Two-Shaft Gas Turbine Cross-Channel Control for Oscillation Damping
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Solution Overview
Problem
In two-shaft gas turbine engines, adjusting the fuel flow rate to control the rotational speed of the low-pressure turbine wheel can induce undesired oscillations in the high-pressure turbine wheel, due to mutual interactions between fuel flow rate and nozzle-guide-vane position adjustments, affecting the efficiency and dynamic performance of the engine.
Innovation Solution
A control system that includes rotational speed sensing systems for both turbine wheels, error calculators, and cross-channel controllers to generate modification signals that decouple the fuel and nozzle-guide-vane control loops, reducing or eliminating the undesired interactions and oscillations by considering the dynamic model of the gas turbine engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel flow rate is adjusted to control the rotational speed of the low-pressure turbine wheel, then the load rotational speed is maintained, but oscillations are induced in the high-pressure turbine wheel
Solution Approach 1:
The control system implements feedback loops that continuously monitor the rotational speeds of both the high-pressure turbine wheel and low-pressure turbine wheel. The measured speeds are compared with reference values, and the resulting errors are used to adjust fuel flow rate and nozzle-guide-vane position in real-time, eliminating oscillations through closed-loop control
Solution Approach 2:
The control system acts as an intermediary between the fuel flow rate adjustment and the nozzle-guide-vane position. By introducing a provisional control signal for the nozzle-guide-vane that is based on the rotational speed error of the high-pressure turbine wheel, the system decouples the two control loops and prevents mutual interactions that cause oscillations
2Reliability
If the nozzle-guide-vane position is adjusted to control the rotational speed of the high-pressure turbine wheel, then the combustion temperature is maintained, but oscillations are induced in the low-pressure turbine wheel
Solution Approach 1:
The control system uses feedback from the low-pressure turbine wheel rotational speed sensor to detect speed deviations. This feedback is processed through the control unit, which adjusts the nozzle-guide-vane position and fuel flow rate to eliminate oscillations and maintain stable rotational speed
Solution Approach 2:
The control system introduces a provisional fuel control signal that is based on the rotational speed error of the low-pressure turbine wheel. This intermediary control signal modifies the fuel flow rate adjustment in a way that counteracts the oscillations induced by nozzle-guide-vane position changes
Data Source
Figure 1
Figure 2(A)~2(E)
Figure 3
AI summary
A two-gas shaft turbine control system (31) is disclosed. The gas turbine control system comprises a fuel controller (35), which receives a speed error signal, indicating whether the low-pressure turbine wheel (11) of the gas turbine (1) is rotating at the desired target speed. The gas turbine control system (31) further comprises an NGV controller (41), which receives a speed error signal, indicating whether the high-pressure turbine wheel (9) of the gas turbine engine (1) is rotating at the desired target speed. Two cross channel controllers are further provided. On the basis of a gas turbine model, a first cross channel controller (43) provides a fuel control modification signal, which is added to a control signal generated by the fuel controller (35). A second cross channel controller (45) provides an NGV control modification signal. The modification signals are aimed at reducing or cancelling the effect of mutual interaction between fuel control and NGV control. A two-shaft gas turbine engine system and a method of operation are further disclosed.