Electronic Decoupling for Combined-Cycle Power Plant Turbines
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Solution Overview
Problem
Existing combined-cycle power plants face limitations in flexibility and efficiency due to rigid coupling between gas turbine speed and grid frequency, leading to restricted optimization of steady-state and transient operations, as well as increased power losses and emissions during dynamic control.
Innovation Solution
Implementing electronic decoupling using frequency converters, such as matrix converters, to independently control the speed of the gas turbine relative to the grid frequency, allowing for flexible operation and optimized power plant performance across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gas turbine is rigidly coupled to the power grid via a fixed transmission ratio, then the grid frequency is maintained, but the flexibility and efficiency of the power plant are reduced
Solution Approach 1:
The patent replaces the mechanical gear unit with a fixed transmission ratio with an electronic frequency converter. The frequency converter electrically couples the gas turbine generator to the power grid, allowing independent control of turbine speed and grid frequency. This substitution enables the gas turbine to operate at variable speeds while maintaining stable grid frequency, thereby resolving the contradiction between reliability and adaptability.
2Reliability
If a mechanical gear unit is used to achieve fixed transmission ratio, then the grid frequency coupling is maintained, but the device complexity and power losses increase
Solution Approach 1:
The patent eliminates the mechanical gear unit by introducing an electronic frequency converter. The converter consists of a generator connected to the gas turbine and a grid connection unit with power electronic converters. This electronic system replaces the mechanical transmission, reducing device complexity, minimizing power losses, and maintaining reliable grid frequency coupling through electronic control.
3Productivity
If the gas turbine operates at variable speeds, then the efficiency and emissions are improved, but the grid frequency stability is compromised
Solution Approach 1:
The patent introduces a frequency converter as an intermediary between the gas turbine generator and the power grid. This intermediary decouples the variable speed operation of the gas turbine from the constant frequency requirement of the grid. The converter transforms the variable frequency output of the generator into stable grid frequency, enabling both variable speed operation for efficiency improvement and stable grid frequency for reliability.
4Ease of manufacture
If a fixed transmission ratio is used, then the design is simplified, but the ability to optimize components for variable conditions is reduced
Solution Approach 1:
The patent transitions from a static fixed transmission ratio to a dynamic electronic frequency converter system. The converter can dynamically adjust the relationship between gas turbine speed and grid frequency based on operating conditions. This dynamic capability allows compressor and turbine components to be optimized for variable operating conditions, improving efficiency and performance while maintaining design feasibility through standardized converter modules.
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 stable, high-efficiency operation with reduced emissions and extended service life, improved power control, and enhanced design flexibility, allowing for better matching of compressor and turbine components to variable conditions, thereby optimizing power plant performance and reducing operational costs.
Implementation Method 1
a frequency converter being provided between the first AC generator and the power grid, the frequency converter having an input connected to the first AC generator and an output connected to the power grid
Data Source
AI summary
A combined-cycle power plant (10) has at least one power train (60) including a steam turbine (24) and a second generator (8) directly driven by the steam turbine (24) and generating alternating current, the output of which generator is connected to a power grid (21) having a given grid frequency (F), and at least one power train (11) of a gas turbine (12) and a first generator (18) driven directly by the gas turbine (12) and generating alternating current with an operating frequency, the output of which generator is connected to a power grid (21) having a predetermined grid frequency. An electronic decoupling device or a variable electronic gear unit (27) decouples the operating frequency from the grid frequency and is arranged between the first generator (18) and the power grid (21). Such a plant allows both flexible steady-state operation with high overall efficiency as well as flexible transient operation.