Optimal controller for synchronous power system with prescribed degree of stability

From a practical point of view, it may not be necessary to fix precisely the eigenvalues of the closed-loop system. If it is ensured that the eigenvalues of the closed-loop system lie within a certain region of the complex plane such as the sector of the left half plane Re(s) < 0, our design for an optimal regulator will be satisfactory. This can be achieved by minimising a quadratic performance index and, at the same time, ensuring that the poles of the closed-loop system lie to the left of the imaginary axis beyond a certain predesignated value ?α, where α > 0, which may be chosen by the designer.An attempt has been made to design an optimal regulator which would satisfy the requirement of positioning the dominant pole in such a way that it would lie to the left of Re(s) = ?α for some α > 0. The performance index chosen is

$\text{∫}\text{0}\text{∞}\text{exp}\text{(2∞t)(}\text{x}{}^{\mathrm{t}}\text{QX}\text{+}\text{u}{}^{\mathrm{T}}\text{R}{}_1\text{u)dt}$

This will ensure that the control law we obtain would give an asymptotically stable closed-loop system with a degree of stability of at least α. Results of the analysis for a simple synchronous power system model with excitation control are presented in this paper.     

Advanced SVC control for damping power system oscillations

A new SVC (static VAR compensation) control for damping of power system oscillations has been developed. To increase system damping an SVC uses a phase angle signal estimated from the measurement of voltage and power at the SVC location. By means of an optimization and identification procedure, optimized design of the damping control with various control concepts can be determined, taking into account nonlinear power systems. As a result of this method it is possible to increase power system damping considerably, in particular in critical situations close to the stability limit, using only locally measured state variables at the SVC, thus leading to an increase in the transmission capability of the power system     

TCSC controller design for damping interarea oscillations

The thyristor controlled series compensator (TCSC), a prominent FACTS device, can rapidly modulate the impedance of a transmission line, resulting in improvement of power system performance. The purpose of the work reported in this paper is to design a controller to damp interarea oscillations. The authors have applied the residue method to linearized power system equations and obtained a generalized form which is suitable for different controller input/output channels and therefore suitable for different control devices. This method, together with modal sensitivities, is applied to TCSCs to determine the location, feedback signal and controller design. The damping result is illustrated by comparing changes in damping ratio and identifying the increase of transfer capacity     

Robust SVC controller design for improving power system damping

The design of a robust controller for a static VAr compensator (SVC) to improve the damping of a power system is presented. The main contributions of the paper are to formulate and to solve the power system damping control problem using robust optimization techniques, and to synthesize the controller with explicit consideration of the system operating condition variations. Nonlinear simulations using the PSCAD/EMTDC software packages have been conducted to evaluate the performance of the closed-loop system. The results have indicated that the designed controller can provide positive damping to the system under a wide range of operating conditions     

一种新型电力系统稳定控制装置

提出了一种新型FACTS装置--多功能柔性功率调节器(FPC),它将飞轮储能技术和传统的同步调相技术有机地结合在一起,同时采用交流励磁和矢量控制等先进技术进行控制.这种装置具有储能、发电、调相等多种功能,将其用于电力系统的稳定性控制,可实现动态有功功率和无功功率同时双向大范围的快速调节,具有增强电力系统稳定性的能力.详细论述了柔性功率调节器的工作原理,建立了装置的稳态等值电路模型,分析了装置在不同运行方式下的功率传递关系.同时,还介绍了FPC的一个主要组成部分--基于SPWM的双VSC变频控制器以及三相SVC的矢量控制原理.用数字仿真的方法研究了FPC与电网进行四象限功率交换的特性.最后,用一个单机无穷大系统,通过仿真分析,验证了FPC所具有的巨大的稳定电力系统的能力.     

Damping controller design for power system oscillations usingglobal signals

This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid     

Multi-band power oscillation damping controller for power system supported by static VAR compensator

Electrical Engineering - Low-frequency electromechanical oscillations damping is powerfully crucial in power system operation. In order to fulfill this requirement, power oscillation damping (POD)...     

