Janis Bubenko

Optimal Short Term Operation Planning of a Large Hydrothermal Power System Based on a Nonlinear Network Flow Concept

This paper presents a procedure for solving the short term generation scheduling problem for a large hydrothermal system that includes transmission limitations. The integrated system is divided into a hydro and a thermal subsystem. A reduced gradient algorithm is employed for the solution of the hydro subproblem. This algorithm is specialized to efficiently solve nonlinear network flow problems with additional constraints of non-netwrk type. The thermal subsystem is solved using a fast unit commitment and dispatch algorithm. A case study with the Swedish system is discussed.

Short term generation scheduling with security constraints

The authors discuss network flow concepts as a means of modeling a large multiriver system with cascaded hydro plants for purposes of generation scheduling. The reservoir dynamics are described by network flow balance equations. A nonlinear modeling approach is taken to represent hydro-plant generating characteristics, and variable reservoir heads are permitted. The system model recognizes security constraints in the form of interregional transmission-capacity limitations. The resulting large-scale mathematical programming problem is solved by using a reduced-gradient algorithm specialized to exploit the embedded network structure of the hydrological system. The additional security constraints are handled by a gradient-protection scheme that is based on estimates of the Lagrange multipliers associated with binding constraints. The estimates of the multipliers are determined by solving a small, quadratic minimization problem. >

From information requirements to DBTG-data structures

The problem of determining, analysis and description of a particular applications information structure (and relations) and the process of mapping the information structure to a “good” data structure (in this case a DBTG-type structure) is considered. The applicability of a top-down oriented design procedure to a relatively large practical data base design case is demonstrated. A conceptual framework and a notation to be used for determining and definition of information requirements, information structure and information relations is suggested. A systematic and partly formalized approach to map an information structure to a DBTG-type data structure is discussed. The problem of analysis and evaluation of alternative DBTG-type structures is also considered.

Semantic similarity relations and computation in schema integration

Schema integration plays an important part in research areas of heterogeneous information systems and semantic interoperability. How to acquire data semantic knowledge from the local schemas, and how to represent the knowledge acquired in support to the schema integration process are two major problems in schema integration research. To find similarities between objects of different schemata at the semantic level is considered to be one of the crucial problems in schema integration. In order to identify such similarities it is necessary to form a set of semantic characteristics the objects may possess. In this paper, we present a set of such characteristics and a set of semantic similarity relations. The relations are classified into four groups, weak semantic relation, compatible semantic relation, equivalence semantic relation and mergeable semantic relation. In addition, based on the semantic similarity relations, we attempt to find semantic similarity between entities compared and compute their semantic similarity degrees (SSD). We also propose a schema integration tool, which makes use of the semantic relations to integrate objects of different schemata.

Computer-aided distribution system planning

Abstract The purpose of this paper is to demonstrate how computerized design models, supported by computer graphics, can aid in electric distribution planning. The models comprise siting and sizing of primary substations, primary feeder routing, and secondary network design.1,2 The modelling is performed with an emphasis on rapid, descriptive design methods with geographical reference in planning data and resulting distribution system layouts. This enables a planner to provide and present many low cost designs, compatible with projected loads and community plans, in a graphical form that is both accurate and easy to understand. The designs may then be completed with further technical and economic analyses and embodied in a utility decision basis for future long- and short-term system perspectives

Generation Expansion Planning for Systems with a High Share of Hydro Power

This paper presents a method for integrating a detailed model of the hydroelectric system into existing power system planning tools. The purpose of the hydro model is not primarily to optimize hydro expansion, but to represent the influence of hydro regulation on the thermal system expansion. Stochastic production costing routines are used to calculate operating costs as a function of hydro production. Linear programming is used to determine the hydro production schedule that minimizes production costs along the planning period, taking into account a number of constraints in the hydro production system. A study with 16 cascaded hydro plants and 25 thermal units is presented and discussed.

From Information Algebra to Enterprise Modelling and Ontologies — a Historical Perspective on Modelling for Information Systems

Evolution of research and practice in the area of conceptual modelling for information systems during more than four decades is examined. It focuses on activities related to research and practice in the early system development phases. It comments on a large number of modelling methods published in the 1960-ies, 70-ies, and 80-ies as well as on the report “Concepts and Terminology of the Conceptual Schema and the Information Base” reporting the work by the ISO working group ISO/TC97/SC5/WG5 in the early 80-ies. Approaches which are based on a temporal and deductive view of the application domain as well as object-oriented modelling languages are acknowledged. The paper continues with a discussion of principles and research problems related to a topic we call “Enterprise Modelling” and “Ontology Modelling”. The role of conceptual modelling in information systems development during all these decades is seen as an approach for capturing fuzzy, ill-defined, informal “real-world” descriptions and user requirements, and then transforming them to formal, in some sense complete, and consistent conceptual specifications. During the last two decades an additional role of modelling has evolved - to support user and stakeholder participation in enterprise analysis and requirements formulation and in development of shared conceptualisations of specific domains.

Voltage optimization using augmented Lagrangian functions and quasi-Newton techniques

This paper shows how the application of augmented Lagrangian functions and quasi-Newton techniques can be utilized for power system voltage optimization. The developed algorithm is attractive for three reasons: 1) it can accommodate power system constraints in a straightforward manner, 2) it is capable of reaching a solution even from infeasible starting-points and 3) it converges in a few iterations. The proposed algorithm offers substantial improvements in the computational efficiency due to: 1) a reduction in the dimensionality of the formulation by exploiting variable reduction and active-reactive decoupling in the AC-network, 2) sparse matrix techniques to selectively generate the required sensitivities and 3) an active set strategy that relaxes all inactive constraints. Computer runs have been performed and the results proves the efficiency of the algorithm.

Optimal seasonal scheduling of natural gas units in a hydro-thermal power system

The paper describes an approach for solving the seasonal operations planning problem of a hydro-thermal system where part of the thermal capacity consists of energy constrained natural gas units. Gas volume available as well as limitations on its use during the year is regulated through import contracts. Two different types of contract are modelled. One where a yearly import volume is fixed and another where a lower bound on the yearly import is fixed. The proposed planning model is intended for economic evaluation of different natural gas import contracts. The problem is decomposed into two parts. One part performs a traditional production costing given a gas schedule. The other part makes use of weekly marginal costs with first order information from the production costing algorithm in order to schedule the gas and in the case of the second type of contract, to decide on how much gas to import. The optimization method used to schedule the gas makes use of an efficient algorithm for solving this type of nonlinear problem. >

Introduction of natural gas in a hydro-thermal system, a multi-objective approach

Abstract This paper demonstrates an approach for solving the planning problem of introducing natural gas as a new major generating source in the Swedish electric power system. This is a large-scale multi-objective planning problem in an uncertain environment. The multi-objective problem is divided into several phases, each dealing with a specific part of the overall problem. The tasks of generating different objectives as well as uncertain variables and feasible plans are addressed. It is discussed how sensitivity analysis can reduce the number of uncertainties and objectives. Models are built in order to relate outcomes to different plans and uncertain variables. Existing methods for encoding uncertainties as well as finding a set of best plans from all specified are incorporated into the presented framework, Finally, a method for estimating the value of reducing the uncertainty is described.