Abstract
The quality and composition of biomass as used in Portugal's thermal power plants is highly variable. The biomass consists mainly of residual forest biomass derived from forestry operations and wood waste from industrial processes, in particular paper and pulp industry. Its quality and composition is influenced by the presence of moisture and inert fragments, the latter being incorporated during collection or as a consequence of adherence to the biomass prior to collection. This variability presents difficulties for the thermal power plants; besides being an additional operational cost, the presence of large amounts of water and inerts in biomass used as a fuel, can result in problems related to the instability of the combustion and the accumulation of ash or rock that have to be removed and discarded. The objective of this paper is to review the main parameters that influence the quality of biomass, while analysing the current state-of-the-art power generation from the biomass sector in Portugal, as a new contribution to earlier studies.

Abstract
This paper explores an innovative approach to model Lead-Acid battery energy storage systems (BESS) in insular power grid applications. In this context, two insular power networks are employed as real case studies. A critical analysis with regards to some BESS design parameters is performed. Finally, a charging sensibility analysis based criterion is proposed with a view to extend BESS life time.

Abstract
This paper focuses on dynamic performance control of modular multilevel converters (MMC) in high-voltage direct current (HVDC) transmission systems. To achieve this objective, a new mathematical model including six state variables of ac-currents and dc-link voltage of MMC, and circulating currents of converter arms are proposed for MMC in d-q reference frame. In addition, a robust control technique with three sub-control loops is designed to provide the stable operation of MMC. In the overall structure of the proposed controller, three outer, central and inner loops have the duties of 1) making the state variables error zero with changeable convergence rate, 2) adding robustness characteristic to the proposed controller, and 3) generating the appropriate reference values for MMC's currents, respectively. The effectiveness of the proposed control algorithm is investigated via MATLAB simulation. The simulation results highlight the capability of the proposed control algorithm in offering an accurate active and reactive power tracking through the control method of MMC, a stabilized dc-link voltage, capacitor voltage balancing of sub-modules, and minimization of circulating currents of converter arms during dynamic transitions and steady state operation.

Abstract
This study presents a new function-based modulation control technique for modular multilevel converters (MMCs). The main contribution of this study is the formulation of two new modulation functions for the required switching signals of the MMC's upper and lower sub-modules, respectively. The output and circulating current equations of the converter are employed to attain the arm's currents which are utilised for the proposed modulation functions, which have two important features: (i) it is much less complex compared to the existing control methods of MMC; and (ii) the proposed controller can be regulated properly to deal with parameter variations in a bid to ensure stable and accurate performance. In this controller, the MMC output current magnitude and phase angle required for special active and reactive power sharing can be easily applied to the modulation functions. Also, the equivalent capacitors of upper and lower sub-modules are discussed based on the proposed modulation functions. Finally, simulations are performed in Matlab/Simulink environment to evaluate the performance of the proposed control technique in both the dynamic conditions of load as well as varying parameters.

Abstract
The decision making framework in power system has changed due to presence of distributed energy resources (DERs). These resources are installed in distribution networks to meet demand locally. Therefore, distribution companies (Discos) are enabled to supply energy through these resources to meet their demand at a minimum operation cost. Moreover, in this framework, the Disco will change its role in the wholesale energy market from price taker to price maker as a decision maker. Moreover, DERs can serve reserve in their normal operation. This opportunity facilitates Disco to provide reserve to the wholesale reserve market. The strategic behavior of a Disco in wholesale energy and reserve markets is modeled in this paper as a bi-level optimization problem. The operation problem of the Disco and the Independent System Operator (ISO) are modeled in the upper-and lower-level problems, respectively. Karush-Kuhn-Tucker (KKT) dualilty theory conditions are employed to transform the proposed nonlinear bi-level problem to a linear single level one. Numerical studies demonstrate the proficiency of the proposed model and the solution methodology.

Abstract
Crete Island is rich in renewable energy resources such as wind and solar. Likewise other European territories, renewable sources already are being explored for power production. Currently a large amount of wind energy on Crete is curtailed during certain daily periods as a result of reduced demand and minimum operating levels on thermal generators. Reducing wind power curtailment magnitude requires additional sources of flexibility in the grid, and electric energy storage is one of them. This paper address wind generation curtailment minimization through the storage of wind energy surplus. NaS (sodium sulfura) battery modelling is used in this study in order to shift wind generation from off-peak to on-peak through a technical-economic analysis, considering the total annualized cost of the storage system and the wind power curtailment based on an annual basis. The obtained results are based on real data, which includes Crete Island demand, renewable and conventional power generation.