Combined Cycle Performance Evaluation and Dynamic Response Simulation

ABSTRACT Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.摘要：与传统的简单循环（如单独运行的燃气轮机或蒸汽轮机）相比，联合循环发电厂具备更高的热效率（超过60%）与更优的发电性能。鉴于本文所评估的发电厂已投入商业运行，为了评估电网在正常运行过程中产生的扰动与频率波动——由于汽轮机所承担的负载与电网频率本质上存在关联——需对该发电厂的控制系统开展进一步优化研发。 为此，本研究开发了一款可模拟控制系统的计算机程序，用以应对此类运行不稳定性，并为发电厂的安全运行提供必要的保护支撑。本开发程序基于MATLAB Simulink®平台搭建。 该发电厂的核心组件包含2台单台额定功率90兆瓦的燃气轮机与1台320兆瓦的蒸汽轮机，总装机容量达500兆瓦。研究首先分别搭建各核心组件的独立模型，待获得稳定的组件模型后，通过余热锅炉将燃气轮机的排气与水-蒸汽循环系统进行连接。用于模型调校的关键参数（如增益、限值与常数）均取自该发电厂的实际运行数据。 仿真结果可用于评估多项核心运行参数；其余可监测参数（如电网扰动期间的机组功率、排气温度、燃料流量与可变静子角度）虽可被获取，但未在本文中展示。本研究通过测试所提出模型的鲁棒性、响应时间、暂态特性、稳态特性与可靠性，完成了相关验证分析。