P. Marannino

Optimal capacitor placement using deterministic and genetic algorithms

A procedure for solving the power capacitor placement problem is presented. The objective is to determine the minimum investment required to satisfy suitable reactive constraints. Due to the discrete nature of reactive compensation devices, optimal capacitor placement leads to a nonlinear programming problem with mixed (discrete and continuous) variables. It is solved with an iterative algorithm based on successive linearizations of the original nonlinear model. The mixed integer linear programming problem to be solved at each iteration of the procedure is tackled by applying both a deterministic method (branch and bound) and genetic algorithm techniques. A hybrid procedure, aiming to exploit the best features of both algorithms is also considered. The proposed procedures are tested and compared with reference to a small CIGRE system and two actual networks derived from the Italian transmission and distribution system.

Emission constrained dynamic dispatch

Abstract Since the early 1970s thermal generation dispatch has been proposed as an effective means of dealing with the problem of air pollution. More restrictive recent legislation has led to the adoption of pollution-limiting techniques and/or the use of less polluting fuels. An emission constrained dispatch, however, is still required either when contingent difficulties in the availability of low pollutant fuels occur or in the presence of meteorological conditions adverse to the diffusion of effluents. In this paper a dynamic dispatch procedure is proposed which is capable of taking into account the integral nature of the emission constraints. The mixing of fuels with different pollution rates and the management of multifuel plants are taken into account with the purpose of obtaining a cost-effective operation for all thermal plants in compliance with emission limitations. A suitably modified version of the Han-Powell algorithm is employed to find a solution for the resulting large-scale nonlinear programming problem. A method is considered to obtain a suboptimal solution of the mixed integer nonlinear programming problem which arises when emission control is achieved by switching from one fuel to another. Tests on a small CIGRE network and on a medium-sized EHV Italian system are presented to validate the proposed procedures.

Generation Expansion Planning in the Age of Green Economy

Generation expansion planning (GEP) is the problem of finding the optimal strategy to plan the construction of new generation plants while satisfying technical and economical constraints. It is a challenging problem due to its nonlinearity, large-scale, and to the discrete nature of the variables describing unit size and allocation. Originally, GEP was faced by vertically integrated utilities with the aim of minimizing production and capital costs. After deregulation, generation companies were forced to consider GEP from the viewpoint of market shares and financial risk. In recent years, increasing concern for environmental protection has driven lots of countries all over the world to promote energy generation from renewable sources. Different incentive systems have been introduced to support the growth of the investments in generation plants exploiting renewable energy. In the present paper, the impact of some of the most popular incentive systems (namely feed-in tariffs, quota obligation, emission trade, and carbon tax) on generation planning is considered, thus obtaining a comprehensive GEP model with a suitably modified objective function and additional constraints. The resulting problem is solved by resorting to the generalized Benders decomposition (GBD) approach and implemented in the Matlab programming language. Tests are presented with reference to the Italian system.

Multiobjective optimization techniques applied to modern power systems

The paper deals with the possible use of multiobjective methodologies in order to improve the knowledge of the power system during the planning and the operation stage. The possible use of several objective functions, the methods used to take into account the different (noninferior) solutions and the procedures that can be adopted to compare the noninferior working points are described and illustrated by some practical examples. The results are relevant to a 64 bus CIGRE test system and show the possibility to obtain useful information for the decision maker.

Enhanced security-constrained OPF with FACTS devices

The features of the new electricity market with the presence of many different operators lead to a new interest in the congestion management. The changes to the market-clearing point schedules required by the presence of bottlenecks in the electric grid can be strongly reduced if flexible ac transmission system (FACTS) devices are suitably installed in the transmission system with the aim of redistributing real and reactive power flows. Their optimal setting and operation mode can be determined by the use of customized security-constrained optimal power flow (SCOPF) programs. This paper deals with the use of FACTS devices as control variables in a compact and reduced SCOPF formulation, focusing on the definition of their control regions and on a new procedure implemented to find a global solution without sticking on local minima. The application of the new SCOPF procedure to a real system is also presented.

