Wind turbine-energy storage control system for delivering constant demand power shared by DFIGs through droop characteristics

This paper investigates embedding Energy Storage (ES) with multiple wind turbines in order to deliver to the grid a smooth and constant power as demanded by the system operator. The demand power is shared by DFIGs proportional to their ratings utilizing classical voltage and frequency droop characteristics. The paper addresses the system control methodologies for delivering constant power to the grid whilst also ensuring good system stability and good utilization of the inherent inertial energy storage capacity of the turbine. A wind farm consisting of DFIG generators feeding an HVDC link is chosen for illustration, but the methods can be applied to many technologies. The simulations, which are done by PSCAD/EMTDC, demonstrate that the total power delivered by the wind farm is constant and equal to the total demand power while each DFIG-ES delivers a constant power proportional to its rating determined by droop characteristics. The calculation of the size of ES (power and energy) for a deterministic wind statistics is beyond the scope of this paper and will be explained in a future paper.