Control Of Large Power Systems Research Articles

АВТОМАТИЗАЦІЯ ПРОТИАВАРІЙНОГО КЕРУВАННЯ ЕНЕРГОСИСТЕМОЮ НА ОСНОВІ ЛОГІКО-ІМОВІРНІСНОГО МОДЕЛЮВАННЯ НАДІЙНОСТІ ПРОДУКЦІЙНИМИ МЕРЕЖАМИ ПЕТРІ

The paper presents the results of research on methods for constructing knowledge bases of decision support systems for dispatch control of power supply systems in crisis situations. Models of products based on Petri nets are proposed for assessing the parameters of reliability of power supply systems. An algorithm for calculating the reliability parameters of the electrical network using analytical matrix equations of Petri nets has been implemented. The work is devoted to the topical problem of intellectualization of power supply systems and means of automation of control of large power systems. The relevance of research in the field of building intelligent power systems is grounded. The basic requirements for the reliability of modern power supply systems are formulated. The concept of intellectualization of power systems and management of their reliability is a stable trend in the development of large energy systems and automated dispatch control systems. The solution to the problem lies in the implementation of intelligent decision support systems. The main task of the work is to model the reliability of the power supply system in order to build an effective knowledge base about the parameters of the reliability of the power supply system. For this purpose, we use a probabilistic approach to assessing reliability. This approach is based on the concepts of the probability of failure-free operation and the probability of failure, which are expressed in terms of the failure rate. On the basis of the obtained models, the construction of intelligent software systems for dispatching can be carried out taking into account the reliability indicators of the components of power supply systems. As a mechanism for formalizing failure circuits in power supply circuits, the production approach of knowledge representation is applied, which implements conjunctive-disjunctive connections of statements associated with failures. The outlined approach is invariant in relation to subject areas, which makes it possible to build effective decision support systems in the field of operational emergency control of the energy system.

Dynamic clustering-based model reduction scheme for damping control of large power systems using series compensators from wide area signals

This paper presents a new scheme of thyristor controlled series compensators (TCSC)-based damping controller for damping inter-area oscillations in bulk power systems based on a wide area measurement system (WAMS). In this regard, the proposed scheme provides an adaptive three-phase step through real-time working mode. In the first step, by proposing dynamic clustering-based technique, wide area signals evaluate the inter-area oscillations of the system which in a real-time procedure identify the corresponding oscillating areas. In the case of reducing the order of power systems through a set of aggregated coherent areas, the proposed scheme implements through the second step which utilizes as a damping controller for damping the inter-area oscillations. In this step, the wide area electromechanical signals use as input data through the proposed TCSC-based damping controller. The corresponding controlling signals consist of inter-area rotor angle (ΔδCOI) and inter-area speed deviation (ΔωCOI) evaluated through center of inertia (COI) frame. In the third step, at each time window (ΔT) through real-time working mode, the proposed scheme examines through a set of fault occurrences which based on online evaluations of the system dynamic responses, the controller parameters adjust adaptively. The proposed controller is an online and non-model-based scheme which properly reduces the system order through a set of coherent areas to provide proper damping performances of inter-area oscillations. The effectiveness of the proposed scheme evaluates through the Iran National Power Grid with the potential of two oscillating areas with proper damping performances for damping the unstable inter-area oscillations.

Optimal Decentralized Control of DC-Segmented Power Systems

DC-segmented power systems consist of ac subsystems connected to each other only by dc lines. DC-segmentation improves the transient stability and transmission capacity of power systems. Centralized control of large power systems entails burdensome communication requirements which are expensive and introduce delays. Decentralized control circumvents these problems, but finding decentralized controllers is intractable for general systems. Poset-causal systems are a special class for which the optimal neighbor-to-neighbor decentralized controller is easy to obtain. In this paper, we show that dc-segmented systems are poset-causal. We observe in numerical examples that the optimal decentralized controller attains almost the same performance as the optimal centralized controller.

On the stability of inverter-based microgrids via LMI optimization

The implementation of a number of individual small distributed energy resources forms the new generation of power systems - the microgrid. For an isolated operating condition of microgrids, the classical stabilizing approaches for control of large power systems are no longer applicable, as the characteristics of microgrids differ significantly from conventional power systems. Therefore, a new control approach must be investigated in order to robustly stabilize microgrids during disturbances, which are caused by load changes and the intermittent nature of alternative energy sources. In the present paper, the stability of inverter-based microgrids is considered. A decentralized state-feedback control approach for inverter-based microgrids with a linear matrix inequality (LMI) stability condition is proposed. Controller gains for inverters are designed by solving the LMI optimization problem. The resulting controller stabilizes the system, guaranteeing zero steady-state frequency deviations. The control approach is then validated via an academical example.

