Abstract
Power systems have been through deep changes in recent years, namely with the operation of competitive electricity markets in the scope and the increasingly intensive use of renewable energy sources and distributed generation. This requires new business models able to cope with the new opportunities that have emerged. Virtual Power Players (VPPs) are a new player type which allows aggregating a diversity of players (Distributed Generation (DG), Storage Agents (SA), Electrical Vehicles (V2G) and consumers), to facilitate their participation in the electricity markets and to provide a set of new services promoting generation and consumption efficiency, while improving players` benefits. A major task of VPPs is the remuneration of generation and services (maintenance, market operation costs and energy reserves), as well as charging energy consumption. This paper proposes a model to implement fair and strategic remuneration and tariff methodologies, able to allow efficient VPP operation and VPP goals accomplishment in the scope of electricity markets.

Abstract
This paper deals with some disturbances that reach the electric power systems. These problems originated some interest due to the changes of the electric loads characteristics, which were predominantly electromechanical and today are predominantly non-linear. This is due to the electronic systems involved. Results of some measurements performed in electric grid of the Oporto Engineering Faculty Campus and in the University of Vila Real (UTAD) are presented and some solutions that had been implemented for the related problems minimization are also described.

Abstract
Electrical Power Quality represents a challenging as much as attracting research topic nowadays, with consequences to all economic areas. Here, we studied the alternatives for reactive compensation in a residential low-voltage distribution grid using the Alternative Transient Program (ATP-EMTP). We developed a simulation model based on the results obtained from field measurements in a low voltage residential distribution grid with non-linear loads. We employed capacitors in different strategic places throughout the grid and changed their configurations, aiming to evaluate the technical viability of the application of reactive compensation. In this way, we investigated a methodology for the optimization of reactive compensation in secondary distribution grids, based on different solutions, in order to improve the voltage profile throughout the grid, as well as the technical losses that occur in a grid of this type. Next, we compared the simulated results with the field measurements. This analysis revealed that both approaches produced similar results, validating the simulation model. We therefore conclude that this model effectively reproduces the real linear and non-linear loads of the residential distribution grid and is suitable to be used in future studies. © 2011 IEEE.

Abstract
Power-Quality (PQ) is a crucial competitive and developing factor to all economic areas. The economic impact resulting from a bad PQ will be drastic to all consumers. Computers, uninterruptible power supplies (UPS), commuted power sources and fluorescent lamps/tubes are examples of nonlinear loads that have for main drawback the consumption of non-sinusoidal current. This paper presents a useful computer tool that can simulate and predict the behavior of non-linear loads and LV power systems with main focus on residential electrical grids. The paper also reviews some of the basic concepts and techniques related with power quality parameters and how they can be computed and presented in the simulation tool. The tool has an easy-to-use, friendly interface, and can be used as a tool to teach design techniques or as a laboratory to study the applicability of methods to real situations. The students can do simulations with their own data on Microsoft™ Windows® based platforms. © 2011 IEEE.

Abstract
Ever since the first studies about biomedical implantable devices, the problem of how to energize them has stood out as both important and notoriously difficult to solve. In order to extend the lifetime of implants, it is imperative to develop power generators that are autonomous, safe and maintenance-free. Energy harvesting is a natural way of meeting these requirements. First, the energy source is theoretically everlasting, a fact that helps to guarantee the autonomy. Second, the energy is obtained from the environment of the application itself, contributing to its safety. Finally, a properly designed energy harvesting system is very unlikely to ever require maintenance. This paper follows this line and describes an electromagnetic power transducer that harvests electrical energy from the human gait and stores it. An efficient power management module uses the stored energy to energize the telemetric system of a smart hip prosthesis implant, enabling the early detection of loosening, the target application of this work. The system is able to extract a total 1912.5 mu J of usable energy under normal walking conditions.

Abstract
This paper describes an improved micro-power electric generator where energy harvested from human movements is used as an everlasting mechanical energy source to suffice smart hip implant electronics power needs. Its architecture is designed so that the mechanical energy promotes the movement of a combination of magnets and a spring embedded inside a Teflon tube, used to reduce friction. The changing magnetic field induces current in two coils so that the output of the generator is the sum of their signals. The end result is like a double generator in one casing. Produced electrical energy is stored in an energy reservoir handed over to a power management module. Experimental results shows that energy harvested from human walking can be used as an effective power source for hip prosthesis implants. (C) 2010 Published by Elsevier Ltd.