Decentralized load frequency controller for a multi-area interconnected power system

This paper proposes a control scheme for the load frequency control (LFC) problem of multi-area power systems. These systems are treated as interconnected dynamical systems. In the design of the proposed controller, each local area network is overlapped with states representing the interconnections with the other local area networks in the global system. Then, a decentralized control scheme is developed as function of the local area state variables and those resulting from the overlapped states which represent an approximation of the interconnection variables. The proposed controller guarantees the asymptotic stability of the overall closed loop system.The simulation results indicate that the proposed control scheme works well. In addition, they show that the controlled system is robust to changes in the parameters of the power system and to bounded input disturbances acting on the system. Moreover, the simulation results show that the controlled system behaves well even when there is a maximum limit on the rate of change in power generation.     

Bacteria foraging optimization algorithm based load frequency controller for interconnected power system

Social foraging behavior of Escherichia coli bacteria has recently been explored to develop a novel algorithm for distributed optimization and control. The Bacterial Foraging Optimization Algorithm (BFOA), as it is called now, is currently gaining popularity in the community of researchers, for its effectiveness in solving certain difficult real world optimization problems. This paper proposes BFOA based Load Frequency Control (LFC) for the suppression of oscillations in power system. A two area non-reheat thermal system is considered to be equipped with proportional plus integral (PI) controllers. BFOA is employed to search for optimal controller parameters by minimizing the time domain objective function. The performance of the proposed controller has been evaluated with the performance of the conventional PI controller and PI controller tuned by genetic algorithm (GA) in order to demonstrate the superior efficiency of the proposed BFOA in tuning PI controller. Simulation results emphasis on the better performance of the optimized PI controller based on BFOA in compare to optimized PI controller based on GA and conventional one over wide range of operating conditions, and system parameters variations.     

Decentralized stochastic adaptive control of interconnected systems

This paper considers the stochastic adaptive control problem for a class of large-scale systems formed by arbitrary interconnection of subsystems with unknown parameters and non-linearities. For the estimation of the unknown parameters of the local controllers, stochastic approximation algorithms are used. Conditions sufficient for global stability of the overall system are established. It is shown that the overall tracking error is bounded by a quantity depending on the size of interconnections.     

Decentralized voltage control in multiarea power system

This paper discusses the feasibility of a decentralized voltage control scheme for large-scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two-point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation. For a large-scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large-scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is presented.     

A robust adaptive LQG/LTR TCSC controller applied to damp power system oscillations

This paper investigates the use of self-tuning Linear Quadratic Gaussian control with Loop Transfer Recovery (LQG/LTR), applied in Thyristor Controlled Series Capacitors (TCSC) installed in interconnected power systems. The proposed robust adaptive controller can improve power system stability margins, damping properly the system's dominant electromechanical modes. Although this TCSC controller is designed mainly to identify and damp inter-area modes, it does not affect negatively the local modes damping, therefore enhancing the overall system performance. The proposed controller properties can be verified using non-linear simulations for a four-machine power system, in different operation conditions.     

Decentralized robust adaptive load frequency control using interactions estimation

In this paper, a new model reference decentralized adaptive output feedback controller is proposed for load-frequency control (LFC) of large-scale power systems with unknown parameters. The main problem with a decentralized robust LFC is that the interactions are treated as disturbances. This results in a conservative control action to maintain stability in the worst-case scenario. Furthermore, to improve the performance of the decentralized LFC, the proposed method estimates the interactions from other subsystems to modify the adaptive controller so that the interactions are effectively neutralized. The other important features of the proposed controller are: (1) no prior information about the system parameters is required, (2) random changes in the operating conditions are traced, (3) only the local input–output data are needed, (4) the robustness of the overall system against the system parameter uncertainties is guaranteed. To show the effectiveness of the proposed controller, a three-area power system is studied. The simulation results are promising and highlight the remarkable performance of the controller even in the presence of both plant parameter changes and high interactions.     

Decentralized load frequency control on each power plant

This paper presents a load frequency control system using a refined controller for interconnected power systems. The controller consists of an integral compensator and state feedback. It has been proven that any transfer function between a reference input and a controlled output or between a disturbance and a controlled output is attained by this controller if it is attainable by realizable linear compensation. Parameters of the controller are determined by the optimal regulator theory and additional calculation. The controller can reduce time deviation and inadvertent interchange without information about tie-lines as well as deviations of frequency and net interchange power. This structural features makes it possible to design the control system for each regulating power plant instead of for the control center. If some state variables are not available, the control system can be designed with the remainder of state variables and a dynamic compensator. Simulation results show that the control system is superior to the TBC system.     

