Mariano Giuseppe Ippolito

Optimal Electrical Distribution Systems Reinforcement Planning Using Gas Micro Turbines by Dynamic Ant Colony Search Algorithm

Distribution systems management is becoming an increasingly complicated issue due to the introduction of new energy trading strategies and new technologies. In this paper, an optimal reinforcement strategy to provide reliable and economic service to customers in a given time frame is investigated. In the new deregulated energy market and considering the incentives coming from the political and economical fields, it is reasonable to consider distributed generation (DG) as a viable option for systems reinforcement. In the paper, the DG technology is considered as a possible solution for distribution systems capacity problems, along several years. Therefore, compound solutions comprising the installation of both feeders and substations reinforcement and DG integration at different times are considered in the formulation of a minimum cost distribution systems reinforcement strategy problem. An application on a medium size network, hypothesizing a scenario of reinforcement also using as DG gas micro-turbines, is carried out using a novel optimization technique allowing the identification of optimal paths in trees or graphs. The proposed technique is the Dynamic Ant Colony Search algorithm

Minimum losses reconfiguration of MV distribution networks through local control of tie-switches

This paper deals with the problem of optimal reconfiguration of radial distribution networks for minimum loss operation. The proposed control strategy of the open-closed status of the tie switches is distributed, since every MV/LV node is provided with local controllers having some measured entities as input. It also does not prevent the system from the future implementation of centralized control; instead, it may represent the first step towards a complete automation of the distribution system. The proposed strategy is organized in hierarchic levels, the highest of which may be in the future a central control. After introducing the general problem of network reconfiguration, a review of the state of art on the subject is reported, even though the solution methodologies are usually related to the centralized formulation of the reconfiguration problem. The proposed local control strategy is outlined, and a detailed description of its different parts is reported with special attention to all the measures for a better performance of the system. Results of a number of simulation runs are reported in order to test the behavior of the proposed local control system in different possible operating conditions.

An Innovative Conversion Device to the Grid Interface of Combined RES-Based Generators and Electric Storage Systems

This paper is focused on the development of an innovative device, which is based on a bidirectional converter, for the interface to the supply utility grid of combined renewable-energy-source-based generators and electric storage systems. The device can be controlled so as to ease the interface between the low-voltage grid and photovoltaic or wind generators combined with lithium-ion LiFePO4 batteries, taking into account the requirements of the reference technical standards for users connection and offering different ancillary services. The operational functioning of the device, the architecture, and its electronic components, as well as laboratory and field test activities and results are described. The conversion device has been developed, and the main results that have been achieved are detailed.

Transition of a distribution system towards an active network. Part II: Economical analysis of selected scenario

This paper outlines the economical issues related to the transition of the energy generation for a real MV/LV distribution system from a ‘fuel based’ one to a distributed and smart ‘renewables based’ one. It is the prosecution of a companion paper, which addressed the technical issues connected to such transition. The study has been carried out by University of Palermo and ENEA (Italy), on a portion of real MV/LV distribution system of the research center ENEA of Casaccia (Rome, Italy). The analysis is carried out for a specific scenario chosen among those proposed in the companion paper.

A new device for the control and the connection to the grid of combined RES-based generators and electric storage systems

In this paper a new device for the control and the connection to the supply utility grid of combined RES-based generators and electric storage systems is presented. The device is a bidirectional converter that can be controlled so as to facilitate the interface between the low voltage grid and photovoltaic or wind generators combined with batteries, contemporary addressing the requirements of the reference technical standards for users connection and providing different ancillary services. In the paper the functioning of the device and its circuit diagram are described, the single parts are shown and the potentiality of its control system are commented.

An efficient iterative method for load-flow solution in radial distribution networks

In this paper, an efficient method for radial distribution networks solution is proposed. The efficiency of the presented strategy makes it suitable for distribution automation applications. The method is based on an iterative algorithm with some special procedures to increase the convergence speed; the bus voltages are considered as state variables according to approaches that are common in literature. After the presentation of the general problem and of the state of the art on the subject, the proposed methodology is treated in detail. It uses a simple matrix representation for the network topology and branch current flows management. The method has been applied to some test systems already used in literature so as to put into evidence its properties mostly in terms of calculation times reduction. The obtained results confirm that it outperforms other solution methods for radial networks.

