A discrete-time coordinated adaptive stabilizer for multimachine power systems

A digital PSS design technique for a multimachine power system suitable for easy integration into the power system control hierarchy at the generating plant level is presented in the paper. The adaptive inputs are obtained at each unit as feedback from local measurements, and the reference models in the proposed PSS scheme are designed to reflect the dynamic interaction between each generating unit (GU) and the multimachine system. The effectiveness of the proposed technique is demonstrated on a multimachine power system using computer simulation studies.     

Nonlinear adaptive decentralized stabilization control for multimachine power systems

This paper presents a decentralized adaptive backstepping controller to dampen oscillations and improve the transient stability to parametric uncertainties in multimachine power systems. The proposed design on the i ^th synchronous generator uses only local information and operates without the need for remote signals from the other generators. The design of the nonlinear controller is based on a modified fourth-order nonlinear model of a synchronous generator, and the automatic voltage regulator model is considered so as to decrease the steady state voltage error. The construction of both the control law and the associated Lyapunov function is systematically designed within the design methodology. A 3-machine power system is used to demonstrate the effectiveness of the proposed controller over two other controllers, namely a conventional damping controller (power system stabilizer) and one designed using the feedback linearization techniques. Recommended by Editorial Board member Gang Tao under the direction of Editor Jae Weon Choi. This work was supported by the Korea Electrical Engineering and Science Research Institute, which is funded by Ministry of Commerce, Industry and Energy. Shan-Ying Li received the B.S. degrees in Computer Science and M.S. degree in Electrical Engineering from Northeast DianLi University, China, in 1997 and 2002, respectively. She obtained the Ph.D. degree in Electrical Engineering from Seoul National University, Korea, in 2008. She is a Post Doctor in North China Electric Power Research Institute, North China Grid Co., Ltd., China. Her research interests are in the areas of advanced control and stability applications on power systems. Sang-Seung Lee received the M.S.E.E. and Ph.D. degrees in Electrical Engineering at Seoul National University. Currently, he is with Power System Research Division of KESRI, Seoul National University, Korea. His interest areas are nonlinear/adaptive control theory, North-East Asia power system interconnection, distributed/small generation, distributed transmission/distribution load flow algorithm, regional/local energy system, PSS (power system stabilizer), and RCM (Reliability Centered Maintenance). Yong Tae Yoon was born in Korea on April 20, 1971. He received the B.S. degree, M.Eng. and Ph.D. degrees from M.I.T., USA in 1995, 1997, and 2001, respectively. Currently, he is an Assistant Professor in the School of Electrical Engineering and Computer Science at Seoul National University, Korea. His special field of interest includes electric power network economics, power system reliability, and the incentive regulation of independent transmission companies. Jong-Keun Park received the B.S. degree in Electrical Engineering from Seoul National University, Seoul, Korea in 1973 and the M.S. and Ph.D. degrees in Electrical Engineering from The University of Tokyo, Japan in 1979 and 1982, respectively. He is currently a Professor of School of Electrical Engineering, Seoul National University. In 1992, he attended as a Visiting Professor at Technology and Policy Program and Laboratory for Electromagnetic and Electronic Systems, Massachusetts Institute of Technology. He is a Senior Member of the IEEE, a Fellow of the IEE, and a Member of Japan Institute of Electrical Engineers (JIEE).     

Perturbation estimation based coordinated adaptive passive control for multimachine power systems

This paper proposes a perturbation estimation based coordinated adaptive passive control (PECAPC) of generators excitation system and thyristor-controlled series capacitor (TCSC) devices for complex, uncertain and interconnected multimachine power systems. Discussion begins with the PECAPC design, in which the combinatorial effect of system uncertainties, unmodelled dynamics and external disturbances is aggregated into a perturbation term, and estimated online by a perturbation observer (PO). PECAPC aims to achieve a coordinated adaptive control between the excitation controller (EC) and TCSC controller based on the nonlinearly functional estimate of the perturbation. In this control scheme an explicit control Lyapunov function (CLF) and the strict assumption of linearly parametric uncertainties made on system structures can be avoided. A decentralized stabilizing EC for each generator is firstly designed. Then a coordinated TCSC controller is developed to passivize the whole system, which improves system damping through reshaping the distributed energies in power systems. Case studies are carried out on a single machine infinite bus (SMIB) and a three-machine system, respectively. Simulation results show that the PECAPC-based EC and TCSC controller can coordinate each other to improve the power system stability, finally a hardware-in-the-loop (HIL) test is carried out to verify its implementation feasibility.     

Synthesis of a stabilizing control problem for a multimachine power system with phase shifter

A systematic procedure is considered for the synthesis of a stabilizing control method for a multimachine power system with phase shifter, taking into account the velocity governor. A new approach is presented, which uses a coordinate-transformation technique and an optimization technique. The application of this method to a stabilizing control problem for a power system is illustrated by considering a 3-machine power system with phase-shifter control, taking into account an additional control vector for the governing system with one time constant. The synthesized controls are then used to improve the power-system transient stability to a remarkable degree and to restore the power-system transients rapidly to the stable-equilibrium point. Numerical results arc given.     

