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.     

Dynamic equivalents for transient stability studies of electrical power systems

Along with the growth in size of electrical power systems, attention is increasingly being given to various reduction techniques of dynamic system models for transient stability studies. One of these is the topological reduction that includes coherency-based aggregation. A theorem from the nonlinear vibrations theory is applied to derive analytical coherency-criteria for a classical model of the system. A simplified algorithm of coherency recognition is given and results for a sample system are shown. Important properties of topological equivalents are proved and a relationship to modal reduction is pointed out.     

A robust decentralized approach to the multiarea frequency control of power systems

It is an important problem in multiarea power systems to attenuate the frequency deviation due to load change. Since power systems are spatially dispersive, decentralized control is more practical than lumped control. In this paper, we propose two robust decentralized control schemes for this problem. The difficulty with this problem is that the linearized model of a multiarea power system with frequency deviations as outputs is a MIMO system that has a transmission zero at s = 0. They key idea is to change the output of one subsystem so that the resulting new plant does not have any zero at s = 0. The new outputs are chosen carefully so that the regulation of the new outputs can guarantee the regulation of all frequency deviations and tieline power. Further, parameter uncertainty is taken into account in the controller design to achieve robustness. Simulation shows that the proposed methods are effective. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 68–76, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10004     

Economical preventive control of power flow after disturbances in the decentralized power system

This paper discusses the preventive controls of the generator outputs to improve security in the decentralized power system. Preventive controls of the power system can improve security level. However, the preventive control requires too much computation time because of too many considerable faults in the power system. Multiarea decentralization can be considered to reduce computation time of the power flow calculation. It is assumed that the effects of disturbances in the external systems are relatively smaller than the effects of disturbances in the study area. Linearized sensitivity analysis is used to evaluate the effects of the external systems to reduce computation time. Linear programming is used to determine the control signals of generators considering the incremental cost of generators. The New England 38 buses system is used as an example system to check the validity of the algorithm in this paper. The calculations of the example system show satisfactory results.     

Basic concept and decentralized autonomous control of super‐distributed energy systems

New small‐scale dispersed generation systems, such as fuel cells and micro gas turbines, have made remarkable advances lately and they will be applied practically in the near future. Although a large number of researches on the introduction of small‐scale dispersed generation systems have been carried out, only a small number of small‐scale dispersed generation systems are considered in these researches. Therefore, little is known about problems to be solved when a large number of small‐scale dispersed generation systems are introduced into electric power systems. This paper deals with a super‐distributed energy system that consists of a great number of dispersed generation systems such as fuel cells, micro gas turbines, and so on. The behavior of a customer with a dispersed generation system is simulated as the Ising model in statistical mechanics. The necessity of a distribution network in super‐distributed energy systems is discussed based on the Ising model. The feasibility of decentralized autonomous control using vicinity information is also investigated on the basis of stability analysis of the Hopfield neural network model. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 43–55, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10368     

Design of decentralized variable structure stabilizers for multimachine power systems

Variable structure (VS) stabilizers possess the advantages of better transient response, insensitivity to plant parameter variations, etc. In general, variable structure controls involve measurements from all the states, which is not possible in a multimachine power system (MMPS). In this paper, the switching planes for the variable structure stabilizers are selected in such a way that computation of switching planes involves local state variables only. The coefficients of the switching plane equation are determined using the Riccati equation approach. Through the approximation of neglecting non-diagonal blocks of the state space matrix, at the design stage, a decentralized Variable Structure stabilizer (VS stabilizer) is obtained. To accept the switching plane so obtained, a check of the closed loop eigenvalues is made with the actual state space matrix. After computation of the switching plane, the variable gains are also selected in such a way that control signal computation involves only local state variables. This is possible as the gains of nonlocal state variables are small compared with local variables. The response of the system with variable structure stabilizers indicates that the system performance is improved.     