Multi-agent-system-based decentralized coordinated control for large power systems

In this paper, a decentralized coordinated control based on multi-agent system (MAS) is proposed to improve the transient stability of large power system. First, a two-hierarchical MAS is structured, which consists of upper level agent for implementing coordinated control and lower level generator unit agents for implementing decentralized control. Then, the transient stability of large power systems is analyzed based on controlling unstable equilibrium point (CUEP) method. According to transient stability assessment indexes, the upper level agent judges whether it need be activated to send coordinated control command. Afterwards, decentralized controller that is implemented by every generator unit agent, and decentralized coordinated controller is executed by the two-hierarchical MAS, are respectively designed by using H∞ robust control method integrated linear matrix inequality (LMI) technique. Finally, the effectiveness of the proposed control scheme is tested by means of simulation study.

Compliance Analysis of PMU Algorithms and Devices for Wide-Area Stabilizing Control of Large Power Systems

For the first time, IEEE Std. C37.118.1-2011 now provides metrics for PMU dynamic performance in terms of classes P and M filter designs. This paper attempts to determine whether fulfilling these requirements makes the PMU inherently well suited for stability control applications such as wide-area power system stabilizers (PSSs). In this aim, we considered two different frequency-adaptive approaches for class-P and -M compliance to ensure operation over a wide frequency range. The first is based on a finite-impulse response (FIR) with no overshoot in either the phase or the amplitude step responses, while the second is Kalman filter-based (EKF), which allows for a more refined out-of-band interference rejection at the cost of a phase step response with overshoot. These two approaches are benchmarked against Hydro-Quebec`s existing PSS requirements and the conclusion is that the total vector error-based response time is not indicative of the phase lag within the frequency band of interest, nor of the 3-dB bandwidth under sinusoidal amplitude/frequency modulation phenomena, which are key criteria when specifying PSS PMUs. Using simulated and field-recorded network fault responses, we also show that a class-M PMU is unsatisfactory for wide-area stabilizing control, unless its performance is improved during the fault period, which is not covered by Std. C37.118.1-2011.

Delay-dependent H∞ robust control for large power systems based on two-level hierarchical decentralised coordinated control structure

This article focuses on a novel two-level hierarchical decentralised coordinated control which consists of several local fuzzy power system stabilisers (LFPSSs) for each generator at the first level tuned by supervisory power system stabiliser (SPSS) at the secondary level for the transient stabilisation improvement of large power systems. First, in order to compensate the inherent nonlinear interconnections between subsystems in system dynamic model, a direct feedback linearisation compensator is proposed to act through the local excitation machine. Afterwards, the T–S fuzzy model-based decentralised LFPSS for each generator is designed. Then, for the purpose of improving dynamic performance, the SPSS is designed by using the remote signals from the wide area measurements system. However, there are unavoidable delays involved before the remote signals are received at the SPSS site or the control signals of SPSS are sent to the local systems. Taking consideration of the multiple delays, by using less conservative delay-dependent Lyapunov approach, the authors develop a delay-dependent H∞ robust control technique based on the decentralised coordinated control structure. Some sufficient conditions for the system stabilisation are presented in terms of linear matrix inequalities dependent only on the upper bounds of the time delays. Finally, the effectiveness of the proposed control scheme is demonstrated through simulation examples.

A new dynamic security enhancement method via genetic algorithms integrated with neural network based tools

In this paper, a new dynamic security assessment and generation rescheduling method utilizing genetic algorithms (GAs) which are integrated with probabilistic neural networks (PNNs) and adaptive neuro fuzzy inference systems (ANFISs) is proposed for the preventive control of large power systems against transient instabilities. By the proposed approach, PNNs are employed in a feasible manner to calculate the security regions accurately during the assessment and control. The security constrained generation rescheduling is implemented through a GA which optimizes the total fuel cost or the generation shifting during the preventive control. The steady-state solutions of the variables required for the GA are smoothly performed by the use of an ANFIS. The proposed methods are demonstrated on the 17-generator 163-bus Iowa power system and on the 50-generator 145-bus IEEE test system successfully and the effectiveness of the approaches is discussed.

