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The increasing penetration level of the Renewable Energy Sources (R ES) and their variability can compromise the proper operation of an electrical grid. The microgrid is being analysed as a solution to obtain a high penetration of RES in a controlled way. Due to the stochastic nature of the RES, the Energy Storage Systems must be used to maintain the energy and power balance between generation and demand. The limits of the storage technologies that are nowadays available make it necessary to associate more than one storage technology creating a Hybrid Energy Storage System (HESS) in order to satisfy the specifica tions of a microgrid application: high energy autonomy, power capacity and fast response. This paper analyses by means of simulations and experimen tally the feasibility of a promising topology based on a Three Level Neutral Point Clamped (3LNPC) converter. The reduced power losses, improved THD and the fact of being an integrated solution are the advantages of this system. An islanding operation case study where a HESS formed by a SuperCapacitor (SC) and a Vanadium Redox Battery (VRB) supplies power to a resistive AC load that is suddenly reduced is analysed by means of simulations and experimentally. The simulation and experimental results prove the feasibility of the presented topology and of the control system to divide the power between the SC (fast power variations) and the VRB (low frequency part of the power).

Temperature is a determinant parameter in terms of performance, lifespan and safety working with li-ion batteries. Working above 45ºC, in hot climates, has direct influence in the cycle life of the battery and can cause a dangerous failure if higher temperatures are reached; besides, performance of li-ion batteries in cold climates is very poor due to the high internal resistance they present under these ambient conditions. Being able to predict the temperature of a li-ion cell or the temperature distribution in a module for any working condition without testing the device is considered important when designing energy storage systems based on li-ion batteries. Thus, this paper presents a methodology to achieve the equivalent thermal parameters governing the behavior of a single li-ion cell and the power losses within it; different experimental tests are combined with an analytical expression of the power losses inside a cell to reach this target. The parameters obtained are used to develop a model in matlab/simulink and another model solved with CFD software. Simulation results show good agreement with experimental results with a maximum error of 2ºC committed during the validation of the methodology.Keywords-Thermal equivalent model; Li-ion cell; behavioural model. I.

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INSPEC Accession Number: 15432073International audienceIn this paper, the transient operation of a Three-Level Neutral Point Clamped (3LNPC) four-leg inverter equipped with an innovative control strategy able to improve the power quality in renewable energy based weak grids is investigated. The 3LNPC four-leg inverter is controlled to manage a Hybrid Energy Storage System in order to satisfy the energy/power demand in a weak grid and simultaneously to balance the AC voltage during unbalanced 3-phase loads. The proposed control strategy uses a special designed offset for the DC power/energy division and the decomposition of the supply three-phase voltage and current into symmetrical components using phasor representation for voltage balance. Real time simulations and experimental tests have been performed using a RT-LAB simulator, a 3LNPC converter prototype and an experimental MicroGrid in order to prove the effectiveness of the proposed system in a weak grid context