基于分散控制理论的多机系统低频振荡抑制

常规的电力系统低频振荡抑制措施是在发电机励磁系统中加装电力系统稳定器(PSS),然而它在多机电力系统中的应用并没有充分的理论研究.将大系统分散控制原理应用于多机电力系统低频振荡抑制问题,只要分散阻尼控制器(DDC)的阶数足够高,分散闭环控制系统的低频振荡模态总可以在复平面内任意配置.分析了PSS与DDC的关系,论证了PSS是DDC的一种特殊形式,因而从理论上说明了DDC比PSS优越.将DDC的优化配置表示为一个带不等式约束的非光滑优化问题并用遗传算法求解.以新英格兰测试系统和我国西北电网为算例的计算结果表明,在发电机励磁系统中加装DDC是一种有效的低频振荡抑制新措施.     

负序功率方向闭锁转子二次谐波匝间保护的调试方法

通过对BFZ—2型发电机匝间保护装置和BFG—40型负序方向闭锁元件原理的分析，结合实际情况，提出了该套保护的调试方法，并对该套保护的性能做了评价。     

Theoretical and practical dynamic equivalents in multimachine power systems: Part 2: Construction of practical equivalent

A practical dynamic equivalent of a machine group is constructed, based on the single-machine theoretical equivalent formulated in the first part.     

Theoretical and practical dynamic equivalents in multimachine power systems : Part 1: Construction of coherency-based theoretical equivalent

Taking account of the structural conditions for theoretical coherency, a single machine equivalent circuit is determined. This is an extension of the Thévenin theorem to electromechanic circuits and will be used as the basis for constructing a practical dynamic equivalent in the second part of the paper.     

Preventive control in an autonomous decentralized system

For more rational operation and control of future electric power systems which would continue to expand in size and complexity, an autonomous decentralized control system is proposed as one of the new control architectures. In the autonomous decentralized control system, each generating station and substation behaves independently and cooperatively without being controlled by the central station. Besides the inherent fault-tolerant characteristics of the architecture, flexible and rapid control depending on the circumstances can be achieved. In this paper, the fundamental logic of preventive control in an autonomous decentralized system is developed. It is based on the bidding method in which each station proposes its own output taking into consideration its own situation and cooperation with others. The economic load dispatch including preventive control can be performed, based on the bidding rule adopting the equivalent incremental generating cost curve in which the security constraints are incorporated. Application of the logic to a model system revealed satisfactory control performance for preventing the overload of transmission lines and the undervoltage.     

一类时变互联不确定大系统的鲁棒分散自适应控制

研究了一类时变不确定大系统的分散镇定问题,其不确定性是范数有界不确定性和不确定性的界未知,且不满足匹配条件。基于Lyapunov稳定性理论,设计了两类分散自适应无记忆状态反馈控制,给出了系统状态渐近稳定的充分条件。通过数值例子验证了所提方法的有效性。     

Robust decentralized control of multiterminal DC/AC power systems

A multiterminal DC system embedded in a conventional AC power system can be used as a control element for damping inter-area oscillation. Three methods for decnetralized control of multiterminal DC/AC power systems are proposed. The robustness problems associated with DC control systems are discussed and the sufficient stability criteria are introduced. A power system example, which employs five DC terminals to damp out inter-area oscillations due to the AC power system dynamics, indicates that the proposed methods are realistic for robust decentralized control system design of DC/AC power systems.     

Network equivalents and expert system application for voltage andVAR control in large-scale power systems

This paper presents an application of the steady-state network equivalents and an expert system for voltage and reactive power (VAr) control in large-scale power systems. A steady-state network equivalencing technique is used to construct the “three-tier” subsystem which is adequate to solve voltage violation problems. An expert system utilises the sensitivity tree method to select the optimal set of control actions to alleviate the voltage problem. The expert system was developed using the VP-EXPERT system shell. VP-EXPERT interacts with the power system analysis software providing analysis of the network sensitivity matrix and data for the knowledge base. Practical application of the developed expert system is demonstrated on the example of the Hydro-Electric Commission (HEC) power system of Tasmania, however the proposed approach is not limited by the system size     