Conditions for theoretical coherency in multimachine power systems

The problem of electromechanic coherency in multimachine power systems is considered. Properties of theoretical coherency are defined in a rigorous way and related to necessary and sufficient structure conditions to be satisfied by a suitable set of electromechanical parameters and by the load-flow values in the initial equilibrium point before the start of a disturbance. The relations between coherency based nonlinear dynamic equivalents and modal reduced linearized models are illustrated. The structural conditions for theoretical coherency can be given the meaning of uncontrollability conditions. The analysis of the theoretical coherency represents the starting point for a following analysis of the practical coherency.     

Torque-angle loops in multimachine power systems

The synchronizing and damping torques are derived from the torque-angle loop of a single machine infinite bus-bar system. This paper uses frequency response methods to generalize the analysis to an n machine system. A transfer function matrix G(s) is derived to relate the n-vector of electrical torques to the n-vector of rotor angles. The characteristic locus method is used to decompose the stability analysis into n torque-angle loops each of which is similar to the torque-angle loop of a single machine infinite bus-bar system. The method is used to analyse the dynamic stability of an uncontrolled multimachine power system. It is shown that the stability can be assessed by the evaluation of a set of eigenvalues of G(0) which can be considered as a set of synchronizing torque coefficients.     

Implementation and experimental studies of an adaptive self-optimizing power system stabilizer

This paper describes the implementation and experimental studies of an adaptive self-optimizing pole shifting power system stabilizer. Using an Intel iSBC386/21 single-board computer, the adaptive power system stabilizer has been tested on a physical model of a single-machine infinite-bus power system. Under different operating conditions and disturbances, the behavior of the proposed adaptive stabilizer was investigated. Comparison has also been made to a digital-type conventional fixed-parameter power system stabilizer. Results of the experimental studies show that the proposed adaptive stabilizer outperforms the conventional stabilizer.     

Discrete-time decentralized optimal controllers for multimachine power systems

Decentralized compensation of large-scale power systems has the appealing feature that local substations may be controlled by a small subset of state or output variables. In this paper, the problem of decentralized control by discrete-time compensation is addressed. By formulating the dynamics of each subsystem and including the interaction terms with other subsystems, a performance measure is constructed, based upon local desired system performance. This resulting controller is optimal, even if the subsystems are strongly coupled. An example using a 10-machine power system is provided to illustrate the improvement of the system response to faults when compared to classical excitation control.     

Scalar-Lyapunov-function method for single- and multimachine problems in power systems

A systematic method is proposed to derive appropriate Lyapunov functions for single- and multimachine problems in power systems that will enable suitable stability-region estimates to be determined. Initially, the Lyapunov function for a simplified second-order system is derived. This function is then modified to form a suitable Lyapunov function for the actual non-linear system under study. Six examples for single- and multimachine problems are considered.     

Derivation of completely controllable and completely observable state models for multimachine power system stability studies†

The object of the present paper is to develop state models for multimachine power system stability studies which are completely controllable and completely observable. They are necessary for any stability studies based on the second method of Lyapunov. Starting from the definition of the degree of a rational function matrix, the minimal realizations for a two- and three-machine power system with uniform and nonuniform damping are obtained and are shown to be completely controllable and completely observable. A generalization for an H-machine power system follows as a natural consequence. Further, the present work provides the theoretical basis for the proper choice of state variables, i.e. relative rotor angles instead of absolute rotor angles as state variables.     

Robust adaptive control for a single-machine infinite-bus power system with an SVC

In this paper, a new control synthesis framework is developed to solve a robust stabilization problem for a single-machine infinite-bus power system with a static var compensator (SVC). The uncertainties in the infinite bus voltage and the internal and external reactances to the generating station are considered. First, control inputs for the excitation and the SVC are obtained via immersion and invariance (I&I). Then, the controller is redesigned using a parameter update law and a filter using indirect I&I adaptive control and a two-time-scale technique. The transient and steady-state performances are enhanced by introducing class K functions. The simulation results show that the developed controller improves the system performance.     

Probabilistic assessment of small disturbance stability in multimachine power systems

In planning electric power systems, it is always necessary to assess whether small-disturbance (SD) instability phenomena occur at prefixed system operating conditions. This analysis can become very difficult when the problem data are uncertain. In such cases the use of deterministic approaches is inadequate and the application of probabilistic analysis techniques is the most feasible alternative. This paper presents a new and practical probabilistic approach for the assessment of SD stability in multimachine power systems taking into account the uncertainties associated with bus load forecasting and treating loads as random uncorrelated variables with normal distributions. This approach proves suitable for determining the risk of SD instability for each expected system operating condition and for systematically individualizing all factors that can affect the probability of SD instability in large power systems. A numerical example illustrates the capability of the proposed technique.     

On the inclusion of transfer conductances in Lyapunov functions for multimachine power systems

It is the usual practice to neglect transfer conductances while forming the Lyapunov functions for stability analysis of multimachine power systems. It is shown in this note that with certain approximations it is possible to construct valid Lyapunov functions for such systems which includes effects of transfer conductances.     

