João Tomé Saraiva

Fuzzy modelling of power system optimal load flow

A fuzzy model for power system operation is presented. Uncertainties in loads and generations are modeled as fuzzy numbers. System behavior under known (while uncertain) injections is dealt with by a DC fuzzy power flow model. System optimal (while uncertain) operation is calculated with linear programming procedures in which the problem nature and structure allow some efficient techniques such as Dantzig-Wolfe decomposition and dual simplex to be used. Among the results, one obtains a fuzzy cost value for system operation and possibility distributions for branch power flows and power generations. Some risk analysis is possible, as system robustness and exposure indices can be derived and hedging policies can be investigated. >

Generation/transmission power system reliability evaluation by Monte-Carlo simulation assuming a fuzzy load description

This paper presents a Monte Carlo algorithm considering loads defined by fuzzy numbers. In this methodology states are sampled according to the probabilistic models governing the life cycle of system components while fuzzy concepts are used to model uncertainty related to future load behavior. This model can be used to evaluate generation/transmission power system reliability for long term planning studies as one uses the more adequate uncertainty models for each type of data. For each sampled state a fuzzy optimal power flow is run so that one builds its power not supplied membership function. The paper proposes new indices reflecting the integration of probabilistic models and fuzzy concepts and discusses the application of variance reduction techniques if loads are defined by fuzzy numbers. A case-study based on the IEEE 30 bus system illustrates this methodology.

Impact on some planning decisions from a fuzzy modelling of power systems

In this paper, system component reinforcements are analyzed from the perspective of their impact in increasing flexibility in system design. The proposed framework integrates a fuzzy optimal power flow model through which one can derive, as a function of load uncertainties, possibility distributions for generation, power flows and power not supplied. Exposure and robustness indices, based on risk analysis concepts, are defined. These indices can be used to rank the expansion alternatives, giving the planner insight to system behavior in the face of adverse futures. Their use in conjunction with investment assessments is proposed as a necessary step in a decision making methodology. >

Load allocation in DMS with a fuzzy state estimator

This paper describes a load allocation model to be used in a distribution management system (DMS) environment. A process of rough allocation is initiated, based on information on actual measurements and on data about installed capacity and power and energy consumption at LV substations. This process generates a fuzzy load allocation, which is then corrected by a fuzzy state estimator procedure in order to generate a crisp power flow compatible set of load allocations, coherent with available real time measurements recorded in the SCADA.

Generation and load uncertainties incorporated in load flow studies

A fuzzy AC load flow model is presented in which fuzzy data are used to obtain possibility distributions of voltages, active and reactive flows and losses, currents, and generated powers. These distributions are compared with the ones obtained through a Monte Carlo based simulation in order to evaluate the errors inherent to the fuzzy AC load flow.<<ETX>>

Evaluation of the performance of a fuzzy optimal power flow algorithm

In this paper an improved DC fuzzy optimal power flow (FOPF) model for power system planning purposes formulated as a multi-parametric programming problem is briefly presented. This model uses fuzzy set theory concepts to represent information about loads expressed in a subjective way by experts or integrating a certain degree of uncertainty about the future. The proposed algorithm has a heuristic nature so that it is important to evaluate the quality of the derived membership functions. A sampling procedure is used to build membership functions to be compared with the ones obtained using the FOPF algorithm. In the paper results obtained for two networks based on the IEEE 24 and 30 bus test systems are presented and discussed.<<ETX>>

Evaluation of electrification alternatives in developing countries-the SOLARGIS tool

This paper presents a methodology developed within the SOLARGIS project-a Joule project-aiming at evaluating the potential of integrating renewable forms of energy into dispersed electricity production. With this project, the authors also wanted to demonstrate the efficiency of GIS-geographical information systems-as a tool to analyse the integration of renewable forms of energy. In this paper, the authors present the methodologies developed to identify renewable resources in a given geographic region, to detect high potential areas for wind farm siting and to evaluate the efficiency and market of isolated systems to be used for dispersed rural electrification. In this last methodology, the authors used fuzzy models to describe the uncertainties in demand and cost values.

Optimal storage dispatch in a consumer setting with local generation resources

While in the past the installation of distributed generation systems was oftentimes motivated by attractive feed-in tariffs, many consumers now install such systems to increase their self-sufficiency in order to avoid rising electricity cost. However, due to the intermittency of photovoltaic systems and the dependency of cogeneration units on the thermal demand, there remains a significant mismatch between local generation and demand. Electrical storage devices can align generation and demand, minimizing the mentioned gap and hence the amount of energy that needs to be taken from the grid. This paper describes a model to determine the optimal dispatch of such a system, taking the thermal system into account in order to account for the dependency of cogeneration units. A mixed integer program is presented, which identifies the cost minimizing operation schedule. This model is tested using a case study considering realistic values taken from the German case.

Transmission expansion planning — A multiyear PSO based approach considering load uncertainties

This paper describes a multiyear dynamic Transmission Expansion Planning, TEP, model to select and schedule along the planning horizon transmission expansion projects taken from a list supplied by the planner. The selection of the most adequate set of projects from this list is driven by the minimization of the investment plus operation costs while enforcing a number of constraints related with technical, financial and reliability issues. The developed approach also admits that nodal loads are modeled by triangular fuzzy numbers as a way to ensure obtaining more robust plans that is plans not only adequate for a deterministic set of future loads but plans that can accommodate load uncertainty. Finally, given the discrete nature of the problem, it was adopted a discrete version of the Evolutionary Particle Swarm Optimization algorithm, DEPSO, that proved very effective and shows good performance on several tests ran with the IEEE RTS system.

Economics of energy storage in a residential consumer context

With the increase of electricity tariffs and the decreasing costs for distributed generation technologies, more and more residential consumers are deploying local generation systems to satisfy their electricity demand in order to reduce overall cost. Typically, however, a mismatch between electricity generation and demand remains. Storage systems enable consumers to reduce this mismatch by storing locally generated electricity for later consumption, instead of feeding excess generation into the grid. This paper analyzes the economics of storage installations in a residential consumer context. A linear program is presented to determine the optimal dispatch, and Simulated Annealing is used to identify the cost minimizing system configuration. The developed approach is tested for a multi-family house in Germany.