Dynamic analysis of intelligent load frequency control of interconnected nonlinear conventional and renewable power system

Abstract

In this thesis, a variable structure concept sliding mode based load frequency control is developed on a two-area interconnected power system. The power system contains reheat, and hydraulic turbines which are distributed in these two areas respectively. Both governor dead band and generation rate constraint are included in the model of this power system. Our control goal is to regulate the frequency error, tie-line power error and area control error despite the presences of external load disturbance and system uncertainties. The sliding mode based load frequency controller is simulated on this two-area interconnected nonlinear power system. The simulation results verify the effectiveness of the controller. The main idea behind the development is to design the performance evaluation based on fuzzy controller for two areas interconnected hydro-thermal power plant is proposed. To enhance the performance of fuzzy logic controller sliding surface is included. The sliding concept arises due to variable structure concept (VSC). The objective of VSC has been greatly extended from stabilization to other control functions. The most distinguished feature of VSC is its ability to result in very robust control systems. In control system, sliding mode control is a nonlinear control method that alters the dynamics of a nonlinear system by application of a discontinuous control signal that forces the system to "slide" along a cross section of the systems normal behavior. It can switch from one continuous structure to another based on the current position in the state space. The multiple control structures are designed so that trajectories always move toward an adjacent region with a different control structure and so the ultimate trajectory will not exist entirely within one control structure. Instead, it will slide along the boundaries of the control structures. The motion of the system as it slides along these boundaries is called a sliding mode and the geometrical locus consisting of the boundaries is called the sliding surface. The method alters the dynamics of a nonlinear system by application of a high-frequency switching control. The proposed sliding mode control method is compared with proportional integral and hybrid neuro fuzzy control method. Here, proportional integral and hybrid neuro fuzzy control method is chosen because it is a dominant control method in industry for the load frequency control. The time required to stay 2% to 5% of any response final value that is the settling time of this response. The designed model confirms that settling time is consider for 0.01% of final value and it shows the robustness, stability and high performance of the controller. The settling time of the designed controller is 24.66 seconds and 25.65 seconds for combined hydro-thermal plant frequency and tie line power deviation respectively. The settling time of the designed controller is minimum compare to other controllers. A new unique model is developed using generation rate constraint and governor dead band which is applied in variable structure concept sliding mode fuzzy logic controller. The model gives better dynamics compare to conventional models. The proposed fuzzy logic controller maintains the stability and proves its superiority compared to other conventional fuzzy models. The settling time, percent of peak overshoots, frequency deviations of proposed model are much better than other conventional fuzzy controller. Simulation results demonstrate the effectiveness of the control strategy by successfully driving the frequency error and tie-line error; it shows the robustness of the controller against compare to other controller.