensate the load change effect on engine speed and fan propeller rotor speed control.