1,720,984 research outputs found
A distributed computing approach for real-time transient stability analysis
No full textOn-line Dynamic Security Assessment (DSA) is a challenge computing problem. A key problem in DSA is the analysis of a large number of dynamic stability contingencies every 10-20 minutes using on-line data. In order to speed up the transient stability analysis, parallel processing has been applied and several results can be found in the literature. In this paper, we present a distributed approach for real-time transient stability analysis. Distributed computing is economically attractive providing the processing power of supercomputing at a lower cost. Several distributed software environments like the Parallel Virtual Machine (PVM) allow an effective use of heterogeneous clusters of workstations. Both functional and domain decomposition of the transient stability problem were tested under PVM on a homogeneous cluster of eight DEC ALPHA and on an IBM SP2 machine. Functional decomposition has been obtained by the Shifted-Picard algorithm, whereas domain decomposition has been obtained concurrently running different contingencies on different nodes of the cluster, using the Very Dishonest Newton algorithm. In order to assess the performance of these approaches, time domain simulations, adopting detailed modeling for synchronous machines, have been carried out on a realistic-sized network comprising 2583 buses and 511 generators. © 1996 IEEE
Synthesis of A Sequential Stable Decentralized Controller for Flexible A.C. Long Distance Transmission Systems
No full textThe use of Static VAR Compensators (SVCs) in long distance transmission systenis is an effective means to damp voltage fluctuations and to improve the system stability,
both under small and large disturbances. Additional advantages can be obtained by adopting Thyristor Controlled Phase Sliiftcrs (TCPSs) able to regulate the active power flow,
to reduce the power arid frequency dcviations atid lo increase the transmission system capacity.
The control actions ol these compoments must be co-ordinated with a control strategy associated to synchronous In this paper, a systernatic procedure for
the co- ordinated design of decentralized controllers associated to the generating units and the TCPSs at the sending end, as well as to all the SVCs
distributed at intermediate substations of an A.C. long distance transmission system, has been developed. The proposed procedure is organized in two steps.
The sequential design of the controllers associated to the Pf and QV channels allows to drive oscillatory arid aperiodic modes in a selective way.
Additionally, sequential stability is assured at each step of the procedure. An example is presented to illustrate the validity and usefulness of the suggested approach
Impact of advanced technologies on the Italian Electricity Market
No full textIn this paper, the impact of the adoption of Combined-Cycle Gas-Turbine (CCGT) power generation on the Italian energy market is assessed. The study is developed by using the data on new CCGT installations foreseen by the Italian System Operator (Gestore della Rete di Trasmissione Nazionale, GRTN). The Generation Companies (GenCos) participate to the market with their conventional and/or CCGT power plants, through an incremental cost based- supply bid for every generating unit The CC power plant incremental costs are evaluated and implemented in a market model representing the Day Ahead Energy Market (DAEM) structure, as stated by Regulator, in order to assess energy price and dispatched power. In particular, the simulation tool is able to maximize the Social Welfare with a double side multistage bid structur
A distributed computing approach for real-time transient stability analysis
No full textA challenge in the power system area is the implementation of realtime transient stability analysis. Time domain simulations of power system dynamics have been developed for over three decades and are routinely used for off-line planning and operations planning studies. The computational requirements for simulating power systems dynamics, even for few seconds after fault, represent the main impediment to the use of conventional transient stability programs in real-time. Parallel processing has been extensively used to speed up transient stability analysis and several results can be found in the literature. In recent years, distributed environments built out of pools of networked workstations have been widely used for solving computationally intensive problems that once belonged exclusively to the domain of supercomputers. The success of "cluster computing" is essentially due to the increasing power of workstations, based on fast RISC (Reduced Instruction Set Computer) microprocessors. Moreover, the development of high speed networks, capable to sustain up to Obitis, drastically narrowed the bandwidth and latency gap between an interconnection network in a parallel machine and a communication network in a distributed system. Distributed computing is also economically attractive with respect to traditional parallel computers, allowing to potentially provide at lower cost the processing power of a supercomputer. Heterogeneity and portability are primary goals of the developed distributed systems and programming environments. Heterogeneity allows to connect different machines from different vendors in a single virtual parallel computing environment. These important features can be achieved using programming environments recently developed, such as the Parallel Virtual Machine (PVM) from Oak Ridge National Laboratory and Emory University. The feasibility of real-time transient stability has been investigated exploiting both domain and functional decompositions, on a homogeneous cluster of eight Digital ALPHA and on an IBM SP2 machine. To test the functional decomposition, the Shifted-Picard algorithm has been implemented under PYM, whereas a scaled domain decomposition has been tested running multiple contingencies on different nodes of cluster systems, using the Very Dishonest Newton (VDHN) algorithm, which is the fastest sequential algorithm. In order to assess the performance of these approaches, time domain simulations adopting detailed modeling for synchronous machines have been carried out on a realistic sized network comprising 2583 buses and 511 generators. The distributed Shifted Picard algorithm is characterized by low performance. At first, this is surprising, since previous experiments on parallel environments showed interesting speedups. In order to understand the reason for this behavior, we have conducted a further investigation