机器人的鲁棒自适应分散跟踪控制

提供了一种鲁棒自适应控制策略,用于不确定性机器人的发迹跟踪,该控制器由一个ＰＤ线性反馈、一个立方项偿和非线性项构成。控制律采用分散形式,通过对二自由度机器人的仿真,证明该方法能使跟踪误差快速趋近于零。     

Design of a robust variable structure controller for improving power system dynamic stability

This paper proposes a nonlinear robust controller for improving power system dynamic stability. The design procedure of the controller which uses a nonlinear transformation technique and the variable structure control (VSC) theory is discussed. A method of eliminating the chattering encountered in variable structure controllers is also presented. Performance of the proposed controller in a simple power system, a single machine connected to infinite bus, is investigated using computer simulations. Robust performance of the controller is verified using a number of studies.     

Comprehensive modelling of the unified power flow controller for power system control

In this paper, comprehensive modelling of the unified power flow controller (UPFC) for power flow, voltage, angle and impedance controls is presented. The control modes include some thirteen different power flow, voltage, angle and impedance control functions. The similarities and differences between some of the control modes and those of traditional transformers and series compensation devices are also discussed. The control modes were successfully implemented in a Newton power flow algorithm. Numerical examples are given on the IEEE 30-bus system and the IEEE 118-bus system to illustrate the feasibility and the performance of the Newton power flow algorithm.     

Quasi oppositional harmony search algorithm based controller tuning for load frequency control of multi-source multi-area power system

This paper deals with the load frequency control (LFC) study of single-area and interconnected two-area power system having diversified power sources. The two areas considered in the present study are identical. Each area is having thermal, hydro and gas based power plants. Split-shaft model of gas turbine is used in the present work as one of the diversified generating unit for the purpose of LFC study. Optimal gains of the classical controllers (like integral controller, proportional–integral controller and proportional–integral–derivative (PID) controller, one installed at a time in the studied models) are obtained by using a novel music-inspired metaheuristic harmony search algorithm (HSA) which incorporates quasi opposition based learning technique for memory initialization and also for generation jumping. Single-area power system with diverse power sources is considered and its optimal transient performances are obtained and compared for step load perturbation. The same approach is further extended to two-area interconnected power system consisting of diverse power sources with nominal values of area input parameters. The performance of PID controller is found to be the best one for the studied power system models. It is also revealed that the performance of the interconnected two-area power system with AC–DC tie line is better in comparison to AC tie line.     

Decentralized load frequency based on H∞ control

This paper presents a decentralized load frequency control (LFC) based on H_∞ optimal control theory with an observer. A few LFC schemes have been proposed based on the optimal control theory, but they have not considered the change of system parameters in operation and the characteristics of load disturbances in a target system. In this paper, H_∞ robust control is introduced to address such problems. Owing to its practical merit, the proposed control scheme is a decentralized LFC. Employing observer theory, the proposed method requires only frequency and tie‐line power deviation in each area. Numerical simulations are shown to demonstrate the effectiveness of the proposed method. H_∞ control was proven to show greater effectiveness of damping disturbance over the conventional optimal control by the design of control systems aimed at restricting the H_∞ norm of its transfer function. In particular, when a decentralized LFC is applied, by reducing the system size, H_∞ norm is easier to dampen; thus H_∞ control is more effective in the decentralized control. Future research topics include the design of H_∞ control system with a weight on frequency response. © 2001 Scripta Technica, Electr Eng Jpn, 136(3): 28–38, 2001     

Decentralized adaptive backstepping control of electric power systems

In this paper, a decentralized adaptive backstepping excitation controller, tuned using a Particle Swarm Optimization technique (PSO), is designed for stability enhancement of multi-machine power systems. To achieve decentralization, each machine is modeled as an independent uncertain dynamic subsystem, where the uncertainty is a disturbance that represents the effects of the rest of the system on that particular machine. This disturbance is expressed as a polynomial function of electric power deviation, and its parameters are adapted using PSO. The proposed technique is illustrated with a two-area benchmark power system. This system exhibits inter-area oscillations which are effectively damped with the proposed decentralized controllers under severe contingencies, for which traditional power system stabilizers fail.     

