On-line Dispatch Research Articles

Identification of Suitable Learning Algorithm for Neural Network based On-Line Economic Load Dispatch Problem

This paper identifies suitable learning algorithm for neural network based Economic Load Dispatch (ELD). ELD is an important problem in real time power system planning and Operation. The conventional methods used for economic load dispatch are iterative techniques & takes longer time for computation. Neural Network (NN) provides an alternate solution for on-line Load Dispatch. The on-line Load Dispatch requires the NN model to be accurate, simple and structurally compact to ensure faster execution time for effective load dispatch. This in turn to a large extent depends on the type of Neural Learning algorithms used to train the Neural Architecture. The feed forward neural architecture is trained off-line using three types of learning algorithms to solve economic load dispatch problem. Their performance is compared in terms of accuracy, computational complexity and structural compactness. The results are validated for IEEE 26 Bus system. The promising results obtained are presented.

A Modified on-Line Rolling Generation Dispatch Model for Accommodating Large-Scale Wind Power

This paper proposes an improved strategy for on-line rolling generation dispatch. Based on the framework of Lagrange dual relaxation, the problem is transformed and decomposed into primal-problem and N subproblems multipliers and system constrains are satisfied iteratively. The sub-problems are solved by an efficient dynamic programming algorithm without changing the condition of convergence of the framework. Numerical results indicate that the proposed method is fast and efficient in dealing with numerous system constrains.

Transient stability-constrained optimal power flow for online dispatch and nodal price evaluation in power systems with flexible AC transmission system devices

This study develops a new method for economic dispatch together with nodal price calculations which includes transient stability constraints and, at the same time, optimises the reference inputs to the flexible AC transmission system (FACTS) devices for enhancing system stability and reducing nodal prices. The method draws on the sensitivity analysis of time-domain transient stability simulation results to derive a set of linearised stability constraints expressed in terms of generator active-powers and FACTS devices input references. The optimal power flow (OPF) formulation based on the Newton's algorithm augmented with the set of stability inequality constraints is applied for forming economic dispatch solution and nodal prices. The solutions obtained also include the Lagrange multipliers associated with all of the constraints. Based on the Lagrange multipliers, individual components, including those associated with stability constraints, of the nodal prices are directly identified for assisting the market participants to make investment decisions. The sensitivity technique for forming the set of transient stability constraints lends itself to parallel-computing implementation. Therefore the additional computing-time requirement is minimal, given that the transient stability simulations can be performed independently of one another and outside the OPF loop. Representative studies and results are presented here.

Implementing Real-Time Optimization Models: A Case Application From The Motor Carrier Industry

Online models for real-time operations planning face a host of implementation issues that do not arise in more strategic arenas. We use the seemingly simple problem of assigning drivers to loads in the truckload motor carrier industry as an instance to study the issues that arise in the process of implementing a real-time dispatch system. Although the project was moderately successful, our focus is not on documenting the benefits, but rather on summarizing the challenges that arose. The most significant theme running through the implementation hurdles we encountered was the lack of information available to the model. Computers are very good at processing vast quantities of information; humans are very good at challenging the information that is in the computer and augmenting computer-provided data with head knowledge. Our study includes a careful comparison of actual decisions with model recommendations, using a six-month database of actual transactions. This comparison is the first we have seen of its kind and provides the most rigorous evaluation of an online dispatch model that we have seen. Although the model was well used, the results demonstrate that significant improvements could have been obtained if the level of model utilization had been even higher.

