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. >

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A review of recent advances in economic dispatch

Advanced load flow models for the static VAr compensator (SVC) are presented in this paper. The models are incorporated into existing load flow (LF) and optimal power flow (OPF) Newton algorithms. Unlike SVC models available in open literature the new models depart from the generator representation of the SVC and are based instead on the variable shunt susceptance concept. In particular, a SVC model which uses the firing angle as the state variable provides key information for cases when the load flow solution is used to initialize other power system applications, e.g., harmonic analysis. The SVC state variables are combined with the nodal voltage magnitudes and angles of the network in a single frame-of-reference for a unified, iterative solution through Newton methods. Both algorithms, the LF and the OPF exhibit very strong convergence characteristics, regardless of network size and the number of controllable devices. Results are presented which demonstrate the prowess of the new SVC models.

Advanced SVC models for Newton-Raphson load flow and Newton optimal power flow studies

The authors consider an application of Newton's optimal power flow to the solution of the secondary voltage/reactive power control in transmission networks. An efficient computer program based on the latest achievements in sparse matrix/vector techniques has been developed for this purpose. It is characterized by good robustness, accuracy and speed. A combined objective function appropriate for various system load levels with suitable constraints for the treatment of power system security and economy is also proposed. For the real-time voltage/receiver power control, a suboptimal power flow procedure has been derived by using the reduced set of control variables. This procedure is based on sensitivity theory applied to the determination of zones for the secondary voltage/reactive power control and a corresponding reduced set of regulating sources, whose reactive outputs represent control variables in the optimal power flow program. As a result, the optimal power flow program output becomes a schedule to be used by operators in the process of the real-time voltage/reactive power control in both normal and emergency operating states. >

Application of Newton's optimal power flow in voltage/reactive power control

The paper presents the model of a voltage source converter -high voltage direct current (VSC-HVDC) suitable for optimal power flow (OPF) solutions using Newton's algorithm. The VSC-HVDC's ability to provide independent control of the converters ac voltage magnitudes and phase angles relative to the system voltage, which allows the use of separate active and reactive power control loops for system regulation, is well represented by the model. In this new development in Newton OPF, the VSC-HVDC system equations are incorporated directly into the matrix W for a unified optimal solution in a single frame-of-reference. The multipliers method is used to handle all inequality constraints of variables, leading to highly efficient OPF solutions of constrained power networks. The solution approach does not require structural changes in the linearised system of equations during the iterative process using Newton's method. The effectiveness of the VSC-HVDC model and its proposed implementation in Newton OPF is demonstrated by means of two sample systems.

Modeling of VSC-Based HVDC Systems for a Newton-Raphson OPF Algorithm

The optimal power flow (OPF) problem with discrete control variables is an NP-hard problem in its exact formulation. To cope with the immense computational-difficulty of this problem, we propose an ordinal optimization theory-based algorithm to solve for a good enough solution with high probability. Aiming for hard optimization problems, the ordinal optimization theory, in contrast to heuristic methods, guarantee to provide a top n% solution among all with probability more than 0.95. The approach of our ordinal optimization theory-based algorithm consists of three stages. First, select heuristically a large set of candidate solutions. Then, use a simplified model to select a subset of most promising solutions. Finally, evaluate the candidate promising-solutions of the reduced subset using the exact model. We have demonstrated the computational efficiency of our algorithm and the quality of the obtained solution by comparing with the competing methods and the conventional approach through simulations.

https://ir.nctu.edu.tw:443/bitstream/11536/27079/1/000188951000037.pdf

An ordinal optimization theory-based algorithm for solving the optimal power flow problem with discrete control variables

An OPF (optimal power flow) program based on the Newton methodology has been implemented, as the first step in the development of a VAr (reactive-volt-ampere) planning program for the Taiwan Power Company. The strength of the Newton method was demonstrated by extensive system tests. Of particular importance is the demonstration that binding inequality constraints could be selected and enforced reliably and efficiently. Different levels of functional capabilities regarding infeasible solutions have been identified; and test results showed that they could be satisfied effectively. Detailed test results on the selection and enforcement of binding inequality constraints are presented in an effort to clarify some uncertainties that have persisted in this key aspect of the Newton-OPF methodology. >

Experiences with implementing optimal power flow for reactive scheduling in the Taiwan power system

Due to fast economic growth on the island of Taiwan, load demand in Taiwan Power Company (TPC) has been rapidly increasing in the past ten years and is expected to continue throughout the next decade. By 1995, the peak load demand in Taiwan is forecasted to reach 16,000 MW, an increase of 60% from the present level of 10,000 MW. Several new generating units have been under construction to meet the future demand. As a result, additional transmission lines are needed to avoid overloads on present lines. The objective of this paper is to report the results from a recent study which was aimed at reaching an optimal transmission expansion plan by comparing the relative merits of three feasible alternatives: EHV lines (345 KV), UHV lines (765 KV), and HVDC lines (± 250 KV). At present, the main factors considered in transmission expansion planning in TPC are the maximum power transfer limits, fault currents, transient stability, system losses, and cost [1]. In addition to these factors used in current practice, oscillatory stability of the power system under each expansion plan will be extensively studied. In particular, the low frequency electromechanical oscillations which tend to appear in a longitudinal power system such as the one in Taiwan will be investigated. The dampings of these oscillation modes are essential in system operation and planning, especially in the case when the transmission line is heavily loaded.

Lin Chia-Jen

Papers

Experiences with implementing optimal power flow for reactive scheduling in the Taiwan power system

Oscillatory stability considerations in transmission expansion planning