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.     

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.     

高压直流换流站分散鲁棒自适应控制器的设计

针对高压直流输电系统（HVDC），提出了一种换流站的分散鲁棒自适应控制器的设计方法，设计中引入自适应非线性阻尼项来抑制系统非线性不确定参数和未知有界干扰的影响，同时采用反演设计方法来克服控制器设计的复杂性，最后获得高压直流输电系统换流站的分散鲁棒自适应控制策略的一般表达式，并提供了整个系统的稳定性证明，所得控制器仅利用本地测量量实现，控制策略具有分散性和适应性，通过NETOMAC数字仿真，仿真结果证明该控制器比常规的PI控制器具有更好的控制效果。     

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。     

多机电力系统中STATCOM与发电机励磁的协调控制

针对一个典型的两区域且区间联络线中间带STATCOM的4机电力系统，应用信息结构约束下的最优协调控制理论与算法，设计了输出反馈的线性二次型（LQ）分散控制规律，得到的励磁控制器考虑了机组原有PID自动电压调节器（AVR）的结构约束，并通过在STATCOM安装处构造一个能反映区间振荡模式的就地观测量，以抑制区间低频振荡。应用数字仿真研究了所得控制规律的性能，结果表明，协调控制器大大地提高了系统暂态稳定水平和区间传输容量，而且，由于采用了完全分散的信息模式和输出反馈方式，控制器实现代价低、可靠性高，易于实际应用。     

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.     

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.     

Robust hierarchized controllers using wide area measurements in power systems

In this paper, we present a new method for robust centralized controller design using LMI’s with applications to power systems. This method makes possible to increase the damping rate of the decentralized system (that is, power system with PSS’s). It considers delays added to the signals that travel from the generators to the central controller. The robust hierarchized controller is composed by two control layers: the first one consists on decentralized controllers, that are applied independently to each machine of the system, what guarantees the stability and a minimum damping rate; the second one is composed by a centralized controller, that receives delayed information from all machines of the system, and it sends control signals to all generators. The centralized controller algorithm is robust, once it considers various operative conditions for the power system, and it also permits the choice of the communication delays.     

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.     

Decentralized suboptimal control of a complex power system using the modified Bellman-Lyapunov equation

This paper is concerned with the decentralized control of the dynamic behaviour of a complex power system. Two different approaches are suggested here for the design of suboptimal decentralized controllers using the modified Bellman-Lyapunov equation via optimal techniques. In the first approach, suboptimal control laws for the turbine power are constructed with the aid of a special Lyapunov function for the system as a whole. This method of attack aims at ensuring suboptimal dynamic conditions for the system as a nonlinear large-scale dynamic system. In the second approach, suboptimal control laws are deduced with the aid of a vector Lyapunov function, which is constructed by the decomposition of the power system into interconnected subsystems.     

部分分散控制及其在单元机组协调控制中的应用

针对强耦合多变量对象控制系统设计中分散控制不能满足高性能要求,而多变量先进控制算法结构复杂、较难推广的现象,研究基于扩展对象的部分分散控制器设计。设计过程首先通过结构分析法得出部分分散控制器结构,再对其对象进行非方扩展,利用非方内模法设计相应非方分散控制器并转化为部分分散控制器,最后应用扩展μ交互法进行稳定性分析。将该方法应用于一500 MW单元机组协调控制系统的仿真研究,结果表明:部分分散控制系统能达到与多变量协调控制系统相近的性能,并且部分分散控制结构更加简单、设计及调试方法更加容易。     

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。     

考虑GRC的多区域电力系统负荷频率分散控制

本文讨论了将突迭分解分散控制理论应用于区域性电力系统的负荷频率控制(LFC)的可行性,并提出了一种新的控制系统设计方法。该方法不仅保持了交造分解分散控制的一切优点,考虑了发电速度的限制,而且有效地改善了控制系统的动态品质。对两区域电力系统进行的LFC系统设计及仿真,结果表明本设计方法是可行的,且具有一定的优越性。     

