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.     

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     

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.     

A multiagent approach to power system normal operation

Recently, the electric utility industry worldwide has been facing pressure to be deregulated or restructured in order to increase its efficiency, to reduce operational cost, or to give consumers more alternatives. For this aspect, a great deal more research is needed to achieve a better, intelligent knowledge process. The present centralized system for power system control, operation, and planning must be remodeled to cope with these situations. With the promotion for the deregulation of the electric power system, the definition of the objective function for the optimization problem such as outage work operation for electric power systems is becoming critical. Currently, agents are an intense focus in many subfields of computer science and artificial intelligence. Agents are being used in an increasingly wide variety of applications. In this paper, we developed a power system normal operation application by multiagent architecture. Our multiagent system consists of several facilitator agents, equipment agents, and switch‐box agents. Facilitator agent acts as a manager for negotiation process between agents. Equipment agent corresponds to the element of the electric power system, such as bus, transformer, and transmission line, while switch‐box agent is the pseudo object which consists of neighboring current breakers and disconnecting switches. The proposed system realizes the appropriate switching operations by interacting with corresponding agents. The proposed approach is applied to a simple network, and the results show that the proposed multiagent system is an efficient decentralized approach for solving power system normal operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 26–33, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10227     

Load-flow equivalents for decentralized monitor and control of power systems

Load-flow calculation on electric power systems is one of the most fundamental analyses in system operation and planning. There are many reasons to calculate load-flow solutions, and the contingency evaluation is a representative one. In contingency evaluation, it is necessary to repeat load-flow calculation for tremendous patterns depending on branch or generation outages. Then, computing efforts are generally very heavy. Thus various techniques have been proposed to reduce computing time, especially by adopting equivalencing for external network. On the other hand, the network equivalents techniques also become important at present from the viewpoint of the necessity of decentralized monitor and control on bulk power systems. This paper describes a newly developed method of load-flow equivalents based on the Ward equivalent for both direct (dc) solution and (ac) solution. Numerical results also are shown to clarify the accuracies and practicality of the proposed method through the comparison of the representative REI approach.     

Autonomous decentralized system for torque control of high‐power permanent magnet synchronous motor

An autonomous decentralized system (ADS) for the control of a high‐power permanent magnet synchronous motor (PMSM) presented in this paper. The system decentralizes a centralized control system into several autonomous subsystems. Thus the power supply and power electronic devices of the control system can be replaced by smaller ones, thereby obtaining better fault tolerance of the system. The subsystems are connected only through the data field, which, in this paper consists of feedback elements and communication modules. This structure enables the autonomous controllability and autonomous coordinability of the system. The mathematical model of the PMSM with decentralized stator coils is proposed. This model takes into account the self‐ and mutual inductance of the coil, as well as the effect of the stator slot‐pitch angle. In addition, an autonomous algorithm for the torque control of the PMSM with decentralized stator coils is proposed, and the fault‐tolerance design is developed. Experimental results of the torque control and fault‐tolerance control confirm the validity of the proposed system. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

考虑电动汽车集群的互联电网负荷频率分散预测控制

随着大量电动汽车接入互联电网,其移动的充电模式会给电网带来一定的冲击,反过来,电动汽车作为一种移动式储能单元可参与互联电网调频,但目前的研究都是集中式或分散式的V2G控制上.在电动汽车储能电池动态模型的基础上,构建含电动汽车集群的多区域互联电网负荷频率控制模型,基于广域监测系统,结合模型预测控制实现了多区域电网负荷频率广域分散预测控制.在MATLAB/Simulink中搭建三区域互联电网模型,并进行仿真分析.算例结果表明,电动汽车作为移动式储能单元参与互联电网调频,可以在短时间内平抑电网频率波动;而文中提出的广域分散预测控制方法较经典的PI控制方法,能将三区域电网的频率偏差限制在更小的范围内波动,又能较快地恢复至稳态值.     

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.     

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.     

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.     

