Large-scale optimal power flow: effects of initialization, decoupling and discretization
TL;DR: In this article, the authors present the results of extensive numerical testing of a second-order OPF solution method using a 1500 bus network under various loading conditions, and three issues were studied: sensitivity of the solution with respect to the initial conditions, accuracy of decoupling the original OPF problem into separate active power and reactive power problems, and effects of the discretization of transformer taps on solutions.
Abstract: This paper presents the results of extensive numerical testing of a second-order OPF solution method. The testing was conducted using a 1500 bus network under various loading conditions. Three issues were studied: ? Sensitivity of the solution with respect to the initial conditions ? Accuracy of decoupling the original OPF problem into separate active power and the reactive power OPF problems ? Effects of the discretization of transformer taps on solutions. The first issue is particularly important in an EMS environment. An OPF must produce consistent solutions if it is to be used to guide the decision-making of power system operators. This requires that the OPF solution not be sensitive to the (arbitrarily or randomly) selected starting point used by the OPF program, and that changes in the OPF solution point be consistent with the changes in the power system operating constraints. Such changes include the evolution of bus loads over time, control variables which move to their limits over time, and changes in topology due to disturbances. Hence the first objective of the OPF testing was to study the sensitivity of OPF solutions to the choice of initial points. The second issue is of importance because most of the OPF approaches proposed by EMS vendors rely on decoupling of the active and reactive OPF problems in order to achieve acceptable computational performance.
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TL;DR: In this paper, a review of literature on optimal power flow tracing progress in this area over from 1962-93 is presented. Part I deals with the application of nonlinear and quadratic programming.
Abstract: The paper presents a review of literature on optimal power flow tracing progress in this area over from 1962-93. Part I deals with the application of nonlinear and quadratic programming.
832 citations
TL;DR: A number of functional operating constraints, such as branch flow limits, load bus voltage magnitude limits, and generator reactive capabilities, are included as penalties in the GA fitness function (FF).
Abstract: This paper presents an enhanced genetic algorithm (EGA) for the solution of the optimal power flow (OPF) with both continuous and discrete control variables. The continuous control variables modeled are unit active power outputs and generator-bus voltage magnitudes, while the discrete ones are transformer-tap settings and switchable shunt devices. A number of functional operating constraints, such as branch flow limits, load bus voltage magnitude limits, and generator reactive capabilities, are included as penalties in the GA fitness function (FF). Advanced and problem-specific operators are introduced in order to enhance the algorithm's efficiency and accuracy. Numerical results on two test systems are presented and compared with results of other approaches.
620 citations
Cites background from "Large-scale optimal power flow: eff..."
...Whereas the effects of discretization on load tap changing transformers are small and usually negligible [20], the rounding of switchable shunt devices may lead to voltage infeasibility, especially when the discrete VAR steps are large, and requires special logic [22]....
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...However, they are not guaranteed to converge to the global optimum of the general nonconvex OPF problem, although there exists some empirical evidence on the uniqueness of the OPF solution within the domain of interest [20]....
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TL;DR: A survey of publications in the fields of optimal power flow and dispatching can be found in this article, where the authors suggest a classification of methods based on the choice of optimization techniques and a single flow-chart-type figure, which indicates the relationship between methods, their chronology, and their popularity.
Abstract: A survey is presented of publications in the fields of optimal power flow and dispatching. It suggests a classification of methods based on the choice of optimization techniques. The survey is summarized in a single flow-chart-type figure, which indicates the relationship between methods, their chronology, and their popularity. This figure is based on a compilation of over three hundred publications. >
616 citations
TL;DR: In this article, the authors describe developments that have transformed the LP (linear programming) approach into a truly general-purpose OPF (optimal power flow) solver, with computational and other advantages over even recent nonlinear programming (NLP) methods.
Abstract: The authors describe developments that have transformed the LP (linear programming) approach into a truly general-purpose OPF (optimal power flow) solver, with computational and other advantages over even recent nonlinear programming (NLP) methods. it is pointed out that the nonseparable loss-minimization problem can now be solved, giving the same results as NLP on power systems of any size and type. Coupled formulations, where for instance voltages and VAr become constraints on MW scheduling, are handled. Former limitations on the modeling of generator cost curves have been eliminated. In addition, the approach accommodates a large variety of power system operating limits, including the very important category of contingency constraints. All of the reported enhancements are fully implemented in the production OPF software described here, and most have already been utilized within the industry. >
517 citations
TL;DR: Optimal power flow (OPF) has become one of the most important and widely studied nonlinear optimization problems as mentioned in this paper, and there is an extremely wide variety of OPF formulations and solution methods.
