The performance of the index is illustrated by analyzing the results of transient stability studies of the CIGRE test power system and the. Hellenic Interconnected ...
This rule is the performance criterion. Its practical meaning is the next: if P1 is the initial consequence of a severe disturbance, then P2 is the direct consequence of P 1 and P3 is the indirect consequence of P1 through knowledge of P2. The implementation of this criterion is made by using the fuzzy sets theory. According to this theory, the proposition P1 is represented by a fuzzy set A which consists of atomic terms representing the magnitude of the accelerations values, for each operating state. This set may induce a fuzzy set C consisting of atomic terms representing the magnitude of the kinetic energies value, which also represents the system stability condition. This induction is made by using a fuzzy relation table showing the relationship between the values of accelerations and the values of kinetic energies, under different operating modes of the system. The unlabeled set C is compared with six predescribed fuzzy sets Lj, = 1, 2,- -, 6 which represent the possible membership distributions of the terms that represent the magnitude of the kinetic energies value, under Very Unstable, Unstable, Critically Unstable, Critically Stable, Stable, and Very Stable conditions of system operation. The semantic similarity of C and f,, = 1, 2, * *, 6, is examined by computing a modified form of Bhattacharya distance. Thus, the label of the fuzzy set fj that corresponds to the minimum value of the computed distances is assigned to the fuzzy set C. This label is a linguistic term that indicates the transient stability of the system in a fuzzy manner as a unique index. The performance of the index is illustrated by analyzing the results of transient stability studies of the CIGRE test power system and the Hellenic Interconnected Power System. The results of this analysis show that the stability evaluation is made in a fast and secure manner. Moreover, the way of derivation of the index makes the latter flexible and adaptable to the needs and requirements of the analysis of any system.
89 WM201-5
August 1989
A Framework for Integrated Resource Planning: The Role of Natural Gas Fired Generation in New England R. D. Tabors, Member, S. R. Connors, C. G. Bespolka, D. C. White, Fellow, and C. J. Andrews The Energy Laboratory Massachusetts Institute of Technology New England is similar to other areas in the United States in terms of the issues facing its electric utilities. The fuel price shocks of the seventies, and cascading impacts of PURPA and other legislative actions have affected the supply decisions and demand response of New England's electric consumers. Environmental concerns and consumer challenges to the electric utilities' decisions have served to open up the debate on how utilities will meet future demands for electricity. It is not uncommon to find environmental and conservation advocates sitting with utility executives and public utility commissioners seeking solutions to providing the region with reliable,
competitively priced electricity. Integrated Resource Planning requires, by its nature, a multiobjective multi-player analytic framework. The framework presented in this paper focuses on the development of trade-offs between attributes whose inherent value is dependent on the perspective of the individual player. The methodology accepts the reality that there is no optimum solution, in that the future is essentially unknowable. For this reason the framework is based on the comparative analysis of multiple scenarios concerning alternative futures. As will be discussed below a scenario is defined as a combination of technological options [over which the decision-maker has control] and uncertainties [beyond the control of the decision-maker]. The framework allows the resource planner to utilize existing, accepted planning and financial tools to develop the information upon
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which the trade-off analysis is based. High speed and inexpensive computational capabilities make the generation and evaluation of multiple scenarios possible. In this analysis, shown in Figure 1, the Electric Generation Expansion Analysis System [EGEAS] was used as the core production-cost simulation model (ref. EPRI 1 529-1). Used in conjunction with other analytic models, a wide range of options and uncertainties can be evaluated. By evaluating how different supply strategies perform under a variety of possible futures, robust strategies can be identified. In our case study, capacity expansion strategies were evaluated against a range of possible changes in electric demand, fuel prices, fuel availability and regulatory actions. The comparative performance of various strategies over the range of possible future events identifies the most robust or least vulnerable strategies with respect to price, reliability, environmental emissions and other important measures. The Integrated Resource Planning framework was used to evaluate the relative impacts of an overlapping pair of capacity expansion strategies involving natural gas-fired generation. These options were evaluated for a set of uncertainties effecting the delivery of electric power to the New England Region over a period of twenty years, starting in 1988. The options considered for the study were the target generation mix of new capacity over the period, and the target reserve margin for the New England region. The two capacity-expansion strategies were combined with four sets of uncertainties. Briefly these are: (1) Load Growth Uncertainty (four paths), (2) Fuel Price Escalation (four sets), (3) Natural Gas Availability (two ceilings), and (4) Capacity Expansion Constraints (existence or non-existence of a hypothetical fuel-use act). Results of the analysis are: * Insufficient supplies of natural gas always lead to higher electricity prices. This is a result of the forced fuel switching to the more expensive No. 2 fuel oil that occurs when the natural gas ceiling is reached. * Base case supplies, based on current "Open Season" proposals, were not adequate to meet demand in all the scenarios, with the exception of several cases in the Additional Demand-Side Management load growth trajectory. This occurred even with the four month dual fueling requirement for new, large gas-fired units. * Insufficient supplies of natural gas led to greater environmental emissions, since the substitute fuel, No. 2 oil, generates greater atmospheric emissions. In summary, the results emphasize the necessity of focusing on regional gas supply issues, particularly for those planning strategies that include significant use of natural gas.
