Energy Storage Systems – Grid Connection Using Synchronverters

We investigate the design of future energy storage systems by exploring one particular solution, in simulations. We use Lithium-ion batteries for storage, a dual active bridge (DAB) for DC to DC conversion and a synchronverter to transfer energy from the DC bus to the utility grid. We show how some recent improvements to the synchronverter algorithm can be combined with a battery management algorithm that will charge or discharge the batteries to achieve a maximal profit for the operator of the storage station, while at the same time contributing to the stability of the grid by providing frequency droop, voltage droop inertia and fault ride-through. We discuss different open loop and closed loop control algorithms for the DAB as well as for the overall system that will further increase its efficiency. We simulate the use of two DABs, one for the positive DC voltage and one for the negative one, with a 5KW three-level synchronverter working on the 230V grid. Keywords—Synchronverter; energy storage system; dual active bridge; droop control; model predictive control.