Stabilizing interconnected power systems using static phase shifters

This paper presents a digital simulation study of proposed thyristor controlled static phase shifter applications in steady state stability enhancement of interconnected power systems. Incorporation of a detailed linearized model of a static phase shifter into the dynamics of the interconnected power system facilitates the investigation of different control strategies for static phase shifters to damp the electromechanical and torsional oscillations.     

Power system stability enhancement using static phase shifter

The role of static phase shifters in improving power system stability is investigated. A new technique, based on the nonlinear variable structure control principle, is used to formulate a control algorithm for the static phase shifter. Parameter uncertainty has been considered in the proposed scheme. Computer simulations show that a static phase shifter with the new control scheme has produced significant improvement in power system performance     

利用移相器进行电力系统网损优化控制

提出了一种利用移相器进行电力系统网损化优化控制的统一方法，该方法可以统一优化系统中不同种类的多个移相器的参数以求实现网损最小化的目的。在参数优化过程中，该方法计及了线路潮流的约束和移相器参数约束。算例分析表明，此方法具有通用性强，使用方便的特点，是一种研究移相器及其潮流控制的有效工具。     

可控制动电阻控制器广域协调优化方法研究

提出一种基于广域测量系统和三级共态预估算法的可控制动电阻控制器广域协调优化方法.将多机系统中的可控制动电阻控制器分成本地控制器和协调控制器两层,采用三级共态预估算法对分散的本地控制器进行非线性协调优化,使系统获得全局最优的控制效果.所提方法计算量小,并能在本地形成闭环反馈控制,适合于在线应用.仿真结果表明所提方法可以明显提高系统的暂态稳定性,并改善系统的动态品质.     

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.     

Decentralized two-level excitation control of multimachine power systems

A two-level decentralized scheme for the excitation control of multimachine power systems is presented. The control strategy is based on decomposing the control signal for each machine into two components generated by controllers at two different levels. At the first level, controllers are designed to optimize the performance of each generating unit, totally ignoring the couplings among the machines. The second control components are chosen to reduce the machine performance degradations due to the presence of interactions. With the developed two-level control scheme each machine is controlled entirely from its own state. The effectiveness of the proposed approach is illustrated by a numerical example involving a four-generator system.     

Decentralized bounded input bounded output stabilization of perturbed interconnected time-delay power systems with energy storages

This paper presents a new decentralized bounded input bounded output (BIBO) stabilization problem for a class of interconnected time-delay systems and its application to power systems with energy storages. We first provide conditions for the derivation of an ellipsoid that bounds a given linear functions of the state vector. Then, a design procedure is proposed to synthesize decentralized static output feedback controllers. The designed controllers guarantee that a given linear functions of the state vector, starting from any initial condition, converges exponentially to its prescribed zones. To deal with the time-delay issue, we use an improved weighted integral inequality recently reported in the literature to derive less conservative exponential stability conditions. Then, our presented control approach is applied to an interconnected power system integrated energy storages with multiple time delays. We synthesis decentralized static output feedback load frequency controllers to guarantee that the system frequency and interchanged power converge to their prescribed zones exponentially from any initial conditions. The controller’s construction is simpler and easier for implementation due to only the local output measurements are required. In order to systematically obtain the controller gains, an effective procedure using linear matrix inequality based stabilisation criteria, which can be solved by various computation tools, is provided. Finally, the effectiveness of the proposed control scheme is verified by comprehensive simulations.     

含风电的交直流互联电网AGC两级分层模型预测控制

随着大规模风电接入交直流互联电网,传统的自动发电控制(AGC)方法难以有效地抑制风功率波动带来的频率稳定问题。为此,提出基于两级分层模型预测的AGC策略。该两级分层控制方法在下层对多个区域电网采用分散式模型预测控制;在上层对下层分散的控制器采用动态协调控制方式。以含多电源的两区域交直流互联电网AGC模型为例,仿真结果表明:与集中式模型预测控制和分散式模型预测控制方法相比,文中所提控制策略不仅对频率和联络线功率等具有良好的控制效果,还兼具高可靠性。     

Two-level optimal load–frequency control for multi-area power systems

In large-scale power systems, classical centralized control approaches may fail due to geographically distribution of information and decentralized controllers result in sub-optimal solution for load–frequency control (LFC) problems. In this paper, a two-level structure is presented to obtain optimal solution for LFC problems and also reduce the computational complexity of centralized controllers. In this approach, an interconnected multi-area power system is decomposed into several sub-systems (areas) at the first-level. Then an optimization problem in each area is solved separately, with respect to its local information and interaction signals coming from other areas. At the second-level, by updating the interaction signals and using an iterative procedure, the local controllers will converge to the overall optimal solution. By parallel solving of areas, the computational time of the algorithm is reduced in contrast to centralized controllers. This approach is applicable to any interconnected large-scale power system. However, for simulation purposes, a three-are power system is presented to show advantages and optimality of the proposed algorithm.     