A microcomputer based adaptive regulator for power system applications

The paper presents the design of an adaptive regulator for excitation control of a synchronous generator connected to an infinite bus through a double-circuit transmission line. The regulator, which is derived by simplification of the well known minimum-variance self-tuning controller, uses a variable forgetting factor stochastic approximation variant of the recursive least-square parameter estimator. This low order self-tuning algorithm is based on 3-parameter identification and is suitable for implementation with a single-chip microcomputer having restricted processing power, limited on-chip program storage and limited on-chip data storage capabilities. Simulation results are presented for a sample power system which is subjected to disturbances such as 3-phase short circuits, changes in terminal voltage and stochastic load variations. Tests using an LSI-11/23 microcomputer show acceptable performance in eliminating steady state errors and adapting rapidly to any changes in system operating conditions.     

Eigenvalue assignments in multimachine power systems using tabu search algorithm

Applying tabu search (TS) optimization technique to multimachine power system stabilizer (PSS) design is presented in this paper. The proposed approach employs TS to search for optimal or near optimal settings of PSS parameters that shift the system eigenvalues associated with the electromechanical modes to the left of a vertical line in the s-plane. Incorporation of TS algorithm in PSS design significantly reduces the computational burden. One of the main advantages of the proposed approach is its robustness to the initial guess. The performance of the proposed PSS under different disturbances and loading conditions is investigated for multimachine power systems. The eigenvalue analysis and the nonlinear simulation results show the effectiveness of the proposed PSSs to damp out the local as well as the interarea modes of oscillations and work effectively over a wide range of loading conditions and system configurations.     

Nonlinear decentralized controller design for multimachine power systems using Hamiltonian function method

In this paper, we first express a multimachine power system as a Hamiltonian control system with dissipation. Then, using the Hamiltonian function method a decentralized excitation control scheme, as a static measurable feedback, is proposed to stabilize the multimachine power system. Then, it is shown that the control scheme with properly chosen parameters is also an H_∞ control, which solves the problem of disturbance attenuation simultaneously. Finally, the design technique is demonstrated by a three-machine power system.     

Computation of regions of transient stability of multimachine power systems

A major difficulty in applying Lyapunov theory to the problem of specifying transient stability regions ofn-machine power systems is computational complexity, which increases markedly withn. This note outlines a method, requiring only a nominal amount of computation, to determine such regions.     

Transient stabilization of multimachine power systems with nontrivial transfer conductances

We provide a solution to the long-standing problem of transient stabilization of multimachine power systems with nonnegligible transfer conductances. More specifically, we consider the full 3n-dimensional model of the n-generator system with lossy transmission lines and loads and prove the existence of a nonlinear static state feedback law for the generator excitation field that ensures asymptotic stability of the operating point with a well-defined estimate of the domain of attraction provided by a bona fide Lyapunov function. To design the control law we apply the recently introduced interconnection and damping assignment passivity-based control methodology that endows the closed-loop system with a port-controlled Hamiltonian structure with desired total energy function. The latter consists of terms akin to kinetic and potential energies, thus has a clear physical interpretation. Our derivations underscore the deleterious effects of resistive elements which, as is well known, hamper the assignment of simple "gradient" energy functions and compel us to include nonstandard cross terms. A key step in the construction is the modification of the energy transfer between the electrical and the mechanical parts of the system which is obtained via the introduction of state-modulated interconnections that play the role of multipliers in classical passivity theory.     

基于神经网络的电力系统暂态稳定分布式自适应控制

针对电力系统中普遍存在的系统非线性和参数不确定性等问题,提出一种基于径向基函数神经网络(RBFNN)的分布式自适应控制器,以提高多机电力系统的暂态稳定性.利用基于RBFNN的方法对系统中的未知非线性项和外部扰动进行补偿,设计相应的自适应参数估计方法,逼近未知非线性项的理想权值矩阵.该策略基于多智能体框架,分布式控制器通...     

Robust adaptive fuzzy logic power system stabilizer

This paper introduces a robust adaptive fuzzy controller as a power system stabilizer (RFPSS) used to damp inter-area modes of oscillation following disturbances in power systems. In contrast to the IEEE standard multi-band power system stabilizer (MB-PSS), robust adaptive fuzzy-based stabilizers are more efficient because they cope with oscillations at different operating points. The proposed controller adopts a dynamic inversion approach. Since feedback linearization is practically imperfect, components that ensure robust and adaptive performance are included in the control law to compensate for modelling errors and achieve acceptable tracking errors. Two fuzzy systems are implemented. The first system models the nominal values of the system’s nonlinearities. The second system is an adaptive one that compensates for modelling errors. A feedback linearization-based control law is implemented using the identified model. The gains of the controller are tuned via a particle swarm optimization routine to ensure system stability and minimum sum of the squares of the speed deviations. A bench-mark problem of a 4-machine 2-area power system is used to demonstrate the performance of the proposed controller and to show its superiority over other conventional stabilizers used in the literature.