Robust analysis and design of load frequency controller for power systems

Robust load frequency control for power systems is discussed. A detailed robustness analysis of the existing control laws shows that parameter variation is not a critical issue but more attention should be paid to the unmodeled dynamics in robust load frequency controller design. A new robust load frequency control method is then proposed considering the unmodeled dynamics of power systems. Finally, a new configuration is proposed to overcome the effects of generation rate constraints (GRC). Simulation results show that the design method and the anti-GRC configuration are effective.     

Decentralized robust controller design for robots with torque saturation constraint

Decentralized robust tracking control problems for robots with control input amplitude limitation are investigated. The robust controller, proposed in our previous paper, is improved to avoid windup caused by amplitude limitation. To cope with the difficulties in calculating the controller parameters, a method based on evolutionary optimization is presented. Simulation results verify the effectiveness of the improved controller.     

Optimal robust adaptive fuzzy synergetic power system stabilizer design

A new particle swarm optimized robust indirect adaptive power system stabilizer is developed based on recently developed synergetic control methodology. Fuzzy systems are used in an adaptive scheme to approximate the system using a nonlinear model while synergetic control guarantees robustness and the use of a chatter free continuous control law which makes the controller easy to implement. In addition the controller parameters are optimized using PSO approach. Simulation of severe operating conditions of a power system is conducted to validate the effectiveness of the proposed approach while stability is guaranteed via Lyapunov synthesis.     

Decentralized nonlinear H∞ controller for large scale power systems

The aim of this paper is to design nonlinear decentralized controllers for multi-machine power systems. The design procedure is based on H_∞ control theory and consists of two parts. First, the feedback linearization technique is used. Then, a robust controller is designed using the linear matrix inequalities (LMI) approach. The controller has two blocks. One, is a nonlinear function of some local measurable signals such as the generator active and reactive powers, the rotor speed and the armature current. The other block is a PID controller. The linear H_∞ theory is used to tune the PID parameters. The method results in a controller which is easy for implementing in practice. The performance of the controller is tested on a sample multi-machine power system model. Simulation results show the effectiveness, robustness and good performance of the proposed controller.     

Widely convergent method for finding solutions of simultaneous nonlinear equations

The authors propose a new approach for solving the nonlinear problem, based on a model-reference adaptive control (MRAC). The algorithm is composed of three parts: a plant containing unknown parameters, a reference model for compactly specifying the desired output and an adaptation mechanism for updating the adjustable parameters. The structure of the adaptation mechanism is explicitly designed so that the asymptotical stability is guaranteed according to Lyapunov theorem. The method reformulates the algebraic nonlinear equations into a set of ordinary differential equations, whose equilibrium point corresponds to the solution of the original nonlinear problems. The stability and region of attraction coincide with entire state space no matter whether the parameters reside in solvable region or unsolvable region.     

Decentralized two-level excitation control of multimachine power systems

A two-level decentralized scheme for the excitation control of multimachine power systems is presented. The control strategy is based on decomposing the control signal for each machine into two components generated by controllers at two different levels. At the first level, controllers are designed to optimize the performance of each generating unit, totally ignoring the couplings among the machines. The second control components are chosen to reduce the machine performance degradations due to the presence of interactions. With the developed two-level control scheme each machine is controlled entirely from its own state. The effectiveness of the proposed approach is illustrated by a numerical example involving a four-generator system.     

Decentralized robust tracking control for uncertain robots

To realize decentralized robust tracking control for robots with uncertain parameters, a new design method is proposed. A robust tracking controller designed by this method consists of two parts: a feedforward controller and a feedback robust controller. A feedforward control is first applied and error dynamics are introduced. For each joint error subsystem a robust controller is designed in two steps: first, a nominal controller is designed for the nominal plant to achieve desired tracking performance, then a robust compensator is added to restrain the influence of the perturbation, that is the difference of the real plant from the nominal plant. The controller designed by the proposed method is a linear time-invariant one. It is shown that robust stability and robust tracking property can be achieved by applying the controller with a sufficiently wide frequency bandwidth. An important feature of the method is that the controller parameters can be tuned on-line easily.List of symbols _max(B), _min(B) the maximum and minimum eigenvalues, respectively, of a symmetric positive definite matrix B - -