分散模糊负荷频率控制器的优化设计

本文针对多区域互联电力系统的特点，建立了一个考虑各区域扰动影响的综合性能指标，并对比例因子采用智能调整措施，提出了一种分散模糊负荷频率控制器的优化设计方法，对一个两区域互联电力系统的数字仿真结果表明，所设计的分散模糊负荷频率控制器具有良好的控制效果和较强的鲁棒性。     

Control schemes and transient characteristics of a high‐speed phase shifter for power flow control in power transmission systems

In recent years, attention has been paid to the concept of FACTS (Flexible AC Transmission Systems), along with significant progress in power electronic technology. A high‐speed phase shifter, which is one of the most promising devices in the FACTS concept, has the potential of power flow control and/or voltage stability in power transmission systems. In this paper, theory and experiment reveal that conventional high‐speed phase shifters may cause power swings in a transient state as a result of coupling between instantaneous active and reactive power control loops. Thus, two new control schemes for a high‐speed phase shifter are proposed to achieve both power flow control and power swing damping. The second proposed control scheme is based on the control scheme of an already proposed series active filter. Simulated and experimental results agree well with analytical results, not only in steady states but also in transient states. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 74–82, 1999     

互联电力系统模糊负荷频率控制器的优化设计

通过建立一个改进了的带修正因子的模糊（ｆｕｚｚｙ）控制表的数学表达式和一个综合性能指标，提出了一种互联电力系统分散Ｆｕｚｚｙ负荷频率控制器的自动优化设计方法。对一个两区域互联电力系统的数字仿真结果表明：所设计的分散Ｆｕｚｚｙ负荷频率控制器具有良好的控制性能。     

Stability analysis and decentralizedcontrol of inverter-based ac microgrid

This work considers the problem of decentralized control of inverter-based ac micro-grid in different operation modes. The main objectives are to (i) design decentralized frequency and voltage controllers, to gather with power sharing, without information exchange between microsources (ii) design passive dynamic controllers which ensure stability of the entire microgrid system (iii) capture nonlinear, interconnected and large-scale dynamic of the micro-grid system withmeshed topology as a port-Hamiltonian formulation (iv) expand the property of shifted-energy function in the context of decentralized control of ac micro-grid (v) analysis of system stability in large signal point of view. More precisely, to deal with nonlinear, interconnected and large-scale structure of micro-grid systems, the port-Hamiltonian formulation is used to capture the dynamic of micro-grid components including microsource, distribution line and load dynamics as well as interconnection controllers. Furthermore, to deal with large signal stability problem of the microgrid system in the grid-connected and islanded conditions, the shifted-Hamiltonian energy function is served as a storage function to ensure incremental passivity and stability of the microgrid system. Moreover, it is shown that the aggregating of the microgrid dynamic and the decentralized controller dynamics satisfies the incremental passivity. Finally, the effectiveness of the proposed controllers is evaluated through simulation studies. The different scenarios including grid-connected and islanded modes as well as transition between both modes are simulated. The simulation conforms that the decentralized control dynamics are suited to achieve the desired objective of frequency synchronization, voltage control and power sharing in the grid-connected and islanded modes. The simulation results demonstrate the effectiveness of the proposed control strategy.     

A decentralized nonlinear feedback controller with prescribed degree of stability for damping power system oscillations

Nonlinear feedback linearization techniques are being used for transforming nonlinear power system dynamics into closed loop systems, whose dynamics are linear over wide range of operating conditions. This facilitates use of linear techniques for designing feedback controllers to damp out oscillations. The advantage of using such feedback controllers is that they do not depend on the system operating conditions unlike the conventional controllers, for example a conventional power system stabilizer. A nonlinear feedback law is proposed in this work, which converts a nonlinear power system into closed loop decentralized linear time varying systems. A feedback controller has been designed using linear quadratic regulator with prescribed degree of stability to stabilize the decentralized linear time varying systems. The performance of the proposed method has been tested on a 16-machine, 68-bus system representing interconnected New England Test system (NETS) and New York Power System (NYPS).     

