Abstract

Abstract
The scope of this work is to find the best approach to control advanced inverters used to connect electric vehicles to the grid. Phase-locked Loop (PLL) is a grid voltage phase detection that makes use of an orthogonal voltage to lock the grid phase. This method is suitable for both single and three phase systems, although in single-phase, because they have less information, more advanced systems are required. The easiest way to obtain the orthogonal voltage system is using a transport delay block to introduce a phase shift of 90 degrees with respect to the fundamental frequency of the grid voltage. This method is known as Synchronous Reference Frame PLL (SRF-PLL). The use of inverse Park transformation is also possible. To lower the complexity and increasing the filtering of the output signals, methods using adaptive filters are a good alternative. For this approach, the use of a second order generalized integrator (SOGI) or Adaptive Notch filter combined with PLL, Enhanced PLL (EPLL) and Quadrature PLL (QPLL), leads to satisfactory results. © 2011 INESC Coimbra.

Abstract
Restructuring of power markets has helped in the penetration of Distributed Generation (DG) in the electricity networks. Microgrids are Low Voltage distribution networks comprising various distributed generators (DG), storage devices and controllable loads that can operate interconnected or isolated from the main distribution grid, as a controlled entity. This paper describes the main functions of the Microgrid Central Controller required for the optimization of Microgrid operation its interconnected operation. This is achieved by maximizing its value, i.e. optimizing production of the local DGs and power exchanges with the main distribution grid.

Abstract
In the present paper an advanced control system for the optimal operation and management of medium size power systems with large penetration from renewable power sources is presented. This control system is aimed to assist the power system operators in their managing task, by proposing them optimal actions for the economic and secure management of the power system. The control system is composed of various modules performing functions like short-term forecasting of the load and of the renewable sources, economic dispatch of the power units and on-line dynamic security assessment. The pilot control system is being installed and evaluated in the Greek island of Lemnos.

Abstract
A new type of bus for load flow analysis is proposed in this paper; this type of bus, named PX, is particularly suited for modelling elements like static compensators or asynchronous generators. The inclusion of this PX bus in the Fast Decoupled Load Flow method is presented and discussed. Numerical results are reported when applying this approach to solve load flow problems in two standard systems.

Abstract
Operation problems that result from MV distribution networks with local asynchronous generation sources connected are examined. In order to analyze steady-state operating situations, a load-flow calculation must be performed. The presence of asynchronous generators imposes the adoption of a consistent bus modelization using a new bus type, the PX bus, where P is the active generated power and X is a nonlinear magnetizing reactance. This approach introduces some modifications in the conventional load-flow algorithms, thereby increasing the total number of iterations.