Damping of power system oscillations with output feedback and stripeigenvalue assignment

This paper presents a modified optimal controller for an interconnected power system. The design method does not need the specification of weighting matrices. The eigenvalues of electromechanical and exciter modes would be shifted to a prespecified vertical strip. For practical implementation, the design method only uses partial output feedback. For demonstrating the effectiveness of damping enhancement, eigenvalue analysis and nonlinear simulation results are used to show that the proposed controller gives significant improvement in the dynamic performance of the interconnected power system     

Optimal decentralized damping of low-frequency oscillations under control energy constraints

The problem of damping the low-frequency electromechanical oscillations in electrical power systems is dealt with by a parameter optimization approach. The design procedure is then applied to the synthesis of the stabilizing decentralized controllers for two nationwide power networks.     

应用储能系统抑制电力系统低频振荡原理研究

基于线性化等面积法则和小干扰分析方法,提出储能系统抑制电力系统低频振荡的原理和方法.通过对装有储能系统的单机无穷大系统进行理论分析和仿真测试,结果表明储能阻尼控制能够提供系统阻尼,且控制储能系统和电力系统之间的有功功率交换获得阻尼的效果比控制无功功率交换获得阻尼的效果要好的多.     

A distributed simulation based approach for detailed and decentralized power system transient stability analysis

This paper presents a distributed computing approach for piecewise transient stability (T/S) analysis of large-scale electrical networks using Diakoptics and large change sensitivity (LCS) concepts. Detailed T/S analysis in a secure and federative manner based on geographically decomposition using local computational resources is the greatest benefit realized by this method of analysis. In this way, with the minimum communications between subnetworks the same results as the conventional untorn T/S analysis can be achieved. Since the bottleneck in distributed computation is low speed network communication, a new latency exploitation technique is introduced for numerically solving system differential equations. The technique uses different step size in each subnetwork to decrease the number of numerical operations and data communications for a given total simulation time. The proposed distributed T/S method is implemented successfully across computer networks and its performance is studied using a 14 bus IEEE test system and some various large-scale networks up to 3000 buses. The presented results are compared with those obtained from conventional untorn T/S simulation.     

分散保性能状态反馈励磁控制器

提出一种新型的电力系统鲁棒分散励磁控制方法,该方法基于LMI技术处理被控系统的参数不确定性。控制器采用线性反馈实现,其控制参数在有界范围内的变化能保证闭环系统的渐近稳定性。在IEEE3机9节点系统上进行的算例验证了分散保性能控制的有效性和鲁棒性。     

A self-tuning fuzzy PI controller for TCSC to improve power system stability

In this paper, a self-tuning fuzzy PI controller (STFPIC) is proposed for thyristor-controlled series capacitor (TCSC) to improve power system dynamic performance. In a STFPIC controller, the output-scaling factor is adjusted on-line by an updating factor (α). The value of α is determined from a fuzzy rule-base defined on error (e) and change of error (Δe) of the controlled variable. The proposed self-tuning controller is designed using a very simple control rule-base and the most natural and unbiased membership functions (MFs) (symmetric triangles with equal base and 50% overlap with neighboring MFs). The comparative performances of the proposed STFPIC and the standard fuzzy PI controller (FPIC) have been investigated on two multi-machine power systems (namely, 4 machine, 2 area system and 10 machine 39 bus system) through detailed non-linear simulation studies using MATLAB/SIMULINK. From the simulation studies it has been found out that for damping oscillations, the performance of the proposed STFPIC is better than that obtained by the standard FPIC. Moreover, the proposed STFPIC as well as the FPIC have been found to be quite effective in damping oscillations over a wide range of operating conditions and are quite effective in enhancing the power carrying capability of the power system significantly.     

