Coordinated Air-Fuel Control for Gas Turbines
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Solution Overview
Problem
Existing gas turbine control systems face challenges in coordinating air and fuel supply due to the non-intuitive relationship between turbine speed error and exhaust temperature error, making it difficult to design and tune cross channel controllers, which can lead to issues like lean blowout, exhaust over-temperature, and compressor surge.
Innovation Solution
A coordinated air-fuel controller operates in 'demand space' using a steady-state air versus fuel model to directly coordinate air and fuel supply, processing error signals through transfer functions to generate control signals for fuel and air actuators, thereby reflecting constraints within the fuel supply system and improving coordination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cross channel controller is used to control air and fuel supply based on turbine speed error and exhaust temperature error, then the control system can maintain turbine speed and temperature, but the non-intuitive relationship between speed error and temperature error makes the controller difficult to design and tune
Solution Approach 1:
The patent introduces a steady-state air-fuel model as an intermediary component that receives fuel controller output and generates expected combustion air controller output. This mediator translates the complex relationship between turbine speed error and exhaust temperature error into a more intuitive air-fuel ratio relationship, simplifying the controller design while maintaining control stability
Solution Approach 2:
The control system is segmented into distinct functional blocks: fuel controller, combustion air controller, and steady-state air-fuel model. Each block performs a specific function with clear inputs and outputs, making the overall system easier to design, tune, and maintain while preserving the reliability of coordinated air-fuel control
2Productivity
If traditional cross channel control is used, then basic air-fuel control is achieved, but adverse conditions like lean blowout, exhaust over-temperature, and compressor surge can occur
Solution Approach 1:
The steady-state air-fuel model provides a feedback mechanism where the expected combustion air controller output is compared with the actual combustion air controller output. This feedback ensures that the air-fuel ratio remains within safe operating limits, preventing lean blowout, exhaust over-temperature, and compressor surge while maintaining responsive control
Solution Approach 2:
The controller proactively prevents adverse conditions by using the steady-state air-fuel model to predict expected air controller output before actual operating conditions deviate into dangerous zones. This preliminary anti-action counteracts potential harmful effects before they manifest, maintaining safe operation during transient conditions
Data Source
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AI summary
A coordinated air-fuel controller (13) and associated method provide a fuel controller (23), a combustion air controller (25) and a steady-state air versus fuel model (15). The fuel controller (23) generates a fuel control output signal (33) and the combustion air controller (25) generates a combustion air control output signal (47). The fuel controller (23) determines a preliminary fuel control signal (41) based on at least one of first and second loop control signals, and determines the fuel control output signal (33) based on the preliminary fuel control signal (41). The steady-state air versus fuel model (15) processes the preliminary fuel control signal (41) to determine an expected steady-state combustion air control signal (53). The combustion air controller (25) determines a preliminary combustion air control signal (51) based on at least one of a third loop control signal (37c) and a fourth loop control signal (37c), and determines the combustion air control output signal (47) based on the preliminary combustion air control signal (51) and the expected steady-state combustion air control signal (53).