First and second order methods for voltage collapse assessment and security enhancement

The paper deals with the applications of steady-state approaches to the assessment of the maximum loadability of the electric system and to the determination of control actions suitable to avoid the voltage collapse. Following current research trends, first order indicators, derived by the linearization of the load flow (LF) equations and by the eigen/singular value analysis are adopted to determine the distance from the voltage collapse. In addition, a new second order performance index, obtained by the maximum singular value of the inverse LF Jacobian and by its sensitivities with respect to the system parameters, is proposed. The same second order information is adopted in a procedure for the security enhancement. It allows preventive rescheduling in alarm states and load shedding in emergency. The performances of the investigated indices are shown with reference to a small test network and to the large EHV Italian system.

Steady-state and dynamic approaches for the evaluation of loadability margins in the presence of secondary voltage regulation

The electricity markets are changing the power system operation. The increasing power exchanges make it necessary to operate the transmission grids closer and closer to security limits. A problem posed to power system engineers is therefore to find a suitable methodology to combine the results of both steady-state and dynamic tools: this can reduce the overall computational effort and the difficulty in the interpretation of results. The paper presents a detailed comparison of the computations that can be performed through steady-state and dynamic procedures regarding the power system security. In particular, the analysis of the loadability margins available on the corridor between the Italian power system and the Union for the Coordination of the Transmission of Electricity (UCTE) grids is carried out using both steady-state and dynamic tools; the results are compared, pointing out also the security enhancement given by a hierarchical voltage control.

A W-matrix based fast decoupled load flow for contingency studies on vector computers

The authors deal with an application of the inverse factors method (W-matrix method) to a fast decoupled load flow procedure for steady-state contingency analysis. The W-matrix method, originally developed for the solution of sparse sets of linear equations on multiple instruction/multiple data (MIMD) computers, can also be made effective for vector computers. The recurrence problem is overcome by reordering the addition operations required in a forward and backward solution. Matrix partitioning is employed to find the best tradeoff between the number of fill-ins added to the W matrix and the increased efficiency of vector operations achieved through a reduced number of partitions. The effect of different bus ordering algorithms on the partition number is also considered. Operation reordering is employed to make the bus power computation phase very fast in comparison to traditional bus-wise calculation. Tests were performed on the IEEE 118 bus system, some different configurations of the Italian EHV system and a European equivalent network with up to about 700 buses using a 4-CPU CRAY Y-MP8/432 and a 4-CPU Alliant FX/80 computer. >

A second order method for contingency severity assessment with respect to voltage collapse

The increase in power transfer among areas of interconnected systems, and the reduction of reactive power reserves, force system operators and planners to consider the contingency analysis also from the voltage/reactive point of view. In this paper, second order information derived from the singular value analysis of the Jacobian of load flow equations is used to obtain an effective ranking of contingencies with respect to the voltage collapse. Besides, a quantification of the risk associated to a contingency is provided by a procedure that calculates quasilinear indices useful both in planning and in operation. The effectiveness of the presented indices is supported by the analysis of the perturbation on the Italian power system in August 1994.

An OPF-based procedure for fast TTC analyses

Around the world the new competitive framework and the environmental opposition to the construction of new lines are driving transmission systems to operate closer and closer to their limits. On the other hand, network congestion becomes the main limitation to the power exchanges in the liberalized markets. A suitable calculation of the total transfer capability (TTC) and the analysis of its dependence on some system parameters are of primary importance both for an actual suitable operation of the electricity market and for an adequate planning of the network reinforcements. The main focus of this paper is the definition of a new procedure based on an advanced real power security constrained optimal power flow for the fast evaluation of TTC. Important byproducts of the optimization program are represented by the TTC sensitivities with respect to the thermal limits of the binding constraints on the transmission lines and to the allocation and the size of the new generation sites. The procedure has been employed for the assessment of the impact of the installation of new plants on the TTC between Italy and the neighboring UCTE countries and of the adequacy of the planned interconnection corridor reinforcement in forecasted scenarios at the year 2010.