Combined-Cycle Droop Control for Stable Turbine Load Sharing
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Solution Overview
Problem
Combined cycle power plants face challenges in achieving optimal droop settings and MW margins for primary frequency control, particularly when steam turbines operate in sliding pressure mode, leading to inefficient and unstable load sharing among gas and steam turbines.
Innovation Solution
A control system that automatically calculates and optimizes droop settings and MW margins for both gas and steam turbines in real-time, considering HRSG storage values and turbine availability, ensuring stable frequency regulation without manual intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power generation units operate at full capacity, then productivity is maximized, but frequency control capability deteriorates due to lack of MW margin
Solution Approach 1:
The patent implements dynamic droop settings that automatically adjust based on real-time operating conditions. The control system continuously monitors turbine availability, HRSG storage values, and grid frequency requirements to optimize the droop characteristic, enabling the plant to maintain frequency control capability while operating at higher capacity levels than traditional fixed droop settings would allow
Solution Approach 2:
The system changes the droop parameter dynamically rather than using a fixed value. By calculating optimal droop settings based on current steam turbine availability, gas turbine load, and HRSG steam storage conditions, the system adapts the control parameter to maintain frequency regulation capability across varying operating points, resolving the contradiction between full capacity operation and frequency control readiness
2Measurement precision
If manual optimization of droop settings is performed, then frequency control precision is improved, but operation complexity increases and response time decreases
Solution Approach 1:
The control system performs self-optimization by automatically calculating and adjusting droop settings based on real-time plant conditions. The system monitors HRSG steam storage, turbine availability, and grid frequency requirements, then autonomously determines optimal droop characteristics without requiring manual intervention from operators, thereby maintaining high frequency control precision while simplifying operations
Solution Approach 2:
The system implements continuous feedback loops that monitor frequency deviations, turbine performance, and HRSG storage levels. This feedback information is used by the control algorithm to dynamically adjust droop settings, ensuring optimal frequency control precision while eliminating the need for manual optimization processes
3Adaptability or versatility
If steam turbines operate in sliding pressure mode, then adaptability to load changes is improved, but load sharing stability deteriorates
Solution Approach 1:
The patent applies dynamic droop settings specifically tailored for sliding pressure mode operation. The control system continuously adjusts the droop characteristic based on real-time steam storage levels and turbine availability, enabling the steam turbine to adapt flexibly to load changes while maintaining stable load sharing with the gas turbine through optimized control parameters
Solution Approach 2:
The system dynamically changes the droop parameter to compensate for the inherent instability of sliding pressure mode. By adjusting the droop setting based on HRSG storage values and turbine performance conditions, the system maintains load sharing stability while preserving the adaptability benefits of sliding pressure operation
4Reliability
If MW margin is increased for frequency control, then frequency control reliability is improved, but power generation output decreases
Solution Approach 1:
The system dynamically optimizes the balance between MW margin and power generation output by continuously adjusting droop settings based on real-time conditions. This enables the plant to maintain adequate frequency control reliability while minimizing the impact on power generation output, achieving a more favorable trade-off than traditional fixed droop approaches
Data Source
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AI summary
A power plant is operable to provide primary frequency control for a grid. The power plant includes a gas turbine operable to power a first generator that is synchronized to the power grid and to produce an exhaust gas, the gas turbine operated at a power level that defines a non-zero first MW margin and including a first control system having a first droop setting, and a heat recovery steam generator (HRSG) operable to generate high pressure steam in response to the passage of the exhaust gas through the HRSG. A steam turbine is operable to power a second generator that is synchronized to the power grid, the steam turbine is operated at a power level that defines a non- zero second MW margin and includes a second control system having a second droop setting, the second droop setting set to a value based at least in part on the second MW margin. The first control system calculates the first droop setting based at least in part on the first MW margin, the second droop setting, the second MW margin, and a regional required total droop for the combination of the gas turbine and the steam turbine.