M. Trovato

A regional energy planning methodology including renewable energy sources and environmental constraints

In this paper, a bottom-up energy system optimisation model is proposed in order to support planning policies for promoting the use of renewable energy sources. A linear programming optimisation methodology based on the energy flow optimisation model (EFOM) is adopted, detailing the primary energy sources exploitation (including biomass, solid waste, process by-products), power and heat generation, emissions and end-use sectors. The modelling framework is enhanced in order to adapt the model to the characteristics and requirements of the region under investigation. In particular, a detailed description of the industrial cogeneration system, that turns out to be the more efficient and increasingly spread, is incorporated in the regional model. The optimisation process, aiming to reduce environmental impact and economical efforts, provides feasible generation settlements that take into account the installation of combined cycle power plants, wind power, solid-waste and biomass exploitation together with industrial combined heat and power (CHP) systems. The proposed methodology is applied to case of the Apulia region in the Southern Italy.

On-line dynamic preventive control: an algorithm for transient security dispatch

This paper describes the philosophy and the implementation of a preventive control algorithm for application in power system dynamic security assessment. The methodology consists of an optimization procedure where: the objective function takes into account economic costs; inequality constraints confine the trajectory of the system in a practical domain of the state space; and equality constraints derive from the discretization of the differential-algebraic equations of the power system sparse representation. The algorithm has been implemented to reschedule the power system generation in order to guarantee transient stability. The feasibility of the approach is shown through computer simulation tests on a realistic sized test network.

Planning and Operating Combined Wind-Storage System in Electricity Market

The increasing penetration of renewable sources in power systems yields various issues in network operation. Most of them are related to uncertainties of energy production. In particular, the variability of wind source does not allow for accurate forecasting of power generation. Production plans may not be accomplished, incurring penalties for system unbalance. For this reason, the use of an energy storage system can improve integration of wind energy in production planning and dispatch. In this paper, an approach for planning and operating an energy storage system for a wind farm in the electricity market is proposed. To this purpose, electrochemical batteries are employed to compensate for generation variations in order to set up a reliable hourly delivery profile, complying with market requirements. The delivery plan can be settled according to energy prices, as well. Moreover, an economic feasibility analysis is carried out on the combined wind-storage system.

A neural network-based method for voltage security monitoring

In this paper, a neural network-based method is proposed for monitoring the online voltage security of electric power systems. Using a dynamic model of the system, voltage stability is measured totally, considering a suitable stability index for the whole system, and locally, by defining appropriate voltage-margins for detecting the area of the system where the instability phenomenon arises. A three-layer feedforward neural network is trained to give, as outputs to a pre-defined set of input variables, the expected values of the above defined indices. The neural network is designed by using a fast learning strategy that allows the optimal number of hidden neurons to be easily determined. Moreover, it is shown that, in the operation mode, the system power-margin and the bus power-margins can be easily evaluated using the value of the voltage stability index given by the designed NN. The effectiveness of the proposed approach has been demonstrated on the IEEE 118-bus test system.

A Gauss-Jacobi-Block-Newton method for parallel transient stability analysis (of power systems)

A parallel method for the transient stability simulation of power systems is presented. The trapezoidal rule is used to discretize the set of algebraic-differential equations which describes the transient stability problem. A parallel Block-Newton relaxation technique is used to solve the overall set of algebraic equations concurrently on all the time steps. The parallelism in space of the problem is also exploited. Furthermore, the parallel-in-time formulation is used to change the time steps between iterations by a nested iteration multigrid technique, in order to enhance the convergence of the algorithm. The method has the same reliability and model-handling characteristics of typical dishonest Newton-like procedures. Test results on realistic power systems are presented to show the capability and usefulness of the suggested technique. >

Risk-Constrained Profit Maximization in Day-Ahead Electricity Market

The deregulation of the electricity industry has caused for the generation company (Genco) the need of tools for measuring and managing the risk, beyond the classical problem of generating unit scheduling. In this paper, a probabilistic framework for the problem of managing risk faced by Gencos trading in day-ahead energy market is proposed. In particular, a stochastic forecast of electricity price and the technical features of hydrothermal units are considered. The approach is based on an optimization procedure for maximizing expected profits in the presence of risk constraints. Conditional value at risk for the distribution of daily profit is used as risk measure.

A generalized approach to the analysis of voltage stability in electric power systems

Abstract In this paper a new method for analysing the voltage stability problem in electric power systems is presented. The approach starts with a linearized model in state space form of a multi-machine power system, then rigorous voltage stability conditions are derived on the basis of a suitable aggregated model of the original system capable of retaining the dynamics of voltages at generator and load nodes. The approach allows a systematic individualization of all the dynamic factors which affect voltage instability phenomena and suggests the appropriate representation which has to be adopted for each dynamic component of the system. The validity and usefulness of the suggested method are illustrated by carrying out simulation studies on a sample power system.

A qualitative approach to the transient stability analysis [of power systems]

With the growing stress on todays power systems, there is a urgent need for implementing online dynamic security assessment (DSA). Among the functions of DSA, the most time-consuming function is the dynamic contingency analysis. In this paper, it has been assumed that during this analysis, one is not interested in obtaining trajectories with a very high accuracy but is primarily interested in a qualitative answer to the question: is the power system stable or not? Subsequently, only unstable or marginally stable cases have to be considered for more detailed analyses and preventive control. This idea is applied to parallel-in-time algorithms for transient stability analysis in order to stop the simulation as soon as the stability is detected by the condition of potential energy boundary surface (PEBS) crossing. The effectiveness of the approach has been validated on the New England test system and a realistic-sized network with 662 buses. An implementation on the nCUBE multiprocessor of a particular parallel-in-time algorithm allows the speed up derived from the proposed approach to be assessed.

State space representation of interconnected power systems for dynamic interaction studies

Abstract In this paper a linearized model of an interconnected power system in state space form is presented in order to analyse the dynamic interactions of its components across the interconnection network. The model, modularly structured, proves flexible and includes detailed descriptions of generators with their control devices, static and dynamic loads. The mathematical representation of the system is formulated such that the effect of interconnection on system characteristic polynomial and system dynamic stability can be systematically investigated. Additionally, a suitable index is defined to measure the degree of dynamic interaction which may occur between the machines of the interconnected power system. A numerical example is included using a four-generator ten-bus system to illustrate the capability of the developed model and the usefulness of the proposed technique.

Advanced steady-state models of UPFC for power system studies

In this paper, focus is on the UPFC steady-state modeling for the implementation of the device in the Newton-Raphson load flow algorithm. Two models, deriving from the known voltage source model (VSM), are presented and analyzed in detail. One is a power injection model (PIM) and the other one is the new shunt admittance model (SAM). Each one of these models represents a more robust and feasible alternative to the VSM because it bypasses the difficulties arising from the VSM, maintaining its advantages, though. Different simulations are presented in the paper to test and compare the models: Newtons quadratic convergence of the load flow algorithm is guaranteed by implementing the PIM and the SAM, with high convergence speeds.