Combined-Cycle Power System Frequency Stabilization
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Solution Overview
Problem
Combined-cycle power systems face challenges in rapidly and effectively responding to grid frequency transients due to limitations in thermal energy storage and response times, leading to potential stress on components and inefficiencies in maintaining power reserves.
Innovation Solution
A method and apparatus for operating a combined-cycle power system that synchronizes steam and combustion turbines with the grid frequency, using a controller to modulate steam flow and air inlet guide vane positions to manage thermal energy reserves and facilitate uniform frequency recovery, allowing for simultaneous adjustments of both turbines to address frequency deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If steam turbine control valves are modulated to respond to grid frequency transients, then frequency recovery is facilitated, but thermal energy reserves may be depleted too rapidly causing component stress
Solution Approach 1:
The control system dynamically adjusts the steam turbine control valve modulation rate based on real-time assessment of thermal energy reserves and component stress thresholds. The valve modulation is not fixed but adapts its rate and extent to balance frequency recovery needs with thermal energy conservation and component protection
Solution Approach 2:
The system continuously monitors thermal energy reserves, turbine operating conditions, and grid frequency deviations. This feedback information is used to adjust the valve modulation strategy in real-time, preventing excessive thermal energy depletion and component stress while maintaining effective frequency recovery
2Speed
If steam turbine responds rapidly to frequency transients using stored thermal energy, then frequency recovery is accelerated, but the duration of effective response is limited
Solution Approach 1:
The system pre-charges thermal energy reserves in the steam generation system during normal operating conditions. This preliminary accumulation of thermal energy ensures that when frequency transients occur, the steam turbine has sufficient stored energy to respond rapidly and sustain the response for the required duration
Solution Approach 2:
The control system dynamically coordinates between steam turbine valve modulation and combustion turbine air inlet guide vane positioning to extend the effective response duration. As thermal energy reserves are depleted, the system adjusts the coordination strategy to maintain sustained frequency support
3Productivity
If combustion turbine air inlet guide vanes are modulated simultaneously with steam turbine valves, then frequency recovery is enhanced, but system complexity increases
Solution Approach 1:
The control system merges the control of steam turbine valves and combustion turbine air inlet guide vanes into a coordinated frequency recovery strategy. Both control elements work together in a unified control framework that assesses their combined effect on frequency recovery and thermal energy management
Solution Approach 2:
The controller acts as an intermediary that coordinates between the steam turbine control system and combustion turbine control system. It translates grid frequency deviations into coordinated valve and vane modulation commands, managing the complexity by providing a centralized control intelligence layer
4Speed
If steam turbine control valves open quickly to release thermal energy, then frequency transient is mitigated faster, but thermal energy reserve is depleted too rapidly
Solution Approach 1:
The control system dynamically determines the optimal valve opening rate based on real-time thermal energy reserve levels and the severity of the frequency transient. The valve modulation rate is not fixed but adapts to balance the need for rapid frequency mitigation with the need to preserve sufficient thermal energy reserves for sustained response
Solution Approach 2:
The system applies partial valve opening rather than full opening, modulating the degree of action to match the actual frequency deviation and thermal energy availability. This prevents excessive thermal energy depletion while providing sufficient frequency support
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables more stable and efficient grid frequency control, reducing the risk of component stress and maintaining high thermal efficiency, thereby improving the system's responsiveness and operational stability during frequency transients.
Implementation Method 1
The steam generated is channeled to a turbine wherein the thermal energy of the steam is converted to mechanical energy to rotate the rotor of the turbine
Implementation Method 2
Many known CTGs ignite a fuel-air mixture in a combustor assembly and generate a combustion gas stream that is channeled to a turbine assembly
Implementation Method 3
The power generated is proportional to the rate of combustion gas flow to the turbine and the temperature of the gas flow stream
Implementation Method 4
The generator frequency is normally synchronized to the electric power grid frequency and rotates at a speed substantially similar to the grid frequency
Data Source
AI summary
Methods and apparatus for operating a combined-cycle power system are provided. The method includes operating the steam turbine, the combustion turbine, and the steam source at steady state operating conditions. Upon sensing a grid frequency deviation away from the standardized grid frequency value, determining a current thermal energy capacity of the steam source, determining a rate of frequency recovery available using the current thermal energy capacity of the steam source and a predetermined rate of change of the at least one steam turbine control valve, if the determined rate of frequency recovery available is greater than the grid frequency deviation, mitigating the frequency deviation using the current thermal energy capacity, if the determined rate of frequency recovery available is less than the grid frequency deviation then mitigating the frequency deviation using the current thermal energy capacity substantially simultaneously with a power level increase of the combustion turbine.