Santi Agatino Rizzo

Generalized Systematic Approach to Assess Distribution System Reliability With Renewable Distributed Generators and Microgrids

This paper presents an innovative generalized systematic approach and related analytical formulation to evaluate distribution system reliability in smart grids where islanded operation of microgrids helps to improve local and overall reliability. In order to do this, the analytical formulation involves the adequacy calculation of conventional and renewable distributed generators supplying microgrids by using probabilistic models. Adequacy is computed by means of a new general analytical expression which takes into account load shedding (user load disconnection) and curtailment (user load reduction) policies.

Reliability Assessment of Distribution Systems Considering Telecontrolled Switches and Microgrids

Telecontrol of distribution switching devices is recognized as a major means for reducing interruption duration after a fault occurrence in modern distribution systems, since it allows one to isolate the faulted sections and to restore the healthy ones as quickly as possible. In order to reduce interruption frequency as well, it is necessary to increase the number of series automatic circuit breakers. Further benefits in terms of service continuity improvement can be obtained by allowing islanded operation of relatively small portions of distribution network (microgrids) in the presence of distributed energy resources in order to supply the local load autonomously during upstream faults. This paper aims to describe an innovative systematic method and its related analytical formulation to evaluate distribution system reliability indices accounting for advanced operation practices such as those based on telecontrol and islanding.

Modelling of Microgrid-Renewable Generators Accounting for Power-Output Correlation

The possibility to operate in islanding mode some portions of a distribution network, after fault occurrence, helps to improve system reliability. In this perspective, it is crucial to estimate the ability of distributed generators (DGs) to meet the local load. A major issue in the adequacy assessment is to take into account the correlation existing among the power outputs of DGs based on the same renewable intermittent primary energy source (sun, wind). This paper presents a new modelling approach to provide the hourly generation models for each type of renewable DGs, by taking into account both power correlation and hardware availability. An interesting aspect of the proposed approach is that it encompasses such correlation, avoiding the analytical calculation of its value. An innovative method to obtain hourly load models is also presented. Finally, a method to evaluate analytically loss of load probability by using the proposed generation and load models is also described. Both the presented method and Monte Carlo simulations (MCS) are applied to the IEEE RBTS-BUS6. Applying the proposed models and analytical method actually enables obtaining benchmark results to test approximated models and/or MCS results.

A Parallel Version of the Self-Adaptive Low-High Evaluation Evolutionary-Algorithm for Electromagnetic Device Optimization

The self-adaptive low-high evaluation evolutionary-algorithm (SALHE-EA) is used to solve multimodal optimization problems. SALHE-EA is able to find the multiple optima of a single objective function (OF) and to give an idea of the fitness landscape in the neighborhood of these optima. This aspect is of crucial importance when the single OF is obtained using the weighted sum of the OFs, each related to a different goal of the optimization problem. This paper presents an improved version of SALHE-EA. This new version has several new features and, mainly, the suitability for parallelization.

SALHE-EA: A New Evolutionary Algorithm for Multi-Objective Optimization of Electromagnetic Devices

This paper presents a new evolutionary algorithm (EA) for the optimization of electromagnetic devices called SALHE-EA (self-adaptive low-high evaluations – evolutionary algorithm). Its main aspects are identification of the optima of the objective function and evaluation of their sensitivity. Moreover, SALHE-EA works well if combined with the deterministic pattern search (PS) method, forming a good hybrid method. It performs well in the design of electromagnetic devices when the optimization of a multimodal function is required.

Optimal control to minimize operating costs and emissions of MV autonomous micro-grids with renewable energy sources

The paper is intended to propose an optimal control strategy for autonomous micro-grids that focuses on the possibility to minimize the overall micro-grid operating cost, borne by the Micro-Grid Operator in order to provide power distribution to customers, while minimizing the pollutants emissions and assuming that all the power made available by the renewable energy sources is injected into the micro-grid. The proposed procedure can be implemented thanks to a hierarchical control architecture. The optimization procedure has been verified by computer simulations on a test network. The numerical results show that it is possible to find optimal feasible solutions that improve the operating conditions of the micro-grid with respect to the ones obtained as a result of the generators local control.

A comparison between hybrid methods: FEM-BEM versus FEM-DBCI

Purpose – The purpose of this paper is to compare the hybrid FEM-BEM and FEM-DBCI methods for the solution of open-boundary static and quasi-static electromagnetic field problems. Design/methodology/approach – After a brief review of the two methods (both coupling a differential equation for the interior problem with an integral equation for the exterior one), they are compared in terms of accuracy, memory and computing time requirements by means of a set of simple examples. Findings – The comparison suggests that FEM-BEM is more accurate than FEM-DBCI but requires more computing time. Practical implications – Then FEM-DBCI appears more appropriate for applications which require a shorter computing time, for example in the stochastic optimization of electromagnetic devices. Conversely, FEM-BEM is more appropriate in cases in which a high level of precision is required in a single computation. Originality/value – Note that the FEM-BEM considered in this paper is a non standard one in which the nodes of the...

Optimal investment assessment for distribution reliability through a multi-objective evolutionary algorithm

Reliability is an increasingly important issue in power systems. As well known, problems in distribution systems are the main responsible of customer unavailability. In the last years, the utility interest in the improvement of the reliability in power systems is continuously growing thanks to the deregulation of the electricity market. It is known that inserting switches along the network positively affects the distribution systems reliability but, of course, it involves utility costs. This paper deals with the optimal choice of number, type and location of telecontrolled/automated circuit breakers and sectionalizers in distribution systems taking into account their cost. The optimization problem has been solved by means of a multi-objective evolutionary algorithm able to provide the minimum cost investment required to obtain a given network reliability, as well as the maximum reliability that can be achieved for a given economic investment.

FEM-DBCI Solution of Open-Boundary Electrostatic Problems in the Presence of Floating Potential Conductors

This paper extends the hybrid finite-element method-Dirichlet boundary condition iteration method for the solution of open-boundary electrostatic problems to the case, in which some floating potential conductors are present in the system. The iterative solution scheme of the basic method is modified in order to deal with the unknown values of the potential of these conductors.

Efficient Analysis of Grounding Systems by Means of the Hybrid FEM–DBCI Method

In the design of a grounding system, technical and normative constraints have to be met. Therefore, it is necessary to use a tool that is able to accurately estimate the values of the significant parameters of the grounding system, such as earth resistance and touch-and-step voltages. The computation of such quantities calls for the solution of a 3-D open-boundary static electromagnetic field problem, which should take into account the nonhomogeneous structure of soil. The hybrid finite-element method-Dirichlet boundary condition iteration method is applied to the solutions of such problems. A great advantage of this method is that it directly provides the electric potential distribution on the earth surface as part of the solution. Some grounding systems are analyzed, and the comparisons of the results with those obtained by other methods are made.