Abstract: Over the past half-century, Optimal Power Flow (OPF) has become one of the most important and widely studied nonlinear optimization problems. In general, OPF seeks to optimize the operation of electric power generation, transmission, and distribution networks subject to system constraints and control limits. Within this framework, however, there is an extremely wide variety of OPF formulations and solution methods. Moreover, the nature of OPF continues to evolve due to modern electricity markets and renewable resource integration. In this two-part survey, we survey both the classical and recent OPF literature in order to provide a sound context for the state of the art in OPF formulation and solution methods. The survey contributes a comprehensive discussion of specific optimization techniques that have been applied to OPF, with an emphasis on the advantages, disadvantages, and computational characteristics of each. Part I of the survey (this article) provides an introduction and surveys the deterministic optimization methods that have been applied to OPF. Part II of the survey examines the recent trend towards stochastic, or non-deterministic, search techniques and hybrid methods for OPF.
483 citations
References
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Enel1
TL;DR: An automatic optimization procedure suitable for large scale systems is presented based on security and economy aspects of reactive power scheduling and minimizes active losses expressed in terms of the reactive control variables.
Abstract: In this paper the security and the economy aspects of reactive power scheduling are emphasized and an automatic optimization procedure suitable for large scale systems is presented. Two objective functions have been implemented; the first one, based on security, distributes the reactive power generation among the units as proportional as possible to their ratings. The second one minimizes tle active losses expressed in terms of the reactive control variables. In both these optimization problems the control variables are partitioned into two subsets:-the terminal voltages at the generation buses-the LTC transformer tap settings.
43 citations
TL;DR: In this paper, a small test system which possesses some of the characteristics of realistic power systems portraying local plant stability, interarea stability, and voltage collapse has been used for demonstration of the arguments.
Abstract: Following the recent advancements in optimal power flow (OPF) methods, a number of utilities are either in the process of, or considering, the implementation of an OPF program on their energy management systems. Important considerations which can compromise the effectiveness of OPF and, in some cases, can result in security implications are outlined. A small test system which possesses some of the characteristics of realistic power systems portraying local plant stability, interarea stability, and voltage collapse has been used for demonstration of the arguments. Suggestions are provided to serve as safeguards in assessing and using the present OPF algorithms and as requirements in the future generation of OPF methods. >
22 citations
Enel1
TL;DR: In this paper, an Advance Dispatching (AD) activity is added between the day before scheduling and the on-line Economic Dispatch (ED) activity to improve the system operation before the availability of a closed-loop ED and for supplying security constrained participation factors to the regulating units when ED is operating.
Abstract: In a modern control center the availability of the on-line state-estimation and load forecasting can be exploited by the system operators in order to redefine optimal and secure operation strategies a very short period in advance. Therefore in the system control hierarchy an Advance Dispatching (AD) activity is added between the day before scheduling and the on-line Economic Dispatch (ED). AD is a useful tool for improving the system operation before the availability of a closed-loop ED and for supplying security constrained participation factors to the regulating units when ED is operating. To be more precise AD modifies the day before scheduling by supplying the optimal trajectories of the thermal units over very short time periods taking into due account the load predictions (30 minutes ahead) and the actual security constraints which include dynamic limitations upon the rates of change of the thermal generator MW outputs. For the real-time environment, the AD computational procedures have to be quick and reliable in spite of the additional burden of the dynamic constraints. These objectives have been accomplished by introducing appropriate simplifications in the optimal control problem which is a result of the dynamic dispatch formulation. Although accuracy in critical newtork security constraints and in active losses rappresentation is still provided for, the adoption of a parametric linear programming algorithm in the AD procedure provides a very fast and adeguate solution to the problem.
21 citations
TL;DR: A suitably modified version of the Han-Powell algorithm is adopted which employs an alternative technique in the construction and in the updating of the Hessian matrix of the Lagrangian function which allows to handle large-scale problems arising from the optimization of a large system on the framework of a minute subdivision of the dispatch interval.
13 citations