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.

A review of selected optimal power flow literature to 1993. I. Nonlinear and quadratic programming approaches

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. >

A survey of the optimal power flow literature

A survey is presented of papers and reports that address various aspects of economic dispatch. The time period considered is 1977-88. Four related areas of economic dispatch are identified and papers published in the general areas of economic dispatch are classified into these. These areas are: optimal power flow, economic dispatch in relation to AGC, dynamic dispatch, and economic dispatch with nonconventional generation sources. >

/pdf/a-review-of-recent-advances-in-economic-dispatch-enueg8mqmk.pdf

A review of recent advances in economic dispatch

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.

Security analysis and optimization

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. >

Further developments in LP-based optimal power flow

This paper presents applications of an efficient computerized technique for power system dynamic system security assessment using the transient energy function (TEF) method. The technique exploits the sensitivities of the unnormalized transient energy margin with respect to operating indices and critical interface flows in order to arrive at the stability limits for various system outage states and operating conditions, that would be required for on-line application. The paper describes the sensitivity technique and demonstrates a practical application to the dynamic security problem in one portion of the Ontario Hydro system including results of the validation and accuracy tests of the technique.

Dynamic Security Assessment Utilizing the Transient Energy Function Method

This paper reports the results of a detailed study of on-line voltage/var control performed on the Ontario Hydro system. The first part of the study is an assessment of active transmission loss savings obtained by optimizing generator voltages and transformer taps with an Optimal Power Flow program using data from a state estimator. In the second part of the study, the question is addressed of how frequently the generator voltages and transformer tape should be optimized in order to achieve a large percentage of the loss savings indentified in the first part. The study showed that the reduction in active losses is sufficient to justify further effort toward implementing voltage control. The results of the second part showed that for the load curve studied, most of the savings could be achieved with voltage control cycle times of about one hour. A new quadratic programming-based optimal power flow algorithm is also presented which exhibits execution times suitable for real-time applications. Sample execution times are given for various systems which confirm that exact optimal power flow solutions can be obtained in a fraction of the control cycle times suggested in the second part of the study.

Assessment of Real-Time Optimal Voltage Control

This paper deals with the demonstration of the Transient Energy Function (TEF) method in large, realistic power networks. Documented examples of application in power system operation and associated software development for systems up to 228-generators and 1644-buses are given. An overview of the analytical and computational problems encountered in the large scale application of the TEF method is presented. Approaches used to overcome the problems are provided, and the relevant improvements and modifications to the TEF software are discussed.

Direct Transient Stability Analysis Using Energy Functions Application to Large Power Networks

This paper summarizes improvements in the application of load models in power system stability studies by utilizing end-user energy consumption data to identify the composition of loads. The project included derivation and compilation of customer load characteristics for the Ontario Hydro System and subsequent interfacing with a transient stability program. Results from these models were compared with recordings of a recent Ontario Hydro system disturbance.

V. F. Carvalho

Papers

Dynamic Security Assessment Utilizing the Transient Energy Function Method

Assessment of Real-Time Optimal Voltage Control

Direct Transient Stability Analysis Using Energy Functions Application to Large Power Networks

Load Models for Large-Scale Stability Studies from End-User Consumption