TCIPC提高暂态稳定性的PI控制器设计

在研究可控相间功率控制器(Thyristor Controlled Interphase Power Controller,TCIPC)的基本结构和潮流控制原理基础上,建立了在dq0坐标下TCIPC支路电流、端口电压及控制的传输功率之间关系的数学模型;依据TCIPC功角特性说明了调节IPC电感支路参数可以控制联络线传输功率达到改善系统稳定性的机理;基于TCIPC的感抗参数与联络线传输功率的关系,以电流作为TCIPC晶闸管触发控制的同步信号,将感抗期望值作为该控制器的参考信号,设计了TCIPC触发角校正的PI定阻抗控制器;并搭建了带IPC简单系统模型进行仿真.仿真结果验证了该控制器的有效性,并说明通过对TCIPC感抗的控制,可以改善带IPC系统的暂态稳定性.     

Decentralized robust adaptive-output feedback controller for power system load frequency control

In this paper, a new model reference-decentralized robust adaptive-output feedback controller is proposed for the load frequency control (LFC) of large-scale power systems with unknown parameters. This control strategy requires only local input–output data and can follow random changes in the operating conditions. The controller is designed such that the trajectory errors and the control gains of each area remain uniformly bounded. In the proposed method, firstly an adaptive observer is designed to estimate the state variables and system parameters using local data only. Then a locally linear combination of the estimated states and the model reference states are used to design a robust adaptive-output feedback controller for each area. Simulation results for a three-area power system show that the proposed controller achieves good performance even in the presence of plant parameter changes and system non-linearities. Received: 18 October 2001/Accepted: 24 October 2001     

A unified model for the analysis of FACTS devices in damping powersystem oscillations. III. Unified power flow controller

For pt.II see ibid., vol.13, no.4, p.1355-62 (1998). This paper presents the establishment of the linearized Phillips-Heffron model of a power system installed with a unified power flow controller (UPFC). Two applications based on the Phillips-Heffron model are demonstrated: (1) study on the effect of UPFC DC voltage regulator on power system oscillation stability; and (2) selection of damping control signal for the design of UPFC damping controller     

Banishing blackouts [power system oscillations stability]

This paper describes the recent technological advances in managing the oscillatory stability of power systems to avoid potentially serious grid disturbances. While the tools for dynamic modeling of power systems have long been available and remain an essential part of tackling power system instabilities, it is not advisable to depend on model-based approaches exclusively. Emerging technologies that can be used to observe dynamics within networks have proven to be increasingly valuable for increasing power transfers and defending against blackouts.     

Improved fuzzy logic controller for SVC in power system damping using global signals

Static Var Compensator (SVC) is a shunt-type FACTS device, which is used in power systems primarily for the purpose of voltage and reactive power control. In this paper, an improved fuzzy logic-based supplementary controller for SVC is developed for damping the rotor angle oscillations and to improve the stability of the power system. The generator speed and the electrical power are chosen as global input signals for the proposed fuzzy logic controller (FLC). The effectiveness and feasibility of the proposed control is demonstrated with single-machine infinite bus (SMIB) system, three-machine nine-bus WSCC system and New England 10-machine system, which shows the improvement over the use of a fixed parameter controller and existing FLC.     

A decentralized control system for stabilizing multimachine power systems

A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.     

Fuzzy based damping controller for TCSC using local measurements to enhance transient stability of power systems

This paper proposes a local fuzzy based damping controller (LFDC) for thyristor controlled series capacitor (TCSC) to improve transient stability of power systems. In order to implement the proposed scheme, detailed model of TCSC, based on actual behavior of thyristor valves, is adopted. The LFDC uses the frequency at the TCSC bus as a local feedback signal, to control the firing angle. The parameters of fuzzy controller are tuned using an off-line method through chaotic optimization algorithm (COA). To verify the proposed LFDC, numerical simulations are carried out in Matlab/Simpower toolbox for the following case studies: two-area two-machine (TATM), WSCC three-machine nine-bus and Kundur’s two-area four-machine (TAFM) systems under various faults types. In this regard, to more evaluate the effectiveness of the proposed method, the simulation results are compared with the wide-area fuzzy based damping controller (WFDC). Moreover, the transient behavior of the detailed and phasor models of the TCSC is discussed in the TATM power system. The simulation results confirm that the proposed LFDC is an efficient tool for transient stability improvement since it utilizes only local signals, which are easily available.