Load Frequency Control (LFC) is one the most important issues in electrical power system design/operation and is becoming much more significant recently with increasing size, changing structure and complexity in interconnected power systems. In practice LFC systems use simple Proportional-Integral (PI) or Integral (I) controllers. However, since the PI or I control parameters are usually tuned based on classical or trial-and-error approaches, they are incapable of obtaining good dynamic performance for various load changes scenarios in multi-area power system. For this reason, in this study the PI and I control parameters are tuned based on Hybrid Particle Swarm Optimization (HPSO) algorithm method for LFC control in two-area power system. Because HPSO is an optimization method, therefore, in the uncertainty area of controller parameters, finds the best parameters for controller and obtained controller is an optimal controller. A two-area power system example is given to illustrate proposed methods. To show effectiveness of proposed method and compare the performance of optimized PI and I type controllers, several time-domain simulation for various load changes scenarios are presented. Simulation results emphasis on the better performance of optimized PI controller in compared to optimized I controller in LFC.

An industrial plant, such a power system, always contains parametric uncertainties. In the design of a controller the uncertainties have to be considered. Otherwise, if the real plant differs from the assumed plant model, a controller, designed based on classical controller design approaches, may not ensure the stability of the overall system. In this paper design of robust control for the UPFC controllers including power -flow and DC voltage regulator, using a Η loop-shaping design via a normalized coprime factorization approach, where loop-shape refers to magnitude of the loop transfer function L = GK as function of frequency is presented. As an example, we have designed a case for the system to compare the proposed method with a conventional method (classical P-I controller). AS the results of the linear and nonlinear simulations, the validity of the proposed method has been confirmed.

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New approach based on structured singular value (µ-synthesis) was proposed for the robust decentralized unified power flow controller (UPFC) design. To achieve decentralization, using the Schauder fixed point theorem the synthesis and analysis of multi-input multi-output (MIMO) control system translated into a set of equivalent multi-input single-output (MISO) control system. Power systems similar to other industrial plants contain different kinds of uncertainties which should be considered in controller design procedure. For this reason, the idea of µ-synthesis technique being used for designing of UPFC controllers. The proposed µ-based controller had a decentralized scheme and advantage of a decentralized controller design reduction in the controller complexity and suitability for practical implementation. The effectiveness of the proposed control strategy evaluated under operating conditions on damping of low frequency oscillations in comparison with the classical controller to demonstrate its robust performance through nonlinear time simulation and some performance indices

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