The increasing use of the Renewable Energy Sources (RES) and the intermittency of the power generated by them create stability, reliability and power quality problems in the main electrical grid. The microgrid is called to be a feasible alternative to solve these issues. As it is a weak electrical grid, the microgrid is very sensitive to load or generation changes. To reduce the effect of these variations and to better harness the energy generated by RES, the Energy Storage Systems (ESS) are used. As the different ESS technologies that are currently available are not enough to satisfy the wide frequency spectrum of the generated energy, the use of a Hybrid Energy Storage System (HESS) is necessary. A HESS is usually formed by two complementary storage devices that can be associated in many different topologies. Of course, the two devices have to be coordinated by an Energy Management System (EMS). In this paper the different topologies and energy management algorithms that have been applied in the RES and microgrid contexts have been analysed and compared. A review of the latest papers related to the use of HESS to facilitate the integration of the RES in the microgrid context is carried out. Some examples of the (hybrid) electric vehicles are also addressed, as the use of the HESS is more extended in this field than in the field of the microgrids.

International audienceA high penetration of the Renewable Energy Sources (RES) can create stability, reliability and power quality problems in the main electrical grid due to their stochastic nature. The microgrid is one of the analysed solutions to solve this problem. In this context, the storage becomes necessary to better harness the energy generated by RES and to maintain the proper operation of the microgrid. This paper addresses the control of the bidirectional DC-DC converters used to interface a parallel connected Hybrid Energy Storage System (HESS) formed by a Vanadium Redox Battery (VRB) and a SuperCapacitor (SC) bank. The linear controllers have been widely used due to their simple design and implementation. However, their operation is limited to a certain operation range. The variability of the analysed system makes the use of a more robust controller necessary. In this work a PI based two-loop control system and a PI type sliding mode controller (SMC) are compared by means of simulations using the Matlab-Simulink software. Some rules are fixed to facilitate the design process of the SMC and the advantages of using a nonlinear controller are stressed

Microgrids can potentially improve security, quality, reliability and availability of electricity supply for many applications. In order to achieve these benefits when a microgrid with a substantial amount of stochastic generation operates in grid connected mode but also during islanding mode, the use of storage systems is essential. The main goal of the storage is to perform power balance during islanding mode and to avoid the effect of the renewable energy sources intermittency and load fluctuations to the grid. However, none of the currently available Energy Storage Systems (ESS) has the necessary high power and energy densities to face the effect of different disturbances coming from the load or renewable energy sources. Thus, the association of more than one storage technology in a Hybrid Energy Storage System (HESS) can be used to satisfy the above mentioned requirements. Generally, separate DC/DC converters are required to interconnect the different ESS with an inverter in order to supply the distributed system in a microgrid. The present work proposes the association of a Vanadium-Redox flow battery (VRB) with supercapacitors and a Three-level Neutral Point Clamped Inverter Interface for energy management in a microgrid. The power converter control and the energy management are also detailed. Simulation results are presented to prove the feasibility of the proposed system.