scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Some deficiencies in optimal power flow

TL;DR: In this article, the use of equivalents causes errors, the methods for adjusting discrete variables are suboptimal, and the number of control actions is too large to be executed, and approaches for correcting them are discussed.
Abstract: Optimal power flow programs have deficiencies that limit their practical value and scope of application. Three of these deficiencies are: (1) the use of equivalents causes errors, (2) the methods for adjusting discrete variables are suboptimal; and (3) the number of control actions is too large to be executed. These deficiencies are explained, and approaches for correcting them are discussed. >
Citations
More filters
Journal ArticleDOI
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 methods from "Some deficiencies in optimal power ..."

  • ...To avoid the prohibitive computational requirements of mixed-integer programming, discrete control variables are initially treated as continuous, and post-processing discretization logic is subsequently applied [21], [22]....

    [...]

Journal ArticleDOI
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

Journal ArticleDOI
01 Dec 1987
TL;DR: This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.
Abstract: An operationally "secure" power system is one with low probability of blackout or equipment damage. The power system control processes needed to maintain a designated security level at minimum operating cost are extremely complicated. They increasingly depend upon on-line computer security analysis and optimization. This on-line technology is still relatively new, with enormous further potential. Since security and optimality are normally conflicting requirements of power system control, it is inappropriate to treat them separately. Therefore, they are slowly becoming coalesced into a unified hierarchical mathematical problem formulation: one that is, however, far too complex to afford anything but an approximate, near-optimal solution. The practical validity of this unifying trend relies on being able to incorporate all significant security constraints within the process. The main two current computational tools in this field are contingency analysis and special operations-oriented versions of optimal power flow (OPF). Contingency analysis identifies potential emergencies through extensive "what if?." simulations on the power system network. OPF is a major extension to the conventional dispatch calculation. It can respect system static security limits, and can schedule reactive as well as active power. Moreover, the advanced versions of OPF include or interface with contingency analysis. This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.

533 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: In this paper, the main challenges to the security constrained optimal power flow (SCOPF) computations are discussed, focusing mainly on: approaches to reduce the size of the problem by either efficiently identifying the binding contingencies and including only these contingencies in the SCOPF or by using approximate models for the post-contingency states, and the handling of discrete variables.

393 citations

References
More filters
Journal ArticleDOI
TL;DR: In this paper, a direct simultaneous solution for all of the unknowns in the Lagrangian function on each iteration is proposed, where each iteration minimizes a quadratic approximation of the Lagrangeian.
Abstract: The classical optimal power flow problem with a nonseparable objective function can be solved by an explicit Newton approach. Efficient, robust solutions can be obtained for problems of any practical size or kind. Solution effort is approximately proportional to network size, and is relatively independent of the number of controls or binding inequalities. The key idea is a direct simultaneous solution for all of the unknowns in the Lagrangian function on each iteration. Each iteration minimizes a quadratic approximation of the Lagrangian. For any given set of binding constraints the process converges to the Kuhn-Tucker conditions in a few iterations. The challenge in algorithm development is to efficiently identify the binding inequalities.

817 citations

Journal ArticleDOI
TL;DR: A linear programming method for security dispatch and emergency control calculations on large power systems is presented, which works directly with the normal power-system variables and limits, and incorporates the usual sparse matrix techniques.
Abstract: A linear programming (LP) method for security dispatch and emergency control calculations on large power systems is presented. The method is reliable, fast, flexible, easy to program, and requires little computer storage. It works directly with the normal power-system variables and limits, and incorporates the usual sparse matrix techniques. An important feature of the method is that it handles multi-segment generator cost curves neatly and efficiently.

396 citations

Journal ArticleDOI
TL;DR: In this paper, the principles and main methods for load-flow equivalence, with due emphasis given to on-line applications, are reviewed and a critical analysis of the properties of the different methods is made, to assist in choosing the most suitable ones for practical application.
Abstract: This paper reviews the principles and main methods for load-flow equivalencing, with due emphasis given to on-line applications. Unreduced Load Flow, Ward, REI, Linearization, and Identification methods are covered, introducing a number of new ideas and versions. A critical analysis of the properties of the different methods is made, to assist in choosing the most suitable ones for practical application.

183 citations

Journal ArticleDOI
TL;DR: In this paper, a current injection scheme is used to simulate the change in topology of a base network. But the injected currents are applied to the terminals of the elements of a socalled base network corresponding to those actually switched.
Abstract: Strategic switching can be achieved by a current injection scheme which simulates the change in topology. The injected currents are applied to the terminals of the elements of a socalled base network corresponding to those actually switched. This requires that the base network must contain all elements in the "in" state. The injected currents to be used as a compensation in the commonly employed system matrices (Y, Z) for the real change in topology can be taken as control variables in an optimization procedure for the switching problem. With the aid of a method similar to linear programming (LP) objective functions such as line current, short circuit current or even losses can be formulated. By means of a switching sequence consisting of elementary switching operations the desired objective function will be brought to its optimum value.

151 citations

Journal ArticleDOI
TL;DR: In this paper, a new optimization method is applied to optimal power flow analysis, based on transforming the original problem to that of solving a sequence of linearly constrained subproblems using an augmented Lagrangian type objective function.
Abstract: A new optimization method is applied to optimal power flow analysis. The method is shown to be well suited to large scale (500 buses or more) power systems in that it is computationally efficient and is particularly effective with infeasible starting points. The optimization approach is based on transforming the original problem to that of solving a sequence of linearly constrained subproblems using an augmented Lagrangian type objective function. A fundamental feature of this algorithm (developed by Murtagh and Saunders) is that the solution converges quadratically on the nonlinear power flow constraints, rather than being forced to satisfy the constraints throughout the iterative process. To demonstrate the performance of this algorithm, a set of descent directions, which includes quasi-Newton (variable metric), conjugate directions, and steepest descent, are compared on the basis of convergence and computational effort for a 118 bus and a 600 bus power system.

141 citations