(493c) Dynamic Modeling and Control of Gas Turbines in Combined Cycle Power Plants

The use of Gas turbines for electric power generation has increased tremendously over the past few decades. Even though there have been a lot of improvements in their structure, the gas turbines are limited by their thermal efficiency, usually capping off around the 30-40% mark. This problem has been solved by using a steam turbine connected to the gas turbine, which utilizes the exhaust heat to produce more power, thereby increasing the efficiency of the Combined Cycle Power Plant (CCPP) to about 60% or more. In this article, a modeling procedure for the dynamic simulation of a Combined Cycle Power Plant (CCPP) has been presented. Initially, an overview of the various techniques including the Rowen’s model for the modeling of gas turbines using the platform Matlab/Simulink has been presented. Later, a simple procedure has been used to extract the parameters of the Rowen’s model for a 19.1 MW twin-shaft gas turbine installed on the Draugen platform in the Norwegian Sea using the operational and performance data. This procedure is based on the simple laws of Physics and a few thermodynamic assumptions. Using Matlab/Simulink platform, the model has been simulated and the results are verified with the operational data. The model utilizes a Frequency/Load controller to control the frequency and the electrical power generated by the gas turbine generator. The impact of frequency and load changes on the dynamic behavior of the gas turbine has been studied. Furthermore, a detailed model of a Combined Cycle Power Plant (CCPP) has been studied, using a heat recovery system, which includes a steam turbine as a bottoming cycle. Finally, a control analysis for tuning the parameters of the Frequency/Load controller has been performed and the results are discussed.