Three-level Neutral Point Clamped Inverter Interface for flow battery/supercapacitor Energy Storage System used for microgrids

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.