WAM-signal-based decentralised fuzzy control for large power systems with unavailable states

For the stability enhancement of large power systems, this study introduces a novel decentralised fuzzy control design method by using wide-area measurement (WAM) signals. First, a set of equivalent Takagi-Sugeno (T-S) fuzzy models are extended in order to accurately represent the non-linear dynamics of large power systems. Furthermore, taking consideration of systemic states not all available, a fuzzy observer is proposed to estimate these states. Then, a fuzzy-observer-based decentralised state feedback controller is designed. Based on Lyapunov functional approach and H ∞ control method, some sufficient conditions for the existence of the controller are cast into the feasible problem of LMIs, by which the system can be asymptotically stabilised. Moreover, the minimising approach is proposed to search the suboptimal upper bound value of H ∞ performance function. Finally, the better control performances of the proposed methods are shown by the simulation examples.

Computation of Transfer Function Dominant Zeros With Applications to Oscillation Damping Control of Large Power Systems

This paper demonstrates that transfer function zeros are equal to the poles of a new inverse system, which is valid even for the strictly proper case. This is a new finding, which is important from practical as well as theoretical viewpoints. Hence, the dominant zeros can be computed as the dominant poles of the inverse transfer function by the recent efficient SADPA and SAMDP algorithms, which are applicable to large-scale systems as well. The importance of computing dominant zeros and the performance of the algorithms are illustrated by examples from large practical power system models. These examples constitute new practical uses for single-input single-output (SISO) and multi-input multi-output (MIMO) zeros, which may be of benefit to power system simulation studies and field tests related to oscillation damping control.

Development of a broadband real-time fully-digital simulator for the study and control of large power systems

While transient stability (TST) programs can represent very large systems, they are unable to model power electronic devices in detail since they use relatively large time steps and balanced representation of the network. Electromagnetic transients (EMT) simulators, on the other hand, can model relatively small systems in detail using small time steps. By interfacing both simulation tools, it will be possible to develop a broadband simulator capable of modeling large systems, but including detailed representation where required. The simulator would provide for studies ranging from fast transient to transient, dynamic, and voltage stability, with applications including closed-loop protection and control studies, as well as on-line dynamic security assessment (DSA). In this paper, we present the latest development work related to the realization of a broadband fully-digital simulator, which would be capable of meeting the challenge obtaining real-time solutions of very large networks using sufficiently small integration time steps such that power electronic devices (FACTS or HVDC) could be modeled at the device level with sufficient time resolution.

State-space system identification-toward MIMO models for modal analysis and optimization of bulk power systems

This paper provides an introduction to a reduced-order, small-signal identification approach to modal analysis and control of large power systems. Being based on system-wide responses to low-energy pulse excitations generated using conventional time-domain simulation software such as PSS/E or EMTSP, it readily takes full advantage of the large built-in model database. The proposed multi-input-multi-output (MIMO) minimal realization reveals naturally the dominant modes attached specifically to a given device, as well as the transfer functions relating selected measurement and observation sites. It plays a complementary role to direct computation of the full-scale linearized model using a comprehensive program such as MASS, after a summary of the theoretical work initiated at Hydro-Quebec in the early 1990s to promote this approach and put it into routine use, we present the main challenges in developing a production grade computer code. Detailed examples inspired by actual network studies at Hydro-Quebec are discussed, the most complex of them involving the identification of a 125th order MIMO model with 26 inputs and 26 outputs.

Application of functional modelling to the solution of electrical power system optimization problems

This paper presents theoretical foundations for the application of the principles of functional modelling (FM) to the electrical power systems optimization problems and concrete algorithms for the solution of such of them as optimal operation and optimal development problems. A FM type algorithm includes operations executed on several levels of analysis: lower (subsystems) levels and higher (system) level. On the lower levels functional characteristics of subsystems and their internal variables are calculated, on the higher level boundary variables are computed. Important advantage of FM algorithms is that results obtained with them on each iteration are identical to those of basic sequential algorithms from which they are derived. It is shown in this paper and elsewhere that application of FM algorithms, especially in their parallel realization, can greatly increase effectiveness of optimization problems solution in electrical power systems. Especially efficient is their application to real time operation control of large power systems.