Robust multi-objective optimal dispatch of distributed energy resources in micro-grids

Modern distribution systems are implemented through micro grids: small power networks where generation is close to consumption and ICT supports the coordinated management of the different energy resources. In such systems, the central control unit manages energy dispatch from the different sources according to different criteria (technical, economical and environmental) and takes care of tertiary regulation. Such optimization for the tertiary regulation is performed with a time interval that typically is of 24 hours. This is due to the fact that it is necessary to take into account the charge and discharge cycles of storage systems. On the other hand, such long time leads to large errors in the prediction of energy generation and consumption. In this paper an algorithmic approach allows to overcome this problem. It is indeed possible to integrate uncertainty within the problem formulation attaining a dispatch plan for all the energy sources that will not lead to constraints violations even if the objective functions variables and parameters are affected by uncertainty. The results on a medium size system show the ease and effectiveness of the proposed approach.

Crowded comparison operators for constraints handling in NSGA-II for optimal design of the compensation system in electrical distribution networks

This paper proposes an improvement of an efficient multiobjective optimization algorithm, Non-dominated Sorting Genetic Algorithm II, NSGA-II, that has been here applied to solve the problem of optimal capacitors placement in distribution systems. The studied improvement involves the Crowded Comparison Operator and modifies it in order to handle several constraints. The problem of optimal location and sizing of capacitor banks for losses reduction and voltage profile flattening in medium voltage (MV) automated distribution systems is a difficult combinatorial constrained optimization problem which is deeply studied in literature. In this paper, the efficiency of the proposed Crowded Comparison Operator, CCO1, is compared to the efficiency of another Crowded Comparison Operator, CCO2, whose definition derives from the constraint-domination principle proposed by Deb et al. The two operators are tested on difficult test problems as well as on the optimal capacitors placement problem.

Economic impact of medium-scale battery storage systems in presence of flexible electricity tariffs for end-user applications

This article addresses the question if it is cost-effective to use medium-scale battery storage systems for time-of-use (TMO) energy cost applications at a consumer level, assuming flexible electricity tariffs in the Italian electricity market. TMO application allows customers to reduce their electricity bill charging the storage when off-peak time periods are applied and discharge it during on-peak periods, when electricity energy prices are high. The analysis is carried out taking into account three different electrochemical storage technologies. The economical comparison shows that, at the current costs of storage technologies and at the electricity tariffs currently offered in Italy, the use of battery systems for TMO energy cost applications is not economically advantageous for a medium-scale public institution facility. However, the aggregation of different benefits for the same storage technology, such as voltage support, deferral of investment in T&D network upgrades, reducing T&D losses and so on could modify this assumption.

A simple method to assess loadability of radial distribution networks

This paper proposes a simple method to asses loadability in radial distribution systems. The relevant problem of voltage stability has been dealt with in past times with reference to higher voltage systems for generation and transmission. In more recent papers, the problem has been considered also at distribution level, since the new electrical energy market requirements and the increasing loadings are now more and more influencing these systems. The proposed method is based on a static approach and proceeds by first evaluating the stability indices and then the different loadability factors (related to real, reactive and apparent power). These calculations are carried out by identifying, starting from the network state in a defined loading condition, an equivalent in terms of the transfer of power from the source node to the different network nodes. Then the node showing the lowest stability index represents the weakest node in the system in terms of voltage stability; the real, reactive or apparent loading factor of the equivalent between the supply node and the weakest node represents the maximum loading increase (real, reactive or apparent) that the network can stand without voltage collapse. Finally, for the considered loading factors, the results on different test systems are reported and the comparison with heuristically attained loading factors prove that the obtained results show a small error, whose sign however preserves the systems security.