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The increasing penetration of Electric Vehicles (EVs) in LV distribution networks can potentially cause voltage quality issues such as voltage unbalance and under-voltage conditions. According to the EV charger characteristics, some strategies can be adopted to mitigate the aforementioned effects. Smart decentralized charging controls seem to be a more practical solution than centralized controls, since there is no need for communication because they rely only on local measurements. The four most relevant decentralized charging strategies, two for single-phase and two for three-phase EV chargers, have been implemented in a typical three-phase four-wire European LV distribution network. Simulations have been carried out for scenarios with single-phase EV chargers, three-phase EV chargers, and a combination of both. Single-phase controls are aimed at under-voltage regulation, while three-phase controls are focused on mitigating voltage unbalance. Results show that the implementation of a decentralized EV charging control is an adequate solution for Distribution System Operators (DSOs) since it improves the reliability and security of the network. Moreover, even though decentralized charging control does not use any communication, the combination of three-phase and single-phase controls is able to mitigate voltage unbalance while preventing the under-voltage condition.

Abstract-The method presented in this paper addresses the problem of voltage sag state estimation (VSSE). The problem consists in estimating the voltage sags frequency at non-monitored buses from the number of sags measured at monitored sites. Usually, due to limitations on the number of available voltage sag monitors, this is an underdetermined problem. In this approach, the mathematical formulation presented is based on the fault positions concept and is solved by means of the Singular Value Decomposition (SVD) technique. The proposed estimation method has been validated by using the IEEE 118 test system and the results obtained have been very satisfactory.Index Terms-voltage sags (dips), power quality monitoring, power system, Power Quality. I. INTRODUCTIONOLTAGE sags (also known as voltage dips) are a frequent power quality disturbance that can cause failure or malfunctioning to very common devices used in industrial and tertiary sectors. This disturbance, as with other power quality problems, must be approached from a compatibility point of view that requires characterizing the equipment sensitivity as well as the power system behavior. This paper relies on this second aspect.In order to describe the voltage sags performance in the power system, a method must be established that can provide representative values of the expected number and characteristics of voltage sags at system buses. To quantify the system behavior, a great emphasis has been placed recently on the use of different quality indices. Some of these indices are defined at a site level (for a specific point of the supply system), but there are others defined at a system level (for the whole system) [1]- [4]. For assessing site indices, monitoring the power supply at the site of interest can directly provide the information to evaluate the index. However, in order to calculate voltage sag indices of the whole system, ideally the monitoring of all sites should be required. Clearly, such a monitoring program is not economically justifiable.This work has been financed by the Ministerio de Ciencia e Innovación (MICINN), Spain, under project ENE2010-17459 (CON) A. Hernández, R. M. de Castro and M. Izzeddine are with the

This paper focuses on Hybrid Energy Storage Systems (HESS), consisting of a combination of batteries and Electric Double Layer Capacitors (EDLC), for electric urban busses. The aim of the paper is to develop a methodology to determine the hybridization percentage that allows the electric bus to work with the highest efficiency while reducing battery aging, depending on the chosen topology, control strategy, and driving cycle. Three power electronic topologies are qualitatively analyzed based on different criteria, with the topology selected as the favorite being analyzed in detail. The whole system under study is comprised of the following elements: a battery pack (LiFePO4 batteries), an EDLC pack, up to two DC-DC converters (depending on the topology), and an equivalent load, which behaves as an electric bus drive (including motion resistances and inertia). Mathematical models for the battery, EDLCs, DC-DC converter, and the vehicle itself are developed for this analysis. The methodology presented in this work, as the main scientific contribution, considers performance variation (energy efficiency and battery aging) and hybridization percentage (ratio between batteries and EDLCs, defined in terms of mass), using a power load profile based on standard driving cycles. The results state that there is a hybridization percentage that increases energy efficiency and reduces battery aging, maximizing the economic benefits of the vehicle, for every combination of topology, type of storage device, control strategy, and driving cycle.