89 WM 197-5 August 1989
A Supplementary Adaptive Var Unit Controller for Power System Damping J. R. Smith, D. A. Pierre, 1. Sadighi, and M. H. Nehrir Electrical Engineering Department, Montana State University, Bozeman, MT J. F. Hauer, Bonneville Power Administration Portland, OR
Summary This paper describes a multivariable adaptive LQ control strategy for static var compensators (SVC's) which can be added to a fixed controller already present in order to enhance the robustness and effectiveness of the var unit in damping power system oscillations. The control strategy uses only local bus information to damp electromechanical oscillations occurring in the network. Simulation results to test the controller effectiveness for a variety of conditions are presented using a nine-bus network.
IEEE Power Engineering Review, August August 1989 Engineering Review,
The adaptive control strategy presented here is an extension of a self-tuning adaptive control strategy reported in [1]. Major improvements in controller performance have been developed by extending the single input, single output system previously reported to a single input, two output system. This extension also results in an adaptive controller which can function as a supplementary damping controller added on to an existing SVC voltage magnitude controller. The input to the power system is the effective susceptance that the SVC presents to the network by virtue of firing angle control. The system outputs are chosen to be filtered versions of local bus voltage magnitude error (Y2), and local bus frequency deviation (yl). The choice of these two signals as outputs enables control of two fundamental aspects of power transfer between different parts of the network. The conventional controller being used in this study is a proportional plus integral (PI) controller. The parameters for this Pi controller were studied using eigenvalue analysis to determine appropriate values for maximum damping. It was found that this PI controller is not capable of providing very much damping to either of the system operating points that were considered. The Pi controller is effective in forcing the steady-state voltage error to zero, and this is the role this Pi controller plays in the overall scheme while the adaptive controller provides most of the system damping. Under steady-state system operation the output, ua, of the adaptive controller is zero, and the susceptance of the SVC is regulated by the bus voltage error signal acting through a low-pass filter and the Pi regulator. Under transient conditions, the adaptive control signal ua, adds to the up, value and enhances system damping. The adaptive control startegy presented here is one approach to extending the robustness of controllers in a power system environment. The results presented in this paper demonstrate the improved performance and flexibility of this adaptive LQ control strategy when it is extended to a multivariable model by including two local outputs.
DLC by exogenously changing the system load
to reflect the expected results of load management. As such, the results from such methods fail to recognize the temporal correlation between load and available generating capacity and therefore do not produce accurate assessments of the impacts of DLC on system reliability performance. In this paper, a dynamic DLC model with constraints such as realizable DLC capacity, upper limit on control time, etc. on its use is developed and its impacts on generating system reliability performance are studied. A conceptual block diagram on this dynamic DLC model is shown in figure 1. The results obtained from this study indicate that the reliability implications of exogenous and dynamic modeling of Direct Load Control are quite different. It is shown that accurate modeling of DLC can not be made using exogenous load models, but requires models which recognize the dynamics of operation and the temporal correlation of load and available generating capacity. Monte Carlo simulation models seem best suited for this application. Operational constraints have an important effect on the system reliability improvements afforded by DLC and must be accurately modeled. In particular constraints such as realizable DLC capacity, upper limits on control time, maximum off-time periods, and maximum payback period durations have important influences on system realibility performance. Results of calculations on sample systems show that DLC is a very effective form of load management and that past analyses of the reliability benefits of DLC using exogenous load models have greatly underestimated the system reliability benefits of DLC.
References [1 I J. R. Smith, D. A. Pierre, D. A. Rudberg, I. Sadighi, A. P. Johnson, and J. F. Hauer, "An Enhanced LQ Adaptive VAR Unit Controller for Power System Damping," paper no. 88SM692-6, presented at the IEEE Summer Power Meeting, July 1988.
89 WM 188-4 August 1989
Modeling and Evaluation of the System Reliability Effects of Direct Load Control Hossein Salehfar, Member, IEEE and A. D. Patton, Fellow Member, IEEE Electric Power Institute Texas A&M University College Station, Texas One area of Load Management (LM) assessment that has not been investigated accurately and thoroughly, on a quantitative basis, is the impact of dynamic (moment-to-moment) dispatch of load (Direct Load Control) on generating system reliability performance. One of the most important objectives of LM is reduction in the amount of generating capacity required to supply system load at an acceptable reliability level. Accordingly, evaluation of this benefit of the Direct Load Control (DLC) form of LM requires accurate assessment of the dynamic effects of DLC on system reliability performance. A literature review has revealed that there has been little work done, if any, on the dynamic characteristics of DLC as related to system reliability. The models that have been developed to date to assess the reliability implications of LM do not simulate the dynamics of DLC and generating systems together,
on
a
Fig. 1. Dynamic DLC Conceptual Block Diagram
moment-to-moment basis. Al-
though the effectiveness of LM systems is very dependent upon the relationships between time, load, and available system capacity, these programs, using load duration curves as the load model, model
IEEE Power Engineering Review, August 19899
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