A hierarchical system for economic dispatch with environmental constraints

This paper presents a new hierarchical power dispatch system which uses a combination of the offline and the online subsystems to both minimize the cost and reduce the SO/sub 2/ emission. A hierarchical structure is introduced in the offline subsystem which enables the subsystem to generate a coarse-to-fine guideline for balancing the cost and the emission. The online dispatch is computed according to the guideline provided by the offline system. The dispatch is fed back to update the offline computation layer by layer. In this way, the offline guideline can always be adapted to the current situation, and the overall dispatch tends to be optimal for a whole year period. The system is tested by using the data from the Cincinnati Gas and Electric Company.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new method for calculating loss coefficients [of power systems

A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of /spl theta//sub j/ versus PG/sub n/ is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on A/sub jn/-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications. >

Dynamic economic dispatch for large scale power systems: a Lagrangian relaxation approach

The dynamic multi-period economic dispatch problem for large-scale power systems is modelled as a linear programming problem. The model considers loading and deloading rates, limits on generators outputs, spinning reserve requirements and group power import-export limits. The solution algorithm is based on Lagrangian relaxation and on exploiting the intimate relationship between optimizing the dual Lagrangian function and Dantzig-Wolfe decomposition. The relaxation is carried out so that the relaxed problem is decomposable to a number of subproblems corresponding to the periods in the dispatch horizon. These are solved simply by using priority lists. The dual Lagrangian function is optimized using subgradient optimization. If an overall solution feasible in all constraints and sufficiently close to a computed best lower bound is discovered during subgradient optimization, it is deemed optimal. Otherwise, Dantzig-Wolfe decomposition is invoked, using almost all the information generated during subgradient optimization to ensure a speedy conclusion. The computational efficiency of the algorithm renders it suitable for on-line dispatch.

Different time-scale approaches to the real power dispatch of thermal units

Different time-scale approaches to the dispatch problem are proposed for the centralized control of real power. In particular, the problem of optimally sharing a time-varying load among the committed thermal units of an electrical power system is addressed. It is shown that the real power dispatch of the thermal units is handled at different time scales as a dynamic problem where rate of change limits , environmental constraints, and the security constraints of the traditional static approach are taken into account. The adoption of the same general model guarantees the coherency of the results in the three phases of day-before scheduling, advance dispatch, and online dispatch. A modified gradient projection algorithm, which suitably exploits some good second-order information, has been adopted for the solution of the large-scale problem arising from the discretization of the dynamic model. The resulting procedure is capable of solving the very large day-before scheduling (more than 2000 variables and 4000 constraints for the Italian EHV system) in a few minutes, as well as providing the solution of the advanced dispatch problem in no more than 10 s even when a corrective rescheduling is required.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamic Secure Economic Dispatch For Large Scale Power Systems

Dynamic multi-period economic dispatch for large-scale power systems is considered. The formulation presented caters for loading and deloading rates, limits on generators outputs, spinning reserves requirements and group power import-export limits. It is also suitable for implementation within a constraint relaxation strategy. The solution algorithm is based on a Dantzig-Wolfe decomposition, which yields a capacitated transshipment subproblem along with a master problem solved by the Revised Simplex method.The computational efficiency of the algorithm renders it suitable for on-line dispatch.

Multiperiod secure economic dispatch for large-scale power systems

Dynamic multi-period economic dispatch for large-scale power systems is considered; the formulation presented provides for loading and deloading rates, limits on generator outputs, spinning-reserve requirements and group power import-export limits. It is also suitable for implementation within a constraint relaxation strategy. The solution algorithm is based on a Dantzig-Wolfe decomposition, which yields a capacitated transshipment subproblem along with a master problem solved by the revised simplex method. The computational efficiency of the algorithm renders it suitable for on-line dispatch.

The operation and control of the CEGB power system‡

The paper briefly describes how the CEGB power system is controlled, from the operational planning phase through to the on-line dispatch of generation to meet the varying consumer demand. These activities are highly dependent on studies carried out on the Board's large central computing facility and on assistance provided to the operators by a network of computers located in the Control Centres. Brief reference is made to developments which are in hand or planned in this area. The paper goes on to describe a research project oriented to developments in on-line control in the longer term. Through it the problems of computer-aided dispatching will be investigated and the potential benefits of this evolution in the control procedure will be evaluated.

Optimal power flows

The state of the art of optimal flows at the end of 1978 is reviewed. The different aspects of the problem statement are established in the most complete way possible; then methods for the solution of the static optimization are presented and filed, with a brief description of the most typical ones, trying to show the respective merits of each family, and with a discussion of points of special interest. Finally, dynamic aspects with applications to online dispatch are investigated.