Reconfiguration, by exchanging the functional links between the elements of the system, represents one of the most important measures which can improve the operational performance of a distribution system. The authors propose an original method, aiming at achieving such optimization through the reconfiguration of distribution systems taking into account various criteria in a flexible and robust approach. The novelty of the method consists in: the criteria for optimization are evaluated on active power distribution systems (containing distributed generators connected directly to the main distribution system and microgrids operated in grid-connected mode); the original formulation (Pareto optimality) of the optimization problem and an original genetic algorithm (based on NSGA-II) to solve the problem in a non-prohibitive execution time. The comparative tests performed on test systems have demonstrated the accuracy and promptness of the proposed algorithm.

The concept of microgrid was first introduced in 2001 as a solution for reliable integration of distributed generation and for harnessing their multiple advantages. Specific control and energy management systems must be designed for the microgrid operation in order to ensure reliable, secure and economical operation; either in grid-connected or stand-alone operating mode. The problem of energy management in microgrids consists of finding the optimal or near optimal unit commitment and dispatch of the available sources and energy storage systems so that certain selected criteria are achieved. In most cases, energy management problem do not satisfy the Bellman's principle of optimality because of the energy storage systems. Consequently, in this paper, an original fast heuristic algorithm for the energy management on stand-alone microgrids, which avoids wastage of the existing renewable potential at each time interval, is presented. A typical test microgrid has been analysed in order to demonstrate the accuracy and the promptness of the proposed algorithm. The obtained cost of energy is low (the quality of the solution is high), the primary adjustment reserve is correspondingly assured by the energy storage system and the execution runtime is very short (a fast algorithm). Furthermore, the proposed algorithm can be used for real-time energy management systems.

The growth of distributed generation (DG) which is consumer driven and not centrally planned presents a number of challenges and opportunities specific mainly to low voltage (LV) distributed networks. The growth of DG in order to meet the UK government's environmental targets for 2010 will taken into consideration for example the following LV distribution network constraints: steady-state voltage limits, voltage unbalanced limits and harmonic limits. This paper presents an algorithm developed by the authors in order to perform load flow calculation in unbalanced and harmonic polluted low voltage radial networks with distributed generation. The authors propose to model the harmonic complex quantities (a set of complex quantities corresponding to each harmonic component) through abstract data types with complex parameters. For harmonic polluted and unbalanced radial electric networks that include distributed generators, it was considered the backward/forward sweep with some specifications and adaptations.

The reconstruction or revitalization of electrical substations provides the possibility to introduce very powerful new switchgears, and as a result, to simplify the substation circuit diagram. Taking into account these tendencies, the authors propose a systematical method for establishing the optimal structure of electrical substations for increasing the operational level of reliability at the lowest economic cost. The graph theory is used to solve this particular problem. A (multi)graph will be associated to the network under study, where the bus system are taken for nodes, while the power lines and the (auto)transformers are considered as branches. By developing this model, the task of finding the critical equipment is reduced to the determination of (multi)graph critical nodes (articulation points) and critical branches (isthmuses). The paper presents an original method that, using the determination of critical equipment (systems of buses, transformers, power lines), indicates the most appropriate (minimal) structure for electrical substation circuit diagrams