on the distributed SP algorithm. A communication model has been developed to take into account the main issues involved when a distributed environment is used. The tests carried out have shown that this model must account for the contention of the shared physical medium. Moreover, the SP algorithm was loosely synchronized, to guarantee a deterministic convergence behavior. Thus, the communication pattern resulted to be regular and symmetric, i.e. at a fixed time all the processors attempted to use the shared network. Although this property is effective for parallel processing solutions, our experience has shown that in distributed computing a more chaotic communication pattern would have produced better results, being at any given time the network resources exploited by at most one processing element on average. However, we were forced to this choice because asynchronous algorithms, due to their unforeseeable behavior, are not acceptable for real-time applications. The scaled domain decomposition has been implemented on the same test bed, using on each node the VDHN algorithm. In this case, the size of the problem (i.e the number of contingencies) scales with the available processor number. Overheads due to PVM and disk I/O have been considered in performance evaluation. As shown in Figure 1, domain decomposition and VDHN algorithm has provided the best results: the overall efficiency never drops below 89.16 percent with respect to the linear one on the SP2 machine and 84.88 percent on the ALPHA cluster. This efficiency loss is mainly due to the time spent in program loading, load imbalance, software overhead, multitasking of Unix operating system and communication operations. Although we overlapped whenever possible computation and communication, the main source of this loss remains the protocol support of the Unix I/O subsystem. Exploiting this approach, real-time contingency analysis can be achieved solving several tens of transient stability analyses on an 8 node IBM 5P2 and DEC-ALPHA cluster. (Figure Presented) Figure 1. Speedup of the distributed VDHN vs. number of processors
Voltage stability analysis of electric power systems with frequency dependent loads
No full textDuring the last decade great attention has been devoted in the technical literature to voltage stability problems of interconnected power systems. However, power system operators have found that voltage collapses often occur in a real system at a load condition different from the one predicted by simulation studies. One of the causes that makes the use of present approaches unreliable is the lack of adequate models for static loads, which are traditionally represented by constant power or, generally, by voltage dependent characteristics. To overcome this difficulty, the paper proposes a new and practical procedure for analysing the effects of static load modelling on the voltage stability limit of power systems. To this purpose an accurate model for static loads is used which takes into account their frequency dependence. This is very important to avoid unacceptable inaccuracies in determining the actual voltage stability limits of heavily loaded and isolated power systems. Two numerical examples illustrate the capability and usefulness of the proposed technique
A qualitative approach to the transient stability analysis
No full textWith the growing stress on today's power systemsthere is a urgent need for implementing on-line Dynamic Security Assessment (DSA). Among the functions of DSA, the most time-consuming function is the dynamic contingency analysis. In this paper, it has been assumed that during this analysis, one is not interested in obtaining trajectories with a very high accuracy but is primarily interested in a qualitative answer to the question: is the system stable or not? Subsequently, only unstable or marginally stable cases have to be considered for more detailed analyses and preventive control. This idea is applied to parallel-in-time algorithms for transient stability analysis in order to stop the simulation as soon as the stability is detected by the condition of Potential Energy Boundary Surface (PEBS) crossing. The effectiveness of the approach has been validated on the New England test system and a realistic-sized network with 662 buses. An implementation on the nCUBE multiprocessor of a particular parallel-in-time algorithm allows the speed up derived from the proposed approach to be assesse
Sequential design of a decentralized control structure for power system stabilizers
No full textIn this paper, a new procedure is developed for designing power system stabilizers under the constraint of sequential stability. This constraint is an important feature of a large scale decentralized control and deals with the property of a design technique that allows the controllers to be adjusted one at a time such that the system remains stable at all times. This constraint is due to the impossibility to adjust all decentralized controllers to the power system simultaneously (due to unavoidable delays in the communication system). The procedure adopts a linearized model of the power system in the state space representation. The stabilizing signal requires the linear feedback of the local variables only. The suggested design procedure is tested on the standard New England 39-bus system
A new parallel-in-time algorithm for power system on-line transient stability simulations
No full textOnline voltage stability assessment of load centers by using neural networks
No full textThis paper presents a neural network based method for evaluating online voltage stability conditions for a selected load center of an electric power system. Starting with a dynamic model of the system, a suitable index is defined to evaluate the proximity of the power network to voltage collapse. Then, a three-layer feedforward neural network is trained to give, as output to a prespecified set of inputs, the expected value of the voltage stability index. For this purpose, two different neural network architectures are proposed. The error back-propagation algorithm is used in this paper to train the chosen neural network structure. Moreover, it is shown that a good estimate of the real power margin of the selected load center can also be obtained using the value of the output of the designed neural network. To demonstrate the effectiveness of the proposed neural network based approach for voltage stability monitoring, a sample power system is considered. Test results show that neural networks can yield, in real time, an accurate assessment of voltage stability conditions
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