Abstract
This study focuses on multi-objective optimization of the PID controllers for optimal speed control for an isolated steam turbine. In complex operations, optimal tuning plays an imperative role in maintaining the product quality and process safety. This study focuses on the comparison of the optimal PID tuning using Multi-objective Genetic Algorithm (NSGA-II) against normal genetic algorithm and Ziegler Nichols methods for the speed control of an isolated steam turbine. Isolated steam turbine not being connected to the grid; hence is usually used in refineries as steam turbine, where a hydraulic governor is used for the speed control. The PID controller for the system has been designed and implemented using MATLAB and SIMULINK and the results of the design methods have been compared, analysed and conclusions indicates that the significant improvement of results have been obtained by the Multi-Objective GA based optimization of PID as much faster response is obtained as compared to the ordinary GA and Ziegler Nichols method.
Highlights
PID-Proportional, Integral and Derivative controllers alone contribute 90% of the total controllers used today (Åström and Hägglund, 2001; Zhao et al, 2011) and their simplicity of design and the ease of implementation complements their application
An isolated steam turbine has been considered i.e., the turbine is not connected to the grid and the speed is controlled using a hydraulic governor
For designing the PID controller, Ziegler Nichols frequency response has been used followed by the optimization using genetic algorithm and multi-objective genetic algorithm
Summary
PID-Proportional, Integral and Derivative controllers alone contribute 90% of the total controllers used today (Åström and Hägglund, 2001; Zhao et al, 2011) and their simplicity of design and the ease of implementation complements their application. An isolated steam turbine has been considered i.e., the turbine is not connected to the grid and the speed is controlled using a hydraulic governor. The hydraulic governor regulates the steam flow in the turbine (Basu and Samiran, 2012; Ismail, 2012). The system must be flexible enough to adapt with the changing conditions and regulate the process efficiently. For designing the PID controller, Ziegler Nichols frequency response has been used followed by the optimization using genetic algorithm and multi-objective genetic algorithm. The optimization has been carried out by the minimizing the objective function, stated as “Sum of the integral of the squared error and the sum of the integral of the absolute error” (Das et al, 2011). According to the results obtained, considerably better results have been obtained in case of the Multi-objective GA tuned PID controllers
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