Nonlinear decentralized disturbance attenuation excitation controlvia new recursive design for multi-machine power systems

In this paper, a new nonlinear decentralized disturbance attenuation excitation control for multi-machine power systems is proposed based on recursive design without linearization treatment. The proposed controller improves system robustness to dynamic uncertainties and also attenuates bounded exogenous disturbances on the system in the sense of L₂-gain. Computer test results on a 6-machine system show clearly that the proposed excitation control strategy can enhance transient stability of power systems more effectively than other excitation controllers     

Automatic generation control: Decentralized area-wise optimal solution

A decentralized scheme is proposed for the design of automatic generation control (AGC) for interconnected power systems. This scheme uses the natural structural properties of interconnected power systems and gives a new method for decentralized AGC regulator design, using the existing theory of proportional-plus-integral linear regulators applied to each individual power area. It is shown that a decentralized design, based upon the expansion-contraction theory of large-scale systems with overlapping and modified linear regulators with incomplete subsystem feedback, is suitable to handle the design of AGC regulators for present-day interconnected power systems. The resulting AGC retains the autonomous area control concept and load distribution property of conventional AGC regulators, while at the same time allows for improved transients and stability margins for interconnected areas. The application of this decentralized AGC scheme is illustrated on a 17th-order model of a two-area interconnected power system.     

不确定互联电力系统的分散鲁棒控制

针对不确定互联电力系统,提出了一种分散鲁棒输出反馈控制器的设计方法.为了使参数不确定性符合工程实际和简化控制器的求解,引入数值界的形式对不确定性进行描述.该方法将控制器的设计归结为一组矩阵不等式的求解问题,采用同伦迭代算法,通过固定不同的变量,将非线性矩阵不等式转化为两组线性矩阵不等式并交替求解.仿真结果表明所获得的控制器使得互联电力系统鲁棒稳定,阻尼转矩充足,满足给定的性能指标,并且具有良好的抑制大扰动的能力.     

Power system security enhancement by OPF with phase shifter

This paper presents an integrated optimal power flow (OPF) with phase shifter approach to enhance power system security. The general OPF calculations are hourly based and the control variables of OPF are continuous. However, the calculations of phase shifter are daily based, and the variables related to phase shifter are discrete. Therefore, the general OPF cannot be directly used to solve this problem. The paper develops the rule-based OPF with phase shifter scheme to bridge the problems. In order to effectively alleviate the line overloads, the ranking of phase shifter locations is conducted based on contingency analysis and sensitivity analysis. The best phase shifter sites are identified and selected into a rule-based system accordingly. The handshaking procedure between the adjustment of the selected phase shifters and OPF calculation is proposed using a rule-based method. The hourly-based OPF problem is solved by the extended quadratic interior point method. The IEEE 30-bus system is used to test the proposed scheme     

Optimal variable structure controller for the load-frequency control of interconnected hydrothermal power systems

A new approach is presented for the load-frequency control of interconnected power systems using the theory of variable-structure systems and linear optimal control theory. A systematic procedure for the selection of the switching hyperplane, which is of vital importance in the design of variable-structure controllers, is developed by minimizing a performance index in the sliding mode operation. The proposed control scheme is illustrated by digital simulation of an interconnected power system consisting of a hydro power plant and a steam power plant.     

Mixed-sensitivity approach to H/sub /spl infin// control of power system oscillations employing multiple FACTS devices

This paper demonstrates the enhancement of inter-area mode damping by multiple flexible AC transmission systems (FACTS) devices. Power system damping control design is formulated as an output disturbance rejection problem. A decentralized H/sub /spl infin// damping control design based on the mixed-sensitivity formulation in the linear matrix inequality (LMI) framework is carried out. A systematic procedure for selecting the weights for shaping the open loop plant for control design is suggested. A 16-machine, five-area study system reinforced with a controllable series capacitor (CSC), a static VAr compensator (SVC), and a controllable phase shifter (CPS) at different locations is considered. The controllers designed for these devices are found to effectively damp out inter-area oscillations. The damping performance of the controllers is examined in the frequency and time domains for various operating scenarios. The controllers are found to be robust in the face of varying power-flow patterns, nature of loads, tie-line strengths, and system nonlinearities, including device saturations.