基于控制系统四元组形式的发电机非线性分散鲁棒控制

分析了仅包含状态变量、输出变量、控制变量的控制系统常规三元组形式应用到发电机分散鲁棒控制时遇到的困难，为克服这些困难提出了包含状态变量、输出变量、控制变量、量测变量的控制系统四元组形式的概念。量测变量的引入使得发电机综合控制模型本身变为各机解耦、与外部系统网络参数及动态无关，在此模型下设计出分散鲁棒控制器是自然的。此模型可以考虑系统包含各种动态元件如FACTS元件、HVDC系统等情况，在此四元组模型下，通过直接寻求控制量与控制目标之间关系的关联度方法将发电机控制的四元组模型完全线性化，通过励磁控制使发电机端电压具有良好的动态特性，通过汽门控制提高发电机功角暂态稳定性。数字仿真表明，所设计的基于控制系统四元组形式的发电机非线性分散鲁棒综合控制器是有效的。     

汽轮发电机汽门开度的分散非线性预测控制

基于非线性预测控制理论,设计出具有闭型解析解控制律的汽轮发电机汽门开度分散非线性预测控制器。该控制器并不要求进行在线优化计算,从而避免了繁重的计算负担。控制器的输入为当地可测量信号且与网络参数无关,从而实现了分散控制。通过在6机22母线系统的仿真结果表明,该控制器能提高电力系统的暂态稳定性和动态性能。     

Comparison of Centralized and Decentralized Systems in Power System Restoration

This paper proposes a multiagent approach to decentralized power system restoration for distribution system networks and presents a comparison of centralized and decentralized systems for power system restoration. Numerous studies have been conducted on power system restoration problems. From the viewpoint of system structures, this research can be divided into two categories: centralized systems and decentralized systems. In this study, we solve a power system restoration problem for a power distribution network by two different methods: mathematical programming (MIP) and the proposed multiagent‐based method (MAS). The proposed multiagent system consists of several distributing substation agents (DSAGs) and load agents (LAGs). An LAG corresponds to the customer load, and a DSAG supplies electricity to the LAG. From the simulation results, it can be seen that the proposed system can reach the right solution by making use of only local information and that the solution quality is better than that of the centralized system (MIP). This means that the proposed multiagent restoration system is a promising approach to larger scale distribution networks.     

Hierarchical decentralized autonomous control in super‐distributed energy systems

This paper deals with a decentralized autonomous control strategy of a super‐distributed energy system with a hierarchical structure in order to reduce the complexity of control. In this paper, distribution systems are assumed to be composed of multiple small‐scale power systems in which many customers with dispersed generators exist. A small‐scale power system can be considered as a unit with a generator state and a load state, or as a customer with dispersed generators. Control components of small‐scale power systems are interconnected with each other and are used to operate distribution systems. An expanded decentralized autonomous control method for a super‐distributed energy system with a hierarchical structure is proposed on the basis of the Hopfield neural network. It is demonstrated that super‐distributed energy systems with a hierarchical structure can be controlled autonomously by applying the proposed method. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

自律分散式AVC系统在地区电网中的应用

针对传统集中式AVC系统存在的问题,结合自律分散系统的思想,提出正常情况下集中控制与故障情况下自律分散控制相结合的控制模式,构建了地区电网自律分散式AVC系统;在地区电网内部进行分区,将大规模地区电网的无功优化问题分解为若干小规模子系统的优化问题,对粒子群算法进行改进,采用多线程技术实现各区域并行计算;并结合地区电网的...     

Enhancement of interconnected power system stability using a control strategy involving static phase shifters

The static phase shifting transformer is one of the potential options of the recently proposed FACTS (flexible AC transmission systems). Promising results have been obtained for enhancing the small-disturbance and the transient stability of interconnected power systems.

In this paper, the important concept of involving in the same control strategy both generating units and static phase shifters has been considered. A systematic procedure for designing co-ordinated and decentralized controllers of these components is provided to assure a satisfactory dynamic performance of an interconnected power system under both small and large perturbations. The approach uses optimal control theory as a basis for the co-ordination of static phase shifter and governor controllers. A suboptimal decentralized control scheme is derived from the designed optimal controller by using a ‘minimum norm’ nearness criterion. The resulting feedback control signals for each generating unit and for each phase shifter is expressed in terms of measurable and local variables only.

Test results show the effectiveness of the proposed control strategy and the usefulness of control actions on static phase shifters.     

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     

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.     

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     

On the eigenvalue control of electromechanical oscillations byadaptive power system stabilizer

The eigenvalue control strategy, which utilizes an adaptive power system stabilizer, is presented for the decentralized control of damping and frequency of electromechanical oscillations in power systems. The control procedure includes the complete identification of the decoupled subsystem model in real-time from local measurements only and the assignment of its estimated electromechanical eigenvalue by the change of stabilizer parameters. The robustness and efficiency of the proposed adaptive controller to enhance overall system stability are illustrated by several examples, including the three-machine power system model