Dynamic model for power systems with multiple FACTS controllers

Computer simulation and analysis of power systems are necessary for both planning and operation. This requires an appropriate mathematical model of the system that includes many inter-related linear/nonlinear differential and algebraic equations. Such mathematical model is also needed for the design of globally coordinated controllers to improve power system dynamic performance and stability. This paper presents a procedure for finding comprehensive dynamic models of power systems fitted with shunt and/or series connected FACTS controllers such as STATCOM, SSSC, and UPFC. In this procedure, individual components of a power system are modeled using appropriate frame of references. Then all related equations are transformed to a common network frame of reference and tied to each other through the Y-matrix of the transmission network. The procedure is tested on the Western System Coordinating Council (WSCC) test system including FACTS controllers by performing computer simulations of the system for three-phase short circuit faults. MATLAB/Simulink software package is used for the simulations.     

Decentralized stability-enhancing control of synchronous generator

This paper describes new structures for stability-enhancing excitation controllers designed using a nonlinear multi-machine system model and Lyapunov's direct method. Two control structures are presented: a hierarchical structure In which the AVR is the master controller and the PSS the slave controller and a traditional structure in which the PSS constitutes a supplementary loop to the main AVR. Both controllers are shown to be robust, as the damping they introduce into the system is insensitive to changes in both the system topology/parameters and the pattern of network flows. Each individual controller contributes positively to the overall system damping with no undesirable interaction between controllers. These features should allow a decentralized approach to the design of the AVR+PSS. Such a design approach is compatible with the new competitive market structures and should result in savings on commissioning costs. Simulation results for a multi-machine power system are presented that confirm the above and show that the two control structures are very effective in damping both local and inter-area power swings     

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).     

Mode selective damping of power system electromechanical oscillations for large power systems using supplementary remote signals

This paper presents the design of local decentralized power system stabilizer (PSS) controllers, using selected suitable remote signals as supplementary inputs, for a separate better damping of specific inter-area modes, for large-scale power systems. System identification technique is used for deriving lower order state-space models suitable for control design. The lower-order model is identified by probing the network in open loop with low-energy pulses or random signals. The identification technique is then applied to signal responses, generated by time-domain simulations of the large-scale model, to obtain reduced-order model. Lower-order equivalent models, thus obtained, are used to design each local PSS controller separately for each of the inter-area modes of interest. The PSS controller uses only those local and remote input signals in which the assigned single inter-area mode is most observable and is located at a generator which is most effective in controlling that mode. The PSS controller, designed for a particular single inter-area mode, also works mainly in a frequency band given by the natural frequency of the assigned mode. The locations of the local PSS controllers are obtained based on the amplitude gains of the frequency responses of the best-suited measurement to the inputs of all generators in the interconnected system. For the selection of suitable local and supplementary remote input signals, the features or measurements from the whole system are pre-selected first by engineering judgment and then using a clustering feature selection technique. Final selection of local and remote input signals is based on the degree of observability of the considered single mode in them. To provide robust behavior, H_∞ control theory together with an algebraic Riccati equation approach has been applied to design the controllers. The effectiveness of the resulting PSS controllers is demonstrated through digital simulation studies conducted on a sixteen-machine, three-area test power system.     

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.     

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     

Decentralized adaptive backstepping control of electric power systems

In this paper, a decentralized adaptive backstepping excitation controller, tuned using a Particle Swarm Optimization technique (PSO), is designed for stability enhancement of multi-machine power systems. To achieve decentralization, each machine is modeled as an independent uncertain dynamic subsystem, where the uncertainty is a disturbance that represents the effects of the rest of the system on that particular machine. This disturbance is expressed as a polynomial function of electric power deviation, and its parameters are adapted using PSO. The proposed technique is illustrated with a two-area benchmark power system. This system exhibits inter-area oscillations which are effectively damped with the proposed decentralized controllers under severe contingencies, for which traditional power system stabilizers fail.