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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Neural-network-based adaptive UPFC for improving transient stability performance of power system

This paper uses the recently proposed H/sub /spl infin//-learning method, for updating the parameter of the radial basis function neural network (RBFNN) used as a control scheme for the unified power flow controller (UPFC) to improve the transient stability performance of a multimachine power system. The RBFNN uses a single neuron architecture whose input is proportional to the difference in error and the updating of its parameters is carried via a proportional value of the error. Also, the coefficients of the difference of error, error, and auxiliary signal used for improving damping performance are depicted by a genetic algorithm. The performance of the newly designed controller is evaluated in a four-machine power system subjected to different types of disturbances. The newly designed single-neuron RBFNN-based UPFC exhibits better damping performance compared to the conventional PID as well as the extended Kalman filter (EKF) updating-based RBFNN scheme, making the unstable cases stable. Its simple architecture reduces the computational burden, thereby making it attractive for real-time implementation. Also, all the machines are being equipped with the conventional power system stabilizer (PSS) to study the coordinated effect of UPFC and PSS in the system.     

Design of decentralized robust controller for voltage regulation and stabilization of multimachine power systems

This paper presents a decentralized state-feedback controller design based on robust control theory to ensure system stability and voltage regulation in multimachine power systems. The power system is decomposed in n subsystems each represented by a state-space model with bounded parameter uncertainties and unknown input disturbances of class L _∞ which model couplings with the generators of the others subsystems. The proposed controller designed according to a Riccati-based approach is robust with respect to uncertain network parameters and counteracts the effects of the disturbances. A stability analysis in presence of L _∞ disturbances is also given. The control law is straightforward and cost effective because it is function of constant gains and of local measurable machine variables. Numerical simulations give evidence of the achievements in terms of system transient stability as well as voltage regulation, also in comparison with another design technique.     

A power system nonlinear adaptive decentralized controller design

In this paper, a novel excitation control is designed for improvement of transient stability of power systems. The control algorithm is based on the adaptive backstepping method in a recursive way without linearizing the system model. Lyapunov function method is applied in designing the controller to ensure the convergence of the power angle, relative speed of the generator and the active electrical power delivered by the generator when a large fault occurs. Compared with the existing nonlinear decentralized control approaches, the proposed controller has no requirement for the bounds of interconnections in the power system. And the new approach does not need the existence of solution of a designed algebraic Riccati equation. Furthermore, the transient stability performance of power systems can also be improved by the designed control approach. The efficacy of the designed controller has been demonstrated in a multimachine power system. Simulation results show transient stability enhancement of a power system in the face of a large sudden fault.     

电力线载波技术实现变流器的分布式控制

本文介绍了北京福星晓程公司PL3200芯片的主要特点、结构、载波通信原理以及基于该芯片的电力线载波通信应用的硬件电路设计原理,并给出了将该芯片构成的电力线载波通信系统应用于蓄电池化成分布式测控系统的数据通信的方案。     

矿井宽压输入自适应电源系统设计

针对现有矿用电源适应的电压波动范围窄、使用不便等问题,提出一种基于全控桥移相整流技术的AC80～830V宽压输入自适应电源系统设计方案。该电源主电路采用晶闸管控制方式,控制电路采用PIC16F1937单片机实现瞬时电压跟踪控制,使得输入电压变动时输出电压稳定工作在DC110～350V。仿真实验结果表明,该电源系统工作稳定、可靠。