Decentralized Control of Large Power System by H∞ Control Based Excitation Control System

In this paper we apply the decentralized H∞ control theory to interconnected multi-machine power systems. The idea is to design a local controller for each generator model so as to globally stability and optimal performance with consideration to interactions among multi-machine systems. The proposed excitation controller enables a power system to remain stable over a wide range of operating conditions. We also propose the design method of the advanced type of multi-input PSS(Power System Stabilizer) on the basis of H∞ theory.

Damping control design based on time-domain identified models

This paper presents an integrated approach for designing damping controllers for large power systems. First, a low-order model is identified from a time simulation of the nonlinear power system model. Then an exact multi-modal decomposition is used to develop design indices for selecting on appropriate input signal to the controller. The method is illustrated with the design of thyristor-controlled series compensator damping controllers in two test systems.

Design of decentralized controllers for large power systems considering sparsity

This paper proposes a method for the design of power system controllers aimed at damping out electromechanical oscillations. It can be applied to the design of both power system stabilizers (PSSs) for synchronous generators and supplementary signals associated with other damping sources. Some attractive features of the method are: the parameters of all controllers are jointly determined, there is no restriction on the type of supplementary signals to be used, and controller structures are compatible with those nowadays employed in electric utilities. The control problem solution exploits sparsity, combining a system description which preserves a sparse structure with an adequate mathematical formulation of the optimal design approach. The resulting method is thus made applicable to large power systems. Results for two test systems, including a large 750-bus system, are presented. For both systems, settings for several power system stabilizers are simultaneously determined. The results are validated by using both eigenvalue analysis and nonlinear simulation.

Optimal control of SMES systems for maximum power system stability and damping

Fast development of power electronics and computers has provided the basis for an accelerated development of various flexible AC transmission systems (FACTS). Some of these systems have already been successfully applied while others are constantly being evaluated for future applications in order to improve the transmission capability, stability and dynamic performance of existing power systems. Superconducting energy storage systems (SMES) represent an interesting prospective FACTS technology since they can generate/absorb active and reactive power in rapid response to power system requirements. SMES' systems are considered for a variety of applications: automatic generation control; fast spinning reserve; peak generation and load sh fting; improving stability, dynamics, transmission efficiency and voltage performance; etc. A number of such applications have been studied and a few experimental systems have been built and evaluated. SMES application is particularly interesting for long transmission systems such as Hydro-Quebec's, for example. This paper presents the use of the optimal control of SMES systems to achieve transient stability and damping of the power system. The synthesis of an optimal controller is illustrated on a two-machine equivalent for simplicity. Solving this problem yields some important conclusions with regard to the control and efficiency of active and reactive power when applied to improve system stability and damping. Implementation aspects of the optimal control for large power systems are discussed.

Coherency Based Design of Decentralized Optimal Controllers for Stabilization of Large Power Systems

This paper gives a new procedure for the design of decentralized optimal controllers for very large power systems. The group of machines, comprising one decentralized area is identified by a coherency recognition algorithm. The coupling between the elements within the group is strong and the coupling between groups are weak. This principle is used to identify the groups. A pole assignment technique, which requires calculation of one eigenvector only, for shifting one eigenvalue is used. This method requires only less computer storage and less computing time, yet achieving results very much comparable with the design of full controllers. The procedure is illustrated with an example. This has very good applications in the design of optimal controllers for large power systems and in their dynamic analysis.

A Network Description Language for Real Time Control of Power Systems

The paper presents the specifications and characteristic features of a language specifically adapted for the control of large power systems. To begin with, a brief overview of the impact of computers in Energy Control Centers is presented. The use of on-line computer systems for decision making in power systems has necessitated the need for developing more specific methodology which would take into account the particularities of power systems. Our approach has been motivated by the fact that the information on the topology of a network at a given instant forms the basis of all real time control algorithms. The strategy of remote control of network topology could be an effective way of assuring security and economy in power system operations. We propose a special purpose language for describing the operations on a power system, with a view to meeting the following aims.-to construct an operational data base. Provide means of on line updating.-to provide the primitives for the automatic generation of a logically related elementary switching sequence (close/open switch) from a set of global instructions defined in the operator level language. The generation of the elementary sequence takes into account operational or legal restrictions.

Control of Large Power Systems Based on Situation Recognition and High Speed Simulation

The operation of large power systems places an increasing importance on the security of the system which must be evaluated in steady state, transient, and long term dynamic situations. A method based on situation and high speed simulation for on-line security computations is proposed and analyzed. The method combines the advantages of high speed hybrid computer simulation and pattern recognition methods, and, at the same time, has the flexibility of a pure digital simulation.