Abstract
With the advent of power system restructuring, there is now competition on the generation activity and the generation mix changed in many countries with the incentives to induce investments in renewables, in many cases, using volatile primary resources. Given this increase of the installed capacity in wind parks and PV stations as well as in hydro stations (as a way to address the mentioned volatility), investments in large thermal stations became more risky. In this scope, this paper describes a long term generation expansion planning model that can be used by generation companies to investigate the profitability of new thermal generation investments considering the increasing presence of renewables. This long term simulation tool uses System Dynamics, a framework particularly suited to mode the long term dependencies between different variables while incorporating delays on some decisions. At a final section this paper includes a Case Study based on a generation system that corresponds to a scaled version of the Portuguese system.

Abstract
This paper presents a multiyear dynamic transmission expansion planning, TEP, model aiming at minimizing operation and investment costs along the entire planning horizon while ensuring an adequate quality of service and enforcing constraints modeling the operation of the network along the planning horizon. The developed model profits from the experience of planners when preparing a list of possible branch (lines and transformers) additions each of them associated to the corresponding investment cost. The objective of solving a TEP problem is to select a number of elements of this list and provide its scheduling along the planning horizon such that one is facing a mixed integer optimization problem. In this case, this problem was solved using a discrete evolutionary particle swarm optimization algorithm, DEPSO. based on already reported EPSO approaches but particularly suited to treat discrete problems. Apart from detailing the developed DEPSO, this paper describes the mathematical formulation of the TEP problem and the adopted solution algorithm. It also includes results of the application of the DEPSO to the TEP problem using two test networks widely used by other researchers on this area.

Abstract
This paper presents an integrated model to deal with complex bids and network security constraints in electricity markets. Apart from purely economic aspects, power systems operation is also driven by technical issues that quite often turn unfeasible purely economic schedules. This is the case of up and down ramps and minimum technical limits of generators, nodal voltage ranges and branch flow limits. The activities of the Market and System Operators are quite often organized in terms of a sequential set of actions that may not guarantee identifying the best global solution. This suggests addressing the problem in a more integrated way and adopting a well known optimization technique, as Simulated Annealing. This paper describes the mathematical formulation of the problem, the adopted solution algorithm and details a case study based on the IEEE 24 bus/38 branch system.

Abstract
This paper addresses the problem of providing frequency control services, including inertia emulation and primary frequency control, from offshore wind farms connected through a multiterminal HVDC network. The proposed strategy consists of a cascading control mechanism based on dc voltage regulation at the onshore converters and frequency regulation at the offshore converters. The control scheme involves only local measurements and actions avoiding security and reliability issues of control structures based on remote information. The effectiveness of the proposed strategy is illustrated in a test system that consists of two nonsynchronous areas linked by a multiterminal HVDC grid where two offshore wind farms are also connected.

Abstract

Abstract
MicroGrids comprise low voltage distribution systems with distributed energy sources, storage devices and controllable loads, operated connected to the main power network or autonomously, in a controlled coordinated way. In case of MicroGrids autonomous operation, management of instantaneous active power balance imposes unique challenges. Traditionally, power grids are supplied by sources having rotating masses and these are regarded as essential for the inherent stability of the system. In contrast, MicroGrids are dominated by inverter interfaced sources that are inertia-less, but do offer the possibility of a more flexible operation. When a forced or scheduled islanding takes place in a MicroGrid, it must have the ability to operate stably and autonomously, requiring the use of suitable control strategies. The MicroGrid power sources can also be exploited in order to locally promote a service restoration strategy following a general blackout. A sequence of actions for the black start procedure is also presented and it is expected to be an advantage in terms of reliability as a result from the presence of very large amounts of dispersed generation in distribution grids. © Springer-Verlag Berlin Heidelberg 2012.