Stabilization of inter-area and/or oscillatory modes in large-scale power system by voltage impedance power system (VIPS) apparatus based on decentralized control scheme

New technologies such as power electronics have made it possible to change continuously the impedance of a power system not only to control power flow but also to enhance stability. A power system incorporating a variable impedance apparatus such as a variable series capacitor (VSrC) and high-speed phase shifter (HSPS) is called VIPS (Variable Impedance Power System) by the authors. This paper proposes a novel control method of VIPS apparatus such as VSrC and HSPS installed at an interconnecting point for stabilizing inter-area unstable and/or oscillatory modes. The proposed design method of the control system is a kind of hierarchical decentralized control method of a large-scale power system based on a Lyapunov function. Under the proposed control scheme, each subsystem can be stabilized independently by local controllers such as AVR, speed governor and PSS, and then the whole interconnected system can be stabilized by VIPS apparatus taking into account interactions between subsystems. The effectiveness and robustness of the VIPS apparatus control are shown by numerical examples with model systems including a large-scale power system.     

Optimal memoryless regulator of large‐scale systems with time delays in the interconnections and the states via decentralized control

A method to construct optimal memoryless regulators of large‐scale systems with time delays in the interconnections and the states is proposed. Each feedback gain of decentralized control laws is obtained directly from solutions of simultaneous linear matrix inequalities. First, a sufficient condition for the stability of the overall closed‐ loop system is presented. Then it is extended so that the overall system and each subsystem remain stable, even if all or some of the interconnections between subsystems are cut. Lastly, a simplification of the implementation is discussed in the perspective of feedback loop reduction. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(4): 42–50, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21191     

满足互联条件相似组合大系统的鲁棒分散控制

研究了一类相似组合大系统,此类系统的互联项不是对称的且不满足匹配条件,为了设计出系统的分散控制器,本文提出了一种二步法设计方案,充分地利用了系统的互联项的有利作用。首先,设计出系统的假想的互联项－－满足匹配条件,并利用它把系统改变成新的形式。然后,基于系统的新形式,采用常规的设计方法,设计出系统的分散控制器。此控制器确保系统二次稳定。     

Decentralized control based on equilibrium point control for a three-machine electric power model system

Electric power systems have become larger and more complex year by year, and the number of decentralized power sources is rapidly increasing, Tberefore, to guarantee high reliability and security, decentralized control based on the decentralization of power systems needs to be developed. In this paper, a decentralized system is constructed by viewing the whole system from the perspective of the generator-bus with the largest power. Since the decentralized system is identified as a one-machine infinite-bus power model system with AVR and GOV, the equilibrium point control, proposed by the authors for a one-machine system, can be applied to it. Control inputs u_a · u_g for AVR · GOV are determined, and the equilibrium points of the decentralized system can be moved by changing the feedback gains. In particular, the unstable equilibrium point is set near the outside of the limiters for AVR · GOV, and stability in the limiters is guaranteed. Thus, it is shown that, by repeating the same steps for other generators, decentralized control for the three-machine model system can be attained. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 28–36, 1998     

Decentralized system identification for electric power system

Research on decentralized control of an electric power system is important for stabilizing control problems. In particular, since an electric power system is a large-scale nonlinear control system, decentralized (not divided) systems with cooperation should be constructed. This paper presents ways to construct decentralized systems for an electric power system. In section 2, swing data of a three-machine model system are obtained, in section 3, coefficient parameters of the model equation based on one-machine infinite-bus system with AVR and GOV are estimated by the least square method. In section 4, the equivalence calculated using estimated values is discussed, and the effect of conditions on fault is considered. Finally, section 5 is devoted to summarizing results of decentralized system identification.     

浙大中控ECS-100分散控制系统在大武口电厂#3机组改造中的应用

大武口发电厂在#3机组大修过程中,4台100MW机组原设计采用DDZ—II型单元组合仪表控制,采用淅大中控ECS-100分散控制系统对原有单元组合仪表控制系统进行了全面的改造,本文主要就此次改造过程中的系统功能、规模、软件、硬件和特点等方面进行了介绍。